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Editorial

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47 pages, 370 KiB

Open AccessEditorial

Acknowledgement to Reviewers of Energies in 2017

by Energies Editorial Office

MDPI AG, St. Alban-Anlage 66, 4052 Basel, Switzerland

Energies 2018, 11(1), 231; https://doi.org/10.3390/en11010231 - 18 Jan 2018

Viewed by 6999

Abstract

Peer review is an essential part in the publication process, ensuring that Energies maintains high quality standards for its published papers [...]
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Research

Jump to: Editorial, Review, Other

1197 KiB

Open AccessArticle

A Parallel Restoration for Black Start of Microgrids Considering Characteristics of Distributed Generations

by Jing Wang

, Longhua Mu^*

, Fan Zhang and Xin Zhang

Department of Electrical Engineering, Tongji University, Shanghai 201084, China

Energies 2018, 11(1), 1; https://doi.org/10.3390/en11010001 - 21 Dec 2017

Cited by 106 | Viewed by 4758

Abstract

The black start capability is vital for microgrids, which can potentially improve the reliability of the power grid. This paper proposes a black start strategy for microgrids based on a parallel restoration strategy. Considering the characteristics of distributed generations (DGs), an evaluation model, [...] Read more.

The black start capability is vital for microgrids, which can potentially improve the reliability of the power grid. This paper proposes a black start strategy for microgrids based on a parallel restoration strategy. Considering the characteristics of distributed generations (DGs), an evaluation model, which is used to assess the black start capability of DGs, is established by adopting the variation coefficient method. Thus, the DGs with good black start capability, which are selected by a diversity sequence method, are restored first in parallel under the constraints of DGs and network. During the selection process of recovery paths, line weight and node importance degree are proposed under the consideration of the node topological importance and the load importance as well as the backbone network restoration time. Therefore, the whole optimization of the reconstructed network is realized. Finally, the simulation results verify the feasibility and effectiveness of the strategy. Full article

(This article belongs to the Special Issue Emerging Power Electronics Technologies for Power Systems and Machine Drives)

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4877 KiB

Open AccessFeature PaperArticle

The Energy Saving Potential of Occupancy-Based Lighting Control Strategies in Open-Plan Offices: The Influence of Occupancy Patterns

by Christel De Bakker^*, Tom Van de Voort and Alexander Rosemann

Building Lighting Group, Department of the Built Environment, Technical University Eindhoven, Groene Loper 6, 5600 MB Eindhoven, The Netherlands

Energies 2018, 11(1), 2; https://doi.org/10.3390/en11010002 - 21 Dec 2017

Cited by 30 | Viewed by 6642

Abstract

Occupancy-based lighting control strategies have been proven to be effective in diminishing offices’ energy consumption. These strategies have typically worked by controlling lighting at the room level but, recently, lighting systems have begun to be equipped with sensors on a more fine-grained level, [...] Read more.

Occupancy-based lighting control strategies have been proven to be effective in diminishing offices’ energy consumption. These strategies have typically worked by controlling lighting at the room level but, recently, lighting systems have begun to be equipped with sensors on a more fine-grained level, enabling lighting control at the desk level. For some office cases, however, the savings gained using this strategy may not outweigh the costs and design efforts compared to room control. This is because, in some offices, individual occupancy patterns are similar, hence the difference in savings between desk and room control would be minimal. This study examined the influence of occupancy pattern variance within an office space on the relative energy savings of control strategies with different control zone sizes. We applied stochastic modeling to estimate the occupancy patterns, as this method can account for uncertainty. To validate our model, simulation results were compared to earlier studies and real measurements, which demonstrated that our simulations provided realistic occupancy patterns. Next, office cases varying in both job-function type distribution and office policy were investigated on energy savings potential to determine the influence of occupancy pattern variance. The relative energy savings potential of the different control strategies differed minimally for the test cases, suggesting that variations in individual occupancy patterns negligibly influence energy savings. In all cases, lighting control at the desk level showed a significantly higher energy savings potential than strategies with lower control zone granularity, suggesting that it is useful to implement occupancy-based lighting at the desk level in all office cases. This strategy should, thus, receive more attention from both researchers and lighting designers. Full article

(This article belongs to the Special Issue Smart Lighting Environments: Sensing and Control)

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9171 KiB

Open AccessArticle

Online Parameter Identification and State of Charge Estimation of Lithium-Ion Batteries Based on Forgetting Factor Recursive Least Squares and Nonlinear Kalman Filter

by Bizhong Xia¹, Zizhou Lao¹, Ruifeng Zhang^1,2,*, Yong Tian¹, Guanghao Chen¹

, Zhen Sun¹

, Wei Wang², Wei Sun², Yongzhi Lai², Mingwang Wang² and Huawen Wang²

¹ Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, China

² Sunwoda Electronic Co., Ltd., Shenzhen 518108, China

Energies 2018, 11(1), 3; https://doi.org/10.3390/en11010003 - 21 Dec 2017

Cited by 91 | Viewed by 8031

Abstract

State of charge (SOC) estimation is the core of any battery management system. Most closed-loop SOC estimation algorithms are based on the equivalent circuit model with fixed parameters. However, the parameters of the equivalent circuit model will change as temperature or SOC changes, [...] Read more.

State of charge (SOC) estimation is the core of any battery management system. Most closed-loop SOC estimation algorithms are based on the equivalent circuit model with fixed parameters. However, the parameters of the equivalent circuit model will change as temperature or SOC changes, resulting in reduced SOC estimation accuracy. In this paper, two SOC estimation algorithms with online parameter identification are proposed to solve this problem based on forgetting factor recursive least squares (FFRLS) and nonlinear Kalman filter. The parameters of a Thevenin model are constantly updated by FFRLS. The nonlinear Kalman filter is used to perform the recursive operation to estimate SOC. Experiments in variable temperature environments verify the effectiveness of the proposed algorithms. A combination of four driving cycles is loaded on lithium-ion batteries to test the adaptability of the approaches to different working conditions. Under certain conditions, the average error of the SOC estimation dropped from 5.6% to 1.1% after adding the online parameters identification, showing that the estimation accuracy of proposed algorithms is greatly improved. Besides, simulated measurement noise is added to the test data to prove the robustness of the algorithms. Full article

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22107 KiB

Open AccessArticle

Multi-Phase Modular Drive System: A Case Study in Electrical Aircraft Applications

by Charles Onambele^1,2, Moataz Elsied², Augustin Mpanda Mabwe^1,2,* and Ahmed El Hajjaji¹

¹ Modeling, Information & Systems Lab (MIS), University of Picardie Jules Verne, 80025 Amiens, France

² Graduate School of Electronic and Electrical Engineering, ESIEE Amiens, 80080 Amiens, France

Energies 2018, 11(1), 5; https://doi.org/10.3390/en11010005 - 21 Dec 2017

Cited by 8 | Viewed by 6438

Abstract

In this article, an advanced multiphase modular power drive prototype is developed for More Electric Aircraft (MEA). The proposed drive is designed to supply a multi-phase permanent magnet (PM) motor rating 120 kW with 24 slots and 11 pole pairs. The power converter [...] Read more.

In this article, an advanced multiphase modular power drive prototype is developed for More Electric Aircraft (MEA). The proposed drive is designed to supply a multi-phase permanent magnet (PM) motor rating 120 kW with 24 slots and 11 pole pairs. The power converter of the drive system is based on Silicon Carbide Metal Oxide Semiconductor Field-Effect Transistor (SiC MOSFET) technology to operate at high voltage, high frequency and low reverse recovery current. Firstly, an experimental characterization test is performed for the selected SiC power module in harsh conditions to evaluate the switching energy losses. Secondly, a finite element thermal analysis based on Ansys-Icepak is accomplished to validate the selected cooling system for the power converter. Thirdly, a co-simulation model is developed using Matlab-Simulink and LTspice^® to evaluate the SiC power module impact on the performance of a multiphase drive system at different operating conditions. The results obtained show that the dynamic performance and efficiency of the power drive are significantly improved, which makes the proposed system an excellent candidate for future aircraft applications. Full article

(This article belongs to the Special Issue Emerging Power Electronics Technologies for Power Systems and Machine Drives)

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2532 KiB

Open AccessArticle

Different Mechanism Effect between Gas-Solid and Liquid-Solid Interface on the Three-Phase Coexistence Hydrate System Dissociation in Seawater: A Molecular Dynamics Simulation Study

by Zhixue Sun^1,*, Haoxuan Wang¹, Jun Yao¹, Chengwei Yang², Jianlong Kou¹, Kelvin Bongole¹, Ying Xin¹, Weina Li¹ and Xuchen Zhu¹

¹ School of Petroleum Engineering, China University of Petroleum (East China), Qingdao 266580, China

² Exploration & Development Research Institute, Petro China Changqing Oilfield Company, Xi’an 136201, China

Energies 2018, 11(1), 6; https://doi.org/10.3390/en11010006 - 21 Dec 2017

Cited by 7 | Viewed by 4202

Abstract

Almost 98% of methane hydrate is stored in the seawater environment, the study of microscopic mechanism for methane hydrate dissociation on the sea floor is of great significance to the development of hydrate production, involving a three-phase coexistence system of seawater (3.5% NaCl) [...] Read more.

Almost 98% of methane hydrate is stored in the seawater environment, the study of microscopic mechanism for methane hydrate dissociation on the sea floor is of great significance to the development of hydrate production, involving a three-phase coexistence system of seawater (3.5% NaCl) + hydrate + methane gas. The molecular dynamics method is used to simulate the hydrate dissociation process. The dissociation of hydrate system depends on diffusion of methane molecules from partially open cages and a layer by layer breakdown of the closed cages. The presence of liquid or gas phases adjacent to the hydrate has an effect on the rate of hydrate dissociation. At the beginning of dissociation process, hydrate layers that are in contact with liquid phase dissociated faster than layers adjacent to the gas phase. As the dissociation continues, the thickness of water film near the hydrate-liquid interface became larger than the hydrate-gas interface giving more resistance to the hydrate dissociation. Dissociation rate of hydrate layers adjacent to gas phase gradually exceeds the dissociation rate of layers adjacent to the liquid phase. The difficulty of methane diffusion in the hydrate-liquid side also brings about change in dissociation rate. Full article

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10103 KiB

Open AccessArticle

Design Method for the Coil-System and the Soft Switching Technology for High-Frequency and High-Efficiency Wireless Power Transfer Systems

by Xu Liu¹

, Jianhua Liu¹, Jianjing Wang², Chonglin Wang¹ and Xibo Yuan^1,2,*

¹ School of Electrical and Power Engineering, China University of Mining and Technology, Xuzhou 221008, China

² Electrical Energy Management Research Group, University of Bristol, Bristol BS8 1TH, UK

Energies 2018, 11(1), 7; https://doi.org/10.3390/en11010007 - 21 Dec 2017

Cited by 14 | Viewed by 5462

Abstract

Increasing the resonant frequency of a wireless power transfer (WPT) system effectively improves the power transfer efficiency between the transmit and the receive coils but significantly limits the power transfer capacity with the same coils. Therefore, this paper proposes a coil design method [...] Read more.

Increasing the resonant frequency of a wireless power transfer (WPT) system effectively improves the power transfer efficiency between the transmit and the receive coils but significantly limits the power transfer capacity with the same coils. Therefore, this paper proposes a coil design method for a series-series (SS) compensated WPT system which can power up the same load with the same DC input voltage & current but with increased resonant frequency. For WPT systems with higher resonant frequencies, a new method of realizing soft-switching by tuning driving frequency is proposed which does not need to change any hardware in the WPT system and can effectively reduce switching losses generated in the inverter. Eighty-five kHz, 200 kHz and 500 kHz WPT systems are built up to validate the proposed methods. Experimental results show that all these three WPT systems can deliver around 3.3 kW power to the same load (15 Ω) with 200 V input voltage and 20 A input current as expected and achieve more than 85% coil-system efficiency and 79% system overall efficiency. With the soft-switching technique, inverter efficiency can be improved from 81.91% to 98.60% in the 500 kHz WPT system. Full article

(This article belongs to the Special Issue Emerging Power Electronics Technologies for Power Systems and Machine Drives)

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1021 KiB

Open AccessArticle

The Next-Generation U.S. Retail Electricity Market with Customers and Prosumers—A Bibliographical Survey

by Tao Chen¹, Qais Alsafasfeh², Hajir Pourbabak¹

and Wencong Su^1,*

¹ Department of Electrical Engineering, University of Michigan-Dearborn, Dearborn, MI 48128, USA

² Department of Electrical Power and Mechatronics Engineering, Tafila Technical University, Tafila 66110, Jordan

Energies 2018, 11(1), 8; https://doi.org/10.3390/en11010008 - 21 Dec 2017

Cited by 56 | Viewed by 7570

Abstract

Due to the rapidly-changing technologies in the power industry, many new references addressing the frameworks and business models of the next-generation retail electricity market are entering the research community. In particular, considering new customers with considerable demand response awareness and so-called prosumers with [...] Read more.

Due to the rapidly-changing technologies in the power industry, many new references addressing the frameworks and business models of the next-generation retail electricity market are entering the research community. In particular, considering new customers with considerable demand response awareness and so-called prosumers with localized power generation based on distributed energy resources (DERs), the next-generation retail electricity market infrastructure will be a level playing field for local energy transactions, strategic pricing scheme design, new business model design and building an innovative energy ecosystem. Consequently, there is an urgent need to keep track of international experiences and activities taking place in the field of the market mechanism design problem at the distribution level. This paper provides a comprehensive survey of recent technology developments and aims to inspire awareness of the further deregulation of the electricity market, especially in areas close to customers. We mainly bring attention to the more than 90 articles published during the past five years. The collected literature has been divided into different sections to discuss different aspects of the next-generation retail electricity market under the deregulated power industry. Full article

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1086 KiB

Open AccessArticle

Optimization of the Operation of Smart Rural Grids through a Novel Energy Management System

by Francesc Girbau-LListuella^*

, Francisco Díaz-González and Andreas Sumper

Centre d’Innovació Tecnològica en Convertidors Estàtics i Accionaments (CITCEA-UPC), Departament d’Enginyeria Elèctrica, Universitat Politècnica de Catalunya ETS d’Enginyeria Industrial de Barcelona, Av. Diagonal, 647, Pl. 2, 08028 Barcelona, Spain

Energies 2018, 11(1), 9; https://doi.org/10.3390/en11010009 - 21 Dec 2017

Cited by 10 | Viewed by 3908

Abstract

The paper proposes an innovative Energy Management System (EMS) that optimizes the grid operation based on economic and technical criteria. The EMS inputs the demand and renewable generation forecasts, electricity prices and the status of the distributed storages through the network, and solves [...] Read more.

The paper proposes an innovative Energy Management System (EMS) that optimizes the grid operation based on economic and technical criteria. The EMS inputs the demand and renewable generation forecasts, electricity prices and the status of the distributed storages through the network, and solves with an optimal quarter-hourly dispatch for controllable resources. The performance of the EMS is quantified through diverse proposed metrics. The analyses were based on a real rural grid from the European FP7 project Smart Rural Grid. The performance of the EMS has been evaluated through some scenarios varying the penetration of distributed generation. The obtained results demonstrate that the inclusion of the EMS from both a technical point of view and an economic perspective for the adopted grid is justified. At the technical level, the inclusion of the EMS permits us to significantly increase the power quality in weak and radial networks. At the economic level and from a certain threshold value in renewables’ penetration, the EMS reduces the energy costs for the grid participants, minimizing imports from the external grid and compensating the toll to be paid in the form of the losses incurred by including additional equipment in the network (i.e., distributed storage). Full article

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5840 KiB

Open AccessArticle

Improving Engine Oil Warm Up through Waste Heat Recovery

by Davide Di Battista^*

and Roberto Cipollone

Department of Industrial and Information Engineering and Economics, University of L’Aquila, 67100 L’Aquila, Italy

Energies 2018, 11(1), 10; https://doi.org/10.3390/en11010010 - 21 Dec 2017

Cited by 20 | Viewed by 7159

Abstract

In the transportation sector, engine oil thermal management has not yet received the attention it deserves in the path towards carbon dioxide and pollutants reduction. During the homologation cycle (which represents a typical daily trip), oil temperature reaches its thermal steady value, which [...] Read more.

In the transportation sector, engine oil thermal management has not yet received the attention it deserves in the path towards carbon dioxide and pollutants reduction. During the homologation cycle (which represents a typical daily trip), oil temperature reaches its thermal steady value, which insures best performances in terms of viscosity, only in the final part of the trip, when most part of the harmful emissions have been already emitted; therefore, a warm up acceleration would surely represent a strong beneficial action. In this paper, a faster warming up of the lubricant oil was done using the heat owned by the exhaust gases, which was almost immediately ready after the engine ignition, in the early part of a driving cycle. An experimental activity has been developed in a turbocharged engine (F1C 3L IVECO), modifying the oil circuit in order to heat up the oil during the cold phase of a homologation cycle by the exhaust gases. A significant reduction of fuel consumption and pollutant emissions savings has been experimentally demonstrated. Also, the interaction between the modified oil circuit, engine, coolant circuit, and exhaust line has been investigated in order to have a system view of the new heating oil technology. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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6785 KiB

Open AccessArticle

Nearshore Wave Predictions Using Data Mining Techniques during Typhoons: A Case Study near Taiwan’s Northeastern Coast

by Chih-Chiang Wei

Department of Marine Environmental Informatics, National Taiwan Ocean University, No. 2, Beining Rd., Jhongjheng District, Keelung City 20224, Taiwan

Energies 2018, 11(1), 11; https://doi.org/10.3390/en11010011 - 21 Dec 2017

Cited by 20 | Viewed by 4221

Abstract

Seasonal typhoons provide energy into the wave field in summer and autumn in Taiwan. Typhoons lead to abundant wave energy near the coastal area and cause storm surges that can destroy offshore facilities. The potential for wave energy can be obtained from analyzing [...] Read more.

Seasonal typhoons provide energy into the wave field in summer and autumn in Taiwan. Typhoons lead to abundant wave energy near the coastal area and cause storm surges that can destroy offshore facilities. The potential for wave energy can be obtained from analyzing the wave height. To develop an effective model for predicting typhoon-induced wave height near coastal areas, this study employed various popular data mining models—namely k-nearest neighbors (kNN), linear regressions (LR), model trees (M5), multilayer perceptron (MLP) neural network, and support vector regression (SVR) algorithms—as forecasting techniques. The principal component analysis (PCA) was then performed to reduce the potential variables from the original data at the first stage of data preprocessing. The experimental site was the Longdong buoy off the northeastern coast of Taiwan. Data on typhoons that occurred during 2002–2011 and 2012–2013 were collected for training and testing, respectively. This study designed four PCA cases, namely EV1, TV90, TV95, and ORI: EV1 used eigenvalues higher than 1.0 as principal components; TV90 and TV95 used the total variance percentages of 90% and 95%, respectively; and ORI used the original data. The forecast horizons varying from 1 h to 6 h were evaluated. The results show that (1) in the PCA model’ cases, when the number of attributes decreases, computing time decreases and prediction error increases; (2) regarding classified wave heights, M5 provides excellent outcomes at the small wavelet wavelet level; MLP has favorable outcomes at the large wavelet and small/moderate wave levels; meanwhile, SVR gives optimal outcomes at the long wave and high/very high wave levels; and (3) for performance of lead times, MLP and SVR achieve more favorable relative weighted performance without consideration of computational complexity; however, MLP and SVR might obtain lower performance when computational complexity is considered. Full article

(This article belongs to the Special Issue Data Science and Big Data in Energy Forecasting)

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8344 KiB

Open AccessArticle

A New Insight into Shale-Gas Accumulation Conditions and Favorable Areas of the Xinkailing Formation in the Wuning Area, North-West Jiangxi, China

by Shangru Li^1,2, Li Zeng^1,2, Zhongpeng Wang^1,2,*, Jinchuan Zhang³ and Dong Ma^4,*

¹ Jiangxi Geo-Engineering (Group) Corporation, Nanchang 330001, China

² GanZhongNan Institute of Geology and Mineral Exploration, Nanchang 330001, China

³ School of Energy Resources, China University of Geosciences, Beijing 100089, China

⁴ School of Petroleum Engineering, Yangtze Univeristy, Wuhan 430100, China

Energies 2018, 11(1), 12; https://doi.org/10.3390/en11010012 - 21 Dec 2017

Cited by 9 | Viewed by 4326

Abstract

In north-west Jiangxi, China, most shale-gas exploration has been focused on the Lower Cambrian Hetang and Guanyintang formations, whereas the Upper Ordovician Xinkailing formation shale has been ignored for years due to heavy weathering. This study systematically analyzed gas source conditions, reservoir conditions [...] Read more.

In north-west Jiangxi, China, most shale-gas exploration has been focused on the Lower Cambrian Hetang and Guanyintang formations, whereas the Upper Ordovician Xinkailing formation shale has been ignored for years due to heavy weathering. This study systematically analyzed gas source conditions, reservoir conditions and gas-bearing ability in order to reveal the shale-gas accumulation conditions of the Xinkailing formation. The results show that the Xinkailing formation is characterized by thick deposition of black shale (10–80 m), high organic content (with total organic carbon between 1.18% and 3.11%, on average greater than 2%), relatively moderate thermal evolution (with vitrinite reflectance between 2.83% and 3.21%), high brittle-mineral content (greater than 40%), abundant nanopores and micro-fractures, very good adsorption ability (adsorption content between 2.12 m³/t and 3.47 m³/t, on average about 2.50 m³/t), and strong sealing ability in the underlying and overlying layers, all of which favor the generation and accumulation of shale gas. The Wuning-Lixi and Jinkou-Zhelin areas of the Xinkailing formation were selected as the most realistic and favorable targets for shale-gas exploration and exploitation. In conclusion, the Wuning area has great potential and can provide a breakthrough in shale gas with further investigation. Full article

(This article belongs to the Special Issue Unconventional Natural Gas (UNG) Recoveries 2018)

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2529 KiB

Open AccessArticle

Machine Learning for Wind Turbine Blades Maintenance Management

by Alfredo Arcos Jiménez¹, Carlos Quiterio Gómez Muñoz² and Fausto Pedro García Márquez^1,*

¹ Ingenium Research Group, Castilla-La Mancha University, 13071 Ciudad Real, Spain

² Ingeniería Industrial y Aeroespacial, Universidad Europea Madrid, Villaviciosa de Odón, 28670 Madrid, Spain

Energies 2018, 11(1), 13; https://doi.org/10.3390/en11010013 - 21 Dec 2017

Cited by 88 | Viewed by 9451

Abstract

Delamination in Wind Turbine Blades (WTB) is a common structural problem that can generate large costs. Delamination is the separation of layers of a composite material, which produces points of stress concentration. These points suffer greater traction and compression forces in working conditions, [...] Read more.

Delamination in Wind Turbine Blades (WTB) is a common structural problem that can generate large costs. Delamination is the separation of layers of a composite material, which produces points of stress concentration. These points suffer greater traction and compression forces in working conditions, and they can trigger cracks, and partial or total breakage of the blade. Early detection of delamination is crucial for the prevention of breakages and downtime. The main novelty presented in this paper has been to apply an approach for detecting and diagnosing the delamination WTB. The approach is based on signal processing of guided waves, and multiclass pattern recognition using machine learning. Delamination was induced in the WTB to check the accuracy of the approach. The signal is denoised by wavelet transform. The autoregressive Yule–Walker model is employed for feature extraction, and Akaike’s information criterion method for feature selection. The classifiers are quadratic discriminant analysis, k-nearest neighbors, decision trees, and neural network multilayer perceptron. The confusion matrix is employed to evaluate the classification, especially the receiver operating characteristic analysis by: recall, specificity, precision, and F-score. Full article

(This article belongs to the Collection Wind Turbines)

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Open AccessArticle

A Quantitative Risk Analysis Method for the High Hazard Mechanical System in Petroleum and Petrochemical Industry

by Yang Tang^1,2,*, Jiajia Jing³, Zhidong Zhang³ and Yan Yang⁴

¹ School of Mechatronic Engineering, Southwest Petroleum University, Chengdu 610500, China

² Key Laboratory of Oil &Gas Equipment, Ministry of Education (Southwest Petroleum University), Chengdu 610500, China

³ Drilling & Production Engineering Technology Research Institute, Chuanqing Drilling Engineering Company Limited, CNPC, Guanghan 618000, China

⁴ School of Sciences, Southwest Petroleum University, Chengdu 610500, China

Energies 2018, 11(1), 14; https://doi.org/10.3390/en11010014 - 22 Dec 2017

Cited by 23 | Viewed by 8815

Abstract

The high hazard mechanical system (HHMS) has three characteristics in the petroleum and petrochemical industry (PPI): high risk, high cost, and high technology requirements. For a HHMS, part, component, and subsystem failures will result in varying degrees and various types of risk consequences, [...] Read more.

The high hazard mechanical system (HHMS) has three characteristics in the petroleum and petrochemical industry (PPI): high risk, high cost, and high technology requirements. For a HHMS, part, component, and subsystem failures will result in varying degrees and various types of risk consequences, including unexpected downtime, production losses, economic costs, safety accidents, and environmental pollution. Thus, obtaining the quantitative risk level and distribution in a HHMS to control major risk accidents and ensure safe production is of vital importance. However, the structure of the HHMS is more complex than some other systems, making the quantitative risk analysis process more difficult. Additionally, a variety of uncertain risk data hinder the realization of quantitative risk analysis. A few quantitative risk analysis techniques and studies for HHMS exist, especially in the PPI. Therefore, a study on the quantitative risk analysis method for HHMS was completed to obtain the risk level and distribution of high-risk objects. Firstly, Fuzzy Set Theory (FST) was applied to address the uncertain risk data for the occurrence probability (OP) and consequence severity (CS) in the risk analysis process. Secondly, a fuzzy fault tree analysis (FFTA) and a fuzzy event tree analysis (FETA) were used to achieve quantitative risk analysis and calculation. Thirdly, a fuzzy bow-tie model (FBTM) was established to obtain a quantitative risk assessment result according to the analysis results of the FFTA and FETA. Finally, the feasibility and practicability of the method were verified with a case study on the quantitative risk analysis of one reciprocating pump system (RPS). The quantitative risk analysis method for HHMS can provide more accurate and scientific data support for the development of Asset Integrity Management (AIM) systems in the PPI. Full article

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Open AccessArticle

Magnet Shape Optimization of Two-Layer Spoke-Type Axial Flux Interior Permanent Magnet Machines

by Feng Chai, Yunlong Bi and Yulong Pei^*

School of Electrical Engineering and Automation, Harbin Institute of Technology, Harbin 150001, China

Energies 2018, 11(1), 15; https://doi.org/10.3390/en11010015 - 23 Dec 2017

Cited by 3 | Viewed by 6536

Abstract

In this paper, the two-layer spoke-type (TLST) axial flux interior permanent magnet (AFIPM) machine is proposed. Simple flux barriers are added to optimize the air gap flux density, in which way there is no need to change the surface of the rotor. The [...] Read more.

In this paper, the two-layer spoke-type (TLST) axial flux interior permanent magnet (AFIPM) machine is proposed. Simple flux barriers are added to optimize the air gap flux density, in which way there is no need to change the surface of the rotor. The optimization principle is revealed and the advantages of the TLST AFIPM machine compared with the spoke-type (ST) AFIPM machine are clarified. An optimization design process based on magnetic equivalent circuit combined with idealized and improved air gap flux density waveform is proposed, in which way the calculation time is saved by avoiding an excess of finite element method (FEM) simulations. Finally, 3D FEM simulation is adopted to verify the optimization results. Full article

(This article belongs to the Collection Electric and Hybrid Vehicles Collection)

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Open AccessArticle

Value-Creation Potential from Multi-Market Trading for a Hydropower Producer

by Marte Fodstad^1,*, Mats Mathisen Aarlott² and Kjetil Trovik Midthun²

¹ SINTEF Energy Research, 7034 Trondheim, Norway

² SINTEF Technology and Society, 7034 Trondheim, Norway

Energies 2018, 11(1), 16; https://doi.org/10.3390/en11010016 - 22 Dec 2017

Cited by 4 | Viewed by 3355

Abstract

We study a hydropower producer’s potential for value-creation from multi-market trading given the price variations in the markets and the flexibility provided through access to hydro reservoirs. We use a perfect foresight optimization model for a price-taking hydropower producer co-optimizing his trades in [...] Read more.

We study a hydropower producer’s potential for value-creation from multi-market trading given the price variations in the markets and the flexibility provided through access to hydro reservoirs. We use a perfect foresight optimization model for a price-taking hydropower producer co-optimizing his trades in the day-ahead, intra-day and balancing markets. The model is used on real market data from Norway, Sweden and Germany. The study shows a theoretical potential for added value when selling energy in multiple markets relative to optimal day-ahead sale. Most of this value is achievable also when the perfect foresight is limited to the period from day-ahead bidding until operation. Flexible production plants achieve the largest relative added values for multi-market sales, and has the largest benefit from a long horizon with perfect foresight. Full article

(This article belongs to the Special Issue Hydropower 2017)

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5696 KiB

Open AccessArticle

Characteristics of the Sliding Electric Contact of Pantograph/Contact Wire Systems in Electric Railways

by Guangning Wu, Jie Wu, Wenfu Wei^*

, Yue Zhou, Zefeng Yang and Guoqiang Gao^*

School of Electrical Engineering, Southwest Jiaotong University, Chengdu 610031, China

Energies 2018, 11(1), 17; https://doi.org/10.3390/en11010017 - 22 Dec 2017

Cited by 30 | Viewed by 4486

Abstract

The sliding electric contact of pantograph/contact wire systems plays a significant part in the current collection stability and operation life of pantograph/contact wire systems. This paper addresses the evolutionary process of sliding electric contact of pantograph/contact wire systems by analyzing three key characteristics [...] Read more.

The sliding electric contact of pantograph/contact wire systems plays a significant part in the current collection stability and operation life of pantograph/contact wire systems. This paper addresses the evolutionary process of sliding electric contact of pantograph/contact wire systems by analyzing three key characteristics including contact resistance, temperature distribution and microstructure. The influence of electric current on contact resistance was interpreted. Furthermore, the evolution of the spatial temperature distribution of the carbon strip was obtained in the zigzag movement, while the dominant role of electric effect in temperature rise was demonstrated. In the end, the wear morphology differences under pure friction and current-carrying conditions were analyzed. The formation of radial cracks was illustrated and its influenced on the wear process was discussed. Full article

(This article belongs to the Section F: Electrical Engineering)

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Open AccessArticle

Internal Force Response of a Pile in an Inhomogeneous Temperature Field

by Dan Zhang^1,2,*

, Yian Wang¹ and Jian Cheng¹

¹ School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China

² Nanjing University (Suzhou) High-Tech Institute, Suzhou 215123, China

Energies 2018, 11(1), 18; https://doi.org/10.3390/en11010018 - 22 Dec 2017

Cited by 32 | Viewed by 3129

Abstract

An inhomogeneous temperature field was built in an experimental model of sand with an embedded pile. The temperature of the soil, as well as the temperature and strain on opposite sides of the pile were investigated in the process of temperature balance. The [...] Read more.

An inhomogeneous temperature field was built in an experimental model of sand with an embedded pile. The temperature of the soil, as well as the temperature and strain on opposite sides of the pile were investigated in the process of temperature balance. The effect of the inhomogeneous temperature field on the internal force of the pile was analyzed. The experimental results show that the inhomogeneous temperature field will cause a bending deformation in the pile body according to the FBG (fiber Bragg grating) strain sensors. The distribution of the bending moment along the length of the pile is related to the temperature difference. The maximum bending moments reached −25.7 N·m when the temperature difference was about 1.3 °C. Therefore, the influence of the inhomogeneous temperature field o· the internal force of the foundation pile should be taken into account in the applications of a ground source heat pump system. Full article

(This article belongs to the Special Issue Geothermal Heating and Cooling)

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2881 KiB

Open AccessArticle

Parameters Identification and Sensitive Characteristics Analysis for Lithium-Ion Batteries of Electric Vehicles

by Yun Zhang^1,2

, Yunlong Shang², Naxin Cui²

and Chenghui Zhang^2,*

¹ School of Electrical Engineering, University of Jinan, Jinan 250022, China

² School of Control Science and Engineering, Shandong University, Jinan 250061, China

Energies 2018, 11(1), 19; https://doi.org/10.3390/en11010019 - 22 Dec 2017

Cited by 18 | Viewed by 4905

Abstract

This paper mainly investigates the sensitive characteristics of lithium-ion batteries so as to provide scientific basises for simplifying the design of the state estimator that adapt to various environments. Three lithium-ion batteries are chosen as the experimental samples. The samples were tested at [...] Read more.

This paper mainly investigates the sensitive characteristics of lithium-ion batteries so as to provide scientific basises for simplifying the design of the state estimator that adapt to various environments. Three lithium-ion batteries are chosen as the experimental samples. The samples were tested at various temperatures (−20

^{\circ}

C, −10

^{\circ}

C, 0

^{\circ}

C , 10

^{\circ}

C , 25

^{\circ}

C) and various current rates (0.5C, 1C, 1.5C) using a battery test bench. A physical equivalent circuit model is developed to capture the dynamic characteristics of the batteries. The experimental results show that all battery parameters are time-varying and have different sensitivity to temperature, current rate and state of charge (SOC). The sensitivity of battery to temperature, current rate and SOC increases the difficulty in battery modeling because of the change of parameters. The further simulation experiments show that the model output has a higher sensitivity to the change of ohmic resistance than that of other parameters. Based on the experimental and simulation results obtained here, it is expected that the adaptive parameter state estimator design could be simplified in the near future. Full article

(This article belongs to the Special Issue Intelligent Management and Control of Energy Storage Systems)

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713 KiB

Open AccessArticle

Pathways to Decarbonise the European Car Fleet: A Scenario Analysis Using the Backcasting Approach

by Arne Höltl^1,*, Cathy Macharis¹ and Klaas De Brucker²

¹ Department of Business Technology and Operations, Research Group MOBI, Vrije Universiteit Brussel, Pleinlaan 2, BE-1050 Brussels, Belgium

² Research Centre for Economics and Corporate Sustainability (ECON-CEDON), Faculty of Economics and Business, KU Leuven, Warmoesberg 26, BE-1000 Brussels, Belgium

Energies 2018, 11(1), 20; https://doi.org/10.3390/en11010020 - 22 Dec 2017

Cited by 23 | Viewed by 4493

Abstract

This paper analyses decarbonisation scenarios for the European passenger car fleet in 2050. The scenarios have been developed using the backcasting approach and aim to reduce greenhouse gas (GHG) emissions of passenger cars to a level defined in the Transport White paper that [...] Read more.

This paper analyses decarbonisation scenarios for the European passenger car fleet in 2050. The scenarios have been developed using the backcasting approach and aim to reduce greenhouse gas (GHG) emissions of passenger cars to a level defined in the Transport White paper that is 60% below 1990 levels. Considering the emission levels of 2010, a yearly reduction of 1.7% is required in order to achieve the target. Car emissions were decomposed into the main emission factors of mobility, efficiency and carbon intensity. How these factors change over time depends on various external factors: the pace of technological improvements, the future role of cars in society’s mobility system and the priority given to decarbonising energy demand. The analysis showed that if car mobility and ownership continue to increase as expected in a ‘business as usual’ case, a share of 97% plug-in hybrid or battery electric vehicles might be required by 2050, together with a substantial decrease in greenhouse gas emission from electricity production. A transition to more advanced car technology such as automated driving, advanced batteries or lightweight materials in vehicle production would raise vehicle efficiency. Should car mobility continue at a high level, an early technology transition will be required. Full article

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6280 KiB

Open AccessArticle

A Hybrid Fault-Tolerant Strategy for Severe Sensor Failure Scenarios in Late-Stage Offshore DFIG-WT

by Wei Li¹, Gengyin Li¹, Kai Ni^2,*

, Yihua Hu²

and Xinhua Li²

¹ State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University, Changping District, Beijing 102206, China

² Department of Electrical Engineering and Electronics, University of Liverpool, Liverpool L69 3GJ, UK

Energies 2018, 11(1), 21; https://doi.org/10.3390/en11010021 - 22 Dec 2017

Cited by 3 | Viewed by 3113

Abstract

As the phase current sensors and rotor speed/position sensor are prone to fail in the late stage of an offshore doubly-fed induction generator based wind turbine (DFIG-WT), this paper investigates a hybrid fault-tolerant strategy for a severe sensor failure scenario. The phase current [...] Read more.

As the phase current sensors and rotor speed/position sensor are prone to fail in the late stage of an offshore doubly-fed induction generator based wind turbine (DFIG-WT), this paper investigates a hybrid fault-tolerant strategy for a severe sensor failure scenario. The phase current sensors in the back-to-back (BTB) converter and the speed/position sensor are in the faulty states simultaneously. Based on the 7th-order doubly-fed induction generator (DFIG) dynamic state space model, the extended Kalman filter (EKF) algorithm is applied for rotor speed and position estimation. In addition, good robustness of this sensorless control algorithm to system uncertainties and measurement disturbances is presented. Besides, a single DC-link current sensor based phase current reconstruction scheme is utilized for deriving the phase current information according to the switching states. A duty ratio adjustment strategy is proposed to avoid missing the sampling points in a switching period, which is simple to implement. Furthermore, the additional active time of the targeted nonzero switching states is complemented so that the reference voltage vector remains in the same position as that before duty ratio adjustment. The validity of the proposed hybrid fault-tolerant sensorless control strategy is demonstrated by simulation results in Matlab/Simulink2017a by considering harsh operating environments. Full article

(This article belongs to the Section F: Electrical Engineering)

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2999 KiB

Open AccessArticle

An MILP Method for Design of Distributed Energy Resource System Considering Stochastic Energy Supply and Demand

by Zhigang Duan^1,2,*, Yamin Yan¹, Xiaohan Yan¹, Qi Liao¹, Wan Zhang¹, Yongtu Liang¹ and Tianqi Xia³

¹ Beijing Key Laboratory of Urban oil and Gas Distribution Technology, China University of Petroleum-Beijing, Fuxue Road No. 18, Changping District, Beijing 102249, China

² Sino-Pipeline International Company Limited, Dongzhimen North Street No. 9, Dongcheng District, Beijing 100010, China

³ Center for Spatial Information Science, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa-shi 277-8568, Chiba, Japan

Energies 2018, 11(1), 22; https://doi.org/10.3390/en11010022 - 22 Dec 2017

Cited by 17 | Viewed by 3647

Abstract

A distributed energy resource (DER) system, which can be defined as a medium or small energy conversion and utilization system with various functions for meeting multiple targets, is directly oriented towards users and achieves on-site production and energy supply according to users’ demands. [...] Read more.

A distributed energy resource (DER) system, which can be defined as a medium or small energy conversion and utilization system with various functions for meeting multiple targets, is directly oriented towards users and achieves on-site production and energy supply according to users’ demands. Optimization research on system construction has recently become an important issue. In this paper, simple stochastic mathematical equations were used to interpret the optimal design problem of a DER system, and based on this, a novel method for solving the optimization problem, which has multi-dimensional stochastic uncertainties (involving the price of input-energy and energy supply and demand), was put forward. A mixed-integer linear programming (MILP) model was established for the optimal design of the DER system by combining the ideas of mean value and variance, aiming to minimize the total costs, including facility costs, energy purchase costs, and loss caused by energy supply shortage, and considering the energy balance and facility performance constraints. In the end, a DER system design for an office building district in Xuzhou, China, was taken as an example to verify the model. The influences of uncertainty on the selection of system facilities and the economic evaluation were analyzed. The result indicated that uncertainty of energy demand played a significant role in optimal design, whereas energy price played a negligible role. With respect to economy, if uncertainties are not considered in system design, it will result in a short supply, and therefore the total cost will increase considerably. The calculation convergence was compared with previous work. The implementation results showed the practicality and efficiency of the proposed method. Full article

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6164 KiB

Open AccessFeature PaperArticle

Complimentary Force Allocation Control for a Dual-Mover Linear Switched Reluctance Machine

by J. F. Pan¹, Weiyu Wang¹, Bo Zhang¹

, Eric Cheng², Jianping Yuan³, Li Qiu^1,* and Xiaoyu Wu^1,*

¹ College of Mechatronics and Control Engineering, Shenzhen University, Shenzhen 518060, China

² Department of Electrical Engineering, Hong Kong Polytechnic University, Hong Kong, China

³ Laboratory of Advanced Unmanned Systems Technology, Research Institute of Northwestern Polytechnical University in Shenzhen, Shenzhen 518060, China

Energies 2018, 11(1), 23; https://doi.org/10.3390/en11010023 - 22 Dec 2017

Cited by 7 | Viewed by 2870

Abstract

This paper inspects the complementary force allocation control schemes for an integrated, dual-mover linear switched reluctance machine (LSRM). The performance of the total force is realized by the coordination of the two movers. First, the structure and characteristics of the LSRM are investigated. [...] Read more.

This paper inspects the complementary force allocation control schemes for an integrated, dual-mover linear switched reluctance machine (LSRM). The performance of the total force is realized by the coordination of the two movers. First, the structure and characteristics of the LSRM are investigated. Then, a complimentary force allocation control scheme for the two movers is proposed. Next, three force allocation methods—constant proportion, constant proportion with a saturation interval and error compensation, and the variable proportion allocation strategies—are proposed and analyzed, respectively. Experimental results demonstrate that the complimentary force interaction between the two movers can effectively reduce the total amount of force ripples from each method. The results under the variable proportion method also show that dynamic error values falling into 0.044 mm and −0.04 mm under the unit ramp force reference can be achieved. With the sinusoidal force reference with an amplitude of 60 N and a frequency of 0.5 Hz, a dynamic force control precision of 0.062 N and 0.091 N can also be obtained. Full article

(This article belongs to the Special Issue Networked and Distributed Control Systems)

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7224 KiB

Open AccessArticle

Distributed Variable Droop Curve Control Strategies in Smart Microgrid

by Changhong Deng, Yahong Chen^*

, Jin Tan

, Pei Xia, Ning Liang

, Weiwei Yao

and Yuan-ao Zhang

School of Electrical Engineering, Wuhan University, Wuhan 430072, Hubei, China

Energies 2018, 11(1), 24; https://doi.org/10.3390/en11010024 - 22 Dec 2017

Cited by 3 | Viewed by 3940

Abstract

In micro grid (MG), active/reactive power sharing for all dis-patchable units is an important issue. To meet fluctuating loads’ active and reactive power demands, the units generally adopt primary P-f and Q-U droop control methods. However, at different state of charge (SOC) values, [...] Read more.

In micro grid (MG), active/reactive power sharing for all dis-patchable units is an important issue. To meet fluctuating loads’ active and reactive power demands, the units generally adopt primary P-f and Q-U droop control methods. However, at different state of charge (SOC) values, the capability of Lead Acid Battery Bank (LABB) based units to take loads varies in a large range; active power should not be shared according to the units P capacities in a constant ratio. Besides, influenced by the output and line impedance between units, reactive power is not able to be shared in proportion to the units Q capacities. Another problem, after MG power balance requirement is satisfied, frequency and voltage are deviating from their rated values thus power quality is reduced. This paper presents a new smart MG which is based on the multi agent system. To solve the problems mentioned above, P-f and Q-U droop curves are adjusted dynamically and autonomously in local agents. To improve the power quality, secondary restoration function is realized in a decentralized way, the computation tasks are assigned to local, the computation capability and communication reliability requirements for central PC are low, and operation reliability is high. Simulation results back the proposed methods. Full article

(This article belongs to the Special Issue Advanced Operation and Control of Smart Microgrids)

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7775 KiB

Open AccessArticle

Impact of Thermal Pretreatment Temperatures on Woody Biomass Chemical Composition, Physical Properties and Microstructure

by Ping Wang^*

and Bret H. Howard

Department of Energy (DOE), National Energy Technology Laboratory (NETL), 626 Cochrans Mill Road, Pittsburgh, PA 15236, USA

Energies 2018, 11(1), 25; https://doi.org/10.3390/en11010025 - 23 Dec 2017

Cited by 35 | Viewed by 5831

Abstract

Thermal pretreatment of biomass by torrefaction and low temperature pyrolysis has the potential for generating high quality and more suitable fuels. To utilize a model to describe the complex and dynamic changes taking place during these two treatments for process design, optimization and [...] Read more.

Thermal pretreatment of biomass by torrefaction and low temperature pyrolysis has the potential for generating high quality and more suitable fuels. To utilize a model to describe the complex and dynamic changes taking place during these two treatments for process design, optimization and scale-up, detailed data is needed on the property evolution during treatment of well-defined individual biomass particles. The objectives of this study are to investigate the influence of thermal pretreatment temperatures on wood biomass biochemical compositions, physical properties and microstructure. Wild cherry wood was selected as a model biomass and prepared for this study. The well-defined wood particle samples were consecutively heated at 220, 260, 300, 350, 450 and 550 °C for 0.5 h under nitrogen. Untreated and treated samples were characterized for biochemical composition changes (cellulose, hemicellulose, and lignin) by thermogravimetric analyzer (TGA), physical properties (color, dimensions, weight, density and grindablity), chemical property (proximate analysis and heating value) and microstructural changes by scanning electron microscopy (SEM). Hemicellulose was mostly decomposed in the samples treated at 260 and 300 °C and resulted in the cell walls weakening resulting in improved grindability. The dimensions of the wood were reduced in all directions and shrinkage increased with increased treatment temperature and weight loss. With increased treatment temperature, losses of weight and volume increased and bulk density decreased. The low temperature pyrolyzed wood samples improved solid fuel property with high fuel ratio, which are close to lignite/bituminous coal. Morphology of the wood remained intact through the treatment range but the cell walls were thinner. These results will improve the understanding of the property changes of the biomass during pretreatment and will help to develop models for process simulation and potential application of the treated biomass. Full article

(This article belongs to the Special Issue Woody Biomass for Bioenergy Production)

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7813 KiB

Open AccessArticle

Control of Variable Speed Wind Turbines with Doubly Fed Asynchronous Generators for Stand-Alone Applications

by Santiago Arnaltes

, Jose Luis Rodriguez-Amenedo and Miguel E. Montilla-DJesus^*

Electrical Engineering Department, Carlos III University of Madrid, Av. de la Universidad 30, Leganés, 28911 Madrid, Spain

Energies 2018, 11(1), 26; https://doi.org/10.3390/en11010026 - 23 Dec 2017

Cited by 30 | Viewed by 5666

Abstract

This paper addresses the design and implementation of a novel control of a variable speed wind turbine with doubly fed induction generator for stand-alone applications. In opposition to grid-tied applications, in stand-alone systems the voltage and frequency must be generated by the doubly [...] Read more.

This paper addresses the design and implementation of a novel control of a variable speed wind turbine with doubly fed induction generator for stand-alone applications. In opposition to grid-tied applications, in stand-alone systems the voltage and frequency must be generated by the doubly fed induction generator. Therefore, a voltage and frequency controller is required for supplying the load at constant voltage and frequency. This controller is implemented by orientation of the generator stator flux vector along a synchronous reference axis. In this way, constant voltage and frequency is obtained and the generator will supply the active and reactive power demanded by the load, while the wind turbine will be responsible for achieving power balance in the system. Then, power control is assumed by the pitch actuator controlling the rotational speed of the wind turbine for power balancing. A load shedding mechanism is needed if the load power exceeds the maximum available wind power. Detailed simulation results are presented and discussed to demonstrate the capabilities and contributions of the proposed control scheme. Full article

(This article belongs to the Special Issue Wind Turbine Loads and Wind Plant Performance)

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13458 KiB

Open AccessArticle

Improving Transient Response of Power Converter in a Stand-Alone Microgrid Using Virtual Synchronous Generator

by Cao-Khang Nguyen¹, Thai-Thanh Nguyen¹

, Hyeong-Jun Yoo¹ and Hak-Man Kim^1,2,*

¹ Department of Electrical Engineering, Incheon National University, Songdo-dong, 119 Academy-ro, Yeonsu-gu, Incheon 22012, Korea

² Research Institute for Northeast Asian Super Grid, Incheon National University, 119 Academy-ro, Yeonsu-gu, Incheon 22012, Korea

Energies 2018, 11(1), 27; https://doi.org/10.3390/en11010027 - 23 Dec 2017

Cited by 18 | Viewed by 5201

Abstract

Multiple power converters based on the droop controllers have been used widely in the microgrid (MG) system. However, owing to the different response time among several types of power converters such as grid-feeding and grid-forming converters, low frequency oscillation occurs with high overshoot [...] Read more.

Multiple power converters based on the droop controllers have been used widely in the microgrid (MG) system. However, owing to the different response time among several types of power converters such as grid-feeding and grid-forming converters, low frequency oscillation occurs with high overshoot in the transient state. This paper proposes a novel control strategy based on the virtual synchronous generator (VSG) for improving transient response of parallel power converters during large disturbance in the stand-alone microgrid. The proposed VSG control, which inherits the transient state characteristic of the synchronous generator, can provide inertia virtually to the system. The transient response of voltage and frequency is improved, while the total system inertia response is compensated. Thus, the system stability can be enhanced by using the proposed VSG control. Additionally, the small signal analysis of the conventional VSG controller and the proposed VSG controller are carried out to show the effectiveness of the proposed VSG controller. The derivation of frequency, which is used to evaluate the inertia support of the VSG controller to the MG system, is discussed. The simulation result demonstrates that the overshoot of the transient response can be reduced, and the system stability is improved when the proposed VSG controller is applied. The MG system based on the real-time simulator OP5600 (OPAL-RT Technologies, Montreal, QC, Canada) is carried out to verify the feasibility of the proposed VSG controller. Full article

(This article belongs to the Special Issue Distribution System Operation and Control)

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2080 KiB

Open AccessArticle

Remaining Useful Life Estimation of Aircraft Engines Using a Modified Similarity and Supporting Vector Machine (SVM) Approach

by Zhongzhe Chen^1,*, Shuchen Cao² and Zijian Mao¹

¹ School of Mechanical and Electrical Engineering, University of Electronic and Science Technology of China, Chengdu 611731, China

² Department of Mathematics, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA

Energies 2018, 11(1), 28; https://doi.org/10.3390/en11010028 - 23 Dec 2017

Cited by 76 | Viewed by 6061

Abstract

As the main power source for aircrafts, the reliability of an aero engine is critical for ensuring the safety of aircrafts. Prognostics and health management (PHM) on an aero engine can not only improve its safety, maintenance strategy and availability, but also reduce [...] Read more.

As the main power source for aircrafts, the reliability of an aero engine is critical for ensuring the safety of aircrafts. Prognostics and health management (PHM) on an aero engine can not only improve its safety, maintenance strategy and availability, but also reduce its operation and maintenance costs. Residual useful life (RUL) estimation is a key technology in the research of PHM. According to monitored performance data from the engine’s different positions, how to estimate RUL of an aircraft engine by utilizing these data is a challenge for ensuring the engine integrity and safety. In this paper, a framework for RUL estimation of an aircraft engine is proposed by using the whole lifecycle data and performance-deteriorated parameter data without failures based on the theory of similarity and supporting vector machine (SVM). Moreover, a new state of health indicator is introduced for the aircraft engine based on the preprocessing of raw data. Finally, the proposed method is validated by using 2008 PHM data challenge competition data, which shows its effectiveness and practicality. Full article

(This article belongs to the Special Issue Structural Prognostics and Health Management in Power & Energy Systems)

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9258 KiB

Open AccessArticle

Simulation and Empirical Studies of the Commercial SI Engine Performance and Its Emission Levels When Running on a CNG and Hydrogen Blend

by Rafaa Saaidia^1,2,*, Mohamed Ali Jemni¹ and Mohamed Salah Abid¹

¹ Laboratory of the Electromechanical System, Department of Mechanical Engineering, National School of Engineers of Sfax (ENIS), BP. 1173, 3038 Sfax, Tunisia

² Technical and Vocational Training Corporation, Department of Mechanical Engineering, Bishah Technical College, BP. 688, 61922 Bishah, Province of Assir, Saudi Arabia

Energies 2018, 11(1), 29; https://doi.org/10.3390/en11010029 - 23 Dec 2017

Cited by 6 | Viewed by 4475

Abstract

This article is a report on a simulation based on Computational Fluid Dynamics (CFD) and an empirical investigation of in-cylinder flow characteristics, In addition, it assesses the performance and emission levels of a commercial-spark ignited engine running on a CNG and Hydrogen blend [...] Read more.

This article is a report on a simulation based on Computational Fluid Dynamics (CFD) and an empirical investigation of in-cylinder flow characteristics, In addition, it assesses the performance and emission levels of a commercial-spark ignited engine running on a CNG and Hydrogen blend in different ratios. The main objective was to determine the optimum hydrogen ratio that would yield the best brake torque and release the least polluting gases. The in-cylinder flow velocity and turbulence aspects were investigated during the intake stroke in order to analyze the intake flow behavior. To reach this goal, a 3D CFD code was adopted. For various engine speeds were investigated for gasoline, CNG and hydrogen and CNG blend (HCNG) fueled engines via external mixtures. The variation of brake torque (BT), NO_X and CO emissions. A series of tests were conducted on the engine within the speed range of 1000 to 5000 rpm. For this purpose, a commercial Hyundai Sonata S.I engine was modified to operate with a blend of CNG and Hydrogen in different ratios. The experiments attempted to determine the optimum allowable hydrogen ratio with CNG for normal engine operation. The engine performance and the emission levels were also analyzed. At the engine speed of 4200 rpm, the results revealed that beyond a ratio of 50% of the volume of hydrogen added to CNG a backfire phenomenon appeared. Below this ratio (0~40%) of the hydrogen volume, the CNG and Hydrogen blend seemed to be beneficial for the engine performance and for curtailing the emission level. However, at low engine speeds, the NO_X concentration increased simultaneously with hydrogen content. In contrast, at high engine speeds, the NO_X concentration decreased to its lowest level compared to that reached with gasoline as a running fuel. The concentration levels of HC, CO₂, and CO decreased with the increase of hydrogen percentage. Full article

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1895 KiB

Open AccessArticle

Statistics to Detect Low-Intensity Anomalies in PV Systems

by Silvano Vergura^*

and Mario Carpentieri

Department of Electrical and Information Engineering, Polytechnic University of Bari, 70125 Bari, Italy

Energies 2018, 11(1), 30; https://doi.org/10.3390/en11010030 - 23 Dec 2017

Cited by 8 | Viewed by 2688

Abstract

The aim of this paper is the monitoring of the energy performance of Photovoltaic (PV) plants in order to detect the presence of low-intensity anomalies, before they become failures or faults. The approach is based on several statistical tools, which are applied iteratively [...] Read more.

The aim of this paper is the monitoring of the energy performance of Photovoltaic (PV) plants in order to detect the presence of low-intensity anomalies, before they become failures or faults. The approach is based on several statistical tools, which are applied iteratively as the data are acquired. At every loop, new data are added to the previous ones, and a proposed procedure is applied to the new dataset, therefore the analysis is carried out on cumulative data. In this way, it is possible to track some specific parameters and to monitor that identical arrays in the same operating conditions produce the same energy. The procedure is based on parametric (ANOVA) and non-parametric tests, and results effective in locating anomalies. Three cumulative case studies, based on a real operating PV plant, are analyzed. Full article

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1894 KiB

Open AccessArticle

Calibration of Mine Ventilation Network Models Using the Non-Linear Optimization Algorithm

by Guang Xu^1,2

, Jinxin Huang^1,*

, Baisheng Nie³, Duncan Chalmers⁴ and Zhuoming Yang³

¹ Department of Mining Engineering and Metallurgical Engineering, Western Australian School of Mines, Curtin University, Kalgoorlie 6430, Australia

² State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology, Xuzhou 221100, China

³ School of Resources and Safety Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China

⁴ School of Mining Engineering, University of New South Wales, Sydney 2052, Australia

Energies 2018, 11(1), 31; https://doi.org/10.3390/en11010031 - 23 Dec 2017

Cited by 29 | Viewed by 5987

Abstract

Effective ventilation planning is vital to underground mining. To ensure stable operation of the ventilation system and to avoid airflow disorder, mine ventilation network (MVN) models have been widely used in simulating and optimizing the mine ventilation system. However, one of the challenges [...] Read more.

Effective ventilation planning is vital to underground mining. To ensure stable operation of the ventilation system and to avoid airflow disorder, mine ventilation network (MVN) models have been widely used in simulating and optimizing the mine ventilation system. However, one of the challenges for MVN model simulation is that the simulated airflow distribution results do not match the measured data. To solve this problem, a simple and effective calibration method is proposed based on the non-linear optimization algorithm. The calibrated model not only makes simulated airflow distribution results in accordance with the on-site measured data, but also controls the errors of other parameters within a minimum range. The proposed method was then applied to calibrate an MVN model in a real case, which is built based on ventilation survey results and Ventsim software. Finally, airflow simulation experiments are carried out respectively using data before and after calibration, whose results were compared and analyzed. This showed that the simulated airflows in the calibrated model agreed much better to the ventilation survey data, which verifies the effectiveness of calibrating method. Full article

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19 pages, 3708 KiB

Open AccessArticle

High-Precision Speed Control Based on Multiple Phase-Shift Resonant Controllers for Gimbal System in MSCMG

by Jian Feng¹

, Qing Wang² and Kun Liu^1,*

¹ College of Aerospace Science and Engineering, National University of Defense Technology, Changsha 410073, China

² Shanghai Institute of Spaceflight Control Technology, Shanghai 210011, China

Energies 2018, 11(1), 32; https://doi.org/10.3390/en11010032 - 1 Jan 2018

Cited by 11 | Viewed by 3971

Abstract

The high precision speed control of gimbal servo system in magnetically suspended control moment gyro (MSCMG) suffers from periodic torque disturbances, which lead to periodic fluctuations in speed control. This paper proposes a novel multiple phase-shift resonant controller (MPRC) for a gimbal servo [...] Read more.

The high precision speed control of gimbal servo system in magnetically suspended control moment gyro (MSCMG) suffers from periodic torque disturbances, which lead to periodic fluctuations in speed control. This paper proposes a novel multiple phase-shift resonant controller (MPRC) for a gimbal servo system to suppress the periodic torque ripples whose frequencies vary with the operational speed of the gimbal servo motor and high-speed motor. First, the periodic torque ripples caused by cogging torque, flux harmonics and the dynamic unbalance of the high speed rotor are analyzed. Second, the principle and structure of MPRC parallel with proportional integral (PI) controllers are discussed. The design and stability analysis of the proposed MPRC plus PI control scheme are given both for the current loop and speed loop. The closed-loop stability is ensured by adjusting the phase in the entire operational speed range. Finally, the effectiveness of the proposed control method is verified through simulation and experimental results. Full article

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5442 KiB

Open AccessArticle

The Lubricity of Ternary Fuel Mixture Blends as a Way to Assess Diesel Engine Durability

by Abul Kalam Azad^*

, Mohammad Golam Rasul, Subhash Chandra Sharma and Mohammad Masud Kamal Khan

School of Engineering and Technology, Central Queensland University, Melbourne, VIC 3000, Australia

Energies 2018, 11(1), 33; https://doi.org/10.3390/en11010033 - 24 Dec 2017

Cited by 14 | Viewed by 4098

Abstract

The study deals with the lubrication characteristics of ternary fuel mixture blends to assess diesel engine durability by using better performing fuels, namely Mandarin Crambe and Paraffin (ManCr_Pa) and Avocado Bush nut and Paraffin (AvBn_Pa). Tribological parameters of friction coefficient, wear, and lubrication [...] Read more.

The study deals with the lubrication characteristics of ternary fuel mixture blends to assess diesel engine durability by using better performing fuels, namely Mandarin Crambe and Paraffin (ManCr_Pa) and Avocado Bush nut and Paraffin (AvBn_Pa). Tribological parameters of friction coefficient, wear, and lubrication stability were measured to assess the impact of these fuels on engine durability. The tests were conducted on a four-ball tribotester using the American Society for Testing Materials (ASTM) D4172 standard; friction coefficient and wear scar diameter for the fuels were measured. The wear scar surface morphology of the ball metals was evaluated by a high-performance scanning electron microscope with energy dispersive X-ray SEM/EDX analysis. The corrosive behaviour of the fuels was also assessed by evaluating images from the SEM/EDX tests. Finally, the engine durability, reliability, and longevity were also evaluated based on the measured tribological parameters. Full article

(This article belongs to the Collection Bioenergy and Biofuel)

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5282 KiB

Open AccessArticle

A Real-Time Accurate Model and Its Predictive Fuzzy PID Controller for Pumped Storage Unit via Error Compensation

by Jianzhong Zhou, Zhigao Zhao^*, Chu Zhang, Chaoshun Li and Yanhe Xu

School of Hydropower and Information Engineering, Hubei Key Laboratory of Digital Valley Science and Technology; Huazhong University of Science and Technology, Wuhan 430074, China

Energies 2018, 11(1), 35; https://doi.org/10.3390/en11010035 - 24 Dec 2017

Cited by 25 | Viewed by 3904

Abstract

Model simulation and control of pumped storage unit (PSU) are essential to improve the dynamic quality of power station. Only under the premise of the PSU models reflecting the actual transient process, the novel control method can be properly applied in the engineering. [...] Read more.

Model simulation and control of pumped storage unit (PSU) are essential to improve the dynamic quality of power station. Only under the premise of the PSU models reflecting the actual transient process, the novel control method can be properly applied in the engineering. The contributions of this paper are that (1) a real-time accurate equivalent circuit model (RAECM) of PSU via error compensation is proposed to reconcile the conflict between real-time online simulation and accuracy under various operating conditions, and (2) an adaptive predicted fuzzy PID controller (APFPID) based on RAECM is put forward to overcome the instability of conventional control under no-load conditions with low water head. Respectively, all hydraulic factors in pipeline system are fully considered based on equivalent lumped-circuits theorem. The pretreatment, which consists of improved Suter-transformation and BP neural network, and online simulation method featured by two iterative loops are synthetically proposed to improve the solving accuracy of the pump-turbine. Moreover, the modified formulas for compensating error are derived with variable-spatial discretization to improve the accuracy of the real-time simulation further. The implicit RadauIIA method is verified to be more suitable for PSUGS owing to wider stable domain. Then, APFPID controller is constructed based on the integration of fuzzy PID and the model predictive control. Rolling prediction by RAECM is proposed to replace rolling optimization with its computational speed guaranteed. Finally, the simulation and on-site measurements are compared to prove trustworthy of RAECM under various running conditions. Comparative experiments also indicate that APFPID controller outperforms other controllers in most cases, especially low water head conditions. Satisfying results of RAECM have been achieved in engineering and it provides a novel model reference for PSUGS. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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3167 KiB

Open AccessArticle

A Novel High Accuracy PV Cell Model Including Self Heating and Parameter Variation

by Aurel Gontean^*

, Septimiu Lica

, Szilard Bularka, Roland Szabo

and Dan Lascu

Applied Electronics Department, Politehnica University Timisoara, Timisoara 300006, Romania

Energies 2018, 11(1), 36; https://doi.org/10.3390/en11010036 - 24 Dec 2017

Cited by 20 | Viewed by 4578

Abstract

This paper proposes a novel model for a PV cell with parameters variance dependency on temperature and irradiance included. The model relies on commercial available data, calculates the cell parameters for standard conditions and then extrapolates them for the whole operating range. An [...] Read more.

This paper proposes a novel model for a PV cell with parameters variance dependency on temperature and irradiance included. The model relies on commercial available data, calculates the cell parameters for standard conditions and then extrapolates them for the whole operating range. An up-to-date review of the PV modeling is also included with series and parallel parasitic resistance values and dependencies discussed. The parameters variance is analyzed and included in the proposed PV model, where the self-heating phenomenon is also considered. Each parameter variance is compared to the results from different authors. The model includes only standard components and can be run on any SPICE-based simulator. Unlike other approaches that consider the internal temperature as a parameter, our proposal relies on air temperature as an input and computes the actual internal temperature accordingly. Finally, the model is validated via experiments and comparisons to similar approaches are provided. Full article

(This article belongs to the Section L: Energy Sources)

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4997 KiB

Open AccessArticle

Comparative Modeling of a Parabolic Trough Collectors Solar Power Plant with MARS Models

by Jose Ramón Rogada¹, Lourdes A. Barcia², Juan Angel Martinez³, Mario Menendez¹ and Francisco Javier De Cos Juez^1,*

¹ Department of Exploitation and Prospection of Mining, University of Oviedo, 33004 Asturias, Spain

² NORMAGRUP TECHNOLOGY S.A. Llanera, 33420 Asturias, Spain

³ Department of Electrical Engineering, University of Oviedo, 33004 Asturias, Spain

Energies 2018, 11(1), 37; https://doi.org/10.3390/en11010037 - 25 Dec 2017

Cited by 6 | Viewed by 4697

Abstract

Power plants producing energy through solar fields use a heat transfer fluid that lends itself to be influenced and changed by different variables. In solar power plants, a heat transfer fluid (HTF) is used to transfer the thermal energy of solar radiation through [...] Read more.

Power plants producing energy through solar fields use a heat transfer fluid that lends itself to be influenced and changed by different variables. In solar power plants, a heat transfer fluid (HTF) is used to transfer the thermal energy of solar radiation through parabolic collectors to a water vapor Rankine cycle. In this way, a turbine is driven that produces electricity when coupled to an electric generator. These plants have a heat transfer system that converts the solar radiation into heat through a HTF, and transfers that thermal energy to the water vapor heat exchangers. The best possible performance in the Rankine cycle, and therefore in the thermal plant, is obtained when the HTF reaches its maximum temperature when leaving the solar field (SF). In addition, it is necessary that the HTF does not exceed its own maximum operating temperature, above which it degrades. The optimum temperature of the HTF is difficult to obtain, since the working conditions of the plant can change abruptly from moment to moment. Guaranteeing that this HTF operates at its optimal temperature to produce electricity through a Rankine cycle is a priority. The oil flowing through the solar field has the disadvantage of having a thermal limit. Therefore, this research focuses on trying to make sure that this fluid comes out of the solar field with the highest possible temperature. Modeling using data mining is revealed as an important tool for forecasting the performance of this kind of power plant. The purpose of this document is to provide a model that can be used to optimize the temperature control of the fluid without interfering with the normal operation of the plant. The results obtained with this model should be necessarily contrasted with those obtained in a real plant. Initially, we compare the PID (proportional–integral–derivative) models used in previous studies for the optimization of this type of plant with modeling using the multivariate adaptive regression splines (MARS) model. Full article

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4617 KiB

Open AccessArticle

Evaluation of the Internal and Borehole Resistances during Thermal Response Tests and Impact on Ground Heat Exchanger Design

by Louis Lamarche^1,*, Jasmin Raymond² and Claude Hugo Koubikana Pambou²

¹ De génie mécanique, École de Technologie Supérieure, Montreal, QC H3C1K3, Canada

² Centre Eau Terre Environnement, Institut national de la recherche scientifique, Québec City, QC G1K9A9, Canada

Energies 2018, 11(1), 38; https://doi.org/10.3390/en11010038 - 25 Dec 2017

Cited by 16 | Viewed by 4018

Abstract

The main parameters evaluated with a conventional thermal response test (TRT) are the subsurface thermal conductivity surrounding the borehole and the effective borehole thermal resistance, when averaging the inlet and outlet temperature of a ground heat exchanger with the arithmetic mean. This effective [...] Read more.

The main parameters evaluated with a conventional thermal response test (TRT) are the subsurface thermal conductivity surrounding the borehole and the effective borehole thermal resistance, when averaging the inlet and outlet temperature of a ground heat exchanger with the arithmetic mean. This effective resistance depends on two resistances: the 2D borehole resistance (R_b) and the 2D internal resistance (R_a) which is associated to the short-circuit effect between pipes in the borehole. This paper presents a field method to evaluate these two components separately. Two approaches are proposed. In the first case, the temperature at the bottom of the borehole is measured at the same time as the inlet and outlet temperatures as done in a conventional TRT. In the second case, different flow rates are used during the experiment to infer the internal resistance. Both approaches assumed a predefined temperature profile inside the borehole. The methods were applied to real experimental tests and compared with numerical simulations. Interesting results were found by comparison with theoretical resistances calculated with the multipole method. The motivation for this work is evidenced by analyzing the impact of the internal resistance on a typical geothermal system design. It is shown to be important to know both resistance components to predict the variation of the effective resistance when the flow rate and the height of the boreholes are changed during the design process. Full article

(This article belongs to the Special Issue Geothermal Heating and Cooling)

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2599 KiB

Open AccessArticle

Toward Complete Utilization of Miscanthus in a Hot-Water Extraction-Based Biorefinery

by Kuo-Ting Wang

, Chengyan Jing, Christopher Wood, Aditi Nagardeolekar

, Neil Kohan, Prajakta Dongre, Thomas E. Amidon and Biljana M. Bujanovic^*

Department of Paper and Bioprocess Engineering, SUNY College of Environmental Science and Forestry, 1 Forestry Drive, Syracuse, NY 13210, USA

Energies 2018, 11(1), 39; https://doi.org/10.3390/en11010039 - 25 Dec 2017

Cited by 24 | Viewed by 5182

Abstract

Miscanthus (Miscanthus sp. Family: Poaceae) was hot-water extracted (two h, at 160 °C) at three scales: laboratory (Parr reactor, 300 cm³), intermediate (M/K digester, 4000 cm³), and pilot (65 ft³-digester, 1.841 × 10⁶ cm [...] Read more.

Miscanthus (Miscanthus sp. Family: Poaceae) was hot-water extracted (two h, at 160 °C) at three scales: laboratory (Parr reactor, 300 cm³), intermediate (M/K digester, 4000 cm³), and pilot (65 ft³-digester, 1.841 × 10⁶ cm³). Hot-water extracted miscanthus, hydrolyzate, and lignin recovered from hydrolyzate were characterized and evaluated for potential uses aiming at complete utilization of miscanthus. Effects of scale-up on digester yield, removal of hemicelluloses, deashing, delignification degree, lignin recovery and purity, and cellulose retention were studied. The scale-dependent results demonstrated that before implementation, hot-water extraction (HWE) should be evaluated on a scale larger than a laboratory scale. The production of energy-enriched fuel pellets from hot-water extracted miscanthus, especially in combination with recovered lignin is recommended, as energy of combustion increased gradually from native to hot-water extracted miscanthus to recovered lignin. The native and pilot-scale hot-water extracted miscanthus samples were also subjected to enzymatic hydrolysis using a cellulase-hemicellulase cocktail, to produce fermentable sugars. Hot-water extracted biomass released higher amount of glucose and xylose verifying benefits of HWE as an effective pretreatment for xylan-rich lignocellulosics. The recovered lignin was used to prepare a formaldehyde-free alternative to phenol-formaldehyde resins and as an antioxidant. Promising results were obtained for these lignin valorization pathways. Full article

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5484 KiB

Open AccessArticle

Research on Strategies and Methods Suppressing Permanent Magnet Demagnetization in Permanent Magnet Synchronous Motors Based on a Multi-Physical Field and Rotor Multi-Topology Structure

by Lin Li¹, Weili Li^1,*, Dong Li¹, Jinyang Li² and Yu Fan¹

¹ School of Electrical Engineering, Beijing Jiaotong University, Beijing 100044, China

² School of Electrical Engineering and Automation, Harbin Institute of Technology, Harbin 150001, China

Energies 2018, 11(1), 40; https://doi.org/10.3390/en11010040 - 25 Dec 2017

Cited by 3 | Viewed by 3373

Abstract

In this paper, a permanent magnet synchronous motor (PMSM) with sleeves on the rotor outer surface is investigated. The purpose of sleeves is to fix the permanent magnets and protect them from being destroyed by the large centrifugal force. However, the sleeve material [...] Read more.

In this paper, a permanent magnet synchronous motor (PMSM) with sleeves on the rotor outer surface is investigated. The purpose of sleeves is to fix the permanent magnets and protect them from being destroyed by the large centrifugal force. However, the sleeve material characteristics have a great influence on the PMSM, and therewith, most of the rotor eddy-current losses are generated in the rotor sleeve, which could increase the device temperature and even cause thermal demagnetization of the magnets. Thus, a sleeve scheme design with low eddy-current losses is necessary, and a method suppressing the local temperature peak of permanent magnets is presented. The 3-D electromagnetic finite element model of a 12.5 kW, 2000 r/min PMSM with a segmented sleeve is established, and the electromagnetic field is calculated by using the finite element method. The results show the effectiveness of the presented method in reducing the eddy current losses in the rotor. Using the thermal method, it can be found that the maximum temperature position and zone of permanent magnet will change. Thus, some strategies are comparatively analyzed in order to obtain the change rule of the position and zone. The obtained conclusions may provide a useful reference for the design and research of PMSMs. Full article

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13096 KiB

Open AccessArticle

Development and Analysis of a Novel Spherical 2-Degree-of-Freedom (2-DOF) Hybrid Stepping Motor

by Binglin Lu and Yanliang Xu^*

College of Electrical Engineering, Shandong University, Jinan 250061, China

Energies 2018, 11(1), 41; https://doi.org/10.3390/en11010041 - 25 Dec 2017

Cited by 3 | Viewed by 5457

Abstract

A novel spherical two-degree-of-freedom (2-DOF) hybrid stepping motor is proposed in this paper, which has a simple and compact mechanical structure and is easy to manufacture, assemble, control and apply. The motor is composed of two sub-motors, each of which is a hybrid [...] Read more.

A novel spherical two-degree-of-freedom (2-DOF) hybrid stepping motor is proposed in this paper, which has a simple and compact mechanical structure and is easy to manufacture, assemble, control and apply. The motor is composed of two sub-motors, each of which is a hybrid stepping type with an arc-shaped stator and a specially designed bearing structure. The rotational axes of these two sub-motors cross at the sphere center, and this structure enables the 2-DOF motor to move in any direction. Due to the mutual influence of permanent magnet (PM) leakage flux between the two sub-motors, the 3-D magnetic field distribution inside the motor becomes more complex, and thus the 2-D equivalent magnetic field analysis method is proposed, with two types of 2-D equivalent motor models established. The accurate one can take into account of the PM leakage flux influence yet is only suitable for solving motor’s static and steady state problem, whilst the simplified one can solve all the problems and is applicable for the more typical situation where the PM leakage flux influence can be almost neglected via optimal structure design. A prototype of the proposed spherical 2-DOF motor with outside diameter of 50 mm is newly manufactured and experimented to validate the feasibility of motor’s operational principle, and the accuracy of both 2-D equivalent motor models is verified by the 3-D finite element analysis (3-D FEA) calculation results. Based on the 2-D equivalent motor models, the 2-D FEA is employed for the performance analysis, such as no-load back electromotive force (EMF), tooth-layer permeance harmonics, detent torque, pull-out torque, unbalanced force, etc., which is characterized by time- saving, high accuracy and good versatility. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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4199 KiB

Open AccessArticle

A Transient Analytical Model for Predicting Wellbore/Reservoir Temperature and Stresses during Drilling with Fluid Circulation

by Bisheng Wu^1,*, Tianle Liu^2,*, Xi Zhang¹, Bailin Wu¹, Robert G. Jeffrey³ and Andrew P. Bunger^4,5

¹ CSIRO Energy, Clayton, VIC 3168, Australia

² Faculty of Engineering, China University of Geosciences, Wuhan 430074, China

³ SCT Operations, Wollongong, NSW 2500, Australia

⁴ Department of Civil and Environmental Engineering, University of Pittsburgh, Pittsburgh, PA 15261, USA

⁵ Department of Chemical and Petroleum Engineering, University of Pittsburgh, Pittsburgh, PA 15261, USA

Energies 2018, 11(1), 42; https://doi.org/10.3390/en11010042 - 25 Dec 2017

Cited by 18 | Viewed by 4904

Abstract

Accurate characterization of heat transfer in a wellbore during drilling, which includes fluid circulation, is important for wellbore stability analysis. In this work, a pseudo-3D model is developed to simultaneously calculate the heat exchange between the flowing fluid and the surrounding media (drill [...] Read more.

Accurate characterization of heat transfer in a wellbore during drilling, which includes fluid circulation, is important for wellbore stability analysis. In this work, a pseudo-3D model is developed to simultaneously calculate the heat exchange between the flowing fluid and the surrounding media (drill pipe and rock formation) and the in-plane thermoelastic stresses. The cold drilling fluid descends through the drill pipe at constant injection rates and returns to the ground surface via the annulus. The fluid circulation will decrease the wellbore bottom temperature and reduce the near-wellbore high compressive stress, potentially leading to tensile fracturing of the well. The governing equations for the coupled heat transfer stress problem are formulated to ensure that the most important parameters are taken into account. The wellbore is subject to a non-hydrostatic in situ far-field stress field. In modeling heat exchange between fluid and surrounding media, the heat transfer coefficients are dependent on fluid properties and flow behavior. Analytical solutions in the Laplace space are obtained for the temperatures of the fluid in both the drill pipe and annulus and for the temperature and stress changes in the formation. The numerical results in the time domain are obtained by using an efficient inversion approach. In particular, the near-well stresses are compared for the cases with fixed and time-dependent cooling wellbore conditions. This comparison indicates that the using a fixed temperature wellbore conditions may over-estimate or under-estimate the bottom-hole stress change, potentially leading to wellbore stability problems. Full article

(This article belongs to the Special Issue Selected Papers from Sixth Annual Conference for the Development and Utilization of Deep Geothermal Energy)

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21 pages, 4591 KiB

Open AccessArticle

Rate Decline Analysis for Modeling Volume Fractured Well Production in Naturally Fractured Reservoirs

by Mingxian Wang, Zifei Fan, Guoqiang Xing^*

, Wenqi Zhao, Heng Song and Penghui Su

Research Institute of Petroleum Exploration and Development, PetroChina, Beijing 100083, China

Energies 2018, 11(1), 43; https://doi.org/10.3390/en11010043 - 1 Jan 2018

Cited by 11 | Viewed by 4087

Abstract

Based on the property discontinuity in the radial direction, this paper develops a new composite model to simulate the productivity of volume fractured wells in naturally fractured reservoirs. The analytical solution of this model is derived in detail and its accuracy is verified [...] Read more.

Based on the property discontinuity in the radial direction, this paper develops a new composite model to simulate the productivity of volume fractured wells in naturally fractured reservoirs. The analytical solution of this model is derived in detail and its accuracy is verified by the same model’s numerical solution. Detailed analyses of the traditional transient and cumulative rate are provided for the composite model. Results show that volume fracturing mainly contributes to the early-flow period’s production rate. As interregional diffusivity ratio increases or interregional conductivity ratio decreases, the transient rate at the same wellbore pressure increases. Three characteristic decline stages may be observed on transient rate curves and the shape of traditional rate curves in the middle- and late-flow periods depends on naturally fractured medium and boundary condition. By introducing a new pseudo-steady constant, new Blasingame type curves are also established and their features are more salient than those of traditional rate curves. Five typical flow regimes can be observed on these new type curves. Sensitivity analysis indicates that new Blasingame type curves for varied interregional diffusivity ratio, interregional conductivity ratio, interporosity coefficient and dimensionless reservoir radius, except storativity ratio, will normalize in the late-flow period. Full article

(This article belongs to the Special Issue Mathematical and Computational Modeling in Geothermal Engineering)

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19 pages, 9171 KiB

Open AccessArticle

Transient Stability Analysis of Islanded AC Microgrids with a Significant Share of Virtual Synchronous Generators

by Chang Yuan, Peilin Xie^*

, Dan Yang and Xiangning Xiao

State Key Laboratory for Alternate Electrical Power System with Renewable Energy Source, North China Electric Power University, Beijing 102206, China

Energies 2018, 11(1), 44; https://doi.org/10.3390/en11010044 - 1 Jan 2018

Cited by 21 | Viewed by 5395

Abstract

As an advanced control method that could bring extra inertia and damping characteristics to inverter-based distributed generators, the virtual synchronous generator (VSG) has recently drawn considerable attention. VSGs are expected to enhance the frequency regulation capability of the local power grid, especially the [...] Read more.

As an advanced control method that could bring extra inertia and damping characteristics to inverter-based distributed generators, the virtual synchronous generator (VSG) has recently drawn considerable attention. VSGs are expected to enhance the frequency regulation capability of the local power grid, especially the AC microgrid in island mode. However, the cost of that performance promotion is potential instability. In this paper, the unstable phenomena of the islanded microgrid dominated by SGs and distributed generators (DSs) are addressed after mathematical modeling and detailed eigenvalue analyses respectively. The influence of VSG key parameters, e.g., virtual inertia, damping factor, and droop coefficient on system stability is investigated, and the corresponding mathematical calculation method of unstable region is obtained. The theoretical analysis is well supported by time domain simulation results. The predicted frequency oscillation suggests the consideration of stability constrain during the VSG parameters design procedure. Full article

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12 pages, 5563 KiB

Open AccessArticle

A Three-Phase Dynamic Wireless Charging System with Constant Output Voltage

by Ruikun Mai

, Hongchao Li, Yeran Liu, Kunzhuo Zhou, Ling Fu^* and Zhengyou He^*

School of Electrical Engineering, Southwest Jiaotong University, Chengdu 610031, China

Energies 2018, 11(1), 45; https://doi.org/10.3390/en11010045 - 1 Jan 2018

Cited by 16 | Viewed by 4647

Abstract

A dynamic wireless power transfer (WPT) system is an effective method, which can reduce charging time and extend the driving range of the electric vehicles. In the dynamic WPT systems, the output voltage may fluctuate when the receiver moves along the transmitter coils. [...] Read more.

A dynamic wireless power transfer (WPT) system is an effective method, which can reduce charging time and extend the driving range of the electric vehicles. In the dynamic WPT systems, the output voltage may fluctuate when the receiver moves along the transmitter coils. This paper proposes a three-phase dynamic WPT charging system with overlapped three-phase transmitter coils. The overlap length is optimized to depress the fluctuation of the output voltage. These coils are powered by a three-phase inverter to generate an even magnetic field, and a unipolar coil is employed as a receiver to simplify the coil structure of the secondary side. Based on the proposed three-phase coil structure, the output voltage characteristics of the system are analyzed in detail. A 500 W dynamic charging prototype is established to validate the proposed dynamic charging system. Experimental results show that the output voltage fluctuation is within ±3.05%. The maximum system efficiency reaches 89.94%. Full article

(This article belongs to the Special Issue Wireless Power Transfer and Energy Harvesting Technologies)

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2328 KiB

Open AccessArticle

Simultaneous Provision of Flexible Ramping Product and Demand Relief by Interruptible Loads Considering Economic Incentives

by Jiahua Hu¹, Fushuan Wen^2,3,*, Ke Wang⁴, Yuchun Huang⁴ and Md. Abdus Salam⁵

¹ School of Electrical Engineering, Zhejiang University, No. 38 Zheda Rd., Hangzhou 310027, China

² Department for Management of Science and Technology Development, Ton Duc Thang University, Ho Chi Minh City, Vietnam

³ Faculty of Electrical and Electronics Engineering, Ton Duc Thang University, Ho Chi Minh City, Vietnam

⁴ Guangzhou Power Supply Company Limited, Guangzhou 510620, China

⁵ Department of Electrical and Electronic Engineering, Universiti Teknologi Brunei, Bandar Seri Begawan BE1410, Brunei

Energies 2018, 11(1), 46; https://doi.org/10.3390/en11010046 - 26 Dec 2017

Cited by 19 | Viewed by 3679

Abstract

To cope with the net load variability in real time, sufficient ramp capability from controllable resources is required. To address the issue of insufficient ramp capacity in real time operations, flexible ramping products (FRPs) have been adopted by some Independent System Operators (ISOs) [...] Read more.

To cope with the net load variability in real time, sufficient ramp capability from controllable resources is required. To address the issue of insufficient ramp capacity in real time operations, flexible ramping products (FRPs) have been adopted by some Independent System Operators (ISOs) in the USA as a new market design. The inherent variability and uncertainty caused by renewable energy sources (RESs) call for new FRP providers apart from conventional generating units. The so-called interruptible load (IL) has proved to be useful in maintaining the supply-demand balance by providing demand relief and can be a viable FRP provider in practice. Given this background, this work presents a stochastic real-time unit commitment model considering ramp requirement and simultaneous provision of IL for FRP and demand relief. Load serving entities (LSEs) are included in the proposed model and act as mediators between the ISO and multiple ILs. In particular, incentive compatible contracts are designed to encourage customers to reveal their true outage costs. Case studies indicate both the system and LSEs can benefit by employing the proposed method and ILs can gain the highest profits by signing up a favorable contract. Full article

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1112 KiB

Open AccessArticle

Co-Digestion of Napier Grass and Its Silage with Cow Dung for Bio-Hydrogen and Methane Production by Two-Stage Anaerobic Digestion Process

by Wipa Prapinagsorn^1,2, Sureewan Sittijunda³ and Alissara Reungsang^1,4,*

¹ Department of Biotechnology, Faculty of Technology, Khon Kaen University, Khon Kaen 40002, Thailand

² Faculty of Agriculture, Uttaradit Rajabhat University, Uttaradit 53000, Thailand

³ Faculty of Environment and Resource Studies, Mahidol University, Nakhon Pathom 73170, Thailand

⁴ Research Group for Development of Microbial Hydrogen Production Process from Biomass-Khon Kaen University, Khon Kaen 40002, Thailand

Energies 2018, 11(1), 47; https://doi.org/10.3390/en11010047 - 26 Dec 2017

Cited by 26 | Viewed by 6664

Abstract

The objective of this study was to efficiently utilize the napier grass and its silage to produce bio-hydrogen and methane by a two-stage process in batch mode. First, the production of hydrogen from a co-digestion of grass with cow dung and silage with [...] Read more.

The objective of this study was to efficiently utilize the napier grass and its silage to produce bio-hydrogen and methane by a two-stage process in batch mode. First, the production of hydrogen from a co-digestion of grass with cow dung and silage with cow dung by Clostridium butyricum Thailand Institute of Scientific and Technological Research (TISTR) 1032 was conducted. The results indicated that bio-hydrogen production by C. butyricum TISTR 1032 gave a higher hydrogen yield (HY) than without C. butyricum addition. The HY of 6.98 and 27.71 mL H₂/g-Volatile solid_added (VS_added), were obtained from a co-digestion of grass with cow dung and silage with cow dung by C. butyricum, respectively. The hydrogenic effluent and solid residue left over after hydrogen fermentation were further used as substrates for methane production (Batch I). Methane yield (MY) from hydrogenic effluent of grass with cow dung and silage with cow dung were 169.87 and 141.33 mL CH₄/g-COD_added (COD: chemical oxygen demand), respectively. The maximum MY of 210.10 and 177.79 mL CH₄/g-VS_added, respectively, were attained from solid residues left over after bio-hydrogen production pretreated by enzyme (cellulase cocktail) and alkali (NaOH). Afterward, solid residue left over after methane production (Batch I) was used as the substrate for methane production (Batch II). A maximum MY of 370.39 and 370.99 mL CH₄/g-VS_added were achieved from solid residue repeatedly pretreated by alkaline plus enzyme, respectively. The overall energy yield in the two-stage bio-hydrogen and methane production process was derived from a bio-hydrogen production, a methane production from hydrogenic effluent, methane production of pretreated solid residue (Batch I) and methane production of repeatedly pretreated solid residue (Batch II), which yielded 480.27 and 204.70 MJ/g-VS_added, respectively. Full article

(This article belongs to the Collection Bioenergy and Biofuel)

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2973 KiB

Open AccessFeature PaperArticle

Economic Model Predictive and Feedback Control of a Smart Grid Prosumer Node

by Francesco Liberati^1,*

and Alessandro Di Giorgio²

¹ Innovations and Networks Executive Agency (INEA), Chaussée de Wavre 910, 1040 Etterbeek, Belgium

² Department of Computer, Control and Management Engineering, “Sapienza” University of Rome, Via Ariosto 25, 00185 Rome, Italy

Energies 2018, 11(1), 48; https://doi.org/10.3390/en11010048 - 26 Dec 2017

Cited by 7 | Viewed by 3857

Abstract

This paper presents a two-level control scheme for the energy management of an electricity prosumer node equipped with controllable loads, local generation, and storage devices. The main control objective is to optimize the prosumer’s energy bill by means of intelligent load shifting and [...] Read more.

This paper presents a two-level control scheme for the energy management of an electricity prosumer node equipped with controllable loads, local generation, and storage devices. The main control objective is to optimize the prosumer’s energy bill by means of intelligent load shifting and storage control. A generalized tariff model including both volumetric and capacity components is considered, and user preferences as well as all technical constraints are respected. Simulations based on real household consumption data acquired with a sampling period of 1 s are discussed. The proposed control scheme bestows the prosumer node with the flexibility needed to support smart grid use cases such as bill optimization (i.e., local energy trading), control of the profile at the point of connection with the grid, demand response, and reaction to main supply faults (e.g., islanding operation), etc. Full article

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2330 KiB

Open AccessArticle

Verification of Energy Reduction Effect through Control Optimization of Supply Air Temperature in VRF-OAP System

by Je Hyeon Lee¹, Hyun Jin Yoon¹, Piljae Im² and Young-hak Song^3,*

¹ Department of Digital Appliances R&D Team, Samsung Electronics, 129, Samsung-ro, Yeongtong-gu, Suwon-si, Gyeonggi-do 16677, Korea

² Building Technologies Research and Integration Center (BTRIC), Oak Ridge National Laboratory (ORNL), One Bethel Valley Road, Oak Ridge, TN 37831, USA

³ Department of Architectural Engineering, ERI, Gyeongsang National University, Jinju daero 501, Jinju City 52828, Korea

Energies 2018, 11(1), 49; https://doi.org/10.3390/en11010049 - 27 Dec 2017

Cited by 20 | Viewed by 4616

Abstract

This paper developed an algorithm that controls the supply air temperature in the variable refrigerant flow (VRF), outdoor air processing unit (OAP) system, according to indoor and outdoor temperature and humidity, and verified the effects after applying the algorithm to real buildings. The [...] Read more.

This paper developed an algorithm that controls the supply air temperature in the variable refrigerant flow (VRF), outdoor air processing unit (OAP) system, according to indoor and outdoor temperature and humidity, and verified the effects after applying the algorithm to real buildings. The VRF-OAP system refers to a heating, ventilation, and air conditioning (HVAC) system to complement a ventilation function, which is not provided in the VRF system. It is a system that supplies air indoors by heat treatment of outdoor air through the OAP, as a number of indoor units and OAPs are connected to the outdoor unit in the VRF system simultaneously. This paper conducted experiments with regard to changes in efficiency and the cooling capabilities of each unit and system according to supply air temperature in the OAP using a multicalorimeter. Based on these results, an algorithm that controlled the temperature of the supply air in the OAP was developed considering indoor and outdoor temperatures and humidity. The algorithm was applied in the test building to verify the effects of energy reduction and the effects on indoor temperature and humidity. Loads were changed by adjusting the number of conditioned rooms to verify the effect of the algorithm according to various load conditions. In the field test results, the energy reduction effect was approximately 15–17% at a 100% load, and 4–20% at a 75% load. However, no significant effects were shown at a 50% load. The indoor temperature and humidity reached a comfortable level. Full article

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691 KiB

Open AccessArticle

Organosolv Fractionation of Softwood Biomass for Biofuel and Biorefinery Applications

by Christos Nitsos, Ulrika Rova

and Paul Christakopoulos^*

Biochemical Process Engineering, Division of Chemical Engineering, Department of Civil, Environmental and Natural Resources Engineering, Luleå University of Technology, 971-87 Luleå, Sweden

Energies 2018, 11(1), 50; https://doi.org/10.3390/en11010050 - 27 Dec 2017

Cited by 102 | Viewed by 8637

Abstract

Softwoods represent a significant fraction of the available lignocellulosic biomass for conversion into a variety of bio-based products. Its inherent recalcitrance, however, makes its successful utilization an ongoing challenge. In the current work the research efforts for the fractionation and utilization of softwood [...] Read more.

Softwoods represent a significant fraction of the available lignocellulosic biomass for conversion into a variety of bio-based products. Its inherent recalcitrance, however, makes its successful utilization an ongoing challenge. In the current work the research efforts for the fractionation and utilization of softwood biomass with the organosolv process are reviewed. A short introduction into the specific challenges of softwood utilization, the development of the biorefinery concept, as well as the initial efforts for the development of organosolv as a pulping method is also provided for better understanding of the related research framework. The effect of organosolv pretreatment at various conditions, in the fractionation efficiency of wood components, enzymatic hydrolysis and bioethanol production yields is then discussed. Specific attention is given in the effect of the pretreated biomass properties such as residual lignin on enzymatic hydrolysis. Finally, the valorization of organosolv lignin via the production of biofuels, chemicals, and materials is also described. Full article

(This article belongs to the Special Issue Thermo Fluid Conversion of Biomass)

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1475 KiB

Open AccessArticle

Active Splitting in Longitudinal Power Systems based on a WAMPC

by Felipe Arraño-Vargas^*

, Claudia Rahmann

, Felipe Valencia and Luis Vargas

Department of Electrical Engineering, University of Chile, Av. Tupper 2007, Santiago 8370451, Chile

Energies 2018, 11(1), 51; https://doi.org/10.3390/en11010051 - 27 Dec 2017

Cited by 6 | Viewed by 3656

Abstract

This paper proposes an active splitting scheme especially suitable for longitudinal power systems (LPS). The proposed scheme is based on a modified out-of-step (OOS) algorithm combined with an angle difference method using synchrophasor measurements. The remedial actions are based on the detection of [...] Read more.

This paper proposes an active splitting scheme especially suitable for longitudinal power systems (LPS). The proposed scheme is based on a modified out-of-step (OOS) algorithm combined with an angle difference method using synchrophasor measurements. The remedial actions are based on the detection of possible loss of synchronism due to severe disturbances. The scheme was tested on a detailed dynamic model of the Central Interconnected System of Chile, a good example of extreme LPS. Obtained results show that remedial actions taken by the proposed protection scheme are able to avoid the total collapse of the system during critical contingencies. Full article

(This article belongs to the Section F: Electrical Engineering)

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3784 KiB

Open AccessArticle

Coordinated Control of Wind Turbine and Energy Storage System for Reducing Wind Power Fluctuation

by Chunghun Kim¹

, Eduard Muljadi² and Chung Choo Chung^1,*

¹ Department of Electrical Engineering, Hanyang University, Seoul 133-791, Korea

² National Renewable Energy Laboratory, Golden, CO 80401, USA

Energies 2018, 11(1), 52; https://doi.org/10.3390/en11010052 - 27 Dec 2017

Cited by 30 | Viewed by 5614

Abstract

This paper proposes a method for the coordinated control of a wind turbine and an energy storage system (ESS). Because wind power (WP) is highly dependent on wind speed, which is variable, severe stability problems can be caused in power systems, especially when [...] Read more.

This paper proposes a method for the coordinated control of a wind turbine and an energy storage system (ESS). Because wind power (WP) is highly dependent on wind speed, which is variable, severe stability problems can be caused in power systems, especially when the WP has a high penetration level. To solve this problem, many power generation corporations or grid operators have begun using ESSs. An ESS has very quick response and good performance for reducing the impact of WP fluctuation; however, its installation cost is high. Therefore, it is important to design the control algorithm by considering both the ESS capacity and WP fluctuation. Thus, we propose a control algorithm to mitigate the WP fluctuation by using the coordinated control between the wind turbine and the ESS by considering the ESS capacity and the WP fluctuation. Using de-loaded control, according to the WP fluctuation and ESS capacity, we can expand the ESS lifespan and improve grid reliability by avoiding the extreme value of state of charge (SoC) (i.e., 0 or 1 pu). The effectiveness of the proposed method was validated via MATLAB/Simulink by considering a small power system that includes both a wind turbine generator and conventional generators that react to system frequency deviation. We found that the proposed method has better performance in SoC management, thereby improving the frequency regulation by mitigating the impact of the WP fluctuation on the small power system. Full article

(This article belongs to the Special Issue Distributed and Renewable Power Generation)

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3304 KiB

Open AccessFeature PaperArticle

Toward Development of a Stochastic Wake Model: Validation Using LES and Turbine Loads

by Jae Sang Moon^1,*

, Lance Manuel¹

, Matthew J. Churchfield², Sang Lee³ and Paul S. Veers²

¹ Department of Civil, Architectural and Environmental Engineering, University of Texas at Austin, Austin, TX 78712, USA

² National Renewable Energy Laboratory, Golden, CO 80303, USA

³ Department of Mechanical Engineering, University of New Mexico, Albuquerque, NM 87131, USA

Energies 2018, 11(1), 53; https://doi.org/10.3390/en11010053 - 28 Dec 2017

Cited by 6 | Viewed by 3657

Abstract

Wind turbines within an array do not experience free-stream undisturbed flow fields. Rather, the flow fields on internal turbines are influenced by wakes generated by upwind unit and exhibit different dynamic characteristics relative to the free stream. The International Electrotechnical Commission (IEC) standard [...] Read more.

Wind turbines within an array do not experience free-stream undisturbed flow fields. Rather, the flow fields on internal turbines are influenced by wakes generated by upwind unit and exhibit different dynamic characteristics relative to the free stream. The International Electrotechnical Commission (IEC) standard 61400-1 for the design of wind turbines only considers a deterministic wake model for the design of a wind plant. This study is focused on the development of a stochastic model for waked wind fields. First, high-fidelity physics-based waked wind velocity fields are generated using Large-Eddy Simulation (LES). Stochastic characteristics of these LES waked wind velocity field, including mean and turbulence components, are analyzed. Wake-related mean and turbulence field-related parameters are then estimated for use with a stochastic model, using Multivariate Multiple Linear Regression (MMLR) with the LES data. To validate the simulated wind fields based on the stochastic model, wind turbine tower and blade loads are generated using aeroelastic simulation for utility-scale wind turbine models and compared with those based directly on the LES inflow. The study’s overall objective is to offer efficient and validated stochastic approaches that are computationally tractable for assessing the performance and loads of turbines operating in wakes. Full article

(This article belongs to the Special Issue Wind Turbine Loads and Wind Plant Performance)

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1871 KiB

Open AccessArticle

Potential of Phaeodactylum tricornutum for Biodiesel Production under Natural Conditions in Chile

by Monique Branco-Vieira^1,2,3,*, Sergio San Martin⁴, Cristian Agurto⁴, Marco Aurélio dos Santos¹, Marcos A. V. Freitas¹, Teresa M. Mata³, António A. Martins³ and Nídia S. Caetano^2,3

¹ Energy Planning Program, Federal University of Rio de Janeiro, 21941-914 Rio de Janeiro, Brazil

² CIETI, School of Engineering (ISEP), Polytechnic Institute of Porto (IPP), 4200-072 Porto, Portugal

³ LEPABE, Faculty of Engineering, University of Porto, 4200-465 Porto, Portugal

⁴ GIBMAR, Biotechnology Centre, Concepción University, 4070386 Concepción, Chile

Energies 2018, 11(1), 54; https://doi.org/10.3390/en11010054 - 28 Dec 2017

Cited by 37 | Viewed by 6523

Abstract

Diatoms are very diverse and highly productive organisms, found in a wide variety of environments. This study aims to analyze the growth and lipid composition of Phaeodactylum tricornutum, cultured in an outdoor pilot-scale bubble column photobioreactor under natural conditions in Chile for biodiesel [...] Read more.

Diatoms are very diverse and highly productive organisms, found in a wide variety of environments. This study aims to analyze the growth and lipid composition of Phaeodactylum tricornutum, cultured in an outdoor pilot-scale bubble column photobioreactor under natural conditions in Chile for biodiesel production. Results showed that P. tricornutum cultures reached their highest biomass concentration (0.96 ± 0.04 kg m⁻³) after 14 days of culturing, at the stationary phase, with a volumetric productivity of 0.13 kg m⁻³ d⁻¹. Biomass samples showed a total lipid content of 9.08 ± 0.38 wt %. The fatty acid methyl ester analysis revealed a composition of 24.39% C16-C18 fatty acids, 42.34% saturated fatty acids, 21.91% monounsaturated fatty acids and 31.41% polyunsaturated fatty acids. These findings suggest that P. tricornutum oil can be used as an alternative raw material for the production of biodiesel capable of meeting international quality standards. Full article

(This article belongs to the Special Issue Selected Papers from ICEER 2017: 2017 the 4th International Conference on Energy and Environment Research)

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7937 KiB

Open AccessArticle

Battery Dimensioning and Life Cycle Costs Analysis for a Heavy-Duty Truck Considering the Requirements of Long-Haul Transportation

by Ivan Mareev^1,*, Jan Becker^1,2 and Dirk Uwe Sauer^1,2,3

¹ Electrochemical Energy Conversion and Storage Systems Group, Institute for Power Electronics and Electrical Drives (ISEA), RWTH Aachen University, Jaegerstr. 17/19, 52066 Aachen, Germany

² Juelich Aachen Research Alliance, JARA-Energy, 52425 Juelich, Germany

³ Institute for Power Generation and Storage Systems (PGS), E.ON Energy Research Center, RWTH Aachen University, Mathieustr. 10, 52074 Aachen, Germany

Energies 2018, 11(1), 55; https://doi.org/10.3390/en11010055 - 28 Dec 2017

Cited by 86 | Viewed by 12736

Abstract

The use of heavy-duty battery electric trucks for long-haul transportation is challenging because of the required high energy amounts and thus the high capacity of traction batteries. Furthermore a high capacity battery implies high initial costs for the electric vehicle. This study investigates [...] Read more.

The use of heavy-duty battery electric trucks for long-haul transportation is challenging because of the required high energy amounts and thus the high capacity of traction batteries. Furthermore a high capacity battery implies high initial costs for the electric vehicle. This study investigates the required battery capacity for battery electric trucks considering the requirements of long-haul transportation in Germany and compares the life cycle costs of battery electric trucks and conventional diesel trucks in different transportation scenarios. The average consumption is simulated for different battery electric truck configurations on the main German highways and transportation scenarios incorporating battery charging during driver rest periods. The results show that in average case the required battery would restrict the payload to only 80% of a usual diesel truck payload that might be acceptable considering the statistical payload use. The life cycle costs in the examined scenarios also considering the charging infrastructure show that battery electric trucks can already perform on the same costs level as diesel trucks in certain scenarios. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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11668 KiB

Open AccessArticle

A Theoretical-Experimental Comparison of an Improved Ammonia-Water Bubble Absorber by Means of a Helical Static Mixer

by Jesús Cerezo^1,*

, Roberto Best², Jorge Jesús Chan³

, Rosenberg J. Romero¹

, Jorge I. Hernandez² and Fernando Lara⁴

¹ Centro de Investigación en Ingeniería y Ciencias Aplicadas, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, Cuernavaca 62209, Morelos, Mexico

² Instituto de Energías Renovables, Universidad Nacional Autónoma de México, Temixco 62580, Morelos, Mexico

³ Universidad Autónoma de Campeche, Av. Agustín Melgar s/n, Buenavista 24030, Campeche, Mexico

⁴ Facultad de Ingeniería, Universidad Autónoma de Baja California, Blvd. Benito Juárez y Calle de la Normal s/n, Insurgentes Este, Mexicali 21280, Baja California, Mexico

Energies 2018, 11(1), 56; https://doi.org/10.3390/en11010056 - 28 Dec 2017

Cited by 7 | Viewed by 3680

Abstract

The heat transfer in double pipe heat exchangers is very poor. This complicates its application in absorption cooling systems, however, the implementation of simple passive techniques should help to increase the heat and mass transfer mainly in the absorber. This paper carried out [...] Read more.

The heat transfer in double pipe heat exchangers is very poor. This complicates its application in absorption cooling systems, however, the implementation of simple passive techniques should help to increase the heat and mass transfer mainly in the absorber. This paper carried out a simulation and its experimental comparison of a NH₃-H₂O bubble absorption process using a double tube heat exchanger with a helical screw static mixer in both central and annular sides. The experimental results showed that the absorption heat load per area is 31.61% higher with the helical screw mixer than the smooth tube. The theoretical and experimental comparison showed that the absorption heat load difference values were 28.0 and 21.9% for smooth tube and the helical mixer, respectively. These difference values were caused by the calculation of the log mean temperature difference in equilibrium conditions to avoid the overlap of solution temperatures. Therefore, the theoretical and experimental results should be improved when the absorption heat is included in the heat transfer equation or avoiding the operation condition when output is lower than input solution temperature. Full article

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19 pages, 6496 KiB

Open AccessArticle

H_∞ Robust Control of an LCL-Type Grid-Connected Inverter with Large-Scale Grid Impedance Perturbation

by Yingjie Wang^1,*

, Jiashi Wang¹, Wei Zeng¹, Haiyuan Liu² and Yushuo Chai¹

¹ School of Electrical and Power Engineering, China University of Mining and Technology, Xuzhou 221000, China

² School of Information and Control Engineering, China University of Mining and Technology, Xuzhou 221000, China

Energies 2018, 11(1), 57; https://doi.org/10.3390/en11010057 - 1 Jan 2018

Cited by 18 | Viewed by 3528

Abstract

In the distributed power generation system (DPGS), there may be a large range perturbation values of equivalent grid impedance at the point of common coupling (PCC). Perturbation of the impedance will cause resonant frequency variation of the Inductance Capacitance Inductance (LCL) filter on [...] Read more.

In the distributed power generation system (DPGS), there may be a large range perturbation values of equivalent grid impedance at the point of common coupling (PCC). Perturbation of the impedance will cause resonant frequency variation of the Inductance Capacitance Inductance (LCL) filter on a large scale, affecting the quality of the grid current of the grid-connected inverter (GCI) and even causing resonance. To deal with this problem, a novel H_∞ robust control strategy based on mixed-sensitivity optimization is proposed in this paper. Its generalized controlled object is augmented by properly selecting weighting functions in order to consider both tracking performance around power frequency and the stability margin in a high frequency of the GCI. For convenient implementation, the H_∞ robust controller is simplified by model reduction from the seventh order to the third order. By comparison with a traditional control strategy with a quasi-proportional resonance controller, the proposed H_∞ robust control strategy avoids crossing 180 degrees at the resonant frequency point in the phase frequency characteristic of current loop, and moves the phase frequency characteristic left. It guarantees a sufficient margin of stability throughout the designed range of grid impedance perturbation values and avoids the difficulty of parameter setting. Finally, the experimental results support the theoretical analyses and demonstrate the feasibility of the proposed strategy. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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4287 KiB

Open AccessArticle

Output Power Smoothing and Voltage Regulation of a Fixed Speed Wind Generator in the Partial Load Region Using STATCOM and a Pitch Angle Controller

by Kanasottu Anil Naik^*

and Chandra Prakash Gupta

Department of Electrical Engineering, Indian Institute of Technology Roorkee, Roorkee 247667, India

Energies 2018, 11(1), 58; https://doi.org/10.3390/en11010058 - 29 Dec 2017

Cited by 13 | Viewed by 5067

Abstract

The output power and terminal voltage of the fixed speed induction generator fluctuate in the partial load region where the wind speed is below the rated vale, resulting in fluctuations in the grid frequency and voltage. In this paper, a novel pitch angle [...] Read more.

The output power and terminal voltage of the fixed speed induction generator fluctuate in the partial load region where the wind speed is below the rated vale, resulting in fluctuations in the grid frequency and voltage. In this paper, a novel pitch angle control strategy has developed by introducing an exponential moving average (EMA) concept from which the controller reference power (signal) can be set for below-rated wind speeds. Therefore, the employed pitch angle controller together with static synchronous compensator (STATCOM), named the unified voltage and pitch angle controller (UVPC), addresses the objective of smoothing the output power and terminal voltage regulation of a wind generator, subjected to below-rated wind speed variations. Moreover, an interval type-2 fuzzy logic technique has incorporated in the pitch angle controller design, since it is more efficient in handling the uncertainties in membership functions and rules than its traditional fuzzy logic counterparts. Simulation results clearly show that the proposed UVPC effectively smoothens out the generator output power and also regulates the terminal voltage at its constant magnitude. Full article

(This article belongs to the Special Issue Wind Generators Modelling and Control)

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16 pages, 7773 KiB

Open AccessArticle

An Online State of Charge Estimation Algorithm for Lithium-Ion Batteries Using an Improved Adaptive Cubature Kalman Filter

by Zhibing Zeng, Jindong Tian, Dong Li and Yong Tian^*

College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China

Energies 2018, 11(1), 59; https://doi.org/10.3390/en11010059 - 1 Jan 2018

Cited by 66 | Viewed by 4660

Abstract

An accurate state of charge (SOC) estimation of the on-board lithium-ion battery is of paramount importance for the efficient and reliable operation of electric vehicles (EVs). Aiming to improve the accuracy and reliability of battery SOC estimation, an improved adaptive Cubature Kalman filter [...] Read more.

An accurate state of charge (SOC) estimation of the on-board lithium-ion battery is of paramount importance for the efficient and reliable operation of electric vehicles (EVs). Aiming to improve the accuracy and reliability of battery SOC estimation, an improved adaptive Cubature Kalman filter (ACKF) is proposed in this paper. The battery model parameters are online identified with the forgetting factor recursive least squares (FRLS) algorithm so that the accuracy of SOC estimation can be further improved. The proposed method is evaluated by two driving cycles, i.e., the New European Driving Cycle (NEDC) and the Federal Urban Driving Schedule (FUDS), and compared with the existing unscented Kalman filter (UKF) and standard CKF algorithms to verify its superiority. The experimental results reveal that comparing with the UKF and standard CKF, the improved ACKF algorithm has a faster convergence rate to different initial SOC errors with higher estimation accuracy. The root mean square error of SOC estimation without initial SOC error is less than 0.5% under both the NEDC and FUDS cycles. Full article

(This article belongs to the Section D: Energy Storage and Application)

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20 pages, 4506 KiB

Open AccessArticle

Analysis on the Amplitude and Frequency Characteristics of the Rotor Unbalanced Magnetic Pull of a Multi-Pole Synchronous Generator with Inter-Turn Short Circuit of Field Windings

by Guangtao Zhang, Junyong Wu and Liangliang Hao^*

School of Electrical Engineering, Beijing Jiaotong University, Beijing 100044, China

Energies 2018, 11(1), 60; https://doi.org/10.3390/en11010060 - 1 Jan 2018

Cited by 10 | Viewed by 4463

Abstract

Inter-turn short circuit of field windings (ISCFW) is a common generator fault which can result in serious safety accidents for power systems, if the fault is not eliminated in time. Taking advantage of the electrical and mechanical characteristics of the generator after a [...] Read more.

Inter-turn short circuit of field windings (ISCFW) is a common generator fault which can result in serious safety accidents for power systems, if the fault is not eliminated in time. Taking advantage of the electrical and mechanical characteristics of the generator after a fault as a fault criterion is a new idea for fault monitoring, so finding out the frequency and amplitude frequency characteristics of rotor unbalanced magnetic pull (UMP)—the vibration excitation source of the fault—is the basis and key of the research. Taking a six-pole generator as an example, the effects of harmonic magnetic motive force (MMF) interaction on rotor UMP, as well as the frequency characteristics of rotor UMP after generator faults in different stator windings, are obtained based on the analysis of the air-gap MMF of the generator after a fault, and the results of theoretical analysis are verified by simulation. Based on the above results, the simulation calculation on rotor UMP of generators with three stator winding forms under different operating conditions has been achieved, to get the relation between rotor UMP amplitude and active power and field current, and to find out the mechanism of rotor UMP amplitude change along with operating conditions and effect of stator winding forms on UMP amplitude by theoretical analysis. The conclusions are of important significance for studying fault mechanical characteristics of generators and lay a foundation for online monitoring on ISCFW by integrating mechanical and electrical information. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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17 pages, 6639 KiB

Open AccessArticle

Performance Investigation and Optimization of a Novel Hybrid Saturated-Core Fault-Current Limiter Considering the Leakage Effect

by Liangliang Wei^1,2

, Baichao Chen¹, Yushun Liu³

, Cuihua Tian¹, Jiaxin Yuan^1,*, Yuxin Bu⁴ and Tianan Zhu⁵

¹ School of Electrical Engineering, Wuhan University, No.299, Bayi Street, Wuchang District, Wuhan 430072, China

² Department of Electrical Engineering, Graduate School of Engineering, Kyoto University, Yoshida-honmachi, Sakyo-ku, Kyoto 606-8501, Japan

³ Anhui Grid Co., Anhui Electric Power Research Institute, No.73, Jinzhai Road, Hefei 230022, China

⁴ State Grid Taiyuan Power Supply Company, No.89, Binzhou North Road, Taiyuan 030012, China

⁵ State Grid Yichang Power Supply Company, No.42, Chengdong road, Yichang 443000, China

Energies 2018, 11(1), 61; https://doi.org/10.3390/en11010061 - 1 Jan 2018

Cited by 7 | Viewed by 3024

Abstract

To reduce the requirement of DC-biasing capacity and improve the biasing ability of a permanent magnet (PM), a novel hybrid saturated-core fault-current limiter (HSCFCL) is proposed in this paper. Compared with traditional saturated-core fault-current limiter (SCFCL), the HSCFCL has the advantages of small [...] Read more.

To reduce the requirement of DC-biasing capacity and improve the biasing ability of a permanent magnet (PM), a novel hybrid saturated-core fault-current limiter (HSCFCL) is proposed in this paper. Compared with traditional saturated-core fault-current limiter (SCFCL), the HSCFCL has the advantages of small size, low DC-biasing capacity, a high biasing ability of the PM and excellent limiting performance. Firstly, the principle and the magnetic circuit model of the HSCFCL are introduced. Then, the improvement of DC-biasing capacity with a PM is analyzed. In addition, the influence of the leakage-flux effect on the biasing ability of the PM is presented in detail, and a small-section optimal structure is proposed to improve the biasing ability of the PM. Finally, to validate the principle and performance of the HSCFCL, various electromagnetic simulations, optimization studies and experiments are carried out. The simulation and experimental results demonstrate the effectiveness of the proposed method. Full article

(This article belongs to the Section F: Electrical Engineering)

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497 KiB

Open AccessArticle

Comparative Analysis of P2P Architectures for Energy Trading and Sharing

by Olamide Jogunola¹

, Augustine Ikpehai¹

, Kelvin Anoh¹

, Bamidele Adebisi^1,*

, Mohammad Hammoudeh¹

, Haris Gacanin² and Georgina Harris¹

¹ Faculty of Science and Engineering, Manchester Metropolitan University, Manchester M1 5GD, UK

² Nokia-Bell Labs, Copernicuslaan 50, 2018 Antwerp, Belgium

Energies 2018, 11(1), 62; https://doi.org/10.3390/en11010062 - 29 Dec 2017

Cited by 68 | Viewed by 7463

Abstract

Rising awareness and emergence of smart technologies have inspired new thinking in energy system management. Whilst integration of distributed energy resources in micro-grids (MGs) has become the technique of choice for consumers to generate their energy, it also provides a unique opportunity to [...] Read more.

Rising awareness and emergence of smart technologies have inspired new thinking in energy system management. Whilst integration of distributed energy resources in micro-grids (MGs) has become the technique of choice for consumers to generate their energy, it also provides a unique opportunity to explore energy trading and sharing amongst them. This paper investigates peer-to-peer (P2P) communication architectures for prosumers’ energy trading and sharing. The performances of common P2P protocols are evaluated under the stringent communication requirements of energy networks defined in IEEE 1547.3-2007. Simulation results show that the structured P2P protocol exhibits a reliability of 99.997% in peer discovery and message delivery whilst the unstructured P2P protocol yields 98%, both of which are consistent with the requirements of MG applications. These two architectures exhibit high scalability with a latency of 0.5 s at a relatively low bandwidth consumption, thus, showing promising potential in their adoption for prosumer to prosumer communication. Full article

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2218 KiB

Open AccessArticle

Dynamic Power Flow Cascading Failure Analysis of Wind Power Integration with Complex Network Theory

by Yushu Sun¹

, Xisheng Tang^1,*, Guowei Zhang¹, Fufeng Miao² and Ping Wang³

¹ Institute of Electrical Engineering, Chinese Academy of Sciences, Haidian District, Beijing 100190, China

² State Grid Henan Power Company Economic and Technological Research Institute, Zhengzhou 450052, China

³ Jiangsu Province Electrochemical Energy Storage Technology Key Laboratory, Taizhou 225500, China

Energies 2018, 11(1), 63; https://doi.org/10.3390/en11010063 - 29 Dec 2017

Cited by 14 | Viewed by 3373

Abstract

The impact of the rapid development of large-scale centralized wind power farms on the power system is drawing more and more attention. Some topics about grid-connected wind power are discussed from the view of complex network theory in this paper. Firstly, a complex [...] Read more.

The impact of the rapid development of large-scale centralized wind power farms on the power system is drawing more and more attention. Some topics about grid-connected wind power are discussed from the view of complex network theory in this paper. Firstly, a complex network cascading failure model is established, combined with dynamic AC power flow (DACPF). Then, the IEEE 30 bus system is used to analyze its validity using the simulations of nodes removal, wind power integration, as well as the change of current and voltage boundaries. Furthermore, the influences of wind power before and after smoothing are investigated. Also, different wind power coupling locations are studied. Finally, some significant conclusions are obtained to provide references for large-scale wind power integration. Full article

(This article belongs to the Section F: Electrical Engineering)

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15 pages, 5541 KiB

Open AccessArticle

Practical On-Board Measurement of Lithium Ion Battery Impedance Based on Distributed Voltage and Current Sampling

by Xuezhe Wei^1,2, Xueyuan Wang^1,2

and Haifeng Dai^1,2,*

¹ Clean Energy Automotive Engineering Center, Tongji University, Shanghai 201804, China

² School of Automotive Studies, Tongji University, Shanghai 201804, China

Energies 2018, 11(1), 64; https://doi.org/10.3390/en11010064 - 1 Jan 2018

Cited by 33 | Viewed by 7131

Abstract

Battery impedance based state estimation methods receive extensive attention due to its close relation to internal dynamic processes and the mechanism of a battery. In order to provide impedance for a battery management system (BMS), a practical on-board impedance measuring method based on [...] Read more.

Battery impedance based state estimation methods receive extensive attention due to its close relation to internal dynamic processes and the mechanism of a battery. In order to provide impedance for a battery management system (BMS), a practical on-board impedance measuring method based on distributed signal sampling is proposed and implemented. Battery cell perturbing current and its response voltage for impedance calculation are sampled separately to be compatible with BMS. A digital dual-channel orthogonal lock-in amplifier is used to calculate the impedance. With the signal synchronization, the battery impedance is obtained and compensated. And the relative impedance can also be obtained without knowing the current. For verification, an impedance measuring system made up of electronic units sampling and processing signals and a DC-AC converter generating AC perturbing current is designed. A type of 8 Ah LiFePO₄ battery is chosen and the valuable frequency range for state estimations is determined with a series of experiments. The battery cells are connected in series and the impedance is measured with the prototype. It is shown that the measurement error of the impedance modulus at 0.1 Hz–500 Hz at 5 °C–35 °C is less than 4.5% and the impedance phase error is less than 3% at <10 Hz at room temperature. In addition, the relative impedance can also be tracked well with the designed system. Full article

(This article belongs to the Special Issue 2nd Young Scholar’s Symposium on Battery Design and Management (BDM 2017))

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17 pages, 3250 KiB

Open AccessArticle

Energy Consumption Prediction of a Greenhouse and Optimization of Daily Average Temperature

by Yongtao Shen^†

, Ruihua Wei^† and Lihong Xu^*

¹ College of Electronics and Information Engineering, Tongji University, Shanghai 201804, China

^† These authors contributed equally to this work and should be considered co-first authors.

Energies 2018, 11(1), 65; https://doi.org/10.3390/en11010065 - 1 Jan 2018

Cited by 100 | Viewed by 9697

Abstract

Greenhouses are high energy-consuming and anti-seasonal production facilities. In some cases, energy consumption in greenhouses accounts for 50% of the cost of greenhouse production. The high energy consumption has become a major factor hindering the development of greenhouses. In order to improve the [...] Read more.

Greenhouses are high energy-consuming and anti-seasonal production facilities. In some cases, energy consumption in greenhouses accounts for 50% of the cost of greenhouse production. The high energy consumption has become a major factor hindering the development of greenhouses. In order to improve the energy efficiency of the greenhouse, it is important to predict its energy consumption. In this study, the energy consumption mathematical model of a Venlo greenhouse is established based on the principle of energy conservation. Three optimization algorithms are used to identify the parameters which are difficult to determine in the energy consumption model. In order to examine the accuracy of the model, some verifications are made. The goal of achieving high yield, high quality and high efficiency production is a problem in the study of greenhouse environment control. Combining the prediction model of greenhouse energy consumption with the relatively accurate weather forecast data for the next week, the energy consumption of greenhouse under different weather conditions is predicted. Taking the minimum energy consumption as the objective function, the indoor daily average temperatures of 7 days are optimized to provide the theoretical reference for the decision-making of heating in the greenhouse. The results show that the optimized average daily temperatures save 9% of the energy cost during a cold wave. Full article

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13 pages, 3455 KiB

Open AccessArticle

Rotor Position Self-Sensing of SRM Using PSO-RVM

by Qianwen Xiang, Ye Yuan^*, Yanjun Yu and Kunhua Chen

School of Electrical and Information Engineering, Jiangsu University, Zhenjiang 212013, China

Energies 2018, 11(1), 66; https://doi.org/10.3390/en11010066 - 1 Jan 2018

Cited by 6 | Viewed by 3387

Abstract

The motors’ flux-linkage, current and angle obtained from the system with sensors were chosen as the sample data, and the estimation model of rotor position based on relevance vector machine (RVM) was built by training the sample data. The kernel function parameter in [...] Read more.

The motors’ flux-linkage, current and angle obtained from the system with sensors were chosen as the sample data, and the estimation model of rotor position based on relevance vector machine (RVM) was built by training the sample data. The kernel function parameter in RVM model was optimized by the particle swarm algorithm in order to increase the fitting precision and generalization ability of RVM model. It achieved higher prediction accuracy with staying at the same on-line testing time as the RVM. And because the short on-line computation, the motor can operate at 3000 r/min in sensorless control with particle swarm optimization-relevance vector machine (PSO-RVM), which is higher than support vector machine (SVM) and neural network (NN). By simulation and experiment on the test motor, it is verified that the proposed estimation model can obtain the angle of full electrical period accurately under low speed and high speed operations in current chopped control and angle position control, which has satisfactory estimation precision. Full article

(This article belongs to the Special Issue Emerging Power Electronics Technologies for Power Systems and Machine Drives)

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16 pages, 5006 KiB

Open AccessArticle

Combined Supporting Technology with Bolt-Grouting and Floor Pressure-Relief for Deep Chamber: An Underground Coal Mine Case Study

by Xinxian Zhai¹, Guangshuai Huang^1,*, Chengyu Chen² and Rubo Li³

¹ School of Energy Science and Engineering, Henan Polytechnic University, Jiaozuo 454000, China

² Xinzhuang Coal Mine, Henan Shenhuo Coal and Electricity Co., Ltd., Yongcheng 476600, China

³ Tian’an Coal Mining Company Limited of Pingdingshan City, Pingdingshan 467000, China

Energies 2018, 11(1), 67; https://doi.org/10.3390/en11010067 - 1 Jan 2018

Cited by 24 | Viewed by 3425

Abstract

Based on the engineering geological conditions of the Number 2 chamber in the slope at Xinzhuang coal mine, which is located in the eastern part of Yongcheng City, Henan Province, China, the authors conducted a systematic research on the anchoring-grouting and the floor [...] Read more.

Based on the engineering geological conditions of the Number 2 chamber in the slope at Xinzhuang coal mine, which is located in the eastern part of Yongcheng City, Henan Province, China, the authors conducted a systematic research on the anchoring-grouting and the floor pressure-relief supporting technology by using theoretical analysis, numerical calculation and field industrial test. Results showed that: (1) the lithology of the surrounding rock was poor, and the stress and effective loading coefficient on the chamber surrounding rock were high due to the abutment pressure that was induced by the shaft protective pillar. Both of them resulted in the floor heave and the surrounding rock deformation damage of the chamber; (2) The numerical calculation showed that, after the floor pressure-relief slot was excavated in the head chamber, the vertical stress of the floor surrounding rock of chamber and the horizontal stress of the side surrounding rock were significantly reduced when compared with the stress before the pressure-relief, and the floor vertical displacement basically remained unchanged. So the floor pressure-relief slot could effectively control the chamber floor heave and was helpful for the long-term stability of the chamber. After the severe deformation chamber was renovated by using a combined support with bolt-mesh-shotcreting and anchor cables, several other techniques were also applied to ensure the stability of the chamber. The floor pressure-relief slot was excavated, both the roof and the sides surrounding rock of chamber were grouted with grouting bolt, and both sides and the floor (including pressure-relief slot) of the chamber were grouted with anchor cable bundles. After implementation of above systematic techniques, the surrounding rock of chamber is in a stable state, which demonstrated that the field test is successful. The combined supporting technology with the anchoring-grouting and the floor pressure-relief has an important practical significance for the long-term stability of the chamber to ensure the safe and efficient production of the mine. Full article

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21 pages, 3089 KiB

Open AccessArticle

Hourly Solar Radiation Forecasting Using a Volterra-Least Squares Support Vector Machine Model Combined with Signal Decomposition

by Zhenyu Wang

, Cuixia Tian, Qibing Zhu^* and Min Huang

Key Laboratory of Advanced Process Control for Light Industry (Ministry of Education), Jiangnan University, Wuxi 214122, China

Energies 2018, 11(1), 68; https://doi.org/10.3390/en11010068 - 1 Jan 2018

Cited by 31 | Viewed by 3715

Abstract

Accurate solar forecasting facilitates the integration of solar generation into the grid by reducing the integration and operational costs associated with solar intermittencies. A novel solar radiation forecasting method was proposed in this paper, which uses two kinds of adaptive single decomposition algorithm, [...] Read more.

Accurate solar forecasting facilitates the integration of solar generation into the grid by reducing the integration and operational costs associated with solar intermittencies. A novel solar radiation forecasting method was proposed in this paper, which uses two kinds of adaptive single decomposition algorithm, namely, empirical mode decomposition (EMD) and local mean decomposition (LMD), to decompose the strong non-stationary solar radiation sequence into a set of simpler components. The least squares support vector machine (LSSVM) and the Volterra model were employed to build forecasting sub-models for high-frequency components and low-frequency components, respectively, and the sub-forecasting results of each component were superimposed to obtain the final forecast results. The historical solar radiation data collected on Golden (CO, USA), in 2014 were used to evaluate the accuracy of the proposed model and its comparison with that of the ARIMA, the persistent model. The comparison demonstrated that the superior performance of the proposed hybrid method. Full article

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19 pages, 7256 KiB

Open AccessArticle

Investigation of Sectional-Stage Loading Strategies on a Two-Stage Turbocharged Heavy-Duty Diesel Engine under Transient Operation with EGR

by Zhongchang Liu, Xing Yuan

, Jing Tian^*, Yongqiang Han, Runzhao Li and Guanlong Gao

State Key Laboratory of Automotive Simulation and Control, Jilin University, Changchun 130025, China

Energies 2018, 11(1), 69; https://doi.org/10.3390/en11010069 - 1 Jan 2018

Cited by 7 | Viewed by 4512

Abstract

The influence of loading strategies on combustion and emissions parameters is experimentally and numerically studied under typical 5 s transient conditions of constant speed and increasing torque. The experiment is conducted on a two-stage turbocharged heavy-duty diesel engine with a constant opening valve [...] Read more.

The influence of loading strategies on combustion and emissions parameters is experimentally and numerically studied under typical 5 s transient conditions of constant speed and increasing torque. The experiment is conducted on a two-stage turbocharged heavy-duty diesel engine with a constant opening valve high-pressure exhaust gas recirculation (EGR) system. The test results show that: compared with the full-stage loading (FSL) strategy (constant loading rate during the entire transient process), the sectional-stage loading (SSL) strategies (holding a certain time at 50% load) can significantly reduce soot emissions (by 41.3%); the greater the first-stage loading rate, the better the torque response performance, which maximally increases by 56.7%. Besides, longer loading holding time can effectively restrain the overshoot of EGR rate and advance the combustion phase (CA10, CA50) at medium and large loads. However, the larger second-stage loading rate slightly deteriorates the combustion and emission performance. This deterioration situation can be markedly suppressed by adopting a suitable loading hold time. Full article

(This article belongs to the Special Issue Recent Advances in Internal Combustion Engines Operation and Emissions)

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1163 KiB

Open AccessArticle

Spatial and Temporal Day-Ahead Total Daily Solar Irradiation Forecasting: Ensemble Forecasting Based on the Empirical Biasing

by Min-Kyu Baek and Duehee Lee^*

Electrical Engineering, Konkuk University, Seoul 05029, Korea

Energies 2018, 11(1), 70; https://doi.org/10.3390/en11010070 - 29 Dec 2017

Cited by 10 | Viewed by 2996

Abstract

Total daily solar irradiation for the next day is forecasted through an ensemble of multiple machine learning algorithms using forecasted weather scenarios from numerical weather prediction (NWP) models. The weather scenarios were predicted at grid points whose longitudes and latitudes are integers, but [...] Read more.

Total daily solar irradiation for the next day is forecasted through an ensemble of multiple machine learning algorithms using forecasted weather scenarios from numerical weather prediction (NWP) models. The weather scenarios were predicted at grid points whose longitudes and latitudes are integers, but the total daily solar irradiation was measured at non-integer grid points. Therefore, six interpolation functions are used to interpolate weather scenarios at non-integer grid points, and their performances are compared. Furthermore, when the total daily solar irradiation for the next day is forecasted, many data trimming techniques, such as outlier detection, input data clustering, input data pre-processing, and output data post-processing techniques, are developed and compared. Finally, various combinations of these ensemble techniques, different NWP scenarios, and machine learning algorithms are compared. The best model is to combine multiple forecasting machines through weighted averaging and to use all NWP scenarios. Full article

(This article belongs to the Section L: Energy Sources)

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16 pages, 6413 KiB

Open AccessArticle

Flux-Angle-Difference Feedback Control for the Brushless Doubly Fed Machine

by Chaoying Xia^*, Xiaoxin Hou and Feng Chen

School of Electrical and Information Engineering, Tianjin University, No. 92 Weijin Road, Tianjin 300072, China

Energies 2018, 11(1), 71; https://doi.org/10.3390/en11010071 - 1 Jan 2018

Cited by 5 | Viewed by 3013 | Correction

Abstract

In direct torque control (DTC) of the brushless doubly fed machine (BDFM) system, the inverter switching voltage vectors cannot always meet the control requirements, and the torque will lose control. For the losing control problem, this paper presents a solution of indirectly controlling [...] Read more.

In direct torque control (DTC) of the brushless doubly fed machine (BDFM) system, the inverter switching voltage vectors cannot always meet the control requirements, and the torque will lose control. For the losing control problem, this paper presents a solution of indirectly controlling torque by controlling the angle difference between the power motor (PM) stator flux and the control motor (CM) stator flux (called as the flux-angle-difference). Firstly, based on the CM static coordinate system BDFM model, the derivative equations of CM stator flux amplitude, the torque, and the flux-angle-difference are deduced. The losing control problem of BDFM’s DTC is studied by utilizing the CM stator flux amplitude and the torque derivatives. From the flux-angle-difference derivative, it is found that the phase angles of the flux-angle-difference derivative curves remain unchanged. Based on this property, by replacing the torque hysteresis comparator of conventional DTC with a flux-angle-difference hysteresis comparator, a modified control strategy called flux-angle-difference feedback control (FADFC) is proposed to solve the losing control problem. Finally, the validity and the good dynamic characteristic of the FADFC strategy are verified by simulation results. Full article

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3460 KiB

Open AccessArticle

A Liquid Desiccant Enhanced Two Stage Evaporative Cooling System—Development and Performance Evaluation of a Test Rig

by M. Mujahid Rafique^1,2

, Shafiqur Rehman^3,*

, Luai M. Alhems³ and Muhammad Ali Shakir⁴

¹ Department of Mechanical Engineering, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia

² Independent Scholar, Toba Tek Singh 36050, Pakistan

³ Center for Engineering Research, Research Institute, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia

⁴ Department of Mechanical Engineering, University College of Engineering and Technology, University of Sargodha, Sargodha 40100, Pakistan

Energies 2018, 11(1), 72; https://doi.org/10.3390/en11010072 - 29 Dec 2017

Cited by 11 | Viewed by 6375

Abstract

Desiccant technology is found to be a good alternative to conventional cooling systems. It can provide better thermal comfort under hot and humid climatic conditions. The major component of a liquid desiccant cooling system is the desiccant dehumidifier which controls the latent cooling [...] Read more.

Desiccant technology is found to be a good alternative to conventional cooling systems. It can provide better thermal comfort under hot and humid climatic conditions. The major component of a liquid desiccant cooling system is the desiccant dehumidifier which controls the latent cooling load. In this paper, a newly developed liquid desiccant enhanced evaporative cooling system has been tested experimentally. The effects of ambient conditions and other parameters on the performance of the system are investigated. The system performance curves which help to determine the air outlet conditions and coefficient of performance (COP) of the system are drawn for a wide range of ambient air humidity ratios (0.010–0.026 kg/kg), ambient air temperature (25–40 °C), process air flow rate (1.5–8.0 kg/m²·s), regeneration air flow rate (1.5–4.5 kg/m²·s), and regeneration temperature (55–85 °C). The results showed that better supply air conditions are achieved for hot and humid climatic conditions with effectiveness of the system largely dependent on process and regeneration air flow rates, regeneration temperature, and humidity ratio of process air. The dehumidification performance is increased by 62% for a change of ambient air humidity ratio from 0.01 to 0.025 kg/kg. The thermal coefficient of performance improved by 50% for the above variation in humidity ratio. This shows that such thermally activated systems are feasible options for hot and humid climatic conditions as indicated by better performance under these conditions. Full article

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23 pages, 5651 KiB

Open AccessArticle

Thermodynamic and Environmental Analysis of Scaling up Cogeneration Units Driven by Sugarcane Biomass to Enhance Power Exports

by João Paulo Guerra, Fernando Henrique Cardoso

, Alex Nogueira and Luiz Kulay^*

Chemical Engineering Department, Polytechnic School of the University of São Paulo, Avenida Professor Lineu Prestes, 580, Bloco 18—Conjunto das Químicas, São Paulo 05508-000, SP, Brazil

Energies 2018, 11(1), 73; https://doi.org/10.3390/en11010073 - 1 Jan 2018

Cited by 21 | Viewed by 5490

Abstract

When manual harvesting of sugarcane was discontinued in many regions of Brazil, interest in power generation by burning the bagasse and straw in cogeneration units rose. Exergy analysis is often applied to increase the thermodynamic yield of these plants by identifying irreversibility and [...] Read more.

When manual harvesting of sugarcane was discontinued in many regions of Brazil, interest in power generation by burning the bagasse and straw in cogeneration units rose. Exergy analysis is often applied to increase the thermodynamic yield of these plants by identifying irreversibility and work availability. Conversely, pressure for adopting clean energy requires these systems to be evaluated for suitable environmental performance. This study identified and discussed the thermodynamic and environmental effects of scaling up systems that operate according Rankine cycle with reheating. Ten scenarios have been designed considering different levels of steam pressure and addition rates of straw remaining in the sugarcane cultivation. The thermodynamic analysis revealed a 37% improvement in the exergy efficiency and 63% of increasing in power generation to raise the steam pressure from 20 to 100 bar. Moreover, the use of 50% of residual straw into units operating at 100 bar can more than double the amount of electricity exported. If addressed considering a life cycle perspective, the use of straw improves the environmental performance of the cogeneration for Climate Change and Particle Matter Formation but provides additional impacts in terms of Water and Fossil resources depletions. Full article

(This article belongs to the Special Issue Sustainable and Renewable Energy Systems)

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16 pages, 5581 KiB

Open AccessArticle

Power Transformer Spatial Acoustic Radiation Characteristics Analysis under Multiple Operating Conditions

by Liming Ying¹, Donghui Wang^1,*

, Jinwei Wang¹, Guodong Wang², Xiaowen Wu³ and Jiangtao Liu⁴

¹ School of Electrical Engineering, Wuhan University, Wuhan 430072, China

² State Grid Yantai Power Supply Company, Yantai 265199, China

³ State Grid Hunan Electric Power Corporation Research Institute, Changsha 410007, China

⁴ Department of Physics and Electrical Engineering, Hubei University of Education, Wuhan 430205, China

Energies 2018, 11(1), 74; https://doi.org/10.3390/en11010074 - 1 Jan 2018

Cited by 7 | Viewed by 4319

Abstract

Spatial acoustic radiation characteristics analysis is the precondition of reducing the noise influence of outdoor power transformer while multi-physical field coupling method can be applied to quantify and reveal these acoustic characteristics of a running power transformer. In this study, based on the [...] Read more.

Spatial acoustic radiation characteristics analysis is the precondition of reducing the noise influence of outdoor power transformer while multi-physical field coupling method can be applied to quantify and reveal these acoustic characteristics of a running power transformer. In this study, based on the theoretical analysis about noise generation and dissemination process, an acoustic radiation model about oil-immersed power transformer was established and verified with field test data in time and frequency domain. Then, far-field analysis and directivity analysis were accomplished to characterize acoustic field of power transformer under multiple operating conditions. Finally, the acoustic radiation influence on potential surrounding buildings were analyzed and discussed. The visual results and conclusion provide acoustic guide for the optimal planning and design about both power substation and ambient buildings. Full article

(This article belongs to the Special Issue Emerging Power Electronics Technologies for Power Systems and Machine Drives)

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21 pages, 3562 KiB

Open AccessArticle

ACT-R Cognitive Model Based Trajectory Planning Method Study for Electric Vehicle’s Active Obstacle Avoidance System

by Aijuan Li^1,*

, Wanzhong Zhao^2,*, Xibo Wang¹ and Xuyun Qiu¹

¹ School of Automotive Engineering, Shan Dong Jiao Tong University, Jinan 250357, China

² Energy and Power Engineering College, Nanjing University of Aeronautics & Astronautics, Nanjing 210016, China

Energies 2018, 11(1), 75; https://doi.org/10.3390/en11010075 - 1 Jan 2018

Cited by 14 | Viewed by 4566

Abstract

The active obstacle avoidance system is one of the important components of the electric vehicle active safety system. In order to realize the active obstacle avoidance system driving the vehicle smoothly and without collision in complex road situation, a new dynamical trajectory planning [...] Read more.

The active obstacle avoidance system is one of the important components of the electric vehicle active safety system. In order to realize the active obstacle avoidance system driving the vehicle smoothly and without collision in complex road situation, a new dynamical trajectory planning method based on ACT-R (Adaptive Control of Thought-Rational) cognitive model is introduced. Firstly, the ACT-R cognitive architecture is introduced and the trajectory planning method’s framework structure based on ACT-R cognitive model is built. Secondly, the modeling method of ACT-R cognitive model is introduced, the main module of ACT-R cognitive model includes the initialized behavior module, trajectory planning module, estimated behavioral module, and weight adjustment behavior module. Finally, the verification of the trajectory planning method is conducted by the simulation and experiment results. The simulation and experiment results showed that the method of AR (ACT-R) is effective and feasible. The AR method is better than the methods that are based on the OC (Optimal Control) and FN (fuzzy neural network fusion); this paper’s method has more human behavior characteristics and can meet the demand of different constraints. Full article

(This article belongs to the Special Issue The International Symposium on Electric Vehicles (ISEV2017))

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27 pages, 5614 KiB

Open AccessArticle

Improved Krill Herd Algorithm with Novel Constraint Handling Method for Solving Optimal Power Flow Problems

by Gonggui Chen^1,2,*, Zhengmei Lu^1,2 and Zhizhong Zhang³

¹ Key Laboratory of Network Control & Intelligent Instrument, Chongqing University of Posts and Telecommunications, Ministry of Education, Chongqing 400065, China

² Research Center on Complex Power System Analysis and Control, Chongqing University of Posts and Telecommunications, Chongqing 400065, China

³ Key Laboratory of Communication Network and Testing Technology, Chongqing University of Posts and Telecommunications, Chongqing 400065, China

Energies 2018, 11(1), 76; https://doi.org/10.3390/en11010076 - 1 Jan 2018

Cited by 28 | Viewed by 3498

Abstract

As one of the most important tools used in operation and planning of power systems, the optimal power flow (OPF) problem considering the economy and security is large-scale, complex and hard to solve. In this paper, an improved krill herd algorithm (IKHA) has [...] Read more.

As one of the most important tools used in operation and planning of power systems, the optimal power flow (OPF) problem considering the economy and security is large-scale, complex and hard to solve. In this paper, an improved krill herd algorithm (IKHA) has been proposed. In IKHA, the onlooker search mechanism is introduced to reduce the probability of falling into local optimum; and the parameter values of the proposed algorithm including inertia weight and step-length scale factor are varied according to the iteration of evolutionary process, which improves the exploration and exploitation capabilities. Moreover, a novel constraint handling method is proposed to guide the individual to the feasible space and ensure that the optimal solution satisfies the security constraints. Then, IKHA is combined with the novel constraint handling method to solve the multi-constrained OPF problem, and its performance is tested on the IEEE 30 bus, IEEE 57 bus and IEEE 118 bus systems for 10 different simulation cases containing linear and non-linear objective functions. The simulation results demonstrate that the proposed method can solve the OPF problem successfully and obtain better solutions compared with other methods reported in the recent literatures, which prove the feasibility and effectiveness of the improvements in this work. Full article

(This article belongs to the Section F: Electrical Engineering)

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15 pages, 5214 KiB

Open AccessArticle

Anisotropy in Thermal Recovery of Oil Shale—Part 1: Thermal Conductivity, Wave Velocity and Crack Propagation

by Guoying Wang

, Dong Yang^*, Zhiqin Kang and Jing Zhao

Institute of Mining Technology, Taiyuan University of Technology, Taiyuan 030024, China

Energies 2018, 11(1), 77; https://doi.org/10.3390/en11010077 - 1 Jan 2018

Cited by 22 | Viewed by 5063

Abstract

In this paper, the evolution of thermal conductivity, wave velocity and microscopic crack propagation both parallel and perpendicular to the bedding plane in anisotropic rock oil shale were studied at temperatures ranging from room temperature to 600 °C. The results show that the [...] Read more.

In this paper, the evolution of thermal conductivity, wave velocity and microscopic crack propagation both parallel and perpendicular to the bedding plane in anisotropic rock oil shale were studied at temperatures ranging from room temperature to 600 °C. The results show that the thermal conductivity of the perpendicular to bedding direction (K_PER) (PER: perpendicular to beeding direction), wave velocity of perpendicular to bedding diretion (V_PER), thermal conduction coefficient of parallel to beeding direction (K_PAR) and wave velocity of parallel to beeding direction (V_PAR) (PAR: parallel to bedding direction) decreased with the increase in temperature, but the rates are different. K_PER and V_PER linearly decreased with increasing temperature from room temperature to 350 °C, with an obvious decrease at 400 °C corresponding to a large number of cracks generated along the bedding direction. K_PER, V_PER, K_PAR and V_PAR generally maintained fixed values from 500 °C to 600 °C. 400 °C has been identified as the threshold temperature for anisotropic evolution of oil shale thermal physics. In addition, the relationship between the thermal conductivity and wave velocity based on the anisotropy of oil shale was fitted using linear regression. The research in this paper can provide reference for the efficient thermal recovery of oil shale, thermal recovery of heavy oil reservoirs and the thermodynamic engineering in other sedimentary rocks. Full article

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2510 KiB

Open AccessArticle

Modeling Aggregate Hourly Energy Consumption in a Regional Building Stock

by Anna Kipping and Erik Trømborg^*

Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, P.O. Box 5003, N-1432 Ås, Norway

Energies 2018, 11(1), 78; https://doi.org/10.3390/en11010078 - 29 Dec 2017

Cited by 11 | Viewed by 5001

Abstract

Sound estimates of future heat and electricity demand with high temporal and spatial resolution are needed for energy system planning, grid design, and evaluating demand-side management options and polices on regional and national levels. In this study, smart meter data on electricity consumption [...] Read more.

Sound estimates of future heat and electricity demand with high temporal and spatial resolution are needed for energy system planning, grid design, and evaluating demand-side management options and polices on regional and national levels. In this study, smart meter data on electricity consumption in buildings are combined with cross-sectional building information to model hourly electricity consumption within the household and service sectors on a regional basis in Norway. The same modeling approach is applied to model aggregate hourly district heat consumption in three different consumer groups located in Oslo. A comparison of modeled and metered hourly energy consumption shows that hourly variations and aggregate consumption per county and year are reproduced well by the models. However, for some smaller regions, modeled annual electricity consumption is over- or underestimated by more than 20%. Our results indicate that the presented method is useful for modeling the current and future hourly energy consumption of a regional building stock, but that larger and more detailed training datasets are required to improve the models, and more detailed building stock statistics on regional level are needed to generate useful estimates on aggregate regional energy consumption. Full article

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15 pages, 4352 KiB

Open AccessArticle

Study on the Evaluation Index System and Evaluation Method of Voltage Stability of Distribution Network with High DG Penetration

by Jingjing Tu^*

, Zhongdong Yin and Yonghai Xu

School of Electrical & Electronic Engineering, North China Electric Power University, Beijing 102206, China

Energies 2018, 11(1), 79; https://doi.org/10.3390/en11010079 - 1 Jan 2018

Cited by 10 | Viewed by 3140

Abstract

With the development of new energy technologies, distributed generation (DG) plays a growing role in power distribution networks. Although it solves the power supply problem in some areas, it also poses a challenge to the traditional power grid. To help with this problem, [...] Read more.

With the development of new energy technologies, distributed generation (DG) plays a growing role in power distribution networks. Although it solves the power supply problem in some areas, it also poses a challenge to the traditional power grid. To help with this problem, we establish a static voltage stability analysis model for high penetration DG, taking into account its large capacity, and the high fluctuations of its output. Based on the theoretical analysis and the mathematical derivation, we propose an improved voltage stability evaluation index (IVSE) accounting for DG. Finally, using the typical circuit of the IEEE 33 & 69 node system, we simulate high penetration DG access in different locations and capacities. In the simulations, the traditional power flow equation is modified by a continuous parametric equation accounting for DG. Based on consideration of the system transmission power limit, voltage stability margin and system loss, the value of IVSE is demonstrated, in comparison with the traditional index. Thus, we verify that the IVSE index is easy to understand, simple to calculate, and highly versatile. Full article

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15 pages, 2502 KiB

Open AccessArticle

Well Test Analysis for Fractured and Vuggy Carbonate Reservoirs of Well Drilling in Large Scale Cave

by Cuiqiao Xing¹, Hongjun Yin^1,*, Kexin Liu¹, Xingke Li^1,2 and Jing Fu³

¹ College of Petroleum Engineering, Northeast Petroleum University, Daqing 163318, Heilongjiang, China

² Oil and Gas Engineering Institute of the Jilin Oilfield, Songyuan 138000, Jilin, China

³ Mewbourne School of Petroleum & Geological Engineering, The University of Oklahoma, Norman, OK 73019, USA

Energies 2018, 11(1), 80; https://doi.org/10.3390/en11010080 - 1 Jan 2018

Cited by 21 | Viewed by 5526

Abstract

A well test analysis model for fractured and vuggy carbonate reservoir of wells drilling in large scale cave considering wellbore storage and skin factor is established in this paper. The Laplace transformation and Stehfest numerical inversion are applied to obtain the results of [...] Read more.

A well test analysis model for fractured and vuggy carbonate reservoir of wells drilling in large scale cave considering wellbore storage and skin factor is established in this paper. The Laplace transformation and Stehfest numerical inversion are applied to obtain the results of wellbore pressure. Through the sensitivity analysis of different parameters for the well test typical curves, it is found that the change of the well test curves is in accordance with the theoretical analysis. With the increase of skin factor, the hump of well test typical curves is steeper. The storage ratio influences the depth and width of the concave in the pressure derivative curves. The cross flow coefficient mainly affects the position of the concave occurrence in the pressure derivative curves. The dimensionless reservoir radius mainly affects the middle and late stages of the log-log pressure type curves, and the later well test curves will be upturned for sealed boundary. The duration of the early stage of the log-log curves will become longer when drilling in large scale cave. The effective well radius is increased to a certain extent, which is in full agreement with the conclusions in this paper. The size of the caves has the same effect on the well test typical curves as wellbore storage coefficient. Due to acidification, fracturing, and other reasons, the boundary of the cave will collapse. Therefore, considering the wellbore storage coefficient and skin effect is very important during well testing. However, the existing models for well testing of fractured and vuggy carbonate reservoir often ignore the wellbore storage coefficient and skin effect. For fractured and vuggy carbonate reservoirs of well drilling in large scale cave, the existing models are not applicable. Since the previous models are mostly based on the triple-porosity medium and the equivalent continuum. The well test model for well drilling in large scale cave of fracture-cavity carbonate reservoirs with wellbore storage coefficient and skin factor in this work has significant application value for oil field. Full article

(This article belongs to the Section D: Energy Storage and Application)

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1894 KiB

Open AccessArticle

Estimation for Expected Energy Not Served of Power Systems Using the Screening Methodology of Cascading Outages in South Korea

by Bokyung Goo and Jin Hur^*

Department of Electrical Engineering, Sangmyung University, Seoul 03016, Korea

Energies 2018, 11(1), 81; https://doi.org/10.3390/en11010081 - 29 Dec 2017

Cited by 4 | Viewed by 3381

Abstract

The uncertainty of complex power systems increases the possibility of large blackouts due to the expectations of physical events, such as equipment failures, protection failures, control actions failure, operator error, and cyber-attacks. Cascading outage is a sequence of dependent failures of individual components [...] Read more.

The uncertainty of complex power systems increases the possibility of large blackouts due to the expectations of physical events, such as equipment failures, protection failures, control actions failure, operator error, and cyber-attacks. Cascading outage is a sequence of dependent failures of individual components that successively weaken the power system. A procedure to identify and evaluate the initiating events and perform sequential cascading analysis is needed. In this paper, we propose a new screening methodology based on sequential contingency simulation of cascading outages, including probabilistic analysis and visualization model. Performance of a detail cascading analysis using practical power systems is suggested and discussed. The proposed screening methodology will play a key role in identifying the uncontrolled successive loss of system elements. Full article

(This article belongs to the Special Issue Risk-Based Methods Applied to Power and Energy Systems)

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2791 KiB

Open AccessArticle

Simultaneous Production of Transformer Insulating Oil and Value-Added Glycerol Carbonates from Soybean Oil by Lipase-Catalyzed Transesterification in Dimethyl Carbonate

by Keon Hee Kim and Eun Yeol Lee^*

Department of Chemical Engineering, Kyung Hee University, Gyeonggi-do 17104, Korea

Energies 2018, 11(1), 82; https://doi.org/10.3390/en11010082 - 30 Dec 2017

Cited by 10 | Viewed by 4332

Abstract

Fatty acid methyl esters (FAMEs), as a transformer insulating oil, and value-added glycerol derivatives were simultaneously synthesized from soybean oil by transesterification using Lipozyme 435 in dimethyl carbonate (DMC). The conversion of transformer insulating oil and glycerol derivatives reached 92% and 72%, respectively, [...] Read more.

Fatty acid methyl esters (FAMEs), as a transformer insulating oil, and value-added glycerol derivatives were simultaneously synthesized from soybean oil by transesterification using Lipozyme 435 in dimethyl carbonate (DMC). The conversion of transformer insulating oil and glycerol derivatives reached 92% and 72%, respectively, under optimum conditions (DMC-to-oil molar ratio of 4.5:1 with 0.5 v/v % water and 15 wt. % Lipozyme 435 at 70 °C) in one-pot batch reactions. The purified transformer insulating oil possessed a dielectric breakdown voltage of 82.0 kV, which is sufficiently high for transformer insulation oil applications. Other properties such as density, dielectric breakdown voltage, and viscosity were comparable or superior to those of mineral oil, confirming that achieved material could be used as an alternative transformer insulating oil. Additionally, the glycerol was simultaneously converted into glycerol derivatives, which can be utilized as ingredients for cosmetics or monomers for bio-based plastics. This study clearly demonstrates that transformer insulating oil and value-added glycerol derivatives were simultaneously produced based on the zero-waste utilization of soybean oil. Full article

(This article belongs to the Section L: Energy Sources)

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3964 KiB

Open AccessArticle

A Risk-Based Methodology and Tool Combining Threat Analysis and Power System Security Assessment

by Emanuele Ciapessoni^1,*, Diego Cirio¹, Andrea Pitto¹, Pietro Marcacci¹, Matteo Lacavalla¹, Stefano Massucco², Federico Silvestro² and Marino Sforna³

¹ Ricerca sul Sistema Energetico RSE S.p.A., Via Rubattino 54, Milan 20134, Italy

² Department of Naval, Electric, Electronic and Telecommunication Engineering, University of Genova, Via Opera Pia 11a, Genova 16145, Italy

³ TERNA (Italian TSO), V. G. Galilei 18, Pero (MI) 20016, Italy

Energies 2018, 11(1), 83; https://doi.org/10.3390/en11010083 - 30 Dec 2017

Cited by 13 | Viewed by 4332

Abstract

A thorough investigation of power system security requires the analysis of the vulnerabilities to natural and man-related threats which potentially trigger multiple contingencies. In particular, extreme weather events are becoming more and more frequent due to climate changes and often cause large load [...] Read more.

A thorough investigation of power system security requires the analysis of the vulnerabilities to natural and man-related threats which potentially trigger multiple contingencies. In particular, extreme weather events are becoming more and more frequent due to climate changes and often cause large load disruptions on the system, thus the support for security enhancement gets tricky. Exploiting data coming from forecasting systems in a security assessment environment can help assess the risk of operating power systems subject to the disturbances provoked by the weather event itself. In this context, the paper proposes a security assessment methodology, based on an updated definition of risk suitable for power system risk evaluations. Big data analytics can be useful to get an accurate model for weather-related threats. The relevant software (SW) platform integrates the security assessment methodology with prediction systems which provide short term forecasts of the threats affecting the system. The application results on a real wet snow threat scenario in the Italian High Voltage grid demonstrate the effectiveness of the proposed approach with respect to conventional security approaches, by complementing the conventional “N − 1” security criterion and exploiting big data to link the security assessment phase to the analysis of incumbent threats. Full article

(This article belongs to the Special Issue Risk-Based Methods Applied to Power and Energy Systems)

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3865 KiB

Open AccessArticle

Study of an Altered Magnetic Circuit of a Permanent Magnet Linear Generator for Wave Power

by Jennifer Leijon^1,*, Jonathan Sjölund¹, Boel Ekergård², Cecilia Boström¹, Sandra Eriksson¹, Irina Temiz¹

and Mats Leijon^1,3

¹ Department of Engineering Sciences, Uppsala University, Box 534, 751 21 Uppsala, Sweden

² Seabased Industry AB, Verkstadsgatan 4, 453 30 Lysekil, Sweden

³ Department of Electrical Engineering, Chalmers University of Technology, 412 96 Gothenburg, Sweden

Energies 2018, 11(1), 84; https://doi.org/10.3390/en11010084 - 31 Dec 2017

Cited by 6 | Viewed by 6503

Abstract

The wave energy converter (WEC) studied and developed at Uppsala University in Sweden is a point absorbing buoy connected to a linear generator (LG) on the seabed. Previous studies have improved the sustainability of the generator, changing its magnets from Nd₂Fe [...] Read more.

The wave energy converter (WEC) studied and developed at Uppsala University in Sweden is a point absorbing buoy connected to a linear generator (LG) on the seabed. Previous studies have improved the sustainability of the generator, changing its magnets from Nd₂Fe₁₄B-magnets to ferrites. In this paper, the magnetic circuit of the linear generator is further studied. Ferrite magnets of two different types (Y30 and Y40) are studied along with different shapes of pole shoes for the system. The finite element method (FEM) simulations in a program called Ace are performed. The results show that a linear generator including both Y30 and Y40 magnets and shortened T-shaped pole shoes can generate a similar magnetic energy in the airgap as a linear generator only containing Y40 magnets and rectangular pole shoes. This shows that the magnetic circuit can be altered, opening up sizes and strengths of magnets for different retailers, and thereby possibly lowering magnet cost and transportation. This work was previously presented as a conference at the European Wave and Tidal Energy Conference (EWTEC) 2017 in Cork, Ireland; this manuscript has been carefully revised and some discussions, on magnet costs for example, have been added to this paper. Full article

(This article belongs to the Special Issue Electric Machines and Drives for Renewable Energy Harvesting 2017)

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29 pages, 5654 KiB

Open AccessArticle

Application and Comparison of Metaheuristic and New Metamodel Based Global Optimization Methods to the Optimal Operation of Active Distribution Networks

by Hao Xiao¹

, Wei Pei^1,*, Zuomin Dong²

, Li Kong¹ and Dan Wang³

¹ Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing 100190, China

² Department of Mechanical Engineering and Institute of Integrated Energy Systems, University of Victoria, Victoria, BC V8W2Y2, Canada

³ Key Lab of Smart Grid of Min of Education, Tianjin University, Tianjin 300072, China

Energies 2018, 11(1), 85; https://doi.org/10.3390/en11010085 - 1 Jan 2018

Cited by 25 | Viewed by 5591

Abstract

As an imperative part of smart grids (SG) technology, the optimal operation of active distribution networks (ADNs) is critical to the best utilization of renewable energy and minimization of network power losses. However, the increasing penetration of distributed renewable energy sources with uncertain [...] Read more.

As an imperative part of smart grids (SG) technology, the optimal operation of active distribution networks (ADNs) is critical to the best utilization of renewable energy and minimization of network power losses. However, the increasing penetration of distributed renewable energy sources with uncertain power generation and growing demands for higher quality power distribution are turning the optimal operation scheduling of ADN into complex and global optimization problems with non-unimodal, discontinuous and computation intensive objective functions that are difficult to solve, constituting a critical obstacle to the further advance of SG and ADN technology. In this work, power generation from renewable energy sources and network load demands are estimated using probability distribution models to capture the variation trends of load fluctuation, solar radiation and wind speed, and probability scenario generation and reduction methods are introduced to capture uncertainties and to reduce computation. The Open Distribution System Simulator (OpenDSS) is used in modeling the ADNs to support quick changes to network designs and configurations. The optimal operation of the ADN, is achieved by minimizing both network voltage deviation and power loss under the probability-based varying power supplies and loads. In solving the computation intensive ADN operation scheduling optimization problem, several novel metamodel-based global optimization (MBGO) methods have been introduced and applied. A comparative study has been carried out to compare the conventional metaheuristic global optimization (GO) and MBGO methods to better understand their advantages, drawbacks and limitations, and to provide guidelines for subsequent ADN and smart grid scheduling optimizations. Simulation studies have been carried out on the modified IEEE 13, 33 and 123 node networks to represent ADN test cases. The MBGO methods were found to be more suitable for small- and medium-scale ADN optimal operation scheduling problems, while the metaheuristic GO algorithms are more effective in the optimal operation scheduling of large-scale ADNs with relatively straightforward objective functions that require limited computational time. This research provides solution for ADN optimal operations, and forms the foundation for ADN design optimization. Full article

(This article belongs to the Special Issue From Smart Metering to Demand Side Management)

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16 pages, 4961 KiB

Open AccessArticle

Long-Term Battery Voltage, Power, and Surface Temperature Prediction Using a Model-Based Extreme Learning Machine

by Xiaopeng Tang¹, Ke Yao², Boyang Liu¹, Wengui Hu² and Furong Gao^1,2,*

¹ Department of Chemical and Biological Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China

² Guangzhou HKUST Fok Ying Tung Research Institute, Guangzhou 510000, China

Energies 2018, 11(1), 86; https://doi.org/10.3390/en11010086 - 3 Jan 2018

Cited by 42 | Viewed by 5308

Abstract

A battery’s state-of-power (SOP) refers to the maximum power that can be extracted from the battery within a short period of time (e.g., 10 s or 30 s). However, as its use in applications is growing, such as in automatic cars, the ability [...] Read more.

A battery’s state-of-power (SOP) refers to the maximum power that can be extracted from the battery within a short period of time (e.g., 10 s or 30 s). However, as its use in applications is growing, such as in automatic cars, the ability to predict a longer usage time is required. To be able to do this, two issues should be considered: (1) the influence of both the ambient temperature and the rise in temperature caused by Joule heat, and (2) the influence of changes in the state of charge (SOC). In response, we propose the use of a model-based extreme learning machine (Model-ELM, MELM) to predict the battery future voltage, power, and surface temperature for any given load current. The standard ELM is a kind of single-layer feedforward network (SLFN). We propose using a set of rough models to replace the active functions (such as logsig()) in the ELM for better generalization performance. The model parameters and initial SOC in these “rough models” are randomly selected within a given range, so little prior knowledge about the battery is required. Moreover, the identification of the complex nonlinear system can be transferred into a standard least squares problem, which is suitable for online applications. The proposed method was tested and compared with RLS (Recursive Least Square)-based methods at different ambient temperatures to verify its superiority. The temperature prediction accuracy is higher than ±1.5 °C, and the RMSE (Root Mean Square Error) of the power prediction is less than 0.25 W. It should be noted that the accuracy of the proposed method does not rely on the accuracy of the state estimation such as SOC, thereby improving its robustness. Full article

(This article belongs to the Special Issue The International Symposium on Electric Vehicles (ISEV2017))

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15 pages, 3563 KiB

Open AccessArticle

Behavior Anomaly Indicators Based on Reference Patterns—Application to the Gearbox and Electrical Generator of a Wind Turbine

by Angel Gil¹, Miguel A. Sanz-Bobi^1,*

and Miguel A. Rodríguez-López²

¹ Institute for Research in Technology and Telematics and Computer Science Department, Comillas Pontifical University, 28015 Madrid, Spain

² Acciona Energía S.A., 31621 Sarriguren, Navarra, Spain

Energies 2018, 11(1), 87; https://doi.org/10.3390/en11010087 - 1 Jan 2018

Cited by 15 | Viewed by 3898

Abstract

This paper presents indicators of non-expected behavior in components of a wind turbine. These indicators are used to alert about the working conditions of these components that are not usual, according to the normal behavior observed for similar conditions of wind speed and [...] Read more.

This paper presents indicators of non-expected behavior in components of a wind turbine. These indicators are used to alert about the working conditions of these components that are not usual, according to the normal behavior observed for similar conditions of wind speed and power generated. In order to obtain these indicators, reference patterns of behavior for the components studied were defined. The patterns were obtained from real data of the wind turbine covering all of the possible working conditions. The technique of self-organized maps was used for discovering such reference patterns. Once they were obtained, new data, not included in the training set, was passed through the patterns in order to verify if the behavior observed corresponds or not to that expected. If they do not coincide, an anomaly of behavior is detected than can be useful for soon alert of possible failure mode or at least to know that the component was under working conditions that could cause risk of fault. The periods of unexpected behavior are the base for the indicators proposed in this paper. Real cases to show the elaboration of the indicators, and their corresponding results are provided. Full article

(This article belongs to the Special Issue Wind Turbine Loads and Wind Plant Performance)

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15 pages, 1290 KiB

Open AccessArticle

Power Estimation of Multiple Two-State Loads Using A Probabilistic Non-Intrusive Approach

by Nilson Henao^1,*

, Kodjo Agbossou¹, Sousso Kelouwani², Sayed Saeed Hosseini¹ and Michael Fournier³

¹ Department of Electrical and Computer Engineering, Université du Québec, Trois-Rivieres, QC G9A 5H7, Canada

² Department of Mechanical Engineering, Université du Québec, Trois-Rivières, QC G9A 5H7, Canada

³ Laboratoire des Technologies de l’Énergie, Institut de Recherche Hydro-Québec, Shawinigan, QC G9N 7N5, Canada

Energies 2018, 11(1), 88; https://doi.org/10.3390/en11010088 - 1 Jan 2018

Cited by 11 | Viewed by 2980

Abstract

This paper investigates a non-intrusive approach of retrieving electric space heater (ESH) power profiles from a residential aggregated signal. In cold-climate regions with heating appliances controlled by electronic thermostats, an accurate non-intrusive recognition of power profiles is a challenging task. Accordingly, a robust [...] Read more.

This paper investigates a non-intrusive approach of retrieving electric space heater (ESH) power profiles from a residential aggregated signal. In cold-climate regions with heating appliances controlled by electronic thermostats, an accurate non-intrusive recognition of power profiles is a challenging task. Accordingly, a robust disaggregation approach based on the difference factorial hidden Markov model (DFHMM) and the Kronecker operation is contributed. The proposed method aims to uncover the underlying stochastic tow-state models of ESHs using their common prior knowledge. The major advantage of the developed load-monitoring architecture consists of modeling simplicity and inference as well as load-detection efficacy in the presence of perturbations from other unknown loads. The experimental results prove the effectiveness of the method in manipulating the challenging case of multiple two-state loads with a high event overlapping probability. Full article

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15 pages, 13560 KiB

Open AccessArticle

Development of an Advanced Rule-Based Control Strategy for a PHEV Using Machine Learning

by Hanho Son

, Hyunhwa Kim, Sungho Hwang

and Hyunsoo Kim^*

School of Mechanical Engineering, Sungkyunkwan University, Seobu-ro, Suwon-si 2066, Korea

Energies 2018, 11(1), 89; https://doi.org/10.3390/en11010089 - 1 Jan 2018

Cited by 16 | Viewed by 3676

Abstract

This paper presents an advanced rule-based mode control strategy (ARBC) for a plug-in hybrid electric vehicle (PHEV) considering the driving cycle characteristics and present battery state of charge (SOC). Using dynamic programming (DP) results, the behavior of the optimal operating mode was investigated [...] Read more.

This paper presents an advanced rule-based mode control strategy (ARBC) for a plug-in hybrid electric vehicle (PHEV) considering the driving cycle characteristics and present battery state of charge (SOC). Using dynamic programming (DP) results, the behavior of the optimal operating mode was investigated for city (UDDS×2, JC08 ×2) and highway (HWFET ×2, NEDC ×2) driving cycles. It was found that the operating mode selection varies according to the driving cycle characteristics and battery SOC. To consider these characteristics, a predictive mode control map was developed using the machine learning algorithm, and ARBC was proposed, which can be implemented in real-time environments. The performance of ARBC was evaluated by comparing it with rule-based mode control (RBC), which is a CD-CS mode control strategy. It was found that the equivalent fuel economy of ARBC was improved by 1.9–3.3% by selecting the proper operating mode from the viewpoint of system efficiency for the whole driving cycle, regardless of the battery SOC. Full article

(This article belongs to the Section F: Electrical Engineering)

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17 pages, 3638 KiB

Open AccessArticle

Experimental Study on the Heat Release Operational Characteristics of a Soil Coupled Ground Heat Exchanger with Assisted Cooling Tower

by Weibo Yang^1,2,3,4,*, Binbin Yang¹ and Rui Xu¹

¹ School of Hydraulic, Energy and Power Engineering, Yangzhou University, Yangzhou 225127, Jiangsu, China

² State Key Laboratory for Geo Mechanics and Deep Underground Engineering, China University of Mining & Technology, Xuzhou 221008, Jiangsu, China

³ Key Laboratory of Thermo-Fluid Science and Engineering (Xi’an Jiaotong University), Ministry of Education, Xi’an 710049, China

⁴ Key Laboratory of Efficient & Clean Energy Utilization, the Education Department of Hunan Province, Changsha 410114, China

Energies 2018, 11(1), 90; https://doi.org/10.3390/en11010090 - 1 Jan 2018

Cited by 4 | Viewed by 3370

Abstract

Hybrid ground source heat pump systems (HGSHPS) with assisted cooling towers is one of the most efficient cooling and heating technologies for buildings with cooling-dominated loads. For the system, the coupled heat release mode between the ground heat exchanger (GHE) and cooling tower [...] Read more.

Hybrid ground source heat pump systems (HGSHPS) with assisted cooling towers is one of the most efficient cooling and heating technologies for buildings with cooling-dominated loads. For the system, the coupled heat release mode between the ground heat exchanger (GHE) and cooling tower is vital for underground soil temperature recovery characteristics and system operation performance. In order to obtain the heat release operation characteristics with different coupled modes of the GHE and cooling tower, a set of multi-functional heat release experimental systems of soil coupled GHE with assisted cooling tower was constructed. The experimental investigations on the system heat release operation characteristics operated in the separate GHE heat release mode, combination heat release mode and day and night alternate heat release mode were undertaken based on the experimental system. The results show that for the separate GHE heat release mode, the heat release rate of GHE rises rapidly during the first two hours of operation, then, gradually tends to be steady, and the soil excess temperatures at various depths gradually rise with time. For the combination heat release mode with continuous operation of cooling tower, in view of reducing soil heat accumulation and accelerating soil temperature recovery, it is more conducive to the heat release by opening the cooling tower on sunny days. For the combination heat release mode with intermittent operation of cooling tower, when the total time ratio of cooling tower running to stop is constant, the intermittent time is longer, the better the effect of soil temperature recovery. Additionally, the soil temperature recovery rate can be improved greatly by the release heat operation of cooling tower during night, and the longer the cooling tower runs, the closer the soil temperature is to the initial temperature. Full article

(This article belongs to the Special Issue Geothermal Heating and Cooling)

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16 pages, 3658 KiB

Open AccessArticle

An Improved Grey Model and Scenario Analysis for Carbon Intensity Forecasting in the Pearl River Delta Region of China

by Fei Ye¹

, Xinxiu Xie¹, Li Zhang^1,* and Xiaoling Hu^2,*

¹ School of Business Administration, South China University of Technology, 510640 Guangzhou, China

² Guangdong Food and Drug Vocational College, Guangzhou, China

Energies 2018, 11(1), 91; https://doi.org/10.3390/en11010091 - 1 Jan 2018

Cited by 11 | Viewed by 3313

Abstract

In this paper, an improved grey model and scenario analysis, GA-GM(1,N) is proposed to forecast the carbon intensity in the Pearl River Delta (PRD) region, one of the most developed regions in China. Moreover, to show the advantage and feasibility of the proposed [...] Read more.

In this paper, an improved grey model and scenario analysis, GA-GM(1,N) is proposed to forecast the carbon intensity in the Pearl River Delta (PRD) region, one of the most developed regions in China. Moreover, to show the advantage and feasibility of the proposed model, the forecasting results of the GA-GM(1,N) model are compared with that of a single-variable grey model (GM (1,1)) and a multivariable form (GM(1,N)). Data from one sample period (2005–2012) are used to develop the models, and data from another sample period (2013–2015) are used to test them. The mean absolute percentage error (MAPE) is applied to measure the accuracy of prediction. The results show that, of the three models, GA-GM(1,N) produces the best carbon intensity forecasts, with MAPEs of 0.4–1.4% and 0.04–0.4% in the development and testing periods respectively. This indicates that the optimization of the genetic algorithm is effective. The realization of carbon reduction targets in different cities is also explored by combining grey models with scenario analysis. Only Guangzhou could achieve its reduction target under all scenarios, and it can serve as a reference for other cities. Policy recommendations are provided based on these results. Full article

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15 pages, 6325 KiB

Open AccessArticle

Three-D Numerical Thermal Analysis of Electric Motor with Cooling Jacket

by Zabdur Rehman

and Kwanjae Seong^*

Department of Mechanical, Robotics and Energy Engineering, Dongguk University-Seoul, Jung-Gu, Seoul 04620, Korea

Energies 2018, 11(1), 92; https://doi.org/10.3390/en11010092 - 1 Jan 2018

Cited by 65 | Viewed by 10997

Abstract

The need of a sustainable clean future has paved the way for environmental friendly electric vehicle technology. In electric vehicles, overloading is limited by the maximum temperature rise in the electric motor. Although an improved cooling jacket design is of vital importance in [...] Read more.

The need of a sustainable clean future has paved the way for environmental friendly electric vehicle technology. In electric vehicles, overloading is limited by the maximum temperature rise in the electric motor. Although an improved cooling jacket design is of vital importance in lowering the maximum temperature of the motor, there has not been as much study in the thermal analysis of motors compared to electromagnetic design studies. In this study, a three-dimensional steady state numerical method is used to investigate the performance of a cooling jacket using water as the primary coolant of a three-phase induction motor with special emphasis on the maximum temperature and the required pumping power. The effective thermal conductivity approach is employed to model the stator winding, stator yoke, rotor winding and rotor yoke. Heat transfer by induced air is treated as forced convection at the motor ends and effective conductivity is obtained for air in the stator-rotor gap. Motor power losses, i.e., copper and iron losses, are treated as heat generation sources. The effect of bearings and end windings is not considered in the current model. Pressure and temperature distributions under various coolant flow rates, number of flow passes and different cooling jacket configurations are obtained. The study is successful in identifying the hot spots and understanding the critical parameters that affect the temperature profile. The cooling jacket configuration affects the region of maximum temperature inside the motor. Increasing the number of flow passes and coolant flow rate decreases maximum motor temperature but results in an increase in the pumping power. Of the cooling jacket configurations and operating conditions investigated, a cooling jacket with six passes at a flow rate of 10 LPM with two-port configuration was found to be optimal for a 90-kW induction motor for safe operation at the maximum output. Full article

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11 pages, 1531 KiB

Open AccessArticle

On the Evolution of the Integral Time Scale within Wind Farms

by Huiwen Liu^1,2

, Imran Hayat³

, Yaqing Jin² and Leonardo P. Chamorro^2,3,4,*

¹ College of Water Conservancy and Hydropower Engineering, Hohai University, Nanjing 210024, China

² Mechanical Science and Engineering, University of Illinois, Urbana, IL 61801, USA

³ Aerospace Engineering, University of Illinois, Urbana, IL 61801, USA

⁴ Civil and Environmental Engineering, University of Illinois, Urbana, IL 61801, USA

Energies 2018, 11(1), 93; https://doi.org/10.3390/en11010093 - 2 Jan 2018

Cited by 32 | Viewed by 5473

Abstract

A wind-tunnel investigation was carried out to characterize the spatial distribution of the integral time scale (

T^{u}

) within, and in the vicinity of, two model wind farms. The turbine arrays were placed over a rough wall and operated under high [...] Read more.

A wind-tunnel investigation was carried out to characterize the spatial distribution of the integral time scale (

T^{u}

) within, and in the vicinity of, two model wind farms. The turbine arrays were placed over a rough wall and operated under high turbulence. The two layouts consisted of aligned units distinguished only by the streamwise spacing (

{Δ x}_{_{T}}

) between the devices, set at five and ten rotor diameters

d_{T}

(or

S_{x} = Δ x_{_{T}} / d_{T} =

5 and 10). They shared the same spanwise spacing between turbines of 2.5

d_{T}

; this resulted in arrays of 8 × 3 and 5 × 3 horizontal-axis turbines. Hotwire anemometry was used to characterize the instantaneous velocity at various vertical and transverse locations along the central column of the wind farms. Results show that

T^{u}

was modulated by the wind farm layout. It was significantly reduced within the wind farms and right above them, where the internal boundary layer develops. The undisturbed levels above the wind farms were recovered only at ≈

d_{T} / 2

above the top tip. This quantity appeared to reach adjusted values starting the fifth row of turbines in the

S_{x} = 5

wind farm, and earlier in the

S_{x} = 10

counterpart. Within the adjusted zone, the distribution of

T^{u}

at hub height exhibited a negligible growth in the

S_{x} = 5

case; whereas it underwent a mild growth in the

S_{x} = 10

wind farm. In addition, the flow impinging the inner turbines exhibited

T^{u} / T_{i n c}^{u} < 1

, where

T_{i n c}^{u}

is the integral time scale of the overall incoming flow. Specifically,

T^{u} \to β T_{i n c}^{u}

at

z = z_{h u b}

, where

β < 1

within standard layouts of wind farms, in particular

β \approx 0.5

and 0.7 for

S_{x} = 5

and 10. Full article

(This article belongs to the Collection Wind Turbines)

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12 pages, 3047 KiB

Open AccessArticle

Heating and Cooling Degree-Days Maps of Pakistan

by Khuram Pervez Amber^1,*, Muhammad Waqar Aslam², Faraz Ikram¹, Anila Kousar³, Hafiz Muhammad Ali⁴, Naveed Akram¹

, Kamran Afzal¹ and Haroon Mushtaq¹

¹ Department of Mechanical Engineering, Mirpur University of Science and Technology (MUST), Mirpur 10250 (AJK), Pakistan

² Department of Computer System Engineering, Mirpur University of Science and Technology (MUST), Mirpur 10250 (AJK), Pakistan

³ Department of Electrical (Power) Engineering, Mirpur University of Science and Technology (MUST), Mirpur 10250 (AJK), Pakistan

⁴ Department of Mechanical Engineering, University of Engineering and Technology (UET), Taxila 47080, Pakistan

Energies 2018, 11(1), 94; https://doi.org/10.3390/en11010094 - 2 Jan 2018

Cited by 34 | Viewed by 12687

Abstract

The building sector consumes about 40% of the world’s primary energy. Seasonal climatic conditions have a significant effect on the energy consumption in buildings. One of the famous methods used for decoding this seasonal variation in buildings energy consumption is the “Degree Days [...] Read more.

The building sector consumes about 40% of the world’s primary energy. Seasonal climatic conditions have a significant effect on the energy consumption in buildings. One of the famous methods used for decoding this seasonal variation in buildings energy consumption is the “Degree Days Method”. Data has been widely published for the heating and cooling degree days of different countries. Unfortunately, there is very limited and outdated published data for the heating and cooling degree-days of Pakistan. In this study, yearly average heating and cooling degree-days for different regions of Pakistan are established by using 30 year long-term measured data for different base temperatures. The data is presented in tables and figures whereas heating and cooling degree-day maps of Pakistan have been developed. Full article

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15 pages, 2914 KiB

Open AccessArticle

An Improved Ant Lion Optimization Algorithm and Its Application in Hydraulic Turbine Governing System Parameter Identification

by Tian Tian¹, Changyu Liu^1,*, Qi Guo², Yi Yuan², Wei Li² and Qiurong Yan³

¹ School of Hydropower and Information Engineering, Huazhong University of Science and Technology, Wuhan 430074, China

² State Key Laboratory of HVDC Technology (Electric Power Research Institute Co., Ltd., CSG), Guangzhou 510663, China

³ College of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan 430074, China

Energies 2018, 11(1), 95; https://doi.org/10.3390/en11010095 - 2 Jan 2018

Cited by 52 | Viewed by 5251

Abstract

In this paper, an improved ant lion optimization (IALO) algorithm for parameter identification of hydraulic turbine governing system (HTGS) is proposed. In the proposed algorithm, the search space is explored by the ant lion optimization first, and then the domain is searched by [...] Read more.

In this paper, an improved ant lion optimization (IALO) algorithm for parameter identification of hydraulic turbine governing system (HTGS) is proposed. In the proposed algorithm, the search space is explored by the ant lion optimization first, and then the domain is searched by the particle swarm optimization (PSO) in each iteration cycle. A chaotic mutation operation namely Logistics map is introduced for the elite to break out of the local optimum. In mutation operation, a serial-parallel combined method is developed to increase the diversity of mutant population. When the proposed IALO algorithm is applied in the parameter identification of HTGS, the comparative simulation results show that the proposed IALO algorithm has the highest accuracy among different optimization algorithms, and the proposed IALO algorithm has a good convergence characteristic and high stability. Full article

(This article belongs to the Section F: Electrical Engineering)

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17 pages, 8766 KiB

Open AccessArticle

Digital Generator Control Unit Design for a Variable Frequency Synchronous Generator in MEA

by Weilin Li^1,*, Yang Yang² and Xiaobin Zhang¹

¹ Department of Electrical Engineering, College of Automation, Northwestern Polytechnical University, Xi’an 710072, China

² Aviation Key Laboratory of Science and Technology on Aerospace Power System, Shaanxi Aero Electric Co. Ltd., Shaanxi 713107, China

Energies 2018, 11(1), 96; https://doi.org/10.3390/en11010096 - 2 Jan 2018

Cited by 13 | Viewed by 6207

Abstract

Variable frequency power generation systems have been adopted for modern aircraft power systems, thus, a new generator control unit (GCU) must be designed to regulate the output voltage and obtain high quality power supply under a wide frequency range from 360 Hz to [...] Read more.

Variable frequency power generation systems have been adopted for modern aircraft power systems, thus, a new generator control unit (GCU) must be designed to regulate the output voltage and obtain high quality power supply under a wide frequency range from 360 Hz to 800 Hz. In this paper, a dual digital signal processor (DSP) structure-based GCU was proposed. Multi-loop control structure was adopted with the controller parameters varying adaptively at different working conditions to obtain better performance. Different root-mean-square (RMS) calculation algorithms have been compared and the final RMS calculation scheme was determined to realize the trade-off between accuracy and computing efficiency. Experimental results show considerable performance improvements of the generator output voltage under various operating conditions with the proposed GCU. Full article

(This article belongs to the Section F: Electrical Engineering)

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35 pages, 9472 KiB

Open AccessArticle

The Multi-Objective Optimization Algorithm Based on Sperm Fertilization Procedure (MOSFP) Method for Solving Wireless Sensor Networks Optimization Problems in Smart Grid Applications

by Hisham A. Shehadeh

, Mohd Yamani Idna Idris^*, Ismail Ahmedy

, Roziana Ramli and Noorzaily Mohamed Noor

Department of Computer System and Technology, Faculty of Computer Science and Information Technology, University of Malaya, Kuala Lumpur 50603, Malaysia

Energies 2018, 11(1), 97; https://doi.org/10.3390/en11010097 - 2 Jan 2018

Cited by 25 | Viewed by 5480

Abstract

Prior studies in Wireless Sensor Network (WSN) optimization mostly concentrate on maximizing network coverage and minimizing network energy consumption. However, there are other factors that could affect the WSN Quality of Service (QoS). In this paper, four objective functions that affect WSN QoS, [...] Read more.

Prior studies in Wireless Sensor Network (WSN) optimization mostly concentrate on maximizing network coverage and minimizing network energy consumption. However, there are other factors that could affect the WSN Quality of Service (QoS). In this paper, four objective functions that affect WSN QoS, namely end-to-end delay, end-to-end latency, network throughput and energy efficiency are studied. Optimal value of packet payload size that is able to minimize the end-to-end delay and end-to-end latency, while also maximizing the network throughput and energy efficiency is sought. To do this, a smart grid application case study together with a WSN QoS model is used to find the optimal value of the packet payload size. Our proposed method, named Multi-Objective Optimization Algorithm Based on Sperm Fertilization Procedure (MOSFP), along with other three state-of-the-art multi-objective optimization algorithms known as OMOPSO, NSGA-II and SPEA2, are utilized in this study. Different packet payload sizes are supplied to the algorithms and their optimal value is derived. From the experiments, the knee point and the intersection point of all the obtained Pareto fronts for all the algorithms show that the optimal packet payload size that manages the trade-offs between the four objective functions is equal to 45 bytes. The results also show that the performance of our proposed MOSFP method is highly competitive and found to have the best average value compared to the other three algorithms. Furthermore, the overall performance of MOSFP on four objective functions outperformed OMOPSO, NSGA-II and SPEA2 by 3%, 6% and 51%, respectively. Full article

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19 pages, 1917 KiB

Open AccessArticle

Renewable Energy Assisted Traffic Aware Cellular Base Station Energy Cooperation

by Faran Ahmed¹, Muhammad Naeem¹, Waleed Ejaz^2,*, Muhammad Iqbal¹, Alagan Anpalagan² and Hyung Seok Kim^3,*

¹ Department of Electrical Engineering, COMSATS Institute of Information Technology, Wah 47040, Pakistan

² Department of Electrical and Computer Engineering, Ryerson University, Toronto, ON M5B 2K3, Canada

³ Department of Information and Communication Engineering, Sejong University, Seoul 05006, Korea

Energies 2018, 11(1), 99; https://doi.org/10.3390/en11010099 - 2 Jan 2018

Cited by 21 | Viewed by 4729

Abstract

With global concern for climate change, and for cutting down the energy cost, especially in off grid areas, use of renewable energy has been gaining widespread attention in many areas including cellular communication. The base station (BS) has emerged as a strong candidate [...] Read more.

With global concern for climate change, and for cutting down the energy cost, especially in off grid areas, use of renewable energy has been gaining widespread attention in many areas including cellular communication. The base station (BS) has emerged as a strong candidate for the integration of renewable energy sources (RES), particularly solar and wind. The incorporation of renewable energy opens many possibilities for energy conservation through strategies such as energy cooperation between BSs during the off-peak hours, when the energy harvested from renewable energy sources may become surplus. In this paper, we present the case for cellular BSs enabled with renewable energy sources (RES) to have an arrangement in which the BS provide surplus energy to a neighboring BS, thus minimizing the use of conventional energy. A realistic objective is developed for northern region of Pakistan, which entails modeling of solar panels and wind-turbine according to the average solar irradiation and wind speed of the region. We also model the dynamic load of the BS, which depicts temporal fluctuations with traffic variations. Based on these models we initiate an energy cooperation scheme between the BS in which an energy cost minimization framework is mathematically modeled and solved through the interior point method algorithm. Results are obtained for different times of the year for different number of base stations showing respective energy cost savings. Full article

(This article belongs to the Section L: Energy Sources)

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14 pages, 3112 KiB

Open AccessArticle

Circuit Breaker Rate-of-Rise Recovery Voltage in Ultra-High Voltage Lines with Hybrid Reactive Power Compensation

by Hongshun Liu^1,*

, Zhen Wang¹, Jingjing Yang¹, Bin Li² and Ang Ren¹

¹ School of Electrical Engineering, Shandong University, Jinan 250061, China

² Rizhao Power Supply Company of State Grid Shandong Electric Power Company, Rizhao 276826, China

Energies 2018, 11(1), 100; https://doi.org/10.3390/en11010100 - 2 Jan 2018

Cited by 10 | Viewed by 3983

Abstract

With the development of ultra-high voltage (UHV) technology, hybrid reactive power compensation (HRPC) will be widely applied in the future. To study the mechanism by which HRPC influences the characteristics of circuit breakers in UHV transmission lines, this paper establishes an improved electromagnetic [...] Read more.

With the development of ultra-high voltage (UHV) technology, hybrid reactive power compensation (HRPC) will be widely applied in the future. To study the mechanism by which HRPC influences the characteristics of circuit breakers in UHV transmission lines, this paper establishes an improved electromagnetic coupling transmission line model for out-of-phase and short-line faults. Based on the HRPC equivalent model, a simulation analysis was performed on the characteristics of the circuit breaker when a fault occurs. Using an equivalent lumped parameter circuit, the rate-of-rise of recovery voltage (RRRV) computational formula was deduced and computed. The RRRV variation in the circuit breakers in the system, with and without HRPC, was obtained. Given the circuit breaker interruption characteristics, the research results provide an analysis foundation and a theoretical basis for optimizing the HRPC parameters and selecting the arrangements of circuit breakers in an UHV transmission line. Full article

(This article belongs to the Section F: Electrical Engineering)

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23 pages, 9135 KiB

Open AccessArticle

A Practical Approach to Localize Simultaneous Triple Open-Switches for a PWM Inverter-Fed Permanent Magnet Synchronous Machine Drive System

by Jae-Hwan Song and Kyeong-Hwa Kim^*

Department of Electrical and Information Engineering, Seoul National University of Science and Technology, 232 Gongneung-ro, Nowon-gu, Seoul 01811, Korea

Energies 2018, 11(1), 101; https://doi.org/10.3390/en11010101 - 2 Jan 2018

Cited by 5 | Viewed by 4795

Abstract

In order to overcome the limitations of conventional diagnosis methods, this paper proposes a reliable and practical on-line fault localization scheme for a pulse width modulation (PWM) inverter-fed permanent magnet synchronous machine (PMSM) drive system even when the inverter has simultaneous open faults [...] Read more.

In order to overcome the limitations of conventional diagnosis methods, this paper proposes a reliable and practical on-line fault localization scheme for a pulse width modulation (PWM) inverter-fed permanent magnet synchronous machine (PMSM) drive system even when the inverter has simultaneous open faults in up to three switches. An open-switch fault is usually initiated by an accidental over-current, or electrical and thermal stresses. This fault may induce crucial secondary damage in the drive system since it is easily propagated and produces a continuous harmful effect on other system components. The open-switch faults in inverters often occur in a very complicated manner. Due to this reason, it was only recently that real-time diagnosis schemes under the open-switch faults in multiple switches have been presented in a few references. However, to alleviate the complexity and exactness issues, most of the conventional diagnosis schemes have considered the open faults only in two simultaneous switches until now, which is not generally the case. Even though the fault detection is simple and immediate, the exact fault localization is not a simple task, especially when there are open faults in three simultaneous switches because different open-switch fault locations may develop the same fault signature. To deal with such a problem, free-wheeling mode detection is introduced in this paper for the purpose of identifying the exact fault group and the faulty switch location. Then main objective of this paper is to realize a reliable fault localization algorithm under the condition of simultaneous open-switches (up to three) on an online basis without requiring any extra hardware or sensors in order that the algorithm can be easily installed in main CPU of a commercial drive system. For this purpose, the open faults in simultaneous switches are categorized into seven different fault groups. The entire system is implemented on a digital controller by using TMS320F28335 digital signal processor (DSP). The experimental results are presented under various open fault conditions to validate the usefulness of the proposed open-switch fault localization scheme. Full article

(This article belongs to the Special Issue Emerging Power Electronics Technologies for Power Systems and Machine Drives)

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11 pages, 4371 KiB

Open AccessArticle

Influence of Spatial Relationships between Key Strata on the Height of Mining-Induced Fracture Zone: A Case Study of Thick Coal Seam Mining

by Peng Li¹, Xufeng Wang^1,2,3,*, Wenhao Cao¹, Dongsheng Zhang^1,4, Dongdong Qin¹ and Hongzhi Wang¹

¹ School of Mines, China University of Mining & Technology, Xuzhou 221116, China

² The Jiangsu Laboratory of Mining-Induced Seismicity Monitoring, China University of Mining & Technology, Xuzhou 221116, China

³ Key Laboratory of Deep Coal Resource Mining, China University of Mining & Technology, Xuzhou 221116, China

⁴ State Key Laboratory of Coal Resources and Safe Mining, China University of Mining & Technology, Xuzhou 221116, China

Energies 2018, 11(1), 102; https://doi.org/10.3390/en11010102 - 3 Jan 2018

Cited by 16 | Viewed by 3384

Abstract

The behavior of the overburden of working face 20104 at the Wangjialing coal mine was investigated using borehole imaging. The measured height of the conductive fracture zone (CFZ) in the overburden, 148 m, is significantly different from the height that is predicted by [...] Read more.

The behavior of the overburden of working face 20104 at the Wangjialing coal mine was investigated using borehole imaging. The measured height of the conductive fracture zone (CFZ) in the overburden, 148 m, is significantly different from the height that is predicted by an empirical formula. The spatial relationships between key strata (KS) required for their fracturing and their influence on the CFZ’s height were analyzed. The results demonstrate that the spatial relationships between adjacent KS are a major factor behind the abnormal increase in the height of CFZ relative to the coal seam. The height of linkage (HoL) between KS was introduced and an equation for calculating this height was proposed. The study found that the fracturing of a KS could induce fracturing of the adjacent KS above it if their height difference was smaller than the HoL between them. Otherwise, the fractures resulting from the lower KS would terminate at the bottom of the higher KS. When the location of a high KS satisfies certain requirement, the spatial linkage between adjacent KS will allow for the conductive fractures arising in a lower KS to propagate through the high KS as well as the strata controlled by it, thus increasing the height of CFZ in overburden. Full article

(This article belongs to the Section L: Energy Sources)

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16 pages, 2145 KiB

Open AccessArticle

Coordinated Control Schemes of Super-Capacitor and Kinetic Energy of DFIG for System Frequency Support

by Liansong Xiong¹, Yujun Li^2,*, Yixin Zhu³, Ping Yang^4,5 and Zhirong Xu^4,5

¹ School of Automation, Nanjing Institute of Technology, Nanjing 211167, China

² School of Electrical Engineering, Xi’an Jiaotong University, Xi’an 710049, China

³ School of Internet of Things Engineering, Jiangnan University, Wuxi 214122, China

⁴ School of Electric Power, South China University of Technology, Guangzhou 510006, China

⁵ Guangdong Key Laboratory of Clean Energy Technology, Guangzhou 510640, China

Energies 2018, 11(1), 103; https://doi.org/10.3390/en11010103 - 3 Jan 2018

Cited by 34 | Viewed by 4383

Abstract

This paper mainly focuses on how to provide frequency supports by the doubly fed induction generator (DFIG) during system disturbances. Two coordinated controls that enable system frequency supports by DFIG-based wind turbines (WTs) are proposed in this paper. The first control scheme seeks [...] Read more.

This paper mainly focuses on how to provide frequency supports by the doubly fed induction generator (DFIG) during system disturbances. Two coordinated controls that enable system frequency supports by DFIG-based wind turbines (WTs) are proposed in this paper. The first control scheme seeks to render system support via simultaneously utilizing the energy from the installed super-capacitor between the back-to-back converter of DFIG, and WT rotational kinetic energy (KE). The second one stabilizes system frequency by firstly exerting the installed super-capacitor energy and then WT rotational KE via a unique cascading control. Both proposed coordinated control schemes jointly utilize two virtual inertia sources, namely super-capacitor in the DFIG and rotor rotational mass in the WT to fast provide system frequency support. However, the second proposed one stands itself out by reducing its impaired impacts on the overall wind energy production. Two proposed controls on rapidly providing frequency support are effectively verified and compared in detail by different system disturbances in the DIgSILENT/Powerfactory software. Full article

(This article belongs to the Section F: Electrical Engineering)

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19 pages, 2699 KiB

Open AccessArticle

Harmonic Modelling of the Wind Turbine Induction Generator for Dynamic Analysis of Power Quality

by Héctor García^1,2,*, Juan Segundo³, Osvaldo Rodríguez-Hernández²

, Rafael Campos-Amezcua²

and Oscar Jaramillo²

¹ Consejo Nacional de Ciencia y Tecnología (CONACYT), 03940 México, Mexico

² Renewable Energies Institute, National Autonomous University of Mexico, A.P. 34, 62580 Temixco, Mor., México, Mexico

³ Faculty of Engineering, Autonomous University of San Luis Potosí, Manuel Nava No. 8, San Luis Potosí S.L.P., 78290 México, Mexico

Energies 2018, 11(1), 104; https://doi.org/10.3390/en11010104 - 3 Jan 2018

Cited by 12 | Viewed by 5053

Abstract

Given the increasing integration of wind-based generation systems into the electric grid, efforts have been made to deal with the problem of power quality associated with the intermittent nature of these systems. This paper presents a new modelling approach oriented towards harmonic distortion [...] Read more.

Given the increasing integration of wind-based generation systems into the electric grid, efforts have been made to deal with the problem of power quality associated with the intermittent nature of these systems. This paper presents a new modelling approach oriented towards harmonic distortion analysis of the induction machine for wind power applications. The model is developed using companion harmonic circuit modelling, which is a natural approach for analysis of the adverse effects of harmonic distortion in electric power systems, and represents an easier solution method than the well known dynamic harmonic domain, since it solves algebraic equations instead of state-space differential equations. The structure of the companion circuits simplifies both the formulation and solution for power systems with wind-based generation systems. This approach is especially useful for analysis of the harmonic interaction in transient and steady states between the wind power generator and the power system, whose interconnection is made through electronic converters. The proposed model allows us to compute the dynamics of the wind turbine, which are influenced by disturbances such as changes in the wind velocity, voltage fluctuations, electric waveform distortion, and mechanical vibrations, among other factors. Moreover, the cross-coupling between harmonic components at different frequencies is considered. The proposed model represents an integral framework of the electrical and mechanical subsystems of a wind turbine, allowing for analysis of the interactions between them, and understanding power quality degradation behaviour as well as causes and consequences, while also giving useful information on the field of simulation and control. To test the performance of the proposed model, a test power system is used to obtain the behaviour of a wind turbine induction generator in response to typical power quality disturbances, i.e., harmonic distortion, and voltage sags and swells. Then, the dynamics of the variables considering their harmonic interactions are analysed. Full article

(This article belongs to the Special Issue Wind Generators Modelling and Control)

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23 pages, 883 KiB

Open AccessArticle

Modelling and Designing Cryogenic Hydrogen Tanks for Future Aircraft Applications

by Christopher Winnefeld¹, Thomas Kadyk²

, Boris Bensmann^1,*, Ulrike Krewer²

and Richard Hanke-Rauschenbach¹

¹ Institute of Electric Power Systems, Leibniz Universität Hannover, Appelstr. 9a, 30167 Hanover, Germany

² Institute of Energy and Process Systems Engineering, TU Braunschweig, Franz-Liszt-Straße 35, 38106 Braunschweig, Germany

Energies 2018, 11(1), 105; https://doi.org/10.3390/en11010105 - 3 Jan 2018

Cited by 96 | Viewed by 13908

Abstract

In the near future, the challenges to reduce the economic and social dependency on fossil fuels must be faced increasingly. A sustainable and efficient energy supply based on renewable energies enables large-scale applications of electro-fuels for, e.g., the transport sector. The high gravimetric [...] Read more.

In the near future, the challenges to reduce the economic and social dependency on fossil fuels must be faced increasingly. A sustainable and efficient energy supply based on renewable energies enables large-scale applications of electro-fuels for, e.g., the transport sector. The high gravimetric energy density makes liquefied hydrogen a reasonable candidate for energy storage in a light-weight application, such as aviation. Current aircraft structures are designed to accommodate jet fuel and gas turbines allowing a limited retrofitting only. New designs, such as the blended-wing-body, enable a more flexible integration of new storage technologies and energy converters, e.g., cryogenic hydrogen tanks and fuel cells. Against this background, a tank-design model is formulated, which considers geometrical, mechanical and thermal aspects, as well as specific mission profiles while considering a power supply by a fuel cell. This design approach enables the determination of required tank mass and storage density, respectively. A new evaluation value is defined including the vented hydrogen mass throughout the flight enabling more transparent insights on mass shares. Subsequently, a systematic approach in tank partitioning leads to associated compromises regarding the tank weight. The analysis shows that cryogenic hydrogen tanks are highly competitive with kerosene tanks in terms of overall mass, which is further improved by the use of a fuel cell. Full article

(This article belongs to the Special Issue Towards a Transformation to Sustainable Aviation Systems)

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20 pages, 9681 KiB

Open AccessArticle

The Recurrence Interval Difference of Power Load in Heavy/Light Industries of China

by Chi Zhang¹, Zhengning Pu^1,*

and Jiasha Fu^2,3,*

¹ School of Economics and Management, Southeast University, Nanjing 211102, China

² Research Institute of Economics and Management, Southwestern University of Finance and Economics, 55 Guanghuacun Street, Chengdu 610074, China

³ Survey and Research Center for China Household Finance, Southwestern University of Finance and Economics, 55 Guanghuacun Street, Chengdu 610074, China

Energies 2018, 11(1), 106; https://doi.org/10.3390/en11010106 - 3 Jan 2018

Cited by 5 | Viewed by 3608

Abstract

The significant fluctuation of industrial electricity consumption has a high impact on power load, which makes the research on recurrence intervals between extreme events of theoretical and practical significance. The study uses a high-frequency data of heavy and light industries and employs recurrence [...] Read more.

The significant fluctuation of industrial electricity consumption has a high impact on power load, which makes the research on recurrence intervals between extreme events of theoretical and practical significance. The study uses a high-frequency data of heavy and light industries and employs recurrence interval analysis in different thresholds. We find that the reoccurrence interval of volatility can fit with the stretched exponential function and the probability density functions of recurrence intervals in various thresholds shows a scaling behavior. Then, the conditional probability density function and the multifractal detrended fluctuation analysis demonstrate the existence of short-range correlation, long-range correlation, and multifractal properties, respectively. We further construct a hazard function, introduce recurrence intervals into VaR calculation and establish a functional relationship between average recurrence interval and threshold. Following this result, we also shed light on policy discussion for multi-industrial electricity supply management. Full article

(This article belongs to the Special Issue Selected Papers from the 8th Annual Conference of Energy Economics and Management)

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17 pages, 5589 KiB

Open AccessArticle

Influence of Stator MMF Harmonics on the Utilization of Reluctance Torque in Six-Phase PMA-SynRM with FSCW

by Luming Cheng

, Yi Sui, Ping Zheng^*, Zuosheng Yin and Chuanze Wang

Department of Electrical Engineering, Harbin Institute of Technology, Harbin 150080, China

Energies 2018, 11(1), 108; https://doi.org/10.3390/en11010108 - 3 Jan 2018

Cited by 11 | Viewed by 7088

Abstract

Although fractional-slot concentrated winding (FSCW) offers many significant advantages, such as short end-turn windings, high slot filling factor, and low cogging torque, it is frequently limited by excessive stator magnetomotive force (MMF) harmonics which will induce high eddy losses in the permanent magnets [...] Read more.

Although fractional-slot concentrated winding (FSCW) offers many significant advantages, such as short end-turn windings, high slot filling factor, and low cogging torque, it is frequently limited by excessive stator magnetomotive force (MMF) harmonics which will induce high eddy losses in the permanent magnets (PMs). What is more, in the literature, it can be observed that the reluctance torque of the salient-pole machine with FSCW is usually much lower than that obtained with integral slot winding. To explore the underlying reason why the reluctance torque in a salient machine with FSCW significantly decreases, a new six-phase FSCW with 24 slots and 10 poles, which can significantly reduce the undesirable stator MMF harmonics, is obtained by using the concept of stator shifting. Then, two permanent-magnet-assisted synchronous reluctance machines (PMA-SynRMs) with the proposed winding layout and conventional asymmetric 12-slot/10-pole six-phase winding layout are designed and simulated by the finite-element method (FEM). The reluctance torque, total torque, and d/q-axis inductances with different current phase angles are also compared under different loaded conditions. The results show that a reduction in stator MMF harmonics can indeed lead to a significant enhancement in reluctance torque under heavy loaded conditions, while the dominance will diminish under light loaded conditions. Full article

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14 pages, 1801 KiB

Open AccessArticle

Drying and Pelletizing Analysis of Waste from Cork Granulated Industry

by Francisco José Sepúlveda^*

, José Ignacio Arranz

, María Teresa Miranda, Irene Montero

and Carmen Victoria Rojas

Department of Mechanical Engineering, Energy and Materials, Industrial Engineering School, University of Extremadura, Avenue Elvas s/n, 06006 Badajoz, Spain

Energies 2018, 11(1), 109; https://doi.org/10.3390/en11010109 - 3 Jan 2018

Cited by 11 | Viewed by 3244

Abstract

Cork granulated industries generate a considerable amount of wastes, such as grinding powder and granulometric separation powder. Some of these industries have started using these wastes as fuels for their own boilers, mixing them previously. However, there are differences between both wastes, especially [...] Read more.

Cork granulated industries generate a considerable amount of wastes, such as grinding powder and granulometric separation powder. Some of these industries have started using these wastes as fuels for their own boilers, mixing them previously. However, there are differences between both wastes, especially the high moisture of grinding powder. This fact causes stratification during storage and makes boiler feed and its control more difficult, due to the heterogeneity of the resulting fuel. In the present research work, an overall study for combined pelletizing of these two wastes was carried out, with the aim of assessing their use in the same industries where they were generated or for other industrial uses. Thus, the optimum conditions for the highest yield of the pelletizing process were determined, and an analysis of the dry residue from grinding powder was carried out. Finally, the total specific energy was determined for the whole process. Among the main findings, it should be pointed out the obtaining of pellets with suitable physical properties and the high ash content that makes its possible commercialization difficult. Concerning the specific energy used, most of it corresponded to the drying process of grinding powder, recommending that it come from an exothermic process of cork granulated industry. Full article

(This article belongs to the Section L: Energy Sources)

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24 pages, 12136 KiB

Open AccessArticle

Net Power Coefficient of Vertical and Horizontal Wind Turbines with Crossflow Runners

by Toni Pujol^1,*

, Albert Massaguer¹

, Eduard Massaguer², Lino Montoro¹ and Martí Comamala¹

¹ Department of Mechanical Engineering and Industrial Construction, University of Girona, c/Universitat de Girona 4, 17003 Girona, Spain

² Nabla Thermoelectrics, c/Llibertat 71, 17820 Banyoles, Spain

Energies 2018, 11(1), 110; https://doi.org/10.3390/en11010110 - 3 Jan 2018

Cited by 14 | Viewed by 5977

Abstract

The feasibility of using crossflow runners as single rotors in vertical-axis wind turbines (VAWT) or as blades in horizontal-axis wind turbines (HAWT) is numerically studied. A computational fluid dynamics model is validated from data obtained in a wind tunnel. Three crossflow runners with [...] Read more.

The feasibility of using crossflow runners as single rotors in vertical-axis wind turbines (VAWT) or as blades in horizontal-axis wind turbines (HAWT) is numerically studied. A computational fluid dynamics model is validated from data obtained in a wind tunnel. Three crossflow runners with different number of blades are tested. Values of drag, lift and torque coefficients are numerically obtained at different turning velocities. Power coefficients C_p for crossflow VAWT and HAWT are calculated for different tip-speed ratios (TSR) and runner spin ratios (α). Since crossflow HAWT consume electrical energy for spinning the runners, the net power coefficient is estimated. Simulations indicate that a crossflow runner as a single rotor in VAWT should have a high solidity and work at low TSR. Crossflow runners working as blades in HAWT may achieve low drag to lift ratios but the C_p is penalized by the amount of energy required for spinning the runners. The optimum working condition of crossflow HAWT is located within a narrow band of low TSR and α reaching C_p values < 0.2 only. Full article

(This article belongs to the Section L: Energy Sources)

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15 pages, 11237 KiB

Open AccessArticle

Impacts of Water Flow Rate on Freezing Prevention of Air-Cooled Heat Exchangers in Power Plants

by Yonghong Guo, Huimin Wei, Xiaoru Yang, Weijia Wang

, Xiaoze Du^*

and Lijun Yang

Key Laboratory of Condition Monitoring and Control for Power Plant Equipments of Ministry of Education, School of Energy Power and Mechanical Engineering, North China Electric Power University, Beijing 102206, China

Energies 2018, 11(1), 112; https://doi.org/10.3390/en11010112 - 3 Jan 2018

Cited by 4 | Viewed by 2990

Abstract

Under cold ambient conditions, the freezing risk of air-cooled heat exchangers, especially the frontal finned tube bundles, has been a critical concern in power plants. Based on the freezing conditions of the cooling deltas under windy conditions, the flow and heat transfer characteristics [...] Read more.

Under cold ambient conditions, the freezing risk of air-cooled heat exchangers, especially the frontal finned tube bundles, has been a critical concern in power plants. Based on the freezing conditions of the cooling deltas under windy conditions, the flow and heat transfer characteristics of natural draft dry cooling system (NDDCS) with 30%, 40% and 50% increased water flow rates are investigated in this work, and the outlet circulating water temperatures of the easily freezing cooling deltas and sectors are obtained. The results show that the deltas in the middle front and rear sectors become free from freezing at all wind speeds when the circulating water flow rate is increased. For the frontal sector with increased water flow rate, the outlet water temperatures of deltas increase conspicuously at 4 m/s and 8 m/s, while as the wind speed rises to 16 m/s, these deltas still face serious freezing risks due to the huge heat rejection to ambient air. Therefore, freezing prevention of air-cooled NDDCS heat exchangers can be achieved by increasing the water flow rates at small wind speeds, while as the wind speed becomes high, the water flow redistribution is suggested for the frontal and middle sectors due to their big performance difference. Full article

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16 pages, 7750 KiB

Open AccessArticle

Performance Improvement for Reduction of Resonance in a Grid-Connected Inverter System Using an Improved DPWM Method

by Jin-Hyuk Park and Kyo-Beum Lee^*

Department of Electrical and Computer Engineering, Ajou University, 206, World cup-ro, Yeongtong-gu, Suwon 16499, Korea

Energies 2018, 11(1), 113; https://doi.org/10.3390/en11010113 - 3 Jan 2018

Cited by 9 | Viewed by 4582

Abstract

This paper proposes discontinuous pulse width modulation (DPWM) for a grid-connected inverter system using an LCL-filter which consists of two inductors and a capacitor that is connected in parallel per phase. The modulation signal is discontinuously changed, and the harmonic voltages are generated [...] Read more.

This paper proposes discontinuous pulse width modulation (DPWM) for a grid-connected inverter system using an LCL-filter which consists of two inductors and a capacitor that is connected in parallel per phase. The modulation signal is discontinuously changed, and the harmonic voltages are generated in the wide frequency range at the output terminal of the inverter when the conventional DPWM is used. If these harmonic voltages are present in the resonance frequency band by an LCL-filter, then the resonance problem of the grid current occurs. To suppress the resonance problem, the proposed DPWM injects the sixth harmonic to the modulation signal. Therefore, in the improved DPWM, harmonic voltages at the output terminal of the inverter are sufficiently reduced because the discontinuous change of the modulation signal disappears. The proposed DPWM method is verified by a Powersim (PSIM) simulation (Powersim Inc., Rockville, MD, USA) and experiments with a 3-kW neutral-point clamped (NPC)-type grid-connected inverter system. Full article

(This article belongs to the Special Issue Advanced Control Techniques for Power Converters)

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12 pages, 2315 KiB

Open AccessArticle

Flat Concentrator Photovoltaic System with Lateral Displacement Tracking for Residential Rooftops

by Ngoc Hai Vu^*

and Seoyong Shin^*

Department of Information and Communication Engineering, Myongji University, 116 Myongji-ro, Cheoin-gu, Yongin, Gyeonggi-do 17058, Korea

Energies 2018, 11(1), 114; https://doi.org/10.3390/en11010114 - 3 Jan 2018

Cited by 6 | Viewed by 5526

Abstract

We present a design for a flat concentrating photovoltaic (CPV) system that requires only lateral displacement for sun-tracking, intended for residential rooftop applications. Compared with flat-plate photovoltaics (PVs), CPV technology is essential for reducing the use of semi-conductor materials, which also enables cheaper [...] Read more.

We present a design for a flat concentrating photovoltaic (CPV) system that requires only lateral displacement for sun-tracking, intended for residential rooftop applications. Compared with flat-plate photovoltaics (PVs), CPV technology is essential for reducing the use of semi-conductor materials, which also enables cheaper solar power generation. Existing CPV designs are more bulky and complex than traditional PV panel techniques and are therefore better suited to solar farms than rooftop use. In this study, we explore an alternate approach, employing a mirror-coated lenslet array, to demonstrate a flat CPV system for rooftop installation. This mirror-coated lenslet array collects solar radiation and concentrates it with a very short focal length. The lateral movement of lenslet focal points according to a changing incident angle of sunlight allows for the use of a lateral displacement tracking mechanism. A square array of solar cells integrated on a transparent sheet is placed on top of a mirror-coated lenslet array to collect focused sunlight and convert it to electricity. The proposed CPV panel can be achieved with a 35 mm thickness. Simulation models were developed using commercial optical design software (LightTools). The simulation demonstrates an optical efficiency of up to 89.5% when the concentration ratio of the system is fixed to 50×. The simplicity of the structure enables cheaper mass production. Our quest for a lateral displacement sun-tracking mechanism also shows that the system has a high tolerance, thereby enabling cost savings by replacing a highly precise, active sun-tracking system with a lower-accuracy system. The presented flat CPV is a strong candidate for a low-cost, high-efficiency solar energy system that can be installed on the rooftops of residential buildings to deliver energy savings. Full article

(This article belongs to the Special Issue Building renewable energy and thermal energy storage system 2018)

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17 pages, 2644 KiB

Open AccessArticle

Solar Heat Gain Coefficient Analysis of a Slim-Type Double Skin Window System: Using an Experimental and a Simulation Method

by Kyung-joo Cho^* and Dong-woo Cho

Korea Institute of Civil Engineering & Building Technology, 283 Goyangdae-Ro, Ilsanseo-Gu, Goyang-Si, Gyeonggi-Do 10223, Korea

Energies 2018, 11(1), 115; https://doi.org/10.3390/en11010115 - 3 Jan 2018

Cited by 15 | Viewed by 4453

Abstract

Double skin facade systems are known to be capable of preventing overheating in curtain wall buildings to a certain degree. The system induces the efficient blocking of sunlight using a center blind during the summer season. Moreover, it enables overheated air in the [...] Read more.

Double skin facade systems are known to be capable of preventing overheating in curtain wall buildings to a certain degree. The system induces the efficient blocking of sunlight using a center blind during the summer season. Moreover, it enables overheated air in the cavity layer to be sent outdoors, resulting in a reduction of the use of energy for cooling. However, double skin facade systems can be problematic, in that they must be opened according to seasonal conditions to achieve greater energy consumption efficiencies. In current double skin facade systems, the width of the cavity layer was too wide for residents to easily operate the system. When considering this, research on an easy-to-open 270 mm slim-type double skin window (SDSW) was undertaken in order to confirm its energy efficient performance. First, official testing based on the KS L 9107 Standard was undertaken to analyze solar heat gain coefficients (SHGC) and the cavity air temperatures, according to the open and close conditions of the SDSW’s external windows, enabling an analysis of the effect that the opening of windows had on reducing cooling energy needs. Next, SHGCs and cavity air temperatures were studied according to the different opening conditions of the SDSW’s external window to analyze the most optimal effects on cooling energy reductions by Computational Fluid Dynamics (CFD). Full article

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22 pages, 2041 KiB

Open AccessArticle

Switched Polytopic Controller Applied on a Positive Reconfigurable Power Electronic Converter

by Martín-A. Rodríguez-Licea^1,*,†,‡

, Francisco-J. Perez-Pinal^1,†,‡

, Alejandro-I. Barranco-Gutiérrez^1,†

and Jose-C. Nuñez-Perez²

¹ Consejo Nacional de Ciencia y Tecnología (CONACYT)-Instituto Tecnológico de Celaya, Celaya 38010, Mexico

² Instituto Politécnico Nacional, IPN-CITEDI, Tijuana 22435, Mexico

^† Current address: Antonio Garcia Cubas 600 Col. Fovissste, Celaya, Guanajuato 38010, México

^‡ These authors contributed equally to this work.

Energies 2018, 11(1), 116; https://doi.org/10.3390/en11010116 - 3 Jan 2018

Cited by 3 | Viewed by 3859

Abstract

The reconfigurable power electronic converters (RPECs) are a new generation of systems, which modify their physical configuration in terms of a desired input or output operation characteristic. This kind of converters is very attractive in terms of versatility, compactness, and robustness. They have [...] Read more.

The reconfigurable power electronic converters (RPECs) are a new generation of systems, which modify their physical configuration in terms of a desired input or output operation characteristic. This kind of converters is very attractive in terms of versatility, compactness, and robustness. They have been proposed in areas such as illumination, transport electrification (TE), eenewable energy (RE), smart grids and the internet of things (IoT). However, the resulting converters operate in switched variable operation-regions, rather than over single operation points. As a result, there is a complexity increment on the modeling and control stage such that traditional techniques are no longer valid. In order to overcome these challenges, this paper proposes a kind of switched polytopic controller (SPC) suitable to stabilize an RPEC. Modeling, control, numerical and practical results are reported. To this end, a 400 W positive synchronous bi-directional buck/boost converter is used as a testbed. It is also shown, that the proposed converter and robust controller accomplish a compact, modular and reliable design during different working configuration, operation points and load changes. Full article

(This article belongs to the Special Issue Emerging Power Electronics Technologies for Power Systems and Machine Drives)

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17 pages, 5316 KiB

Open AccessArticle

Comparison of Conductor-Temperature Calculations Based on Different Radial-Position-Temperature Detections for High-Voltage Power Cable

by Lin Yang¹, Weihao Qiu¹, Jichao Huang¹, Yanpeng Hao^1,*, Mingli Fu², Shuai Hou² and Licheng Li¹

¹ School of Electric Power, South China University of Technology, Guangzhou 510640, China

² Electric Power Research Institute, China Southern Power Grid, Guangzhou 510080, China

Energies 2018, 11(1), 117; https://doi.org/10.3390/en11010117 - 3 Jan 2018

Cited by 27 | Viewed by 5302

Abstract

In this paper, the calculation of the conductor temperature is related to the temperature sensor position in high-voltage power cables and four thermal circuits—based on the temperatures of insulation shield, the center of waterproof compound, the aluminum sheath, and the jacket surface are [...] Read more.

In this paper, the calculation of the conductor temperature is related to the temperature sensor position in high-voltage power cables and four thermal circuits—based on the temperatures of insulation shield, the center of waterproof compound, the aluminum sheath, and the jacket surface are established to calculate the conductor temperature. To examine the effectiveness of conductor temperature calculations, simulation models based on flow characteristics of the air gap between the waterproof compound and the aluminum are built up, and thermocouples are placed at the four radial positions in a 110 kV cross-linked polyethylene (XLPE) insulated power cable to measure the temperatures of four positions. In measurements, six cases of current heating test under three laying environments, such as duct, water, and backfilled soil were carried out. Both errors of the conductor temperature calculation and the simulation based on the temperature of insulation shield were significantly smaller than others under all laying environments. It is the uncertainty of the thermal resistivity, together with the difference of the initial temperature of each radial position by the solar radiation, which led to the above results. The thermal capacitance of the air has little impact on errors. The thermal resistance of the air gap is the largest error source. Compromising the temperature-estimation accuracy and the insulation-damage risk, the waterproof compound is the recommended sensor position to improve the accuracy of conductor-temperature calculation. When the thermal resistances were calculated correctly, the aluminum sheath is also the recommended sensor position besides the waterproof compound. Full article

(This article belongs to the Section F: Electrical Engineering)

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14 pages, 5342 KiB

Open AccessArticle

On the Compatibility of Electric Equivalent Circuit Models for Enhanced Flooded Lead Acid Batteries Based on Electrochemical Impedance Spectroscopy

by Can Aksakal^1,2 and Altug Sisman^1,*

¹ Energy Institute, Istanbul Technical University, 34469 Istanbul, Turkey

² INCI GS YUASA, 45030 Manisa, Turkey

Energies 2018, 11(1), 118; https://doi.org/10.3390/en11010118 - 3 Jan 2018

Cited by 16 | Viewed by 7021

Abstract

Electric equivalent circuit (EEC) models have been widely used to interpret the inner dynamics of all type of batteries. Added to this, they also have been used to estimate state of charge (SOC) and state of health (SOH) values in combination with different [...] Read more.

Electric equivalent circuit (EEC) models have been widely used to interpret the inner dynamics of all type of batteries. Added to this, they also have been used to estimate state of charge (SOC) and state of health (SOH) values in combination with different methods. Four EEC models are considered for enhanced flooded lead acid batteries (EFB) which are widely used in micro hybrid vehicles. In this study, impedance and phase prediction capabilities of models throughout a frequency spectrum from 1 mHz to 10 kHz are compared with those of experimental results to investigate their consistency with the data. The battery is charged, discharged, and aged according to appropriate standards which imitates a lifetime of a micro hybrid vehicle battery under high current partial cycling. Impedance tests are repeated between different charge and health states until the end of the battery’s lifetime. It is seen that adding transmission line elements to mimic the high porous electrode electrolyte interface to a double parallel constant phase element resistance model (ZARC) can increase the model data representing capability by 100%. The mean average percentage error (MAPE) of the conventional model with respect to data is 3.2% while the same value of the transmission line added model found as 1.6%. The results can be helpful to represent an EFB in complex simulation environments, which are used in automobile industry. Full article

(This article belongs to the Section D: Energy Storage and Application)

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15 pages, 1749 KiB

Open AccessArticle

Energy Analysis of Cascade Heating with High Back-Pressure Large-Scale Steam Turbine

by Zhihua Ge¹, Fuxiang Zhang¹, Shimeng Sun¹, Jie He¹ and Xiaoze Du^2,*

¹ Key Laboratory of Condition Monitoring and Control for Power Plant Equipment (North China Electric Power University), Ministry of Education, Beijing 102206, China

² School of Energy and Power Engineering, Lanzhou University of Technology, Lanzhou 730050, China

Energies 2018, 11(1), 119; https://doi.org/10.3390/en11010119 - 3 Jan 2018

Cited by 27 | Viewed by 5709

Abstract

To reduce the exergy loss that is caused by the high-grade extraction steam of traditional heating mode of combined heat and power (CHP) generating unit, a high back-pressure cascade heating technology for two jointly constructed large-scale steam turbine power generating units is proposed. [...] Read more.

To reduce the exergy loss that is caused by the high-grade extraction steam of traditional heating mode of combined heat and power (CHP) generating unit, a high back-pressure cascade heating technology for two jointly constructed large-scale steam turbine power generating units is proposed. The Unit 1 makes full use of the exhaust steam heat from high back-pressure turbine, and the Unit 2 uses the original heating mode of extracting steam condensation, which significantly reduces the flow rate of high-grade extraction steam. The typical 2 × 350 MW supercritical CHP units in northern China were selected as object. The boundary conditions for heating were determined based on the actual climatic conditions and heating demands. A model to analyze the performance of the high back-pressure cascade heating supply units for off-design operating conditions was developed. The load distributions between high back-pressure exhaust steam direct supply and extraction steam heating supply were described under various conditions, based on which, the heating efficiency of the CHP units with the high back-pressure cascade heating system was analyzed. The design heating load and maximum heating supply load were determined as well. The results indicate that the average coal consumption rate during the heating season is 205.46 g/kWh for the design heating load after the retrofit, which is about 51.99 g/kWh lower than that of the traditional heating mode. The coal consumption rate of 199.07 g/kWh can be achieved for the maximum heating load. Significant energy saving and CO₂ emission reduction are obtained. Full article

(This article belongs to the Section F: Electrical Engineering)

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13 pages, 3530 KiB

Open AccessArticle

Advanced Control Strategies of Induction Machine: Field Oriented Control, Direct Torque Control and Model Predictive Control

by Fengxiang Wang¹, Zhenbin Zhang^2,3,*, Xuezhu Mei^1,3, José Rodríguez⁴ and Ralph Kennel³

¹ Quanzhou Institute of Equipment Manufacturing, Haixi Institutes, Chinese Academic of Science, Quanzhou 362200, China

² Key Lab of Power System Intelligent Dispatch and Control, Shandong University, Ministry of Education, Jinan 250061, China

³ Institute for Electrical Drive Systems and Power Electronics, Technical University of Munich (TUM), 80333 München, Germany

⁴ Faculty of Engineering, Universidad Andrés Bello, 8370146 Santiago, Chile

Energies 2018, 11(1), 120; https://doi.org/10.3390/en11010120 - 3 Jan 2018

Cited by 207 | Viewed by 11829

Abstract

Field oriented control (FOC), direct torque control (DTC) and finite set model predictive control (FS-MPC) are different strategies for high performance electrical drive systems. FOC uses linear controllers and pulse width modulation (PWM) to control the fundamental components of the load voltages. On [...] Read more.

Field oriented control (FOC), direct torque control (DTC) and finite set model predictive control (FS-MPC) are different strategies for high performance electrical drive systems. FOC uses linear controllers and pulse width modulation (PWM) to control the fundamental components of the load voltages. On the other hand, DTC and FS-MPC are nonlinear strategies that generate directly the voltage vectors in the absence of a modulator. This paper presents all three methods starting from theoretic operating principles, control structures and implementation. Experimental assessment is performed to discuss their advantages and limitations in detail. As main conclusions of this work, it is affirmed that different strategies have their own merits and all meet the requirements of modern high performance drives. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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20 pages, 5109 KiB

Open AccessArticle

A New Control Logic for a Wind-Area on the Balancing Authority Area Control Error Limit Standard for Load Frequency Control

by Yekui Chang

, Rao Liu, Yu Ba and Weidong Li^*

Faculty of Electronic Information and Electrical Engineering, Dalian University of Technology, Dalian 116000, China

Energies 2018, 11(1), 121; https://doi.org/10.3390/en11010121 - 3 Jan 2018

Cited by 3 | Viewed by 3713

Abstract

Nowadays, the Balancing Authority Area Control Error (ACE) Limit (BAAL) Standard has been adopted to replace the Control Performance Standard 2 (CPS2) in the North American power grid. According to the new standard’s mechanism, a new control logic, named “Triggered Monitoring and Graded [...] Read more.

Nowadays, the Balancing Authority Area Control Error (ACE) Limit (BAAL) Standard has been adopted to replace the Control Performance Standard 2 (CPS2) in the North American power grid. According to the new standard’s mechanism, a new control logic, named “Triggered Monitoring and Graded Regulation” (TM-GR) is proposed. Its purpose is to improve wind power utilization, with good BAAL Standard compliance for load frequency control (LFC). With the TM logic, according to the real-time regulating ability of areas and forecasting results of wind power output, the triggering moments to give orders are found and a defined monitoring interval is set to track the succeeding fluctuation of Area Control Error (ACE). With the GR logic, based on whether or not over-limit frequency and over-limit ACE occur simultaneously, unit output is regulated in different grades. In cooperation with the existing control logic of Control Performance Standard 1 (CPS1), the proposed logic has a higher priority. From the test results, with the proposed control logic, the utilization of wind power output increases and, meanwhile, the area’s control performance meets the Standard BAL-001-2 requirements. The standard deviation of the frequency deviation is less than the target value, and the duration of over-limit ACE and over-limit frequency can both be restricted to be less than 30 min. Full article

(This article belongs to the Section F: Electrical Engineering)

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29 pages, 5393 KiB

Open AccessFeature PaperArticle

Energy Flexibility from Large Prosumers to Support Distribution System Operation—A Technical and Legal Case Study on the Amsterdam ArenA Stadium

by Dirk Kuiken^1,*, Heyd F. Más¹, Maryam Haji Ghasemi², Niels Blaauwbroek³

, Thai H. Vo³, Thijs Van der Klauw² and Phuong H. Nguyen³

¹ Faculty of Law, Groningen Centre of Energy Law (GCEL), University of Groningen, Oude Kijk in’t Jatstraat 26, 9712 EK Groningen, The Netherlands

² Department of Electrical Engineering, Mathematics and Computer Science, University of Twente, Drienerlolaan 5, 7522 NB Enschede, The Netherlands

³ Electrical Energy Systems Group, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands

Energies 2018, 11(1), 122; https://doi.org/10.3390/en11010122 - 4 Jan 2018

Cited by 11 | Viewed by 11583

Abstract

To deal with the rising integration of stochastic renewables and energy intensive distributed energy resources (DER) to the electricity network, alternatives to expensive network reinforcements are increasingly needed. An alternative solution often under consideration is integrating flexibility from the consumer side to system [...] Read more.

To deal with the rising integration of stochastic renewables and energy intensive distributed energy resources (DER) to the electricity network, alternatives to expensive network reinforcements are increasingly needed. An alternative solution often under consideration is integrating flexibility from the consumer side to system management. However, such a solution needs to be contemplated from different angles before it can be implemented in practice. To this end, this article considers a case study of the Amsterdam ArenA stadium and its surrounding network where flexibility is expected to be available to support the network in the future. The article studies the technical aspects of using this flexibility to determine to what extent, despite the different, orthogonal goals, the available flexibility can be used by various stakeholders in scenarios with a large load from electric vehicle charging points. Furthermore, a legal study is performed to determine the feasibility of the technical solutions proposed by analysing current European Union (EU) and Dutch law and focusing on the current agreements existing between the parties involved. The article shows that flexibility in the network provided by Amsterdam ArenA is able to significantly increase the number of charging points the network can accommodate. Nonetheless, while several uses of flexibility are feasible under current law, the use of flexibility provided by electric vehicles specifically faces several legal challenges in current arrangements. Full article

(This article belongs to the Special Issue Selected Papers from International Workshop of Energy-Open)

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17 pages, 3657 KiB

Open AccessArticle

Application of Predictive Feedforward Compensator to Microalgae Production in a Raceway Reactor: A Simulation Study

by Andrzej Pawłowski^1,*

, José Luis Guzmán²

, Manuel Berenguel²

, Francisco G. Acíen³

and Sebastián Dormido¹

¹ Departamento de Informática y Automática, ETSII, UNED, 28040 Madrid, Spain

² Departamento de Informática, University of Almería, CIESOL-ceiA3, 04120 Almería, Spain

³ Departamento de Ingeniería, University of Almería, CIESOL-ceiA3, 04120 Almería, Spain

Energies 2018, 11(1), 123; https://doi.org/10.3390/en11010123 - 4 Jan 2018

Cited by 10 | Viewed by 2920

Abstract

In this work, the evaluation of a predictive feedforward compensator is provided in order to highlight its most important advantages and drawbacks. The analyzed technique has been applied to microalgae production process in a raceway photobioreactor. The evaluation of the analyzed disturbance rejection [...] Read more.

In this work, the evaluation of a predictive feedforward compensator is provided in order to highlight its most important advantages and drawbacks. The analyzed technique has been applied to microalgae production process in a raceway photobioreactor. The evaluation of the analyzed disturbance rejection schemes were performed through simulation, considering a nonlinear process model, whereas all controllers were designed using linear model approximations resulting in a realistic evaluation scenario. The predictive feedforward disturbance compensator was coupled with two feedback control techniques, PID (Proportional-Integral-Derivative) and MPC (Model Predictive Control) that are widely used in industrial practice. Moreover, the classical feedforward approach has been used for the purpose of comparison. The performance of the tested technique is evaluated with different indexes that include control performance measurements as well as biomass production performance. The application of the analyzed compensator to microalgae production process allows us to improve the average photosynthesis rate about 6% simultaneously reducing the energy usage about 4%. Full article

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12 pages, 1839 KiB

Open AccessArticle

Evolving Microbial Communities in Cellulose-Fed Microbial Fuel Cell

by Renata Toczyłowska-Mamińska^1,*, Karolina Szymona¹, Patryk Król¹, Karol Gliniewicz^2,3, Katarzyna Pielech-Przybylska⁴, Monika Kloch¹ and Bruce E. Logan⁵

¹ Faculty of Wood Technology, Warsaw University of Life Sciences—WULS, 159 Nowoursynowska St., 02-776 Warsaw, Poland

² Institute of Bioinformatics and Evolutionary Studies (IBEST), University of Idaho, Moscow, ID 83843, USA

³ Department of Biological Sciences, University of Idaho, Moscow, ID 83843, USA

⁴ Institute of Fermentation Technology and Microbiology, 171/173 Wólczanska, 90-924 Łódź, Poland

⁵ Department of Civil and Environmental Engineering, Penn State University, University Park, PA 16802, USA

Energies 2018, 11(1), 124; https://doi.org/10.3390/en11010124 - 4 Jan 2018

Cited by 51 | Viewed by 6917

Abstract

The abundance of cellulosic wastes make them attractive source of energy for producing electricity in microbial fuel cells (MFCs). However, electricity production from cellulose requires obligate anaerobes that can degrade cellulose and transfer electrons to the electrode (exoelectrogens), and thus most previous MFC [...] Read more.

The abundance of cellulosic wastes make them attractive source of energy for producing electricity in microbial fuel cells (MFCs). However, electricity production from cellulose requires obligate anaerobes that can degrade cellulose and transfer electrons to the electrode (exoelectrogens), and thus most previous MFC studies have been conducted using two-chamber systems to avoid oxygen contamination of the anode. Single-chamber, air-cathode MFCs typically produce higher power densities than aqueous catholyte MFCs and avoid energy input for the cathodic reaction. To better understand the bacterial communities that evolve in single-chamber air-cathode MFCs fed cellulose, we examined the changes in the bacterial consortium in an MFC fed cellulose over time. The most predominant bacteria shown to be capable electron generation was Firmicutes, with the fermenters decomposing cellulose Bacteroidetes. The main genera developed after extended operation of the cellulose-fed MFC were cellulolytic strains, fermenters and electrogens that included: Parabacteroides, Proteiniphilum, Catonella and Clostridium. These results demonstrate that different communities evolve in air-cathode MFCs fed cellulose than the previous two-chamber reactors. Full article

(This article belongs to the Collection Bioenergy and Biofuel)

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15 pages, 3139 KiB

Open AccessArticle

Cloud-Based Battery Condition Monitoring and Fault Diagnosis Platform for Large-Scale Lithium-Ion Battery Energy Storage Systems

by Taesic Kim^*

, Darshan Makwana, Amit Adhikaree, Jitendra Shamjibhai Vagdoda and Young Lee

Department of Electrical Engineering and Computer Science, Texas A&M University-Kingsville, MSC 192, 700 University Blvd, Kingsville, TX 78363, USA

Energies 2018, 11(1), 125; https://doi.org/10.3390/en11010125 - 4 Jan 2018

Cited by 90 | Viewed by 11401

Abstract

Performance of the current battery management systems is limited by the on-board embedded systems as the number of battery cells increases in the large-scale lithium-ion (Li-ion) battery energy storage systems (BESSs). Moreover, an expensive supervisory control and data acquisition system is still required [...] Read more.

Performance of the current battery management systems is limited by the on-board embedded systems as the number of battery cells increases in the large-scale lithium-ion (Li-ion) battery energy storage systems (BESSs). Moreover, an expensive supervisory control and data acquisition system is still required for maintenance of the large-scale BESSs. This paper proposes a new cloud-based battery condition monitoring and fault diagnosis platform for the large-scale Li-ion BESSs. The proposed cyber-physical platform incorporates the Internet of Things embedded in the battery modules and the cloud battery management platform. Multithreads of a condition monitoring algorithm and an outlier mining-based battery fault diagnosis algorithm are built in the cloud battery management platform (CBMP). The proposed cloud-based condition monitoring and fault diagnosis platform is validated by using a cyber-physical testbed and a computational cost analysis for the CBMP. Therefore, the proposed platform will support the on-board health monitoring and provide an intelligent and cost-effective maintenance of the large-scale Li-ion BESSs. Full article

(This article belongs to the Section D: Energy Storage and Application)

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17 pages, 5264 KiB

Open AccessArticle

A Novel Power Flow Algorithm for Traction Power Supply Systems Based on the Thévenin Equivalent

by Junqi Zhang

, Mingli Wu^* and Qiujiang Liu

School of Electrical Engineering, Beijing Jiaotong University, Beijing 100044, China

Energies 2018, 11(1), 126; https://doi.org/10.3390/en11010126 - 4 Jan 2018

Cited by 14 | Viewed by 4095

Abstract

With the rapid development of high-speed and heavy-haul railways throughout China, modern large power locomotives and electric multiple units (EMUs) have been applied in main railway lines. The high power requirements have brought about the problem of insufficient power supply capacity (PSC) of [...] Read more.

With the rapid development of high-speed and heavy-haul railways throughout China, modern large power locomotives and electric multiple units (EMUs) have been applied in main railway lines. The high power requirements have brought about the problem of insufficient power supply capacity (PSC) of traction power supply systems (TPSSs). Thus, a convenient method of PSC assessment is meaningful and urgently needed. In this paper, a novel algorithm is proposed based on the Thévenin equivalent in order to calculate the PSC. In this algorithm, node voltage equations are converted into port characteristic equations, and the Newton-Raphson method is exploited to solve them. Based on this algorithm, the PSC of a typical high-speed railway is calculated through the repeated power flow (RPF). Subsequently, the effects of an optimized organization of train operations are analyzed. Compared to conventional algorithms, the proposed one has the advantages of fast convergence and an easy approach to multiple solutions and PV curves, which show vivid and visual information to TPSS designers and operators. A numerical analysis and case studies validate the effectiveness and feasibility of the proposed method, which can help to optimize the organization of train operations and design lines and enhance the reliability and safety of TPSSs. Full article

(This article belongs to the Section F: Electrical Engineering)

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15 pages, 5045 KiB

Open AccessArticle

Numerical Simulations for a Partial Disk MHD Generator Performance

by Lai Li¹, Hu-lin Huang^2,*

and Gui-ping Zhu²

¹ College of Power and Energy Engineering, Nanjing University of Aeronautics & Astronautics, Nanjing 210016, China

² College of Astronautics, Nanjing University of Aeronautics & Astronautics, Nanjing 210016, China

Energies 2018, 11(1), 127; https://doi.org/10.3390/en11010127 - 4 Jan 2018

Cited by 6 | Viewed by 5833

Abstract

In this paper, numerical simulations are carried out to predict the performance of a new designed configuration of the disk magnetohydrodynamic (MHD) generator, which segments the generator into dozens of parts. The behaviors and characteristics of segments are mainly investigated with number of [...] Read more.

In this paper, numerical simulations are carried out to predict the performance of a new designed configuration of the disk magnetohydrodynamic (MHD) generator, which segments the generator into dozens of parts. The behaviors and characteristics of segments are mainly investigated with number of parts at 24, 36, 60, 72, 90 adopted Large Eddy Simulation (LES). The numerical results declared that these division generators approach more stable plasma ionization and better performance than that of the conventional disk MHD generator at the same working conditions. The optimal value can be reached when the angle is 5–10 degrees (36–72 parts). Due to the division of the generator, the internal resistance is larger than that of the conventional disk channel that causes the reduction of Faraday current, hence the Lorentz force,

j_{θ} B

, decreased. Therefore, the radial velocity increased and static pressure decreased. Consequently, the reduction of static pressure contributes to improvement to the plasma uniformity and ionization stability. Those features reveal that the designed configuration has the obvious advantage on raising energy conversion efficiency and power output. Full article

(This article belongs to the Special Issue Emerging Power Electronics Technologies for Power Systems and Machine Drives)

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21 pages, 10027 KiB

Open AccessArticle

Optimal Pole Number and Winding Designs for Low Speed–High Torque Synchronous Reluctance Machines

by Gurutz Artetxe^1,2,*

, Jesus Paredes^1,2, Borja Prieto^1,2, Miguel Martinez-Iturralde^1,2 and Ibon Elosegui^1,2

¹ Ceit, Manuel Lardizabal 15, 20018 Donostia/San Sebastián, Spain

² Tecnun, Universidad de Navarra, Manuel Lardizabal 15, 20018 Donostia/San Sebastián, Spain

Energies 2018, 11(1), 128; https://doi.org/10.3390/en11010128 - 5 Jan 2018

Cited by 17 | Viewed by 8105

Abstract

This paper studies the feasibility of using synchronous reluctance machines (SynRM) for low speed–high torque applications. The challenge lies in obtaining low torque ripple values, high power factor, and, especially, high torque density values, comparable to those of permanent magnet synchronous machines (PMSMs), [...] Read more.

This paper studies the feasibility of using synchronous reluctance machines (SynRM) for low speed–high torque applications. The challenge lies in obtaining low torque ripple values, high power factor, and, especially, high torque density values, comparable to those of permanent magnet synchronous machines (PMSMs), but without resorting to use permanent magnets. A design and calculation procedure based on multistatic finite element analysis is developed and experimentally validated via a 200 Nm, 160 rpm prototype SynRM. After that, machine designs with different rotor pole and stator slot number combinations are studied, together with different winding types: integral-slot distributed-windings (ISDW), fractional-slot distributed-windings (FSDW) and fractional-slot concentrated-windings (FSCW). Some design criteria for low-speed SynRM are drawn from the results of the study. Finally, a performance comparison between a PMSM and a SynRM is performed for the same application and the conclusions of the study are summarized. Full article

(This article belongs to the Special Issue Electric Machines and Drives for Renewable Energy Harvesting 2017)

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20 pages, 4404 KiB

Open AccessFeature PaperArticle

Control and EMS of a Grid-Connected Microgrid with Economical Analysis

by Mohamed El-Hendawi^1,2, Hossam A. Gabbar^1,3,*, Gaber El-Saady² and El-Nobi A. Ibrahim²

¹ Faculty of Engineering and Applied Science, University of Ontario Institute of Technology, 2000 Simcoe Street North, Oshawa, ON L1H7K4, Canada

² Electrical Engineering Department, Faculty of Engineering, Assiut University, Assiut 71515, Egypt

³ Faculty of Energy Systems and Nuclear Science, University of Ontario Institute of Technology, 2000 Simcoe Street North, Oshawa, ON L1H7K4, Canada

Energies 2018, 11(1), 129; https://doi.org/10.3390/en11010129 - 5 Jan 2018

Cited by 53 | Viewed by 6915

Abstract

Recently, significant development has occurred in the field of microgrid and renewable energy systems (RESs). Integrating microgrids and renewable energy sources facilitates a sustainable energy future. This paper proposes a control algorithm and an optimal energy management system (EMS) for a grid-connected microgrid [...] Read more.

Recently, significant development has occurred in the field of microgrid and renewable energy systems (RESs). Integrating microgrids and renewable energy sources facilitates a sustainable energy future. This paper proposes a control algorithm and an optimal energy management system (EMS) for a grid-connected microgrid to minimize its operating cost. The microgrid includes photovoltaic (PV), wind turbine (WT), and energy storage systems (ESS). The interior search algorithm (ISA) optimization technique determines the optimal hour-by-hour scheduling for the microgrid system, while it meets the required load demand based on 24-h ahead forecast data. The control system consists of three stages: EMS, supervisory control and local control. EMS is responsible for providing the control system with the optimum day-ahead scheduling power flow between the microgrid (MG) sources, batteries, loads and the main grid based on an economic analysis. The supervisory control stage is responsible for compensating the mismatch between the scheduled power and the real microgrid power. In addition, this paper presents the local control design to regulate the local power, current and DC voltage of the microgrid. For verification, the proposed model was applied on a real case study in Oshawa (Ontario, Canada) with various load conditions. Full article

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20 pages, 7835 KiB

Open AccessArticle

High Gain Boost Interleaved Converters with Coupled Inductors and with Demagnetizing Circuits

by Michal Frivaldsky^*

, Branislav Hanko, Michal Prazenica and Jan Morgos

Department of Mechatronics and Electronics, Faculty of Electrical Engineering, University of Zilina, Zilina 010 26, Slovakia

Energies 2018, 11(1), 130; https://doi.org/10.3390/en11010130 - 5 Jan 2018

Cited by 23 | Viewed by 7214

Abstract

This paper proposes double interleaved boost converters with high voltage gain and with magnetically coupled inductors, while a third coupled winding is used for magnetic flux reset of the core during converter operation. The topology of the proposal is simple, it does not [...] Read more.

This paper proposes double interleaved boost converters with high voltage gain and with magnetically coupled inductors, while a third coupled winding is used for magnetic flux reset of the core during converter operation. The topology of the proposal is simple, it does not require many additional components compared to standard interleaved topologies, and it improves the transfer characteristics, as well as system efficiency even for high power levels. The investigation of steady-state operation was undertaken. It was discovered that the proposed converter can be designed for a target application where very high voltage gain is required, while adjustment of voltage gain value can be done through duty-cycle variation or by the turns-ratio modification between individual coils. The 1 kW prototype was designed to test the theoretical analysis. The results demonstrate that the proposed converter achieves very high voltage gain (1:8), while for the designed prototype the peak efficiency reaches >96% even when two additional diodes and one winding were implemented within the converter’s main circuit. The dependency of the output voltage stiffness on load change is minimal. Thus, the presented converter might be a proper solution for applications where tight constant DC-bus voltage is required (a DC-DC converter for inverters). Full article

(This article belongs to the Special Issue Emerging Power Electronics Technologies for Power Systems and Machine Drives)

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13 pages, 2377 KiB

Open AccessArticle

Determination of In-Situ Stress and Geomechanical Properties from Borehole Deformation

by Hong Xue Han and Shunde Yin^*

Department of Petroleum Engineering, University of Wyoming, Laramie, WY 82071, USA

Energies 2018, 11(1), 131; https://doi.org/10.3390/en11010131 - 5 Jan 2018

Cited by 30 | Viewed by 5086

Abstract

This paper proposes a cost-effective technique to determine geomechanical properties and in-situ stress from borehole deformation data. In this approach, an artificial neural network (ANN) is applied to map the relationship among in-situ stress, borehole size, geomechanical properties, and borehole displacements. The genetic [...] Read more.

This paper proposes a cost-effective technique to determine geomechanical properties and in-situ stress from borehole deformation data. In this approach, an artificial neural network (ANN) is applied to map the relationship among in-situ stress, borehole size, geomechanical properties, and borehole displacements. The genetic algorithm (GA) searches for the set of unknown stresses and geomechanical properties that matches the objective borehole deformation function. Probabilistic recapitulation (PR) analysis is conducted after each ANN-GA modeling cycle and will be repeated with a reduced number of unknowns for the next ANN-GA modeling cycle until unequivocal results are achieved. The PR-GA-ANN method has been demonstrated by a field case study to estimate borehole size, Young’s modulus, Poisson’s ratio, and the two horizontal stresses using borehole deformation information reported from four-arm caliper log of a vertical borehole. The methodology effectively solves the issue of the multiple solutions (various rock mechanical properties and in-situ stresses combinations) for a certain borehole deformation. The case study also indicated that the calculated horizontal stresses are in reasonable agreement with the filed hydraulic fracture treatment observations and the reported regional stress study of the area. Full article

(This article belongs to the Section L: Energy Sources)

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20 pages, 37511 KiB

Open AccessArticle

A Critical Analysis and Validation of the Accuracy of Wave Overtopping Prediction Formulae for OWECs

by David Gallach-Sánchez^*

, Peter Troch

and Andreas Kortenhaus

Department of Civil Engineering, Ghent University, Technologiepark 904, 9052 Zwijnaarde, Belgium

Energies 2018, 11(1), 133; https://doi.org/10.3390/en11010133 - 5 Jan 2018

Cited by 4 | Viewed by 3132

Abstract

The development of wave energy devices is growing in recent years. One type of device is the overtopping wave energy converter (OWEC), for which the knowledge of the wave overtopping rates is a basic and crucial aspect in their design. In particular, the [...] Read more.

The development of wave energy devices is growing in recent years. One type of device is the overtopping wave energy converter (OWEC), for which the knowledge of the wave overtopping rates is a basic and crucial aspect in their design. In particular, the most interesting range to study is for OWECs with steep slopes to vertical walls, and with very small freeboards and zero freeboards where the overtopping rate is maximized, and which can be generalized as steep low-crested structures. Recently, wave overtopping prediction formulae have been published for this type of structures, although their accuracy has not been fully assessed, as the overtopping data available in this range is scarce. We performed a critical analysis of the overtopping prediction formulae for steep low-crested structures and the validation of the accuracy of these formulae, based on new overtopping data for steep low-crested structures obtained at Ghent University. This paper summarizes the existing knowledge about average wave overtopping, describes the physical model tests performed, analyses the results and compares them to existing prediction formulae. The new dataset extends the wave overtopping data towards vertical walls and zero freeboard structures. In general, the new dataset validated the more recent overtopping formulae focused on steep slopes with small freeboards, although the formulae are underpredicting the average overtopping rates for very small and zero relative crest freeboards. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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17 pages, 3193 KiB

Open AccessArticle

Magnetic Field and Torque Output of Packaged Hydraulic Torque Motor

by Liang Yan^1,2,*, Zihao Duan¹

, Qiongfang Zhang¹, Shiyong Niu³, Yifeng Dong³ and Christopher Gerada⁴

¹ School of Automation Science and Electrical Engineering, Beihang University, Beijing 100083, China

² Research Institute of Beihang University in Shenzhen, Shenzhen 518057, China

³ AVIC Xian Flight Automatic Control Research Institute, Xi’an 710065, China

⁴ Department of Electrical and Electronic Engineering, University of Nottingham, Nottingham NG7 2RD, UK

Energies 2018, 11(1), 134; https://doi.org/10.3390/en11010134 - 5 Jan 2018

Cited by 4 | Viewed by 5034

Abstract

Hydraulic torque motors are one key component in electro-hydraulic servo valves that convert the electrical signal into mechanical motions. The systematic characteristics analysis of the hydraulic torque motor has not been found in the previous research, including the distribution of the electromagnetic field [...] Read more.

Hydraulic torque motors are one key component in electro-hydraulic servo valves that convert the electrical signal into mechanical motions. The systematic characteristics analysis of the hydraulic torque motor has not been found in the previous research, including the distribution of the electromagnetic field and torque output, and particularly the relationship between them. In addition, conventional studies of hydraulic torque motors generally assume an evenly distributed magnetic flux field and ignore the influence of special mechanical geometry in the air gaps, which may compromise the accuracy of analyzing the result and the high-precision motion control performance. Therefore, the objective of this study is to conduct a detailed analysis of the distribution of the magnetic field and torque output; the influence of limiting holes in the air gaps is considered to improve the accuracy of both numerical computation and analytical modeling. The structure and working principle of the torque motor are presented first. The magnetic field distribution in the air gaps and the magnetic saturation in the iron blocks are analyzed by using a numerical approach. Subsequently, the torque generation with respect to the current input and assembly errors is analyzed in detail. This shows that the influence of limiting holes on the magnetic field is consistent with that on torque generation. Following this, a novel modified equivalent magnetic circuit is proposed to formulate the torque output of the hydraulic torque motor analytically. The comparison among the modified equivalent magnetic circuit, the conventional modeling approach and the numerical computation is conducted, and it is found that the proposed method helps to improve the modeling accuracy by taking into account the effect of special geometry inside the air gaps. Full article

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21 pages, 6497 KiB

Open AccessArticle

A Free-Piston Linear Generator Control Strategy for Improving Output Power

by Chi Zhang¹, Feixue Chen^1,2, Long Li², Zhaoping Xu³, Liang Liu³, Guilin Yang¹, Hongyuan Lian¹ and Yingzhong Tian^2,*

¹ Ningbo Institute of Materials Technology & Engineering, Chinese Academy of Sciences, Zhejiang Key Laboratory of Robotics and Intelligent Manufacturing Equipment Technology, Ningbo 315201, China

² School of Mechatronic Engineering and Automation, Shanghai University, Shanghai 200444, China

³ School of Mechanical Engineering, Nanjing University of Science and Technology, Nanjing 210094, China

Energies 2018, 11(1), 135; https://doi.org/10.3390/en11010135 - 5 Jan 2018

Cited by 40 | Viewed by 7341

Abstract

This paper presents a control strategy to improve the output power for a single-cylinder two-stroke free-piston linear generator (FPLG). The comprehensive simulation model of this FPLG is established and the operation principle is introduced. The factors that affect the output power are analyzed [...] Read more.

This paper presents a control strategy to improve the output power for a single-cylinder two-stroke free-piston linear generator (FPLG). The comprehensive simulation model of this FPLG is established and the operation principle is introduced. The factors that affect the output power are analyzed theoretically. The characteristics of the piston motion are studied. Considering the different features of the piston motion respectively in acceleration and deceleration phases, a ladder-like electromagnetic force control strategy is proposed. According to the status of the linear electric machine, the reference profile of the electromagnetic force is divided into four ladder-like stages during one motion cycle. The piston motions, especially the dead center errors, are controlled by regulating the profile of the electromagnetic force. The feasibility and advantage of the proposed control strategy are verified through comparison analyses with two conventional control strategies via MatLab/Simulink. The results state that the proposed control strategy can improve the output power by around 7–10% with the same fuel cycle mass. Full article

(This article belongs to the Special Issue Emerging Power Electronics Technologies for Power Systems and Machine Drives)

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15 pages, 5313 KiB

Open AccessArticle

Entropy-Based Voltage Fault Diagnosis of Battery Systems for Electric Vehicles

by Peng Liu^1,2, Zhenyu Sun^1,2,*

, Zhenpo Wang^1,2,* and Jin Zhang^1,2

¹ National Engineering Laboratory for Electric Vehicles, Beijing Institute of Technology, Beijing 100081, China

² Beijing Co-Innovation Center for Electric Vehicles Lecturer, Beijing 100081, China

Energies 2018, 11(1), 136; https://doi.org/10.3390/en11010136 - 5 Jan 2018

Cited by 76 | Viewed by 7406

Abstract

The battery is a key component and the major fault source in electric vehicles (EVs). Ensuring power battery safety is of great significance to make the diagnosis more effective and predict the occurrence of faults, for the power battery is one of the [...] Read more.

The battery is a key component and the major fault source in electric vehicles (EVs). Ensuring power battery safety is of great significance to make the diagnosis more effective and predict the occurrence of faults, for the power battery is one of the core technologies of EVs. This paper proposes a voltage fault diagnosis detection mechanism using entropy theory which is demonstrated in an EV with a multiple-cell battery system during an actual operation situation. The preliminary analysis, after collecting and preprocessing the typical data periods from Operation Service and Management Center for Electric Vehicle (OSMC-EV) in Beijing, shows that overvoltage fault for Li-ion batteries cell can be observed from the voltage curves. To further locate abnormal cells and predict faults, an entropy weight method is established to calculate the objective weight, which reduces the subjectivity and improves the reliability. The result clearly identifies the abnormity of cell voltage. The proposed diagnostic model can be used for EV real-time diagnosis without laboratory testing methods. It is more effective than traditional methods based on contrastive analysis. Full article

(This article belongs to the Special Issue The International Symposium on Electric Vehicles (ISEV2017))

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22 pages, 3056 KiB

Open AccessArticle

Variance Characteristics of Tropical Radiosonde Winds Using a Vector-Tensor Method

by Jing-Jin Tieo^1,2,*

, Tieh-Yong Koh³

, Martin Skote⁴

and Narasimalu Srikanth^2,*

¹ Interdisciplinary Graduate School, Nanyang Technological University, Singapore 639798, Singapore

² Energy Research Institute @ NTU, Nanyang Technological University, Singapore 637141, Singapore

³ UC, Singapore University of Social Sciences, Singapore 599491, Singapore

⁴ School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore 639798, Singapore

Energies 2018, 11(1), 137; https://doi.org/10.3390/en11010137 - 5 Jan 2018

Cited by 4 | Viewed by 3472

Abstract

In this paper, an exploratory study on the variance characteristics of upper-air winds in a near-equator monsoon region is presented. The data were obtained from historical radiosonde observations from up to 250 stations within the region of interest for the period between 1954 [...] Read more.

In this paper, an exploratory study on the variance characteristics of upper-air winds in a near-equator monsoon region is presented. The data were obtained from historical radiosonde observations from up to 250 stations within the region of interest for the period between 1954 and 2013. An alternative method based on vector statistics was employed in this study which characterises the mean by a vector and the variance by a tensor. Unlike the conventional approach of using scalar wind speeds, this vector-tensor approach allows the directional properties of the variance to be studied. A suite of statistics to describe the geometric properties of the variance tensor was also developed. These characterise the size of the variance, its degree of anisotropy, and the alignment of the preferred direction (if anisotropy is present) with the direction of the mean wind vector. Through analysis of these statistics, several salient trends were observed for the middle troposphere. It was found that the variance size and anisotropy exhibit significant variation with height whereas the alignment with the mean vector varies with the mean wind magnitude instead. It was also found that the scalar variance increases with mean wind speed. Full article

(This article belongs to the Section L: Energy Sources)

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31 pages, 6917 KiB

Open AccessArticle

Informatics Solution for Energy Efficiency Improvement and Consumption Management of Householders

by Simona-Vasilica Oprea^*

, Adela Bâra and Adriana Reveiu

Department of Economic Informatics and Cybernetics, The Bucharest University of Economic Studies, Romana Square 6, Bucharest 010374, Romania

Energies 2018, 11(1), 138; https://doi.org/10.3390/en11010138 - 5 Jan 2018

Cited by 15 | Viewed by 4098

Abstract

Although in 2012 the European Union (EU) has promoted energy efficiency in order to ensure a gradual 20% reduction of energy consumption by 2020, its targets related to energy efficiency have increased and extended to new time horizons. Therefore, in 2016, a new [...] Read more.

Although in 2012 the European Union (EU) has promoted energy efficiency in order to ensure a gradual 20% reduction of energy consumption by 2020, its targets related to energy efficiency have increased and extended to new time horizons. Therefore, in 2016, a new proposal for 2030 of energy efficiency target of 30% has been agreed. However, during the last years, even if the electricity consumption by households decreased in the EU-28, the largest expansion was recorded in Romania. Taking into account that the projected consumption peak is increasing and energy consumption management for residential activities is an important measure for energy efficiency improvement since its ratio from total consumption can be around 25–30%, in this paper, we propose an informatics solution that assists both electricity suppliers/grid operators and consumers. It includes three models for electricity consumption optimization, profiles, clustering and forecast. By this solution, the daily operation of appliances can be optimized and scheduled to minimize the consumption peak and reduce the stress on the grid. For optimization purpose, we propose three algorithms for shifting the operation of the programmable appliances from peak to off-peak hours. This approach enables the supplier to apply attractive time-of-use tariffs due to the fact that by flattening the consumption peak, it becomes more predictable, and thus improves the strategies on the electricity markets. According to the results of the optimization process, we compare the proposed algorithms emphasizing the benefits. For building consumption profiles, we develop a clustering algorithm based on self-organizing maps. By running the algorithm for three scenarios, well-delimited profiles are obtained. As for the consumption forecast, highly accurate feedforward artificial neural networks algorithm with backpropagation is implemented. Finally, we test these algorithms using several datasets showing their performance and integrate them into a web-service informatics solution as a prototype. Full article

(This article belongs to the Special Issue Selected Papers from SEEP2017: The 10th International Conference on Sustainable Energy and Environmental Protection)

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17 pages, 2496 KiB

Open AccessArticle

Photovoltaic and Wind Turbine Integration Applying Cuckoo Search for Probabilistic Reliable Optimal Placement

by R. A. Swief¹, T. S. Abdel-Salam¹ and Noha H. El-Amary^2,*

¹ Faculty of Engineering, Ain Shams University, 11566 Cairo, Egypt

² Arab Academy for Science, Technology and Maritime Transport (AASTMT), 2033 Cairo, Egypt

Energies 2018, 11(1), 139; https://doi.org/10.3390/en11010139 - 6 Jan 2018

Cited by 20 | Viewed by 3550

Abstract

This paper presents an efficient Cuckoo Search Optimization technique to improve the reliability of electrical power systems. Various reliability objective indices such as Energy Not Supplied, System Average Interruption Frequency Index, System Average Interruption, and Duration Index are the main indices indicating reliability. [...] Read more.

This paper presents an efficient Cuckoo Search Optimization technique to improve the reliability of electrical power systems. Various reliability objective indices such as Energy Not Supplied, System Average Interruption Frequency Index, System Average Interruption, and Duration Index are the main indices indicating reliability. The Cuckoo Search Optimization (CSO) technique is applied to optimally place the protection devices, install the distributed generators, and to determine the size of distributed generators in radial feeders for reliability improvement. Distributed generator affects reliability and system power losses and voltage profile. The volatility behaviour for both photovoltaic cells and the wind turbine farms affect the values and the selection of protection devices and distributed generators allocation. To improve reliability, the reconfiguration will take place before installing both protection devices and distributed generators. Assessment of consumer power system reliability is a vital part of distribution system behaviour and development. Distribution system reliability calculation will be relayed on probabilistic reliability indices, which can expect the disruption profile of a distribution system based on the volatility behaviour of added generators and load behaviour. The validity of the anticipated algorithm has been tested using a standard IEEE 69 bus system. Full article

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27 pages, 5997 KiB

Open AccessArticle

Perceived and Reported Reliability of the Electricity Supply at Three Urban Locations in Indonesia

by Kunaifi^1,2,*

and Angèle Reinders¹

¹ Department of Design, Production and Management, Faculty of Engineering Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands

² Department of Electrical Engineering, Faculty of Science and Technology, UIN Suska Riau University, Jl. H.R. Soebrantas No. 115, Pekanbaru 28292, Indonesia

Energies 2018, 11(1), 140; https://doi.org/10.3390/en11010140 - 6 Jan 2018

Cited by 22 | Viewed by 8284

Abstract

This paper focuses on the reliability of electricity supply at three different locations in Indonesia, namely in Sumatra, Timor, and Papua, through a comparison of reported indices of power reliability (SAIFI and SAIDI) and experimental results from user surveys and power measurements. The [...] Read more.

This paper focuses on the reliability of electricity supply at three different locations in Indonesia, namely in Sumatra, Timor, and Papua, through a comparison of reported indices of power reliability (SAIFI and SAIDI) and experimental results from user surveys and power measurements. The reason for this study is the lack of information about the actual, quantified reliability of power supplied by the main grid in Indonesia, while narratives of end-users indicate the reliability might be unsatisfactory. The study was executed using data from 114 randomly-selected respondents in the city of Pekanbaru in Sumatra, 65 in the city of Kupang in Timor and 26 in the city of Jayapura in Papua, totaling 205 respondents. These users experienced a higher unavailability of power delivered by the grid than expressed by the utility-reported SAIDI and SAIFI. Therefore, for this study, new indices are introduced, namely the Perceived (P) SAIDI and SAIFI, which are based on the frequency and duration of blackouts experienced by the users. It is concluded that the reported reliability indices do not always demonstrate the experience of the grid users. P-SAIFIs were 1.3 to 4.6 times higher in Pekanbaru and Kupang, respectively than the utility-reported SAIFIs for the same provinces. Also, P-SAIDIs were 2.6 to 3.9 times higher in Pekanbaru and Kupang, respectively, than the utilities’ SAIDIs. It is therefore not surprising that depending on the location, 14% to 65% of the users own a backup generator and that households are willing to pay $3 to $8 extra per monthly electricity bill or $1c–$3c per kWh for improved reliability. Full article

(This article belongs to the Special Issue Resilience of Energy Systems 2017)

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16 pages, 3964 KiB

Open AccessArticle

An Efficient Topology for Wireless Power Transfer over a Wide Range of Loading Conditions

by Tianqing Li¹

, Xiangzhou Wang¹, Shuhua Zheng^1,* and Chunhua Liu²

¹ School of Automation, Beijing Institute of Technology, Beijing 100081, China

² School of Energy and Environment, City University of Hong Kong, Hong Kong, China

Energies 2018, 11(1), 141; https://doi.org/10.3390/en11010141 - 6 Jan 2018

Cited by 12 | Viewed by 3603

Abstract

Although an inductive power transfer (IPT) system can transfer power efficiently in full-load conditions, its efficiency obviously decreases in light-load conditions. To solve this problem, based on a two-coil IPT system with a series-series compensation topology, a single-ended primary-inductor converter is introduced at [...] Read more.

Although an inductive power transfer (IPT) system can transfer power efficiently in full-load conditions, its efficiency obviously decreases in light-load conditions. To solve this problem, based on a two-coil IPT system with a series-series compensation topology, a single-ended primary-inductor converter is introduced at the secondary side. By adjusting the set effective value of the current in the primary coil, the converter input voltage changes to maintain the equivalent input resistance of the converter in an optimal condition. The system can then transfer the power efficiently with the wide load conditions. Moreover, the system operates at a constant resonance frequency with a high power factor. Both the simulation and experimentation of a prototype with a 10 W IPT system demonstrate the effectiveness of the proposed topology for wireless power transfer. Full article

(This article belongs to the Special Issue Advanced Electric Devices and Technologies for Electric-Drive Robotics)

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12 pages, 6676 KiB

Open AccessArticle

Evaluation of the Theoretical Geothermal Potential of Inferred Geothermal Reservoirs within the Vicano–Cimino and the Sabatini Volcanic Districts (Central Italy) by the Application of the Volume Method

by Daniele Cinti^1,*

, Monia Procesi¹

and Pier Paolo Poncia²

¹ Istituto Nazionale di Geofisica e Vulcanologia (INGV), via di Vigna Murata 605, 00143 Roma, Italy

² Via Camerano 1, 01028 Orte, Italy

Energies 2018, 11(1), 142; https://doi.org/10.3390/en11010142 - 6 Jan 2018

Cited by 7 | Viewed by 3197

Abstract

The evaluation of the theoretical geothermal potential of identified unexploited hydrothermal reservoirs within the Vicano–Cimino and Sabatini volcanic districts (Latium region, Italy) has been made on the basis of a revised version of the classical volume method. This method is based on the [...] Read more.

The evaluation of the theoretical geothermal potential of identified unexploited hydrothermal reservoirs within the Vicano–Cimino and Sabatini volcanic districts (Latium region, Italy) has been made on the basis of a revised version of the classical volume method. This method is based on the distribution of the partial pressure of CO₂ (pCO₂) in shallow and deep aquifers to delimit areas of geothermal interest, according to the hypothesis that zones of high CO₂ flux, either from soil degassing and dissolved into aquifers, are spatially related to deep hydrothermal reservoirs. On the whole, 664 fluid discharges (cold waters, thermal waters, and bubbling pools) have been collected from shallow and deep aquifers in the Vicano–Cimino Volcanic District and the Sabatini Volcanic District for chemical and isotopic composition, in an area of approximately 2800 km². From this large hydro-geochemical dataset the pCO₂ values have been computed and then processed to obtain a contour map of its spatial distribution by using geostatistical techniques (kriging). The map of pCO₂ has been used to draw up the boundaries of potentially exploitable geothermal systems within the two volcanic districts, corresponding to the areas where endogenous CO₂ raise up to the surface from the deep hydrothermal reservoirs. The overall estimated potential productivities and theoretical minimum and maximum thermal power of the two volcanic districts are of about 45 × 10³ t/h and 3681–5594 MWt, respectively. This makes the Vicano–Cimino Volcanic District and the Sabatini Volcanic District very suitable for both direct and indirect exploitation of the geothermal resources, in view of the target to reduce electricity generation from conventional and poorly sustainable energy sources. Full article

(This article belongs to the Section L: Energy Sources)

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15 pages, 2113 KiB

Open AccessArticle

PMU Measurement-Based Intelligent Strategy for Power System Controlled Islanding

by Yi Tang^1,*, Feng Li¹, Chenyi Zheng¹, Qi Wang¹ and Yingjun Wu²

¹ School of Electrical Engineering, Southeast University, Nanjing 210096, China

² College of Automation, Nanjing University of Posts and Telecommunications, Nanjing 210023, China

Energies 2018, 11(1), 143; https://doi.org/10.3390/en11010143 - 7 Jan 2018

Cited by 10 | Viewed by 3601

Abstract

Controlled islanding is an effective remedy to prevent large-area blackouts in a power system under a critically unstable condition. When and where to separate the power system are the essential issues facing controlled islanding. In this paper, both tasks are studied to ensure [...] Read more.

Controlled islanding is an effective remedy to prevent large-area blackouts in a power system under a critically unstable condition. When and where to separate the power system are the essential issues facing controlled islanding. In this paper, both tasks are studied to ensure higher time efficiency and a better post-splitting restoration effect. A transient stability assessment model based on extreme learning machine (ELM) and trajectory fitting (TF) is constructed to determine the start-up criterion for controlled islanding. This model works through prompt stability status judgment with ELM and selective result amendment with TF to ensure that the assessment is both efficient and accurate. Moreover, a splitting surface searching algorithm, subject to minimal power disruption, is proposed for determination of the controlled islanding implementing locations. A highlight of this algorithm is a proposed modified electrical distance concept defined by active power magnitude and reactance on transmission lines that realize a computational burden reduction without feasible solution loss. Finally, the simulation results and comparison analysis based on the New England 39-bus test system validates the implementation effects of the proposed controlled islanding strategy. Full article

(This article belongs to the Section F: Electrical Engineering)

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16 pages, 3162 KiB

Open AccessArticle

Scheduling Model for Renewable Energy Sources Integration in an Insular Power System

by Gerardo J. Osório¹

, Miadreza Shafie-khah¹

, Juan M. Lujano-Rojas² and João P. S. Catalão^1,2,3,*

¹ Centre for Mechanical and Aerospace Science and Technologies (C-MAST), University of Beira Interior, 6201-001 Covilhã, Portugal

² Instituto de Engenharia de Sistemas e Computadores—Investigação e Desenvolvimento (INESC-ID), Instituto Superior Técnico, University of Lisbon, 1049-001 Lisbon, Portugal

³ Institute for Systems and Computer Engineering, Technology and Science (INESC TEC) and Faculty of Engineering of the University of Porto, 4200-465 Porto, Portugal

Energies 2018, 11(1), 144; https://doi.org/10.3390/en11010144 - 7 Jan 2018

Cited by 17 | Viewed by 5452

Abstract

Insular power systems represent an asset and an excellent starting point for the development and analysis of innovative tools and technologies. The integration of renewable energy resources that has taken place in several islands in the south of Europe, particularly in Portugal, has [...] Read more.

Insular power systems represent an asset and an excellent starting point for the development and analysis of innovative tools and technologies. The integration of renewable energy resources that has taken place in several islands in the south of Europe, particularly in Portugal, has brought more uncertainty to production management. In this work, an innovative scheduling model is proposed, which considers the integration of wind and solar resources in an insular power system in Portugal, with a strong conventional generation basis. This study aims to show the benefits of increasing the integration of renewable energy resources in this insular power system, and the objectives are related to minimizing the time for which conventional generation is in operation, maximizing profits, reducing production costs, and consequently, reducing greenhouse gas emissions. Full article

(This article belongs to the Special Issue Distributed Renewable Generation 2018)

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14 pages, 1760 KiB

Open AccessArticle

Power Quality Event Detection Using a Fast Extreme Learning Machine

by Ferhat Ucar^1,*

, Omer F. Alcin²

, Besir Dandil³ and Fikret Ata²

¹ Department of Electrical and Electronics Engineering, Technology Faculty, Firat University, 23119 Elazig, Turkey

² Department of Electrical and Electronics Engineering, Faculty of Engineering and Architecture, Bingol University, 12000 Bingol, Turkey

³ Department of Mechatronics Engineering, Technology Faculty, Firat University, 23119 Elazig, Turkey

Energies 2018, 11(1), 145; https://doi.org/10.3390/en11010145 - 7 Jan 2018

Cited by 47 | Viewed by 6493

Abstract

Monitoring Power Quality Events (PQE) is a crucial task for sustainable and resilient smart grid. This paper proposes a fast and accurate algorithm for monitoring PQEs from a pattern recognition perspective. The proposed method consists of two stages: feature extraction (FE) and decision-making. [...] Read more.

Monitoring Power Quality Events (PQE) is a crucial task for sustainable and resilient smart grid. This paper proposes a fast and accurate algorithm for monitoring PQEs from a pattern recognition perspective. The proposed method consists of two stages: feature extraction (FE) and decision-making. In the first phase, this paper focuses on utilizing a histogram based method that can detect the majority of PQE classes while combining it with a Discrete Wavelet Transform (DWT) based technique that uses a multi-resolution analysis to boost its performance. In the decision stage, Extreme Learning Machine (ELM) classifies the PQE dataset, resulting in high detection performance. A real-world like PQE database is used for a thorough test performance analysis. Results of the study show that the proposed intelligent pattern recognition system makes the classification task accurately. For validation and comparison purposes, a classic neural network based classifier is applied. Full article

(This article belongs to the Special Issue Power Electronics and Power Quality)

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17 pages, 3982 KiB

Open AccessArticle

Effectiveness Analysis and Temperature Effect Mechanism on Chemical and Electrical-Based Transformer Insulation Diagnostic Parameters Obtained from PDC Data

by Hanbo Zheng^1,2,†

, Jiefeng Liu^1,3,*,†

, Yiyi Zhang^1,4,*,†

, Yijie Ma³, Yang Shen³, Xiaochen Zhen³ and Zilai Chen³

¹ Guangxi Key Laboratory of Power System Optimization and Energy Technology, Guangxi University, Nanning 530004, Guangxi, China

² State Grid Henan Electric Power Research Institute, Zhengzhou 450052, Henan, China

³ Shijiazhuang Power Supply Branch of State Grid Electric Power Company, Shijiazhuang 050000, Hebei, China

⁴ National Demonstration Center for Experimental Electrical Engineering Education, Guangxi University, Nanning 530004, Guangxi, China

^† These authors contributed equally to this work.

Energies 2018, 11(1), 146; https://doi.org/10.3390/en11010146 - 8 Jan 2018

Cited by 18 | Viewed by 3766

Abstract

The dielectric monitoring/diagnostic tool, such as Polarization and Depolarization Current (PDC) measurement, is now being widely applied to obtain the status of deteriorated transformers around the world. Nowadays, several works have reported that the chemical and electrical-based transformer insulation diagnostic parameters (absorption ratio, [...] Read more.

The dielectric monitoring/diagnostic tool, such as Polarization and Depolarization Current (PDC) measurement, is now being widely applied to obtain the status of deteriorated transformers around the world. Nowadays, several works have reported that the chemical and electrical-based transformer insulation diagnostic parameters (absorption ratio, polarization index, paper conductivity, oil conductivity, insulation resistance, etc.) can be easily calculated from the PDC data. It is a fact that before using these parameters to obtain the status of deteriorated transformers, the power engineers should prudently investigate the effectiveness of these parameters. However, there are few papers that investigate the important issue. In addition, the understanding of temperature effect mechanism on these parameters should also be prudently studied. In the present work, we firstly prepare several oil-impregnated pressboard specimens with various insulation statuses by using a sequence of thermal ageing and moisture absorption experiments launched in the laboratory, and then the PDC measurement is performed to obtain the chemical and electrical-based transformer insulation diagnostic parameters. Finally, we systematically interpret the effectiveness and temperature effect mechanism on these chemical and electrical-based transformer insulation diagnostic parameters. Full article

(This article belongs to the Section F: Electrical Engineering)

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13 pages, 1364 KiB

Open AccessArticle

Analysis of Combined Cycle Power Plants with Chemical Looping Reforming of Natural Gas and Pre-Combustion CO₂ Capture

by Shareq Mohd Nazir^1,*, Olav Bolland¹

and Shahriar Amini^1,2

¹ Department of Energy and Process Engineering, Norwegian University of Science and Technology, 7491 Trondheim, Norway

² SINTEF Materials and Chemistry, 7034 Trondheim, Norway

Energies 2018, 11(1), 147; https://doi.org/10.3390/en11010147 - 8 Jan 2018

Cited by 21 | Viewed by 5620

Abstract

In this paper, a gas-fired combined cycle power plant subjected to a pre-combustion CO₂ capture method has been analysed under different design conditions and different heat integration options. The power plant configuration includes the chemical looping reforming (CLR) of natural gas (NG), [...] Read more.

In this paper, a gas-fired combined cycle power plant subjected to a pre-combustion CO₂ capture method has been analysed under different design conditions and different heat integration options. The power plant configuration includes the chemical looping reforming (CLR) of natural gas (NG), water gas shift (WGS) process, CO₂ capture and compression, and a hydrogen fuelled combined cycle to produce power. The process is denoted as a CLR-CC process. One of the main parameters that affects the performance of the process is the pressure for the CLR. The process is analysed at different design pressures for the CLR, i.e., 5, 10, 15, 18, 25 and 30 bar. It is observed that the net electrical efficiency increases with an increase in the design pressure in the CLR. Secondly, the type of steam generated from the cooling of process streams also effects the net electrical efficiency of the process. Out of the five different cases including the base case presented in this study, it is observed that the net electrical efficiency of CLR-CCs can be improved to 46.5% (lower heating value of NG basis) by producing high-pressure steam through heat recovery from the pre-combustion process streams and sending it to the Heat Recovery Steam Generator in the power plant. Full article

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18 pages, 3848 KiB

Open AccessArticle

Analytical Investigation of the Heat-Transfer Limits of a Novel Solar Loop-Heat Pipe Employing a Mini-Channel Evaporator

by Thierno M. O. Diallo^1,*, Min Yu¹

, Jinzhi Zhou¹, Xudong Zhao^1,*

, Jie Ji² and David Hardy¹

¹ School of Engineering, University of Hull, Hull HU6 7RX, UK

² Department of Thermal Science and Energy Engineering, University of Science and Technology of China, Hefei 230026, China

Energies 2018, 11(1), 148; https://doi.org/10.3390/en11010148 - 8 Jan 2018

Cited by 14 | Viewed by 5165

Abstract

This paper presents an analytical investigation of heat-transfer limits of a novel solar loop-heat pipe developed for space heating and domestic hot water use. In the loop-heat pipe, the condensate liquid returns to the evaporator via small specially designed holes, using a mini-channel [...] Read more.

This paper presents an analytical investigation of heat-transfer limits of a novel solar loop-heat pipe developed for space heating and domestic hot water use. In the loop-heat pipe, the condensate liquid returns to the evaporator via small specially designed holes, using a mini-channel evaporator. The study considered the commonly known heat-transfer limits of loop-heat pipes, namely, the viscous, sonic, entrainment, boiling and heat-transfer limits due to the two-phase pressure drop in the loop. The analysis considered the main factors that affect the limits in the mini-channel evaporator: the operating temperature, mini-channel aspect ratio, evaporator length, evaporator inclination angle, evaporator-to-condenser height difference and the dimension of the holes. It was found that the entrainment is the main governing limit of the system operation. With the specified loop design and operational conditions, the solar loop-heat pipe can achieve a heat-transport capacity of 725 W. The analytical model presented in this study can be used to optimise the heat-transfer capacity of the novel solar loop-heat pipe. Full article

(This article belongs to the Special Issue Solar Technologies for Buildings)

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9 pages, 3481 KiB

Open AccessArticle

Numerical Simulation of the Thermal Performance of a Dry Storage Cask for Spent Nuclear Fuel

by Heui-Yung Chang¹, Rong-Horng Chen² and Chi-Ming Lai^3,*

¹ Department of Civil and Environmental Engineering, National Kaohsiung University, 700 Kaohsiung University Rd., Kaohsiung 811, Taiwan

² Department of Mechanical and Energy Engineering, National Chiayi University, 300 Syuefu Rd., Chiayi 600, Taiwan

³ Department of Civil Engineering, National Cheng Kung University, 1 University Rd., Tainan 701, Taiwan

Energies 2018, 11(1), 149; https://doi.org/10.3390/en11010149 - 8 Jan 2018

Cited by 7 | Viewed by 4091

Abstract

In this study, the heat flow characteristics and thermal performance of a dry storage cask were investigated via thermal flow experiments and a computational fluid dynamics (CFD) simulation. The results indicate that there are many inner circulations in the flow channel of the [...] Read more.

In this study, the heat flow characteristics and thermal performance of a dry storage cask were investigated via thermal flow experiments and a computational fluid dynamics (CFD) simulation. The results indicate that there are many inner circulations in the flow channel of the cask (the channel width is 10 cm). These circulations affect the channel airflow efficiency, which in turn affects the heat dissipation of the dry storage cask. The daily operating temperatures at the top concrete lid and the upper locations of the concrete cask are higher than those permitted by the design specification. The installation of the salt particle collection device has a limited negative effect on the thermal dissipation performance of the dry storage cask. Full article

(This article belongs to the Section D: Energy Storage and Application)

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20 pages, 1296 KiB

Open AccessArticle

Exploring the Effect of Increased Energy Density on the Environmental Impacts of Traction Batteries: A Comparison of Energy Optimized Lithium-Ion and Lithium-Sulfur Batteries for Mobility Applications

by Felipe Cerdas^1,3,*

, Paul Titscher^2,3

, Nicolas Bognar^1,3, Richard Schmuch⁴

, Martin Winter^4,5, Arno Kwade^2,3

and Christoph Herrmann^1,3

¹ Chair of Sustainable Manufacturing & Life Cycle Engineering, Institute of Machine Tools and Production Technology (IWF), Technische Universität Braunschweig, Langer Kamp 19b, 38106 Braunschweig, Germany

² Institute for Particle Technology (iPAT), Technische Universität Braunschweig, Volkmaroder Straße 5, 38104 Braunschweig, Germany

³ Battery LabFactory Braunschweig (BLB), Technische Universität Braunschweig, Langer Kamp 19, 38106 Braunschweig, Germany

⁴ MEET Battery Research Center, Institute of Physical Chemistry, University of Münster, Corrensstraße 46, 48149 Münster, Germany

⁵ Helmholtz Institute Münster, IEK-12, Forschungszentrum Jülich GmbH, Corrensstraße 46, 48149 Münster, Germany

Energies 2018, 11(1), 150; https://doi.org/10.3390/en11010150 - 8 Jan 2018

Cited by 53 | Viewed by 9863

Abstract

The quest towards increasing the energy density of traction battery technologies has led to the emergence and diversification of battery materials. The lithium sulfur battery (LSB) is in this regard a promising material for batteries due to its specific energy. However, due to [...] Read more.

The quest towards increasing the energy density of traction battery technologies has led to the emergence and diversification of battery materials. The lithium sulfur battery (LSB) is in this regard a promising material for batteries due to its specific energy. However, due to its low volumetric energy density, the LSB faces challenges in mobility applications such as electric vehicles but also other transportation modes. To understand the potential environmental implication of LSB batteries, a comparative Life Cycle Assessment (LCA) was performed. For this study, electrodes for both an NMC111 with an anode graphite and a LSB battery cell with a lithium metal foil as anode were manufactured. Data from disassembly experiments performed on a real battery system for a mid-size passenger vehicle were used to build the required life cycle inventory. The energy consumption during the use phase was calculated using a simulative approach. A set of thirteen impact categories was evaluated and characterized with the ReCiPe methodology. The results of the LCA in this study allow identification of the main sources of environmental problems as well as possible strategies to improve the environmental impact of LSB batteries. In this regard, the high requirements of N-Methyl-2-pyrrolidone (NMP) for the processing of the sulfur cathode and the thickness of the lithium foil were identified as the most important drivers. We make recommendations for necessary further research in order to broaden the understanding concerning the potential environmental implication of the implementation of LSB batteries for mobility applications. Full article

(This article belongs to the Special Issue Towards a Transformation to Sustainable Aviation Systems)

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29 pages, 5923 KiB

Open AccessArticle

An Integrated Start-Up Method for Pumped Storage Units Based on a Novel Artificial Sheep Algorithm

by Zanbin Wang, Chaoshun Li^*, Xinjie Lai, Nan Zhang, Yanhe Xu^* and Jinjiao Hou

School of Hydropower and Information Engineering, Huazhong University of Science and Technology, Wuhan 430074, China

Energies 2018, 11(1), 151; https://doi.org/10.3390/en11010151 - 8 Jan 2018

Cited by 41 | Viewed by 4038

Abstract

Pumped storage units (PSUs) are an important storage tool for power systems containing large-scale renewable energy, and the merit of rapid start-up enable PSUs to modulate and stabilize the power system. In this paper, PSU start-up strategies have been studied and a new [...] Read more.

Pumped storage units (PSUs) are an important storage tool for power systems containing large-scale renewable energy, and the merit of rapid start-up enable PSUs to modulate and stabilize the power system. In this paper, PSU start-up strategies have been studied and a new integrated start-up method has been proposed for the purpose of achieving swift and smooth start-up. A two-phase closed-loop startup strategy, composed of switching Proportion Integration (PI) and Proportion Integration Differentiation (PID) controller is designed, and an integrated optimization scheme is proposed for a synchronous optimization of the parameters in the strategy. To enhance the optimization performance, a novel meta-heuristic called Artificial Sheep Algorithm (ASA) is proposed and applied to solve the optimization task after a sufficient verification with seven popular meta-heuristic algorithms and 13 typical benchmark functions. Simulation model has been built for a China’s PSU and comparative experiments are conducted to evaluate the proposed integrated method. Results show that the start-up performance could be significantly improved on both indices on overshoot and start-up, and up to 34%-time consumption has been reduced under different working condition. The significant improvements on start-up of PSU is interesting and meaning for further application on real unit. Full article

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18 pages, 10463 KiB

Open AccessArticle

Impacts of Bioenergy Policies on Land-Use Change in Nigeria

by Stanley U. Okoro^1,*, Udo Schickhoff¹ and Uwe A. Schneider²

¹ Center for Earth System Research and Sustainability, Institute of Geography, Bundesstrasse 55, 20146 Hamburg, Germany

² Center for Earth System Research and Sustainability, Research Unit Sustainability and Global Change, Grindelberg 5, 20144 Hamburg, Germany

Energies 2018, 11(1), 152; https://doi.org/10.3390/en11010152 - 8 Jan 2018

Cited by 8 | Viewed by 4150

Abstract

In recent years, bioenergy policies have increased the competition for land as well as the risk of adverse environmental impacts resulting from deforestation and greenhouse gas emissions (GHGs). Primary land-use objectives confronting society today include meeting the growing demand for agricultural products, especially [...] Read more.

In recent years, bioenergy policies have increased the competition for land as well as the risk of adverse environmental impacts resulting from deforestation and greenhouse gas emissions (GHGs). Primary land-use objectives confronting society today include meeting the growing demand for agricultural products, especially energy crops, preserving essential ecosystem services for human well-being and long-run agrarian production, and contributing to the climate policy target. Here, future agricultural, societal and environmental consequences of bioenergy policies under different global climate and societal development scenarios were assessed using a novel Forest and Agricultural Sector Optimization Model for Nigeria (NGA–FASOM). The results reveal that, in Nigeria, meeting emission reduction requires an implementation of a minimum carbon price of $80/ton within the forest and agricultural sectors. A carbon price alone is not sufficient to preserve the remaining forests and pasture land in Nigeria when bioenergy is subsidized. Furthermore, the result shows that subsidy on bioenergy does not have any significant effect on the total social welfare. The findings in this study provide a guide for policymakers in designing appropriate policies addressing bioenergy industry issues in Nigeria. Full article

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17 pages, 8384 KiB

Open AccessArticle

A Novel Dual-Permanent-Magnet-Excited Machine with Flux Strengthening Effect for Low-Speed Large-Torque Applications

by Yujun Shi^1,2 and Linni Jian^1,2,*

¹ Department of Electrical and Electronic Engineering, Southern University of Science and Technology, Shenzhen 518055, China

² Shenzhen Key Laboratory of Electric Direct Drive Technology, Shenzhen 518055, China

Energies 2018, 11(1), 153; https://doi.org/10.3390/en11010153 - 8 Jan 2018

Cited by 26 | Viewed by 6200

Abstract

This paper proposes a novel dual-permanent-magnet-excited (DPME) machine. It employs two sets of permanent magnets (PMs). One is on the rotor, the other is on the stator with PM arrays. When compared with the existing DPME machines, not all of the PMs are [...] Read more.

This paper proposes a novel dual-permanent-magnet-excited (DPME) machine. It employs two sets of permanent magnets (PMs). One is on the rotor, the other is on the stator with PM arrays. When compared with the existing DPME machines, not all of the PMs are located in the slots formed by the iron teeth. Specifically, the radially magnetized PMs in the arrays are located under the short iron teeth, while the tangentially magnetized PMs are located in the slots formed by the long stator iron teeth and the radially magnetized PMs. Each long stator iron tooth is sandwiched by two tangentially magnetized PMs with opposite directions, thus resulting in the flux strengthening effect. The simulation analysis indicates that the proposed machine can offer large back EMF with low THD and large torque density with low torque ripple when compared with Machine I from a literature. Meanwhile, by comparison, the proposed machine has great potential in improving the power factor and efficiency. Full article

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16 pages, 5913 KiB

Open AccessArticle

Thermal and Electrical Characterization of a Semi-Transparent Dye-Sensitized Photovoltaic Module under Real Operating Conditions

by Cristina Cornaro^1,2,*

, Ludovica Renzi¹, Marco Pierro^1,3, Aldo Di Carlo^2,4

and Alessandro Guglielmotti⁵

¹ Department of Enterprise Engineering, University of Rome “Tor Vergata”, 00133 Rome, Italy

² CHOSE, University of Rome “Tor Vergata”, 00133 Rome, Italy

³ Institute for Renewable Energy, EURAC Research, 39100 Bolzano, Italy

⁴ Department of Electronic Engineering, University of Rome “Tor Vergata”, 00133 Rome, Italy

⁵ Dyepower, Fonte Nuova, 00013 Rome, Italy

Energies 2018, 11(1), 155; https://doi.org/10.3390/en11010155 - 9 Jan 2018

Cited by 24 | Viewed by 3743

Abstract

Dye-sensitized solar cell technology is having an important role in renewable energy research due to its features and low-cost manufacturing processes. Devices based on this technology appear very well suited for integration into glazing systems due to their characteristics of transparency, color tuning [...] Read more.

Dye-sensitized solar cell technology is having an important role in renewable energy research due to its features and low-cost manufacturing processes. Devices based on this technology appear very well suited for integration into glazing systems due to their characteristics of transparency, color tuning and manufacturing directly on glass substrates. Field data of thermal and electrical characteristics of dye-sensitized solar modules (DSM) are important since they can be used as input of building simulation models for the evaluation of their energy saving potential when integrated into buildings. However, still few studies in the literature provide this information. The study presented here aims to contribute to fill this lack providing a thermal and electrical characterization of a DSM in real operating conditions using a method developed in house. This method uses experimental data coming from test boxes exposed outdoor and dynamic simulation to provide thermal transmittance (U-value) and solar heat gain coefficient (SHGC) of a DSM prototype. The device exhibits a U-value of 3.6 W/m²·K, confirmed by an additional measurement carried on in the lab using a heat flux meter, and a SHGC of 0.2, value compliant with literature results. Electrical characterization shows an increase of module power with respect to temperature resulting DSM being suitable for integration in building facades. Full article

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16 pages, 793 KiB

Open AccessArticle

Cyanobacteria and Microalgae: Thermoeconomic Considerations in Biofuel Production

by Umberto Lucia^*,†

and Giulia Grisolia^†

¹ Dipartimento Energia “Galileo Ferraris”, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy

^† These authors contributed equally to this work.

Energies 2018, 11(1), 156; https://doi.org/10.3390/en11010156 - 9 Jan 2018

Cited by 28 | Viewed by 3441

Abstract

In thermodynamics, the useful work in any process can be evaluated by using the exergy quantity. The analyses of irreversibility are fundamental in the engineering design and in the productive processes’ development in order to obtain the economic growth. Recently, the use has [...] Read more.

In thermodynamics, the useful work in any process can be evaluated by using the exergy quantity. The analyses of irreversibility are fundamental in the engineering design and in the productive processes’ development in order to obtain the economic growth. Recently, the use has been improved also in the thermodynamic analysis of the socio-economic context. Consequently, the exergy lost is linked to the energy cost required to maintain the productive processes themselves. The fundamental role of the fluxes and the interaction between systems and their environment is highlighted. The equivalent wasted primary resource value for the work-hour is proposed as an indicator to support the economic considerations on the biofuel production by using biomass and bacteria. The equivalent wasted primary resource value for the work-hour is proposed as an indicator to support the economic considerations of the biofuel production by using biomass and bacteria. Moreover, the technological considerations can be developed by using the exergy inefficiency. Consequently, bacteria use can be compared with other means of biofuel production, taking into account both the technologies and the economic considerations. Cyanobacteria results as the better organism for biofuel production. Full article

15 pages, 1759 KiB

Open AccessArticle

Esterification Optimization of Crude African Palm Olein Using Response Surface Methodology and Heterogeneous Acid Catalysis

by Francisco Anguebes-Franseschi¹, Mohamed Abatal², Ali Bassam^3,*, Mauricio A. Escalante Soberanis³, Oscar May Tzuc³

, Lauro Bucio-Galindo⁴, Atl Victor Cordova Quiroz¹, Claudia Alejandra Aguilar Ucan¹

and Miguel Angel Ramirez-Elias¹

¹ Facultad de Química, Universidad Autónoma del Carmen, Calle 56 No. 4 Esq. Av. Concordia, Col. Benito Juárez, Ciudad del Carmen 24180, Campeche, Mexico

² Facultad de Ingeniería, Universidad Autónoma del Carmen, Campus III, Avenida Central S/N, Esq. con Fracc. Mundo Maya, Ciudad del Carmen 24115, Campeche, Mexico

³ Facultad de Ingeniería, Universidad Autónoma de Yucatán, Av. Industrias no Contaminantes por Periférico Norte, Apdo, Postal 150 Cordemex, Merida 97000, Yucatan, Mexico

⁴ Instituto de Física, Universidad Nacional Autónoma de México, Circuito de la Investigación Científica Ciudad Universitaria, Mexico D.F. 04510, Mexico

Energies 2018, 11(1), 157; https://doi.org/10.3390/en11010157 - 9 Jan 2018

Cited by 13 | Viewed by 5102

Abstract

In this work, the effect of zeolite montmorillonite KSF in the esterification of free fatty acids (FFAs) of crude African palm olein (Eleaias guinnesis Jacq) was studied. To optimize the esterification of FFAs of the crude African palm olein (CAPO), the response [...] Read more.

In this work, the effect of zeolite montmorillonite KSF in the esterification of free fatty acids (FFAs) of crude African palm olein (Eleaias guinnesis Jacq) was studied. To optimize the esterification of FFAs of the crude African palm olein (CAPO), the response surface methodology (RSM) that was based on a central composite rotatable design (CCRD) was used. The effects of three parameters were investigated: (a) catalyst loading (2.6–9.4 wt %), (b) reaction temperature (133.2–166.2 °C), and (c) reaction time (0.32–3.68 h). The Analysis of variance (ANOVA) indicated that linear terms of catalyst loading (X₁), reaction temperature (X₂), the quadratic term of catalyst loading (

X_{1}^{2}

), temperature reaction (

X_{2}^{2}

), reaction time (

X_{3}^{2}

), the interaction catalyst loading with reaction time (

X_{1}^{*}

X₃), and the interaction reaction temperature with reaction time (

X_{2}^{*}

X₃) have a significant effect (p < 0.05 with a 95% confidence level) on Fatty Methyl Ester (FAME) yield. The result indicated that the optimum reaction conditions to esterification of FFAs were: catalyst loading 9.4 wt %, reaction temperature 155.5 °C, and 3.3 h for reaction time, respectively. Under these conditions, the numerical estimation of FAME yield was 91.81 wt %. This result was experimentally validated obtaining a difference of 1.7% FAME yield, with respect to simulated values. Full article

(This article belongs to the Collection Bioenergy and Biofuel)

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19 pages, 1147 KiB

Open AccessArticle

Optimal Sizing of Energy Storage Systems for the Energy Procurement Problem in Multi-Period Markets under Uncertainties

by Ryusuke Konishi^1,2, Akiko Takeda^2,3 and Masaki Takahashi^2,4,*

¹ Graduate School of Science and Technology, Keio University, Yokohama 223-8522, Japan

² Japan Science and Technology Agency (JST), CREST, Kawaguchi 332-0012, Japan

³ Institute of Statistical Mathematics, Tachikawa 190-8562, Japan

⁴ Faculty of Science and Technology, Keio University, Yokohama 223-8522, Japan

Energies 2018, 11(1), 158; https://doi.org/10.3390/en11010158 - 9 Jan 2018

Cited by 3 | Viewed by 3569

Abstract

In deregulated electricity markets, minimizing the procurement costs of electricity is a critical problem for procurement agencies (PAs). However, uncertainty is inevitable for PAs and includes multiple factors such as market prices, photovoltaic system (PV) output and demand. This study focuses on settlements [...] Read more.

In deregulated electricity markets, minimizing the procurement costs of electricity is a critical problem for procurement agencies (PAs). However, uncertainty is inevitable for PAs and includes multiple factors such as market prices, photovoltaic system (PV) output and demand. This study focuses on settlements in multi-period markets (a day-ahead market and a real-time market) and the installation of energy storage systems (ESSs). ESSs can be utilized for time arbitrage in the day-ahead market and to reduce the purchasing/selling of electricity in the real-time market. However, the high costs of an ESS mean the size of the system needs to be minimized. In addition, when determining the size of an ESS, it is important to identify the size appropriate for each role. Therefore, we employ the concept of a “slow” and a “fast” ESS to quantify the size of a system’s role, based on the values associated with the various uncertainties. Because the problem includes nonlinearity and non-convexity, we solve it within a realistic computational burden by reformulating the problem using reasonable assumptions. Therefore, this study identifies the optimal sizes of ESSs and procurement, taking into account the uncertainties of prices in multi-period markets, PV output and demand. Full article

(This article belongs to the Section F: Electrical Engineering)

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23 pages, 9196 KiB

Open AccessArticle

Cost Optimization of Mooring Solutions for Large Floating Wave Energy Converters

by Jonas Bjerg Thomsen^1,*

, Francesco Ferri¹

, Jens Peter Kofoed¹

and Kevin Black²

¹ Department of Civil Engineering, Aalborg University, Thomas Manns Vej 23, 9220 Aalborg ∅st , Denmark

² Tension Technology International Ltd., 69 Parkway, Eastbourne, East Sussex BN20 9DZ, UK

Energies 2018, 11(1), 159; https://doi.org/10.3390/en11010159 - 9 Jan 2018

Cited by 45 | Viewed by 5958

Abstract

The increasing desire for using renewable energy sources throughout the world has resulted in a considerable amount of research into and development of concepts for wave energy converters. By now, many different concepts exist, but still, the wave energy sector is not at [...] Read more.

The increasing desire for using renewable energy sources throughout the world has resulted in a considerable amount of research into and development of concepts for wave energy converters. By now, many different concepts exist, but still, the wave energy sector is not at a stage that is considered commercial yet, primarily due to the relatively high cost of energy. A considerable amount of the wave energy converters are floating structures, which consequently need mooring systems in order to ensure station keeping. Despite being a well-known concept, mooring in wave energy application has proven to be expensive and has a high rate of failure. Therefore, there is a need for further improvement, investigation into new concepts and sophistication of design procedures. This study uses four Danish wave energy converters, all considered as large floating structures, to investigate a methodology in order to find an inexpensive and reliable mooring solution for each device. The study uses a surrogate-based optimization routine in order to find a feasible solution in only a limited number of evaluations and a constructed cost database for determination of the mooring cost. Based on the outcome, the mooring parameters influencing the cost are identified and the optimum solution determined. Full article

(This article belongs to the Special Issue Wave Energy Potential, Behavior and Extraction)

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20 pages, 10533 KiB

Open AccessArticle

Cyclic Experimental Studies on Damage Evolution Behaviors of Shale Dependent on Structural Orientations and Confining Pressures

by Cheng Cheng^1,2,3 and Xiao Li^1,2,3,*

¹ Key Laboratory of Shale Gas and Geoengineering, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China

² Institutions of Earth Science, Chinese Academy of Sciences, Beijing 100029, China

³ College of Earth Sciences, University of Chinese Academy of Sciences, Beijing 100049, China

Energies 2018, 11(1), 160; https://doi.org/10.3390/en11010160 - 9 Jan 2018

Cited by 29 | Viewed by 3513

Abstract

Damage process of shale is of great importance when considering the wellbore stability and reservoir stimulation during the work of shale gas recovery. As shale has typical transversely isotropic structures and may be under different stress states in the reservoir, the damage process [...] Read more.

Damage process of shale is of great importance when considering the wellbore stability and reservoir stimulation during the work of shale gas recovery. As shale has typical transversely isotropic structures and may be under different stress states in the reservoir, the damage process should be studied while considering both loading directions and confining pressures. A series of cyclic uniaxial and tri-axial compressive tests have been carried out on the shale samples with different oriented weak planes and confining pressures. The dissipated strain energy and its ratio to the releasable elastic strain energy have been studied comparing with the fracturing patterns of the samples. Based on the strain energy dissipation, damage variable is defined and the damage evolution equation is built to describe the damage process of shale samples dependent on loading directions and confining pressures. The damage equation shows that the damage of the shale samples increases as a power function of the axial stress. Under higher confining pressures, the damage is limited in the early loading stage, while it increases significantly with the formation of macro shear fractures when the peak strength is approaching. The change of increasing rate is weak for the shale samples (β = 60°) as the main failure pattern is slip along the weak planes. This study is helpful for understanding the damage process and failure of wellbore, as well as the stimulation effect of the shale gas reservoir. Full article

(This article belongs to the Section L: Energy Sources)

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22 pages, 6503 KiB

Open AccessArticle

Energy Consumption Optimization and User Comfort Management in Residential Buildings Using a Bat Algorithm and Fuzzy Logic

by Muhammad Fayaz and DoHyeun Kim^*

Department of Computer Engineering, Jeju National University, Jeju City 63243, Korea

Energies 2018, 11(1), 161; https://doi.org/10.3390/en11010161 - 9 Jan 2018

Cited by 58 | Viewed by 5718

Abstract

Energy management in residential buildings has grabbed the attention of many scientists for the last few years due to the fact that the residential sector consumes the highest amount of total energy produced by different energy resources. To manage the energy in residential [...] Read more.

Energy management in residential buildings has grabbed the attention of many scientists for the last few years due to the fact that the residential sector consumes the highest amount of total energy produced by different energy resources. To manage the energy in residential buildings effectively, an efficient energy control system is required, capable of decreasing the total energy consumption without compromising the user-preferred environment inside the building. In the literature, many approaches have been proposed to achieve the goals of minimizing the energy consumption and maximizing the user preferred comfort by keeping different parameters under consideration, but all these methods face some problems in resolving the issue properly. The bat algorithm is one of the most recently introduced optimization approaches that has drawn the attention of researchers to apply it for solving different types of optimization problems. In this paper, the bat algorithm is applied for energy optimization in residential buildings, which is one of the most focused optimization problems in recent years. Three environmental parameters, namely temperature, illumination and air quality are bat algorithm inputs and optimized values of these parameters are the outputs. The error difference between the environmental parameters and optimized parameters are inputs of the fuzzy controllers which give energy as output which in turn change the status of the concerned actuators. It is proven from the experimental results that the proposed approach has been effectively successful in managing the whole energy consumption management system. Full article

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14 pages, 3406 KiB

Open AccessArticle

Energy-Saving Performance of Flap-Adjustment-Based Centrifugal Fan

by Genglin Chen¹, Wei Xu^2,*

, Jinyun Zhao³ and Haipeng Zhang¹

¹ School of Electric Power Engineering, China University of Mining & Technology, Xuzhou 221116, China

² Geodetic Institute, Leibniz University Hanover, 30167 Hanover, Germany

³ Taiyuan Province Heating Power Design Co. Ltd., Taiyuan 030006, China

Energies 2018, 11(1), 162; https://doi.org/10.3390/en11010162 - 9 Jan 2018

Cited by 9 | Viewed by 5230

Abstract

The current paper mainly focuses on finding a more appropriate way to enhance the fan performance at off-design conditions. The centrifugal fan (CF) based on flap-adjustment (FA) has been investigated through theoretical, experimental, and finite element methods. To obtain a more predominant performance [...] Read more.

The current paper mainly focuses on finding a more appropriate way to enhance the fan performance at off-design conditions. The centrifugal fan (CF) based on flap-adjustment (FA) has been investigated through theoretical, experimental, and finite element methods. To obtain a more predominant performance of CF from the different adjustments, we carried out a comparative analysis on FA and leading-adjustment (LA) in aerodynamic performances, which included the adjusted angle of blades, total pressure, efficiency, system-efficiency, adjustment-efficiency, and energy-saving rate. The contribution of this paper is the integrated performance curve of the CF. Finally, the results showed that the effects of FA and LA on economic performance and energy savings of the fan varied with the blade angles. Furthermore, FA was feasible, which is more sensitive than LA. Moreover, the CF with FA offered a more extended flow-range of high economic characteristic in comparison with LA. Finally, when the operation flow-range extends, energy-saving rate of the fan with FA would have improvement. Full article

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25 pages, 3431 KiB

Open AccessArticle

Daily Peak Load Forecasting Based on Complete Ensemble Empirical Mode Decomposition with Adaptive Noise and Support Vector Machine Optimized by Modified Grey Wolf Optimization Algorithm

by Shuyu Dai^*, Dongxiao Niu and Yan Li

School of Economics and Management, North China Electric Power University, Beijing 102206, China

Energies 2018, 11(1), 163; https://doi.org/10.3390/en11010163 - 10 Jan 2018

Cited by 68 | Viewed by 6553

Abstract

Daily peak load forecasting is an important part of power load forecasting. The accuracy of its prediction has great influence on the formulation of power generation plan, power grid dispatching, power grid operation and power supply reliability of power system. Therefore, it is [...] Read more.

Daily peak load forecasting is an important part of power load forecasting. The accuracy of its prediction has great influence on the formulation of power generation plan, power grid dispatching, power grid operation and power supply reliability of power system. Therefore, it is of great significance to construct a suitable model to realize the accurate prediction of the daily peak load. A novel daily peak load forecasting model, CEEMDAN-MGWO-SVM (Complete Ensemble Empirical Mode Decomposition with Adaptive Noise and Support Vector Machine Optimized by Modified Grey Wolf Optimization Algorithm), is proposed in this paper. Firstly, the model uses the complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) algorithm to decompose the daily peak load sequence into multiple sub sequences. Then, the model of modified grey wolf optimization and support vector machine (MGWO-SVM) is adopted to forecast the sub sequences. Finally, the forecasting sequence is reconstructed and the forecasting result is obtained. Using CEEMDAN can realize noise reduction for non-stationary daily peak load sequence, which makes the daily peak load sequence more regular. The model adopts the grey wolf optimization algorithm improved by introducing the population dynamic evolution operator and the nonlinear convergence factor to enhance the global search ability and avoid falling into the local optimum, which can better optimize the parameters of the SVM algorithm for improving the forecasting accuracy of daily peak load. In this paper, three cases are used to test the forecasting accuracy of the CEEMDAN-MGWO-SVM model. We choose the models EEMD-MGWO-SVM (Ensemble Empirical Mode Decomposition and Support Vector Machine Optimized by Modified Grey Wolf Optimization Algorithm), MGWO-SVM (Support Vector Machine Optimized by Modified Grey Wolf Optimization Algorithm), GWO-SVM (Support Vector Machine Optimized by Grey Wolf Optimization Algorithm), SVM (Support Vector Machine) and BP neural network to compare with the CEEMDAN-MGWO-SVM model and analyze the forecasting results of the same sample data. The experimental results fully demonstrate the reliability and effectiveness of the CEEMDAN-MGWO-SVM model proposed in this paper for daily peak load forecasting, which shows the strong generalization ability and robustness of the model. Full article

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12 pages, 1559 KiB

Open AccessArticle

Study of Power Flow in an IPT System Based on Poynting Vector Analysis

by Yuan Liu^* and Aiguo Patrick Hu

Electrical and Computer Engineering, The University of Auckland, Auckland 1023, New Zealand

Energies 2018, 11(1), 165; https://doi.org/10.3390/en11010165 - 10 Jan 2018

Cited by 12 | Viewed by 4181

Abstract

This paper analyzes the power distribution and flow of an inductive power transfer (IPT) system with two coupled coils by using the Poynting vector. The system is modelled with a current source flowing through the primary coil, and a uniformly loaded secondary first, [...] Read more.

This paper analyzes the power distribution and flow of an inductive power transfer (IPT) system with two coupled coils by using the Poynting vector. The system is modelled with a current source flowing through the primary coil, and a uniformly loaded secondary first, then the Poynting vector at an arbitrary point is analyzed by calculating the magnetic and electric fields between and around of the two coils. Both analytical analysis and numerical analysis have been undertaken to show the power distribution, and it has found that power distributes as a donut shape in three-dimensional (3D) space and concentrates along the edges in the proposed two-coil setup, instead of locating coaxially along the center path. Furthermore, power flow across the mid-plane between the two coils is analyzed analytically by the surface integral of the Poynting vector, which is compared with the input power from the primary and the output power to the secondary coil via coupled circuit theory. It has shown that for a lossless IPT system, the power transferred across the mid-plane is equal to the input and output power, which validates the Poynting vector approach. The proposed Poynting vector method provides an effective way to analyze the power distribution in the medium between two coupled coils, which cannot be achieved by traditional lumped circuit theories. Full article

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22 pages, 5339 KiB

Open AccessArticle

Exploring Vehicle Level Benefits of Revolutionary Technology Progress via Aircraft Design and Optimization

by Yaolong Liu^1,*

, Ali Elham², Peter Horst² and Martin Hepperle³

¹ Aeronautics Research Centre Niedersachsen (NFL), Technische Universität Braunschweig, Hermann-Blenk-Straße 42, 38108 Braunschweig, Germany

² Institute of Aircraft Design and Lightweight Structures, Technische Universität Braunschweig, Hermann-Blenk-Straße 35, 38108 Braunschweig, Germany

³ Institute of Aerodynamics and Flow Technology, German Aerospace Center, Lilienthalplatz 7, 38108 Braunschweig, Germany

Energies 2018, 11(1), 166; https://doi.org/10.3390/en11010166 - 10 Jan 2018

Cited by 40 | Viewed by 6510

Abstract

It is always a strong motivation for aeronautic researchers and engineers to reduce the aircraft emissions or even to achieve emission-free air transport. In this paper, the impacts of different game-changing technologies together on the reduction of aircraft fuel consumption and emissions are [...] Read more.

It is always a strong motivation for aeronautic researchers and engineers to reduce the aircraft emissions or even to achieve emission-free air transport. In this paper, the impacts of different game-changing technologies together on the reduction of aircraft fuel consumption and emissions are studied. In particular, a general tool has been developed for the technology assessment, integration and also for the overall aircraft multidisciplinary design optimization. The validity and robustness of the tool has been verified through comparative and sensitivity studies. The overall aircraft level technology assessment and optimization showed that promising fuel efficiency improvements are possible. Though, additional strategies are required to reach the aviation emission reduction goals for short and medium range configurations. Full article

(This article belongs to the Special Issue Towards a Transformation to Sustainable Aviation Systems)

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21 pages, 17649 KiB

Open AccessArticle

Laboratory Investigation of Flow Paths in 3D Self-Affine Fractures with Lattice Boltzmann Simulations

by Jiawei Li^1,*, Claudia Cherubini^1,2, Sergio Andres Galindo Torres^1,3, Zi Li¹, Nicola Pastore⁴ and Ling Li¹

¹ School of Civil Engineering, University of Queensland, St Lucia, Brisbane 4072, Australia

² Department of Physics and Earth Sciences, University of Ferrara, via Saragat, 1-44122 Ferrara, Italy

³ Department of Civil Engineering and Industrial Design, University of Liverpool, Liverpool L69 3BX, UK

⁴ DICATECh—Politecnico di Bari, via E. Orabona, 70125 Bari, Italy

Energies 2018, 11(1), 168; https://doi.org/10.3390/en11010168 - 10 Jan 2018

Cited by 8 | Viewed by 4953

Abstract

In this study, laboratory experiments and simulations have been conducted to investigate single water phase flow through self-affine rough fractures. It is the first time that 3D printing technology is proposed for the application of generating self-affine rough fractures. The experimental setup was [...] Read more.

In this study, laboratory experiments and simulations have been conducted to investigate single water phase flow through self-affine rough fractures. It is the first time that 3D printing technology is proposed for the application of generating self-affine rough fractures. The experimental setup was designed to measure the water volume by dividing the discharging surface into five sections with equal distances under constant injection flow rates. Water flow through self-affine rough fractures was simulated numerically by using the Lattice Boltzmann method (LBM). An agreement between the experimental data and the numerical simulation results was achieved. The fractal dimension is positively correlated to fracture surface roughness and the fracture inclination represents the gravity force acting on the water flow. The influences of fracture inclinations, fractal dimensions, and mismatch wavelengths were studied and analyzed, with an emphasis on flow paths through a self-affine rough fracture. Different values of fractal dimensions, fracture inclinations, and mismatch wavelengths result in small changes of flow rates from five sections of discharging surface. However, the section of discharging surface with the largest flow rate remains constant. In addition, it is found that the gravity force can affect flow paths. Combined with the experimental data, the simulation results are used to explain the preferential flow paths through fracture rough surfaces from a new perspective. The results may enhance our understanding of fluid flow through fractures and provide a solid background for further research in the areas of energy exploration and production. Full article

(This article belongs to the Special Issue Flow and Transport Properties of Unconventional Reservoirs)

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22 pages, 10778 KiB

Open AccessArticle

State-Space Approximation of Convolution Term in Time Domain Analysis of a Raft-Type Wave Energy Converter

by Changhai Liu

, Qingjun Yang^* and Gang Bao

Department of Fluid Control and Automation, Harbin Institute of Technology, Harbin 150001, China

Energies 2018, 11(1), 169; https://doi.org/10.3390/en11010169 - 10 Jan 2018

Cited by 10 | Viewed by 4844

Abstract

Two methods, frequency domain analysis and time domain analysis, are widely applied to modeling wave energy converters (WECs). Frequency domain analysis can evaluate the performance of WECs quickly and efficiently, while it refers to a linear model. When it comes to investigations on [...] Read more.

Two methods, frequency domain analysis and time domain analysis, are widely applied to modeling wave energy converters (WECs). Frequency domain analysis can evaluate the performance of WECs quickly and efficiently, while it refers to a linear model. When it comes to investigations on nonlinear characteristics of the power take-off (PTO) unit of WECs or control for improving the WECs’ performance, time domain analysis based on a state-space approximation for the convolution term is more desirable. In this paper, a state-space approximation of the convolution term in a time domain analysis of a raft-type WEC consisting of two rafts and a PTO unit is presented. The state-space model is identified through regression in the frequency domain. Verification of such a type of time domain analysis is conducted by comparison of its simulation results with those calculated by using a frequency domain analysis, and there is a good agreement. Finally, the effects of PTO parameters, wave frequency, surge and heave motions of the joint, and quadratic damping PTO on the power capture ability of the raft-type WEC are investigated. Full article

(This article belongs to the Special Issue Wave Energy Potential, Behavior and Extraction)

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16 pages, 5730 KiB

Open AccessArticle

Hydration of Magnesium Carbonate in a Thermal Energy Storage Process and Its Heating Application Design

by Rickard Erlund^* and Ron Zevenhoven

Thermal and Flow Engineering Laboratory, Åbo Akademi University, 20900 Turku, Finland

Energies 2018, 11(1), 170; https://doi.org/10.3390/en11010170 - 11 Jan 2018

Cited by 11 | Viewed by 6353

Abstract

First ideas of applications design using magnesium (hydro) carbonates mixed with silica gel for day/night and seasonal thermal energy storage are presented. The application implies using solar (or another) heat source for heating up the thermal energy storage (dehydration) unit during daytime or [...] Read more.

First ideas of applications design using magnesium (hydro) carbonates mixed with silica gel for day/night and seasonal thermal energy storage are presented. The application implies using solar (or another) heat source for heating up the thermal energy storage (dehydration) unit during daytime or summertime, of which energy can be discharged (hydration) during night-time or winter. The applications can be used in small houses or bigger buildings. Experimental data are presented, determining and analysing kinetics and operating temperatures for the applications. In this paper the focus is on the hydration part of the process, which is the more challenging part, considering conversion and kinetics. Various operating temperatures for both the reactor and the water (storage) tank are tested and the favourable temperatures are presented and discussed. Applications both using ground heat for water vapour generation and using water vapour from indoor air are presented. The thermal energy storage system with mixed nesquehonite (NQ) and silica gel (SG) can use both low (25–50%) and high (75%) relative humidity (RH) air for hydration. The hydration at 40% RH gives a thermal storage capacity of 0.32 MJ/kg while 75% RH gives a capacity of 0.68 MJ/kg. Full article

(This article belongs to the Special Issue Selected Papers from ECOS 2017—30th International Conference on Efficiency, Cost, Optimisation, Simulation and Environmental Impact of Energy Systems)

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19 pages, 14810 KiB

Open AccessArticle

Fault-Tolerant Control for a Flexible Group Battery Energy Storage System Based on Cascaded Multilevel Converters

by Junhong Song^1,2

, Weige Zhang^1,2, Hui Liang^1,2,*, Jiuchun Jiang^1,2 and Wensong Yu³

¹ National Active Distribution Network Technology Research Center (NANTEC), Beijing Jiaotong University, Beijing 100044, China

² Collaborative Innovation Center of Electric Vehicles in Beijing, Beijing Jiaotong University, Beijing 100044, China

³ FREEDM System Center, North Carolina State University, Raleigh, NC 27606, USA

Energies 2018, 11(1), 171; https://doi.org/10.3390/en11010171 - 11 Jan 2018

Cited by 9 | Viewed by 3674

Abstract

A flexible group battery energy storage system (FGBESS) based on cascaded multilevel converters is attractive for renewable power generation applications because of its high modularity and high power quality. However, reliability is one of the most important issues and the system may suffer [...] Read more.

A flexible group battery energy storage system (FGBESS) based on cascaded multilevel converters is attractive for renewable power generation applications because of its high modularity and high power quality. However, reliability is one of the most important issues and the system may suffer from great financial loss after fault occurs. In this paper, based on conventional fundamental phase shift compensation and third harmonic injection, a hybrid compensation fault-tolerant method is proposed to improve the post-fault performance in the FGBESS. By adjusting initial phase offset and amplitude of injected component, the optimal third harmonic injection is generated in an asymmetric system under each faulty operation. Meanwhile, the optimal redundancy solution under each fault condition is also elaborated comprehensively with a comparison of the presented three fault-tolerant strategies. This takes full advantage of battery utilization and minimizes the loss of energy capacity. Finally, the effectiveness and feasibility of the proposed methods are verified by results obtained from simulations and a 10 kW experimental platform. Full article

(This article belongs to the Special Issue Power Electronics for Energy Storage)

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18 pages, 4463 KiB

Open AccessArticle

Investigation of a Novel Coaxial Power-Split Hybrid Powertrain for Mining Trucks

by Weiwei Yang¹

, Jiejunyi Liang^2,*

, Jue Yang¹ and Nong Zhang²

¹ School of Mechanical Engineering, University of Science and Technology Beijing, Beijing 100083, China

² Faculty of Engineering and IT, University of Technology Sydney, 15 Broadway, Ultimo NSW 2007, Australia

Energies 2018, 11(1), 172; https://doi.org/10.3390/en11010172 - 11 Jan 2018

Cited by 20 | Viewed by 5018

Abstract

Due to the different working conditions and specification requirements of mining trucks when compared to commercial passenger vehicles, better fuel efficiency of mining trucks could lead to more significant economic benefits. Therefore, investigating a hybrid transmission system becomes essential. A coaxial power-split hybrid [...] Read more.

Due to the different working conditions and specification requirements of mining trucks when compared to commercial passenger vehicles, better fuel efficiency of mining trucks could lead to more significant economic benefits. Therefore, investigating a hybrid transmission system becomes essential. A coaxial power-split hybrid powertrain system for mining trucks is presented in this paper. The system is characterized as comprising an engine, a generator (MG1), a motor (MC2), two sets of planetary gears, and a clutch (CL1). There are six primary operation modes for the hybrid system including the electric motor mode, the engine mode, the hybrid electric mode, the hybrid and assist mode, the regenerative mode, and the stationary charging mode. The mathematical model of the coaxial power-split hybrid system is established according to the requirements of vehicle dynamic performance and fuel economy performance in a given driving cycle. A hybrid vehicle model based on a rule-based control strategy is established to evaluate the fuel economy. Compared with the Toyota Hybrid System (THS) and the conventional mechanical vehicle system using a diesel engine, the simulation results based on an enterprise project indicate that the proposed hybrid system can enhance the vehicle’s fuel economy by 8.21% and 22.45%, respectively, during the given mining driving cycle. The simulation results can be used as a reference to study the feasibility of the proposed coaxial hybrid system whose full potential needs to be further investigated by adopting non-causal control strategies. Full article

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25 pages, 9398 KiB

Open AccessArticle

Optimal Control of Wind Farms for Coordinated TSO-DSO Reactive Power Management

by David Sebastian Stock^1,*, Francesco Sala^1,2, Alberto Berizzi² and Lutz Hofmann^1,3

¹ Division Energy Economy and Grid Operation, Fraunhofer Institute for Wind Energy and Energy System Technology (IWES), 34119 Kassel, Germany

² Energy Department, Politecnico di Milano, 20133 Milano, Italy

³ Institute of Electric Power Systems, Leibniz Universität Hannover, 30167 Hannover, Germany

Energies 2018, 11(1), 173; https://doi.org/10.3390/en11010173 - 11 Jan 2018

Cited by 33 | Viewed by 7265

Abstract

The growing importance of renewable generation connected to distribution grids requires an increased coordination between transmission system operators (TSOs) and distribution system operators (DSOs) for reactive power management. This work proposes a practical and effective interaction method based on sequential optimizations to evaluate [...] Read more.

The growing importance of renewable generation connected to distribution grids requires an increased coordination between transmission system operators (TSOs) and distribution system operators (DSOs) for reactive power management. This work proposes a practical and effective interaction method based on sequential optimizations to evaluate the reactive flexibility potential of distribution networks and to dispatch them along with traditional synchronous generators, keeping to a minimum the information exchange. A modular optimal power flow (OPF) tool featuring multi-objective optimization is developed for this purpose. The proposed method is evaluated for a model of a real German 110 kV grid with 1.6 GW of installed wind power capacity and a reduced order model of the surrounding transmission system. Simulations show the benefit of involving wind farms in reactive power support reducing losses both at distribution and transmission level. Different types of setpoints are investigated, showing the feasibility for the DSO to fulfill also individual voltage and reactive power targets over multiple connection points. Finally, some suggestions are presented to achieve a fair coordination, combining both TSO and DSO requirements. Full article

(This article belongs to the Special Issue Wind Generators Modelling and Control)

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16 pages, 3293 KiB

Open AccessArticle

Study on the Low-Temperature Oxidation Law in the Co-Mining Face of Coal and Oil Shale in a Goaf—A Case Study in the Liangjia Coal Mine, China

by Gang Wang^1,2,3,*, Yue Wang², Lulu Sun², Xiang Song², Qiqi Liu², Hao Xu² and Wenzhou Du²

¹ Mine Disaster Prevention and Control-Ministry of State Key Laboratory Breeding Base, Shandong University of Science and Technology, Qingdao 266590, China

² College of Mining and Safety Engineering, Shandong University of Science and Technology, Qingdao 266590, China

³ Hebei State Key Laboratory of Mine Disaster Prevention, North China Institute of Science and Technology, Beijing 101601, China

Energies 2018, 11(1), 174; https://doi.org/10.3390/en11010174 - 11 Jan 2018

Cited by 21 | Viewed by 3700

Abstract

The low-temperature oxidation law of coal and rock mass is the basis to study spontaneous combustion in goafs. In this paper, the low-temperature oxidation laws of coal, oil shale, and mixtures of coal and oil shale were studied by using laboratory programmed heating [...] Read more.

The low-temperature oxidation law of coal and rock mass is the basis to study spontaneous combustion in goafs. In this paper, the low-temperature oxidation laws of coal, oil shale, and mixtures of coal and oil shale were studied by using laboratory programmed heating experiments combined with a field beam tube monitoring system. The results from the programmed heating experiments showed that the heat released from oil shale was less than that from coal. Coal had a lower carbon monoxide (CO)-producing temperature than oil shale, and the mixture showed obvious inhibiting effects on CO production with an average CO concentration of about 38% of that for coal. Index gases were selected in different stages to determine the critical turning point temperature for each stage. The field beam tube monitoring system showed that the temperature field of the 1105 co-mining face of coal and oil shale in the goaf of the Liangjia Coal Mine presented a ladder-like distribution, and CO concentration was the highest for coal and lower for the mixture of coal and oil shale, indicating that the mixture of coal with oil shale had an inhibiting effect on CO production, consistent with the results from the programmed heating experiments. Full article

(This article belongs to the Section L: Energy Sources)

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18 pages, 9101 KiB

Open AccessArticle

Coal Matrix Deformation and Pore Structure Change in High-Pressure Nitrogen Replacement of Methane

by Xiaofeng Ji¹

, Dangyu Song^1,2,*, Xiaoming Ni^2,3, Yunbo Li^1,2 and Haotian Zhao¹

¹ Institute of Resources and Environment, Henan Polytechnic University, Jiaozuo 454000, China

² Collaborative Innovation Center of Coalbed Methane and Shale Gas for Central Plains Economic Region, Jiaozuo 454000, China

³ School of Energy Science and Engineering, Henan Polytechnic University, Jiaozuo 454000, China

Energies 2018, 11(1), 175; https://doi.org/10.3390/en11010175 - 11 Jan 2018

Cited by 11 | Viewed by 3410

Abstract

Coal matrix deformation is one of the main controlling factors for coal reservoir permeability changes in nitrogen foam fracturing. The characteristics and mechanism of coal matrix deformation during the process of adsorption/desorption were studied by isothermal adsorption/desorption experiments with methane and nitrogen. Based [...] Read more.

Coal matrix deformation is one of the main controlling factors for coal reservoir permeability changes in nitrogen foam fracturing. The characteristics and mechanism of coal matrix deformation during the process of adsorption/desorption were studied by isothermal adsorption/desorption experiments with methane and nitrogen. Based on the free-energy theories, the Langmuir equation, and elastic mechanics, mathematical models of coal matrix deformation were developed and the deformation characteristics in adsorption/desorption processes were examined. From the study, we deduced that the coal matrix swelling, caused by methane adsorption, was a Langmuir-type relationship with the gas pressure, and exponentially increased as the adsorption quantity increased. Then, the deformation rate and amplitude of the coal matrix decreased gradually with the increase of the pressure. At the following stage, where nitrogen replaces methane, the coal matrix swelling continued but the deformation amplitude decreased, which was only 19.60% of the methane adsorption stage. At the mixed gas desorption stage, the coal matrix shrank with the reduction of pressure and the shrinkage amount changed logarithmically with the pressure, which had the hysteresis effect when compared with the swelling in adsorption. The mechanism of coal matrix deformation was discussed through a comparison of the change of micropores, mesopores, and also part macropores in the adsorption process. Full article

(This article belongs to the Section L: Energy Sources)

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23 pages, 9345 KiB

Open AccessArticle

Characterisation of Tidal Flows at the European Marine Energy Centre in the Absence of Ocean Waves

by Brian G. Sellar^*

, Gareth Wakelam

, Duncan R. J. Sutherland, David M. Ingram

and Vengatesan Venugopal

School of Engineering, Institute for Energy Systems, The University of Edinburgh, Edinburgh EH9 3DW, UK

Energies 2018, 11(1), 176; https://doi.org/10.3390/en11010176 - 11 Jan 2018

Cited by 67 | Viewed by 6328

Abstract

The data analyses and results presented here are based on the field measurement campaign of the Reliable Data Acquisition Platform for Tidal (ReDAPT) project (Energy Technologies Institute (ETI), U.K. 2010–2015). During ReDAPT, a 1 MW commercial prototype tidal turbine was deployed and operated [...] Read more.

The data analyses and results presented here are based on the field measurement campaign of the Reliable Data Acquisition Platform for Tidal (ReDAPT) project (Energy Technologies Institute (ETI), U.K. 2010–2015). During ReDAPT, a 1 MW commercial prototype tidal turbine was deployed and operated at the Fall of Warness tidal test site within the European Marine Energy Centre (EMEC), Orkney, U.K. Mean flow speeds and Turbulence Intensity (TI) at multiple positions proximal to the machine are considered. Through the implemented wave identification techniques, the dataset can be filtered into conditions where the effects of waves are present or absent. Due to the volume of results, only flow conditions in the absence of waves are reported here. The analysis shows that TI and mean flows are found to vary considerably between flood and ebb tides whilst exhibiting sensitivity to the tidal phase and to the specification of spatial averaging and velocity binning. The principal measurement technique was acoustic Doppler profiling provided by seabed-mounted Diverging-beam Acoustic Doppler Profilers (D-ADP) together with remotely-operable Single-Beam Acoustic Doppler Profilers (SB-ADP) installed at mid-depth on the tidal turbine. This novel configuration allows inter-instrument comparisons, which were conducted. Turbulence intensity averaged over the rotor extents of the ReDAPT turbine for flood tides vary between 16.7% at flow speeds above 0.3 m/s and 11.7% when considering only flow speeds in the turbine operating speed range, which reduces to 10.9% (6.8% relative reduction) following the implementation of noise correction techniques. Equivalent values for ebb tides are 14.7%, 10.1% and 9.3% (7.9% relative reduction). For flood and ebb tides, TI values resulting from noise correction are reduced in absolute terms by 3% and 2% respectively across a wide velocity range and approximately 1% for turbine operating speeds. Through comparison with SB-ADP-derived mid-depth TI values, this correction is shown to be conservative since uncorrected SB-ADP results remain, in relative terms, between 10% and 21% below corrected D-ADP values depending on tidal direction and the range of velocities considered. Results derived from other regions of the water column, those important to floating turbine devices for example, are reported for comparison. Full article

(This article belongs to the Special Issue Marine Energy)

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32 pages, 6144 KiB

Open AccessEditor’s ChoiceArticle

Dynamic Strategies for Yaw and Induction Control of Wind Farms Based on Large-Eddy Simulation and Optimization

by Wim Munters^*

and Johan Meyers

Department of Mechanical Engineering, KU Leuven, Celestijnenlaan 300A, 3001 Leuven, Belgium

Energies 2018, 11(1), 177; https://doi.org/10.3390/en11010177 - 11 Jan 2018

Cited by 122 | Viewed by 7884

Abstract

In wind farms, wakes originating from upstream turbines cause reduced energy extraction and increased loading variability in downstream rows. The prospect of mitigating these detrimental effects through coordinated controllers at the wind-farm level has fueled a multitude of research efforts in wind-farm control. [...] Read more.

In wind farms, wakes originating from upstream turbines cause reduced energy extraction and increased loading variability in downstream rows. The prospect of mitigating these detrimental effects through coordinated controllers at the wind-farm level has fueled a multitude of research efforts in wind-farm control. The main strategies in wind-farm control are to influence the velocity deficits in the wake by deviating from locally optimal axial induction setpoints on the one hand, and steering wakes away from downstream rows through yaw misalignment on the other hand. The current work investigates dynamic induction and yaw control of individual turbines for wind-farm power maximization in large-eddy simulations. To this end, receding-horizon optimal control techniques combined with continuous adjoint gradient evaluations are used. We study a 4 × 4 aligned wind farm, and find that for this farm layout yaw control is more effective than induction control, both for uniform and turbulent inflow conditions. Analysis of optimal yaw controls leads to the definition of two simplified yaw control strategies, in which wake meandering and wake redirection are exploited respectively. Furthermore it is found that dynamic yawing provides significant benefits over static yaw control in turbulent flow environments, whereas this is not the case for uniform inflow. Finally, the potential of combining overinductive axial induction control with yaw control is shown, with power gains that approximate the sum of those achieved by each control strategy separately. Full article

(This article belongs to the Special Issue Wind Turbine Loads and Wind Plant Performance)

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25 pages, 2509 KiB

Open AccessArticle

Impact of Electric Vehicle Charging Station Load on Distribution Network

by Sanchari Deb^1,*, Kari Tammi^2,*

, Karuna Kalita³

and Pinakeshwar Mahanta³

¹ Centre for Energy, Indian Institute of Technology, Guwahati 781039, Assam, India

² Department of Mechanical Engineering, Aalto University, 02150 Espoo, Finland

³ Department of Mechanical Engineering, Indian Institute of Technology, Guwahati 781039, Assam, India

Energies 2018, 11(1), 178; https://doi.org/10.3390/en11010178 - 15 Jan 2018

Cited by 314 | Viewed by 17337

Abstract

Recent concerns about environmental pollution and escalating energy consumption accompanied by the advancements in battery technology have initiated the electrification of the transportation sector. With the universal resurgence of Electric Vehicles (EVs) the adverse impact of the EV charging loads on the operating [...] Read more.

Recent concerns about environmental pollution and escalating energy consumption accompanied by the advancements in battery technology have initiated the electrification of the transportation sector. With the universal resurgence of Electric Vehicles (EVs) the adverse impact of the EV charging loads on the operating parameters of the power system has been noticed. The detrimental impact of EV charging station loads on the electricity distribution network cannot be neglected. The high charging loads of the fast charging stations results in increased peak load demand, reduced reserve margins, voltage instability, and reliability problems. Further, the penalty paid by the utility for the degrading performance of the power system cannot be neglected. This work aims to investigate the impact of the EV charging station loads on the voltage stability, power losses, reliability indices, as well as economic losses of the distribution network. The entire analysis is performed on the IEEE 33 bus test system representing a standard radial distribution network for six different cases of EV charging station placement. It is observed that the system can withstand placement of fast charging stations at the strong buses up to a certain level, but the placement of fast charging stations at the weak buses of the system hampers the smooth operation of the power system. Further, a strategy for the placement of the EV charging stations on the distribution network is proposed based on a novel Voltage stability, Reliability, and Power loss (VRP) index. The results obtained indicate the efficacy of the VRP index. Full article

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21 pages, 1790 KiB

Open AccessArticle

Design Considerations for the Electrical Power Supply of Future Civil Aircraft with Active High-Lift Systems

by J.-K. Mueller^1,*,†, A. Bensmann^2,*,†, B. Bensmann^2,†, T. Fischer^3,†, T. Kadyk^4,†

, G. Narjes^1,†

, F. Kauth^3,†, B. Ponick¹, J. R. Seume³, U. Krewer⁴

, R. Hanke-Rauschenbach² and A. Mertens¹

¹ Institute for Drive Systems and Power Electronics, Leibniz Universität Hannover, 30167 Hannover, Germany

² Institute of Electric Power Systems, Leibniz Universität Hannover, 30167 Hannover, Germany

³ Institute of Turbomachinery and Fluid Dynamics, Leibniz Universität Hannover, 30167 Hannover, Germany

⁴ Institute of Energy and Systems Engineering, TU Braunschweig, 38106 Braunschweig, Germany

^† These authors contributed equally to this work.

Energies 2018, 11(1), 179; https://doi.org/10.3390/en11010179 - 11 Jan 2018

Cited by 16 | Viewed by 7183

Abstract

Active high-lift systems of future civil aircraft allow noise reduction and the use of shorter runways. Powering high-lift systems electrically have a strong impact on the design requirements for the electrical power supply of the aircraft. The active high-lift system of the reference [...] Read more.

Active high-lift systems of future civil aircraft allow noise reduction and the use of shorter runways. Powering high-lift systems electrically have a strong impact on the design requirements for the electrical power supply of the aircraft. The active high-lift system of the reference aircraft design considered in this paper consists of a flexible leading-edge device together with a combination of boundary-layer suction and Coanda-jet blowing. Electrically driven compressors distributed along the aircraft wings provide the required mass flow of pressurized air. Their additional loads significantly increase the electric power demand during take-off and landing, which is commonly provided by electric generators attached to the aircraft engines. The focus of the present study is a feasibility assessment of alternative electric power supply concepts to unburden or eliminate the generator coupled to the aircraft engine. For this purpose, two different concepts using either fuel cells or batteries are outlined and evaluated in terms of weight, efficiency, and technology availability. The most promising, but least developed alternative to the engine-powered electric generator is the usage of fuel cells. The advantages are high power density and short refueling time, compared to the battery storage concept. Full article

(This article belongs to the Special Issue Towards a Transformation to Sustainable Aviation Systems)

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18 pages, 13901 KiB

Open AccessArticle

Performance Estimation and Fault Diagnosis Based on Levenberg–Marquardt Algorithm for a Turbofan Engine

by Junjie Lu, Feng Lu

and Jinquan Huang^*

Jiangsu Province Key Laboratory Power Systems, College of Energy and Power Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

Energies 2018, 11(1), 181; https://doi.org/10.3390/en11010181 - 12 Jan 2018

Cited by 11 | Viewed by 3966

Abstract

Establishing the schemes of accurate and computationally efficient performance estimation and fault diagnosis for turbofan engines has become a new research focus and challenges. It is able to increase reliability and stability of turbofan engine and reduce the life cycle costs. Accurate estimation [...] Read more.

Establishing the schemes of accurate and computationally efficient performance estimation and fault diagnosis for turbofan engines has become a new research focus and challenges. It is able to increase reliability and stability of turbofan engine and reduce the life cycle costs. Accurate estimation of turbofan engine performance counts on thoroughly understanding the components’ performance, which is described by component characteristic maps and the fault of each component can be regarded as the change of characteristic maps. In this paper, a novel method based on a Levenberg–Marquardt (LM) algorithm is proposed to enhance the fidelity of the performance estimation and the credibility of the fault diagnosis for the turbofan engine. The presented method utilizes the LM algorithm to figure out the operating point in the characteristic maps, preparing for performance estimation and fault diagnosis. The accuracy of the proposed method is evaluated for estimating performance parameters in the transient case with Rayleigh process noise and Gaussian measurement noise. The comparison among the extended Kalman filter (EKF) method, the particle filter (PF) method and the proposed method is implemented in the abrupt fault case and the gradual degeneration case and it has been shown that the proposed method has the capability to lead to more accurate result for performance estimation and fault diagnosis of turbofan engine than current popular EKF and PF diagnosis methods. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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16 pages, 1489 KiB

Open AccessArticle

Real-Power Rescheduling of Generators for Congestion Management Using a Novel Satin Bowerbird Optimization Algorithm

by Jagadeeswar Reddy Chintam^* and Mary Daniel

Electrical and Electronics Engineering, Government College of Technology, Coimbatore, Tamilnadu 641013, India

Energies 2018, 11(1), 183; https://doi.org/10.3390/en11010183 - 12 Jan 2018

Cited by 52 | Viewed by 3866

Abstract

In this paper, an efficient meta-heuristic satin bowerbird optimization (SBO) algorithm is presented for congestion management (CM) in the deregulated power system. The main objective of CM is to relieve congestion in the transmission lines using a generation rescheduling-based approach, while satisfying all [...] Read more.

In this paper, an efficient meta-heuristic satin bowerbird optimization (SBO) algorithm is presented for congestion management (CM) in the deregulated power system. The main objective of CM is to relieve congestion in the transmission lines using a generation rescheduling-based approach, while satisfying all the constraints with minimum congestion cost. The SBO is a nature-inspired algorithm, developed based on the ‘male-attracts-the-female for breeding’ principle of the specialized stick structure mechanism of satin birds. The proposed approach is effectively tested on small and large test systems, namely, modified IEEE 30-bus, modified IEEE 57-bus, and IEEE 118-bus test systems. The constraints like line loading, line limits, generator limits, and bus voltage impact, etc., are incorporated into this study. The proposed technique gives superior results with regards to congestion cost and losses compared with various recent optimization algorithms. Full article

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17 pages, 4136 KiB

Open AccessArticle

Time-Section Fusion Pattern Classification Based Day-Ahead Solar Irradiance Ensemble Forecasting Model Using Mutual Iterative Optimization

by Fei Wang^1,2,*

, Zhao Zhen¹, Chun Liu³, Zengqiang Mi¹, Miadreza Shafie-khah⁴

and João P. S. Catalão^4,5,6,*

¹ State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University, Baoding 071003, China

² Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA

³ State Key Laboratory of Operation and Control of Renewable Energy & Storage Systems, China Electric Power Research Institute, Beijing 100192, China

⁴ C-MAST, University of Beira Interior, 6201-001 Covilhã, Portugal

⁵ INESC TEC, Faculty of Engineering of the University of Porto, 4200-465 Porto, Portugal

⁶ INESC-ID, Instituto Superior Técnico, University of Lisbon, 1049-001 Lisbon, Portugal

Energies 2018, 11(1), 184; https://doi.org/10.3390/en11010184 - 12 Jan 2018

Cited by 15 | Viewed by 4208

Abstract

Accurate solar PV power forecasting can provide expected future PV output power so as to help the system operator to dispatch traditional power plants to maintain the balance between supply and demand sides. However, under non-stationary weather conditions, such as cloudy or partly [...] Read more.

Accurate solar PV power forecasting can provide expected future PV output power so as to help the system operator to dispatch traditional power plants to maintain the balance between supply and demand sides. However, under non-stationary weather conditions, such as cloudy or partly cloudy days, the variability of solar irradiance makes the accurate PV power forecasting a very hard task. Ensemble forecasting based on multiple models established by different theory has been proved as an effective means on improving forecasting accuracy. Classification modeling according to different patterns could reduce the complexity and difficulty of intro-class data fitting so as to improve the forecasting accuracy as well. When combining the two above points and focusing on the different fusion pattern specifically in terms of hourly time dimension, a time-section fusion pattern classification based day-ahead solar irradiance ensemble forecasting model using mutual iterative optimization is proposed, which contains multiple forecasting models based on wavelet decomposition (WD), fusion pattern classification model, and fusion models corresponding to each fusion pattern. First, the solar irradiance is forecasted using WD based models at different WD level. Second, the fusion pattern classification recognition model is trained and then applied to recognize the different fusion pattern at each hourly time section. At last, the final forecasting result is obtained using the optimal fusion model corresponding to the data fusion pattern. In addition, a mutual iterative optimization framework for the pattern classification and data fusion models is also proposed to improve the model’s performance. Simulations show that the mutual iterative optimization framework can effectively enhance the performance and coordination of pattern classification and data fusion models. The accuracy of the proposed solar irradiance day-ahead ensemble forecasting model is verified when compared with a standard Artificial Neural Network (ANN) forecasting model, five WD based models and a single ensemble forecasting model without time-section fusion classification. Full article

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19 pages, 1662 KiB

Open AccessArticle

Feature Reduction for Power System Transient Stability Assessment Based on Neighborhood Rough Set and Discernibility Matrix

by Bingyang Li

, Jianmei Xiao and Xihuai Wang^*

Department of Electrical Engineering, Shanghai Maritime University, Shanghai 201306, China

Energies 2018, 11(1), 185; https://doi.org/10.3390/en11010185 - 12 Jan 2018

Cited by 15 | Viewed by 3138

Abstract

In machine learning-based transient stability assessment (TSA) problems, the characteristics of the selected features have a significant impact on the performance of classifiers. Due to the high dimensionality of TSA problems, redundancies usually exist in the original feature space, which will deteriorate the [...] Read more.

In machine learning-based transient stability assessment (TSA) problems, the characteristics of the selected features have a significant impact on the performance of classifiers. Due to the high dimensionality of TSA problems, redundancies usually exist in the original feature space, which will deteriorate the performance of classification. To effectively eliminate redundancies and obtain the optimal feature set, a new feature reduction method based on neighborhood rough set and discernibility matrix is proposed in this paper. First, 32 features are selected to structure the initial feature set based on system principle. An evaluation index based on neighborhood rough set theory is used to characterize the separability of classification problems in the specified feature space. By constructing the discernibility matrix of input features, a feature selection strategy is designed to find the optimal feature set. Finally, comparative experiments based on the proposed feature reduction method and several common feature reduction techniques used in TSA are applied to the New England 39 bus system and Australian simplified 14 generators system. The experimental results illustrate the effectiveness of the proposed feature reduction method. Full article

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17 pages, 1848 KiB

Open AccessArticle

Simulation-Based Analysis of the Potential of Alternative Fuels towards Reducing CO₂ Emissions from Aviation

by Karsten Kieckhäfer^1,*

, Gunnar Quante¹, Christoph Müller¹, Thomas Stefan Spengler¹

, Matthias Lossau² and Wolfgang Jonas²

¹ Institute of Automotive Management and Industrial Production, Technische Universität Braunschweig, Mühlenpfordtstr. 23, D-38106 Braunschweig, Germany

² Institute of Transportation Design, Hochschule für Bildende Künste Braunschweig, Johannes-Selenka-Platz 1, D-38118 Braunschweig, Germany

Energies 2018, 11(1), 186; https://doi.org/10.3390/en11010186 - 12 Jan 2018

Cited by 18 | Viewed by 8158

Abstract

The mid-term framework of global aviation is shaped by air travel demand growth rates of 2–5% p.a. and ambitious targets to reduce aviation-related CO₂ emissions by up to 50% until 2050. Alternative jet fuels such as bio- or electrofuels can be considered [...] Read more.

The mid-term framework of global aviation is shaped by air travel demand growth rates of 2–5% p.a. and ambitious targets to reduce aviation-related CO₂ emissions by up to 50% until 2050. Alternative jet fuels such as bio- or electrofuels can be considered as a potential means towards low-emission aviation. While these fuels offer significant emission reduction potential, their market success depends on manifold influencing factors like the maturity of the production technology or the development of the price of conventional jet fuel. To study the potential for adoption of alternative jet fuels in aviation and the extent to which alternative fuels can contribute to the reduction targets, we deploy a System Dynamics approach. The results indicate that the adoption of alternative fuels and therefore their potential towards low-emissions aviation is rather limited in most scenarios considered since current production processes do not allow for competitive prices compared to conventional jet fuel. This calls for the development of new production processes that allow for economic feasibility of converting biomass or hydrogen into drop-in fuels as well as political measures to promote the adoption of alternative fuels. Full article

(This article belongs to the Special Issue Towards a Transformation to Sustainable Aviation Systems)

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18 pages, 7227 KiB

Open AccessArticle

Development and Test Application of an Auxiliary Power-Integrated System

by Hong Zhang^*

, Zhuang Xing, Jiajian Song and Qiangqiang Yang

School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081, China

Energies 2018, 11(1), 187; https://doi.org/10.3390/en11010187 - 12 Jan 2018

Cited by 4 | Viewed by 5451

Abstract

This paper focuses on the design and test technique of an auxiliary power unit (APU) for a range-extended electric vehicle (RE-EV). The APU system is designed to improve RE-EV power and economy; it integrates the power system, generator system, battery system, and APU [...] Read more.

This paper focuses on the design and test technique of an auxiliary power unit (APU) for a range-extended electric vehicle (RE-EV). The APU system is designed to improve RE-EV power and economy; it integrates the power system, generator system, battery system, and APU controller. The parameters of the APU parts are computed and optimized considering the vehicle power demand and the matching characteristic of the engine and generator. The hardware and software systems are developed for the APU-integrated control system. The APU test bench, combined with the displaying part, the control part, and the bench with its accessory, is constructed. Communication connection in the APU system is established by controller area network (CAN) bus. The APU controller outputs a corresponding signal to the engine control unit (ECU) and motor controller. To verify the rationality of the control strategy and the validity of the control logic, the engine speed control and integrated control experiment of the APU system are completed on the test bench. The test results showed that the test control system is reliable and the relevant control logic is in agreement with simulation analysis. The APU-integrated system could be well suited for application in RE-EVs. Full article

(This article belongs to the Special Issue The International Symposium on Electric Vehicles (ISEV2017))

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21 pages, 2445 KiB

Open AccessArticle

A Novel Algorithm for Optimal Operation of Hydrothermal Power Systems under Considering the Constraints in Transmission Networks

by Thang Trung Nguyen¹

, Bach Hoang Dinh², Nguyen Vu Quynh³

, Minh Quan Duong⁴

and Le Van Dai^5,6,*

¹ Power System Optimization Research Group, Faculty of Electrical and Electronics Engineering, Ton Duc Thang University, Ho Chi Minh City 700000, Vietnam

² Faculty of Electrical and Electronics Engineering, Ton Duc Thang University, Ho Chi Minh City 700000, Vietnam

³ Department of Electrical Engineering, Lac Hong University, Bien Hoa 810000, Vietnam

⁴ Department of Electrical Engineering, The University of Da Nang—University of Science and Technology, Danang 550000, Vietnam

⁵ Institute of Research and Development, Duy Tan University, Danang 550000, Vietnam

⁶ Office of Science Research and Development, Lac Hong University, Bien Hoa 810000, Vietnam

Energies 2018, 11(1), 188; https://doi.org/10.3390/en11010188 - 12 Jan 2018

Cited by 10 | Viewed by 3793

Abstract

This paper proposes an effective novel cuckoo search algorithm (ENCSA) in order to enhance the operation capacity of hydrothermal power systems, considering the constraints in the transmission network, and especially to overcome optimal power flow (OPF) problems. This proposed algorithm is developed on [...] Read more.

This paper proposes an effective novel cuckoo search algorithm (ENCSA) in order to enhance the operation capacity of hydrothermal power systems, considering the constraints in the transmission network, and especially to overcome optimal power flow (OPF) problems. This proposed algorithm is developed on the basis of the conventional cuckoo search algorithm (CSA) by two modified techniques: the first is the self-adaptive technique for generating the second new solutions via discovery of alien eggs, and the second is the high-quality solutions based on a selection technique to keep the best solutions among all new and old solutions. These techniques are able to expand the search zone to overcome the local optimum trap and are able to improve the optimal solution quality and convergence speed as well. Therefore, the proposed method has significant impacts on the searching performances. The efficacy of the proposed method is investigated and verified using IEEE 30 and 118 buses systems via numerical simulation. The obtained results are compared with the conventional cuckoo search algorithm (CCSA) and the modified cuckoo search algorithm (MCSA). As a result, the proposed method can overcome the OPF of hydrothermal power systems better than the conventional ones in terms of the optimal solution quality, convergence speed, and high success rate. Full article

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28 pages, 1419 KiB

Open AccessArticle

An Efficient Demand Side Management System with a New Optimized Home Energy Management Controller in Smart Grid

by Hafiz Majid Hussain¹

, Nadeem Javaid^2,*

, Sohail Iqbal³

, Qadeer Ul Hasan²

, Khursheed Aurangzeb⁴

and Musaed Alhussein⁴

¹ Center for Advanced Studies in Engineering (CASE), Islamabad 44000, Pakistan

² COMSATS Institute of Information Technology, Islamabad 44000, Pakistan

³ SEECS, National University of Science and Technology (NUST), Islamabad 44000, Pakistan

⁴ Computer Engineering Department, College of Computer and Information Sciences, King Saud University, Riyadh 11543, Saudi Arabia.

Energies 2018, 11(1), 190; https://doi.org/10.3390/en11010190 - 12 Jan 2018

Cited by 134 | Viewed by 9362

Abstract

The traditional power grid is inadequate to overcome modern day challenges. As the modern era demands the traditional power grid to be more reliable, resilient, and cost-effective, the concept of smart grid evolves and various methods have been developed to overcome these demands [...] Read more.

The traditional power grid is inadequate to overcome modern day challenges. As the modern era demands the traditional power grid to be more reliable, resilient, and cost-effective, the concept of smart grid evolves and various methods have been developed to overcome these demands which make the smart grid superior over the traditional power grid. One of the essential components of the smart grid, home energy management system (HEMS) enhances the energy efficiency of electricity infrastructure in a residential area. In this aspect, we propose an efficient home energy management controller (EHEMC) based on genetic harmony search algorithm (GHSA) to reduce electricity expense, peak to average ratio (PAR), and maximize user comfort. We consider EHEMC for a single home and multiple homes with real-time electricity pricing (RTEP) and critical peak pricing (CPP) tariffs. In particular, for multiple homes, we classify modes of operation for the appliances according to their energy consumption with varying operation time slots. The constrained optimization problem is solved using heuristic algorithms: wind-driven optimization (WDO), harmony search algorithm (HSA), genetic algorithm (GA), and proposed algorithm GHSA. The proposed algorithm GHSA shows higher search efficiency and dynamic capability to attain optimal solutions as compared to existing algorithms. Simulation results also show that the proposed algorithm GHSA outperforms the existing algorithms in terms of reduction in electricity cost, PAR, and maximize user comfort. Full article

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20 pages, 917 KiB

Open AccessArticle

Determination of Cost-Effective Energy Efficiency Measures in Buildings with the Aid of Multiple Indices

by Theodoros Zachariadis^1,*, Apostolos Michopoulos¹, Yannis Vougiouklakis², Katerina Piripitsi³, Christodoulos Ellinopoulos³ and Benjamin Struss⁴

¹ Department of Environmental Science and Technology, Cyprus University of Technology, 3603 Limassol, Cyprus

² Deutsche Gesellschaft für International Zusammenarbeit (GIZ), 10192 Athens, Greece

³ Ministry of Energy, Commerce, Industry and Tourism of the Republic of Cyprus, 1421 Nicosia, Cyprus

⁴ Deutsche Gesellschaft für International Zusammenarbeit (GIZ), 10785 Berlin, Germany

Energies 2018, 11(1), 191; https://doi.org/10.3390/en11010191 - 12 Jan 2018

Cited by 18 | Viewed by 4180

Abstract

Energy refurbishments of buildings can substantially contribute to economy-wide energy efficiency improvements, leading to decarbonisation and additional sustainability benefits. Prioritising the most economically promising investments is not straightforward because apart from cost-effectiveness calculations, several real-world constraints have to be taken into account. This [...] Read more.

Energy refurbishments of buildings can substantially contribute to economy-wide energy efficiency improvements, leading to decarbonisation and additional sustainability benefits. Prioritising the most economically promising investments is not straightforward because apart from cost-effectiveness calculations, several real-world constraints have to be taken into account. This paper describes an approach to assess the economically viable energy efficiency potential in the building sector of the Mediterranean island of Cyprus, with a combination of detailed engineering modelling, cost-effectiveness calculations and real-world considerations of budgetary, technical, behavioural and market constraints. We examine diverse cost-effectiveness indices and come up with a proposal for prioritising specific energy investments such as the installation of heat pumps, insulation of roofs, and replacement of lighting and electronic equipment—without however ignoring other measures that may be economically less favourable but can realistically be implemented in a limited number of buildings. Finally we address the governance of energy efficiency policies, focusing on weaknesses of the current regulatory environment in Cyprus, which can be generalised for many other countries facing similar dilemmas. Full article

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21 pages, 7743 KiB

Open AccessArticle

Design and Experimental Verification of a 72/48 Switched Reluctance Motor for Low-Speed Direct-Drive Mining Applications

by Esmail Elhomdy^1,2, Guofeng Li^1,*, Jiang Liu¹, Syed Abid Bukhari³

and Wen-Ping Cao^1,3

¹ School of Electrical Engineering, Dalian University of Technology, Dalian 116023, China

² Faculty of Engineering, Blue Nile University, Ad-Damazin 26613, Blue Nile State, Sudan

³ School of Engineering and Applied Science, Aston University, Birmingham B4 7ET, UK

Energies 2018, 11(1), 192; https://doi.org/10.3390/en11010192 - 12 Jan 2018

Cited by 18 | Viewed by 5145

Abstract

Typically, a geared drive system is used to connect an induction motor of 1500 rpm with a Raymond Pulverizer of 105 rpm in mining applications. This system suffers from low efficiency and a heavy motor drive. This paper proposes a novel design of [...] Read more.

Typically, a geared drive system is used to connect an induction motor of 1500 rpm with a Raymond Pulverizer of 105 rpm in mining applications. This system suffers from low efficiency and a heavy motor drive. This paper proposes a novel design of a 75 kW, 72/48 switched reluctance motor (SRM) for a low-speed direct-drive as for mining applications. The paper is focused on the design and comparative evaluation of the proposed machine in order to replace a geared drive system whilst providing a high torque low-speed and direct-drive solution. The machine performance is studied and the switching angle configuration of the machine is also optimised. The efficiency of the whole drive system is found to be as high as 90.19%, whereas the geared induction motor drive provides only an efficiency of 59.32% under similar operating conditions. An SRM prototype was built and experimentally tested. Simulation and experimental results show that the drive system has better performance to substitute the induction motor option in mining applications. Full article

(This article belongs to the Special Issue Emerging Power Electronics Technologies for Power Systems and Machine Drives)

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20 pages, 4147 KiB

Open AccessArticle

Stochastic Model Predictive Fault Tolerant Control Based on Conditional Value at Risk for Wind Energy Conversion System

by Yun-Tao Shi, Xiang Xiang^*

, Li Wang, Yuan Zhang and De-Hui Sun

Key Lab of Field Bus and Automation of Beijing, North China University of Technology, Beijing 100144, China

Energies 2018, 11(1), 193; https://doi.org/10.3390/en11010193 - 12 Jan 2018

Cited by 9 | Viewed by 3792

Abstract

Wind energy has been drawing considerable attention in recent years. However, due to the random nature of wind and high failure rate of wind energy conversion systems (WECSs), how to implement fault-tolerant WECS control is becoming a significant issue. This paper addresses the [...] Read more.

Wind energy has been drawing considerable attention in recent years. However, due to the random nature of wind and high failure rate of wind energy conversion systems (WECSs), how to implement fault-tolerant WECS control is becoming a significant issue. This paper addresses the fault-tolerant control problem of a WECS with a probable actuator fault. A new stochastic model predictive control (SMPC) fault-tolerant controller with the Conditional Value at Risk (CVaR) objective function is proposed in this paper. First, the Markov jump linear model is used to describe the WECS dynamics, which are affected by many stochastic factors, like the wind. The Markov jump linear model can precisely model the random WECS properties. Second, the scenario-based SMPC is used as the controller to address the control problem of the WECS. With this controller, all the possible realizations of the disturbance in prediction horizon are enumerated by scenario trees so that an uncertain SMPC problem can be transformed into a deterministic model predictive control (MPC) problem. Finally, the CVaR object function is adopted to improve the fault-tolerant control performance of the SMPC controller. CVaR can provide a balance between the performance and random failure risks of the system. The Min-Max performance index is introduced to compare the fault-tolerant control performance with the proposed controller. The comparison results show that the proposed method has better fault-tolerant control performance. Full article

(This article belongs to the Special Issue Emerging Power Electronics Technologies for Power Systems and Machine Drives)

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17 pages, 5763 KiB

Open AccessArticle

Impact on Congestion and Fuel Consumption of a Cooperative Adaptive Cruise Control System with Lane-Level Position Estimation

by Edgar Talavera^1,*

, Alberto Díaz-Álvarez²

, Felipe Jiménez²

and José E. Naranjo²

¹ Escuela Técnica Superior de Ingeniería de Sistemas Informáticos (ETSISI), Universidad Politécnica de Madrid (UPM), 28031 Madrid, Spain

² University Institute for Automobile Research (INSIA), Universidad Politécnica de Madrid (UPM), 28031 Madrid, Spain

Energies 2018, 11(1), 194; https://doi.org/10.3390/en11010194 - 13 Jan 2018

Cited by 23 | Viewed by 4984

Abstract

In recent years, vehicular communications systems have evolved and allowed for the improvement of adaptive cruise control (ACC) systems to make them cooperative (cooperative adaptive cruise control, CACC). Conventional ACC systems use sensors on the ego-vehicle, such as radar or computer vision, to [...] Read more.

In recent years, vehicular communications systems have evolved and allowed for the improvement of adaptive cruise control (ACC) systems to make them cooperative (cooperative adaptive cruise control, CACC). Conventional ACC systems use sensors on the ego-vehicle, such as radar or computer vision, to generate their behavioral decisions. However, by having vehicle-to-X (V2X) onboard communications, the need to incorporate perception in the vehicle is drastically reduced. Thus, in this paper a CACC solution is proposed that only uses communications to make its decisions with the help of previous road mapping. At the same time, a method to develop these maps is presented, combining the information of a computer vision system to correct the positions obtained from the navigation system. In addition, the cut-in and cut-out maneuvers for a CACC platoon are taken into account, showing the tests of these situations in real environments with instrumented vehicles. To show the potential of the system in a larger-scale implementation, simulations of the behavior are provided under dense traffic conditions where the positive impact on the reduction of traffic congestion and fuel consumption is appreciated. Full article

(This article belongs to the Special Issue Methods to Improve Energy Use in Road Vehicles)

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19 pages, 2493 KiB

Open AccessArticle

Optimal Scheduling of an Regional Integrated Energy System with Energy Storage Systems for Service Regulation

by Hengrui Ma^1,2, Bo Wang^1,*, Wenzhong Gao², Dichen Liu¹, Yong Sun³ and Zhijun Liu³

¹ School of Electrical Engineering, Wuhan University, Wuhan 430072, China

² Department of Electrical and Computer Engineering, University of Denver, Denver, CO 80210, USA

³ State Grid Jilin Province Electric Power Supply Company, Changchun 130021, China

Energies 2018, 11(1), 195; https://doi.org/10.3390/en11010195 - 14 Jan 2018

Cited by 38 | Viewed by 4052

Abstract

Ancillary services are critical to maintaining the safe and stable operation of power systems that contain a high penetration level of renewable energy resources. As a high-quality regulation resource, the regional integrated energy system (RIES) with energy storage system (ESS) can effectively adjust [...] Read more.

Ancillary services are critical to maintaining the safe and stable operation of power systems that contain a high penetration level of renewable energy resources. As a high-quality regulation resource, the regional integrated energy system (RIES) with energy storage system (ESS) can effectively adjust the non-negligible frequency offset caused by the renewable energy integration into the power system, and help solve the problem of power system frequency stability. In this paper, the optimization model aiming at regional integrated energy system as a participant in the regulation market based on pay-for-performance is established. Meanwhile YALMIP + CPLEX is used to simulate and analyze the total operating cost under different dispatch modes. This paper uses the actual operation model of the PJM regulation market to guide the optimal allocation of regulation resource in the regional integrated energy system, and provides a balance between the power trading revenue and regulation market revenue in order to achieve the maximum profit. Full article

(This article belongs to the Section D: Energy Storage and Application)

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25 pages, 8172 KiB

Open AccessEditor’s ChoiceArticle

Optimal Operation of Interdependent Power Systems and Electrified Transportation Networks

by M. Hadi Amini^1,2,*

and Orkun Karabasoglu³

¹ Department of Electrical and Computer Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA

² School of Electronics and Information Technology, Sun Yat-sen University, Guangzhou 510006, China

³ Department of Industrial Engineering, Yasar University, Izmir, 35100, Turkey

Energies 2018, 11(1), 196; https://doi.org/10.3390/en11010196 - 14 Jan 2018

Cited by 75 | Viewed by 7089

Abstract

Electrified transportation and power systems are mutually coupled networks. In this paper, a novel framework is developed for interdependent power and transportation networks. Our approach constitutes solving an iterative least cost vehicle routing process, which utilizes the communication of electrified vehicles (EVs) with [...] Read more.

Electrified transportation and power systems are mutually coupled networks. In this paper, a novel framework is developed for interdependent power and transportation networks. Our approach constitutes solving an iterative least cost vehicle routing process, which utilizes the communication of electrified vehicles (EVs) with competing charging stations, to exchange data such as electricity price, energy demand, and time of arrival. The EV routing problem is solved to minimize the total cost of travel using the Dijkstra algorithm with the input from EVs battery management system, electricity price from charging stations, powertrain component efficiencies and transportation network traffic conditions. Through the bidirectional communication of EVs with competing charging stations, EVs’ charging demand estimation is done much more accurately. Then the optimal power flow problem is solved for the power system, to find the locational marginal price at load buses where charging stations are connected. Finally, the electricity prices were communicated from the charging stations to the EVs, and the loop is closed. Locational electricity price acts as the shared parameter between the two optimization problems, i.e., optimal power flow and optimal routing problem. Electricity price depends on the power demand, which is affected by the charging of EVs. On the other hand, location of EV charging stations and their different pricing strategies might affect the routing decisions of the EVs. Our novel approach that combines the electrified transportation with power system operation, holds tremendous potential for solving electrified transportation issues and reducing energy costs. The effectiveness of the proposed approach is demonstrated using Shanghai transportation network and IEEE 9-bus test system. The results verify the cost-savings for both power system and transportation networks. Full article

(This article belongs to the Special Issue Distribution System Operation and Control)

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17 pages, 5797 KiB

Open AccessArticle

On the Mathematical Modeling of Line-Start Permanent Magnet Synchronous Motors under Static Eccentricity

by Ibrahem Hussein, Zakariya Al-Hamouz^*

, M. A. Abido

and Abdulaziz Milhem

Electrical Engineering Department, King Fahd University of Petroleum and Minerals, Dhahran 34464, Saudi Arabia

Energies 2018, 11(1), 197; https://doi.org/10.3390/en11010197 - 16 Jan 2018

Cited by 4 | Viewed by 6642

Abstract

Line start permanent magnet synchronous motors experience different types of failures, including static eccentricity. The first step in detecting such failures is the mathematical modeling of the motor under healthy and failed conditions. In this paper, an attempt to develop an accurate mathematical [...] Read more.

Line start permanent magnet synchronous motors experience different types of failures, including static eccentricity. The first step in detecting such failures is the mathematical modeling of the motor under healthy and failed conditions. In this paper, an attempt to develop an accurate mathematical model for this motor under static eccentricity is presented. The model is based on the modified winding function method and coupled magnetic circuits approach. The model parameters are calculated directly from the motor winding layout and its geometry. Static eccentricity effects are considered in the motor inductances calculation. The performance of the line start permanent magnet synchronous motor using the developed mathematical model is investigated using MATLAB/SIMULINK^® software (2013b, MathWorks, Natick, MA, USA) under healthy and static eccentricity condition for different loading values. A finite element method analysis is conducted to verify the mathematical model results, using the commercial JMAG^® software (16.0.02n, JSOL Corporation, Tokyo, Japan). The results show a fine agreement between JMAG^® and the developed mathematical model simulation results. Full article

(This article belongs to the Section F: Electrical Engineering)

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12 pages, 2997 KiB

Open AccessArticle

Measuring the Regional Availability of Forest Biomass for Biofuels and the Potential of GHG Reduction

by Fengli Zhang¹, Dana M. Johnson², Jinjiang Wang^1,*, Shuhai Liu^1,* and Shimin Zhang¹

¹ College of Mechanical and Transportation Engineering, China University of Petroleum, Beijing 102249, China

² School of Business and Economics, Michigan Technological University, Houghton, MI 49931, USA

Energies 2018, 11(1), 198; https://doi.org/10.3390/en11010198 - 15 Jan 2018

Cited by 8 | Viewed by 3449

Abstract

Forest biomass is an important resource for producing bioenergy and reducing greenhouse gas (GHG) emissions. The State of Michigan in the United States (U.S.) is one region recognized for its high potential of supplying forest biomass; however, the long-term availability of timber harvests [...] Read more.

Forest biomass is an important resource for producing bioenergy and reducing greenhouse gas (GHG) emissions. The State of Michigan in the United States (U.S.) is one region recognized for its high potential of supplying forest biomass; however, the long-term availability of timber harvests and the associated harvest residues from this area has not been fully explored. In this study time trend analyses was employed for long term timber assessment and developed mathematical models for harvest residue estimation, as well as the implications of use for ethanol. The GHG savings potential of ethanol over gasoline was also modeled. The methods were applied in Michigan under scenarios of different harvest solutions, harvest types, transportation distances, conversion technologies, and higher heating values over a 50-year period. Our results indicate that the study region has the potential to supply 0.75–1.4 Megatonnes (Mt) dry timber annually and less than 0.05 Mt of dry residue produced from these harvests. This amount of forest biomass could generate 0.15–1.01 Mt of ethanol, which contains 0.68–17.32 GJ of energy. The substitution of ethanol for gasoline as transportation fuel has potential to reduce emissions by 0.043–1.09 Mt CO_2eq annually. The developed method is generalizable in other similar regions of different countries for bioenergy related analyses. Full article

(This article belongs to the Special Issue Woody Biomass for Bioenergy Production)

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12 pages, 2984 KiB

Open AccessArticle

Proposal of the Tubular Daylight System Using Acrylonitrile Butadiene Styrene (ABS) Metalized with Aluminum for Reflective Tube Structure

by Anderson Diogo Spacek^1,*

, João Mota Neto¹, Luciano Dagostin Biléssimo¹, Oswaldo Hideo Ando Junior²

, Marcus Vinícius Ferreira de Santana³ and Celia De Fraga Malfatti⁴

¹ Departament of Mechanic and Automation, SATC, Beneficent Association of Santa Catarina Coal Industry, Street Pascoal Meller, 73, Criciúma SC 88805-380, Brazil

² Departament of Renewable Energies, UNILA, Federal University of Latin American Integration, Av. Sílvio Américo Sasdelli, 1842, Foz do Iguaçu PR 85866-000, Brazil

³ Shared Services Center, Street Madre Benvenuta, 1168, Florianópolis SC 88035-000, Brazil

⁴ Corrosion Research Department, Federal University of Rio Grande do Sul, Avenue Bento Gonçalves 9500, Porto Alegre RS 91501-970, Brazil

Energies 2018, 11(1), 199; https://doi.org/10.3390/en11010199 - 15 Jan 2018

Cited by 13 | Viewed by 4187

Abstract

In the search for alternatives to reduce the consumption of electric energy, the possibility of using natural light for lighting through TDD (tubular daylight devices) or TDGS (tubular daylight guidance systems) appears. These natural luminaires are used in rooms where you want to [...] Read more.

In the search for alternatives to reduce the consumption of electric energy, the possibility of using natural light for lighting through TDD (tubular daylight devices) or TDGS (tubular daylight guidance systems) appears. These natural luminaires are used in rooms where you want to save electricity and enjoy the benefits of natural light. The present work proposes the construction of a tubular system for the conduction of natural light that replaces aluminum with silver (currently marketed by several companies) by polymer metallized with aluminum, offering a low cost. The polymer acrylonitrile butadiene styrene (ABS), coated with aluminum by physical vapor deposition (ionization), was evaluated for some tests to verify characteristics of the structure and the metallized surface. After the tests, the construction of the reflective tube was performed and validated in a real scale of application. The results proved the technical viability of the proposed tube construction for the realization of direct sunlight for illumination using polymeric material. Although it has produced 35% less than the reference tube, it can be marketed at an estimated cost of 50% less. Full article

(This article belongs to the Section L: Energy Sources)

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21 pages, 10725 KiB

Open AccessArticle

Design and Control of a 13.2 kV/10 kVA Single-Phase Solid-State-Transformer with 1.7 kV SiC Devices

by Jeong-Woo Lim¹, Younghoon Cho^1,*

, Han-Sol Lee² and Kwan-Yuhl Cho²

¹ Department of Electrical Engineering, Konkuk University, Seoul 05029, Korea

² Department of Control and Instrumentation Engineering, Korea University of Transportation, Chungju 27469, Korea

Energies 2018, 11(1), 201; https://doi.org/10.3390/en11010201 - 15 Jan 2018

Cited by 6 | Viewed by 6835

Abstract

This paper describes the power stage design, control, and performance evaluation of a 13.2 kV/10 kVA solid-state-transformer (SST) for a power distribution system. The proposed SST consists of 10 modules where each individual module contains a unidirectional three-level power factor correction (PFC) converter [...] Read more.

This paper describes the power stage design, control, and performance evaluation of a 13.2 kV/10 kVA solid-state-transformer (SST) for a power distribution system. The proposed SST consists of 10 modules where each individual module contains a unidirectional three-level power factor correction (PFC) converter for the active-front-end (AFE) stage and an LLC resonant converter for the isolated DC-DC stage. The operating principles of the converters are analyzed and the modulation and the control schemes for the entire module are described in detail. The DC-link voltage imbalance is also less than other SST topologies due to the low number of uncontrollable switching states. In order to simplify the control of the power stage, a modulation strategy for the AFE stage is proposed, and the modulation frequency of the LLC converter is also fixed. In addition, a compensation algorithm is suggested to eliminate the current measurement offset in the AFE stage. The proposed SST achieves the unity power factor at the input AC current regardless of the reactive or nonlinear load and a low voltage regulation at the AC output. In order to verify the effectiveness of the SST, the 13.2 kV/10 kV SST prototype is built and tested. Both the simulation and the experimental results under actual 13.2 kV line show the excellent performance of the proposed SST scheme. Full article

(This article belongs to the Section F: Electrical Engineering)

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13 pages, 393 KiB

Open AccessArticle

Optimization of Pure-Component LNG Cascade Processes with Heat Integration

by Oddmar Eiksund^1,*, Eivind Brodal² and Steven Jackson²

¹ Department of Engineering and Safety, UiT The Arctic University of Norway, 9037 Tromsø, Norway

² Department of Engineering and Safety IVT, UiT The Arctic University of Norway, 9037 Tromsø, Norway

Energies 2018, 11(1), 202; https://doi.org/10.3390/en11010202 - 15 Jan 2018

Cited by 8 | Viewed by 4088

Abstract

Liquefaction of natural gas is an energy-intensive process in which the energy efficiency depends on the number of compressors stages and the heat integration scheme. The aim of the study is to systematically evaluate process performance of pure component cascade processes, present optimized [...] Read more.

Liquefaction of natural gas is an energy-intensive process in which the energy efficiency depends on the number of compressors stages and the heat integration scheme. The aim of the study is to systematically evaluate process performance of pure component cascade processes, present optimized designs for all relevant numbers of compression stages and compare energy consumption between processes with differing levels of complexity. An original method for the evaluation of process performance is developed that utilizes as little human interaction as possible, making it suitable for optimization. This study shows that a pure-component cascade process using the three refrigerants R290, R1150 and R50 must have at least 11 stages to equal the energy efficiency of the best mixed refrigerant process. An optimized configuration for an 11-stage process scheme operating at

20^{\circ} C

ambient temperature is described in detail. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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22 pages, 9493 KiB

Open AccessArticle

Stable Operation and Small-Signal Analysis of Multiple Parallel DG Inverters Based on a Virtual Synchronous Generator Scheme

by Bo Zhang^1,2,*

, Xiangwu Yan^1,2, Dongxue Li¹, Xueyuan Zhang¹, Jinzuo Han¹ and Xiangning Xiao³

¹ Department of Electrical Engineering, North China Electric Power University, Baoding 071003, China

² Key Laboratory of Distributed Energy Storage and Microgrid of Hebei Province, North China Electric Power University, Baoding 071003, China

³ School of Electrical & Electronic Engineering, North China Electric Power University, Beijing 102206, China

Energies 2018, 11(1), 203; https://doi.org/10.3390/en11010203 - 15 Jan 2018

Cited by 30 | Viewed by 5724

Abstract

For a high penetration level of distributed energy resources (DERs) in the grid, virtual synchronous generator (VSG) control is applied to the power electronic converters to mimic the rotating mass and damping property of a conventional synchronous generator (SG), which can support virtual [...] Read more.

For a high penetration level of distributed energy resources (DERs) in the grid, virtual synchronous generator (VSG) control is applied to the power electronic converters to mimic the rotating mass and damping property of a conventional synchronous generator (SG), which can support virtual inertia and damping for the power system. For VSG control, a phase locked loop (PLL) is needed to estimate the angular frequency of the point of common coupling (PCC); however, the deviation of PLL will affect the accuracy of the active power reference, and even the VSG stability control. From this perspective, an enhanced active power controller without PLL was proposed for VSG control. Furthermore, an accurate small-signal model of the multiple parallel VSGs system that considers the dynamic characteristics and the changing of a steady state operation point was derived for system analysis and parameter design. Based on this model, the influence rules of the eigenvalues by droop and virtual inertia were acquired. The simulation and experimental results are presented to verify the validity of the proposed active power controller and parameter design rules. Full article

(This article belongs to the Special Issue Control and Communication in Distributed Generation Systems)

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15 pages, 4039 KiB

Open AccessArticle

Performance Study of a Cylindrical Parabolic Concentrating Solar Water Heater with Nail Type Twisted Tape Inserts in the Copper Absorber Tube

by Amit K. Bhakta^*, Nitesh K. Panday and Shailendra N. Singh

Heat Transfer Laboratory, IIT (ISM), Dhanbad 826004, India

Energies 2018, 11(1), 204; https://doi.org/10.3390/en11010204 - 15 Jan 2018

Cited by 18 | Viewed by 5295

Abstract

This paper reports the overall thermal performance of a cylindrical parabolic concentrating solar water heater (CPCSWH) with inserting nail type twisted tape (NTT) in the copper absorber tube for the nail twist pitch ratios, 4.787, 6.914 and 9.042, respectively. The experiments are conducted [...] Read more.

This paper reports the overall thermal performance of a cylindrical parabolic concentrating solar water heater (CPCSWH) with inserting nail type twisted tape (NTT) in the copper absorber tube for the nail twist pitch ratios, 4.787, 6.914 and 9.042, respectively. The experiments are conducted for a constant volumetric water flow rate and during the time period 9:00 a.m. to 15:00 p.m. The useful heat gain, hourly solar energy collected and hourly solar energy stored in this solar water heater were found to be higher for the nail twist pitch ratio 4.787. The above said parameters were found to be at a peak at noon and observed to follow the path of variation of solar intensity. At the start of the experiment, the value of charging efficiency was observed to be maximum, whereas the maximum values of instantaneous efficiency and overall thermal efficiency were observed at noon. The key finding is that the nail twist pitch ratio enhances the overall thermal performance of the CPCSWH. Full article

(This article belongs to the Section L: Energy Sources)

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16 pages, 3777 KiB

Open AccessArticle

Steam Gasification of Sawdust Biochar Influenced by Chemical Speciation of Alkali and Alkaline Earth Metallic Species

by Dongdong Feng, Yijun Zhao^*, Yu Zhang, Shaozeng Sun and Jianmin Gao

School of Energy Science and Engineering, Harbin Institute of Technology, Harbin 150001, China

Energies 2018, 11(1), 205; https://doi.org/10.3390/en11010205 - 15 Jan 2018

Cited by 19 | Viewed by 4141

Abstract

The effect of chemical speciation (H₂O/NH₄Ac/HCl-soluble and insoluble) of alkali and alkaline earth metallic species on the steam gasification of sawdust biochar was investigated in a lab-scale, fixed-bed reactor, with the method of chemical fractionation analysis. The changes in [...] Read more.

The effect of chemical speciation (H₂O/NH₄Ac/HCl-soluble and insoluble) of alkali and alkaline earth metallic species on the steam gasification of sawdust biochar was investigated in a lab-scale, fixed-bed reactor, with the method of chemical fractionation analysis. The changes in biochar structures and the evolution of biochar reactivity are discussed, with a focus on the contributions of the chemical speciation of alkali and alkaline earth metallic species (AAEMs) on the steam gasification of biochar. The results indicate that H₂O/NH₄Ac/HCl-soluble AAEMs have a significant effect on biochar gasification rates. The release of K occurs mainly in the form of inorganic salts and hydrated ions, while that of Ca occurs mainly as organic ones. The sp³-rich or sp²-sp³ structures and different chemical-speciation AAEMs function together as the preferred active sites during steam gasification. H₂O/HCl-soluble AAEMs could promote the transformation of biochar surface functional groups, from ether/alkene C-O-C to carboxylate COO⁻ in biochar, while they may both be improved by NH₄Ac-soluble AAEMs. H₂O-soluble AAEMs play a crucial catalytic role in biochar reactivity. The effect of NH₄Ac-soluble AAEMs is mainly concentrated in the high-conversion stage (biochar conversion >30%), while that of HCl-soluble AAEMs is reflected in the whole activity-testing stage. Full article

(This article belongs to the Special Issue Biomass Chars: Elaboration, Characterization and Applications Ⅱ)

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12 pages, 1059 KiB

Open AccessArticle

Comparison of Greenhouse Gas Reduction Potential through Renewable Energy Transition in South Korea and Germany

by Alexander Maennel^1,2 and Hyun-Goo Kim^1,*

¹ New & Renewable Energy Resource & Policy Center, Korea Institute of Energy Research, Daejeon 34129, Korea

² Bosch Rexroth AG, Bgm.-Dr.-Nebel-Strasse 2, 97816 Lohr an Main, Germany

Energies 2018, 11(1), 206; https://doi.org/10.3390/en11010206 - 15 Jan 2018

Cited by 38 | Viewed by 6188

Abstract

Germany and South Korea are the world’s sixth and seventh largest emitters of greenhouse gases, respectively; their main sources of pollution being fossil-fueled power plants. Since both countries signed the Paris Agreement in 2016, renewable energy transition is emerging as an effective means [...] Read more.

Germany and South Korea are the world’s sixth and seventh largest emitters of greenhouse gases, respectively; their main sources of pollution being fossil-fueled power plants. Since both countries signed the Paris Agreement in 2016, renewable energy transition is emerging as an effective means and method for avoiding air pollutant emissions and for replacing old fossil-fueled power plants. This paper attempts to evaluate—by using a grid emission factor dependent on a series of energy mix scenarios—the potential for South Korea and Germany to reduce their air pollutants (CO₂, NO_x, SO_x, PM (particulate matter)) until 2030. South Korea plans to reduce greenhouse gas emissions by increasing nuclear power, while Germany aims to do so by shutting down its nuclear power plants and expanding the proportion of renewable energy in the energy mix to over 50%. Therefore, both countries are able to achieve their voluntary greenhouse gas reduction targets in the power sector. However, since the uncertainty of the CO₂ emission factor of coal power plants in South Korea is as high as 10%, efforts to reduce that uncertainty are required in order to produce a reliable assessment of the avoided emissions. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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23 pages, 6209 KiB

Open AccessArticle

Coordinated Engine-Start Control of Single-Motor P2 Hybrid Electric Vehicles with Respect to Different Driving Situations

by Xiangyang Xu^1,2,3, Xiaoxiao Wu^1,2,3, Mick Jordan⁴, Peng Dong^1,2,3,*

and Yang Liu⁵

¹ School of Transportation Science and Engineering, Beihang University, 37 Xueyuan Road, Haidian District, Beijing 100191, China

² Beijing Key Laboratory for High-efficient Power Transmission and System Control of New Energy Resource Vehicle, Beihang University, 37 Xueyuan Road, Haidian District, Beijing 100191, China

³ Dynavolt Tech. and Beihang University Joint Lab for New Energy Resource Vehicle Transmission Technology, Beihang University, 37 Xueyuan Road, Haidian District, Beijing 100191, China

⁴ Institute of Industrial and Automotive Drivetrains, Ruhr-University Bochum, 44801 Bochum, Germany

⁵ Beijing Institute of Space Launch Technology, 1 South Dahongmen Road, Fengtai District, Beijing 100076, China

Energies 2018, 11(1), 207; https://doi.org/10.3390/en11010207 - 15 Jan 2018

Cited by 11 | Viewed by 4862

Abstract

To cut down the costs caused by the additional starter, single-motor P2 hybrid electric vehicles (HEVs) make use of the driving motor to propel the vehicle as well as start the engine, and accordingly the engine-start control becomes more difficult. To satisfy the [...] Read more.

To cut down the costs caused by the additional starter, single-motor P2 hybrid electric vehicles (HEVs) make use of the driving motor to propel the vehicle as well as start the engine, and accordingly the engine-start control becomes more difficult. To satisfy the passengers’ demands, this paper developed different coordinated engine-start control strategies with respect to different situations. First, a detailed model for the single-motor P2 HEVs system was built and related parameters were presented. Then, the coordinated engine-start control architecture for the internal combustion engine (ICE), engine disconnect clutch (EDC), electric motor (EM) and 8-speed automatic transmission (AT) was analyzed. Considering with the different driving situations, soft start strategy and dynamical start strategy are individually proposed. Through the simulation, the above control strategies were validated in accordance with their control objectives. Last, to optimize the trade-off between driving performance and riding comfort, some key parameters were further discussed. This work not only decreases the difficulty of engine-start control in the single-motor P2 HEVs but also is helpful to improve the quality of engine-start. Full article

(This article belongs to the Special Issue Methods to Improve Energy Use in Road Vehicles)

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18 pages, 946 KiB

Open AccessArticle

Mixed Finite Element Simulation with Stability Analysis for Gas Transport in Low-Permeability Reservoirs

by Mohamed F. El-Amin^1,3,*

, Jisheng Kou²

and Shuyu Sun³

¹ College of Engineering, Effat University, Jeddah 21478, Saudi Arabia

² School of Mathematics and Statistics, Hubei Engineering University, Xiaogan 432000, China

³ Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology (KAUST), Jeddah 23955-6900, Saudi Arabia

Energies 2018, 11(1), 208; https://doi.org/10.3390/en11010208 - 15 Jan 2018

Cited by 13 | Viewed by 3123

Abstract

Natural gas exists in considerable quantities in tight reservoirs. Tight formations are rocks with very tiny or poorly connected pors that make flow through them very difficult, i.e., the permeability is very low. The mixed finite element method (MFEM), which is locally conservative, [...] Read more.

Natural gas exists in considerable quantities in tight reservoirs. Tight formations are rocks with very tiny or poorly connected pors that make flow through them very difficult, i.e., the permeability is very low. The mixed finite element method (MFEM), which is locally conservative, is suitable to simulate the flow in porous media. This paper is devoted to developing a mixed finite element (MFE) technique to simulate the gas transport in low permeability reservoirs. The mathematical model, which describes gas transport in low permeability formations, contains slippage effect, as well as adsorption and diffusion mechanisms. The apparent permeability is employed to represent the slippage effect in low-permeability formations. The gas adsorption on the pore surface has been described by Langmuir isotherm model, while the Peng-Robinson equation of state is used in the thermodynamic calculations. Important compatibility conditions must hold to guarantee the stability of the mixed method by adding additional constraints to the numerical discretization. The stability conditions of the MFE scheme has been provided. A theorem and three lemmas on the stability analysis of the mixed finite element method (MFEM) have been established and proven. A semi-implicit scheme is developed to solve the governing equations. Numerical experiments are carried out under various values of the physical parameters. Full article

(This article belongs to the Special Issue Flow and Transport Properties of Unconventional Reservoirs)

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21 pages, 8277 KiB

Open AccessArticle

A New Method for State of Charge Estimation of Lithium-Ion Batteries Using Square Root Cubature Kalman Filter

by Xiangyu Cui¹, Zhu Jing^1,2,*, Maji Luo³, Yazhou Guo³ and Huimin Qiao¹

¹ State Key Laboratory of Advanced Design and Manufacture for Vehicle Body, Hunan University, Changsha 410082, China

² Haima Automobile Group Co., Ltd., Haikou 570216, China

³ Hubei Key Laboratory of Advanced Technology for Automotive Components, Wuhan University of Technology, Wuhan 430070, China

Energies 2018, 11(1), 209; https://doi.org/10.3390/en11010209 - 15 Jan 2018

Cited by 63 | Viewed by 5277

Abstract

State of charge (SOC) is a key parameter for lithium-ion battery management systems. The square root cubature Kalman filter (SRCKF) algorithm has been developed to estimate the SOC of batteries. SRCKF calculates 2n points that have the same weights according to cubature [...] Read more.

State of charge (SOC) is a key parameter for lithium-ion battery management systems. The square root cubature Kalman filter (SRCKF) algorithm has been developed to estimate the SOC of batteries. SRCKF calculates 2n points that have the same weights according to cubature transform to approximate the mean of state variables. After these points are propagated by nonlinear functions, the mean and the variance of the capture can achieve third-order precision of the real values of the nonlinear functions. SRCKF directly propagates and updates the square root of the state covariance matrix in the form of Cholesky decomposition, guarantees the nonnegative quality of the covariance matrix, and avoids the divergence of the filter. Simulink models and the test bench of extended Kalman filter (EKF), Unscented Kalman filter (UKF), cubature Kalman filter (CKF) and SRCKF are built. Three experiments have been carried out to evaluate the performances of the proposed methods. The results of the comparison of accuracy, robustness, and convergence rate with EKF, UKF, CKF and SRCKF are presented. Compared with the traditional EKF, UKF and CKF algorithms, the SRCKF algorithm is found to yield better SOC estimation accuracy, higher robustness and better convergence rate. Full article

(This article belongs to the Special Issue Emerging Power Electronics Technologies for Power Systems and Machine Drives)

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19 pages, 3180 KiB

Open AccessArticle

Robust Power Supply Restoration for Self-Healing Active Distribution Networks Considering the Availability of Distributed Generation

by Qiang Yang^1,*

, Le Jiang¹, Ali Ehsan¹

, Yajing Gao² and Shixiao Guo²

¹ College of Electrical Engineering, Zhejiang University, Hangzhou 310027, China

² State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources (North China Electric Power University), Baoding 071003, China

Energies 2018, 11(1), 210; https://doi.org/10.3390/en11010210 - 15 Jan 2018

Cited by 12 | Viewed by 3993

Abstract

The increasing penetration of distributed generations (DGs) with intermittent and stochastic characteristics into current power distribution networks can lead to increased fault levels and degradation in network protection. As one of the key requirements of active network management (ANM), efficient power supply restoration [...] Read more.

The increasing penetration of distributed generations (DGs) with intermittent and stochastic characteristics into current power distribution networks can lead to increased fault levels and degradation in network protection. As one of the key requirements of active network management (ANM), efficient power supply restoration solution to guarantee network self-healing capability with full consideration of DG uncertainties is demanded. This paper presents a joint power supply restoration through combining the DG local restoration and switcher operation-based restoration to enhance the self-healing capability in active distribution networks considering the availability of distributed generation. The restoration algorithmic solution is designed to be able to carry out power restoration in parallel upon multiple simultaneous faults to maximize the load restoration while additionally minimizing power loss, topology variation and power flow changes due to switcher operations. The performance of the proposed solution is validated based on a 53-bus distribution network with wind power generators through extensive simulation experiments for a range of fault cases and DG scenarios generated based on Heuristic Moment Matching (HMM) method to fully consider the DG randomness. The numerical result in comparison with the existing solutions demonstrates the effectiveness of the proposed power supply restoration solution. Full article

(This article belongs to the Section F: Electrical Engineering)

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15 pages, 2340 KiB

Open AccessArticle

Operational Performance Characterization of a Heat Pump System Utilizing Recycled Water as Heat Sink and Heat Source in a Cool and Dry Climate

by Piljae Im¹, Xiaobing Liu^1,* and Hugh Henderson²

¹ Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA

² Frontier Energy, Inc., Cazenovia, NY 13035, USA

Energies 2018, 11(1), 211; https://doi.org/10.3390/en11010211 - 16 Jan 2018

Cited by 3 | Viewed by 4683

Abstract

The wastewater leaving from homes and businesses contains abundant low-grade energy, which can be utilized through heat pump technology to heat and cool buildings. Although the energy in the wastewater has been successfully utilized to condition buildings in other countries, it is barely [...] Read more.

The wastewater leaving from homes and businesses contains abundant low-grade energy, which can be utilized through heat pump technology to heat and cool buildings. Although the energy in the wastewater has been successfully utilized to condition buildings in other countries, it is barely utilized in the United States, until recently. In 2013, the Denver Museum of Nature & Science at Denver, the United States implemented a unique heat pump system that utilizes recycled wastewater from a municipal water system to cool and heat its 13,000 m² new addition. This recycled water heat pump (RWHP) system uses seven 105 kW (cooling capacity) modular water-to-water heat pumps (WWHPs). Each WWHP uses R-410A refrigerant, has two compressors, and can independently provide either 52 °C hot water (HW) or 7 °C chilled water (CHW) to the building. This paper presents performance characterization results of this RWHP system based on the measured data from December 2014 through August 2015. The annual energy consumption of the RWHP system was also calculated and compared with that of a baseline Heating, Ventilation, and Air Conditioning (HVAC) system which meets the minimum energy efficiencies that are allowed by American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) 90.1-2013. The performance analysis results indicate that recycled water temperatures were favorable for effective operation of heat pumps. As a result, on an annual basis, the RWHP system avoided 50% of source energy consumption (resulting from reduction in natural gas consumption although electricity consumption was increased slightly), reduced CO₂ emissions by 41%, and saved 34% in energy costs as compared with the baseline system. Full article

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26 pages, 15820 KiB

Open AccessArticle

Multi-Step Loading Creep Behavior of Red Sandstone after Thermal Treatments and a Creep Damage Model

by Sheng-Qi Yang^1,*

, Bo Hu¹, Pathegama G. Ranjith^1,2

and Peng Xu¹

¹ State Key Laboratory for Geomechanics and Deep Underground Engineering, School of Mechanics and Civil Engineering, China University of Mining and Technology, Xuzhou 221116, China

² Deep Earth Energy Research Laboratory, Department of Civil Engineering, Monash University, Melbourne 3800, Australia

Energies 2018, 11(1), 212; https://doi.org/10.3390/en11010212 - 16 Jan 2018

Cited by 27 | Viewed by 5270

Abstract

Triaxial compressive creep tests were conducted on red sandstones after different thermal treatments. Subsequently, the thermal influence on the axial, lateral and volumetric creep curves under various stress levels was analyzed. The results show that both the instantaneous and time-based deformation behaviors depended [...] Read more.

Triaxial compressive creep tests were conducted on red sandstones after different thermal treatments. Subsequently, the thermal influence on the axial, lateral and volumetric creep curves under various stress levels was analyzed. The results show that both the instantaneous and time-based deformation behaviors depended largely on the stress and temperature conditions. The instant axial strain increases linearly with increasing deviator stress and the instant deformation modulus decreases non-linearly with temperature. An interesting phenomenon was observed whereby the lateral creep strain had an apparent linear correlation with the axial creep strain. Furthermore, the fitting lines’ slopes of lateral and axial creep strain increase gradually with the increasing deviator stress at identical temperature and first decreases and then increases as temperature is elevated. Then, on the basis of the Burgers creep model and the concept of strain energy, a creep damage model implemented in FLAC^3D (Fast Lagrangian Analysis of Continua 3D) is presented, and this model was able to describe the entire creep process completely including primary creep stage, secondary creep stage, and tertiary creep stage comparing with the experimental and theoretical results based on test data and numerical calculations. The influence of two damage parameters on creep curves and the thermal influence on creep parameters are subsequently discussed. Under the same stress level, the parameters K, G_M and G_K and η_K of creep model decrease with temperature, while the parameter η_M first augments as temperature rise to 300 °C and then decreases as temperature at above 300 °C. The higher is the temperature, the smaller the critical stress ratio (CSR). Full article

(This article belongs to the Special Issue Geothermal Energy: Utilization and Technology 2018)

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13 pages, 6679 KiB

Open AccessArticle

A High Precision Artificial Neural Networks Model for Short-Term Energy Load Forecasting

by Ping-Huan Kuo¹

and Chiou-Jye Huang^2,*

¹ Computer and Intelligent Robot Program for Bachelor Degree, National Pingtung University, Pingtung 90004, Taiwan

² School of Electrical Engineering and Automation, Jiangxi University of Science and Technology, Ganzhou 341000, Jiangxi, China

Energies 2018, 11(1), 213; https://doi.org/10.3390/en11010213 - 16 Jan 2018

Cited by 281 | Viewed by 12022

Abstract

One of the most important research topics in smart grid technology is load forecasting, because accuracy of load forecasting highly influences reliability of the smart grid systems. In the past, load forecasting was obtained by traditional analysis techniques such as time series analysis [...] Read more.

One of the most important research topics in smart grid technology is load forecasting, because accuracy of load forecasting highly influences reliability of the smart grid systems. In the past, load forecasting was obtained by traditional analysis techniques such as time series analysis and linear regression. Since the load forecast focuses on aggregated electricity consumption patterns, researchers have recently integrated deep learning approaches with machine learning techniques. In this study, an accurate deep neural network algorithm for short-term load forecasting (STLF) is introduced. The forecasting performance of proposed algorithm is compared with performances of five artificial intelligence algorithms that are commonly used in load forecasting. The Mean Absolute Percentage Error (MAPE) and Cumulative Variation of Root Mean Square Error (CV-RMSE) are used as accuracy evaluation indexes. The experiment results show that MAPE and CV-RMSE of proposed algorithm are 9.77% and 11.66%, respectively, displaying very high forecasting accuracy. Full article

(This article belongs to the Special Issue Short-Term Load Forecasting by Artificial Intelligent Technologies)

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17 pages, 1738 KiB

Open AccessArticle

Explicit Multipole Formulas for Calculating Thermal Resistance of Single U-Tube Ground Heat Exchangers

by Johan Claesson¹ and Saqib Javed^2,*

¹ Building Physics, Lund University, Lund 221 00, Sweden

² Building Services Engineering, Chalmers Technical University, Gothenburg 412 96, Sweden

Energies 2018, 11(1), 214; https://doi.org/10.3390/en11010214 - 16 Jan 2018

Cited by 23 | Viewed by 4416

Abstract

Borehole thermal resistance is both an important design parameter and a key performance characteristic of a ground heat exchanger. Another quantity that is particularly important for ground heat exchangers is the internal thermal resistance between the heat exchanger pipes. Both these resistances can [...] Read more.

Borehole thermal resistance is both an important design parameter and a key performance characteristic of a ground heat exchanger. Another quantity that is particularly important for ground heat exchangers is the internal thermal resistance between the heat exchanger pipes. Both these resistances can be calculated to a high degree of accuracy by means of the well-known multipole method. However, the multipole method has a fairly intricate mathematical algorithm and is thus not trivial to implement. Consequently, there is considerable interest in developing explicit formulas for calculating borehole resistances. This paper presents derivation and solutions of newly derived second-order and higher-order multipole formulas for calculating borehole thermal resistance and total internal thermal resistance of single U-tube ground heat exchangers. A new and simple form of the first-order multipole formula is also presented. The accuracy of the presented formulas is established by comparing them to the original multipole method. The superiority of the new higher-order multipole formulas over the existing formulas is also demonstrated. Full article

(This article belongs to the Special Issue Geothermal Heating and Cooling)

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16 pages, 3518 KiB

Open AccessArticle

An Optimal and Distributed Demand Response Strategy for Energy Internet Management

by Qian Liu¹, Rui Wang^2,*, Yan Zhang², Guohua Wu² and Jianmai Shi²

¹ North China Institute of Aerospace Engineering, Langfang 065000, China

² College of Systems Engineering, National University of Defense Technology, Changsha 410073, China

Energies 2018, 11(1), 215; https://doi.org/10.3390/en11010215 - 16 Jan 2018

Cited by 12 | Viewed by 3173

Abstract

This study proposes a new model of demand response management for a future smart grid that consists of smart microgrids. The microgrids have energy storage units, responsive loads, controllable distributed generation units, and renewable energy resources. They can buy energy from the utility [...] Read more.

This study proposes a new model of demand response management for a future smart grid that consists of smart microgrids. The microgrids have energy storage units, responsive loads, controllable distributed generation units, and renewable energy resources. They can buy energy from the utility company when the power generation in themselves cannot satisfy the load demand, and sell extra power generation to the utility company. The goal is to optimize the operation schedule of microgrids to minimize the microgrids’ payments and the utility company’s operation cost. A parallel distributed optimization algorithm based on games theory is developed to solve the optimization problem, in which microgrids only need to send their aggregated purchasing/selling energy to the utility company, thus avoid infringing its privacy. Microgrids can update their operation schedule simultaneously. A case study is implemented, and the simulation results show that the proposed method is effective and efficient. Full article

(This article belongs to the Section F: Electrical Engineering)

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26 pages, 4874 KiB

Open AccessEditor’s ChoiceArticle

Conceptual Design of Operation Strategies for Hybrid Electric Aircraft

by Julian Hoelzen¹, Yaolong Liu^2,*

, Boris Bensmann^1,*, Christopher Winnefeld¹, Ali Elham³, Jens Friedrichs⁴ and Richard Hanke-Rauschenbach¹

¹ Institute of Electric Power Systems, Leibniz Universität Hannover, Appelstr. 9a, 30167 Hanover, Germany

² Aeronautics Research Centre Niedersachsen (NFL), Technische Universität Braunschweig, Hermann-Blenk-Straße 42, 38108 Braunschweig, Germany

³ Institute of Aircraft Design and Lightweight Structures, Technische Universität Braunschweig, Hermann-Blenk-Straße 35, 38108 Braunschweig, Germany

⁴ Institute of Jet Propulsion and Turbomachinery, TU Braunschweig, Hermann-Blenk-Straße 37, 38108 Brunswick, Germany

Energies 2018, 11(1), 217; https://doi.org/10.3390/en11010217 - 16 Jan 2018

Cited by 151 | Viewed by 19321

Abstract

Ambitious targets to reduce emissions caused by aviation in the light of an expected ongoing rise of the air transport demand in the future drive the research of propulsion systems with lower CO₂ emissions. Regional hybrid electric aircraft (HEA) powered by conventional [...] Read more.

Ambitious targets to reduce emissions caused by aviation in the light of an expected ongoing rise of the air transport demand in the future drive the research of propulsion systems with lower CO₂ emissions. Regional hybrid electric aircraft (HEA) powered by conventional gas turbines and battery powered electric motors are investigated to test hybrid propulsion operation strategies. Especially the role of the battery within environmentally friendly concepts with significantly reduced carbon footprint is analyzed. Thus, a new simulation approach for HEA is introduced. The main findings underline the importance of choosing the right power-to-energy-ratio of a battery according to the flight mission. The gravimetric energy and power density of the electric storages determine the technologically feasibility of hybrid concepts. Cost competitive HEA configurations are found, but do not promise the targeted CO₂ emission savings, when the well-to-wheel system is regarded with its actual costs. Sensitivity studies are used to determine external levers that favor the profitability of HEA. Full article

(This article belongs to the Special Issue Towards a Transformation to Sustainable Aviation Systems)

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14 pages, 1763 KiB

Open AccessArticle

Modeling the Risk of Commercial Failure for Hydraulic Fracturing Projects Due to Reservoir Heterogeneity

by Hadi Parvizi¹, Sina Rezaei Gomari^1,*, Farhad Nabhani¹ and Abolfazl Dehghan Monfared²

¹ School of Science, Engineering and Design, Teesside University, Middleborough TS1 3BA, UK

² Department of Petroleum Engineering, Petroleum, Gas and Petrochemical Faculty, Persian Gulf University, Bushehr 75169-13817, Iran

Energies 2018, 11(1), 218; https://doi.org/10.3390/en11010218 - 17 Jan 2018

Cited by 11 | Viewed by 3769

Abstract

Hydraulic fracturing technologies play a major role in the global energy supply and affect oil pricing. The current oil price fluctuations within 40 to 55 USD per barrel have caused diminished economical margins for hydraulic fracturing projects. Hence, successful decision making the for [...] Read more.

Hydraulic fracturing technologies play a major role in the global energy supply and affect oil pricing. The current oil price fluctuations within 40 to 55 USD per barrel have caused diminished economical margins for hydraulic fracturing projects. Hence, successful decision making the for execution of hydraulic fracturing projects requires a higher level of integration of technical, commercial, and uncertainty analyses. However, the complexity of hydraulic fracturing modeling, and the sensitivity and the effects of uncertainty of reservoir heterogeneity on well performance renders the integration of such studies rather impractical. The impact of reservoir heterogeneity on hydraulic fracturing performance has been quantified by the introduction of Heterogeneity Impact Factor (HIF) and formulas have been developed to forecast well performance using HIF. These advances provide a platform for introducing a practical approach for introducing the Risk of Commercial Failure (RCF) due to reservoir heterogeneity in hydraulic fracturing projects. This paper defines such a parameter and the methodology to calculate it in a time-efficient manner. The proposed approach has been exercised on a real project in which a RCF of 20% is computed. The analysis also covers the sensitivity on Capital Expenditure (CAPEX), Operational Expenditure (OPEX), gas price, HIF and discount rate. Full article

(This article belongs to the Section L: Energy Sources)

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16 pages, 3741 KiB

Open AccessArticle

Study of Time and Meteorological Characteristics of Wind Speed Correlation in Flat Terrains Based on Operation Data

by Xiaojun Shen^*, Chongcheng Zhou and Xuejiao Fu

Department of Electrical Engineering, Tongji University, Shanghai 200092, China

Energies 2018, 11(1), 219; https://doi.org/10.3390/en11010219 - 17 Jan 2018

Cited by 12 | Viewed by 4026

Abstract

The accurate calculation and characteristic analysis of wind speed correlation (WSC) is the basis of wind farm equivalent modeling, wind power prediction and other advanced applications. It is well known that the accurate calculation of WSC depends on the quality of the raw [...] Read more.

The accurate calculation and characteristic analysis of wind speed correlation (WSC) is the basis of wind farm equivalent modeling, wind power prediction and other advanced applications. It is well known that the accurate calculation of WSC depends on the quality of the raw data, and the WSC of wind turbines is related to spatial, time and meteorological conditions. However, the researches on the statistical analysis of time/meteorological WSC characteristics and the original data quality improvement for WSC calculation are rarely carried out. This paper reviews and redefines the concept and connotation of spatial, time and meteorological WSC. On this basis, a general process is proposed for WSC calculation including data classification, extraction and cleaning. Then the WSC characteristics between wind turbines are analyzed from time and meteorological dimensions based on the actual operation data. In addition, the influence of time WSC and meteorological WSC on wind turbine equivalent modeling and wind power prediction was discussed. The results of case study shows that the proposed general WSC calculation process is feasible and effective; the WSC for different time scales, wind speed ranges and wind directions varies greatly; the spatial WSC cannot characterize the time variability and directionality of the WSC. And the time and meteorological WSC characteristics are of great engineering value to improve the wind turbine equivalent modeling and wind power prediction accuracy, the influence of time scale and meteorological conditions should be considered in the applications of WSC. Full article

(This article belongs to the Section F: Electrical Engineering)

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18 pages, 8666 KiB

Open AccessArticle

Impedance Characterization and Modeling of Lithium-Ion Batteries Considering the Internal Temperature Gradient

by Haifeng Dai^1,2,*, Bo Jiang^1,2 and Xuezhe Wei^1,2

¹ National Fuel Cell Vehicle & Powertrain System Research & Engineering Center, No. 4800, Caoan Road, Shanghai 201804, China

² School of Automotive Studies, Tongji University, No. 4800, Caoan Road, Shanghai 201804, China

Energies 2018, 11(1), 220; https://doi.org/10.3390/en11010220 - 17 Jan 2018

Cited by 74 | Viewed by 9365

Abstract

Battery impedance is essential to the management of lithium-ion batteries for electric vehicles (EVs), and impedance characterization can help to monitor and predict the battery states. Many studies have been undertaken to investigate impedance characterization and the factors that influence impedance. However, few [...] Read more.

Battery impedance is essential to the management of lithium-ion batteries for electric vehicles (EVs), and impedance characterization can help to monitor and predict the battery states. Many studies have been undertaken to investigate impedance characterization and the factors that influence impedance. However, few studies regarding the influence of the internal temperature gradient, which is caused by heat generation during operation, have been presented. We have comprehensively studied the influence of the internal temperature gradient on impedance characterization and the modeling of battery impedance, and have proposed a discretization model to capture battery impedance characterization considering the temperature gradient. Several experiments, including experiments with artificial temperature gradients, are designed and implemented to study the influence of the internal temperature gradient on battery impedance. Based on the experimental results, the parameters of the non-linear impedance model are obtained, and the relationship between the parameters and temperature is further established. The experimental results show that the temperature gradient will influence battery impedance and the temperature distribution can be considered to be approximately linear. The verification results indicate that the proposed discretization model has a good performance and can be used to describe the actual characterization of the battery with an internal temperature gradient. Full article

(This article belongs to the Special Issue 2nd Young Scholar’s Symposium on Battery Design and Management (BDM 2017))

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17 pages, 3116 KiB

Open AccessArticle

The Effect of Using Ethanol-Gasoline Blends on the Mechanical, Energy and Environmental Performance of In-Use Vehicles

by Juan E. Tibaquirá¹, José I. Huertas^2,*

, Sebastián Ospina¹, Luis F. Quirama¹ and José E. Niño²

¹ Mechanical Engineering Department, Universidad Tecnológica de Pereira, Pereira 660003, Colombia

² School of Science and Engineering, Energy and Climate Change Research Group, Tecnológico de Monterrey, Monterrey 64849, Mexico

Energies 2018, 11(1), 221; https://doi.org/10.3390/en11010221 - 17 Jan 2018

Cited by 71 | Viewed by 10212

Abstract

The use of ethanol in gasoline has become a worldwide tendency as an alternative to reduce net CO₂ emissions to the atmosphere, increasing gasoline octane rating and reducing dependence on petroleum products. However, recently environmental authorities in large urban centers have expressed [...] Read more.

The use of ethanol in gasoline has become a worldwide tendency as an alternative to reduce net CO₂ emissions to the atmosphere, increasing gasoline octane rating and reducing dependence on petroleum products. However, recently environmental authorities in large urban centers have expressed their concerns on the true effect of using ethanol blends of up to 20% v/v in in-use vehicles without any modification in the setup of the engine control unit (ECU), and on the variations of these effects along the years of operation of these vehicles. Their main concern is the potential increase in the emissions of volatile organic compounds with high ozone formation potential. To address these concerns, we developed analytical and experimental work testing engines under steady-conditions. We also tested carbureted and fuel-injected vehicles every 10,000 km during their first 100,000 km of operation. We measured the effect of using ethanol-gasoline blends on the power and torque generated, the fuel consumption and CO₂, CO, NOx and unburned hydrocarbon emissions, including volatile organic compounds (VOCs) such as acetaldehyde, formaldehyde, benzene and 1,3-butadiene which are considered important ozone precursors. The obtained results showed statistically no significant differences in these variables when vehicles operate with a blend of 20% v/v ethanol and 80% v/v gasoline (E20) instead of gasoline. Those results remained unchanged during the first 100,000 km of operation of the vehicles. We also observed that when the vehicles operated with E20 at high engine loads, they showed a tendency to operate with greater values of λ (ratio of the actual air-fuel ratio to the stoichiometric air-fuel ratio) when compared to their operation with gasoline. According to the Eco-Indicator-99, these results represent a minor reduction (<1.3%) on the impact to human health, and on the deterioration of the ecosystem. However, it implies a 12.9% deterioration of the natural resources. Thermal equilibrium analysis, at the tailpipe conditions (~100 °C), showed that ethane, formaldehyde, ethylene and ethanol are the most relevant VOCs in terms of the amount of mass emitted. The use of ethanol in the gasoline reduced 20–40% of those emissions. These reductions implied an average reduction of 17% in the ozone formation potential. Full article

(This article belongs to the Collection Bioenergy and Biofuel)

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23 pages, 1654 KiB

Open AccessArticle

Numerical Investigation of AdBlue Droplet Evaporation and Thermal Decomposition in the Context of NO_x-SCR Using a Multi-Component Evaporation Model

by Kaushal Nishad^*

, Amsini Sadiki and Johannes Janicka

Institute of Energy and Power Plant Technology, Technische Universität Darmstadt, 64287 Darmstadt, Germany

Energies 2018, 11(1), 222; https://doi.org/10.3390/en11010222 - 17 Jan 2018

Cited by 27 | Viewed by 6624

Abstract

To cope with the progressive tightening of the emission regulations, gasoline and diesel engines will continuously require highly improved exhaust after-treatment systems. In the case of diesel engines, the selective catalytic reduction (SCR) appears as one of the widely adopted technologies to reduce [...] Read more.

To cope with the progressive tightening of the emission regulations, gasoline and diesel engines will continuously require highly improved exhaust after-treatment systems. In the case of diesel engines, the selective catalytic reduction (SCR) appears as one of the widely adopted technologies to reduce NO_x (nitrogen oxides) emissions. Thereby, with the help of available heat from exhaust gas, the injected urea–water solution (UWS) turns inside the exhaust port immediately into gaseous ammonia (NH₃) by evaporation of mixture and thermal decomposition of urea. The reaction and conversion efficiency mostly depend upon the evaporation and subsequent mixing of the NH₃ into the exhaust gas, which in turn depends upon the engine loading conditions. Up to now, the aggregation of urea after evaporation of water and during the thermal decomposition of urea is not clearly understood. Hence, various scenarios for the urea depletion in the gaseous phase that can be envisaged have to be appraised under SCR operating conditions relying on an appropriate evaporation description. The objective of the present paper is therefore fourfold. First, a reliable multi-component evaporation model that includes a proper binary diffusion coefficient is developed for the first time in the Euler–Lagrangian CFD (computational fluid dynamics) framework to account properly for the distinct evaporation regimes of adBlue droplets under various operating conditions. Second, this model is extended for thermal decomposition of urea in the gaseous phase, where, depending on how the heat of thermal decomposition of urea is provided, different scenarios are considered. Third, since the evaporation model at and around the droplet surface is based on a gas film approach, how the material properties are evaluated in the film influences the process results is reported, also for the first time. Finally, the impact of various ambient temperatures on the adBlue droplet depletion characteristics as well as the effect of gravity is pointed out. The prediction capability of the model variants is assessed by comparing the achieved results to each other and with experimental data. It turns out that satisfactory agreement between experiment and numerical predictions is achieved for a wide range of operating temperatures by using correlations by “Wilke and Lee” for urea and by “Fuller et al.” for water. The results are essentially sensitive to gravity. From subsequent comparisons of different ways to account for the thermal decomposition in the gaseous urea, a significant difference is observed. Finally, the 1/3 film rule widely used for evaluating the material properties in the film shows accurate prediction of both evaporation and thermal decomposition regimes of urea. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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23 pages, 7342 KiB

Open AccessArticle

Gas Transport Model in Organic Shale Nanopores Considering Langmuir Slip Conditions and Diffusion: Pore Confinement, Real Gas, and Geomechanical Effects

by Liehui Zhang¹, Baochao Shan^1,*, Yulong Zhao^1,*, Jia Du², Jun Chen¹ and Xiaoping Tao³

¹ State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, China

² Research Center of China United Coalbed Methane Corporation, Ltd., Beijing 100011, China

³ Xinjiang Oilfield Company Capital Construction Engineering, Karamay, Xinjiang 834000, China

Energies 2018, 11(1), 223; https://doi.org/10.3390/en11010223 - 17 Jan 2018

Cited by 31 | Viewed by 5529

Abstract

Nanopores are extremely developed and randomly distributed in shale gas reservoirs. Due to the rarefied conditions in shale strata, multiple gas transport mechanisms coexist and need further understanding. The commonly used slip models are mostly based on Maxwell slip boundary condition, which assumes [...] Read more.

Nanopores are extremely developed and randomly distributed in shale gas reservoirs. Due to the rarefied conditions in shale strata, multiple gas transport mechanisms coexist and need further understanding. The commonly used slip models are mostly based on Maxwell slip boundary condition, which assumes elastic collisions between gas molecules and solid surfaces. However, gas molecules do not rebound from solid surfaces elastically, but rather are adsorbed on them and then re-emitted after some time lag. A Langmuir slip permeability model was established by introducing Langmuir slip BC. Knudsen diffusion of bulk phase gas and surface diffusion of adsorbed gas were also coupled into our nanopore transport model. Considering the effects of real gas, stress dependence, thermodynamic phase changes due to pore confinement, surface roughness, gas molecular volume, and pore enlargement due to gas desorption during depressurization, a unified gas transport model in organic shale nanopores was established, which was then upscaled by coupling effective porosity and tortuosity to describe practical SGR properties. The bulk phase transport model, single capillary model, and upscaled porous media model were validated by data from experimental data, lattice Boltzmann method or model comparisons. Based on the new gas transport model, the equivalent permeability of different flow mechanisms as well as the flux proportion of each mechanism to total flow rate was investigated in different pore radius and pressure conditions. The study in this paper revealed special gas transport characteristics in shale nonopores and provided a robust foundation for accurate simulation of shale gas production. Full article

(This article belongs to the Special Issue Flow and Transport Properties of Unconventional Reservoirs)

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18 pages, 6419 KiB

Open AccessArticle

Topology-Based Estimation of Missing Smart Meter Readings

by Daisuke Kodaira

and Sekyung Han^*

Department of Electrical Engineering, Kyungpook National University, 80 Daehak-ro, Sangyeok-dong, Buk-gu, Daegu 41566, Korea

Energies 2018, 11(1), 224; https://doi.org/10.3390/en11010224 - 17 Jan 2018

Cited by 10 | Viewed by 4169

Abstract

Smart meters often fail to measure or transmit the data they record when measuring energy consumption, known as meter readings, owing to faulty measuring equipment or unreliable communication modules. Existing studies do not address successive and non-periodical missing meter readings. This paper proposes [...] Read more.

Smart meters often fail to measure or transmit the data they record when measuring energy consumption, known as meter readings, owing to faulty measuring equipment or unreliable communication modules. Existing studies do not address successive and non-periodical missing meter readings. This paper proposes a method whereby missing readings observed at a node are estimated by using circuit theory principles that leverage the voltage and current data from adjacent nodes. A case study is used to demonstrate the ability of the proposed method to successfully estimate the missing readings over an entire day during which outages and unpredictable perturbations occurred. Full article

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13 pages, 3854 KiB

Open AccessArticle

Prediction of Dissolved Gas Concentrations in Transformer Oil Based on the KPCA-FFOA-GRNN Model

by Jun Lin^*

, Gehao Sheng, Yingjie Yan, Jiejie Dai and Xiuchen Jiang

Department of Electrical Engineering, Shanghai Jiaotong University, Shanghai 200240, China

Energies 2018, 11(1), 225; https://doi.org/10.3390/en11010225 - 17 Jan 2018

Cited by 35 | Viewed by 3930

Abstract

The purpose of analyzing the dissolved gas in transformer oil is to determine the transformer’s operating status and is an important basis for fault diagnosis. Accurate prediction of the concentration of dissolved gas in oil can provide an important reference for the evaluation [...] Read more.

The purpose of analyzing the dissolved gas in transformer oil is to determine the transformer’s operating status and is an important basis for fault diagnosis. Accurate prediction of the concentration of dissolved gas in oil can provide an important reference for the evaluation of the state of the transformer. A combined predicting model is proposed based on kernel principal component analysis (KPCA) and a generalized regression neural network (GRNN) using an improved fruit fly optimization algorithm (FFOA) to select the smooth factor. Firstly, based on the idea of using the dissolved gas ratio of oil to diagnose the transformer fault, gas concentration ratios are also used as characteristic parameters. Secondly, the main parameters are selected from the feature parameters using the KPCA method, and the GRNN is then used to predict the gas concentration in the transformer oil. In the training process of the network, the FFOA is used to select the smooth factor of the neural network. Through a concrete example, it is shown that the method proposed in this paper has better data fitting ability and more accurate prediction ability compared with the support vector machine (SVM) and gray model (GM) methods. Full article

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20 pages, 6362 KiB

Open AccessArticle

Applying the Taguchi Method for Investigating the Phase-Locked Loop Dynamics Affected by Hybrid Storage System Parameters

by Mostafa Ahmadzadeh^*, Saeedollah Mortazavi and Mohsen Saniei

Department of Electrical Engineering, Faculty of Engineering, Shahid Chamran University of Ahvaz, Ahvaz 61357-43337, Iran

Energies 2018, 11(1), 226; https://doi.org/10.3390/en11010226 - 17 Jan 2018

Cited by 4 | Viewed by 2930

Abstract

Storage systems play an important role in performance of micro-grids. Storage systems may decrease fluctuations caused by periodic and unpredictable nature of distributed generation resource. Some micro-grids are connected to the network via a grid-interface converter. The phase-locked loop (PLL) is a commonly [...] Read more.

Storage systems play an important role in performance of micro-grids. Storage systems may decrease fluctuations caused by periodic and unpredictable nature of distributed generation resource. Some micro-grids are connected to the network via a grid-interface converter. The phase-locked loop (PLL) is a commonly technique for the grid synchronization of network-connected converters. Various parameters affect the stability of PLL (including the network-side and microgrid-side parameters). The effect of the micro-grid-side parameters on the stability of the PLL has not been studied so far. In this paper, the stability of PLL influenced by microgrid-side parameters has been evaluated after a detailed analytical modeling of micro-grid components (including the production power fluctuations, energy storage system, microgrid-side loads, controller parameters etc.). This paper proposes two new stability analysis criteria for PLL affected by micro-grid and hybrid storage system parameters. Using proposed criteria for stability of PLL, optimized rate of micro-grid and hybrid storage system parameters are obtained using statistical methods (Taguchi approach). Finally, behavior of PLL affected by hybrid storage system is investigated. The simulation results and eigenvalues analysis confirm the theoretical analysis and proposed criteria. Full article

(This article belongs to the Section F: Electrical Engineering)

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22 pages, 5989 KiB

Open AccessArticle

Studies on a Hybrid Full-Bridge/Half-Bridge Bidirectional CLTC Multi-Resonant DC-DC Converter with a Digital Synchronous Rectification Strategy

by Shu-huai Zhang¹, Yi-feng Wang^1,*

, Bo Chen¹, Fu-qiang Han¹ and Qing-cui Wang²

¹ Key Laboratory of Smart Grid of Ministry of Education, Tianjin University, Tianjin 300072, China

² Tianjin Research Institute of Electric Science Co., Ltd. (TRIED), Tianjin 300300, China

Energies 2018, 11(1), 227; https://doi.org/10.3390/en11010227 - 18 Jan 2018

Cited by 8 | Viewed by 4637

Abstract

This study presents a new bidirectional multi-resonant DC-DC converter, which is named CLTC. The converter adds an auxiliary transformer and an extra resonant capacitor based on a LLC resonant DC-DC converter, achieving zero-voltage switching (ZVS) for the input inverting switches and zero-current switching [...] Read more.

This study presents a new bidirectional multi-resonant DC-DC converter, which is named CLTC. The converter adds an auxiliary transformer and an extra resonant capacitor based on a LLC resonant DC-DC converter, achieving zero-voltage switching (ZVS) for the input inverting switches and zero-current switching (ZCS) for the output rectifiers in all load range. The converter also has a wide gain range in two directions. When the load is light, a half-bridge configuration is adopted instead of a full-bridge configuration to solve the problem of voltage regulation. By this method, the voltage gain becomes monotonous and controllable. Besides, the digital synchronous rectification strategy is proposed in forward mode without adding any auxiliary circuit. The conduction time of synchronous rectifiers equals the estimation value of body diodes’ conduction time with the lightest load. Power loss analysis is also conducted in different situations. Finally, the theoretical analysis is validated by a 5 kW prototype. Full article

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11 pages, 379 KiB

Open AccessArticle

How Do Chinese Residents Expect of Government Subsidies on Solar Photovoltaic Power Generation?—A Case of Wuhan, China

by Liping Ding, Fan Zhang^*

and Jing Shuai

School of Economics and Management, Mineral Resource Strategy and Policy Research Center of China, China University of Geosciences, Wuhan 430074, Hubei, China

Energies 2018, 11(1), 228; https://doi.org/10.3390/en11010228 - 18 Jan 2018

Cited by 9 | Viewed by 3816

Abstract

This paper investigates local residents’ expectations of the Chinese government subsidies on solar photovoltaic (PV) power generation. Residents’ demographics including age, educational attainment, income level, gender, and employment fields are analyzed based on a survey study in Wuhan, China. Results of the regression [...] Read more.

This paper investigates local residents’ expectations of the Chinese government subsidies on solar photovoltaic (PV) power generation. Residents’ demographics including age, educational attainment, income level, gender, and employment fields are analyzed based on a survey study in Wuhan, China. Results of the regression analysis on the influence of demographic variables on residents’ expectations indicate that: (1) residents with different demographics have significantly different expectations of the Chinese government subsidies for adopting PV power generation facilities; (2) income, education attainment, and residents’ employment fields have a significant impact on their expectations of government subsidies. With these findings, this paper concludes with useful policy implications. Full article

(This article belongs to the Special Issue Solar Energy Harvesting, Storage and Utilization)

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21 pages, 4094 KiB

Open AccessArticle

A Bi-Level Optimization Approach to Charging Load Regulation of Electric Vehicle Fast Charging Stations Based on a Battery Energy Storage System

by Yan Bao¹, Yu Luo¹, Weige Zhang¹, Mei Huang¹, Le Yi Wang²

and Jiuchun Jiang^1,*

¹ School of Electrical Engineering, Beijing Jiaotong University, Beijing 100044, China

² Department of Electrical and Computer Engineering, Wayne State University, Detroit, MI 48202, USA

Energies 2018, 11(1), 229; https://doi.org/10.3390/en11010229 - 18 Jan 2018

Cited by 28 | Viewed by 5513

Abstract

Fast charging stations enable the high-powered rapid recharging of electric vehicles. However, these stations also face challenges due to power fluctuations, high peak loads, and low load factors, affecting the reliable and economic operation of charging stations and distribution networks. This paper introduces [...] Read more.

Fast charging stations enable the high-powered rapid recharging of electric vehicles. However, these stations also face challenges due to power fluctuations, high peak loads, and low load factors, affecting the reliable and economic operation of charging stations and distribution networks. This paper introduces a battery energy storage system (BESS) for charging load control, which is a more user-friendly approach and is more robust to perturbations. With the goals of peak-shaving, total electricity cost reduction, and minimization of variation in the state-of-charge (SOC) range, a BESS-based bi-level optimization strategy for the charging load regulation of fast charging stations is proposed in this paper. At the first level, a day-ahead optimization strategy generates the optimal planned load curve and the deviation band to be used as a reference for ensuring multiple control objectives through linear programming, and even for avoiding control failure caused by insufficient BESS energy. Based on this day-ahead optimal plan, at a second level, real-time rolling optimization converts the control process to a multistage decision-making problem. The predictive control-based real-time rolling optimization strategy in the proposed model was used to achieve the above control objectives and maintain battery life. Finally, through a horizontal comparison of two control approaches in each case study, and a longitudinal comparison of the control robustness against different degrees of load disturbances in three cases, the results indicated that the proposed control strategy was able to significantly improve the charging load characteristics, even with large disturbances. Meanwhile, the proposed approach ensures the least amount of variation in the range of battery SOC and reduces the total electricity cost, which will be of a considerable benefit to station operators. Full article

(This article belongs to the Special Issue The International Symposium on Electric Vehicles (ISEV2017))

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20 pages, 7556 KiB

Open AccessArticle

Modelling and Simulation of a Hydrostatic Steering System for Agricultural Tractors

by Barbara Zardin^1,*

, Massimo Borghi¹

, Francesco Gherardini¹

and Nicholas Zanasi²

¹ Engineering Department Enzo Ferrari, University of Modena and Reggio Emilia, Via P. Allegri 10, 41124 Modena, Italy

² CNH Industrial, San Matteo, Viale delle Nazioni 55, 41100 Modena, Italy

Energies 2018, 11(1), 230; https://doi.org/10.3390/en11010230 - 18 Jan 2018

Cited by 36 | Viewed by 9684

Abstract

The steering system of a vehicle impacts on the vehicle performance, safety and on the driver’s comfort. Moreover, in off-road vehicles using hydrostatic steering systems, the energy dissipation also becomes a critical issue. These aspects push and motivate innovation, research and analysis in [...] Read more.

The steering system of a vehicle impacts on the vehicle performance, safety and on the driver’s comfort. Moreover, in off-road vehicles using hydrostatic steering systems, the energy dissipation also becomes a critical issue. These aspects push and motivate innovation, research and analysis in the field of agricultural tractors. This paper proposes the modelling and analysis of a hydrostatic steering system for an agricultural tractor to calculate the performance of the system and determine the influence of its main design parameters. The focus here is on the driver’s steering feel, which can improve the driver’s behavior reducing unnecessary steering corrections during the working conditions. The hydrostatic steering system is quite complex and involves a hydraulic circuit and a mechanical mechanism to transmit the steering to the vehicle tires. The detailed lumped parameters model here proposed allows to simulate the dynamic behavior of the steering system and to both enhance the understanding of the system and to improve the design through parameters sensitivity analysis. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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21 pages, 12361 KiB

Open AccessArticle

An Intelligent Fault Diagnosis Method for Bogie Bearings of Metro Vehicles Based on Weighted Improved D-S Evidence Theory

by Jianqiang Liu, Aifeng Chen^* and Nan Zhao

School of Electrical Engineering, Beijing Jiaotong University, Beijing 100044, China

Energies 2018, 11(1), 232; https://doi.org/10.3390/en11010232 - 18 Jan 2018

Cited by 18 | Viewed by 3973

Abstract

Bogie bearings are very important for the safe and normal operation of metro vehicles. The prevailing fault diagnosis methods for bogie bearings generally utilize a single information source, such as vibration, temperature or acoustics. There are some shortcomings in these methods, including low [...] Read more.

Bogie bearings are very important for the safe and normal operation of metro vehicles. The prevailing fault diagnosis methods for bogie bearings generally utilize a single information source, such as vibration, temperature or acoustics. There are some shortcomings in these methods, including low accuracy and poor reliability. To address these shortcomings, this paper proposes an intelligent fault diagnosis method. Based on improved D-S (Dempster-Shafer) evidence theory, this method comprehensively analyzes vibration and temperature signals to diagnose bearing faults. In order to verify the feasibility and effectiveness of the proposed method, this study designed the hardware device and constructed a test platform. Bogie bearings with faults occurring on the outer ring, inner ring and rolling elements were tested on this platform. The diagnosis accuracy rate of the proposed fusion algorithm reached 91%, and the misdiagnosis rate was only 2%. The test results showed that the proposed method can accurately and reliably realize fault diagnosis with a high accuracy rate and a low misdiagnosis rate compared to previous methods. Thus, the proposed fault diagnosis method can accurately and effectively identify the faults of metro vehicle bogie bearings. Full article

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15 pages, 3319 KiB

Open AccessEditor’s ChoiceArticle

Data Analysis of Heating Systems for Buildings—A Tool for Energy Planning, Policies and Systems Simulation

by Michel Noussan¹

and Benedetto Nastasi^2,*

¹ Department of Energy, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy

² Department of Architectural Engineering & Technology, Environmental & Computational Design Section, TU Delft University of Technology, Julianalaan 134, 2628BL Delft, The Netherlands

Energies 2018, 11(1), 233; https://doi.org/10.3390/en11010233 - 18 Jan 2018

Cited by 38 | Viewed by 6526

Abstract

Heating and cooling in buildings is a central aspect for adopting energy efficiency measures and implementing local policies for energy planning. The knowledge of features and performance of those existing systems is fundamental to conceiving realistic energy savings strategies. Thanks to Information and [...] Read more.

Heating and cooling in buildings is a central aspect for adopting energy efficiency measures and implementing local policies for energy planning. The knowledge of features and performance of those existing systems is fundamental to conceiving realistic energy savings strategies. Thanks to Information and Communication Technologies (ICT) development and energy regulations’ progress, the amount of data able to be collected and processed allows detailed analyses on entire regions or even countries. However, big data need to be handled through proper analyses, to identify and highlight the main trends by selecting the most significant information. To do so, careful attention must be paid to data collection and preprocessing, for ensuring the coherence of the associated analyses and the accuracy of results and discussion. This work presents an insightful analysis on building heating systems of the most populated Italian region—Lombardy. From a dataset of almost 2.9 million of heating systems, selected reference values are presented, aiming at describing the features of current heating systems in households, offices and public buildings. Several aspects are considered, including the type of heating systems, their thermal power, fuels, age, nominal and measured efficiency. The results of this work can be a support for local energy planners and policy makers, and for a more accurate simulation of existing energy systems in buildings. Full article

(This article belongs to the Special Issue Energy Production Systems)

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22 pages, 4109 KiB

Open AccessFeature PaperArticle

Linking of Barriers to Energy Efficiency Improvement in Indonesia’s Steel Industry

by Apriani Soepardi^1,2,*

, Pratikto Pratikto², Purnomo Budi Santoso³, Ishardita Pambudi Tama³

and Patrik Thollander⁴

¹ Department of Industrial Engineering, University of National Development “Veteran”, Yogyakarta 55584, Indonesia

² Department of Mechanical Engineering, Brawijaya University, Malang 65145, Indonesia

³ Department of Industrial Engineering, Brawijaya University, Malang 65145, Indonesia

⁴ Department of Management and Engineering, Division of Energy System, Linköping University, Linköping SE-581 83, Sweden

Energies 2018, 11(1), 234; https://doi.org/10.3390/en11010234 - 18 Jan 2018

Cited by 20 | Viewed by 5807

Abstract

Energy use in Indonesia’s steel industry accounts for about 20–35% of total production costs. Consequently, energy end-use efficiency is a crucial measure that is used to reduce energy intensity and decrease production costs. This article aims to investigate the relationships among different barriers [...] Read more.

Energy use in Indonesia’s steel industry accounts for about 20–35% of total production costs. Consequently, energy end-use efficiency is a crucial measure that is used to reduce energy intensity and decrease production costs. This article aims to investigate the relationships among different barriers to energy efficiency improvement (EEI), using a framework with the following six constructs: government policy, the financial–economic factor, the managerial–organizational factor, the technological factor, workforce, and quality and type of feedstock and fuel used. The data were collected from steel firm practitioners in Indonesia, using a questionnaire to test our framework. The results demonstrate that the applied framework was applicable. We find that EEI is moderately influenced by all constructs but that the managerial–organizational factor has the greatest direct effect on improvements and is the most significant factor. Full article

(This article belongs to the Special Issue Sustainable and Renewable Energy Systems)

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16 pages, 7885 KiB

Open AccessArticle

Sensorless Speed Control Based on the Improved Q-MRAS Method for Induction Motor Drives

by Danyang Bao, Hong Wang^*, Xiaojie Wang and Chaoruo Zhang

Power Electronics and Electrical Drives Center, Harbin Institute of Technology (Shenzhen), Shenzhen 518055, China

Energies 2018, 11(1), 235; https://doi.org/10.3390/en11010235 - 19 Jan 2018

Cited by 12 | Viewed by 4180

Abstract

For high-power and high-performance speed control system, speed feedback signals are generally required. The employment of sensorless control technology makes the installation of the system easier and lower-cost, while its reliability needs to be improved. The robustness of the improved instantaneous reactive power [...] Read more.

For high-power and high-performance speed control system, speed feedback signals are generally required. The employment of sensorless control technology makes the installation of the system easier and lower-cost, while its reliability needs to be improved. The robustness of the improved instantaneous reactive power based on the quadrature model reference adaptive system (MRAS) with respect to the variation of the motor inductance parameter is improved by selecting the appropriate reference model and adjustable model. The improved instantaneous reactive power (Q) based on model reference adaptive system (Q-MRAS) algorithm is studied by small signal analysis, and the stability of the control system is verified by the Routh Stability Criterion. The simulation models and experimental platform for the proposed control are built in the laboratory. The feasibility and superiority are verified by the corresponding simulation and experimental results. Full article

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18 pages, 6198 KiB

Open AccessFeature PaperArticle

Energy-Saving Analysis of Solar Heating System with PCM Storage Tank

by Juan Zhao¹, Yasheng Ji¹, Yanping Yuan^1,*, Zhaoli Zhang¹ and Jun Lu²

¹ School of Mechanical Engineering, Southwest Jiaotong University, Chengdu 610031, China

² School of Urban Construction & Environment Engineering, Chongqing University, Chongqing 400045, China

Energies 2018, 11(1), 237; https://doi.org/10.3390/en11010237 - 19 Jan 2018

Cited by 33 | Viewed by 6628

Abstract

A solar heating system (SHS) with a phase change material (PCM) thermal storage tank is proposed with the view that traditional heat water storage tanks present several problems including large space requirements, significant heat loss and unstable system performance. An entire heating season [...] Read more.

A solar heating system (SHS) with a phase change material (PCM) thermal storage tank is proposed with the view that traditional heat water storage tanks present several problems including large space requirements, significant heat loss and unstable system performance. An entire heating season (November–March) is selected as the research period on the basis of numerical models of the SHS-PCM. In addition, taking a public building in Lhasa as the object, the heating conditions, contribution rate of solar energy, and overall energy-saving capability provided by the heating system are analyzed under different PCM storage tanks and different terminal forms. The results show that an SHS with a PCM tank provides a 34% increase in energy saving capability compared to an ordinary water tank heating system. It is suggested that the design selection parameters of the PCM storage tank should specify a daily heat storage capacity that satisfies 70~80% of the entire heating season. A floor radiant system with supply/return water temperatures of 40/35 °C provides the optimal operation and the largest energy saving capability. Full article

(This article belongs to the Special Issue Solar Technologies for Buildings)

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21 pages, 4663 KiB

Open AccessArticle

A New PV Array Fault Diagnosis Method Using Fuzzy C-Mean Clustering and Fuzzy Membership Algorithm

by Qiang Zhao¹, Shuai Shao¹, Lingxing Lu², Xin Liu¹ and Honglu Zhu^2,3,*

¹ School of Control and Computer Engineering, North China Electric Power University, Beijing 102206, China

² School of Renewable Energy, North China Electric Power University, Beijing 102206, China

³ State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University, Changping District, Beijing 102206, China

Energies 2018, 11(1), 238; https://doi.org/10.3390/en11010238 - 19 Jan 2018

Cited by 56 | Viewed by 5264

Abstract

Photovoltaic (PV) power station faults in the natural environment mainly occur in the PV array, and the accurate fault diagnosis is of particular significance for the safe and efficient PV power plant operation. The PV array’s electrical behavior characteristics under fault conditions is [...] Read more.

Photovoltaic (PV) power station faults in the natural environment mainly occur in the PV array, and the accurate fault diagnosis is of particular significance for the safe and efficient PV power plant operation. The PV array’s electrical behavior characteristics under fault conditions is analyzed in this paper, and a novel PV array fault diagnosis method is proposed based on fuzzy C-mean (FCM) and fuzzy membership algorithms. Firstly, clustering analysis of PV array fault samples is conducted using the FCM algorithm, indicating that there is a fixed relationship between the distribution characteristics of cluster centers and the different fault, then the fault samples are classified effectively. The membership degrees of all fault data and cluster centers are then determined by the fuzzy membership algorithm for the final fault diagnosis. Simulation analysis indicated that the diagnostic accuracy of the proposed method was 96%. Field experiments further verified the correctness and effectiveness of the proposed method. In this paper, various types of fault distribution features are effectively identified by the FCM algorithm, whether the PV array operation parameters belong to the fault category is determined by fuzzy membership algorithm, and the advantage of the proposed method is it can classify the fault data from normal operating data without foreknowledge. Full article

(This article belongs to the Special Issue PV System Design and Performance)

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25 pages, 9074 KiB

Open AccessArticle

Frequency Regulation of a Hybrid Wind–Hydro Power Plant in an Isolated Power System

by Guillermo Martínez-Lucas^*

, José Ignacio Sarasúa and José Ángel Sánchez-Fernández

Department of Hydraulic, Energy and Environmental Engineering, Universidad Politécnica de Madrid, C/Profesor Aranguren, 28040 Madrid, Spain

Energies 2018, 11(1), 239; https://doi.org/10.3390/en11010239 - 19 Jan 2018

Cited by 48 | Viewed by 8277

Abstract

Currently, some small islands with high wind potential are trying to reduce the environmental and economic impact of fossil fuels by using renewable resources. Nevertheless, the characteristics of these renewable resources negatively affect the quality of the electrical energy, causing frequency disturbances, especially [...] Read more.

Currently, some small islands with high wind potential are trying to reduce the environmental and economic impact of fossil fuels by using renewable resources. Nevertheless, the characteristics of these renewable resources negatively affect the quality of the electrical energy, causing frequency disturbances, especially in isolated systems. In this study, the combined contribution to frequency regulation of variable speed wind turbines (VSWT) and a pump storage hydropower plant (PSHP) is analyzed. Different control strategies, using the kinetic energy stored in the VSWT, are studied: inertial, proportional, and their combination. In general, the gains of the VSWT controller for interconnected systems proposed in the literature are not adequate for isolated systems. Therefore, a methodology to adjust the controllers, based on exhaustive searches, is proposed for each of the control strategies. The control strategies and methodology have been applied to a hybrid wind–hydro power plant on El Hierro Island in the Canary archipelago. At present, in this isolated power system, frequency regulation is only provided by the PSHP and diesel generators. The improvements in the quality of frequency regulation, including the VSWT contribution, have been proven based on simulating different events related to wind speed, or variations in the power demand. Full article

(This article belongs to the Special Issue Wind Generators Modelling and Control)

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22 pages, 3875 KiB

Open AccessArticle

Gas-Lifting Characteristics of Methane-Water Mixture and Its Potential Application for Self-Eruption Production of Marine Natural Gas Hydrates

by Jinming Zhang^1,2,4

, Xiaosen Li^1,2,3, Zhaoyang Chen^1,2,3,*

, Yu Zhang^1,2,3, Gang Li^1,2,3, Kefeng Yan^1,2,3 and Tao Lv^1,2,4

¹ Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou 510640, China

² Key Laboratory of Gas Hydrate, Chinese Academy of Sciences and Guangzhou Center for Gas Hydrate Research, CAS, Guangzhou 510640, China

³ Guangdong Key Laboratory of New and Renewable Energy Research and Development, Guangzhou 510640, China

⁴ University of the Chinese Academy of Sciences, Beijing 100083, China

Energies 2018, 11(1), 240; https://doi.org/10.3390/en11010240 - 19 Jan 2018

Cited by 6 | Viewed by 4166

Abstract

A gas-lifting production method was firstly proposed to transport the methane-water mixture from natural gas hydrates deposits through marine vertical pipe in this work. Aiming at UBGH2-6 site, SH7 site and GMGS2-8 site, the gas-lifting performance of methane-water mixture in the vertical pipe [...] Read more.

A gas-lifting production method was firstly proposed to transport the methane-water mixture from natural gas hydrates deposits through marine vertical pipe in this work. Aiming at UBGH2-6 site, SH7 site and GMGS2-8 site, the gas-lifting performance of methane-water mixture in the vertical pipe was investigated by numerical calculation. The potential of Natural gas hydrates (NGH) self-eruption production induced by the gas-lifting process under ideal conditions was also studied based on the energy analysis. The calculation results indicate that the gas-lifting method has great advantage in avoiding the secondary hydrates formation in marine vertical pipe and reducing energy consumption. The gas-lifting process in the vertical pipe is testified to be spontaneous in UBGH2-6 site and SH7 site during the initial 4000 and 1000 days, respectively, which indicates the energy consumption for methane-water mixture transportation is saved. Sufficient heat supply for the hydrate dissociation is crucial for the NGH self-eruption production. Sensitivity analysis indicates that the water-gas ratio has more significant influences on gas-lifting performance in the vertical pipe compared to the flow rate. With the decrease of water-gas ratio, the bottomhole pressure decreases rapidly. Thus, the reduction of water production is effective to improve the gas-lifting performance. Full article

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25 pages, 1014 KiB

Open AccessArticle

Modeling Interprovincial Cooperative Energy Saving in China: An Electricity Utilization Perspective

by Lijun Zeng^1,2, Laijun Zhao^1,3,4,*, Qin Wang¹, Bingcheng Wang², Yuan Ma², Wei Cui² and Yujing Xie⁵

¹ Sino-US Global Logistics Institute, Shanghai Jiao Tong University, Shanghai 200030, China

² College of Economics and Management, Shandong University of Science and Technology, Qingdao 266590, China

³ China Institute for Urban Governance, Shanghai Jiao Tong University, Shanghai 200030, China

⁴ Antai College of Economics and Management, Shanghai Jiao Tong University, Shanghai 200030, China

⁵ China Institute of Regulation Research, Zhejiang University of Finance & Economics, Hangzhou 310018, China

Energies 2018, 11(1), 241; https://doi.org/10.3390/en11010241 - 19 Jan 2018

Cited by 19 | Viewed by 3586

Abstract

As the world faces great challenges from climate change and environmental pollution, China urgently requires energy saving, emission reduction, and carbon reduction programmes. However, the non-cooperative energy saving model (NCESM), the simple regulation mode that is China’s main model for energy saving, is [...] Read more.

As the world faces great challenges from climate change and environmental pollution, China urgently requires energy saving, emission reduction, and carbon reduction programmes. However, the non-cooperative energy saving model (NCESM), the simple regulation mode that is China’s main model for energy saving, is not beneficial for optimization of energy and resource distribution, and cannot effectively motivate energy saving at the provincial level. Therefore, we propose an interprovincial cooperative energy saving model (CESM) from the perspective of electricity utilization, with the object of maximizing the benefits from electricity utilization of the cooperation union based on achieving the energy saving goals of the union as a whole. The CESM consists of two parts: (1) an optimization model that calculates the optimal quantities of electricity consumption for each participating province to meet the joint energy saving goal; and (2) a model that distributes the economic benefits of the cooperation among the provinces in the cooperation based on the Shapley value method. We applied the CESM to the case of an interprovincial union of Shanghai, Sichuan, Shanxi, and Gansu in China. The results, based on the data from 2001–2014, show that cooperation can significantly increase the benefits of electricity utilization for each province in the union. The total benefits of the union from utilization of electricity increased 38.38%, or 353.98 billion CNY, while the benefits to Shanghai, Sichuan, Shanxi, and Gansu were 200.28, 58.37, 57.11, and 38.22 billion CNY respectively greater under the CESM than the NCESM. The implementation of the CESM provides the provincial governments not only a flexible and incentive way to achieve short-term goals, but also a feasible and effective path to realize long-term energy saving strategies. To test the impact of different parameter values on the results of the CESM, a sensitivity analysis was conducted. Some policy recommendations are made at the central government level and the provincial government level to promote the implementation of the CESM. Full article

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26 pages, 2475 KiB

Open AccessArticle

Deep Belief Network Based Hybrid Model for Building Energy Consumption Prediction

by Chengdong Li^1,*, Zixiang Ding¹, Jianqiang Yi²

, Yisheng Lv²

and Guiqing Zhang¹

¹ School of Information and Electrical Engineering, Shandong Jianzhu University, Jinan 250101, China

² Institute of Automation, Chinese Academy of Sciences, Beijing 100190, China

Energies 2018, 11(1), 242; https://doi.org/10.3390/en11010242 - 19 Jan 2018

Cited by 55 | Viewed by 6259

Abstract

To enhance the prediction performance for building energy consumption, this paper presents a modified deep belief network (DBN) based hybrid model. The proposed hybrid model combines the outputs from the DBN model with the energy-consuming pattern to yield the final prediction results. The [...] Read more.

To enhance the prediction performance for building energy consumption, this paper presents a modified deep belief network (DBN) based hybrid model. The proposed hybrid model combines the outputs from the DBN model with the energy-consuming pattern to yield the final prediction results. The energy-consuming pattern in this study represents the periodicity property of building energy consumption and can be extracted from the observed historical energy consumption data. The residual data generated by removing the energy-consuming pattern from the original data are utilized to train the modified DBN model. The training of the modified DBN includes two steps, the first one of which adopts the contrastive divergence (CD) algorithm to optimize the hidden parameters in a pre-train way, while the second one determines the output weighting vector by the least squares method. The proposed hybrid model is applied to two kinds of building energy consumption data sets that have different energy-consuming patterns (daily-periodicity and weekly-periodicity). In order to examine the advantages of the proposed model, four popular artificial intelligence methods—the backward propagation neural network (BPNN), the generalized radial basis function neural network (GRBFNN), the extreme learning machine (ELM), and the support vector regressor (SVR) are chosen as the comparative approaches. Experimental results demonstrate that the proposed DBN based hybrid model has the best performance compared with the comparative techniques. Another thing to be mentioned is that all the predictors constructed by utilizing the energy-consuming patterns perform better than those designed only by the original data. This verifies the usefulness of the incorporation of the energy-consuming patterns. The proposed approach can also be extended and applied to some other similar prediction problems that have periodicity patterns, e.g., the traffic flow forecasting and the electricity consumption prediction. Full article

(This article belongs to the Special Issue Short-Term Load Forecasting by Artificial Intelligent Technologies)

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17 pages, 3629 KiB

Open AccessArticle

Adaptively Constrained Stochastic Model Predictive Control for the Optimal Dispatch of Microgrid

by Xiaogang Guo¹, Zhejing Bao^1,*, Zhijie Li² and Wenjun Yan¹

¹ College of Electrical Engineering, Zhejiang University, Hangzhou 310027, China

² Shandong Longkou Electricity Supply Company, State Grid Corporation of China, Longkou 267000, China

Energies 2018, 11(1), 243; https://doi.org/10.3390/en11010243 - 19 Jan 2018

Cited by 12 | Viewed by 3664

Abstract

In this paper, an adaptively constrained stochastic model predictive control (MPC) is proposed to achieve less-conservative coordination between energy storage units and uncertain renewable energy sources (RESs) in a microgrid (MG). Besides the economic objective of MG operation, the limits of state-of-charge (SOC) [...] Read more.

In this paper, an adaptively constrained stochastic model predictive control (MPC) is proposed to achieve less-conservative coordination between energy storage units and uncertain renewable energy sources (RESs) in a microgrid (MG). Besides the economic objective of MG operation, the limits of state-of-charge (SOC) and discharging/charging power of the energy storage unit are formulated as chance constraints when accommodating uncertainties of RESs, considering mild violations of these constraints are allowed during long-term operation, and a closed-loop online update strategy is performed to adaptively tighten or relax constraints according to the actual deviation probability of violation level from the desired one as well as the current change rate of deviation probability. Numerical studies show that the proposed adaptively constrained stochastic MPC for MG optimal operation is much less conservative compared with the scenario optimization based robust MPC, and also presents a better convergence performance to the desired constraint violation level than other online update strategies. Full article

(This article belongs to the Section F: Electrical Engineering)

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15 pages, 1223 KiB

Open AccessArticle

A Distributed Randomized Gradient-Free Algorithm for the Non-Convex Economic Dispatch Problem

by Jun Xie^1,*, Qingyun Yu¹ and Chi Cao²

¹ College of Energy and Electrical Engineering, Hohai University, Nanjing 211100, China

² College of Automation, Nanjing University of Posts and Telecommunications, Nanjing 210023, China

Energies 2018, 11(1), 244; https://doi.org/10.3390/en11010244 - 19 Jan 2018

Cited by 9 | Viewed by 3532

Abstract

In this paper, a distributed randomized gradient-free algorithm (DRGF) is employed to solve the complex non-convex economic dispatch problem whose non-convex constraints include valve-point loading effects, prohibited operating zones, and multiple fuel options. The DRGF uses the Gauss approximation, smoothing parameters, and a [...] Read more.

In this paper, a distributed randomized gradient-free algorithm (DRGF) is employed to solve the complex non-convex economic dispatch problem whose non-convex constraints include valve-point loading effects, prohibited operating zones, and multiple fuel options. The DRGF uses the Gauss approximation, smoothing parameters, and a random sequence to construct distributed randomized gradient-free oracles. By employing a consensus procedure, generation units can gather local information through local communication links and then process the economic dispatch data in a distributed iteration format. Based on the principle of projection optimization, a projection operator is adopted in the DRGF to deal with the discontinuous solution space. The effectiveness of the proposed approach in addressing the non-convex economic dispatch problem is demonstrated by simulations implemented on three standard test systems. Full article

(This article belongs to the Section F: Electrical Engineering)

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33 pages, 13088 KiB

Open AccessArticle

Impact of Optimum Allocation of Renewable Distributed Generations on Distribution Networks Based on Different Optimization Algorithms

by Mohamed A. Tolba^1,2,*

, Hegazy Rezk^3,4, Vladimir Tulsky², Ahmed A. Zaki Diab^2,4

, Almoataz Y. Abdelaziz⁵

and Artem Vanin²

¹ Nuclear Researches Center, Egyptian Atomic Energy Authority (EAEA), 11787 Cairo, Egypt

² Electrical Power Systems Department, NRU, Moscow Power Engineering Institute, 111250 Moscow, Russia

³ College of Engineering at Wadi Aldawaser, Prince Sattam bin Abdulaziz University, 11991 Wadi Aldawaser, Saudi Arabia

⁴ Electrical Engineering Department, Faculty of Engineering, Minia University, 61111 Minia, Egypt

⁵ Electrical Power and Machines Department, Faculty of Engineering, Ain Shams University, 11517 Cairo, Egypt

Energies 2018, 11(1), 245; https://doi.org/10.3390/en11010245 - 19 Jan 2018

Cited by 47 | Viewed by 5072

Abstract

Integration of Renewable Distributed Generations (RDGs) such as photovoltaic (PV) systems and wind turbines (WTs) in distribution networks can be considered a brilliant and efficient solution to the growing demand for energy. This article introduces new robust and effective techniques like hybrid Particle [...] Read more.

Integration of Renewable Distributed Generations (RDGs) such as photovoltaic (PV) systems and wind turbines (WTs) in distribution networks can be considered a brilliant and efficient solution to the growing demand for energy. This article introduces new robust and effective techniques like hybrid Particle Swarm Optimization in addition to a Gravitational Search Algorithm (PSOGSA) and Moth-Flame Optimization (MFO) that are proposed to deduce the optimum location with convenient capacity of RDGs units for minimizing system power losses and operating cost while improving voltage profile and voltage stability. This paper describes two stages. First, the Loss Sensitivity Factors (LSFs) are employed to select the most candidate buses for RDGs location. In the second stage, the PSOGSA and MFO are implemented to deduce the optimal location and capacity of RDGs from the elected buses. The proposed schemes have been applied on 33-bus and 69-bus IEEE standard radial distribution systems. To insure the suggested approaches validity, the numerical results have been compared with other techniques like Backtracking Search Optimization Algorithm (BSOA), Genetic Algorithm (GA), Particle Swarm Algorithm (PSO), Novel combined Genetic Algorithm and Particle Swarm Optimization (GA/PSO), Simulation Annealing Algorithm (SA), and Bacterial Foraging Optimization Algorithm (BFOA). The evaluated results have been confirmed the superiority with high performance of the proposed MFO technique to find the optimal solutions of RDGs units’ allocation. In this regard, the MFO is chosen to solve the problems of Egyptian Middle East distribution network as a practical case study with the optimal integration of RDGs. Full article

(This article belongs to the Special Issue 17TH International Conference on Environment and Electrical Engineering)

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19 pages, 7855 KiB

Open AccessArticle

Assessment of Future Whole-System Value of Large-Scale Pumped Storage Plants in Europe

by Fei Teng^*, Danny Pudjianto, Marko Aunedi

and Goran Strbac

Department of Electrical and Electronic Engineering, Imperial College London, London SW7 2AZ, UK

Energies 2018, 11(1), 246; https://doi.org/10.3390/en11010246 - 19 Jan 2018

Cited by 18 | Viewed by 4612

Abstract

This paper analyses the impacts and benefits of the pumped storage plant (PSP) and its upgrade to variable speed on generation and transmission capacity requirements, capital costs, system operating costs and carbon emissions in the future European electricity system. The combination of a [...] Read more.

This paper analyses the impacts and benefits of the pumped storage plant (PSP) and its upgrade to variable speed on generation and transmission capacity requirements, capital costs, system operating costs and carbon emissions in the future European electricity system. The combination of a deterministic system planning tool, Whole-electricity System Investment Model (WeSIM), and a stochastic system operation optimisation tool, Advanced Stochastic Unit Commitment (ASUC), is used to analyse the whole-system value of PSP technology and to quantify the impact of European balancing market integration and other competing flexible technologies on the value of the PSP. Case studies on the Pan-European system demonstrate that PSPs can reduce the total system cost by up to €13 billion per annum by 2050 in a scenario with a high share of renewables. Upgrading the PSP to variable-speed drive enhances its long-term benefits by 10–20%. On the other hand, balancing market integration across Europe may potentially reduce the overall value of the variable-speed PSP, although the effect can vary across different European regions. The results also suggest that large-scale deployment of demand-side response (DSR) leads to a significant reduction in the value of PSPs, while the value of PSPs increases by circa 18% when the total European interconnection capacity is halved. The benefit of PSPs in reducing emissions is relatively negligible by 2030 but constitutes around 6–10% of total annual carbon emissions from the European power sector by 2050. Full article

(This article belongs to the Special Issue Hydropower 2017)

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11 pages, 4490 KiB

Open AccessArticle

Reducing Energy Demand Using Wheel-Individual Electric Drives to Substitute EPS-Systems

by Jürgen Römer^1,*, Philipp Kautzmann², Michael Frey²

and Frank Gauterin²

¹ Schaeffler Technologies AG & Co., KG, Rintheimer Querallee 2, 76131 Karlsruhe, Germany

² Karlsruhe Institute of Technology, Institute of Vehicle System Technology, Kaiserstr. 12, 76131 Karlsruhe, Germany

Energies 2018, 11(1), 247; https://doi.org/10.3390/en11010247 - 20 Jan 2018

Cited by 12 | Viewed by 5920

Abstract

The energy demand of vehicles is influenced, not only by the drive systems, but also by a number of add-on systems. Electric vehicles must satisfy this energy demand completely from the battery. Hence, the use of power steering systems directly result in a [...] Read more.

The energy demand of vehicles is influenced, not only by the drive systems, but also by a number of add-on systems. Electric vehicles must satisfy this energy demand completely from the battery. Hence, the use of power steering systems directly result in a range reduction. The “e²-Lenk” joint project funded by the German Federal Ministry of Education and Research (BMBF) involves a novel steering concept for electric vehicles to integrate the function of steering assistance into the drive-train. Specific distribution of driving torque at the steered axle allows the steering wheel torque to be influenced to support the steering force. This provides a potential for complete substitution of conventional power steering systems and reduces the vehicle’s energy demand. This paper shows the potential of wheel-individual drives influencing the driver’s steering torque using a control technique based on classical EPS control plans. Compared to conventional power-assisted steering systems, a reduced energy demand becomes evident over a wide range of operating conditions. Full article

(This article belongs to the Special Issue Methods to Improve Energy Use in Road Vehicles)

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18 pages, 8250 KiB

Open AccessArticle

CFD-Driven Valve Shape Optimization for Performance Improvement of a Micro Cross-Flow Turbine

by Endashaw Tesfaye Woldemariam¹, Hirpa G. Lemu^1,* and G. Gary Wang²

¹ Department of Mechanical and Structural Engineering and Materials Science, University of Stavanger, 4036 Stavanger, Norway

² School of Mechatronics System Engineering, Simon Fraser University, Surrey, BC V5A 1S6, Canada

Energies 2018, 11(1), 248; https://doi.org/10.3390/en11010248 - 19 Jan 2018

Cited by 15 | Viewed by 6508

Abstract

Turbines are critical parts in hydropower facilities, and the cross-flow turbine is one of the widely applied turbine designs in small- and micro-hydro facilities. Cross-flow turbines are relatively simple, flexible and less expensive, compared to other conventional hydro-turbines. However, the power generation efficiency [...] Read more.

Turbines are critical parts in hydropower facilities, and the cross-flow turbine is one of the widely applied turbine designs in small- and micro-hydro facilities. Cross-flow turbines are relatively simple, flexible and less expensive, compared to other conventional hydro-turbines. However, the power generation efficiency of cross-flow turbines is not yet well optimized compared to conventional hydro-turbines. In this article, a Computational Fluid Dynamics (CFD)-driven design optimization approach is applied to one of the critical parts of the turbine, the valve. The valve controls the fluid flow, as well as determines the velocity and pressure magnitudes of the fluid jet leaving the nozzle region in the turbine. The Non-Uniform Rational B-Spline (NURBS) function is employed to generate construction points for the valve profile curve. Control points from the function that are highly sensitive to the output power are selected as optimization parameters, leading to the generation of construction points. Metamodel-assisted and metaheuristic optimization tools are used in the optimization. Optimized turbine designs from both optimization methods outperformed the original design with regard to performance of the turbine. Moreover, the metamodel-assisted optimization approach reduced the computational cost, compared to its counterpart. Full article

(This article belongs to the Section L: Energy Sources)

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26 pages, 5235 KiB

Open AccessArticle

Hot Spot Temperature and Grey Target Theory-Based Dynamic Modelling for Reliability Assessment of Transformer Oil-Paper Insulation Systems: A Practical Case Study

by Lefeng Cheng^1,2

, Tao Yu^1,2,*

, Guoping Wang³, Bo Yang⁴ and Lv Zhou⁵

¹ College of Electric Power, South China University of Technology, Guangzhou 510640, China

² Guangdong Key Laboratory of Clean Energy Technology, Guangzhou 510640, China

³ State Grid Huaian Power Supply Company, Huaian 223002, China

⁴ Faculty of Electric Power Engineering, Kunming University of Science and Technology, Kunming 650500, China

⁵ Electrical & Computer Engineering, The University of Auckland, Auckland1142, New Zealand

Energies 2018, 11(1), 249; https://doi.org/10.3390/en11010249 - 19 Jan 2018

Cited by 25 | Viewed by 6008

Abstract

This paper develops a novel dynamic correction method for the reliability assessment of large oil-immersed power transformers. First, with the transformer oil-paper insulation system (TOPIS) as the target of evaluation and the winding hot spot temperature (HST) as the core point, an HST-based [...] Read more.

This paper develops a novel dynamic correction method for the reliability assessment of large oil-immersed power transformers. First, with the transformer oil-paper insulation system (TOPIS) as the target of evaluation and the winding hot spot temperature (HST) as the core point, an HST-based static ageing failure model is built according to the Weibull distribution and Arrhenius reaction law, in order to describe the transformer ageing process and calculate the winding HST for obtaining the failure rate and life expectancy of TOPIS. A grey target theory based dynamic correction model is then developed, combined with the data of Dissolved Gas Analysis (DGA) in power transformer oil, in order to dynamically modify the life expectancy calculated by the built static model, such that the corresponding relationship between the state grade and life expectancy correction coefficient of TOPIS can be built. Furthermore, the life expectancy loss recovery factor is introduced to correct the life expectancy of TOPIS again. Lastly, a practical case study of an operating transformer has been undertaken, in which the failure rate curve after introducing dynamic corrections can be obtained for the reliability assessment of this transformer. The curve shows a better ability of tracking the actual reliability level of transformer, thus verifying the validity of the proposed method and providing a new way for transformer reliability assessment. This contribution presents a novel model for the reliability assessment of TOPIS, in which the DGA data, as a source of information for the dynamic correction, is processed based on the grey target theory, thus the internal faults of power transformer can be diagnosed accurately as well as its life expectancy updated in time, ensuring that the dynamic assessment values can commendably track and reflect the actual operation state of the power transformers. Full article

(This article belongs to the Section F: Electrical Engineering)

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19 pages, 7713 KiB

Open AccessArticle

Improvement of Shade Resilience in Photovoltaic Modules Using Buck Converters in a Smart Module Architecture

by S. Zahra Mirbagheri Golroodbari^*

, Arjen. C. De Waal and Wilfried G. J. H. M. Van Sark

Copernicus Institute, Utrecht University, Heidelberglaan 2, 3584 CS Utrecht, The Netherlands

Energies 2018, 11(1), 250; https://doi.org/10.3390/en11010250 - 19 Jan 2018

Cited by 14 | Viewed by 4545

Abstract

Partial shading has a nonlinear effect on the performance of photovoltaic (PV) modules. Different methods of optimizing energy harvesting under partial shading conditions have been suggested to mitigate this issue. In this paper, a smart PV module architecture is proposed for improvement of [...] Read more.

Partial shading has a nonlinear effect on the performance of photovoltaic (PV) modules. Different methods of optimizing energy harvesting under partial shading conditions have been suggested to mitigate this issue. In this paper, a smart PV module architecture is proposed for improvement of shade resilience in a PV module consisting of 60 silicon solar cells, which compensates the current drops caused by partial shading. The architecture consists of groups of series-connected solar cells in parallel to a DC-DC buck converter. The number of cell groups is optimized with respect to cell and converter specifications using a least-squares support vector machine method. A generic model is developed to simulate the behavior of the smart architecture under different shading patterns, using high time resolution irradiance data. In this research the shading patterns are a combination of random and pole shadows. To investigate the shade resilience, results for the smart architecture are compared with an ideal module, and also ordinary series and parallel connected architectures. Although the annual yield for the smart architecture is 79.5% of the yield of an ideal module, we show that the smart architecture outperforms a standard series connected module by 47%, and a parallel architecture by 13.4%. Full article

(This article belongs to the Special Issue PV System Design and Performance)

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16 pages, 2412 KiB

Open AccessArticle

Aspects Referring Wind Energy Integration from the Power System Point of View in the Region of Southeast Europe. Study Case of Romania

by Simona-Vasilica Oprea^1,*

, Adela Bâra¹ and Goran Majstrović²

¹ Department of Economic Informatics and Cybernetics, The Bucharest University of Economic Studies, Romana Square 6, Bucharest 010374, Romania

² Energy Institute Hrvoje Pozar, Savska cesta 163, PO Box 141, 10 000 Zagreb, Croatia

Energies 2018, 11(1), 251; https://doi.org/10.3390/en11010251 - 20 Jan 2018

Cited by 7 | Viewed by 3339

Abstract

Wind energy integration is a complex target that could refer to different aspects such as: grid capacity; power system; support scheme; environmental; social issues; etc. It is probably the less predictable renewable energy sources (RES) due to its high volatility being difficult to [...] Read more.

Wind energy integration is a complex target that could refer to different aspects such as: grid capacity; power system; support scheme; environmental; social issues; etc. It is probably the less predictable renewable energy sources (RES) due to its high volatility being difficult to be securely integrated into the power systems. This paper will focus on the wind energy integration from the power system point of view, emphasizing the case of Romania. Before going into the Romanian case, the paper analyzes the potential benefits of the regional approach in terms of power system integration, revealing that it can bring significant advantages by reducing the required power reserves or increasing wind power plants (WPP) generation. Currently, the power system integration is one of the major obstacle to large scale wind energy penetration in the region of Southeast (SE) Europe with high wind energy potential. The results of our research consist in proposing a model for estimating the balancing reserves sharing at regional level, comparing regional to country-by-country approach in terms of the power reserve requirements for balancing the operation of WPP. It definitely reveals that by regional Transmission System Operators (TSO) coordination; less reserves are needed; therefore, the space for RES enlarges. We also propose a model for Romanian power system that is able to calculate the installed power of WPP that could operate without considerable interruptions. Also, the model estimates the additional power reserves required for larger wind energy integration. This perspective can provide interesting insights on what should be foreseen as reasonable behavior of the policy makers and investors. Full article

(This article belongs to the Section F: Electrical Engineering)

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28 pages, 8967 KiB

Open AccessArticle

Drag Reduction by Laminar Flow Control

by Nils Beck^1,*, Tim Landa², Arne Seitz³, Loek Boermans⁴, Yaolong Liu¹

and Rolf Radespiel²

¹ Aeronautics Research Center Niedersachsen (NFL), TU Braunschweig, Hermann-Blenk-Straße 27, 38108 Braunschweig, Germany

² Institute of Fluid Mechanics (ISM), TU Braunschweig, Hermann-Blenk-Straße 37, 38108 Braunschweig, Germany

³ Institute of Aerodynamics and Flow Technology (DLR-AS), German Aerospace Center, Lilienthalplatz 7, 38108 Braunschweig, Germany

⁴ Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS Delft, The Netherlands

Energies 2018, 11(1), 252; https://doi.org/10.3390/en11010252 - 20 Jan 2018

Cited by 81 | Viewed by 11854

Abstract

The Energy System Transition in Aviation research project of the Aeronautics Research Center Niedersachsen (NFL) searches for potentially game-changing technologies to reduce the carbon footprint of aviation by promoting and enabling new propulsion and drag reduction technologies. The greatest potential for aerodynamic drag [...] Read more.

The Energy System Transition in Aviation research project of the Aeronautics Research Center Niedersachsen (NFL) searches for potentially game-changing technologies to reduce the carbon footprint of aviation by promoting and enabling new propulsion and drag reduction technologies. The greatest potential for aerodynamic drag reduction is seen in laminar flow control by boundary layer suction. While most of the research so far has been on partial laminarization by application of Natural Laminar Flow (NLF) and Hybrid Laminar Flow Control (HLFC) to wings, complete laminarization of wings, tails and fuselages promises much higher gains. The potential drag reduction and suction requirements, including the necessary compressor power, are calculated on component level using a flow solver with viscid/inviscid coupling and a 3D Reynolds-Averaged Navier-Stokes (RANS) solver. The effect on total aircraft drag is estimated for a state-of-the-art mid-range aircraft configuration using preliminary aircraft design methods, showing that total cruise drag can be halved compared to today’s turbulent aircraft. Full article

(This article belongs to the Special Issue Towards a Transformation to Sustainable Aviation Systems)

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25 pages, 2508 KiB

Open AccessArticle

Multi-Time Scale Model Order Reduction and Stability Consistency Certification of Inverter-Interfaced DG System in AC Microgrid

by Xiaoxiao Meng^1,2

, Qianggang Wang^1,*

, Niancheng Zhou¹, Shuyan Xiao¹ and Yuan Chi³

¹ State Key Laboratory of Power Transmission Equipment & System Security and New Technology, Chongqing University, Chongqing 400044, China

² Department of Energy Technology, Aalborg University, 9220 Aalborg, Denmark

³ School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore

Energies 2018, 11(1), 254; https://doi.org/10.3390/en11010254 - 20 Jan 2018

Cited by 10 | Viewed by 3935

Abstract

AC microgrid mainly comprise inverter-interfaced distributed generators (IIDGs), which are nonlinear complex systems with multiple time scales, including frequency control, time delay measurements, and electromagnetic transients. The droop control-based IIDG in an AC microgrid is selected as the research object in this study, [...] Read more.

AC microgrid mainly comprise inverter-interfaced distributed generators (IIDGs), which are nonlinear complex systems with multiple time scales, including frequency control, time delay measurements, and electromagnetic transients. The droop control-based IIDG in an AC microgrid is selected as the research object in this study, which comprises power droop controller, voltage- and current-loop controllers, and filter and line. The multi-time scale characteristics of the detailed IIDG model are divided based on singular perturbation theory. In addition, the IIDG model order is reduced by neglecting the system fast dynamics. The static and transient stability consistency of the IIDG model order reduction are demonstrated by extracting features of the IIDG small signal model and using the quadratic approximation method of the stability region boundary, respectively. The dynamic response consistencies of the IIDG model order reduction are evaluated using the frequency, damping and amplitude features extracted by the Prony transformation. Results are applicable to provide a simplified model for the dynamic characteristic analysis of IIDG systems in AC microgrid. The accuracy of the proposed method is verified by using the eigenvalue comparison, the transient stability index comparison and the dynamic time-domain simulation. Full article

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16 pages, 3926 KiB

Open AccessArticle

Maximum Permissible Integration Capacity of Renewable DG Units Based on System Loads

by Kadir Doğanşahin^1,*

, Bedri Kekezoğlu¹, Recep Yumurtacı¹, Ozan Erdinç^1,2 and João P. S. Catalão^2,3,4,*

¹ Department of Electrical Engineering, Yildiz Technical University, Istanbul 34220, Turkey

² Instituto de Engenharia de Sistemas e Computadores, Investigação e Desenvolvimento (INESC-ID), Instituto Superior Técnico, University of Lisbon, 1049-001 Lisbon, Portugal

³ Instituto de Engenharia de Sistemas e Computadores, Tecnologia e Ciência (INESC-TEC) and the Faculty of Engineering, University of Porto, 4200-465 Porto, Portugal

⁴ Centre for Mechanical and Aerospace Science and Technologies (C-MAST), University of Beira Interior, 6201-001 Covilha, Portugal

Energies 2018, 11(1), 255; https://doi.org/10.3390/en11010255 - 21 Jan 2018

Cited by 25 | Viewed by 4667

Abstract

Increasing demand for electricity, as well as rising environmental and economic concerns have resulted in renewable energy sources being a center of attraction. Integration of these renewable energy resources into power systems is usually achieved through distributed generation (DG) techniques, and the number [...] Read more.

Increasing demand for electricity, as well as rising environmental and economic concerns have resulted in renewable energy sources being a center of attraction. Integration of these renewable energy resources into power systems is usually achieved through distributed generation (DG) techniques, and the number of such applications increases daily. As conventional power systems do not have an infrastructure that is compatible with these energy sources and generation systems, such integration applications may cause various problems in power systems. Therefore, planning is an essential part of DG integration, especially for power systems with intermittent renewable energy sources with the objective of minimizing problems and maximizing benefits. In this study, a mathematical model is proposed to calculate the maximum permissible DG integration capacity without causing overvoltage problems in the power systems. In the proposed mathematical model, both the minimum loading condition and maximum generation condition are taken into consideration. In order to prove the effectiveness and the consistency of the proposed mathematical model, it is applied to a test system with different case studies, and the results are compared with the results obtained from other models in the literature. Full article

(This article belongs to the Special Issue Distributed Renewable Generation 2018)

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16 pages, 4667 KiB

Open AccessArticle

Numerical Study of Bubble Coalescence and Breakup in the Reactor Fuel Channel with a Vaned Grid

by Tenglong Cong^* and Xiang Zhang

Fundamental Science on Nuclear Safety and Simulation Technology Laboratory, Harbin Engineering University, 145 Nantong St, Harbin 150001, China

Energies 2018, 11(1), 256; https://doi.org/10.3390/en11010256 - 21 Jan 2018

Cited by 7 | Viewed by 3705

Abstract

The characteristics of bubbles of different sizes in fuel assembly are vital to two-phase flow resistance and heat transfer capacity. However, due to the swirl flow caused by the mixing vane, bubbles can crowd at the heated surface, which may anticipate the occurrence [...] Read more.

The characteristics of bubbles of different sizes in fuel assembly are vital to two-phase flow resistance and heat transfer capacity. However, due to the swirl flow caused by the mixing vane, bubbles can crowd at the heated surface, which may anticipate the occurrence of departure from nucleation boiling. In the current work, the adiabatic two-phase flow in a simplified fuel assembly was analyzed by using the Eulerian two-fluid model and the MUSIG (MUltiple SIze Group) model. This computational domain consists of two coolant channels and two sets of vaned spacers, with three sets of periodic boundary conditions at the side faces of the domain. The distributions of vapor phase and bubble diameters were obtained, based on which the effects of mixing vanes on the bubble characteristics were analyzed. Vapor phase crowded at the rod surface in the higher inlet vapor fraction case, but crowded in the channel center in the lower inlet vapor fraction cases. This work can be used as a reference for the design of mixing vanes to avoid the anticipation of departure of nucleation boiling that may be caused by unreasonable design. Full article

(This article belongs to the Section F: Electrical Engineering)

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16 pages, 3453 KiB

Open AccessArticle

An Evaluation of Investment in a PV Power Generation Project in the Gobi Desert Using a Real Options Model

by Yiqing Li^1,2,*, Weiguo Yang², Lixin Tian^1,3 and Jie Yang²

¹ Energy Development and Environmental Protection Strategy Research Center, Jiangsu University, Zhenjiang 212013, China

² Faculty of Science, Jiangsu University, Zhenjiang 212013, China

³ School of Mathematical Sciences, Nanjing Normal University, Nanjing 210046, China

Energies 2018, 11(1), 257; https://doi.org/10.3390/en11010257 - 21 Jan 2018

Cited by 10 | Viewed by 5117

Abstract

This paper presents a policy benefit model of a photovoltaic (PV) power generation project based on real options analysis (ROA) and the two-factor learning curve model. The main purpose is to examine the investment behavior of developing a PV project in the Gobi [...] Read more.

This paper presents a policy benefit model of a photovoltaic (PV) power generation project based on real options analysis (ROA) and the two-factor learning curve model. The main purpose is to examine the investment behavior of developing a PV project in the Gobi desert considering multiple uncertain factors. We take the environmental cost of desertification control into account for the first time in the literature. Four other uncertain factors are thermal power cost, PV power generation cost, carbon prices, and government subsidy. A binary tree method is applied to solve the proposed model, and we obtain both unit decision value and optimal investment time. Our baseline scenario illustrates that ROA is more effective than net present value (NPV) analysis when dealing with uncertainty. Our simulation results show that the government could suffer a loss in accordance with the existing subsidy policy when investing in a PV project. Therefore, the subsidy should be gradually reduced. Finally, the influence of the subsidy policy on decision value is discussed, and an appropriate subsidy is determined accordingly. Full article

(This article belongs to the Section F: Electrical Engineering)

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Review

Jump to: Editorial, Research, Other

5295 KiB

Open AccessReview

A Survey of WEC Reliability, Survival and Design Practices

by Ryan G. Coe^1,*

, Yi-Hsiang Yu² and Jennifer Van Rij²

¹ Sandia National Laboratories, Albuquerque, NM 87185, USA

² National Renewable Energy Laboratory, Golden, CO 80303, USA

Energies 2018, 11(1), 4; https://doi.org/10.3390/en11010004 - 21 Dec 2017

Cited by 44 | Viewed by 5657

Abstract

A wave energy converter must be designed to survive and function efficiently, often in highly energetic ocean environments. This represents a challenging engineering problem, comprising systematic failure mode analysis, environmental characterization, modeling, experimental testing, fatigue and extreme response analysis. While, when compared with [...] Read more.

A wave energy converter must be designed to survive and function efficiently, often in highly energetic ocean environments. This represents a challenging engineering problem, comprising systematic failure mode analysis, environmental characterization, modeling, experimental testing, fatigue and extreme response analysis. While, when compared with other ocean systems such as ships and offshore platforms, there is relatively little experience in wave energy converter design, a great deal of recent work has been done within these various areas. This paper summarizes the general stages and workflow for wave energy converter design, relying on supporting articles to provide insight. By surveying published work on wave energy converter survival and design response analyses, this paper seeks to provide the reader with an understanding of the different components of this process and the range of methodologies that can be brought to bear. In this way, the reader is provided with a large set of tools to perform design response analyses on wave energy converters. Full article

(This article belongs to the Special Issue Wave Energy Potential, Behavior and Extraction)

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18 pages, 1924 KiB

Open AccessEditor’s ChoiceReview

Role and Potential of Direct Interspecies Electron Transfer in Anaerobic Digestion

by Gahyun Baek, Jaai Kim, Jinsu Kim and Changsoo Lee^*

School of Urban and Environmental Engineering, Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Eonyang-eup, Ulju-gun, Ulsan 44919, Korea

Energies 2018, 11(1), 107; https://doi.org/10.3390/en11010107 - 3 Jan 2018

Cited by 247 | Viewed by 13198

Abstract

Anaerobic digestion (AD) is an effective biological treatment for stabilizing organic compounds in waste/wastewater and in simultaneously producing biogas. However, it is often limited by the slow reaction rates of different microorganisms’ syntrophic biological metabolisms. Stable and fast interspecies electron transfer (IET) between [...] Read more.

Anaerobic digestion (AD) is an effective biological treatment for stabilizing organic compounds in waste/wastewater and in simultaneously producing biogas. However, it is often limited by the slow reaction rates of different microorganisms’ syntrophic biological metabolisms. Stable and fast interspecies electron transfer (IET) between volatile fatty acid-oxidizing bacteria and hydrogenotrophic methanogens is crucial for efficient methanogenesis. In this syntrophic interaction, electrons are exchanged via redox mediators such as hydrogen and formate. Recently, direct IET (DIET) has been revealed as an important IET route for AD. Microorganisms undergoing DIET form interspecies electrical connections via membrane-associated cytochromes and conductive pili; thus, redox mediators are not required for electron exchange. This indicates that DIET is more thermodynamically favorable than indirect IET. Recent studies have shown that conductive materials (e.g., iron oxides, activated carbon, biochar, and carbon fibers) can mediate direct electrical connections for DIET. Microorganisms attach to conductive materials’ surfaces or vice versa according to particle size, and form conductive biofilms or aggregates. Different conductive materials promote DIET and improve AD performance in digesters treating different feedstocks, potentially suggesting a new approach to enhancing AD performance. This review discusses the role and potential of DIET in methanogenic systems, especially with conductive materials for promoting DIET. Full article

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19 pages, 8669 KiB

Open AccessReview

Phase Change Materials in Transparent Building Envelopes: A Strengths, Weakness, Opportunities and Threats (SWOT) Analysis

by Ilaria Vigna¹

, Lorenza Bianco¹

, Francesco Goia^2,*

and Valentina Serra¹

¹ Energy Department, TEBE Research Group, Politecnico di Torino, 10129 Turin, Italy

² Department of Architecture and Technology, Norwegian University of Science and Technology, 7491 Trondheim, Norway

Energies 2018, 11(1), 111; https://doi.org/10.3390/en11010111 - 3 Jan 2018

Cited by 46 | Viewed by 7008

Abstract

Building envelopes can play a crucial role in building improvement efficiency, and the adoption of Phase Change Materials (PCMs), coupled with transparent elements, may: (i) allow a better control of the heat flows from/to the outdoor environment, (ii) increase the exploitation of solar [...] Read more.

Building envelopes can play a crucial role in building improvement efficiency, and the adoption of Phase Change Materials (PCMs), coupled with transparent elements, may: (i) allow a better control of the heat flows from/to the outdoor environment, (ii) increase the exploitation of solar energy at a building scale and (iii) modulate light transmission in order to prevent glare effects. Starting from a literature review, focused on experimental works, this research identifies the main possible integrations of PCMs in transparent/translucent building envelope components (in glazing, in shutters and in multilayer façade system) in order to draw a global picture of the potential and limitations of these technologies. Transparent envelopes with PCMs have been classified from the simplest “zero” technology, which integrates the PCM in a double glass unit (DGU), to more complex solutions—with a different number of glass cavities (triple glazed unit TGU), different positions of the PCM layer (internal/external shutter), and in combination with other materials (TIM, aerogel, prismatic solar reflector, PCM curtain controlled by an electric pump). The results of the analysis have been summarised in a Strengths, Weakness, Opportunities and Threats (SWOT) analysis table to underline the strengths and weaknesses of transparent building envelope components with PCMs, and to indicate opportunities and threats for future research and building applications. Full article

(This article belongs to the Special Issue Solar Technologies for Buildings)

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15 pages, 10902 KiB

Open AccessReview

Installation of XLPE-Insulated 400 kV Submarine AC Power Cables under the Dardanelles Strait: A 4 GW Turkish Grid Reinforcement

by Roberto Benato^1,*

, İbrahim Balanuye², Fatih Köksal², Nurhan Ozan² and Ercüment Özdemirci²

¹ Department of Industrial Engineering, University of Padova, 35122 Padova, Italy

² Turkish Electricity Transmission Corporation (TEIAŞ), 06520 Ankara, Turkey

Energies 2018, 11(1), 164; https://doi.org/10.3390/en11010164 - 10 Jan 2018

Cited by 4 | Viewed by 6664

Abstract

This paper describes the 400 kV AC submarine link under the Dardanelles Strait composed of 12 submarine armoured single-core cross-linked polyethylene (XLPE)-insulated cables (plus a back-up power cable). The link consists of two parallel-operated double-circuit links named Lâpseki–Sütlüce I and Lâpseki–Sütlüce II. The [...] Read more.

This paper describes the 400 kV AC submarine link under the Dardanelles Strait composed of 12 submarine armoured single-core cross-linked polyethylene (XLPE)-insulated cables (plus a back-up power cable). The link consists of two parallel-operated double-circuit links named Lâpseki–Sütlüce I and Lâpseki–Sütlüce II. The transmissible power is 4000 MW (1000 MW per circuit) and the average length for a single-core cable is about 4.6 km: the submarine cables are part of overhead lines. This paper gives a wide account of the cable installations and, chiefly, of the cable protections on the seabed: different protection choices were extensively used (i.e., water jetting and mattressing). Full article

(This article belongs to the Section F: Electrical Engineering)

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23 pages, 4007 KiB

Open AccessReview

A Roadmap for Achieving Sustainable Energy Conversion and Storage: Graphene-Based Composites Used Both as an Electrocatalyst for Oxygen Reduction Reactions and an Electrode Material for a Supercapacitor

by Peipei Huo¹

, Peng Zhao², Yin Wang³, Bo Liu^1,*

, Guangchao Yin¹ and Mingdong Dong^3,*

¹ Laboratory of Functional Molecules and Materials, School of Physics and Optoelectronic Engineering, Shandong University of Technology, Xincun West Road 266, Zibo 255000, China

² School of Materials Science and Engineering, Shandong University of Technology, Xincun West Road 266, Zibo 255000, China

³ Interdisciplinary Nanoscience Center (iNANO), Aarhus University, DK-8000 Aarhus C, Denmark

Energies 2018, 11(1), 167; https://doi.org/10.3390/en11010167 - 10 Jan 2018

Cited by 21 | Viewed by 5465

Abstract

Based on its unique features including 2D planar geometry, high specific surface area and electron conductivity, graphene has been intensively studied as oxygen reduction reaction (ORR) electrocatalyst and supercapacitor material. On the one hand, graphene possesses standalone electrocatalytic activity. It can also provide [...] Read more.

Based on its unique features including 2D planar geometry, high specific surface area and electron conductivity, graphene has been intensively studied as oxygen reduction reaction (ORR) electrocatalyst and supercapacitor material. On the one hand, graphene possesses standalone electrocatalytic activity. It can also provide a good support for combining with other materials to generate graphene-based electrocatalysts, where the catalyst-support structure improves the stability and performance of electrocatalysts for ORR. On the other hand, graphene itself and its derivatives demonstrate a promising electrochemical capability as supercapacitors including electric double-layer capacitors (EDLCs) and pseudosupercapacitors. A hybrid supercapacitor (HS) is underlined and the advantages are elaborated. Graphene endows many materials that are capable of faradaic redox reactions with an outstanding pseudocapacitance behavior. In addition, the characteristics of graphene-based composite are also utilized in many respects to provide a porous 3D structure, formulate a novel supercapacitor with innovative design, and construct a flexible and tailorable device. In this review, we will present an overview of the use of graphene-based composites for sustainable energy conversion and storage. Full article

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41 pages, 10447 KiB

Open AccessReview

A Review of Experiments and Modeling of Gas-Liquid Flow in Electrical Submersible Pumps

by Jianjun Zhu^* and Hong-Quan Zhang

McDougall School of Petroleum Engineering, The University of Tulsa, Tulsa, OK 74104, USA

Energies 2018, 11(1), 180; https://doi.org/10.3390/en11010180 - 11 Jan 2018

Cited by 84 | Viewed by 13034

Abstract

As the second most widely used artificial lift method in petroleum production (and first in produced amount), electrical submersible pump (ESP) maintains or increases flow rate by converting kinetic energy to hydraulic pressure of hydrocarbon fluids. To facilitate its optimal working conditions, an [...] Read more.

As the second most widely used artificial lift method in petroleum production (and first in produced amount), electrical submersible pump (ESP) maintains or increases flow rate by converting kinetic energy to hydraulic pressure of hydrocarbon fluids. To facilitate its optimal working conditions, an ESP has to be operated within a narrow application window. Issues like gas involvement, changing production rate and high oil viscosity, greatly impede ESP boosting pressure. Previous experimental studies showed that the presence of gas would cause ESP hydraulic head degradation. The flow behaviors inside ESPs under gassy conditions, such as pressure surging and gas pockets, further deteriorate ESP pressure boosting ability. Therefore, it is important to know what parameters govern the gas-liquid flow structure inside a rotating ESP and how it can be modeled. This paper presents a comprehensive review on the key factors that affect ESP performance under gassy flow conditions. Furthermore, the empirical and mechanistic models for predicting ESP pressure increment are discussed. The computational fluid dynamics (CFD)-based modeling approach for studying the multiphase flow in a rotating ESP is explained as well. The closure relationships that are critical to both mechanistic and numerical models are reviewed, which are helpful for further development of more accurate models for predicting ESP gas-liquid flow behaviors. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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22 pages, 1002 KiB

Open AccessReview

Prospects of Appliance-Level Load Monitoring in Off-the-Shelf Energy Monitors: A Technical Review

by Anwar Ul Haq^*

and Hans-Arno Jacobsen

Department of Informatics (I-13), Bolzmanstr. 3, Technical University Munich, 85748 Garching, Germany

Energies 2018, 11(1), 189; https://doi.org/10.3390/en11010189 - 12 Jan 2018

Cited by 34 | Viewed by 6783

Abstract

The smart grid initiative has encouraged utility companies worldwide to roll-out new and smarter versions of energy meters. Before an extensive roll-out, which is both labor-intensive and incurs high capital costs, consumers need to be incentivised to reap the long-term benefits of such [...] Read more.

The smart grid initiative has encouraged utility companies worldwide to roll-out new and smarter versions of energy meters. Before an extensive roll-out, which is both labor-intensive and incurs high capital costs, consumers need to be incentivised to reap the long-term benefits of such smart meters. Off-the-shelf energy monitors (e-monitors) can provide consumers with an insight into such potential benefits. As e-monitors are owned by the consumer, the consumer has greater control over the data, which significantly reduces the privacy and data confidentiality concerns. Because only limited online technical information is available about e-monitors, we evaluate several existing e-monitors using an online technical survey directly from the vendors. Besides automated e-monitoring, the use of different off-the-shelf e-monitors can also help to demonstrate state-of-the-art techniques such as non-intrusive load monitoring (NILM), data analytics, and the predictive maintenance of appliances. Our survey indicates a trend towards the incorporation of such state-of-the-art capabilities, particularly the appliance-level e-monitoring and load disaggregation. We have also discussed some essential requirements to implement load disaggregation in the next generation e-monitors. In future, these intelligent e-monitoring techniques will encourage effective consumer participation in the demand-side management (DSM) programs. Full article

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23 pages, 956 KiB

Open AccessReview

The Prospect for an Australian–Asian Power Grid: A Critical Appraisal

by Edward Halawa^1,2,*, Geoffrey James³, Xunpeng (Roc) Shi^4,5

, Novieta H. Sari^6,7 and Rabindra Nepal⁸

¹ Barbara Hardy Institute, School of Engineering, University of South Australia, Mawson Lakes, SA 5095, Australia

² Centre for Renewable Energy, Research Institute for the Environment and Livelihoods, Charles Darwin University, Darwin, NT 0909, Australia

³ Institute for Sustainable Futures, University of Technology Sydney, Ultimo, NSW 2007, Australia

⁴ Australia China Relations Institute, University of Technology Sydney, Ultimo, NSW 2007, Australia

⁵ Energy Studies Institute, National University of Singapore, Singapore 119077, Singapore

⁶ Department of Communication, Universitas Nasional, Jakarta 12520, Indonesia

⁷ The School of Geography, Politics and Sociology, Newcastle University, Newcastle upon Tyne NE1 7RU, UK

⁸ School of Economics and Finance, Massey University, Auckland Campus, Albany 0632, New Zealand

Energies 2018, 11(1), 200; https://doi.org/10.3390/en11010200 - 15 Jan 2018

Cited by 30 | Viewed by 8156

Abstract

Australia is an energy net self-sufficient country rich in energy resources, from fossil-based to renewable energy. Australia, a huge continent with low population density, has witnessed impressive reduction in energy consumption in various sectors of activity in recent years. Currently, coal and natural [...] Read more.

Australia is an energy net self-sufficient country rich in energy resources, from fossil-based to renewable energy. Australia, a huge continent with low population density, has witnessed impressive reduction in energy consumption in various sectors of activity in recent years. Currently, coal and natural gas are two of Australia’s major export earners, yet its abundant renewable energy resources such as solar, wind, and tidal, are still underutilized. The majority of Asian countries, on the other hand, are in the middle of economic expansion, with increasing energy consumption and lack of energy resources or lack of energy exploration capability becoming a serious challenge. Electricity interconnection linking two or more independent grids within a country or at cross-border or regional levels has found its way into electricity markets worldwide. This concept allows for electricity exchanges that lead to optimized use and sharing of electricity generated from different sources. The interconnection also enables the long distance exploitation of renewable energy which would otherwise be physically impossible. ASEAN (Association of Southeast Asian Nations) and other regional groupings in Asia have initiated a number of interconnections to gain economic benefits. Asian’s hunger for energy for its economic development, climate change that has become a global and urgent issue to be solved, and Australia’s abundant renewable energy resources have all prompted increasing interest in a super-grid interconnection linking Australia to Asian grids, the Australian–Asian (Power) Grid (AAG). This paper overviews the existing grid interconnections as well as current initiatives at domestic, sub-regional, and regional levels worldwide, with a particular focus on Asia. The paper concludes with a critical appraisal on the benefits, potential, challenges and issues to be encountered by the AAG initiative. Full article

(This article belongs to the Section F: Electrical Engineering)

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28 pages, 697 KiB

Open AccessReview

Hydrothermal Carbonization: Modeling, Final Properties Design and Applications: A Review

by Silvia Román^1,*

, Judy Libra²

, Nicole Berge³, Eduardo Sabio¹, Kyoung Ro⁴, Liang Li³, Beatriz Ledesma¹, Andrés Álvarez¹ and Sunyoung Bae⁵

¹ Department of Applied Physics, University of Extremadura, Avda. Elvas, s/n, 06006 Badajoz, Spain

² Leibniz Institute for Agricultural Engineering and Bioeconomy, Max-Eyth-Allee 100, 14469 Potsdam-Bornim, Germany

³ Department of Civil and Environmental Engineering, University of South Carolina, 300 Main Street, Columbia, SC 29208, USA

⁴ USDA-ARS Coastal Plains Soil, Water, and Plant Research Center, 2611 West Lucas Street, Florence, SC 29501, USA

⁵ Department of Chemistry, Seoul Women’s University, 621 Hwarang-ro, Nowon-gu, Seoul 01797, Korea

Energies 2018, 11(1), 216; https://doi.org/10.3390/en11010216 - 16 Jan 2018

Cited by 151 | Viewed by 12265

Abstract

Active research on biomass hydrothermal carbonization (HTC) continues to demonstrate its advantages over other thermochemical processes, in particular the interesting benefits that are associated with carbonaceous solid products, called hydrochar (HC). The areas of applications of HC range from biofuel to doped porous [...] Read more.

Active research on biomass hydrothermal carbonization (HTC) continues to demonstrate its advantages over other thermochemical processes, in particular the interesting benefits that are associated with carbonaceous solid products, called hydrochar (HC). The areas of applications of HC range from biofuel to doped porous material for adsorption, energy storage, and catalysis. At the same time, intensive research has been aimed at better elucidating the process mechanisms and kinetics, and how the experimental variables (temperature, time, biomass load, feedstock composition, as well as their interactions) affect the distribution between phases and their composition. This review provides an analysis of the state of the art on HTC, mainly with regard to the effect of variables on the process, the associated kinetics, and the characteristics of the solid phase (HC), as well as some of the more studied applications so far. The focus is on research made over the last five years on these topics. Full article

(This article belongs to the Special Issue Thermo Fluid Conversion of Biomass)

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16 pages, 1213 KiB

Open AccessReview

The Innovative Concept of Cold District Heating Networks: A Literature Review

by Marco Pellegrini^*

and Augusto Bianchini

Department of Industrial Engineering (DIN), University of Bologna, Via Fontanelle 40, 47121 Forlì, Italy

Energies 2018, 11(1), 236; https://doi.org/10.3390/en11010236 - 19 Jan 2018

Cited by 65 | Viewed by 10927

Abstract

The development of sustainable and innovative solutions for the production and supply of energy at district level is nowadays one of the main technical challenges. In the past, district heating and cooling networks aimed to achieve greater energy efficiency through the centralization of [...] Read more.

The development of sustainable and innovative solutions for the production and supply of energy at district level is nowadays one of the main technical challenges. In the past, district heating and cooling networks aimed to achieve greater energy efficiency through the centralization of the energy production process but with relevant losses related to heat transport. Moving towards a higher share of renewables and lower demand of primary energy requires redesign of the energy district networks. The novel concept of cold district heating networks aims to combine the advantages of a centralized energy distribution system with low heat losses in energy supply. This combined effect is achieved through the centralized supply of water at relatively low temperatures (in the range 10–25 °C), which is then heated up by decentralized heat pumps. Moreover, cold district heating networks are also very suitable for cooling delivery, since cold water supplying can be directly used for cooling purposes (i.e., free cooling) or to feed decentralized chillers with very high energy efficiency ratio. This paper provides a preliminary literature review of existing cold district heating networks and then qualitatively analyses benefits and drawbacks in comparison with the alternatives currently used to produce heat and cold at district level, including the evaluation of major barriers to its further development. Full article

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29 pages, 21294 KiB

Open AccessReview

Novel Receiver-Enhanced Solar Vapor Generation: Review and Perspectives

by Aikifa Raza, Jin-You Lu, Safa Alzaim, Hongxia Li

and TieJun Zhang^*

Department of Mechanical and Materials Engineering, Masdar Institute, Khalifa University of Science and Technology, P.O. Box 54224, Abu Dhabi, UAE

Energies 2018, 11(1), 253; https://doi.org/10.3390/en11010253 - 20 Jan 2018

Cited by 64 | Viewed by 10772

Abstract

Efficient solar vapor/steam generation is important for various applications ranging from power generation, cooling, desalination systems to compact and portable devices like drinking water purification and sterilization units. However, conventional solar steam generation techniques usually rely on costly and cumbersome optical concentration systems [...] Read more.

Efficient solar vapor/steam generation is important for various applications ranging from power generation, cooling, desalination systems to compact and portable devices like drinking water purification and sterilization units. However, conventional solar steam generation techniques usually rely on costly and cumbersome optical concentration systems and have relatively low efficiency due to bulk heating of the entire liquid volume. Recently, by incorporating novel light harvesting receivers, a new class of solar steam generation systems has emerged with high vapor generation efficiency. They are categorized in two research streams: volumetric and floating solar receivers. In this paper, we review the basic principles of these solar receivers, the mechanism involving from light absorption to the vapor generation, and the associated challenges. We also highlight the two routes to produce high temperature steam using optical and thermal concentration. Finally, we propose a scalable approach to efficiently harvest solar energy using a semi-spectrally selective absorber with near-perfect visible light absorption and low thermal emittance. Our proposed approach represents a new development in thermally concentrated solar distillation systems, which is also cost-effective and easy to fabricate for rapid industrial deployment. Full article

(This article belongs to the Special Issue The Future of Solar Thermal Energy)

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5517 KiB

Open AccessConference Report

Research on a Novel Hydraulic/Electric Synergy Bus

by Kegang Zhao^1,2, Zhihao Liang¹, Yanjun Huang^2,*, Hong Wang², Amir Khajepour² and Yuke Zhen¹

¹ National Local Joint Engineering Laboratory of Automobile Parts Technology, South China University of Technology, Guangzhou 510640, China

² Department of Mechanical and Mechatronics Engineering, University of Waterloo, Waterloo, ON N2L3G1, Canada

Energies 2018, 11(1), 34; https://doi.org/10.3390/en11010034 - 24 Dec 2017

Cited by 14 | Viewed by 4896

Abstract

In recent years, increasing concerns regarding environmental pollution and requirements for lower fossil fuel consumption have increased interest in alternative hybrid powertrains. As a result, this paper presents a novel hydraulic/electric synergy powertrain with multiple working modes. The three energy sources (i.e., engine, [...] Read more.

In recent years, increasing concerns regarding environmental pollution and requirements for lower fossil fuel consumption have increased interest in alternative hybrid powertrains. As a result, this paper presents a novel hydraulic/electric synergy powertrain with multiple working modes. The three energy sources (i.e., engine, battery, and hydraulic accumulator) in this configuration are regulated by a dual planetary gear set to achieve optimal performances. This paper selects the component sizes of a hybrid electric vehicle (HEV), a hydraulic hybrid vehicle (HHV), and a hydraulic/electric synergy vehicle (HESV), based on the dynamic performance of a target vehicle (TV). In addition, this paper develops the forward simulation models of the four aforementioned vehicles in the MATLAB/Simulink/Driveline platform, in which the fuel economy simulations are carried out in relation to the Chinese urban bus cycle. The simulation results show that the fuel consumption of the three hybrid vehicles is similar, but much better than, that of the TV. Finally, based on the operating cost calculations over a five-year working period, the lowest cost ranges of the three hybrid vehicles are determined, which provides a method for choosing the optimal hybrid scheme. Full article

(This article belongs to the Special Issue The International Symposium on Electric Vehicles (ISEV2017))

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11 pages, 1422 KiB

Open AccessBrief Report

A Time for Introducing the Principle of Least Potential Energy in High School Physics

by Yuval Ben-Abu

Department of Physics and Project Unit, Sapir Academic College, Sderot, Hof Ashkelon 79165, Israel

Energies 2018, 11(1), 98; https://doi.org/10.3390/en11010098 - 3 Jan 2018

Cited by 3 | Viewed by 3074

Abstract

Comprehending physical phenomena in topics such as advanced mechanics, quantum mechanics, relativity theory, or particle physics demands one considering the system’s energy, usually under equilibrium constrains. The least potential energy principle (LPEP), which demonstrates an interesting fascinating generalization in physics, is a powerful [...] Read more.

Comprehending physical phenomena in topics such as advanced mechanics, quantum mechanics, relativity theory, or particle physics demands one considering the system’s energy, usually under equilibrium constrains. The least potential energy principle (LPEP), which demonstrates an interesting fascinating generalization in physics, is a powerful tool to understand such physics phenomena. Unfortunately, students at high school and universities are exposed to solely considering the forces acting on the system’s particle and apply the Newton’s laws on the system’s particles. Thus, they gain only partial understanding of the physical phenomena they are confronted with and find enormous difficulties to apply energy consideration when needed. If we wish providing students with necessary background to deal with advanced physics, the LPEP should be introduced already in high schools. The current essay provides examples of physics situations in equilibrium where students can apply the LPEP. Full article

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23 pages, 12813 KiB

Open AccessCase Report

Study on the Effect of Reciprocating Pump Pipeline System Vibration on Oil Transportation Stations

by Hongfang Lu^1,2,*

, Xiaonan Wu³ and Kun Huang¹

¹ School of Petroleum Engineering, Southwest Petroleum University, Chengdu 610500, China

² Trenchless Technology Center, Louisiana Tech University, Ruston, LA 71270, USA

³ School of Civil Engineering and Architecture, Southwest Petroleum University, Chengdu 610500, China

Energies 2018, 11(1), 132; https://doi.org/10.3390/en11010132 - 5 Jan 2018

Cited by 19 | Viewed by 8574

Abstract

Due to the periodic movement of the piston in the reciprocating pump, the fluid will cause a pressure pulsation, and the resulting pipeline vibration may lead to instrument distortion, pipe failure and equipment damage. Therefore, it is necessary to study the vibration phenomena [...] Read more.

Due to the periodic movement of the piston in the reciprocating pump, the fluid will cause a pressure pulsation, and the resulting pipeline vibration may lead to instrument distortion, pipe failure and equipment damage. Therefore, it is necessary to study the vibration phenomena of reciprocating pump pipelines based on pressure pulsation theory. This paper starts from the reciprocating pump pipe pressure pulsation caused by a fluid, pressure pulsation in the pipeline and the unbalanced exciting force is calculated under the action of the reciprocating pump. Then, the numerical simulation model is established based on the pipe beam model, and the rationality of the numerical simulation method is verified by indoor experiments. Finally, a case study is taken as an example to analyze the vibration law of the pipeline system, and vibration reduction measures are proposed. The following main conclusions are drawn from the analysis: (1) unbalanced exciting forces are produced in the elbows or tee joints, and it can also influence the straight pipe to different levels; (2) in actual engineering, it should be possible to prevent the simultaneous settlement of multiple places; (3) the vibration amplitude increases with the pipe thermal stress, and when the oil temperature is higher than 85 °C, it had a greater influence on the vertical vibration amplitude of the pipe. Full article

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22 pages, 4315 KiB

Open AccessConcept Paper

Isobaric Expansion Engines: New Opportunities in Energy Conversion for Heat Engines, Pumps and Compressors

by Maxim Glushenkov¹, Alexander Kronberg^1,*

, Torben Knoke² and Eugeny Y. Kenig^2,3

¹ Encontech B.V. ET/TE, P.O. Box 217, 7500 AE Enschede, The Netherlands

² Chair of Fluid Process Engineering, Paderborn University, Pohlweg 55, 33098 Paderborn, Germany

³ Chair of Thermodynamics and Heat Engines, Gubkin Russian State University of Oil and Gas, Leninsky Prospekt 65, Moscow 119991, Russia

Energies 2018, 11(1), 154; https://doi.org/10.3390/en11010154 - 8 Jan 2018

Cited by 27 | Viewed by 10187

Abstract

Isobaric expansion (IE) engines are a very uncommon type of heat-to-mechanical-power converters, radically different from all well-known heat engines. Useful work is extracted during an isobaric expansion process, i.e., without a polytropic gas/vapour expansion accompanied by a pressure decrease typical of state-of-the-art piston [...] Read more.

Isobaric expansion (IE) engines are a very uncommon type of heat-to-mechanical-power converters, radically different from all well-known heat engines. Useful work is extracted during an isobaric expansion process, i.e., without a polytropic gas/vapour expansion accompanied by a pressure decrease typical of state-of-the-art piston engines, turbines, etc. This distinctive feature permits isobaric expansion machines to serve as very simple and inexpensive heat-driven pumps and compressors as well as heat-to-shaft-power converters with desired speed/torque. Commercial application of such machines, however, is scarce, mainly due to a low efficiency. This article aims to revive the long-known concept by proposing important modifications to make IE machines competitive and cost-effective alternatives to state-of-the-art heat conversion technologies. Experimental and theoretical results supporting the isobaric expansion technology are presented and promising potential applications, including emerging power generation methods, are discussed. It is shown that dense working fluids with high thermal expansion at high process temperature and low compressibility at low temperature make it possible to operate with reasonable thermal efficiencies at ultra-low heat source temperatures (70–100 °C). Regeneration/recuperation of heat can increase the efficiency notably and extend the area of application of these machines to higher heat source temperatures. For heat source temperatures of 200–600 °C, the efficiency of these machines can reach 20–50% thus making them a flexible, economical and energy efficient alternative to many today’s power generation technologies, first of all organic Rankine cycle (ORC). Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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20 pages, 1727 KiB

Open AccessCase Report

Industrial Consumers’ Smart Grid Adoption: Influential Factors and Participation Phases

by Zheng Ma^*, Alla Asmussen and Bo Nørregaard Jørgensen

Center for Energy Informatics, Mærsk Mc-Kinney Møller Institute, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark

Energies 2018, 11(1), 182; https://doi.org/10.3390/en11010182 - 12 Jan 2018

Cited by 23 | Viewed by 5267

Abstract

The participation of industrial consumers in smart grid transition is important due to their consumption footprint, heavy energy use and complexity in the implementation of smart energy technologies. Active involvement of industrial consumers in the development of smart grid solutions is important to [...] Read more.

The participation of industrial consumers in smart grid transition is important due to their consumption footprint, heavy energy use and complexity in the implementation of smart energy technologies. Active involvement of industrial consumers in the development of smart grid solutions is important to ensure the energy system transformation. Despite the importance of industrial consumers has been identified, the empirical studies on the smart grid still mainly address residential and commercial consumers. Therefore, based on four case studies with two industrial consumers, one energy consulting company and one electricity retailer, this paper investigates the factors that influence industrial consumers’ acceptance of smart grid solutions, and how the influential factors are relevant to the smart grid adoption phases. Eleven influential factors are identified that impact on four stages for industrial consumers’ adoption of smart grid solutions (inscription, translation, framing, and stabilization stages). The eleven influential factors are: awareness of multiple contexts, shared support, return-of-investment, ease of use, flexibility and dynamic pricing, liberalization and energy tariff structure, customer focus, solution integration, process improvement, service quality, and company’s green image. Full article

(This article belongs to the Special Issue Industrial Energy Efficiency 2018)

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