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188 KiB

Open AccessEditorial

Biomass Chars: Elaboration, Characterization and Applications

by Mejdi Jeguirim and Lionel Limousy

Energies 2017, 10(12), 2040; https://doi.org/10.3390/en10122040 - 3 Dec 2017

Cited by 7 | Viewed by 2838

Abstract

n/a Full article

(This article belongs to the Special Issue Biomass Chars: Elaboration, Characterization and Applications)

Research

Jump to: Editorial, Review, Other

4579 KiB

Open AccessArticle

Modeling and Experimental Study of a Small Scale Olive Pomace Gasifier for Cogeneration: Energy and Profitability Analysis

by Domenico Borello, Antonio M. Pantaleo, Michele Caucci, Benedetta De Caprariis, Paolo De Filippis and Nilay Shah

Energies 2017, 10(12), 1930; https://doi.org/10.3390/en10121930 - 23 Nov 2017

Cited by 30 | Viewed by 4390

Abstract

A thermodynamic model of a combined heat and power (CHP) plant, fed by syngas produced by dry olive pomace gasification is here presented. An experimental study is carried out to inform the proposed model. The plant is designed to produce electric power (200 [...] Read more.

A thermodynamic model of a combined heat and power (CHP) plant, fed by syngas produced by dry olive pomace gasification is here presented. An experimental study is carried out to inform the proposed model. The plant is designed to produce electric power (200 kW_el) and hot-water by using a cogenerative micro gas turbine (micro GT). Before being released, exhausts are used to dry the biomass from 50% to 17% wb. The ChemCad software is used to model the gasification process, and input data to inform the model are taken from experimental tests. The micro GT and cogeneration sections are modeled assuming data from existing commercial plants. The paper analyzes the whole conversion process from wet biomass to heat and power production, reporting energy balances and costs analysis. The investment profitability is assessed in light of the Italian regulations, which include feed-in-tariffs for biomass based electricity generation. Full article

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

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5872 KiB

Open AccessArticle

Effective Loss Minimization and Allocation of Unbalanced Distribution Network

by Manvir Kaur and Smarajit Ghosh

Energies 2017, 10(12), 1931; https://doi.org/10.3390/en10121931 - 23 Nov 2017

Cited by 12 | Viewed by 3540

Abstract

An efficient distribution network must be able to supply power with good voltage profile. The main objective of the proposed work is to allocate losses of the unbalanced distribution network by the firefly algorithm in regulated and deregulated environments before and after loss [...] Read more.

An efficient distribution network must be able to supply power with good voltage profile. The main objective of the proposed work is to allocate losses of the unbalanced distribution network by the firefly algorithm in regulated and deregulated environments before and after loss minimization. Reconfiguration is one of the methods for loss reduction of unbalanced distribution network. Further, optimal placement of distributed generation and capacitor in the reconfigured unbalanced distribution network can further reduce the loss. The results of reconfigured unbalanced distribution network in regulated environment have already been reported. In this paper reconfiguration of an unbalanced distribution network in a deregulated environment is also carried out using an established Fuzzy Firefly algorithm. Loss sensitivity factor of unbalanced distribution networks is used to get the appropriate location of distributed generation and capacitor to be placed in the unbalanced distribution network. Their ratings have been found out by using bacteria foraging optimization algorithm (BFOA). The suggested loss allocation method using Firefly algorithm is implemented at first on 13 node unbalanced distribution network to check the performance of the proposed loss allocation method when compared to other available method. Finally the proposed method has been implemented on 25 node unbalanced distribution network. Both of the implementations are carried out under MATLAB environment. Full article

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4403 KiB

Open AccessArticle

Optimization of the Heating Element in a Gas-Gas Heater Using an Integrated Analysis Model

by Young Mun Lee, Heeyoon Chung, Seon Ho Kim, Hyeng Sub Bae and Hyung Hee Cho

Energies 2017, 10(12), 1932; https://doi.org/10.3390/en10121932 - 23 Nov 2017

Cited by 5 | Viewed by 9337

Abstract

Gas-gas heaters (GGHs) are used to reheat gases through desulfurization in coal-fired power plants to reduce low-temperature corrosion and white smoke. Wrinkled heating elements are installed inside the GGH to perform effective heat exchange. An optimization study of the heating element shape was [...] Read more.

Gas-gas heaters (GGHs) are used to reheat gases through desulfurization in coal-fired power plants to reduce low-temperature corrosion and white smoke. Wrinkled heating elements are installed inside the GGH to perform effective heat exchange. An optimization study of the heating element shape was conducted to reduce the differential pressure effectively and improve performance. An integrated analysis model was applied. Based on actual operational data, a computational fluid dynamic analysis was conducted on the L-type heating element and GGH system. The experiments applied the optimal latin hypercube sampling method, and numerical analysis was performed for each sample. Based on the response surface, the result of the sample was optimized through the pointer algorithm. For the integrated analysis model, validation was performed by comparison with the actual operational data, and the thermal-fluid characteristics of the heating element and GGH system were analyzed to set three parameters: plate angle, undulated angle, and pitch 1. From the optimization result, increases in the undulated angle and pitch 1 reduce the pressure drop by widening the heating element cross section. By increasing the plate angle, the heat transfer area is secured and the reduced heat transfer coefficient is compensated, improving the GGH performance. Full article

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

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6156 KiB

Open AccessArticle

Design and Performance Analysis of a Coal Bed Gas Drainage Machine Based on Incomplete Non-Circular Gears

by Guiyun Xu, Dezheng Hua, Weijun Dai and Xiaoguang Zhang

Energies 2017, 10(12), 1933; https://doi.org/10.3390/en10121933 - 23 Nov 2017

Cited by 15 | Viewed by 4962

Abstract

In order to solve the problem of reciprocating motion in no beam supported mining machines, putting energy saving as a starting point in Coal Bed Methane (CBM) exploitation, this paper designs a completely non-circular gear automatic reversing vertical drainage machine based on the [...] Read more.

In order to solve the problem of reciprocating motion in no beam supported mining machines, putting energy saving as a starting point in Coal Bed Methane (CBM) exploitation, this paper designs a completely non-circular gear automatic reversing vertical drainage machine based on the theory of non-circular gear transmission. In the field of CBM exploitation, the use of non-circular gears is an attempt at an innovation. First of all, according to the working conditions of the pump and use requirements, a scheme is established whereby the one-way rotary motion of the motor is changed into reciprocating motion so that it could drive the oil pumping rod to achieve the upper and lower mining. Secondly, this paper has designed a new type non-circular gear reversing box as the core component to replace the traditional four beam linkage mechanism and also provides elaborate calculations. Finally, the movement simulation of the non-circular gear reversing gear system is completed. Comparing the motion simulation results with the theoretical ones, the correctness of our theoretical analysis can be verified. Compared with the traditional devices, the new coal seam gas drainage machine model design has nearly 11% higher efficiency, which has obvious energy saving effects and reduces the cost of mining coal seam gas. Full article

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1094 KiB

Open AccessFeature PaperArticle

Principal Mismatch Patterns Across a Simplified Highly Renewable European Electricity Network

by Mads Raunbak, Timo Zeyer, Kun Zhu and Martin Greiner

Energies 2017, 10(12), 1934; https://doi.org/10.3390/en10121934 - 23 Nov 2017

Cited by 18 | Viewed by 4861

Abstract

Due to its spatio-temporal variability, the mismatch between the weather and demand patterns challenges the design of highly renewable energy systems. A principal component analysis is applied to a simplified networked European electricity system with a high share of wind and solar power [...] Read more.

Due to its spatio-temporal variability, the mismatch between the weather and demand patterns challenges the design of highly renewable energy systems. A principal component analysis is applied to a simplified networked European electricity system with a high share of wind and solar power generation. It reveals a small number of important mismatch patterns, which explain most of the system’s required backup and transmission infrastructure. Whereas the first principal component is already able to reproduce most of the temporal mismatch variability for a solar dominated system, a few more principal components are needed for a wind dominated system. Due to its monopole structure the first principal component causes most of the system’s backup infrastructure. The next few principal components have a dipole structure and dominate the transmission infrastructure of the renewable electricity network. Full article

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

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3427 KiB

Open AccessFeature PaperArticle

Prospects for Increased Energy Recovery from Horse Manure—A Case Study of Management Practices, Environmental Impact and Costs

by Åsa Hadin, Karl Hillman and Ola Eriksson

Energies 2017, 10(12), 1935; https://doi.org/10.3390/en10121935 - 23 Nov 2017

Cited by 11 | Viewed by 6134

Abstract

A transition to renewable energy sources and a circular economy has increased interest in renewable resources not usually considered as energy sources or plant nutrient resources. Horse manure exemplifies this, as it is sometimes recycled but not often used for energy purposes. The [...] Read more.

A transition to renewable energy sources and a circular economy has increased interest in renewable resources not usually considered as energy sources or plant nutrient resources. Horse manure exemplifies this, as it is sometimes recycled but not often used for energy purposes. The purpose of this study was to explore horse manure management in a Swedish municipality and prospects for energy recovery. The case study includes a survey of horse manure practices, environmental assessment of horse manure treatment in a biogas plant, including associated transport, compared to on-site unmanaged composting, and finally a simplified economic analysis. It was found that horse manure management was characterized by indoor collection of manure most of the year and storage on concrete slabs or in containers, followed by direct application on arable land. Softwood was predominantly used as bedding, and bedding accounted for a relatively small proportion (13%) of the total mix. Anaerobic digestion was indicated to reduce potential environmental impact in comparison to unmanaged composting, mainly due to biogas substituting use of fossil fuels. The relative environmental impact from transport of manure from horse facilities to anaerobic digestion plant was small. Results also indicate a relatively high cost for horse keepers to change from composting on site to anaerobic digestion in a centralized plant. Full article

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2693 KiB

Open AccessArticle

Search Improvement Process-Chaotic Optimization-Particle Swarm Optimization-Elite Retention Strategy and Improved Combined Cooling-Heating-Power Strategy Based Two-Time Scale Multi-Objective Optimization Model for Stand-Alone Microgrid Operation

by Fei Wang, Lidong Zhou, Hui Ren and Xiaoli Liu

Energies 2017, 10(12), 1936; https://doi.org/10.3390/en10121936 - 23 Nov 2017

Cited by 37 | Viewed by 4770

Abstract

The optimal dispatching model for a stand-alone microgrid (MG) is of great importance to its operation reliability and economy. This paper aims at addressing the difficulties in improving the operational economy and maintaining the power balance under uncertain load demand and renewable generation, [...] Read more.

The optimal dispatching model for a stand-alone microgrid (MG) is of great importance to its operation reliability and economy. This paper aims at addressing the difficulties in improving the operational economy and maintaining the power balance under uncertain load demand and renewable generation, which could be even worse in such abnormal conditions as storms or abnormally low or high temperatures. A new two-time scale multi-objective optimization model, including day-ahead cursory scheduling and real-time scheduling for finer adjustments, is proposed to optimize the operational cost, load shedding compensation and environmental benefit of stand-alone MG through controllable load (CL) and multi-distributed generations (DGs). The main novelty of the proposed model is that the synergetic response of CL and energy storage system (ESS) in real-time scheduling offset the operation uncertainty quickly. And the improved dispatch strategy for combined cooling-heating-power (CCHP) enhanced the system economy while the comfort is guaranteed. An improved algorithm, Search Improvement Process-Chaotic Optimization-Particle Swarm Optimization-Elite Retention Strategy (SIP-CO-PSO-ERS) algorithm with strong searching capability and fast convergence speed, was presented to deal with the problem brought by the increased errors between actual renewable generation and load and prior predictions. Four typical scenarios are designed according to the combinations of day types (work day or weekend) and weather categories (sunny or rainy) to verify the performance of the presented dispatch strategy. The simulation results show that the proposed two-time scale model and SIP-CO-PSO-ERS algorithm exhibit better performance in adaptability, convergence speed and search ability than conventional methods for the stand-alone MG’s operation. Full article

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

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6445 KiB

Open AccessArticle

A Cascade Disaster Caused by Geological and Coupled Hydro-Mechanical Factors—Water Inrush Mechanism from Karst Collapse Column under Confining Pressure

by Hao Li, Haibo Bai, Jianjun Wu, Zhanguo Ma, Kai Ma, Guangming Wu, Yabo Du and Shixin He

Energies 2017, 10(12), 1938; https://doi.org/10.3390/en10121938 - 23 Nov 2017

Cited by 18 | Viewed by 4162

Abstract

The water inrush from karst collapse column (KCC) is a cascading, vicious cycle disaster caused by geological and mining activities, that can cause serious casualties and property losses. The key to preventing this risk is to study the mechanism of water inrush under [...] Read more.

The water inrush from karst collapse column (KCC) is a cascading, vicious cycle disaster caused by geological and mining activities, that can cause serious casualties and property losses. The key to preventing this risk is to study the mechanism of water inrush under confining pressure. Aiming at the investigationg the characteristics of the KCC named X1 in Chensilou mine, a series of methods, including connectivity experiments, water pressure monitoring tests in two side-walls, and numerical simulations based on plastic damage-seepage (PD-S) theory have been developed. The methods are used to test the security of the 2519 mining area, the damage thickness, pore water pressure, and seepage vector in the X1. The results indicate that the X1 has a certain water blocking capacity. In addition, with the decrease of confining pressure and increase of shear stress, deviatoric stress could cause the increase of permeability, the reduction of strength, and the reduction of pore water pressure in KCC. Therefore the increased effective stress in the rock will force the rock to become more fractured. Conversely, the broken rock could cause the change of stress, and further initiate new plastic strains, damage and pore water pressure until a new equilibrium is reached. This cascading water inrush mechanism will contribute to the exploitation of deep coal resources in complex geological and hydrogeological conditions. Full article

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

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6382 KiB

Open AccessArticle

Sensorless Control of Late-Stage Offshore DFIG-WT with FSTP Converters by Using EKF to Ride through Hybrid Faults

by Wei Li, Gengyin Li, Kai Ni, Yihua Hu and Xinhua Li

Energies 2017, 10(12), 1939; https://doi.org/10.3390/en10121939 - 23 Nov 2017

Cited by 3 | Viewed by 3912

Abstract

A hybrid fault scenario in a late-stage offshore doubly-fed induction generator (DFIG)-based wind turbine (DFIG-WT) with converter open-circuit fault and position sensor failure is investigated in this paper. An extended Kalman filter (EKF)-based sensorless control strategy is utilized to eliminate the encoder. Based [...] Read more.

A hybrid fault scenario in a late-stage offshore doubly-fed induction generator (DFIG)-based wind turbine (DFIG-WT) with converter open-circuit fault and position sensor failure is investigated in this paper. An extended Kalman filter (EKF)-based sensorless control strategy is utilized to eliminate the encoder. Based on the detailed analysis of the seventh-order dynamic state space model of DFIG, along with the input voltage signals and measured current signals, the EKF algorithm for DFIG is designed to estimate the rotor speed and position. In addition, the bridge arm open circuit in the back-to-back (BTB) power converter of DFIG is taken as a commonly-encountered fault due to the fragility of semiconductor switches. Four-switch three-phase (FSTP) topology-based fault-tolerant converters are employed for post-fault operation by considering the minimization of switching losses and reducing the circuit complexity. Moreover, a simplified space vector pulse width modulation (SVPWM) technique is proposed to reduce the computational burden, and a voltage balancing scheme is put forward to increase the DC-bus voltage utilization rate. Simulation studies are carried out in MATLAB/Simulink2017a (MathWorks, Natick, MA, USA) to demonstrate the validity of the proposed hybrid fault-tolerant strategy for DFIG-WT, with the wind speed fluctuation, measurement noises and grid voltage sag taken into consideration. Full article

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

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1509 KiB

Open AccessArticle

On Hybrid Energy Utilization in Wireless Sensor Networks

by Mohammad Tala’t, Chih-Min Yu, Meng-Lin Ku and Kai-Ten Feng

Energies 2017, 10(12), 1940; https://doi.org/10.3390/en10121940 - 23 Nov 2017

Cited by 4 | Viewed by 3699

Abstract

In a wireless sensor network (WSN), many applications have limited energy resources for data transmission. In order to accomplish a better green communication for WSN, a hybrid energy scheme can supply a more reliable energy source. In this article, hybrid energy utilization—which consists [...] Read more.

In a wireless sensor network (WSN), many applications have limited energy resources for data transmission. In order to accomplish a better green communication for WSN, a hybrid energy scheme can supply a more reliable energy source. In this article, hybrid energy utilization—which consists of constant energy source and solar harvested energy—is considered for WSN. To minimize constant energy usage from the hybrid source, a Markov decision process (MDP) is designed to find the optimal transmission policy. With a finite packet buffer and a finite battery size, an MDP model is presented to define the states, actions, state transition probabilities, and the cost function including the cost values for all actions. A weighted sum of constant energy source consumption and a packet dropping probability (PDP) are adopted as the cost value, enabling us to find the optimal solution for balancing the minimization of the constant energy source utilization and the PDP using a value iteration algorithm. As shown in the simulation results, the performance of optimal solution using MDP achieves a significant improvement compared to solution without its use. Full article

(This article belongs to the Special Issue Industrial Energy Efficiency 2018)

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6235 KiB

Open AccessArticle

Resilient Prosumer Scenario in a Changing Regulatory Environment—The UniRCon Solution

by Mihai Sanduleac, Irina Ciornei, Mihaela Albu, Lucian Toma, Marta Sturzeanu and João F. Martins

Energies 2017, 10(12), 1941; https://doi.org/10.3390/en10121941 - 23 Nov 2017

Cited by 11 | Viewed by 4551

Abstract

Technological developments are pushing for new solutions based upon massive integration of renewable electricity generation in networks already facing many challenges. This paper presents a novel approach to managing the energy transfer towards prosumers making use of smart management of local energy storage. [...] Read more.

Technological developments are pushing for new solutions based upon massive integration of renewable electricity generation in networks already facing many challenges. This paper presents a novel approach to managing the energy transfer towards prosumers making use of smart management of local energy storage. The proposed design (including storage dimensioning) is based on several operating scenarios in which the prosumer might operate as: (i) a “load only” entity (from a grid perspective), thus exhibiting investment resiliency against regulatory changes and high energy efficiency; or (ii) a prosumer, in case regulatory opportunistic profit might be available. This can be realized within a newly proposed Uni-directional Resilient Consumer (UniRCon) architecture. The major aim of the proposed architecture is to achieve optimal self-consumption while avoiding curtailment even in a changing regulatory environment like, for example, the total lack of incentives for generation based on renewable energy sources (RES). One of the major advantages of the proposed architecture consists in the adaptability to changes in the regulatory and market environment. The term resilience is used with multiple meanings: (a) the prosumer’s financial resilience against regulatory changes when investment calculations assume no-grid injections; (b) the prosumer’s technical resilience, with electrical design based on standalone operation; (c) the resilience of clusters of interconnected end-user installations with enabled community-level electricity exchange, independent of the existing main grid supply; (d) the contribution to grid resilience, by enabling AC microgrid (MG) operation in island mode when large portions of the grid are formed by clusters of UniRCon prosumers (the ease of islanding segmentation of the local grid in case of emergencies). For proof of concept, three use-cases are detailed: (i) photovoltaic (PV) installations connected behind the meter; (ii) PV and storage available and controllable behind the meter; and (iii) the UniRCon architecture. The three use-cases are then compared and assessed for four near-future timelines as starting points for the investment. Numerical simulations show the attractiveness of the UniRCon solution in what concerns both system operation costs and supply resilience. Savings are expressed as opportunity savings arising from difference in tariffs while charging and discharging the storage unit and due to the avoidance of curtailment, as well as special taxes for the connection of PV (depending on regulatory environment). An extension of the UniRCon concept is presented also at community scale, with neighbourhood energy exchange inside a resilient cluster. Full article

(This article belongs to the Special Issue Resilience of Energy Systems 2017)

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1261 KiB

Open AccessArticle

Energy Poverty in China: A Dynamic Analysis Based on a Hybrid Panel Data Decision Model

by Bing Wang, Hua-Nan Li, Xiao-Chen Yuan and Zhen-Ming Sun

Energies 2017, 10(12), 1942; https://doi.org/10.3390/en10121942 - 23 Nov 2017

Cited by 41 | Viewed by 6758

Abstract

Renewable energy can help to tackle energy poverty issues of the availability of modern energy services and the sustainability of energy supply. Based on the concept of the Energy Development Index, published by International Energy Agency, this paper builds the clean energy development [...] Read more.

Renewable energy can help to tackle energy poverty issues of the availability of modern energy services and the sustainability of energy supply. Based on the concept of the Energy Development Index, published by International Energy Agency, this paper builds the clean energy development index and applies the Grey incidence decision method to analyze regional energy poverty issues in China. A model using panel data investigates the influencing factors that are governing energy poverty alleviation and the relationship between energy poverty and social development. The improved index system not only considers the access to modern energy services, but also addresses the cleanliness of energy supply and the transition to clean energy consumption for cooking. The results indicate that due to insufficient clean energy development, China’s Northeast and West regions have experienced increasing energy poverty problems, while energy poverty in the Southwest region has improved considerably because of its renewable energy development. Urbanization, affordability, and renewable energy development can increase access to modern energy services, contributing to energy poverty alleviation. However, the role of rural household consumption levels in energy poverty alleviation should be considered in rural energy policy. Full article

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4770 KiB

Open AccessArticle

Charge and Discharge Analyses of a PCM Storage System Integrated in a High-Temperature Solar Receiver

by Ambra Giovannelli and Muhammad Anser Bashir

Energies 2017, 10(12), 1943; https://doi.org/10.3390/en10121943 - 23 Nov 2017

Cited by 30 | Viewed by 5070

Abstract

Solar Dish Micro Gas Turbine (MGT) systems have the potential to become interesting small-scale power plants in off-grid or mini-grid contexts for electricity or poly-generation production. The main challenging component of such systems is the solar receiver which should operate at high temperatures [...] Read more.

Solar Dish Micro Gas Turbine (MGT) systems have the potential to become interesting small-scale power plants in off-grid or mini-grid contexts for electricity or poly-generation production. The main challenging component of such systems is the solar receiver which should operate at high temperatures with concentrated solar radiations, which strongly vary with time. This paper deals with the design and the analysis of a novel solar receiver integrated with a short-term storage system based on Phase Change Materials to prevent sudden variations in the maximum temperature of the MGT working fluid. Particularly, the charge and discharge behavior of the storage system was analyzed by means of Computational Fluid Dynamic methods to evaluate the potentiality of the concept and the component capabilities. Achieved results were highly satisfactory: the novel solar receiver has a good thermal inertia and can prevent relevant fluctuations in the working fluid temperature for 20–30 min. 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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628 KiB

Open AccessEditor’s ChoiceArticle

Normal Behaviour Models for Wind Turbine Vibrations: Comparison of Neural Networks and a Stochastic Approach

by Pedro G. Lind, Luis Vera-Tudela, Matthias Wächter, Martin Kühn and Joachim Peinke

Energies 2017, 10(12), 1944; https://doi.org/10.3390/en10121944 - 23 Nov 2017

Cited by 41 | Viewed by 6630

Abstract

To monitor wind turbine vibrations, normal behaviour models are built to predict tower top accelerations and drive-train vibrations. Signal deviations from model prediction are labelled as anomalies and are further investigated. In this paper we assess a stochastic approach to reconstruct the 1 [...] Read more.

To monitor wind turbine vibrations, normal behaviour models are built to predict tower top accelerations and drive-train vibrations. Signal deviations from model prediction are labelled as anomalies and are further investigated. In this paper we assess a stochastic approach to reconstruct the 1 Hz tower top acceleration signal, which was measured in a wind turbine located at the wind farm Alpha Ventus in the German North Sea. We compare the resulting data reconstruction with that of a model based on a neural network, which has been previously reported as a data-mining algorithm suitable for reconstructing this signal. Our results present evidence that the stochastic approach outperforms the neural network in the high frequency domain (1 Hz). Although neural network retrieves accurate step-forward predictions, with low mean square errors, the stochastic approach predictions better preserve the statistics and the frequency components of the original signal, retaining high accuracy levels. The implementation of our stochastic approach is available as open source code and can easily be adapted for other situations involving stochastic data reconstruction. Based on our findings we argue that such an approach could be implemented in signal reconstruction for monitoring purposes or for abnormal behaviour detection. Full article

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

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15940 KiB

Open AccessArticle

Numerical Study on the Acoustic Characteristics of an Axial Fan under Rotating Stall Condition

by Lei Zhang, Chuang Yan, Ruiyang He, Kang Li and Qian Zhang

Energies 2017, 10(12), 1945; https://doi.org/10.3390/en10121945 - 23 Nov 2017

Cited by 6 | Viewed by 5226

Abstract

Axial fan is an important piece of equipment in the thermal power plant that provides enough air for combustion of coal. This paper focuses on the aerodynamic noise characteristics of an axial fan in the development from stall inception to stall cells. The [...] Read more.

Axial fan is an important piece of equipment in the thermal power plant that provides enough air for combustion of coal. This paper focuses on the aerodynamic noise characteristics of an axial fan in the development from stall inception to stall cells. The aerodynamic noise characteristic of monitoring region in time and frequency domains was simulated employing the large-eddy simulation (LES), with the addition of throttle setting and the Ffowcs Williams-Hawkings (FW-H) noise model. The numerical results show that, under the design condition, the acoustic pressure presents regular periodicity along with the time. The noise energy is concentrated with high energy of the fundamental frequency and high order harmonics. During the stall inception stage, the acoustic pressure amplitude starts fluctuating and discrete frequencies are increased significantly in the low frequency; among them, there are three obvious discrete frequencies: 27.66 Hz, 46.10 Hz and 64.55 Hz. On the rotating stall condition, the fluctuation of the acoustic pressure level and amplitude are more serious than that mentioned above. During the whole evolution process, the acoustic pressure peak is difficult to keep stable all the time, and a sudden increase of the peak value at the 34.5th revolution corresponds to the relative velocity’s first sudden increase at the time when the valve coefficient is 0.780. Full article

(This article belongs to the Special Issue Engineering Fluid Dynamics 2018)

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9921 KiB

Open AccessArticle

Impacts of Reclassified Brown Coal Reserves on the Energy System and Deep Decarbonisation Target in the Czech Republic

by Lukáš Rečka and Milan Ščasný

Energies 2017, 10(12), 1947; https://doi.org/10.3390/en10121947 - 23 Nov 2017

Cited by 8 | Viewed by 4427

Abstract

In 2015, a 24-year-long prohibition of coal mining within some territories in the North Bohemia coal basin was lifted and as a consequence mining a part of the brown coal reserves might well be resumed. This paper analyses the impacts of maintaining the [...] Read more.

In 2015, a 24-year-long prohibition of coal mining within some territories in the North Bohemia coal basin was lifted and as a consequence mining a part of the brown coal reserves might well be resumed. This paper analyses the impacts of maintaining the ban versus three options for a less environmentally stringent policy on the Czech energy system; fuel- and technology-mix, the costs of generating energy, emissions and related external costs up to 2050. We find that overall the effect of lifting the ban, on coal usage, air pollutant emissions and hence externalities is rather small, up to 1–2% compared to the level of keeping the ban. The small difference in the impacts remains even if changes in the prices of fossil fuels and European Emission Allowances or different development in nuclear power usage are assumed. In fact, changing these assumptions will result in more pronounced differences in the impacts than the four policy options might deliver. Maintaining the ban would not achieve the European Energy Roadmap 2050 target and the newly adopted policy and the other two counter-environmental proposals would miss the 80% reduction target to an even greater degree. The environmental and external health costs attributable to emissions of local air pollutants stemming from power generation are in a range of €26–32 billion over the whole period and decline from about 0.5% of gross domestic product in 2015 to 0.1% in 2050. Full article

(This article belongs to the Special Issue Energy Market Transitions)

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4882 KiB

Open AccessArticle

Internal Combustion Engine Model for Combined Heat and Power (CHP) Systems Design

by Nikolaos Kalantzis, Antonios Pezouvanis and Kambiz M. Ebrahimi

Energies 2017, 10(12), 1948; https://doi.org/10.3390/en10121948 - 25 Nov 2017

Cited by 13 | Viewed by 6676

Abstract

A model based, energy focused, quasi-stationary waste heat driven, internal combustion engine (ICE) centred design methodology for cogeneration (heat and electricity) systems is presented. The developed parametric model could be used for system sizing, performance evaluation, and optimization. This paper presents a systematic [...] Read more.

A model based, energy focused, quasi-stationary waste heat driven, internal combustion engine (ICE) centred design methodology for cogeneration (heat and electricity) systems is presented. The developed parametric model could be used for system sizing, performance evaluation, and optimization. This paper presents a systematic approach to model the behaviour of the CHP system using heat recovery prediction methods. The modular, physics based modelling environment shows the power flow between the system components, with a special emphasis on the ICE subsystems, parameter identification, and model validation. Full article

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

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3899 KiB

Open AccessArticle

Shale Gas Content Calculation of the Triassic Yanchang Formation in the Southeastern Ordos Basin, China

by Jiao Su, Yingchu Shen, Jin Hao and Bo Liu

Energies 2017, 10(12), 1949; https://doi.org/10.3390/en10121949 - 24 Nov 2017

Cited by 10 | Viewed by 3922

Abstract

Shale gas content is the key parameter for shale gas potential evaluation and favorable area prediction. Therefore, it is very important to determine shale gas content accurately. Generally, we use the US Bureau of Mines (USBM) method for coal reservoirs to calculate the [...] Read more.

Shale gas content is the key parameter for shale gas potential evaluation and favorable area prediction. Therefore, it is very important to determine shale gas content accurately. Generally, we use the US Bureau of Mines (USBM) method for coal reservoirs to calculate the gas content of shale reservoirs. However, shale reservoirs are different from coal reservoirs in depth, pressure, core collection, etc. This method would inevitably cause problems. In order to make the USBM method more suitable for shale reservoirs, an improved USBM method is put forward on the basis of systematic analysis of core pressure history and temperature history during shale gas degassing. The improved USBM method modifies the calculation method of the gas loss time, and determines the temperature balance time of water heating. In addition, we give the calculation method of adsorption gas content and free gas content, especially the new method of calculating the oil dissolved gas content and water dissolved gas content that are easily neglected. We used the direct method (USBM and the improved USBM) and the indirect method (including the calculation of adsorption gas, free gas and the dissolved gas method) to calculate the shale gas content of 16 shale samples of the Triassic Yanchang Formation in the Southeastern Ordos Basin, China. The results of the improved USBM method show that the total shale gas content is high, with an average of 3.97 m³/t, and the lost shale gas content is the largest proportion with an average of 62%. The total shale gas content calculated by the improved USBM method is greater than that of the USBM method. The results of the indirect method show that the total shale gas content is large, with an average of 4.11 m³/t, and the adsorption shale gas content is the largest proportion with an average of 71%. The oil dissolved shale gas content which should be paid attention to accounts for about 7.8%. The discrepancy between the direct method and indirect method is reduced by using the improved USBM method, and the improved USBM method could be more practical and accurate than the USBM method. Full article

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5064 KiB

Open AccessArticle

Characterization of the Inlet Port Flow under Steady-State Conditions Using PIV and POD

by Mohammed El-Adawy, Morgan R. Heikal, A. Rashid A. Aziz, Muhammad I. Siddiqui and Shahzad Munir

Energies 2017, 10(12), 1950; https://doi.org/10.3390/en10121950 - 24 Nov 2017

Cited by 32 | Viewed by 4623

Abstract

The current study demonstrates an experimental investigation of the tumble flow structures using Particle Image Velocimetry (PIV) under steady-state conditions considering the central vertical tumble plane. The experiments were carried out on a four-valve, pent-roof Gasoline Direct Injection (GDI) engine head at different [...] Read more.

The current study demonstrates an experimental investigation of the tumble flow structures using Particle Image Velocimetry (PIV) under steady-state conditions considering the central vertical tumble plane. The experiments were carried out on a four-valve, pent-roof Gasoline Direct Injection (GDI) engine head at different valve lifts and with a pressure difference of 150 mmH₂O across the intake valves. Furthermore, the Proper Orthogonal Decomposition (POD) analytical technique was applied to PIV-measured velocity vector maps to characterize the flow structures at various valve lifts, and hence the different rig tumble values. The results show that at low valve lifts (1 to 5 mm), 48.9 to 46.6% of the flow energy is concentrated in the large (mode 1) eddies with only 8.4 to 11.46% in mode 2 and 7.2 to 7.5 in mode 3. At high valve lifts, it can be clearly seen that some of the energy in the large eddies of mode 1 is transferred to the smaller flow structures of modes 2 and 3. This can be clearly seen at valve lift 10 mm where the values of the flow energy were 40.6%, 17.3%, and 8.0% for modes 1, 2, and 3, respectively. Full article

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3023 KiB

Open AccessArticle

Dynamic Equivalent Modeling of a Grid-Tied Microgrid Based on Characteristic Model and Measurement Data

by Changchun Cai, Haolin Liu, Weili Dai, Zhixiang Deng, Jianyong Zhang and Lihua Deng

Energies 2017, 10(12), 1951; https://doi.org/10.3390/en10121951 - 24 Nov 2017

Cited by 12 | Viewed by 5210

Abstract

Microgrids can significantly improve the utilization of distributed generation (DG) and the reliability of the power supply. However, in the grid-tied operational mode, the interaction between the microgrid and the distribution network cannot be ignored. The paper proposes an equivalent modeling method for [...] Read more.

Microgrids can significantly improve the utilization of distributed generation (DG) and the reliability of the power supply. However, in the grid-tied operational mode, the interaction between the microgrid and the distribution network cannot be ignored. The paper proposes an equivalent modeling method for the microgrid under grid-tied mode based on a characteristic model. It can simplify the microgrid model in the numerical simulation of the distribution network. The proposed equivalent model can present the dynamic response of a microgrid but not miss any of its primary characteristics. The characteristic model is represented by a low-order time-varying differential equation with the same characteristics of the original microgrid system. During the modeling process, the voltage and the power exchanged between the microgrid and distribution network are collected as the training data for the identification of model parameters. A recursive damped least squares algorithm (RDLS) is used for the parameter identification. A microgrid system containing different DGs is built to test the proposed modeling method in DIgSILENT, and the results show that the proposed dynamic equivalent modeling method is effective and the characteristic model can present the dynamic behaviors of the detailed model of a microgrid. Full article

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

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2287 KiB

Open AccessArticle

Are Developed Regions in China Achieving Their CO₂ Emissions Reduction Targets on Their Own?—Case of Beijing

by Wen Wen and Qi Wang

Energies 2017, 10(12), 1952; https://doi.org/10.3390/en10121952 - 24 Nov 2017

Cited by 6 | Viewed by 3860

Abstract

The extensive and close economic linkages among different regions of China have effects not only on regional economic growth, but also on CO₂ emissions and carbon leakage among regions. Taking Beijing as a study case, we constructed MRIO models for China’s 30 [...] Read more.

The extensive and close economic linkages among different regions of China have effects not only on regional economic growth, but also on CO₂ emissions and carbon leakage among regions. Taking Beijing as a study case, we constructed MRIO models for China’s 30 provinces and municipalities for 2002, 2007 and 2010, to measure the embodied CO₂ emissions in the interregional trade of China on regional and industrial levels to explore their changes over time, and to analyze the driving forces of the final demand-induced interregional CO₂ emissions through an SDA model. Results showed that Beijing was a surplus region for embodied carbon and the net input embodied CO₂ emissions were in industries with high CO₂ emission coefficients, while the net output embodied carbon was in industries with low carbon-emission coefficients. Beijing’s trade with non-Beijing areas led to an increase in the total CO₂ emissions in China and a composite effect of Beijing and the efficiency effect of non-Beijing areas were the main effects behind the reduction of Beijing’s input embodied carbon. The results have yielded important implications for China’s CO₂ emissions control: first, the embodied CO₂ need be taken into consideration when formulating CO₂ emissions control measures; second, CO₂ emission reduction requirements should be reasonably distributed across the provinces to reduce carbon leakage in interprovincial trade; third, the consumption structure in the production chain needs to be moderately adjusted; and last but not least, financial and technical support for CO₂ emissions control in the central and western provinces should be strengthened. Full article

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298 KiB

Open AccessArticle

Energy-Efficient Subcarrier Pairing and Power Allocation for DF Relay Networks with an Eavesdropper

by Keshav Singh, Meng-Lin Ku, Sudip Biswas and Tharmalingam Ratnarajah

Energies 2017, 10(12), 1953; https://doi.org/10.3390/en10121953 - 24 Nov 2017

Cited by 4 | Viewed by 2910

Abstract

Algorithms for joint subcarrier pairing and power allocation are investigated in order to maximize the worst-case energy efficiency (EE) in dual-hop decode-and-forward (DF) relay networks in the presence of an active eavesdropper. Accordingly, we study the impact of number of subcarriers on the [...] Read more.

Algorithms for joint subcarrier pairing and power allocation are investigated in order to maximize the worst-case energy efficiency (EE) in dual-hop decode-and-forward (DF) relay networks in the presence of an active eavesdropper. Accordingly, we study the impact of number of subcarriers on the trade-off in performance between the EE and the spectrum efficiency (SE). The formulated EE optimization problem is the ratio of the secure SE over the entire power consumption in the network, subject to the constraints of total transmit power and subcarrier pairing. A near-optimal iterative algorithm is proposed to perform the subcarrier pairing and power allocation for achieving the maximum EE in the networks. Furthermore, a suboptimal algorithm is proposed with two-step resource allocation. By considering the subcarrier channel quality of the source-to-relay and relay-to-destination links, the subcarrier pairing is first performed, followed by an energy-efficient iterative power allocation scheme to maximize the EE. Numerical results validate the effectiveness and correctness of the proposed algorithms. Full article

(This article belongs to the Special Issue Energy-Efficient Computing and Networking in the 5G Era)

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1827 KiB

Open AccessArticle

Force Measurements on a VAWT Blade in Parked Conditions

by Anders Goude and Morgan Rossander

Energies 2017, 10(12), 1954; https://doi.org/10.3390/en10121954 - 24 Nov 2017

Cited by 11 | Viewed by 4161

Abstract

The forces on a turbine at extreme wind conditions when the turbine is parked is one of the most important design cases for the survivability of a turbine. In this work, the forces on a blade and its support arms have been measured [...] Read more.

The forces on a turbine at extreme wind conditions when the turbine is parked is one of the most important design cases for the survivability of a turbine. In this work, the forces on a blade and its support arms have been measured on a 12 kW straight-bladed vertical axis wind turbine at an open site. Two cases are tested: one during electrical braking of the turbine, which allows it to rotate slowly, and one with the turbine mechanically fixed with the leading edge of the blade facing the main wind direction. The force variations with respect to wind direction are investigated, and it is seen that significant variations in forces depend on the wind direction. The measurements show that for the fixed case, when subjected to the same wind speed, the forces are lower when the blade faces the wind direction. The results also show that due to the lower forces at this particular wind direction, the average forces for the fixed blade are notably lower. Hence, it is possible to reduce the forces on a turbine blade, simply by taking the dominating wind direction into account when the turbine is parked. The measurements also show that a positive torque is generated from the blade for most wind directions, which causes the turbine to rotate in the electrically-braked case. These rotations will cause increased fatigue loads on the turbine blade. Full article

(This article belongs to the Collection Wind Turbines)

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Open AccessArticle

Perforated Thermal Mass Shading: An Approach to Winter Solar Shading and Energy, Shading and Daylighting Performance

by Lingjiang Huang and Shuangping Zhao

Energies 2017, 10(12), 1955; https://doi.org/10.3390/en10121955 - 24 Nov 2017

Cited by 9 | Viewed by 4874

Abstract

Direct solar irradiance may cause thermal discomfort, even in winter when the ambient temperature is low and especially for high-altitude locations with a high intensity of solar radiation. Thus winter solar shading might be required and, if used, must achieve a balance between [...] Read more.

Direct solar irradiance may cause thermal discomfort, even in winter when the ambient temperature is low and especially for high-altitude locations with a high intensity of solar radiation. Thus winter solar shading might be required and, if used, must achieve a balance between the prevention of the transmittance of solar irradiance, the utilization of passive solar heat and the supply of adequate natural daylighting. These considerations render conventional solutions of solar shading inapplicable in the winter. In this paper, a novel approach to perforated thermal mass shading for winter is reported and examined. The impacts of the perforated percentage and the opening positions of this shading device on energy, shading and daylighting performance were assessed for south- and west-facing orientations. A range of perforated percentages and vertical and horizontal positions were tested using simulations by Energyplus and Daysim. Our results indicate that the proposed perforated thermal mass shading is efficient for the integrated performance of shading, daylighting and energy savings in the south-facing orientation, while it achieves acceptable performance in shading and daylighting in the west-facing orientation for a high-altitude cold climate. Full article

(This article belongs to the Special Issue Solar Energy Application in Buildings)

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5471 KiB

Open AccessArticle

Research on Exergy Flow Composition and Exergy Loss Mechanisms for Waxy Crude Oil Pipeline Transport Processes

by Qinglin Cheng, Yifan Gan, Wenkun Su, Yang Liu, Wei Sun and Ying Xu

Energies 2017, 10(12), 1956; https://doi.org/10.3390/en10121956 - 24 Nov 2017

Cited by 17 | Viewed by 4687

Abstract

The basic theory of exergy was used to derive the formulae of physical and chemical exergy in the process of pipeline transportation, combined with the effect of wax deposition on the thermodynamic parameters including specific heat, density, chemical potential and concentration gradient. On [...] Read more.

The basic theory of exergy was used to derive the formulae of physical and chemical exergy in the process of pipeline transportation, combined with the effect of wax deposition on the thermodynamic parameters including specific heat, density, chemical potential and concentration gradient. On the basis of this, the expression of various exergy losses were derived, and the exergy balance model was then built in the process. For the case study, a waxy crude oil pipeline in China was selected. The mechanism for how wax deposition affected the physical and chemical exergy loss was studied through analyzing the axial pipeline distribution of pressure, temperature, flow rate and thickness of insulation layer. Finally, under the design flow of 66 × 10³ kg·h⁻¹, the orthogonal experimental analysis method was used for comparing the degree of specific factors which could influence the total exergy efficiency. The highest exergy efficiency combination of working conditions was then determined. This research could provide a theoretical basis for guiding safe and economic operation in the actual pipeline transportation process. Full article

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6454 KiB

Open AccessArticle

Asynchronous Fault Location in Transmission Lines Considering Accurate Variation of the Ground-Mode Traveling Wave Velocity

by Rui Liang, Zhi Yang, Nan Peng, Chenglei Liu and Firuz Zare

Energies 2017, 10(12), 1957; https://doi.org/10.3390/en10121957 - 24 Nov 2017

Cited by 21 | Viewed by 3377

Abstract

This paper proposes a grounding fault location method in transmission lines based on time difference of arrival (TDOA) of ground-mode and aerial-mode traveling waves (TWs). The frequency-dependent characteristics of transmission lines cause different frequencies to have different attenuations and phase lags of different [...] Read more.

This paper proposes a grounding fault location method in transmission lines based on time difference of arrival (TDOA) of ground-mode and aerial-mode traveling waves (TWs). The frequency-dependent characteristics of transmission lines cause different frequencies to have different attenuations and phase lags of different frequency components in traveling waves, which leads to the change of TWs velocities with different propagation distances. Due to these different propagation paths, the wave velocity variations of ground-mode should be considered as a main variable while the velocity of aerial-mode can be seen as a constant factor. A quadratic function that can illustrate the tendency of variation of ground-mode wave velocity is proposed by considering the relation between the wave velocity and fault distance. The least squares method is used to solve the quadratic function of different lines. Combining the quadratic formula and the incident TWs of each mode detected at both terminals of the line, a novel fault location method is proposed. First, according to the maximum and minimum ground-mode velocities, a fault scope can be acquired. Then, more accurate fault scopes and ground-mode velocities can be obtained by iteration computation. Finally, an accurate fault position is acquired when the fault scope is sufficiently small. PSCAD/EMTDC software is used to conduct fault simulations in order to verify the feasibility and accuracy of the method. Full article

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Open AccessArticle

Study and Optimization of Design Parameters in Water Loop Heat Pump Systems for Office Buildings in the Iberian Peninsula

by Francisco Javier Fernández, María Belén Folgueras and Inés Suárez

Energies 2017, 10(12), 1958; https://doi.org/10.3390/en10121958 - 24 Nov 2017

Cited by 3 | Viewed by 5026

Abstract

Water loop heat pump (WLHP) air conditioning systems use heat pumps connected to a common water circuit to fulfill the energy demands of different thermal zones in a building. In this study, the energy consumption was analyzed for the air conditioning of an [...] Read more.

Water loop heat pump (WLHP) air conditioning systems use heat pumps connected to a common water circuit to fulfill the energy demands of different thermal zones in a building. In this study, the energy consumption was analyzed for the air conditioning of an office building in the typical climate of four important cities of the Iberian Peninsula. The energy consumption of one water loop heat pump system was compared with a conventional water system. Two design parameters, the range in the control temperatures and the water loop thermal storage size, were tested. Energy redistribution is an important advantage of the WLHP system, but significant savings came from high efficiency parameters in the heat pumps and minor air flow rates in the cooling tower. The low thermal level in the water loop makes this technology appropriate to combine with renewable sources. Using natural gas as the thermal energy source, a mean decrease in CO₂ emissions of 8.1% was reached. Simulations showed that the installation of big thermal storage tanks generated small energy savings. Besides, the total annual consumption in buildings with high internal loads can be reduced by keeping the water loop as cool as possible. 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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10852 KiB

Open AccessArticle

Sliding Mode Controller and Lyapunov Redesign Controller to Improve Microgrid Stability: A Comparative Analysis with CPL Power Variation

by Eklas Hossain, Ron Perez, Sanjeevikumar Padmanaban, Lucian Mihet-Popa, Frede Blaabjerg and Vigna K. Ramachandaramurthy

Energies 2017, 10(12), 1959; https://doi.org/10.3390/en10121959 - 24 Nov 2017

Cited by 25 | Viewed by 5827

Abstract

To mitigate the microgrid instability despite the presence of dense Constant Power Load (CPL) loads in the system, a number of compensation techniques have already been gone through extensive research, proposed, and implemented around the world. In this paper, a storage based load [...] Read more.

To mitigate the microgrid instability despite the presence of dense Constant Power Load (CPL) loads in the system, a number of compensation techniques have already been gone through extensive research, proposed, and implemented around the world. In this paper, a storage based load side compensation technique is used to enhance stability of microgrids. Besides adopting this technique here, Sliding Mode Controller (SMC) and Lyapunov Redesign Controller (LRC), two of the most prominent nonlinear control techniques, are individually implemented to control microgrid system stability with desired robustness. CPL power is then varied to compare robustness of these two control techniques. This investigation revealed the better performance of the LRC system compared to SMC to retain stability in microgrid with dense CPL load. All the necessary results are simulated in Matlab/Simulink platform for authentic verification. Reasons behind inferior SMC performance and ways to mitigate that are also discussed. Finally, the effectiveness of SMC and LRC systems to attain stability in real microgrids is verified by numerical analysis. Full article

(This article belongs to the Special Issue Energy Storage Systems and Power Conversion Electronics for E-Transportation and Smart Grid)

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1614 KiB

Open AccessArticle

Coupled Thermo-Hydro-Mechanical-Chemical Modeling of Water Leak-Off Process during Hydraulic Fracturing in Shale Gas Reservoirs

by Fei Wang, Baoman Li, Yichi Zhang and Shicheng Zhang

Energies 2017, 10(12), 1960; https://doi.org/10.3390/en10121960 - 24 Nov 2017

Cited by 12 | Viewed by 5355

Abstract

The water leak-off during hydraulic fracturing in shale gas reservoirs is a complicated transport behavior involving thermal (T), hydrodynamic (H), mechanical (M) and chemical (C) processes. Although many leak-off models have been published, none of the models fully coupled the transient fluid flow [...] Read more.

The water leak-off during hydraulic fracturing in shale gas reservoirs is a complicated transport behavior involving thermal (T), hydrodynamic (H), mechanical (M) and chemical (C) processes. Although many leak-off models have been published, none of the models fully coupled the transient fluid flow modeling with heat transfer, chemical-potential equilibrium and natural-fracture dilation phenomena. In this paper, a coupled thermo-hydro-mechanical-chemical (THMC) model based on non-equilibrium thermodynamics, hydrodynamics, thermo-poroelastic rock mechanics, and non-isothermal chemical-potential equations is presented to simulate the water leak-off process in shale gas reservoirs. The THMC model takes into account a triple-porosity medium, which includes hydraulic fractures, natural fractures and shale matrix. The leak-off simulation with the THMC model involves all the important processes in this triple-porosity medium, including: (1) water transport driven by hydraulic, capillary, chemical and thermal osmotic convections; (2) gas transport induced by both hydraulic pressure driven convection and adsorption; (3) heat transport driven by thermal convection and conduction; and (4) natural-fracture dilation considered as a thermo-poroelastic rock deformation. The fluid and heat transport, coupled with rock deformation, are described by a set of partial differential equations resulting from the conservation of mass, momentum, and energy. The semi-implicit finite-difference algorithm is proposed to solve these equations. The evolution of pressure, temperature, saturation and salinity profiles of hydraulic fractures, natural fractures and matrix is calculated, revealing the multi-field coupled water leak-off process in shale gas reservoirs. The influences of hydraulic pressure, natural-fracture dilation, chemical osmosis and thermal osmosis on water leak-off are investigated. Results from this study are expected to provide a better understanding of the predominant leak-off mechanisms for slickwater fracturing-fluids in hydraulically fractured shale gas reservoirs. Full article

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

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6767 KiB

Open AccessArticle

A Novel Acoustic Liquid Level Determination Method for Coal Seam Gas Wells Based on Autocorrelation Analysis

by Ximing Zhang, Jianchun Fan, Shengnan Wu and Di Liu

Energies 2017, 10(12), 1961; https://doi.org/10.3390/en10121961 - 24 Nov 2017

Cited by 13 | Viewed by 7505

Abstract

In coal seam gas (CSG) wells, water is periodically removed from the wellbore in order to keep the bottom-hole flowing pressure at low levels, facilitating the desorption of methane gas from the coal bed. In order to calculate gas flow rate and further [...] Read more.

In coal seam gas (CSG) wells, water is periodically removed from the wellbore in order to keep the bottom-hole flowing pressure at low levels, facilitating the desorption of methane gas from the coal bed. In order to calculate gas flow rate and further optimize well performance, it is necessary to accurately monitor the liquid level in real-time. This paper presents a novel method based on autocorrelation function (ACF) analysis for determining the liquid level in CSG wells under intense noise conditions. The method involves the calculation of the acoustic travel time in the annulus and processing the autocorrelation signal in order to extract the weak echo under high background noise. In contrast to previous works, the non-linear dependence of the acoustic velocity on temperature and pressure is taken into account. To locate the liquid level of a coal seam gas well the travel time is computed iteratively with the non-linear velocity model. Afterwards, the proposed method is validated using experimental laboratory investigations that have been developed for liquid level detection under two scenarios, representing the combination of low pressure, weak signal, and intense noise generated by gas flowing and leakage. By adopting an evaluation indicator called Crest Factor, the results have shown the superiority of the ACF-based method compared to Fourier filtering (FFT). In the two scenarios, the maximal measurement error from the proposed method was 0.34% and 0.50%, respectively. The latent periodic characteristic of the reflected signal can be extracted by the ACF-based method even when the noise is larger than 1.42 Pa, which is impossible for FFT-based de-noising. A case study focused on a specific CSG well is presented to illustrate the feasibility of the proposed approach, and also to demonstrate that signal processing with autocorrelation analysis can improve the sensitivity of the detection system. Full article

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

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6341 KiB

Open AccessArticle

A Novel Fault Early Warning Model Based on Fault Gene Table for Smart Distribution Grids

by Min Xiang, Jie Min, Zaiqian Wang and Pan Gao

Energies 2017, 10(12), 1963; https://doi.org/10.3390/en10121963 - 24 Nov 2017

Cited by 7 | Viewed by 5345

Abstract

Since a smart distribution grid has a diversity of components and complicated topology; it is very hard to achieve fault early warning for each part. A fault early warning model for smart distribution grid combining a back propagation (BP) neural network with a [...] Read more.

Since a smart distribution grid has a diversity of components and complicated topology; it is very hard to achieve fault early warning for each part. A fault early warning model for smart distribution grid combining a back propagation (BP) neural network with a gene sequence alignment algorithm is proposed. Firstly; the operational state of smart distribution grid is divided into four states; and a BP neural network is adopted to explore the operational state from the historical fault data of the smart distribution grid. This obtains the relationship between each state transition time sequence and corresponding fault, and is used to construct the fault gene table. Then; a state transition time sequence is obtained online periodically, which is matched with each gene in fault gene table by an improved Smith–Waterman algorithm. If the maximum match score exceeds the given threshold, the relevant fault will be detected early. Finally, plenty of time domain simulation is performed on the proposed fault early warning model to IEEE-14 bus. The simulation results show that the proposed model can achieve efficient early fault warning of smart distribution grids. Full article

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

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5786 KiB

Open AccessArticle

Graphical Diagnosis of Performances in Photovoltaic Systems: A Case Study in Southern Spain

by Isabel Santiago, David Trillo Montero, Juan J. Luna Rodríguez, Isabel M. Moreno Garcia and Emilio J. Palacios Garcia

Energies 2017, 10(12), 1964; https://doi.org/10.3390/en10121964 - 25 Nov 2017

Cited by 11 | Viewed by 5374

Abstract

The starting point of the operation and maintenance tasks in photovoltaic plants is the continuous monitoring and supervision of its components. The great amount of registered data requires a major improvement in the ways this information is processed and analyzed to rapidly detect [...] Read more.

The starting point of the operation and maintenance tasks in photovoltaic plants is the continuous monitoring and supervision of its components. The great amount of registered data requires a major improvement in the ways this information is processed and analyzed to rapidly detect any potential fault, without incurring additional costs. In this paper, a procedure to perform a detailed graphical supported analysis of the operation of photovoltaic installations, based on inverter data, and using a self-developed application, is presented. The program carries out the automated processing of the registered data, providing their access and visualization by means of color maps. These graphs allow a large volume of data set to be simultaneously represented in a readable way, enabling operation and maintenance operators to quickly detect patterns that would require any type of intervention. As a case study, the operation of a grid-connected photovoltaic plant located in southern Spain was studied during a period of three years. The average daily efficiency values of the PV modules and inverters were in the range of 7.6–14.6%, and 73.5–94% respectively. Moreover, the presence of shadings, as well as the hours and days mainly affected by this issue, was easily detected. Full article

(This article belongs to the Special Issue PV System Design and Performance)

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1278 KiB

Open AccessArticle

Two Stage Analysis of Successful Change Implementation of Knowledge Management Strategies in Energy Companies from Romania

by Eduard Gabriel Ceptureanu, Sebastian Ion Ceptureanu, Doina I. Popescu and Liviu Bogdan Vlad

Energies 2017, 10(12), 1965; https://doi.org/10.3390/en10121965 - 25 Nov 2017

Cited by 20 | Viewed by 4796

Abstract

The purpose of this paper is to emphasize the effects of knowledge management strategies toward organizational change in Romanian companies from the energy sector. This study explored a new vision to implement these types of organizational changes successfully in companies from the Romanian [...] Read more.

The purpose of this paper is to emphasize the effects of knowledge management strategies toward organizational change in Romanian companies from the energy sector. This study explored a new vision to implement these types of organizational changes successfully in companies from the Romanian sector of energy and obtain their early benefits by using knowledge management strategies and also reveal the mediating effect of organizational learning and readiness for change. The results highlighted how energy companies can implement an Enterprise Resource Planning (ERP)-based change effectively through KM strategies. The results are equally valuable for all Romanian organizations that are currently changing their working environment. Full article

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1265 KiB

Open AccessArticle

Optimal Capacity Configuration for Energy Hubs Considering Part-Load Characteristics of Generation Units

by Shan Deng, Qinghua Wu, Zhaoxia Jing, Lilan Wu, Feng Wei and Xiaoxin Zhou

Energies 2017, 10(12), 1966; https://doi.org/10.3390/en10121966 - 25 Nov 2017

Cited by 33 | Viewed by 3654

Abstract

The simulation model is one of the key points affecting the optimal planning and operation of energy hubs (EHs). Since treating the efficiencies of generation units as constants would significantly simplify the calculation, only a simplified model is investigated in most research works. [...] Read more.

The simulation model is one of the key points affecting the optimal planning and operation of energy hubs (EHs). Since treating the efficiencies of generation units as constants would significantly simplify the calculation, only a simplified model is investigated in most research works. In this paper, aiming at optimizing the capacity configuration of an EH, we present a part-load characteristics-based (PLCB) model, in which the efficiencies of generation units will change with the fluctuating load. Based on the PLCB model, the accuracy of the EH model can be improved. Furthermore, a two-stage planning method is proposed to solve the optimal capacity configuration problem of the EH. Group Search Optimizer (GSO) is used to determine the optimal size in the first stage, and a mathematical programming method is applied to obtain the optimal operation of the EH in the second stage. Comparative studies using the PLCB model and the simplified model are performed to examine the impacts of equipment part-load characteristics on the sizing results. Simulation results indicate that the proposed model appears to have a better economic performance than the simplified model. Full article

(This article belongs to the Special Issue Decentralised Energy Supply Systems)

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2750 KiB

Open AccessArticle

A Simple and Effective Approach for the Prediction of Turbine Power Production From Wind Speed Forecast

by Marino Marrocu and Luca Massidda

Energies 2017, 10(12), 1967; https://doi.org/10.3390/en10121967 - 25 Nov 2017

Cited by 6 | Viewed by 3588

Abstract

An accurate forecast of the power generated by a wind turbine is of paramount importance for its optimal exploitation. Several forecasting methods have been proposed either based on a physical modeling or using a statistical approach. All of them rely on the availability [...] Read more.

An accurate forecast of the power generated by a wind turbine is of paramount importance for its optimal exploitation. Several forecasting methods have been proposed either based on a physical modeling or using a statistical approach. All of them rely on the availability of high quality measures of local wind speed, corresponding generated power and on numerical weather forecasts. In this paper, a simple and effective wind power forecast technique, based on the probability distribution mapping of wind speed forecast and observed power data, is presented and it is applied to two turbines located on the island of Borkum (Germany) in the North Sea. The wind speed forecast of the ECMWF model at 100 m from the ground is used as the prognostic meteorological parameter. Training procedures are based entirely on relatively short time series of power measurements. Results show that our approach has skills that are similar or better than those obtained using more standard methods when measured with mean absolute error. Full article

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1240 KiB

Open AccessArticle

Impact of DC Voltage Enhancement on Partial Discharges in Medium Voltage Cables—An Empirical Study with Defects at Semicon-Dielectric Interface

by Aditya Shekhar, Xianyong Feng, Angelo Gattozzi, Robert Hebner, Douglas Wardell, Shannon Strank, Armando Rodrigo-Mor, Laura Ramírez-Elizondo and Pavol Bauer

Energies 2017, 10(12), 1968; https://doi.org/10.3390/en10121968 - 26 Nov 2017

Cited by 17 | Viewed by 6443

Abstract

A scientific consensus is emerging on the benefits of direct current (DC) distribution in medium voltage (MV) power systems of ships and cities. At least 50% space savings and increased power transfer capacity are estimated with enhanced voltage DC operation of electric cables. [...] Read more.

A scientific consensus is emerging on the benefits of direct current (DC) distribution in medium voltage (MV) power systems of ships and cities. At least 50% space savings and increased power transfer capacity are estimated with enhanced voltage DC operation of electric cables. The goal of this research is to contribute to developing the empirical knowledge on the insulation performance in order to validate the feasibility of such anticipated gains of DC versus alternating current (AC), and to determine the comparative impact of different operational conditions from a component engineering point of view. The partial discharge (PD) activity in cables is measured under AC and DC conditions as an indicator of insulation performance. Specifically, PDs in defects at the semicon-insulation interface are studied in terms of inception voltage, repetition rate and discharge magnitude. Empirical understanding is drawn for operating voltage and frequency dependence of the discharge behavior in such voids in the range of 10 to 20 kV and 0 to 0.1 Hz, respectively. The change in PD activity with void evolution post temperature-induced ageing process is explored. Full article

(This article belongs to the Special Issue Selected Papers from International Workshop of Energy-Open)

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Open AccessArticle

The Environmental Burdens of Lead-Acid Batteries in China: Insights from an Integrated Material Flow Analysis and Life Cycle Assessment of Lead

by Sha Chen, Zhenyue Lian, Sumei Li, Junbeum Kim, Yipei Li, Lei Cao and Zunwen Liu

Energies 2017, 10(12), 1969; https://doi.org/10.3390/en10121969 - 26 Nov 2017

Cited by 18 | Viewed by 7288

Abstract

Lead-acid batteries (LABs), a widely used energy storage equipment in cars and electric vehicles, are becoming serious problems due to their high environmental impact. In this study, an integrated method, combining material flow analysis with life cycle assessment, was developed to analyze the [...] Read more.

Lead-acid batteries (LABs), a widely used energy storage equipment in cars and electric vehicles, are becoming serious problems due to their high environmental impact. In this study, an integrated method, combining material flow analysis with life cycle assessment, was developed to analyze the environmental emissions and burdens of lead in LABs. The environmental burdens from other materials in LABs were not included. The results indicated that the amount of primary lead used in LABs accounted for 77% of the total lead production in 2014 in China. The amount of discharged lead into the environment was 8.54 × 10⁵ tonnes, which was mainly from raw material extraction (57.2%). The largest environmental burden was from the raw materials extraction and processing, which accounted for 81.7% of the total environmental burdens. The environmental burdens of the environmental toxicity potential, human toxicity potential-cancer, human toxicity potential-non-cancer, water footprint and land use accounted for more than 90% at this stage. Moreover, the environmental burdens from primary lead was much more serious than regenerated lead. On the basis of the results, main practical measures and policies were proposed to reduce the lead emissions and environmental burdens of LABs in China, namely establishing an effective LABs recycling system, enlarging the market share of the legal regenerated lead, regulating the production of regenerated lead, and avoiding the long-distance transportation of the waste LABs. Full article

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Open AccessArticle

Viscosity Models for Polymer Free CO₂ Foam Fracturing Fluid with the Effect of Surfactant Concentration, Salinity and Shear Rate

by Shehzad Ahmed, Khaled Abdalla Elraies, Muhammad Rehan Hashmet and Alvinda Sri Hanamertani

Energies 2017, 10(12), 1970; https://doi.org/10.3390/en10121970 - 26 Nov 2017

Cited by 33 | Viewed by 6551

Abstract

High quality polymer free CO₂ foam possesses unique properties that make it an ideal fluid for fracturing unconventional shales. In this paper, the viscosity of polymer free fracturing foam and its empirical correlations at high pressure high temperature (HPHT) as a function [...] Read more.

High quality polymer free CO₂ foam possesses unique properties that make it an ideal fluid for fracturing unconventional shales. In this paper, the viscosity of polymer free fracturing foam and its empirical correlations at high pressure high temperature (HPHT) as a function of surfactant concentration, salinity, and shear rate are presented. Foams were generated using a widely-used surfactant, i.e., alpha olefin sulfonate (AOS) in the presence of brine and a stabilizer at HPHT. Pressurize foam rheometer was used to find out the viscosity of CO₂ foams at different surfactant concentration (0.25–1 wt %) and salinity (0.5–8 wt %) over a wide range of shear rate (10–500 s⁻¹) at 1500 psi and 80 °C. Experimental results concluded that foam apparent viscosity increases noticeably until the surfactant concentration of 0.5 wt %, whereas, the increment in salinity provided a continuous increase in foam apparent viscosity. Nonlinear regression was performed on experimental data and empirical correlations were developed. Power law model for foam viscosity was modified to accommodate for the effect of shear rate, surfactant concentration, and salinity. Power law indices (K and n) were found to be a strong function of surfactant concentration and salinity. The new correlations accurately predict the foam apparent viscosity under various stimulation scenarios and these can be used for fracture simulation modeling. Full article

(This article belongs to the Special Issue Flow and Transport Properties of Unconventional Reservoirs)

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Open AccessArticle

A Novel Electricity Transaction Mode of Microgrids Based on Blockchain and Continuous Double Auction

by Jian Wang, Qianggang Wang, Niancheng Zhou and Yuan Chi

Energies 2017, 10(12), 1971; https://doi.org/10.3390/en10121971 - 26 Nov 2017

Cited by 161 | Viewed by 9419

Abstract

The installed capacity of distributed generation (DG) based on renewable energy sources has increased continuously in power systems, and its market-oriented transaction is imperative. However, traditional transaction management based on centralized organizations has many disadvantages, such as high operation cost, low transparency, and [...] Read more.

The installed capacity of distributed generation (DG) based on renewable energy sources has increased continuously in power systems, and its market-oriented transaction is imperative. However, traditional transaction management based on centralized organizations has many disadvantages, such as high operation cost, low transparency, and potential risk of transaction data modification. Therefore, a decentralized electricity transaction mode for microgrids is proposed in this study based on blockchain and continuous double auction (CDA) mechanism. A buyer and seller initially complete the transaction matching in the CDA market. In view of the frequent price fluctuation in the CDA market, an adaptive aggressiveness strategy is used to adjust the quotation timely according to market changes. DG and consumer exchange digital certificate of power and expenditure on the blockchain system and the interests of consumers are then guaranteed by multi-signature when DG cannot generate power due to failure or other reasons. The digital certification of electricity assets is replaced by the sequence number with specific tags in the transaction script, and the size of digital certification can be adjusted according to transaction energy quantity. Finally, the feasibility of market mechanism through specific microgrid case and settlement process is also provided. Full article

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Open AccessArticle

Experimental and One-Dimensional Mathematical Modeling of Different Operating Parameters in Direct Formic Acid Fuel Cells

by Shingjiang Jessie Lue, Nai-Yuan Liu, Selvaraj Rajesh Kumar, Kevin Chi-Yang Tseng, Bo-Yan Wang and Chieh-Hsin Leung

Energies 2017, 10(12), 1972; https://doi.org/10.3390/en10121972 - 27 Nov 2017

Cited by 7 | Viewed by 3866

Abstract

The purpose of this work is to develop a one-dimensional mathematical model for predicting the cell performance of a direct formic acid fuel cell and compare this with experimental results. The predicted model can be applied to direct formic acid fuel cells operated [...] Read more.

The purpose of this work is to develop a one-dimensional mathematical model for predicting the cell performance of a direct formic acid fuel cell and compare this with experimental results. The predicted model can be applied to direct formic acid fuel cells operated with different formic acid concentrations, temperatures, and with various electrolytes. Tafel kinetics at the electrodes, thermodynamic equations for formic acid solutions, and the mass-transport parameters of the reactants are used to predict the effective diffusion coefficients of the reactants (oxygen and formic acid) in the porous gas diffusion layers and the associated limiting current densities to ensure the accuracy of the model. This model allows us to estimate fuel cell polarization curves for a wide range of operating conditions. Furthermore, the model is validated with experimental results from operating at 1–5 M of formic acid feed at 30–80 °C, and with Nafion-117 and silane-crosslinked sulfonated poly(styrene-ethylene/butylene-styrene) (sSEBS) membrane electrolytes reinforced in porous polytetrafluoroethylene (PTFE). The cell potential and power densities of experimental outcomes in direct formic acid fuel cells can be adequately predicted using the developed model. Full article

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

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Open AccessArticle

Electrical Components for Marine Renewable Energy Arrays: A Techno-Economic Review

by Adam J. Collin, Anup J. Nambiar, David Bould, Ben Whitby, M. A. Moonem, Benjamin Schenkman, Stanley Atcitty, Paulo Chainho and Aristides E. Kiprakis

Energies 2017, 10(12), 1973; https://doi.org/10.3390/en10121973 - 27 Nov 2017

Cited by 16 | Viewed by 10882

Abstract

This paper presents a review of the main electrical components that are expected to be present in marine renewable energy arrays. The review is put in context by appraising the current needs of the industry and identifying the key components required in both [...] Read more.

This paper presents a review of the main electrical components that are expected to be present in marine renewable energy arrays. The review is put in context by appraising the current needs of the industry and identifying the key components required in both device and array-scale developments. For each component, electrical, mechanical and cost considerations are discussed; with quantitative data collected during the review made freely available for use by the community via an open access online repository. This data collection updates previous research and addresses gaps specific to emerging offshore technologies, such as marine and floating wind, and provides a comprehensive resource for the techno-economic assessment of offshore energy arrays. Full article

(This article belongs to the Special Issue Marine Energy)

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Open AccessArticle

Market Analysis during the First Year of Korea Emission Trading Scheme

by Jaeseok Lee and Jongmin Yu

Energies 2017, 10(12), 1974; https://doi.org/10.3390/en10121974 - 28 Nov 2017

Cited by 9 | Viewed by 4625

Abstract

To derive the supply and demand issues during the first phase of the Korea Emission Trading Scheme (KETS), we investigated the excess or shortage, and the carry-over inflow of carbon emission permits for all of the domestic industries and major corporations. In particular, [...] Read more.

To derive the supply and demand issues during the first phase of the Korea Emission Trading Scheme (KETS), we investigated the excess or shortage, and the carry-over inflow of carbon emission permits for all of the domestic industries and major corporations. In particular, this study explored the supply and future prospects of offset credits, as well as the allocated permits, by forecasting the inflows of offset credits using the amount of certified reduction in domestic boundaries and overseas sources. We observed both the supply and demand of permits and changes in carbon dioxide (CO₂) emission levels during the first phase (2015–2017) by comparing the estimated emission levels and the total permit supply. The results showed that permits were either in surplus or insufficient, depending on the sub-sector, and that a surplus in the supply of permits would occur if companies do not carry over more than 70 million tons of permits to the next period. Full article

(This article belongs to the Special Issue Lessons from the Evaluation of Existing Emission Trading Schemes)

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Hydropower Bidding Using Linearized Start-Ups

by Ellen Krohn Aasgård

Energies 2017, 10(12), 1975; https://doi.org/10.3390/en10121975 - 28 Nov 2017

Cited by 5 | Viewed by 3587

Abstract

Hydropower producers must submit bids to electricity market auctions where they state their willingness to produce power. These bids may be determined using a mixed-integer linear stochastic program. However, for large interconnected river systems, this program may be too complex to be solved [...] Read more.

Hydropower producers must submit bids to electricity market auctions where they state their willingness to produce power. These bids may be determined using a mixed-integer linear stochastic program. However, for large interconnected river systems, this program may be too complex to be solved within the time limits set by current market rules. This paper investigates whether a linear approximation to start-ups can be used to reduce the computational burden without significantly degrading the solution quality. In order to investigate the trade-off of time versus solution quality, linear approximation is compared to a formulation that uses binary variables in a case study that simulates the operation of a reservoir system over time. Full article

(This article belongs to the Special Issue Hydropower 2017)

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Open AccessArticle

Different Models for Forecasting Wind Power Generation: Case Study

by David Barbosa de Alencar, Carolina De Mattos Affonso, Roberto Célio Limão de Oliveira, Jorge Laureano Moya Rodríguez, Jandecy Cabral Leite and José Carlos Reston Filho

Energies 2017, 10(12), 1976; https://doi.org/10.3390/en10121976 - 29 Nov 2017

Cited by 129 | Viewed by 9960

Abstract

Generation of electric energy through wind turbines is one of the practically inexhaustible alternatives of generation. It is considered a source of clean energy, but still needs a lot of research for the development of science and technologies that ensures uniformity in generation, [...] Read more.

Generation of electric energy through wind turbines is one of the practically inexhaustible alternatives of generation. It is considered a source of clean energy, but still needs a lot of research for the development of science and technologies that ensures uniformity in generation, providing a greater participation of this source in the energy matrix, since the wind presents abrupt variations in speed, density and other important variables. In wind-based electrical systems, it is essential to predict at least one day in advance the future values of wind behavior, in order to evaluate the availability of energy for the next period, which is relevant information in the dispatch of the generating units and in the control of the electrical system. This paper develops ultra-short, short, medium and long-term prediction models of wind speed, based on computational intelligence techniques, using artificial neural network models, Autoregressive Integrated Moving Average (ARIMA) and hybrid models including forecasting using wavelets. For the application of the methodology, the meteorological variables of the database of the national organization system of environmental data (SONDA), Petrolina station, from 1 January 2004 to 31 March 2017, were used. A comparison among results by different used approaches is also done and it is also predicted the possibility of power and energy generation using a certain kind of wind generator. Full article

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768 KiB

Open AccessArticle

On Conceptual Structuration and Coupling Methods of Co-Simulation Frameworks in Cyber-Physical Energy System Validation

by Van Hoa Nguyen, Yvon Besanger, Quoc Tuan Tran and Tung Lam Nguyen

Energies 2017, 10(12), 1977; https://doi.org/10.3390/en10121977 - 29 Nov 2017

Cited by 30 | Viewed by 6952

Abstract

Co-simulation is an emerging method for cyber-physical energy system (CPES) assessment and validation. Combining simulators of different domains into a joint experiment, co-simulation provides a holistic framework to consider the whole CPES at system level. In this paper, we present a systematic structuration [...] Read more.

Co-simulation is an emerging method for cyber-physical energy system (CPES) assessment and validation. Combining simulators of different domains into a joint experiment, co-simulation provides a holistic framework to consider the whole CPES at system level. In this paper, we present a systematic structuration of co-simulation based on a conceptual point of view. A co-simulation framework is then considered in its conceptual, semantic, syntactic, dynamic and technical layers. Coupling methods are investigated and classified according to these layers. This paper would serve as a solid theoretical base for specification of future applications of co-simulation and selection of coupling methods in CPES assessment and validation. Full article

(This article belongs to the Special Issue Methods and Concepts for Designing and Validating Smart Grid Systems)

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A New Control-Oriented Semi-Empirical Approach to Predict Engine-Out NOx Emissions in a Euro VI 3.0 L Diesel Engine

by Roberto Finesso, Gilles Hardy, Claudio Maino, Omar Marello and Ezio Spessa

Energies 2017, 10(12), 1978; https://doi.org/10.3390/en10121978 - 29 Nov 2017

Cited by 19 | Viewed by 5092

Abstract

The present study is focused on the development of a new control-oriented semi-empirical model to predict nitrogen oxide (NOx) emissions in a light-duty diesel engine under both steady-state and transient conditions. The model is based on the estimation of the deviations of NOx [...] Read more.

The present study is focused on the development of a new control-oriented semi-empirical model to predict nitrogen oxide (NOx) emissions in a light-duty diesel engine under both steady-state and transient conditions. The model is based on the estimation of the deviations of NOx emissions, with respect to the nominal engine-calibration map values, as a function of the deviations of the intake oxygen concentration and of the combustion phasing. The model also takes into account the effects of engine speed, total injected quantity, and ambient temperature and humidity. The approach has been developed and assessed on an Fiat Powertrain Technologies (FPT) Euro VI 3.0 L diesel engine for light-duty applications, in the frame of a research project in collaboration with FPT Industrial. The model has also been tested on a rapid prototyping device, and it was shown that it requires a very short computational time, thus being suitable for implementation on the Engine Control Unit (ECU) for real-time NOx control tasks. Full article

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

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Open AccessFeature PaperArticle

Prospects for Assessing Enhanced Geothermal System (EGS) Basement Rock Flow Stimulation by Wellbore Temperature Data

by Peter Leary, Peter Malin, Tero Saarno and Ilmo Kukkonen

Energies 2017, 10(12), 1979; https://doi.org/10.3390/en10121979 - 30 Nov 2017

Cited by 9 | Viewed by 5500

Abstract

We use Matlab 3D finite element fluid flow/transport modelling to simulate localized wellbore temperature events of order 0.05–0.1 °C logged in Fennoscandia basement rock at ~1.5 km depths. The temperature events are approximated as steady-state heat transport due to fluid draining from the [...] Read more.

We use Matlab 3D finite element fluid flow/transport modelling to simulate localized wellbore temperature events of order 0.05–0.1 °C logged in Fennoscandia basement rock at ~1.5 km depths. The temperature events are approximated as steady-state heat transport due to fluid draining from the crust into the wellbore via naturally occurring fracture-connectivity structures. Flow simulation is based on the empirics of spatially-correlated fracture-connectivity fluid flow widely attested by well-log, well-core, and well-production data. Matching model wellbore-centric radial temperature profiles to a 2D analytic expression for steady-state radial heat transport with Peclet number P_e ≡ r₀φv₀/D (r₀ = wellbore radius, v₀ = Darcy velocity at r₀, φ = ambient porosity, D = rock-water thermal diffusivity), gives P_e ~ 10–15 for fracture-connectivity flow intersecting the well, and P_e ~ 0 for ambient crust. Darcy flow for model P_e ~ 10 at radius ~10 m from the wellbore gives permeability estimate κ ~ 0.02 Darcy for flow driven by differential fluid pressure between least principal crustal stress pore pressure and hydrostatic wellbore pressure. Model temperature event flow permeability κ_m ~ 0.02 Darcy is related to well-core ambient permeability κ ~ 1 µDarcy by empirical poroperm relation κ_m ~ κ exp(α_mφ) for φ ~ 0.01 and α_m ~ 1000. Our modelling of OTN1 wellbore temperature events helps assess the prospect of reactivating fossilized fracture-connectivity flow for EGS permeability stimulation of basement rock. Full article

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

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Open AccessArticle

A Multifunctional Isolated and Non-Isolated Dual Mode Converter for Renewable Energy Conversion Applications

by Yiwang Wang, Chun Gan, Kai Ni, Xinhua Li, Houjun Tang and Yong Yang

Energies 2017, 10(12), 1980; https://doi.org/10.3390/en10121980 - 30 Nov 2017

Cited by 4 | Viewed by 4033

Abstract

In this paper, a multifunctional isolated and non-isolated dual-mode low-power converter was designed for renewable energy conversion applications such as photovoltaic power generation to achieve different operating modes under bi-directional electrical conversion. The proposed topology consists of a bidirectional non-isolated DC/DC circuit and [...] Read more.

In this paper, a multifunctional isolated and non-isolated dual-mode low-power converter was designed for renewable energy conversion applications such as photovoltaic power generation to achieve different operating modes under bi-directional electrical conversion. The proposed topology consists of a bidirectional non-isolated DC/DC circuit and an isolated converter with a high-frequency transformer, which merge the advantages of both the conventional isolated converter and non-isolated converter with the combination of the two converter technologies. Compared with traditional converters, the multifunctional converter can not only realize conventional bi-directional functions, but can also be applied for many different operation modes and meet the high output/input ratio demands with the two converter circuits operating together. A novel control algorithm was proposed to achieve the various functions of the proposed converter. An experimental platform based on the proposed circuit was established. Both the simulation and experimental results indicated that the proposed converter could provide isolated and non-isolated modes in different applications, which could meet different practical engineering requirements. Full article

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

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Open AccessArticle

Extremely Efficient Design of Organic Thin Film Solar Cells via Learning-Based Optimization

by Mine Kaya and Shima Hajimirza

Energies 2017, 10(12), 1981; https://doi.org/10.3390/en10121981 - 30 Nov 2017

Cited by 11 | Viewed by 4109

Abstract

Design of efficient thin film photovoltaic (PV) cells require optical power absorption to be computed inside a nano-scale structure of photovoltaics, dielectric and plasmonic materials. Calculating power absorption requires Maxwell’s electromagnetic equations which are solved using numerical methods, such as finite difference time [...] Read more.

Design of efficient thin film photovoltaic (PV) cells require optical power absorption to be computed inside a nano-scale structure of photovoltaics, dielectric and plasmonic materials. Calculating power absorption requires Maxwell’s electromagnetic equations which are solved using numerical methods, such as finite difference time domain (FDTD). The computational cost of thin film PV cell design and optimization is therefore cumbersome, due to successive FDTD simulations. This cost can be reduced using a surrogate-based optimization procedure. In this study, we deploy neural networks (NNs) to model optical absorption in organic PV structures. We use the corresponding surrogate-based optimization procedure to maximize light trapping inside thin film organic cells infused with metallic particles. Metallic particles are known to induce plasmonic effects at the metal–semiconductor interface, thus increasing absorption. However, a rigorous design procedure is required to achieve the best performance within known design guidelines. As a result of using NNs to model thin film solar absorption, the required time to complete optimization is decreased by more than five times. The obtained NN model is found to be very reliable. The optimization procedure results in absorption enhancement greater than 200%. Furthermore, we demonstrate that once a reliable surrogate model such as the developed NN is available, it can be used for alternative analyses on the proposed design, such as uncertainty analysis (e.g., fabrication error). Full article

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

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Open AccessArticle

Study of a Coil Heat Exchanger with an Ice Storage System

by Yan Li, Zhe Yan, Chao Yang, Bin Guo, Han Yuan, Jian Zhao and Ning Mei

Energies 2017, 10(12), 1982; https://doi.org/10.3390/en10121982 - 1 Dec 2017

Cited by 7 | Viewed by 7735

Abstract

In this study, a coil heat exchanger with an ice storage system is analyzed by theoretical analysis, numerical analysis, and experimental analysis. The dynamic characteristics of ice thickness variation is studied by means of unstable heat conduction theory in cylindrical coordinates, and the [...] Read more.

In this study, a coil heat exchanger with an ice storage system is analyzed by theoretical analysis, numerical analysis, and experimental analysis. The dynamic characteristics of ice thickness variation is studied by means of unstable heat conduction theory in cylindrical coordinates, and the change rule of the ice layer thickness is obtained. The computational fluid dynamics method is employed to simulate the flow field and ice melting process of the coil heat exchanger. The effect of the agitator height on the flow characteristics and heat transfer characteristics is investigated. The numerical results show that the turbulence intensity of the fluid near the wall of the heat exchanger is the largest with an agitator height of 80 mm. Furthermore, the process of ice melting is analyzed. The ice on the outer side of the evaporator tube close to the container wall melts faster than the inner side and this agrees well with the experimental result. The experimental study on the process of the operational period and deicing of the coil heat exchanger is conducted and the temperature variation curves are obtained by the arrangement of thermocouples. It is found that the temperature of the evaporating tube increases with increasing height in the process of ice storage. 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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Open AccessArticle

Diurnal Thermal Behavior of Photovoltaic Panel with Phase Change Materials under Different Weather Conditions

by Jae-Han Lim, Yoon-Sun Lee and Yoon-Bok Seong

Energies 2017, 10(12), 1983; https://doi.org/10.3390/en10121983 - 1 Dec 2017

Cited by 19 | Viewed by 5328

Abstract

The electric power generation efficiency of photovoltaic (PV) panels depends on the solar irradiation flux and the operating temperature of the solar cell. To increase the power generation efficiency of a PV system, this study evaluated the feasibility of phase change materials (PCMs) [...] Read more.

The electric power generation efficiency of photovoltaic (PV) panels depends on the solar irradiation flux and the operating temperature of the solar cell. To increase the power generation efficiency of a PV system, this study evaluated the feasibility of phase change materials (PCMs) to reduce the temperature rise of solar cells operating under the climate in Seoul, Korea. For this purpose, two PCMs with different phase change characteristics were prepared and the phase change temperatures and thermal conductivities were compared. The diurnal thermal behavior of PV panels with PCMs under the Seoul climate was evaluated using a 2-D transient thermal analysis program. This paper discusses the heat flow characteristics though the PV cell with PCMs and the effects of the PCM types and macro-packed PCM (MPPCM) methods on the operating temperatures under different weather conditions. Selection of the PCM type was more important than the MMPCM methods when PCMs were used to enhance the performance of PV panels and the mean operating temperature of PV cell and total heat flux from the surface could be reduced by increasing the heat transfer rate through the honeycomb grid steel container for PCMs. Considering the mean operating temperature reduction of 4 °C by PCM in this study, an efficiency improvement of approximately 2% can be estimated under the weather conditions of Seoul. Full article

(This article belongs to the Special Issue Solar Energy Application in Buildings)

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Study on Flow in Fractured Porous Media Using Pore-Fracture Network Modeling

by Haijiao Liu, Xuhui Zhang, Xiaobing Lu and Qingjie Liu

Energies 2017, 10(12), 1984; https://doi.org/10.3390/en10121984 - 1 Dec 2017

Cited by 11 | Viewed by 4092

Abstract

Microscopic flow in fractured porous media is a typical problem for the exploitation of tight reservoirs. The rapid-flow in the fractured porous-media is of great significance to efficient and continuous oil/gas exploitation. The fractures are expected to enhance flow conductivity and mass transfer [...] Read more.

Microscopic flow in fractured porous media is a typical problem for the exploitation of tight reservoirs. The rapid-flow in the fractured porous-media is of great significance to efficient and continuous oil/gas exploitation. The fractures are expected to enhance flow conductivity and mass transfer between matrix and fractures, and to improve oil displacement during water flooding. However, the fractures may also lead to water channeling under some conditions. The understanding on the mechanism of the microscopic flow in the fractured porous media has been insufficient until now. In this paper, a two-dimensional pore-fracture network model is presented to study the role of fractures in the flow. The effects of two main dimensionless parameters, fracture length to network length l_f/l and fracture density N_f/N, on the absolute permeability and the oil displacement efficiency are investigated. The results show that the flow in the matrix plays a controlling role at a low fracture density. Once the fracture density exceeds a certain value, the flow is controlled by fractures. With the increase of the fracture density, the oil displacement efficiency develops into three typical stages: when N_f/N < 0.1, the oil displacement efficiency increases rapidly; when 0.1 < N_f/N < 0.5, the oil displacement efficiency changes slowly; and when N_f/N > 0.5, the oil displacement efficiency decreases rapidly. In the case l_f/l > 0.8, the water mainly flows through a concentrated path connected by some fractures, resulting in it bypassing most oil regions, and thus the oil displacement efficiency decreases rapidly, similar to the water channeling. Full article

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

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Open AccessArticle

Large Signal Stabilization of Hybrid AC/DC Micro-Grids Using Nonlinear Robust Controller

by Reza Pejmanfar, Mahmoud Reza Haghifam, Soodabeh Soleymani and Babak Tavassoli

Energies 2017, 10(12), 1985; https://doi.org/10.3390/en10121985 - 1 Dec 2017

Cited by 5 | Viewed by 3393

Abstract

This paper presents a robust nonlinear integrated controller to improve stability of hybrid AC/DC micro-grids under islanding mode. The proposed controller includes two independent controllers where each one is responsible to control one part of the system. First controller will improve the stability [...] Read more.

This paper presents a robust nonlinear integrated controller to improve stability of hybrid AC/DC micro-grids under islanding mode. The proposed controller includes two independent controllers where each one is responsible to control one part of the system. First controller will improve the stability of input DC/DC converter. Using this controller, the voltage of DC bus is fully stabilized such that when a large disturbance occurs, its voltage will become constant without any significant dynamic. The necessity of DC bus regulation which has not been considered in previous studies, is imminent as it not only improves voltage stability of the micro-grid but also protects consumers which are directly connected to the DC bus, against voltage variations. Frequency stability of the micro-grid is provided by the second proposed controller which is applied to output DC/AC converter of the micro-grid. Adaptive method is used to make the controllers proposed in this paper, robust. Duty cycle of converters switches are adjusted such that voltage and frequency of the micro-grid are set on the desired value in minimum possible time under transient disturbances and uncertainty of the loads as well as micro-sources characteristics. Full article

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Open AccessArticle

Using a Local Framework Combining Principal Component Regression and Monte Carlo Simulation for Uncertainty and Sensitivity Analysis of a Domestic Energy Model in Sub-City Areas

by Javier Urquizo, Carlos Calderón and Philip James

Energies 2017, 10(12), 1986; https://doi.org/10.3390/en10121986 - 1 Dec 2017

Cited by 11 | Viewed by 4301

Abstract

Domestic energy modelling is complex, in terms of user input and the approach used to define the model; therefore, there is an increase in the sources of uncertainties. Previous efforts to perform sensitivity and uncertainty analyses have focused on national energy models, while [...] Read more.

Domestic energy modelling is complex, in terms of user input and the approach used to define the model; therefore, there is an increase in the sources of uncertainties. Previous efforts to perform sensitivity and uncertainty analyses have focused on national energy models, while in this research, the objective is to extend traditional sensitivity analysis and use a local framework combining principal component regression and Monte Carlo Simulation. Therefore, in our method the total amount of the energy output’s variance is decomposed, in relative terms, according to the contribution of the different predictor parameters. Our framework provides compelling evidence that local area characteristics are important in energy modelling and those national and regional indexes and values may not properly reflect the local conditions, resulting in programmes and interventions that will be sub-optimal. Furthermore, our uncertainty methodology uses a three dimensional integrative taxonomy and a concept map. The concept map identified concrete terminal causes of uncertainty within the taxonomic framework of sources, issues, sub-issues and a further abstraction of those quantities in terms of accuracy and precision. Understanding uncertainties in this way provides a possible framework for modellers, policy makers and data collectors to improve practice in key areas and to reduce uncertainty. Full article

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Predictive Maintenance of Power Substation Equipment by Infrared Thermography Using a Machine-Learning Approach

by Irfan Ullah, Fan Yang, Rehanullah Khan, Ling Liu, Haisheng Yang, Bing Gao and Kai Sun

Energies 2017, 10(12), 1987; https://doi.org/10.3390/en10121987 - 1 Dec 2017

Cited by 75 | Viewed by 11868

Abstract

A variety of reasons, specifically contact issues, irregular loads, cracks in insulation, defective relays, terminal junctions and other similar issues, increase the internal temperature of electrical instruments. This results in unexpected disturbances and potential damage to power equipment. Therefore, the initial prevention measures [...] Read more.

A variety of reasons, specifically contact issues, irregular loads, cracks in insulation, defective relays, terminal junctions and other similar issues, increase the internal temperature of electrical instruments. This results in unexpected disturbances and potential damage to power equipment. Therefore, the initial prevention measures of thermal anomalies in electrical tools are essential to prevent power-equipment failure. In this article, we address this initial prevention mechanism for power substations using a computer-vision approach by taking advantage of infrared thermal images. The thermal images are taken through infrared cameras without disturbing the working operations of power substations. Thus, this article augments the non-destructive approach to defect analysis in electrical power equipment using computer vision and machine learning. We use a total of 150 thermal pictures of different electrical equipment in 10 different substations in operating conditions, using 300 different hotspots. Our approach uses multi-layered perceptron (MLP) to classify the thermal conditions of components of power substations into “defect” and “non-defect” classes. A total of eleven features, which are first-order and second-order statistical features, are calculated from the thermal sample images. The performance of MLP shows initial accuracy of 79.78%. We further augment the MLP with graph cut to increase accuracy to 84%. We argue that with the successful development and deployment of this new system, the Technology Department of Chongqing can arrange the recommended actions and thus save cost in repair and outages. This can play an important role in the quick and reliable inspection to potentially prevent power substation equipment from failure, which will save the whole system from breakdown. The increased 84% accuracy with the integration of the graph cut shows the efficacy of the proposed defect analysis approach. Full article

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Open AccessArticle

Day-Ahead Wind Power Forecasting Using a Two-Stage Hybrid Modeling Approach Based on SCADA and Meteorological Information, and Evaluating the Impact of Input-Data Dependency on Forecasting Accuracy

by Dehua Zheng, Min Shi, Yifeng Wang, Abinet Tesfaye Eseye and Jianhua Zhang

Energies 2017, 10(12), 1988; https://doi.org/10.3390/en10121988 - 4 Dec 2017

Cited by 31 | Viewed by 5782

Abstract

The power generated by wind generators is usually associated with uncertainties, due to the intermittency of wind speed and other weather variables. This creates a big challenge for transmission system operators (TSOs) and distribution system operators (DSOs) in terms of connecting, controlling and [...] Read more.

The power generated by wind generators is usually associated with uncertainties, due to the intermittency of wind speed and other weather variables. This creates a big challenge for transmission system operators (TSOs) and distribution system operators (DSOs) in terms of connecting, controlling and managing power networks with high-penetration wind energy. Hence, in these power networks, accurate wind power forecasts are essential for their reliable and efficient operation. They support TSOs and DSOs in enhancing the control and management of the power network. In this paper, a novel two-stage hybrid approach based on the combination of the Hilbert-Huang transform (HHT), genetic algorithm (GA) and artificial neural network (ANN) is proposed for day-ahead wind power forecasting. The approach is composed of two stages. The first stage utilizes numerical weather prediction (NWP) meteorological information to predict wind speed at the exact site of the wind farm. The second stage maps actual wind speed vs. power characteristics recorded by SCADA. Then, the wind speed forecast in the first stage for the future day is fed to the second stage to predict the future day’s wind power. Comparative selection of input-data parameter sets for the forecasting model and impact analysis of input-data dependency on forecasting accuracy have also been studied. The proposed approach achieves significant forecasting accuracy improvement compared with three other artificial intelligence-based forecasting approaches and a benchmark model using the smart persistence method. Full article

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

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4250 KiB

Open AccessArticle

Thermal and Electromagnetic Combined Optimization Design of Dry Type Air Core Reactor

by Fating Yuan, Zhao Yuan, Lixue Chen, Yong Wang, Junxiang Liu, Junjia He and Yuan Pan

Energies 2017, 10(12), 1989; https://doi.org/10.3390/en10121989 - 1 Dec 2017

Cited by 13 | Viewed by 3761

Abstract

In this paper, taking the minimum metal conductor usage of an air core reactor as optimization goal, the influence of air ducts width and encapsulation number on thermal efficiency and electromagnetic efficiency are analyzed. Combined with the equation constraint conditions for maximum temperature [...] Read more.

In this paper, taking the minimum metal conductor usage of an air core reactor as optimization goal, the influence of air ducts width and encapsulation number on thermal efficiency and electromagnetic efficiency are analyzed. Combined with the equation constraint conditions for maximum temperature rise conservation, inductance conservation and structure function of reactor considering the change of air ducts width and encapsulation number, the thermal and electromagnetic combined optimization curves are formed, and design results are achieved based on the initial design parameters. Meanwhile, the temperature field simulation model of the reactor is established and the results verify the correctness of the optimization method. According to the design results, the proportionality factor of metal conductor usage is only 0.61 compared with the initial design parameters of the reactor, which shows that the proposed comprehensive optimization method can significantly reduce conductor usage, improving the metal conductor utilization ratio. Full article

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

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3069 KiB

Open AccessArticle

H-Shaped Multiple Linear Motor Drive Platform Control System Design Based on an Inverse System Method

by Caiyan Qin, Chaoning Zhang and Haiyan Lu

Energies 2017, 10(12), 1990; https://doi.org/10.3390/en10121990 - 1 Dec 2017

Cited by 8 | Viewed by 6353

Abstract

Due to its simple mechanical structure and high motion stability, the H-shaped platform has been increasingly widely used in precision measuring, numerical control machining and semiconductor packaging equipment, etc. The H-shaped platform is normally driven by multiple (three) permanent magnet synchronous linear motors. [...] Read more.

Due to its simple mechanical structure and high motion stability, the H-shaped platform has been increasingly widely used in precision measuring, numerical control machining and semiconductor packaging equipment, etc. The H-shaped platform is normally driven by multiple (three) permanent magnet synchronous linear motors. The main challenges for H-shaped platform-control include synchronous control between the two linear motors in the Y direction as well as total positioning error of the platform mover, a combination of position deviation in X and Y directions. To deal with the above challenges, this paper proposes a control strategy based on the inverse system method through state feedback and dynamic decoupling of the thrust force. First, mechanical dynamics equations have been deduced through the analysis of system coupling based on the platform structure. Second, the mathematical model of the linear motors and the relevant coordinate transformation between dq-axis currents and ABC-phase currents are analyzed. Third, after the main concept of inverse system method being explained, the inverse system model of the platform control system has been designed after defining relevant system variables. Inverse system model compensates the original nonlinear coupled system into pseudo-linear decoupled linear system, for which typical linear control methods, like PID, can be adopted to control the system. The simulation model of the control system is built in MATLAB/Simulink and the simulation result shows that the designed control system has both small synchronous deviation and small total trajectory tracking error. Furthermore, the control program has been run on NI controller for both fixed-loop-time and free-loop-time modes, and the test result shows that the average loop computation time needed is rather small, which makes it suitable for real industrial applications. Overall, it proves that the proposed new control strategy can be used in industrial applications that have high-precision and high real-time performance requirements. Full article

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

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Open AccessArticle

Dynamic Power Dispatch Considering Electric Vehicles and Wind Power Using Decomposition Based Multi-Objective Evolutionary Algorithm

by Boyang Qu, Baihao Qiao, Yongsheng Zhu, Jingjing Liang and Ling Wang

Energies 2017, 10(12), 1991; https://doi.org/10.3390/en10121991 - 1 Dec 2017

Cited by 27 | Viewed by 4793

Abstract

The intermittency of wind power and the large-scale integration of electric vehicles (EVs) bring new challenges to the reliability and economy of power system dispatching. In this paper, a novel multi-objective dynamic economic emission dispatch (DEED) model is proposed considering the EVs and [...] Read more.

The intermittency of wind power and the large-scale integration of electric vehicles (EVs) bring new challenges to the reliability and economy of power system dispatching. In this paper, a novel multi-objective dynamic economic emission dispatch (DEED) model is proposed considering the EVs and uncertainties of wind power. The total fuel cost and pollutant emission are considered as the optimization objectives, and the vehicle to grid (V2G) power and the conventional generator output power are set as the decision variables. The stochastic wind power is derived by Weibull probability distribution function. Under the premise of meeting the system energy and user’s travel demand, the charging and discharging behavior of the EVs are dynamically managed. Moreover, we propose a two-step dynamic constraint processing strategy for decision variables based on penalty function, and, on this basis, the Multi-Objective Evolutionary Algorithm Based on Decomposition (MOEA/D) algorithm is improved. The proposed model and approach are verified by the 10-generator system. The results demonstrate that the proposed DEED model and the improved MOEA/D algorithm are effective and reasonable. Full article

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

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Open AccessArticle

Testing for Environmental Kuznets Curve in the EU Agricultural Sector through an Eco-(in)Efficiency Index

by George Vlontzos, Spyros Niavis and Panos Pardalos

Energies 2017, 10(12), 1992; https://doi.org/10.3390/en10121992 - 1 Dec 2017

Cited by 38 | Viewed by 3861

Abstract

Studies on agricultural production practices advance within international literature and new methods are proposed in order to assess the agricultural sustainability, either at farm or macro level. The present paper builds on these advancements and develops a synthetic Eco-(in)efficiency index by employing a [...] Read more.

Studies on agricultural production practices advance within international literature and new methods are proposed in order to assess the agricultural sustainability, either at farm or macro level. The present paper builds on these advancements and develops a synthetic Eco-(in)efficiency index by employing a directional distance function—data envelopment analysis (DEA) model. This index is used in order to assess the sustainability of the EU agricultural sector for the period 1999–2012 on a country level. Furthermore, Eco-(in)efficiency, together with the energy use and greenhouse gas (GHG) emissions are regressed on the gross domestic product (GDP) of EU countries, in order to check for any environmental Kuznets curve relationship existence. Results signify that efficiency improvements are possible, both towards output development and GHG emissions reduction. In addition, the potential of each country in adopting more sustainable production practices is not totally connected with its economic development, as Eco-(in)efficiency and GDP levels of EU countries seem to be linked with an N-Shaped curve. Full article

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Open AccessArticle

Sludge Acts as a Catalyst for Coal during the Co-Combustion Process Investigated by Thermogravimetric Analysis

by Wendi Chen, Fei Wang and Altaf Hussain Kanhar

Energies 2017, 10(12), 1993; https://doi.org/10.3390/en10121993 - 1 Dec 2017

Cited by 19 | Viewed by 4660

Abstract

Sewage sludge in China has the characteristics of low organic content and low heating value compared with other developed countries. Self-sustaining combustion of Chinese sludge cannot be achieved when the moisture content is high. Co-combusting a small amount of sludge in the existing [...] Read more.

Sewage sludge in China has the characteristics of low organic content and low heating value compared with other developed countries. Self-sustaining combustion of Chinese sludge cannot be achieved when the moisture content is high. Co-combusting a small amount of sludge in the existing coal-fired boilers is a usual sludge disposal method in China. Thermogravimetric (TG) and differential scanning calorimetry (DSC) analysis of a bituminous coal, three different sewage sludges, and their blends have been carried out. Fitted curves by linear calculation and actual curves of blends were compared to study the interaction between sludge and coal in their co-combustion process. The results indicate that the interaction between the two fuels takes place during the devolatilization and combustion period. Sludge acts as a catalyst for coal during the co-combustion process because of the large amount of inorganic salts contained in the sludge. Co-combustion of coal and sludge is more efficient than single burning of the two fuels. Full article

(This article belongs to the Collection Bioenergy and Biofuel)

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Open AccessArticle

A Novel Semi-Visualizable Experimental Study of a Plate Gravity Heat Pipe at Unsteady State

by Xiang Gou, Yamei Li, Qiyan Zhang, Imran Ali Shah, Dong Zhao, Shian Liu, Yating Wang, Enyu Wang and Jinxiang Wu

Energies 2017, 10(12), 1994; https://doi.org/10.3390/en10121994 - 1 Dec 2017

Cited by 8 | Viewed by 3746

Abstract

An experimental study on a plate gravity heat pipe (PGHP) with inner cavity size of length 100 mm (X), width 2.5 mm (Y), and height 210 mm (Z) with acetone as the working fluid was carried out. The effects of heating power inputs [...] Read more.

An experimental study on a plate gravity heat pipe (PGHP) with inner cavity size of length 100 mm (X), width 2.5 mm (Y), and height 210 mm (Z) with acetone as the working fluid was carried out. The effects of heating power inputs (80–180 W) and fluid filling ratios (25%, 48%, and 55%) on the start-up temperature, start-up time, temperature difference, and relative thermal resistance on the Z-axis of the PGHP in a vacuum of 1 × 10⁻³ Pa were studied at unsteady state. Furthermore, the gas-liquid two-phase behavior of the interior working fluid of PGHP, and the coupling heat transfer behavior of the boiling liquid and the condensate were observed through a visualizable window under different experimental conditions. The results show that, with the increase of heating power input, the start-up temperature of the PGHP increases and the start-up time is shortened. The start-up temperature of the PGHP was around 33 °C and the start-up time was about 320 s at the heating power input of 120 W and working fluid filling ratio of 55%. The relative thermal resistance and the temperature difference on the Z-axis of the PGHP increase firstly and then decrease with the increase of heating power input at unsteady state. The complex gas-liquid two-phase behavior of the PGHP mainly includes: the formation and growth of bubbles, the merging and break up of bubbles, and the coupling heat transfer between boiling liquid and condensate, which demonstrate that the novel SVPGHP can be used to effectively study the heat transfer process of PGHP. Full article

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Open AccessArticle

Studies on an Electromagnetic Transient Model of Offshore Wind Turbines and Lightning Transient Overvoltage Considering Lightning Channel Wave Impedance

by Li Zhang, Shengwei Fang, Guozheng Wang, Tong Zhao and Liang Zou

Energies 2017, 10(12), 1995; https://doi.org/10.3390/en10121995 - 1 Dec 2017

Cited by 9 | Viewed by 4713

Abstract

In recent years, with the rapid development of offshore wind turbines (WTs), the problem of lightning strikes has become more and more prominent. In order to reduce the failure rate caused by the transient overvoltage of lightning struck offshore WTs, the influencing factors [...] Read more.

In recent years, with the rapid development of offshore wind turbines (WTs), the problem of lightning strikes has become more and more prominent. In order to reduce the failure rate caused by the transient overvoltage of lightning struck offshore WTs, the influencing factors and the response rules of transient overvoltage are analyzed. In this paper, a new integrated electromagnetic transient model of offshore WTs is established by using the numerical calculation method of the electromagnetic field first. Then, based on the lightning model and considering the impedance of the lightning channel, the transient overvoltage of lightning is analyzed. Last, the electromagnetic transient model of offshore WTs is simulated and analyzed by using the alternative transients program electro-magnetic transient program (ATP-EMTP) software. The influence factors of lightning transient overvoltage are studied. The main influencing factors include the sea depth, the blade length, the tower height, the lightning flow parameters, the lightning strike point, and the blade rotation position. The simulation results show that the influencing factors mentioned above have different effects on the lightning transient overvoltage. The results of the study have some guiding significance for the design of the lightning protection of the engine room. Full article

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Open AccessArticle

Assessment of Energy Performance and Emission Control Using Alternative Fuels in Cement Industry through a Process Model

by Azad Rahman, Mohammad G. Rasul, M.M.K. Khan and Subhash C. Sharma

Energies 2017, 10(12), 1996; https://doi.org/10.3390/en10121996 - 1 Dec 2017

Cited by 34 | Viewed by 12404

Abstract

Cement manufacturing is one of the most energy intensive processes and is accountable for substantial pollutant emissions. Increasing energy costs compel stakeholders and researchers to search for alternative options to improve energy performance and reduce CO₂ emissions. Alternative fuels offer a realistic [...] Read more.

Cement manufacturing is one of the most energy intensive processes and is accountable for substantial pollutant emissions. Increasing energy costs compel stakeholders and researchers to search for alternative options to improve energy performance and reduce CO₂ emissions. Alternative fuels offer a realistic solution towards the reduction of the usage of fossil fuels and the mitigation of pollutant emissions. This paper developed a process model of a precalciner kiln system in the cement industry using Aspen Plus software to simulate the effect of five alternative fuels on pollutant emissions and energy performance. The alternatives fuels used were tyre, municipal solid waste (MSW), meat and bone meal (MBM), plastic waste and sugarcane bagasse. The model was developed on the basis of energy and mass balance of the system and was validated against data from a reference cement plant. This study also investigated the effect of these alternative fuels on the quality of the clinker. The results indicated that up to a 4.4% reduction in CO₂ emissions and up to a 6.4% reduction in thermal energy requirement could be achieved using these alternative fuels with 20% mix in coal. It was also found that the alternative fuels had minimum influence on the clinker quality except in the case of MSW. Overall, MBM was found to be a better option as it is capable on reducing energy requirement and CO₂ emissions more than others. The outcomes of the study offer better understanding of the effects of solid alternative fuels to achieve higher energy performance and on mitigating pollutant emissions in cement industry. Full article

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Open AccessArticle

Digital-Control-Based Approximation of Optimal Wave Disturbances Attenuation for Nonlinear Offshore Platforms

by Xiao-Fang Zhong, Yu-Hong Sun, Shi-Yuan Han, Jin Zhou and Dong Wang

Energies 2017, 10(12), 1997; https://doi.org/10.3390/en10121997 - 1 Dec 2017

Cited by 2 | Viewed by 3391

Abstract

The irregular wave disturbance attenuation problem for jacket-type offshore platforms involving the nonlinear characteristics is studied. The main contribution is that a digital-control-based approximation of optimal wave disturbances attenuation controller (AOWDAC) is proposed based on iteration control theory, which consists of a feedback [...] Read more.

The irregular wave disturbance attenuation problem for jacket-type offshore platforms involving the nonlinear characteristics is studied. The main contribution is that a digital-control-based approximation of optimal wave disturbances attenuation controller (AOWDAC) is proposed based on iteration control theory, which consists of a feedback item of offshore state, a feedforward item of wave force and a nonlinear compensated component with iterative sequences. More specifically, by discussing the discrete model of nonlinear offshore platform subject to wave forces generated from the Joint North Sea Wave Project (JONSWAP) wave spectrum and linearized wave theory, the original wave disturbances attenuation problem is formulated as the nonlinear two-point-boundary-value (TPBV) problem. By introducing two vector sequences of system states and nonlinear compensated item, the solution of introduced nonlinear TPBV problem is obtained. Then, a numerical algorithm is designed to realize the feasibility of AOWDAC based on the deviation of performance index between the adjacent iteration processes. Finally, applied the proposed AOWDAC to a jacket-type offshore platform in Bohai Bay, the vibration amplitudes of the displacement and the velocity, and the required energy consumption can be reduced significantly. Full article

(This article belongs to the Special Issue Marine Energy)

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Open AccessArticle

A New Prediction Model for Transformer Winding Hotspot Temperature Fluctuation Based on Fuzzy Information Granulation and an Optimized Wavelet Neural Network

by Li Zhang, Wenfang Zhang, Jinxin Liu, Tong Zhao, Liang Zou and Xinghua Wang

Energies 2017, 10(12), 1998; https://doi.org/10.3390/en10121998 - 1 Dec 2017

Cited by 10 | Viewed by 3396

Abstract

Winding hotspot temperature is the key factor affecting the load capacity and service life of transformers. For the early detection of transformer winding hotspot temperature anomalies, a new prediction model for the hotspot temperature fluctuation range based on fuzzy information granulation (FIG) and [...] Read more.

Winding hotspot temperature is the key factor affecting the load capacity and service life of transformers. For the early detection of transformer winding hotspot temperature anomalies, a new prediction model for the hotspot temperature fluctuation range based on fuzzy information granulation (FIG) and the chaotic particle swarm optimized wavelet neural network (CPSO-WNN) is proposed in this paper. The raw data are firstly processed by FIG to extract useful information from each time window. The extracted information is then used to construct a wavelet neural network (WNN) prediction model. Furthermore, the structural parameters of WNN are optimized by chaotic particle swarm optimization (CPSO) before it is used to predict the fluctuation range of the hotspot temperature. By analyzing the experimental data with four different prediction models, we find that the proposed method is more effective and is of guiding significance for the operation and maintenance of transformers. Full article

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Open AccessArticle

Numerical Simulation Study on Steam-Assisted Gravity Drainage Performance in a Heavy Oil Reservoir with a Bottom Water Zone

by Jun Ni, Xiang Zhou, Qingwang Yuan, Xinqian Lu, Fanhua Zeng and Keliu Wu

Energies 2017, 10(12), 1999; https://doi.org/10.3390/en10121999 - 1 Dec 2017

Cited by 10 | Viewed by 6450

Abstract

In the Pikes Peak oil field near Lloydminster, Canada, a significant amount of heavy oil reserves is located in reservoirs with a bottom water zone. The properties of the bottom water zone and the operation parameters significantly affect oil production performance via the [...] Read more.

In the Pikes Peak oil field near Lloydminster, Canada, a significant amount of heavy oil reserves is located in reservoirs with a bottom water zone. The properties of the bottom water zone and the operation parameters significantly affect oil production performance via the steam-assisted gravity drainage (SAGD) process. Thus, in order to develop this type of heavy oil resource, a full understanding of the effects of these properties is necessary. In this study, the numerical simulation approach was applied to study the effects of properties in the bottom water zone in the SAGD process, such as the initial gas oil ratio, the thickness of the reservoir, and oil saturation of the bottom water zone. In addition, some operation parameters were studied including the injection pressure, the SAGD well pair location, and five different well patterns: (1) two corner wells, (2) triple wells, (3) downhole water sink well, (4) vertical injectors with a horizontal producer, and (5) fishbone well. The numerical simulation results suggest that the properties of the bottom water zone affect production performance extremely. First, both positive and negative effects were observed when solution gas exists in the heavy oil. Second, a logarithmical relationship was investigated between the bottom water production ratio and the thickness of the bottom water zone. Third, a non-linear relation was obtained between the oil recovery factor and oil saturation in the bottom water zone, and a peak oil recovery was achieved at the oil saturation rate of 30% in the bottom water zone. Furthermore, the operation parameters affected the heavy oil production performance. Comparison of the well patterns showed that the two corner wells and the triple wells patterns obtained the highest oil recovery factors of 74.71% and 77.19%, respectively, which are almost twice the oil recovery factors gained in the conventional SAGD process (47.84%). This indicates that the optimized SAGD process with the two corner wells and the triple wells pattern is able to improve SAGD production performance in a heavy oil reservoir with a bottom water zone. Full article

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Open AccessArticle

A Comparative Study of Energy Performance of Fumed Silica Vacuum Insulation Panels in an Apartment Building

by Taesub Lim, Jaewang Seok and Daeung Danny Kim

Energies 2017, 10(12), 2000; https://doi.org/10.3390/en10122000 - 1 Dec 2017

Cited by 11 | Viewed by 3517

Abstract

Building insulation materials has a significant impact on building energy consumptions. However, conventional materials are easily flammable and can cause fire disasters in buildings. Therefore, it is important to select appropriate insulation materials for building energy efficiency and safety and Vacuum Insulation Panels [...] Read more.

Building insulation materials has a significant impact on building energy consumptions. However, conventional materials are easily flammable and can cause fire disasters in buildings. Therefore, it is important to select appropriate insulation materials for building energy efficiency and safety and Vacuum Insulation Panels (VIPs) are increasingly applied to building insulation. Considering this, the present study investigates energy performance of VIPs with design alternatives, such as window systems, infiltration rates, etc., by using energy simulation. Among various VIPs, fumes silica VIPs were chosen. In addition, eight combinations were compared to find the best energy efficient design conditions. The results of the present study showed that building energy performance can be improved with an appropriate combination of design options including fumed silica VIPs. Full article

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Open AccessArticle

Wind Speed Forecasting Based on EMD and GRNN Optimized by FOA

by Dongxiao Niu, Yi Liang and Wei-Chiang Hong

Energies 2017, 10(12), 2001; https://doi.org/10.3390/en10122001 - 1 Dec 2017

Cited by 47 | Viewed by 4739

Abstract

As a kind of clean and renewable energy, wind power is winning more and more attention across the world. Regarding wind power utilization, safety is a core concern and such concern has led to many studies on predicting wind speed. To obtain a [...] Read more.

As a kind of clean and renewable energy, wind power is winning more and more attention across the world. Regarding wind power utilization, safety is a core concern and such concern has led to many studies on predicting wind speed. To obtain a more accurate prediction of the wind speed, this paper adopts a new hybrid forecasting model, combing empirical mode decomposition (EMD) and the general regression neural network (GRNN) optimized by the fruit fly optimization algorithm (FOA). In this new model, the original wind speed series are first decomposed into a collection of intrinsic mode functions (IMFs) and a residue. Next, the inherent relationship (partial correlation) of the datasets is analyzed, and the results are then used to select the input for the forecasting model. Finally, the GRNN with the FOA to optimize the smoothing factor is used to predict each sub-series. The mean absolute percentage error of the forecasting results in two cases are respectively 8.95% and 9.87%, suggesting that the hybrid approach outperforms the compared models, which provides guidance for future wind speed forecasting. Full article

(This article belongs to the Special Issue Hybrid Advanced Optimization Methods with Evolutionary Computation Techniques in Energy Forecasting)

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Open AccessArticle

Phase-Inductance-Based Position Estimation Method for Interior Permanent Magnet Synchronous Motors

by Xin Qiu, Weiye Wang, Jianfei Yang, Jie Jiang and Jiquan Yang

Energies 2017, 10(12), 2002; https://doi.org/10.3390/en10122002 - 1 Dec 2017

Cited by 4 | Viewed by 5181

Abstract

This paper presents a phase-inductance-based position estimation method for interior permanent magnet synchronous motors (IPMSMs). According to the characteristics of phase induction of IPMSMs, the corresponding relationship of the rotor position and the phase inductance is obtained. In order to eliminate the effect [...] Read more.

This paper presents a phase-inductance-based position estimation method for interior permanent magnet synchronous motors (IPMSMs). According to the characteristics of phase induction of IPMSMs, the corresponding relationship of the rotor position and the phase inductance is obtained. In order to eliminate the effect of the zero-sequence component of phase inductance and reduce the rotor position estimation error, the phase inductance difference is employed. With the iterative computation of inductance vectors, the position plane is further subdivided, and the rotor position is extracted by comparing the amplitudes of inductance vectors. To decrease the consumption of computer resources and increase the practicability, a simplified implementation is also investigated. In this method, the rotor position information is achieved easily, with several basic math operations and logical comparisons of phase inductances, without any coordinate transformation or trigonometric function calculation. Based on this position estimation method, the field orientated control (FOC) strategy is established, and the detailed implementation is also provided. A series of experiment results from a prototype demonstrate the correctness and feasibility of the proposed method. Full article

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

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2139 KiB

Open AccessArticle

Optimal Dispatching of Active Distribution Networks Based on Load Equilibrium

by Xiao Han, Ming Zhou, Gengyin Li and Kwang Y. Lee

Energies 2017, 10(12), 2003; https://doi.org/10.3390/en10122003 - 1 Dec 2017

Cited by 5 | Viewed by 3206

Abstract

This paper focuses on the optimal intraday scheduling of a distribution system that includes renewable energy (RE) generation, energy storage systems (ESSs), and thermostatically controlled loads (TCLs). This system also provides time-of-use pricing to customers. Unlike previous studies, this study attempts to examine [...] Read more.

This paper focuses on the optimal intraday scheduling of a distribution system that includes renewable energy (RE) generation, energy storage systems (ESSs), and thermostatically controlled loads (TCLs). This system also provides time-of-use pricing to customers. Unlike previous studies, this study attempts to examine how to optimize the allocation of electric energy and to improve the equilibrium of the load curve. Accordingly, we propose a concept of load equilibrium entropy to quantify the overall equilibrium of the load curve and reflect the allocation optimization of electric energy. Based on this entropy, we built a novel multi-objective optimal dispatching model to minimize the operational cost and maximize the load curve equilibrium. To aggregate TCLs into the optimization objective, we introduced the concept of a virtual power plant (VPP) and proposed a calculation method for VPP operating characteristics based on the equivalent thermal parameter model and the state-queue control method. The Particle Swarm Optimization algorithm was employed to solve the optimization problems. The simulation results illustrated that the proposed dispatching model can achieve cost reductions of system operations, peak load curtailment, and efficiency improvements, and also verified that the load equilibrium entropy can be used as a novel index of load characteristics. Full article

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

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Open AccessArticle

Research on Pulsed Jet Flow Control without External Energy in a Blade Cascade

by Jie Chen, Weiyu Lu, Guoping Huang, Jianfeng Zhu and Jinchun Wang

Energies 2017, 10(12), 2004; https://doi.org/10.3390/en10122004 - 1 Dec 2017

Cited by 13 | Viewed by 4603

Abstract

To control the flow separation in the compressors, a novel pulsed jet concept without external energy injection is proposed. The new concept designs a slot in the middle of the blade and sets a micro device to switch the slot periodically. Such a [...] Read more.

To control the flow separation in the compressors, a novel pulsed jet concept without external energy injection is proposed. The new concept designs a slot in the middle of the blade and sets a micro device to switch the slot periodically. Such a structure is expected to generate a pulsed jet by the pressure difference between the pressure side and the suction side of the blade. In order to analyze the interaction between the pulsed jet and unsteady separated flow, our numerical and experimental study is based on a specific cascade (with a flow separation inside) and a pulsed jet (one of the unsteady flow control method). The experimental and numerical results both show that when the frequency of pulsed jet is approximate to that of the separation vortex, then the control tends to be more effective. Based on the numerical simulations, the proper orthogonal decomposition (POD) is then used to reveal the control mechanism, extracting the different time-space structures from the original field. The results with the aid of POD show that the pulsed jet can redistribute the kinetic energy of each mode, and strengthen or weaken certain modes, particularly, while the steady jet reduces the kinetic energy of high-order modes in whole. Also, pulsed jet with proper parameters can transfer the energy from higher modes to the first flow mode (averaged flow), which is due to the conversion of the spatial vortical structures and the time evolution of the modes. Full article

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Open AccessArticle

A Three-Phase Four-Leg Inverter-Based Active Power Filter for Unbalanced Current Compensation Using a Petri Probabilistic Fuzzy Neural Network

by Kuang-Hsiung Tan, Faa-Jeng Lin and Jun-Hao Chen

Energies 2017, 10(12), 2005; https://doi.org/10.3390/en10122005 - 1 Dec 2017

Cited by 21 | Viewed by 5624

Abstract

A three-phase four-leg inverter-based shunt active power filter (APF) is proposed to compensate three-phase unbalanced currents under unbalanced load conditions in grid-connected operation in this study. Since a DC-link capacitor is required on the DC side of the APF to release or absorb [...] Read more.

A three-phase four-leg inverter-based shunt active power filter (APF) is proposed to compensate three-phase unbalanced currents under unbalanced load conditions in grid-connected operation in this study. Since a DC-link capacitor is required on the DC side of the APF to release or absorb the instantaneous apparent power, the regulation control of the DC-link voltage of the APF is important especially under load variation. In order to improve the regulation control of the DC-link voltage of the shunt APF under variation of three-phase unbalanced load and to compensate the three-phase unbalanced currents effectively, a novel Petri probabilistic fuzzy neural network (PPFNN) controller is proposed to replace the traditional proportional-integral (PI) controller in this study. Furthermore, the network structure and online learning algorithms of the proposed PPFNN are represented in detail. Finally, the effectiveness of the three-phase four-leg inverter-based shunt APF with the proposed PPFNN controller for the regulation of the DC-link voltage and compensation of the three-phase unbalanced current has been demonstrated by some experimental results. Full article

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

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2535 KiB

Open AccessArticle

Performance Evaluation of a Desiccant Dehumidifier with a Heat Recovery Unit

by Kai-Shing Yang, Jian-Sin Wang, Shih-Kuo Wu, Chih-Yung Tseng and Jin-Cherng Shyu

Energies 2017, 10(12), 2006; https://doi.org/10.3390/en10122006 - 1 Dec 2017

Cited by 9 | Viewed by 4126

Abstract

In order to effectively increase the drying rate and reduce the energy consumption, a dryer which reduces the air humidity at the dryer inlet using desiccant and regenerates the desiccant by recovering waste heat using a heat pipe heat exchanger was developed in [...] Read more.

In order to effectively increase the drying rate and reduce the energy consumption, a dryer which reduces the air humidity at the dryer inlet using desiccant and regenerates the desiccant by recovering waste heat using a heat pipe heat exchanger was developed in this study. Both the adsorption rate and desorption rate of the dryer were measured at several ambient temperatures ranging from 15 °C to 35 °C, relative humidity levels of air ranging from 20% to 85%, and airflow rates ranging from 30 m³/h to 150 m³/h. The results showed that the adsorption rate in an environment of high relative humidity of air was 4.89 times higher than that of low relative humidity of air at 15 °C. Moreover, the difference in adsorption rate between two given relative humidity of air increased as the ambient temperature decreased. The specific energy consumption estimated with both energy consumption during desorption and the desorption rate indicated that the energy consumption was 8.27 kJ/g H₂O without using recovered heat, while the energy consumption was 4.77 kJ/g H₂O using recovered heat at 130 °C. Full article

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5923 KiB

Open AccessArticle

An Improved Approach to Estimate Three-Phase Relative Permeability Functions for Heavy-Oil Displacement Involving Instability and Compositional Effects

by Pedram Mahzari, Usman Taura, Alexander J. Cooke and Mehran Sohrabi

Energies 2017, 10(12), 2008; https://doi.org/10.3390/en10122008 - 1 Dec 2017

Cited by 4 | Viewed by 5073

Abstract

Simultaneous three-phase flow of gas, oil and water is a common phenomenon in enhanced oil recovery techniques such as water-alternating-gas (WAG) injection. Reliable reservoir simulations are required to predict the performance of these injections before field application. However, heavy oil displacement by gas [...] Read more.

Simultaneous three-phase flow of gas, oil and water is a common phenomenon in enhanced oil recovery techniques such as water-alternating-gas (WAG) injection. Reliable reservoir simulations are required to predict the performance of these injections before field application. However, heavy oil displacement by gas or water can lead to viscous fingering due to the unfavorable mobility ratio between heavy oil and the displacing fluid. In addition, the injection of partially dissolvable gases such as CO₂ can result in compositional effects, which can bring about a significant reduction of oil viscosity and hence can cause variations of the mobility ratio. Estimations of three-phase relative permeability under such conditions are extremely complex, and using conventional techniques for the estimation can lead to erroneous results. We used the results of four coreflood experiments, carried out on a core, to estimate two-phase and three-phase relative permeability. A new history matching methodology for laboratory experiments was used that takes into account the instability and the compositional effects in the estimation processes. The results demonstrate that a simultaneous CO₂ and water injection (CO₂-simultaneous water and gas (SWAG)) can be adequately matched using the relative permeabilities of a secondary gas/liquid and a tertiary oil/water. In heavy oil WAG injection, the injected water follows the CO₂ path due its lower resistance as a result of the CO₂ dissolution in the oil and the resultant reduction of the oil viscosity. This is contrary to WAG injection in conventional oils, where gas and water open up separate saturations paths. It is also important to include capillary pressure (Pc), even in high permeable porous media, as we observed that the inclusion of capillary pressure dampened the propagation of the viscous fingers and hence helped the front to become stabilized, leading to a more realistic simulated sweep efficiency. Full article

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

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3116 KiB

Open AccessArticle

Energy Performance and Economic Feasibility Study of Historical Building in the City of Matera, Southern Italy

by Gianluca Rospi, Nicola Cardinale and Elisabetta Negro

Energies 2017, 10(12), 2009; https://doi.org/10.3390/en10122009 - 1 Dec 2017

Cited by 16 | Viewed by 3223

Abstract

In this paper a careful energy audit and an energy restoration of some historical buildings was performed. In particular, three cultural heritages buildings situated in the city of Matera in Southern Italy were analysed. To analyse these buildings, an integrated approach based on [...] Read more.

In this paper a careful energy audit and an energy restoration of some historical buildings was performed. In particular, three cultural heritages buildings situated in the city of Matera in Southern Italy were analysed. To analyse these buildings, an integrated approach based on measurements in situ and on dynamic energy simulations was used. Then, some energy efficiency actions were performed, safeguarding the authenticity value of these structures. The thermal conductance, the indoor temperature and the energy consumption were measured in situ and then the numerical virtual model was created by the Energy Plus code (Energy Plus is free, open-source, and cross-platform developed by the U.S. Department of Energy’s and Building Technologies Office) (U.S. Department of Energy’s (DOE) Building Technologies Office (BTO), Washington, DC, USA). The numerical model was validated by using the Inequality Coefficient (IC) and then different parametric energy analyses were performed. The paper analysed different energy improvements and a techno-economic feasibility study was performed for each improvement. This analysis was conducted in dynamic regime by using the Energy-Plus code. In these buildings the thermal system improvements have a better payback time than envelope improvements. Two different thermal system improvements were analysed: the absorption heat pump with thermostatic valves and the compression heat pump with fan coil unit. Moreover, the replacement of present lighting with LED technologies has a payback time near one year. Full article

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

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10136 KiB

Open AccessArticle

Microcosmic Mechanism Investigation on Lightning Arc Damage of Wind Turbine Blades Based on Molecular Reaction Dynamics and Impact Current Experiment

by Li Zhang, Liyang Jiang, Tong Zhao and Liang Zou

Energies 2017, 10(12), 2010; https://doi.org/10.3390/en10122010 - 1 Dec 2017

Cited by 4 | Viewed by 3133

Abstract

PVC and balsa wood are usually used in the interlayer structures of wind turbine blades. In this paper, a comparative study on the lightning damage characteristics of the two materials was carried out by molecular dynamic simulations and impact current experiments. The simulations [...] Read more.

PVC and balsa wood are usually used in the interlayer structures of wind turbine blades. In this paper, a comparative study on the lightning damage characteristics of the two materials was carried out by molecular dynamic simulations and impact current experiments. The simulations show that the glycosidic bonds in cellulose break first, which leads to a strong decrease in the degree of polymerization (DP) of cellulose (while the DP of PVC changes irregularly), then C−O bonds in the pyranoid ring break and the main chain of cellulose is destroyed, producing small molecule fractions and a lot of gas molecules. There are two steps in the pyrolysis of PVC. H and Cl atoms fall off the main chain and combined for form HCl, which needs less energy and occurs earlier than cellulose pyrolysis at 2000 K, but cellulose generates more gas products than PVC at the same temperature. Thus the damages to balsa wood and PVC mainly appear as fiber fractures and pore extension, respectively, which are consistent with the morphological features of the damage to the two materials in the impact current experiments. The experimental results also show that the pyrolysis temperature of PVC was lower than that of balsa wood, and the residual strength decreases faster in PVC than in balsa wood with the increase of peak current. This study should play an important guiding role for lightning protection and material selection of wind turbine blades. Full article

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Open AccessArticle

Experimental Study on Bluff-Body Stabilized Premixed Flame with a Central Air/Fuel Jet

by Yiheng Tong, Shuang Chen, Mao Li, Zhongshan Li and Jens Klingmann

Energies 2017, 10(12), 2011; https://doi.org/10.3390/en10122011 - 1 Dec 2017

Cited by 7 | Viewed by 9630

Abstract

Bluff-body flame holders are commonly employed in many industrial applications. A bluff-body is usually adopted to enhance the downstream mixing of the combustion products and the fresh fuel-air mixtures, thus to improve the flame stability and to control the combustion process. In the [...] Read more.

Bluff-body flame holders are commonly employed in many industrial applications. A bluff-body is usually adopted to enhance the downstream mixing of the combustion products and the fresh fuel-air mixtures, thus to improve the flame stability and to control the combustion process. In the present paper, flames stabilized by a conical-shape bluff-body flame holder with a central air/fuel jet were studied. Effects of both a central air jet and a central fuel jet on the structures and lean blowout limits of the premixed annular flames, and on the temperature on the upper surface of the bluff-body were investigated and presented. It was revealed that a central jet led to a considerable reduction of the temperature on the upper surface of the bluff-body. It was proposed to be caused by the alternation of flow structures (in the case with a central air jet) altogether with the flame lifting from the burner (in the case with a central fuel jet). Thus, it might be used to solve the problem of the bluff-body with high heat loads in practical applications. The flame stability characteristics, for example the unstable flame dynamics and the lean blowout limits, varied with the injection of an air or fuel jet through the central pipe. Different blowout behaviors, being with or without the occurrence of flame split and flashing, caused by a central air jet were presented in the paper. In addition, when a small amount of central fuel jet (i.e., U_f/U_a = 0.045) was injected into the flow fields, an unsteady circular motion of the flame tip along the outer edge of the bluff-body was observed as well. Whereas, with an increase in the amount of the central fuel jet, the flame detached from the outer edge of the bluff-body and then became much more unstable. With a central air or fuel jet injecting into the flow field, premixed flames stabilized by the bluff-body became more unstable and easier to blowout. Full article

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

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1008 KiB

Open AccessArticle

Indirect State-of-Health Estimation for Lithium-Ion Batteries under Randomized Use

by Jinsong Yu, Baohua Mo, Diyin Tang, Jie Yang, Jiuqing Wan and Jingjing Liu

Energies 2017, 10(12), 2012; https://doi.org/10.3390/en10122012 - 1 Dec 2017

Cited by 27 | Viewed by 3818

Abstract

Lithium-ion batteries are widely used in many systems. Because they provide a power source to the whole system, their state-of-health (SOH) is very important for a system’s proper operation. A direct way to estimate the SOH is through the measurement of the battery’s [...] Read more.

Lithium-ion batteries are widely used in many systems. Because they provide a power source to the whole system, their state-of-health (SOH) is very important for a system’s proper operation. A direct way to estimate the SOH is through the measurement of the battery’s capacity; however, this measurement during the battery’s operation is not that easy in practice. Moreover, the battery is always running under randomized loading conditions, which makes the SOH estimation even more difficult. Therefore, this paper proposes an indirect SOH estimation method that relies on indirect health indicators (HIs) that can be measured easily during the battery’s operation. These indicators are extracted from the battery’s voltage and current and the number of cycles the battery has been through, which are far easier to measure than the battery’s capacity. An empirical model based on an elastic net is developed to build the quantitative relationship between the SOH and these indirect HIs, considering the possible multi-collinearity between these HIs. To further improve the accuracy of SOH estimation, we introduce a particle filter to automatically update the model when capacity data are obtained occasionally. We use a real dataset to demonstrate our proposed method, showing quite a good performance of the SOH estimation. The results of the SOH estimation in the experiment are quite satisfactory, which indicates that the method is effective and accurate enough to be used in real practice. Full article

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Open AccessArticle

Solution Validation for a Double Façade Prototype

by Pau Fonseca i Casas, Antoni Fonseca i Casas, Nuria Garrido-Soriano, Alfonso Godoy, Wendys-Carolina Pujols and Jesus Garcia

Energies 2017, 10(12), 2013; https://doi.org/10.3390/en10122013 - 1 Dec 2017

Cited by 3 | Viewed by 2996

Abstract

A Solution Validation involves comparing the data obtained from the system that are implemented following the model recommendations, as well as the model results. This paper presents a Solution Validation that has been performed with the aim of certifying that a set of [...] Read more.

A Solution Validation involves comparing the data obtained from the system that are implemented following the model recommendations, as well as the model results. This paper presents a Solution Validation that has been performed with the aim of certifying that a set of computer-optimized designs, for a double façade, are consistent with reality. To validate the results obtained through simulation models, based on dynamic thermal calculation and using Computational Fluid Dynamic techniques, a comparison with the data obtained by monitoring a real implemented prototype has been carried out. The new validated model can be used to describe the system thermal behavior in different climatic zones without having to build a new prototype. The good performance of the proposed double façade solution is confirmed since the validation assures there is a considerable energy saving, preserving and even improving interior comfort. This work shows all the processes in the Solution Validation depicting some of the problems we faced and represents an example of this kind of validation that often is not considered in a simulation project. Full article

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

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Open AccessArticle

Comparison of Model-Based Control Solutions for Severe Riser-Induced Slugs

by Simon Pedersen, Esmaeil Jahanshahi, Zhenyu Yang and Sigurd Skogestad

Energies 2017, 10(12), 2014; https://doi.org/10.3390/en10122014 - 1 Dec 2017

Cited by 6 | Viewed by 3008

Abstract

Control solutions for eliminating severe riser-induced slugs in offshore oil & gas pipeline installations are key topics in offshore Exploration and Production (E&P) processes. This study describes the identification, analysis and control of a low-dimensional control-oriented model of a lab-scaled slug testing facility. [...] Read more.

Control solutions for eliminating severe riser-induced slugs in offshore oil & gas pipeline installations are key topics in offshore Exploration and Production (E&P) processes. This study describes the identification, analysis and control of a low-dimensional control-oriented model of a lab-scaled slug testing facility. The model is analyzed and used for anti-slug control development for both lowpoint and topside transmitter solutions. For the controlled variables’ comparison it is concluded that the topside pressure transmitter (

P_{t}

) is the most difficult output to apply directly for anti-slug control due to the inverse response. However, as

P_{t}

often is the only accessible measurement on offshore platforms this study focuses on the controller development for both

P_{t}

and the lowpoint pressure transmitter (

P_{b}

). All the control solutions are based on linear control schemes and the performance of the controllers are evaluated from simulations with both the non-linear MATLAB and OLGA models. Furthermore, the controllers are studied with input disturbances and parametric variations to evaluate their robustness. For both pressure transmitters the

H_{\infty}

loop-shaping controller gives the best performance as it is relatively robust to disturbances and has a fast convergence rate. However,

P_{t}

does not increase the closed-loop bifurcation point significantly and is also sensitive to disturbances. Thus the study concludes that the best option for single-input-single-output (SISO) systems is to control

P_{b}

with a

H_{\infty}

loop-shaping controller. It is suggested that for cases where only topside transmitters are available a cascaded combination of the outlet mass flow and

P_{t}

could be considered to improve the performance. Full article

(This article belongs to the Special Issue Oil and Gas Engineering)

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Open AccessArticle

Orthogonal Test Analysis on Conditions Affecting Electricity Generation Performance of an Enhanced Geothermal System at Yangbajing Geothermal Field

by Yuchao Zeng, Liansheng Tang, Nengyou Wu, Jing Song and Yifei Cao

Energies 2017, 10(12), 2015; https://doi.org/10.3390/en10122015 - 1 Dec 2017

Cited by 4 | Viewed by 2992

Abstract

The main conditions affecting electricity generation performance of an enhanced geothermal system (EGS) include reservoir porosity, reservoir permeability, rock heat conductivity, water production rate and injection temperature. Presently there is lack of systematic research the relative importance of the five aforementioned conditions. The [...] Read more.

The main conditions affecting electricity generation performance of an enhanced geothermal system (EGS) include reservoir porosity, reservoir permeability, rock heat conductivity, water production rate and injection temperature. Presently there is lack of systematic research the relative importance of the five aforementioned conditions. The orthogonal test method is a statistical approach to analyze multi-factor and multi-level influence on system performance. In this work, based on the geological data at Yangbajing geothermal field, we analyzed the five conditions affecting the electricity generation performance of EGS, and ranked the relative importance of the five factors. The results show that the order of the relative importance of the conditions on electric power is water production rate > injection temperature > reservoir porosity > rock heat conductivity > reservoir permeability; the order of the relative importance of the conditions on reservoir impedance is reservoir permeability > injection temperature > water production rate > reservoir porosity > rock heat conductivity; the order of the relative importance of the conditions on pump power is water production rate > reservoir permeability > injection temperature > reservoir porosity > rock heat conductivity, and; the order of the relative importance of the conditions on energy efficiency is water production rate > reservoir permeability > reservoir porosity > injection temperature > rock heat conductivity. The construction of an EGS reservoir should be located at a formation with higher reservoir porosity or rock heat conductivity, while the determination of reservoir permeability, water production rate and injection temperature should be based on the comprehensive target. Full article

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

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Open AccessArticle

Maximum Power Point Tracking Control of a Thermoelectric Generation System Using the Extremum Seeking Control Method

by Ssennoga Twaha, Jie Zhu, Luqman Maraaba, Kuo Huang, Bo Li and Yuying Yan

Energies 2017, 10(12), 2016; https://doi.org/10.3390/en10122016 - 1 Dec 2017

Cited by 12 | Viewed by 5961

Abstract

This study proposes and implements maximum power Point Tracking (MPPT) control on thermoelectric generation system using an extremum seeking control (ESC) algorithm. The MPPT is applied to guarantee maximum power extraction from the TEG system. The work has been carried out through modelling [...] Read more.

This study proposes and implements maximum power Point Tracking (MPPT) control on thermoelectric generation system using an extremum seeking control (ESC) algorithm. The MPPT is applied to guarantee maximum power extraction from the TEG system. The work has been carried out through modelling of thermoelectric generator/dc-dc converter system using Matlab/Simulink. The effectiveness of ESC technique has been assessed by comparing the results with those of the Perturb and Observe (P&O) MPPT method under the same operating conditions. Results indicate that ESC MPPT method extracts more power than the P&O technique, where the output power of ESC technique is higher than that of P&O by 0.47 W or 6.1% at a hot side temperature of 200 °C. It is also noted that the ESC MPPT based model is almost fourfold faster than the P&O method. This is attributed to smaller MPPT circuit of ESC compared to that of P&O, hence we conclude that the ESC MPPT method outperforms the P&O technique. Full article

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Open AccessArticle

National Options for a Sustainable Nuclear Energy System: MCDM Evaluation Using an Improved Integrated Weighting Approach

by Ruxing Gao, Hyo On Nam, Won Il Ko and Hong Jang

Energies 2017, 10(12), 2017; https://doi.org/10.3390/en10122017 - 1 Dec 2017

Cited by 41 | Viewed by 4679

Abstract

While the prospects look bright for nuclear energy development in China, no consensus about an optimum transitional path towards sustainability of the nuclear fuel cycle has been achieved. Herein, we present a preliminary study of decision making for China’s future nuclear energy systems, [...] Read more.

While the prospects look bright for nuclear energy development in China, no consensus about an optimum transitional path towards sustainability of the nuclear fuel cycle has been achieved. Herein, we present a preliminary study of decision making for China’s future nuclear energy systems, combined with a dynamic analysis model. In terms of sustainability assessment based on environmental, economic, and social considerations, we compared and ranked the four candidate options of nuclear fuel cycles combined with an integrated evaluation analysis using the Multi-Criteria Decision Making (MCDM) method. An improved integrated weighting method was first applied in the nuclear fuel cycle evaluation study. This method synthesizes diverse subjective/objective weighting methods to evaluate conflicting criteria among the competing decision makers at different levels of expertise and experience. The results suggest that the fuel cycle option of direct recycling of spent fuel through fast reactors is the most competitive candidate, while the fuel cycle option of direct disposal of all spent fuel without recycling is the least attractive for China, from a sustainability perspective. In summary, this study provided a well-informed decision-making tool to support the development of national nuclear energy strategies. Full article

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

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11098 KiB

Open AccessArticle

Loss Model and Efficiency Analysis of Tram Auxiliary Converter Based on a SiC Device

by Hao Liu, Xianjin Huang, Fei Lin and Zhongping Yang

Energies 2017, 10(12), 2018; https://doi.org/10.3390/en10122018 - 1 Dec 2017

Cited by 7 | Viewed by 6921

Abstract

Currently, the auxiliary converter in the auxiliary power supply system of a modern tram adopts Si IGBT as its switching device and with the 1700 V/225 A SiC MOSFET module commercially available from Cree, an auxiliary converter using all SiC devices is now [...] Read more.

Currently, the auxiliary converter in the auxiliary power supply system of a modern tram adopts Si IGBT as its switching device and with the 1700 V/225 A SiC MOSFET module commercially available from Cree, an auxiliary converter using all SiC devices is now possible. A SiC auxiliary converter prototype is developed during this study. The author(s) derive the loss calculation formula of the SiC auxiliary converter according to the system topology and principle and each part loss in this system can be calculated based on the device datasheet. Then, the static and dynamic characteristics of the SiC MOSFET module used in the system are tested, which aids in fully understanding the performance of the SiC devices and provides data support for the establishment of the PLECS loss simulation model. Additionally, according to the actual circuit parameters, the PLECS loss simulation model is set up. This simulation model can simulate the actual operating conditions of the auxiliary converter system and calculate the loss of each switching device. Finally, the loss of the SiC auxiliary converter prototype is measured and through comparison it is found that the loss calculation theory and PLECS loss simulation model is valuable. Furthermore, the thermal images of the system can prove the conclusion about loss distribution to some extent. Moreover, these two methods have the advantages of less variables and fast calculation for high power applications. The loss models may aid in optimizing the switching frequency and improving the efficiency of the system. Full article

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

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2222 KiB

Open AccessArticle

Global Feedback Control for Coordinated Linear Switched Reluctance Machines Network with Full-State Observation and Internal Model Compensation

by Bo Zhang, Jianping Yuan, J. F. Pan, Xiaoyu Wu, Jianjun Luo and Li Qiu

Energies 2017, 10(12), 2019; https://doi.org/10.3390/en10122019 - 2 Dec 2017

Viewed by 3074

Abstract

This paper discusses the tracking coordination of a linear switched reluctance machine (LSRM) network based on a global feedback control strategy with a full-state observation framework. The observer is allocated on the follower instead of the leader to form a leader–follower–observer network, by [...] Read more.

This paper discusses the tracking coordination of a linear switched reluctance machine (LSRM) network based on a global feedback control strategy with a full-state observation framework. The observer is allocated on the follower instead of the leader to form a leader–follower–observer network, by utilizing the leader as the global feedback tracking controller and the observer as the observation of the full states. The internal model compensator (IMC) is applied to the leader for the improvement of the network performance. The full-state information of the LSRM network is reconfigured by the output of the LSRM where the observer is located to provide necessary feedback information to the leader. Then, the controllability and observability of the leader–follower–observer network with the IMC are inspected, serving as a basis for the design of the global controller with the IMC and full-state observer. Experimentation verifies the effectiveness of the proposed network control scheme and the results demonstrate that both the absolute and the relative accuracy can be simultaneously improved, compared to the LSRM network with only the consensus algorithm and no global feedback mechanism. Full article

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

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Open AccessArticle

Investigation of Heat Pump Operation Strategies with Thermal Storage in Heating Conditions

by Wangsik Jung, Dongjun Kim, Byung Ha Kang and Young Soo Chang

Energies 2017, 10(12), 2020; https://doi.org/10.3390/en10122020 - 1 Dec 2017

Cited by 13 | Viewed by 5551

Abstract

A heat pump with thermal storage system is a system that operates a heat pump during nighttime using inexpensive electricity; during this time, the generated thermal energy is stored in a thermal storage tank. The stored thermal energy is used by the heat [...] Read more.

A heat pump with thermal storage system is a system that operates a heat pump during nighttime using inexpensive electricity; during this time, the generated thermal energy is stored in a thermal storage tank. The stored thermal energy is used by the heat pump during daytime. Based on a model of a dual latent thermal storage tank and a heat pump, this study conducts control simulations using both conventional and advanced methods for heating in a building. Conventional methods include the thermal storage priority method and the heat pump priority method, while advanced approaches include the region control method and the dynamic programming method. The heating load required for an office building is identified using TRNSYS (Transient system simulation), used for simulations of various control methods. The thermal storage priority method shows a low coefficient of performance (COP), while the heat pump priority method leads to high electricity costs due to the low use of thermal storage. In contrast, electricity costs are lower for the region control method, which operates using the optimal part load ratio of the heat pump, and for dynamic programming, which operates the system by following the minimum cost path. According to simulation results for the winter season, the electricity costs using the dynamic programming method are 17% and 9% lower than those of the heat pump priority and thermal storage priority methods, respectively. The region control method shows results similar to the dynamic programming method with respect to electricity costs. In conclusion, advanced control methods are proven to have advantages over conventional methods in terms of power consumption and electricity costs. Full article

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Open AccessArticle

Optimizing the Structure of the Straight Cone Nozzle and the Parameters of Borehole Hydraulic Mining for Huadian Oil Shale Based on Experimental Research

by Jiwei Wen and Chen Chen

Energies 2017, 10(12), 2021; https://doi.org/10.3390/en10122021 - 1 Dec 2017

Cited by 16 | Viewed by 4392

Abstract

Oil shale is a kind of potential alternative energy source for petroleum and has attracted the attention of energy researchers all over the world. Borehole hydraulic mining has more prominent advantages than both conventional open-pit mining and underground mining. It is very important [...] Read more.

Oil shale is a kind of potential alternative energy source for petroleum and has attracted the attention of energy researchers all over the world. Borehole hydraulic mining has more prominent advantages than both conventional open-pit mining and underground mining. It is very important to attempt to use the borehole hydraulic mining method to exploit underground oil shale. The nozzle is the key component of borehole hydraulic mining and reasonable mining parameters are also crucial in exploiting underground oil shale efficiently. The straight cone nozzle and the oil shale of Huadian area will be taken as the research objects. The self-developed, multifunctional, experimental device can test both the jet’s performance as well as the breaking of oil shale by the high-pressure water jet using the straight cone nozzle and varying structural parameters. Comprehensive analysis of the results of an orthogonal experimental design, including range analysis and variance analysis, demonstrate the optimal structural parameters of a straight cone nozzle as follows: the outlet diameter is 4 mm, the length to diameter ratio is 2.5, and the contraction angle is 60°. In addition, in order to maximize the efficiency of borehole hydraulic mining for Huadian oil shale, the non-submerged jet should be placed parallel to the oil shale bedding. These results can provide scientific and valuable references for borehole hydraulic mining of oil shale. Full article

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

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Open AccessArticle

Identification of Power Transformer Winding Mechanical Fault Types Based on Online IFRA by Support Vector Machine

by Zhongyong Zhao, Chao Tang, Qu Zhou, Lingna Xu, Yingang Gui and Chenguo Yao

Energies 2017, 10(12), 2022; https://doi.org/10.3390/en10122022 - 1 Dec 2017

Cited by 26 | Viewed by 5024

Abstract

A transformer is the most valuable and expensive property for power utility, thus ensuring its reliable operation is a major task for both operators and researchers. Online impulse frequency response analysis has proven to be a promising technique for detecting transformer internal winding [...] Read more.

A transformer is the most valuable and expensive property for power utility, thus ensuring its reliable operation is a major task for both operators and researchers. Online impulse frequency response analysis has proven to be a promising technique for detecting transformer internal winding mechanical deformation faults when a power transformer is in service. However, as so far, there is still no reliable standard code for frequency response signature interpretation and quantification. This paper tries to utilize a machine learning method, namely the support vector machine, to identify and classify the winding mechanical fault types, based on online impulse frequency response analysis. Actual transformer fault data from a specially manufactured model transformer are collected and analyzed. Two feature vectors are proposed and the diagnostic results are predicted. The diagnostic results indicate the satisfied classifying accuracy by the proposed method. Full article

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Open AccessArticle

Hybrid Electromagnetic and Triboelectric Nanogenerators with Multi-Impact for Wideband Frequency Energy Harvesting

by Jianxiong Zhu, Aochen Wang, Haibing Hu and Hua Zhu

Energies 2017, 10(12), 2024; https://doi.org/10.3390/en10122024 - 1 Dec 2017

Cited by 32 | Viewed by 6367

Abstract

We present a hybrid electromagnetic generator (EMG) and triboelectric nanogenerator (TENG) using a multi-impact approach for broad-bandwidth-frequency (10–45 Hz) energy harvesting. The TENG and the EMG were located at the middle and the free end of the cantilever beam, respectively. When the system [...] Read more.

We present a hybrid electromagnetic generator (EMG) and triboelectric nanogenerator (TENG) using a multi-impact approach for broad-bandwidth-frequency (10–45 Hz) energy harvesting. The TENG and the EMG were located at the middle and the free end of the cantilever beam, respectively. When the system was subjected to an external vibration, the cantilever beam would be in a nonlinear response with multiple impacts from a low frequency oscillator. The mathematical model included a TENG oscillator which can have multiple impacts on the cantilever, and the nonlinear Lorenz force which comes from the motion of the coil in the electromagnetic field. Due to the strong nonlinearity of the impacts from the TENG oscillator and the limited space for the free tip of the cantilever, the dynamic response of the cantilever presented a much broader bandwidth, with a frequency range from 10–45 Hz. We also found that the average generated power from TENG and EMG can reach up to 30 μW/m² and 53 μW, respectively. Moreover, the dynamic responses of the hybrid EMG and TENG were carefully analyzed, and we found that the measured experimental results and the numerical simulations results were in good agreement. Full article

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

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Open AccessArticle

The Tripartite Game Model for Electricity Pricing in Consideration of the Power Quality

by Tianlei Zang, Yueping Xiang and Jianwei Yang

Energies 2017, 10(12), 2025; https://doi.org/10.3390/en10122025 - 1 Dec 2017

Cited by 9 | Viewed by 3755

Abstract

Under the Energy Internet concept the distribution and management of resources in the electricity market have been gradually transiting from a centralized pattern to a decentralized pattern. Correspondingly, the methodological model for the analysis of economic behaviors needs to be upgraded too. Based [...] Read more.

Under the Energy Internet concept the distribution and management of resources in the electricity market have been gradually transiting from a centralized pattern to a decentralized pattern. Correspondingly, the methodological model for the analysis of economic behaviors needs to be upgraded too. Based on the idea of non-cooperative game theory, this paper puts forward a tripartite game model for electricity pricing in consideration of the power quality, which is applicable to the electricity market under the Energy Internet with distributed generation, including the State Grid Corporation of China (SGCC), generating companies (GENCOs) and the marketers which correspond to the regional power-retailing companies. Then, the sequential quadratic programming based on the quasi-Newton method is given to solve the game model. Finally, four sets of tests with different game factors are carried out to verify the validity and feasibility of the proposed model and algorithm. The SGCC price, the cost and the number of GENCOs and the cross-regional environment are considered in each test, respectively. The results show that this model can adapt well to the various conditions. Full article

(This article belongs to the Special Issue Energy Market Transitions)

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Open AccessArticle

Research on CO₂ Emission Reduction Mechanism of China’s Iron and Steel Industry under Various Emission Reduction Policies

by Ye Duan, Nan Li, Hailin Mu and Shusen Gui

Energies 2017, 10(12), 2026; https://doi.org/10.3390/en10122026 - 1 Dec 2017

Cited by 15 | Viewed by 5007

Abstract

In this paper, a two-stage dynamic game model of China’s iron and steel industry is constructed. Carbon tax levy, product subsidy, carbon capture and sequestration (CCS) and other factors are included in the emission reduction mechanism. The effects of emissions reduction and the [...] Read more.

In this paper, a two-stage dynamic game model of China’s iron and steel industry is constructed. Carbon tax levy, product subsidy, carbon capture and sequestration (CCS) and other factors are included in the emission reduction mechanism. The effects of emissions reduction and the economic impact of China’s overall steel industry (and that of its six main regions) are investigated for the first time under different scenarios. As new findings, we report the following: (1) Not all factors declined. The overall social welfare, consumer surplus, output and emissions decrease with a gradual increase in the reduction target, whereas the carbon tax value, unit value of product subsidies and total subsidies show a rising trend; (2) A combination of multiple emissions reduction policies is more effective than a single policy. With the implementation of a combined policy, regional output polarization has eased; (3) Steel output does not exceed 950 million tons, far below the current peak. These results will help the industry to formulate reasonable emissions reduction and output targets. In short, in effort to eliminate industry poverty and to alleviate overcapacity, the industry should not only adopt the various coordinated reduction policies, but also fully consider regional differences and reduction needs. 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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Open AccessArticle

Simulation Models to Size and Retrofit District Heating Systems

by Kevin Sartor

Energies 2017, 10(12), 2027; https://doi.org/10.3390/en10122027 - 1 Dec 2017

Cited by 7 | Viewed by 3921

Abstract

District heating networks are considered as convenient systems to supply heat to consumers while reducing CO

_{2}

emissions and increasing renewable energies use. However, to make them as profitable as possible, they have to be developed, operated and sized carefully. In order to [...] Read more.

District heating networks are considered as convenient systems to supply heat to consumers while reducing CO

_{2}

emissions and increasing renewable energies use. However, to make them as profitable as possible, they have to be developed, operated and sized carefully. In order to cope with these objectives, simulation tools are required to analyze several configuration schemes and control methods. Indeed, the most common problems are heat losses, the electric pump consumption and the peak heat demand while ensuring the comfort of the users. In this contribution, a dynamic simulation model of all the components of the network is described. It is dedicated to assess some energetic, environmental and economic indicators. Finally, the methodology is used on an existing application test case namely the district heating network of the University of Liège to study the pump control and minimize the district heating network heat losses. Full article

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

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Open AccessArticle

Determining the Flexible Ramping Capacity of Electric Vehicles to Enhance Locational Flexibility

by Dam Kim, Hungyu Kwon, Mun-Kyeom Kim, Jong-Keun Park and Hyeongon Park

Energies 2017, 10(12), 2028; https://doi.org/10.3390/en10122028 - 1 Dec 2017

Cited by 10 | Viewed by 3171

Abstract

A high penetration level of renewable energy in a power system increases variability and uncertainty, which can lead to ramping capability shortage. This makes the stable operation of a power system difficult. However, appropriate management of electric vehicles (EVs) can overcome such difficulties. [...] Read more.

A high penetration level of renewable energy in a power system increases variability and uncertainty, which can lead to ramping capability shortage. This makes the stable operation of a power system difficult. However, appropriate management of electric vehicles (EVs) can overcome such difficulties. In this study, EVs were applied as a flexible ramping product (FRP), and a method was developed to increase the system ramping capability. When increasing the FRP to the amount required for the system, the effect on transmission lines cannot be neglected. Thus, the required FRP considering transmission constraints is calculated separately for each zone to secure deliverability. To make adjustment possible, the zonal available capacity is calculated by considering the probabilities of the location and the plugged and charged states of EVs. The applicability of EVs as an FRP resource is examined, and the results showed that they can be used at a more significant level considering the transmission constraints. Full article

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

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Open AccessArticle

A Metaheuristic Approach to the Multi-Objective Unit Commitment Problem Combining Economic and Environmental Criteria

by Luís A. C. Roque, Dalila B. M. M. Fontes and Fernando A. C. C. Fontes

Energies 2017, 10(12), 2029; https://doi.org/10.3390/en10122029 - 1 Dec 2017

Cited by 11 | Viewed by 4182

Abstract

We consider a Unit Commitment Problem (UCP) addressing not only the economic objective of minimizing the total production costs—as is done in the standard UCP—but also addressing environmental concerns. Our approach utilizes a multi-objective formulation and includes in the objective function a criterion [...] Read more.

We consider a Unit Commitment Problem (UCP) addressing not only the economic objective of minimizing the total production costs—as is done in the standard UCP—but also addressing environmental concerns. Our approach utilizes a multi-objective formulation and includes in the objective function a criterion to minimize the emission of pollutants. Environmental concerns are having a significant impact on the operation of power systems related to the emissions from fossil-fuelled power plants. However, the standard UCP, which minimizes just the total production costs, is inadequate to address environmental concerns. We propose to address the UCP with environmental concerns as a multi-objective problem and use a metaheuristic approach combined with a non-dominated sorting procedure to solve it. The metaheuristic developed is a variant of an evolutionary algorithm, known as Biased Random Key Genetic Algorithm. Computational experiments have been carried out on benchmark problems with up to 100 generation units for a 24 h scheduling horizon. The performance of the method, as well as the quality, diversity and the distribution characteristics of the solutions obtained are analysed. It is shown that the method proposed compares favourably against alternative approaches in most cases analysed. 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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Open AccessArticle

System Efficiency Improvement for Electric Vehicles Adopting a Permanent Magnet Synchronous Motor Direct Drive System

by Chengming Zhang, Qingbo Guo, Liyi Li, Mingyi Wang and Tiecheng Wang

Energies 2017, 10(12), 2030; https://doi.org/10.3390/en10122030 - 1 Dec 2017

Cited by 19 | Viewed by 7001

Abstract

To improve the endurance mileage of electric vehicles (EVs), it is important to decrease the energy consumption of the Permanent Magnet Synchronous Motor (PMSM) drive system. This paper proposes a novel loss optimization control strategy named system efficiency improvement control which can optimize [...] Read more.

To improve the endurance mileage of electric vehicles (EVs), it is important to decrease the energy consumption of the Permanent Magnet Synchronous Motor (PMSM) drive system. This paper proposes a novel loss optimization control strategy named system efficiency improvement control which can optimize both inverter and motor losses. A nonlinear power converter loss model is built to fit the nonlinear characteristics of power devices. This paper uses double Fourier integral analysis to analytically calculate the fundamental and harmonic components of motor current by which the fundamental motor loss and harmonic motor loss can be accurately analyzed. From these loss models, a whole-frequency-domain system loss model is derived and presented. Based on the system loss model, the system efficiency improvement control method applies the genetic algorithm to adjust the motor current and PWM frequency together to optimize the inverter and motor losses by which the system efficiency can be significantly improved without seriously influence on the system stability over the whole operation range of EVs. The optimal effects of system efficiency is verified by the experimental results in both Si-IGBT-based PMSM system and SiC-MOSFET-based system. Full article

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

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Open AccessArticle

South Korean Household’s Willingness to Pay for Replacing Coal with Natural Gas? A View from CO₂ Emissions Reduction

by Seul-Ye Lim, Hyo-Jin Kim and Seung-Hoon Yoo

Energies 2017, 10(12), 2031; https://doi.org/10.3390/en10122031 - 2 Dec 2017

Cited by 20 | Viewed by 3193

Abstract

Coal is currently a major electric power generation source in South Korea when considering that forty-three percent of electricity that was generated during the first quarter of 2017 came from coal. The amount of CO₂ emissions from coal-fired power plant is two [...] Read more.

Coal is currently a major electric power generation source in South Korea when considering that forty-three percent of electricity that was generated during the first quarter of 2017 came from coal. The amount of CO₂ emissions from coal-fired power plant is two times larger than that from natural gas (NG)-fired power plant in the country. In this regard, the Korean government is trying to replace some amount of coal that is used for generation with NG to reduce CO₂ emissions. However, the cost of NG-fired generation is about 1.25 times higher than that of coal-fired generation. Thus, the policy-makers demand information about the household willingness to pay (WTP) for the replacement to mitigate CO₂ emissions. This paper applies the contingent valuation (CV) approach, and assesses the household’s WTP for replacing one kWh of coal-fired power with that of NG-fired power. For this purpose, a total of 1000 South Korean households were involved in the CV survey employing a dichotomous choice question. In addition to the current electricity price, KRW 121.52 (USD 0.11) per kWh, the respondents were willing to pay KRW 25.35 (USD 0.02) per kWh. The costs of NG-fired and coal-fired generation are KRW 100.13 and 78.05, respectively, per kWh. The difference between the two is KRW 22.08 per kWh, which is smaller than the mean additional WTP (KRW 25.35 per kWh). The household’s additional WTP is bigger than the actual additional cost. It is concluded that the switch of power generation source from coal to NG to reduce CO₂ emissions can be supported by South Korean households. Full article

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Open AccessArticle

Coupled Model of Heat and Mass Balance for Droplet Growth in Wet Steam Non-Equilibrium Homogeneous Condensation Flow

by Xu Han, Zhonghe Han, Wei Zeng, Jiangbo Qian and Zhi Wang

Energies 2017, 10(12), 2033; https://doi.org/10.3390/en10122033 - 2 Dec 2017

Cited by 15 | Viewed by 4538

Abstract

Because of the complexity of wet steam two-phase condensation flow, many problems remain to be solved. The important part of condensation theory—the calculation of the water droplet growth model in the transition zone—is not ideal; thus, it is necessary to develop a water [...] Read more.

Because of the complexity of wet steam two-phase condensation flow, many problems remain to be solved. The important part of condensation theory—the calculation of the water droplet growth model in the transition zone—is not ideal; thus, it is necessary to develop a water droplet growth model with full-scale range. On the basis of the heat and mass transfer equilibrium in droplet growth, a coupled model of heat and mass balance for droplet growth is proposed. To verify the accuracy of this model, the differences and applicable ranges of various models were analysed using the experimental data of Peters and Meyer and two widely used models. In the free molecular flow region, the heat and mass balance model coincides with the Young low-pressure correction model. In the transition region, the heat and mass balance model agrees well with the experimental values of Peters and Meyer. In the continuous flow region, the heat and mass balance model coincides with the Gyarmathy model. Therefore, the heat and mass balance model can be used to accurately describe the growth process of water droplets in the arbitrary range of Knudsen numbers. Full article

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Open AccessArticle

Phase Equilibria of the CH₄-CO₂ Binary and the CH₄-CO₂-H₂O Ternary Mixtures in the Presence of a CO₂-Rich Liquid Phase

by Ludovic Nicolas Legoix, Livio Ruffine, Jean-Pierre Donval and Matthias Haeckel

Energies 2017, 10(12), 2034; https://doi.org/10.3390/en10122034 - 2 Dec 2017

Cited by 19 | Viewed by 6947

Abstract

The knowledge of the phase behavior of carbon dioxide (CO₂)-rich mixtures is a key factor to understand the chemistry and migration of natural volcanic CO₂ seeps in the marine environment, as well as to develop engineering processes for CO₂ [...] Read more.

The knowledge of the phase behavior of carbon dioxide (CO₂)-rich mixtures is a key factor to understand the chemistry and migration of natural volcanic CO₂ seeps in the marine environment, as well as to develop engineering processes for CO₂ sequestration coupled to methane (CH₄) production from gas hydrate deposits. In both cases, it is important to gain insights into the interactions of the CO₂-rich phase—liquid or gas—with the aqueous medium (H₂O) in the pore space below the seafloor or in the ocean. Thus, the CH₄-CO₂ binary and CH₄-CO₂-H₂O ternary mixtures were investigated at relevant pressure and temperature conditions. The solubility of CH₄ in liquid CO₂ (vapor-liquid equilibrium) was determined in laboratory experiments and then modelled with the Soave–Redlich–Kwong equation of state (EoS) consisting of an optimized binary interaction parameter k_ij_{(CH₄-CO₂)} = 1.32 × 10⁻³ × T − 0.251 describing the non-ideality of the mixture. The hydrate-liquid-liquid equilibrium (HLLE) was measured in addition to the composition of the CO₂-rich fluid phase in the presence of H₂O. In contrast to the behavior in the presence of vapor, gas hydrates become more stable when increasing the CH₄ content, and the relative proportion of CH₄ to CO₂ decreases in the CO₂-rich phase after gas hydrate formation. Full article

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

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Open AccessArticle

Hybrid Hydrogen and Mechanical Distributed Energy Storage

by Stefano Ubertini, Andrea Luigi Facci and Luca Andreassi

Energies 2017, 10(12), 2035; https://doi.org/10.3390/en10122035 - 2 Dec 2017

Cited by 21 | Viewed by 4499

Abstract

Effective energy storage technologies represent one of the key elements to solving the growing challenges of electrical energy supply of the 21st century. Several energy storage systems are available, from ones that are technologically mature to others still at a research stage. Each [...] Read more.

Effective energy storage technologies represent one of the key elements to solving the growing challenges of electrical energy supply of the 21st century. Several energy storage systems are available, from ones that are technologically mature to others still at a research stage. Each technology has its inherent limitations that make its use economically or practically feasible only for specific applications. The present paper aims at integrating hydrogen generation into compressed air energy storage systems to avoid natural gas combustion or thermal energy storage. A proper design of such a hybrid storage system could provide high roundtrip efficiencies together with enhanced flexibility thanks to the possibility of providing additional energy outputs (heat, cooling, and hydrogen as a fuel), in a distributed energy storage framework. Such a system could be directly connected to the power grid at the distribution level to reduce power and energy intermittence problems related to renewable energy generation. Similarly, it could be located close to the user (e.g., office buildings, commercial centers, industrial plants, hospitals, etc.). Finally, it could be integrated in decentralized energy generation systems to reduce the peak electricity demand charges and energy costs, to increase power generation efficiency, to enhance the security of electrical energy supply, and to facilitate the market penetration of small renewable energy systems. Different configurations have been investigated (simple hybrid storage system, regenerate system, multistage system) demonstrating the compressed air and hydrogen storage systems effectiveness in improving energy source flexibility and efficiency, and possibly in reducing the costs of energy supply. Round-trip efficiency up to 65% can be easily reached. The analysis is conducted through a mixed theoretical-numerical approach, which allows the definition of the most relevant physical parameters affecting the system performance. Full article

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

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Open AccessArticle

Fuzzy Logic Based MPPT Controller for a PV System

by Carlos Robles Algarín, John Taborda Giraldo and Omar Rodríguez Álvarez

Energies 2017, 10(12), 2036; https://doi.org/10.3390/en10122036 - 2 Dec 2017

Cited by 144 | Viewed by 13933

Abstract

The output power of a photovoltaic (PV) module depends on the solar irradiance and the operating temperature; therefore, it is necessary to implement maximum power point tracking controllers (MPPT) to obtain the maximum power of a PV system regardless of variations in climatic [...] Read more.

The output power of a photovoltaic (PV) module depends on the solar irradiance and the operating temperature; therefore, it is necessary to implement maximum power point tracking controllers (MPPT) to obtain the maximum power of a PV system regardless of variations in climatic conditions. The traditional solution for MPPT controllers is the perturbation and observation (P&O) algorithm, which presents oscillation problems around the operating point; the reason why improving the results obtained with this algorithm has become an important goal to reach for researchers. This paper presents the design and modeling of a fuzzy controller for tracking the maximum power point of a PV System. Matlab/Simulink (MathWorks, Natick, MA, USA) was used for the modeling of the components of a 65 W PV system: PV module, buck converter and fuzzy controller; highlighting as main novelty the use of a mathematical model for the PV module, which, unlike diode based models, only needs to calculate the curve fitting parameter. A P&O controller to compare the results obtained with the fuzzy control was designed. The simulation results demonstrated the superiority of the fuzzy controller in terms of settling time, power loss and oscillations at the operating point. Full article

(This article belongs to the Special Issue PV System Design and Performance)

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Open AccessArticle

A Single-Phase Multilevel PV Generation System with an Improved Ripple Correlation Control MPPT Algorithm

by Manel Hammami and Gabriele Grandi

Energies 2017, 10(12), 2037; https://doi.org/10.3390/en10122037 - 3 Dec 2017

Cited by 19 | Viewed by 4195

Abstract

The implementation of maximum power point tracking (MPPT) schemes by the ripple correlation control (RCC) algorithm is presented in this paper. A reference is made to single-phase single-stage multilevel photovoltaic (PV) generation systems, when the inverter input variables (PV voltage and PV current) [...] Read more.

The implementation of maximum power point tracking (MPPT) schemes by the ripple correlation control (RCC) algorithm is presented in this paper. A reference is made to single-phase single-stage multilevel photovoltaic (PV) generation systems, when the inverter input variables (PV voltage and PV current) have multiple low-frequency (ripple) harmonics. The harmonic analysis is carried out with reference to a multilevel configuration consisting of an H-bridge inverter and level doubling network (LDN) cell, leading to the multilevel inverter having double the output voltage levels as compared to the basic H-bridge inverter topology (i.e., five levels vs. three levels). The LDN cell is basically a half-bridge fed by a floating capacitor, with self-balancing voltage capability. The multilevel configuration introduces additional PV voltage and current low-frequency harmonics, perturbing the basic implementation of the RCC scheme (based on the second harmonic component), leading to malfunctioning. The proposed RCC algorithm employs the PV current and voltage harmonics at a specific frequency for the estimation of the voltage derivative of power dP/dV (or dI/dV), driving the PV operating point toward the maximum power point (MPP) in a faster and more precise manner. The steady-state and transient performances of the proposed RCC-MPPT schemes have been preliminarily tested and compared using MATLAB/Simulink. Results have been verified by experimental tests considering the whole multilevel PV generation system, including real PV modules, multilevel insulated-gate bipolar transistor (IGBT) inverters, and utility grids. Full article

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Open AccessArticle

Improving an Integer Linear Programming Model of an Ecovat Buffer by Adding Long-Term Planning

by Gijs J. H. de Goeijen, Gerard J. M. Smit and Johann L. Hurink

Energies 2017, 10(12), 2039; https://doi.org/10.3390/en10122039 - 3 Dec 2017

Cited by 7 | Viewed by 10645

Abstract

The Ecovat is a seasonal thermal storage solution consisting of a large underground water tank divided into a number of virtual segments that can be individually charged and discharged. The goal of the Ecovat is to supply heat demand to a neighborhood throughout [...] Read more.

The Ecovat is a seasonal thermal storage solution consisting of a large underground water tank divided into a number of virtual segments that can be individually charged and discharged. The goal of the Ecovat is to supply heat demand to a neighborhood throughout the entire year. In this work, we extend an integer linear programming model to describe the charging and discharging of such an Ecovat buffer by adding a long-term (yearly) planning step to the model. We compare the results from the model using this extension to previously obtained results and show significant improvements when looking at the combination of costs and the energy content of the buffer at the end of the optimization. Furthermore, we show that the model is very robust against prediction errors. For this, we compare two different cases: one case in which we assume perfect predictions are available and one case in which we assume no predictions are available. The largest observed difference in costs between these two cases is less than 2%. Full article

(This article belongs to the Special Issue Selected Papers from International Workshop of Energy-Open)

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Open AccessArticle

Energy Production Analysis and Optimization of Mini-Grid in Remote Areas: The Case Study of Habaswein, Kenya

by Andrea Micangeli, Riccardo Del Citto, Isaac Nzue Kiva, Simone Giovanni Santori, Valeria Gambino, Jeremiah Kiplagat, Daniele Viganò, Davide Fioriti and Davide Poli

Energies 2017, 10(12), 2041; https://doi.org/10.3390/en10122041 - 3 Dec 2017

Cited by 50 | Viewed by 7991

Abstract

Rural electrification in remote areas of developing countries has several challenges which hinder energy access to the population. For instance, the extension of the national grid to provide electricity in these areas is largely not viable. The Kenyan Government has put a target [...] Read more.

Rural electrification in remote areas of developing countries has several challenges which hinder energy access to the population. For instance, the extension of the national grid to provide electricity in these areas is largely not viable. The Kenyan Government has put a target to achieve universal energy access by the year 2020. To realize this objective, the focus of the program is being shifted to establishing off-grid power stations in rural areas. Among rural areas to be electrified is Habaswein, which is a settlement in Kenya’s northeastern region without connection to the national power grid, and where Kenya Power installed a stand-alone hybrid mini-grid. Based on field observations, power generation data analysis, evaluation of the potential energy resources and simulations, this research intends to evaluate the performance of the Habaswein mini-grid and optimize the existing hybrid generation system to enhance its reliability and reduce the operation costs. The result will be a suggestion of how Kenyan rural areas could be sustainably electrified by using renewable energy based off-grid power stations. It will contribute to bridge the current research gap in this area, and it will be a vital tool to researchers, implementers and the policy makers in energy sector. Full article

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

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Open AccessArticle

New Performance Indices for Voltage Stability Analysis in a Power System

by Isaiah Adebayo and Yanxia Sun

Energies 2017, 10(12), 2042; https://doi.org/10.3390/en10122042 - 3 Dec 2017

Cited by 30 | Viewed by 3906

Abstract

The frequent occurrence of voltage instability in a modern power system is alarming and thus, has been of great concern to power system utilities. In this paper, a new performance index based on the power flow solutions for voltage stability assessment of a [...] Read more.

The frequent occurrence of voltage instability in a modern power system is alarming and thus, has been of great concern to power system utilities. In this paper, a new performance index based on the power flow solutions for voltage stability assessment of a power system is presented. First, the voltage deviation with respect to reactive power load variation at each load bus is found. Thereafter, the performance voltage bus index for each load bus is computed. An improved modal analysis technique (IMAT) is used to identify weak nodes that are liable to voltage instability in a power system. This technique uses a submatrix of the full Jacobian matrix for voltage stability analysis. Comparison of the proposed method is done with existing voltage stability indices and the conventional modal analysis technique (CMAT). The effectiveness of all the approaches presented are tested on both Western system coordinating Council (WSCC) 9-bus, IEEE 30 bus and IEEE 57 bus test systems. Results obtained show that the proposed techniques can serve as an alternative tool to other conventional techniques for voltage stability assessment in a power system and can be of tremendous benefits in the planning and operation of a power system by system operators. Full article

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

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Open AccessArticle

Performance Prediction of Centrifugal Compressor for Drop-In Testing Using Low Global Warming Potential Alternative Refrigerants and Performance Test Codes

by Joo Hoon Park, Youhwan Shin and Jin Taek Chung

Energies 2017, 10(12), 2043; https://doi.org/10.3390/en10122043 - 3 Dec 2017

Cited by 5 | Viewed by 4786

Abstract

As environmental regulations to stall global warming are strengthened around the world, studies using newly developed low global warming potential (GWP) alternative refrigerants are increasing. In this study, substitute refrigerants, R-1234ze (E) and R-1233zd (E), were used in the centrifugal compressor of an [...] Read more.

As environmental regulations to stall global warming are strengthened around the world, studies using newly developed low global warming potential (GWP) alternative refrigerants are increasing. In this study, substitute refrigerants, R-1234ze (E) and R-1233zd (E), were used in the centrifugal compressor of an R-134a 2-stage centrifugal chiller with a fixed rotational speed. Performance predictions and thermodynamic analyses of the centrifugal compressor for drop-in testing were performed. A performance prediction method based on the existing ASME PTC-10 performance test code was proposed. The proposed method yielded the expected operating area and operating point of the centrifugal compressor with alternative refrigerants. The thermodynamic performance of the first and second stages of the centrifugal compressor was calculated as the polytropic state. To verify the suitability of the proposed method, the drop-in test results of the two alternative refrigerants were compared. The predicted operating range based on the permissible deviation of ASME PTC-10 confirmed that the temperature difference was very small at the same efficiency. Because the drop-in test of R-1234ze (E) was performed within the expected operating range, the centrifugal compressor using R-1234ze (E) is considered well predicted. However, the predictions of the operating point and operating range of R-1233zd (E) were lower than those of the drop-in test. The proposed performance prediction method will assist in understanding thermodynamic performance at the expected operating point and operating area of a centrifugal compressor using alternative gases based on limited design and structure information. Full article

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Open AccessArticle

Two-Sided Tacit Collusion: Another Step towards the Role of Demand-Side

by Mehdi Jabbari Zideh and Seyed Saeid Mohtavipour

Energies 2017, 10(12), 2045; https://doi.org/10.3390/en10122045 - 3 Dec 2017

Cited by 11 | Viewed by 4257

Abstract

In the context of agent-based simulation framework of collusion, this paper seeks for two-sided tacit collusion among supply-side and demand-side participants in a constrained network and impacts of this collusion on the market outcomes. Tacit collusion frequently occurs in electricity markets due to [...] Read more.

In the context of agent-based simulation framework of collusion, this paper seeks for two-sided tacit collusion among supply-side and demand-side participants in a constrained network and impacts of this collusion on the market outcomes. Tacit collusion frequently occurs in electricity markets due to strategic behavior of market participants arose from daily repetition of energy auctions. To attain detailed analysis of tacit collusion, state-action-reward-state-action (SARSA) learning algorithm and the standard Boltzmann exploration strategy based on the Q-value are used to model market participants’ behavior. A model is presented that integrates exploration and exploitation into a single framework, with the purpose of tuning exploration in the algorithm. In order to appraise the feasibility of collusion, a theoretical study on a three-node power system with three scenarios is depicted considering three Gencos and two Discos which proves the formation of two-sided tacit collusion between Genco and Disco. Simulation results show different collusive strategies of participants and how parameters of the algorithm impact on simulation outcomes. It is also shown that congestion on transmission line has a significant influence on behavior of market participants. Full article

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

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Open AccessArticle

Design and Experiment of Nonlinear Observer with Adaptive Gains for Battery State of Charge Estimation

by Linhui Zhao, Guohuang Ji and Zhiyuan Liu

Energies 2017, 10(12), 2046; https://doi.org/10.3390/en10122046 - 3 Dec 2017

Cited by 7 | Viewed by 3589

Abstract

State of charge (SOC) is an important evaluation index for lithium-ion batteries (LIBs) in electric vehicles (EVs). This paper proposes a nonlinear observer with a new adaptive gain structure for SOC estimation based on a second-order RC model. It is able to dynamically [...] Read more.

State of charge (SOC) is an important evaluation index for lithium-ion batteries (LIBs) in electric vehicles (EVs). This paper proposes a nonlinear observer with a new adaptive gain structure for SOC estimation based on a second-order RC model. It is able to dynamically adjust the gains and obtain a better balance between convergence speed and estimation accuracy with less computational time. A sufficient condition is derived to guarantee the uniform asymptotic stability of the observer, and its robustness with respect to disturbances and uncertainties is analyzed with the help of input-to-state stability (ISS) theory. A selection guide of the observer gains in practical application is presented. The estimation accuracy and convergence rate of the observer are evaluated and compared with those of extended Kalman filter (EKF) based on multi-temperature datasets from two different types of LIB cells. The robustness against different disturbances and uncertainties that may appear in a real vehicle is validated and discussed in detail. The experimental results show that the proposed observer is capable of achieving better performance with less computational time in comparison to EKF for different types of LIB cells under various working conditions. The observer is also capable of estimating SOC accurately for real life conditions according to the validation results of datasets from a battery management system (BMS) in an EV battery pack. Furthermore, the observer is simple enough, and is suitable for implementation on embedded hardware for LIB cells of EVs. Full article

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Open AccessArticle

Segmentation of Residential Gas Consumers Using Clustering Analysis

by Marta P. Fernandes, Joaquim L. Viegas, Susana M. Vieira and João M. C. Sousa

Energies 2017, 10(12), 2047; https://doi.org/10.3390/en10122047 - 4 Dec 2017

Cited by 11 | Viewed by 4155

Abstract

The growing environmental concerns and liberalization of energy markets have resulted in an increased competition between utilities and a strong focus on efficiency. To develop new energy efficiency measures and optimize operations, utilities seek new market-related insights and customer engagement strategies. This paper [...] Read more.

The growing environmental concerns and liberalization of energy markets have resulted in an increased competition between utilities and a strong focus on efficiency. To develop new energy efficiency measures and optimize operations, utilities seek new market-related insights and customer engagement strategies. This paper proposes a clustering-based methodology to define the segmentation of residential gas consumers. The segments of gas consumers are obtained through a detailed clustering analysis using smart metering data. Insights are derived from the segmentation, where the segments result from the clustering process and are characterized based on the consumption profiles, as well as according to information regarding consumers’ socio-economic and household key features. The study is based on a sample of approximately one thousand households over one year. The representative load profiles of consumers are essentially characterized by two evident consumption peaks, one in the morning and the other in the evening, and an off-peak consumption. Significant insights can be derived from this methodology regarding typical consumption curves of the different segments of consumers in the population. This knowledge can assist energy utilities and policy makers in the development of consumer engagement strategies, demand forecasting tools and in the design of more sophisticated tariff systems. Full article

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7480 KiB

Open AccessArticle

Power Characteristics Analysis of a Novel Double-Stator Magnetic Geared Permanent Magnet Generator

by Shehu Salihu Mustafa, Norhisam Misron, Mohammad Lutfi Othman and Hanamoto Tsuyoshi

Energies 2017, 10(12), 2048; https://doi.org/10.3390/en10122048 - 4 Dec 2017

Cited by 5 | Viewed by 6501

Abstract

This paper presents the design, fabrication and experimental power analysis of a novel double-stator magnetic geared permanent magnet (DSMGPM) machine which comprises of a double-stator permanent-magnet (PM) machine integrated a with triple rotor magnetic gear. The proposed machine can upscale the low-speed rotating [...] Read more.

This paper presents the design, fabrication and experimental power analysis of a novel double-stator magnetic geared permanent magnet (DSMGPM) machine which comprises of a double-stator permanent-magnet (PM) machine integrated a with triple rotor magnetic gear. The proposed machine can upscale the low-speed rotating magnetic field of the prime PMs on the prime rotor by using the modulation effect produced from the pole-pieces to high-speed rotating magnetic field from the field PMs. The low-speed prime rotor can also increase the speed of the field PM rotor and excite the coil windings to induce an electromotive force (EMF) resulting in electrical power. Thus, the machine is proposed for power generation in low-speed renewable energy applications such as wind turbines and tidal power generators. The proposed machine topology is presented and discussed while the performance power characteristics are evaluated experimentally. A prototype is fabricated and the measured results are in good agreement with the calculated results, therefore validating the proposed magnetic geared machine design. Full article

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Open AccessArticle

A Virtual Synchronous Generator Based Hierarchical Control Scheme of Distributed Generation Systems

by Gang Yao, Zhichong Lu, Yide Wang, Mohamed Benbouzid and Luc Moreau

Energies 2017, 10(12), 2049; https://doi.org/10.3390/en10122049 - 4 Dec 2017

Cited by 24 | Viewed by 6698

Abstract

Sustainable energy-based generation systems, such as photovoltaic and wind turbine generation systems, normally adopt inverters to connect to the grid. These power electronic interfaces possess the characteristics of small inertia and small output impedance, which create difficulties to stabilize the voltage and frequency [...] Read more.

Sustainable energy-based generation systems, such as photovoltaic and wind turbine generation systems, normally adopt inverters to connect to the grid. These power electronic interfaces possess the characteristics of small inertia and small output impedance, which create difficulties to stabilize the voltage and frequency of a distributed power source. To deal with this problem, a Virtual Synchronous Generator (VSG)-based inverter control method is presented in this paper by introducing virtual inertia and damping coefficient into the control loop to emulate the dynamic behavior of a traditional synchronous generator. Based on this VSG control method, a three-layer hierarchical control scheme is further proposed to increase the control accuracy of the voltage and frequency in a VSG-based distributed generation system with parallel inverters. The principle of the VSG control method, the system stability analysis, the design process of the hierarchical control structure, and the frequency/voltage secondary regulation processes are all specified in this paper. Finally, some numerical simulations are carried out and the effectiveness of proposed control scheme is verified by the simulation results analysis. Full article

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

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Open AccessArticle

Investigation of the Ampacity of a Prefabricated Straight-Through Joint of High Voltage Cable

by Pengyu Wang, Gang Liu, Hui Ma, Yigang Liu and Tao Xu

Energies 2017, 10(12), 2050; https://doi.org/10.3390/en10122050 - 4 Dec 2017

Cited by 27 | Viewed by 5584

Abstract

This paper presents a theoretical and experimental study on the ampacity of the prefabricated straight-through joint of a 110 kV high voltage cable. Thermal modelling revealed that the critical spot limiting the ampacity of this type of cable joint is located on its [...] Read more.

This paper presents a theoretical and experimental study on the ampacity of the prefabricated straight-through joint of a 110 kV high voltage cable. Thermal modelling revealed that the critical spot limiting the ampacity of this type of cable joint is located on its crosslinked polyethylene (XLPE) insulation section. The axial distribution of the thermal field in this type of cable joint was also determined. An algorithm for assessing ampacity in this type of cable joint was developed. Experiments were conducted on a real cable system with a prefabricated straight-through joint under different loading conditions. The experiments show a good agreement with the thermal modelling results. Full article

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

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Open AccessArticle

An Improved Continuous-Time Model Predictive Control of Permanent Magnetic Synchronous Motors for a Wide-Speed Range

by Dandan Su, Chengning Zhang and Yugang Dong

Energies 2017, 10(12), 2051; https://doi.org/10.3390/en10122051 - 4 Dec 2017

Cited by 15 | Viewed by 4257

Abstract

This paper proposes an improved continuous-time model predictive control (CTMPC) of permanent magnetic synchronous motors (PMSMs) for a wide-speed range, including the constant torque region and the flux-weakening (FW) region. In the constant torque region, the mathematic models of PMSMs in dq-axes are [...] Read more.

This paper proposes an improved continuous-time model predictive control (CTMPC) of permanent magnetic synchronous motors (PMSMs) for a wide-speed range, including the constant torque region and the flux-weakening (FW) region. In the constant torque region, the mathematic models of PMSMs in dq-axes are decoupled without the limitation of DC-link voltage. However, in the FW region, the mathematic models of PMSMs in dq-axes are cross-coupled together with the limitation of DC-link voltage. A nonlinear PMSMs mathematic model in the FW region is presented based on the voltage angle. The solving of the nonlinear mathematic model of PMSMs in FW region will lead to heavy computation load for digital signal processing (DSP). To overcome such a problem, a linearization method of the voltage angle is also proposed to reduce the computation load. The selection of transiting points between the constant torque region and FW regions is researched to improve the performance of the driven system. Compared with the proportional integral (PI) controller, the proposed CTMPC has obvious advantages in dealing with systems’ nonlinear constraints and improving system performance by restraining overshoot current under step torque changing. Both simulation and experimental results confirm the effectiveness of the proposed method in achieving good steady-state performance and smooth switching between the constant torque and FW regions. Full article

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

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Open AccessArticle

Unified Brake Service by a Hierarchical Controller for Active Deceleration Control in an Electric and Automated Vehicle

by Yuliang Nie, Yahui Liu, Shuo Cheng, Mingming Mei and Lingyun Xiao

Energies 2017, 10(12), 2052; https://doi.org/10.3390/en10122052 - 4 Dec 2017

Cited by 8 | Viewed by 4446

Abstract

Unified brake service is a universal service for generating certain brake force to meet the demand deceleration and is essential for an automated driving system. However, it is rather difficult to control the pressure in the wheel cylinders to reach the target deceleration [...] Read more.

Unified brake service is a universal service for generating certain brake force to meet the demand deceleration and is essential for an automated driving system. However, it is rather difficult to control the pressure in the wheel cylinders to reach the target deceleration of the automated vehicle, which is the key issue of the active deceleration control system (ADC). This paper proposes a hierarchical control method to actively control vehicle deceleration with active-brake actuators. In the upper hierarchical, the target pressure of wheel cylinders is obtained by dynamic equations of a pure electric vehicle. In the lower hierarchical, the solenoid valve instructions and the pump speed of hydraulic control unit (HCU) are determined to satisfy the desired pressure with the feedback of measured wheel cylinder pressure by pressure sensors. Results of road experiments of a pure electric and automated vehicle indicate that the proposed method realizes the target deceleration accurately and efficiently. Full article

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

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Open AccessArticle

Coordinated Control of a Wind-Methanol-Fuel Cell System with Hydrogen Storage

by Tiejiang Yuan, Qingxi Duan, Xiangping Chen, Xufeng Yuan, Wenping Cao, Juan Hu and Quanmin Zhu

Energies 2017, 10(12), 2053; https://doi.org/10.3390/en10122053 - 4 Dec 2017

Cited by 7 | Viewed by 3596

Abstract

This paper presents a wind-methanol-fuel cell system with hydrogen storage. It can manage various energy flow to provide stable wind power supply, produce constant methanol, and reduce CO₂ emissions. Firstly, this study establishes the theoretical basis and formulation algorithms. And then, computational [...] Read more.

This paper presents a wind-methanol-fuel cell system with hydrogen storage. It can manage various energy flow to provide stable wind power supply, produce constant methanol, and reduce CO₂ emissions. Firstly, this study establishes the theoretical basis and formulation algorithms. And then, computational experiments are developed with MATLAB/Simulink (R2016a, MathWorks, Natick, MA, USA). Real data are used to fit the developed models in the study. From the test results, the developed system can generate maximum electricity whilst maintaining a stable production of methanol with the aid of a hybrid energy storage system (HESS). A sophisticated control scheme is also developed to coordinate these actions to achieve satisfactory system performance. Full article

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Open AccessArticle

Norway as a Battery for the Future European Power System—Impacts on the Hydropower System

by Ingeborg Graabak, Stefan Jaehnert, Magnus Korpås and Birger Mo

Energies 2017, 10(12), 2054; https://doi.org/10.3390/en10122054 - 4 Dec 2017

Cited by 36 | Viewed by 8403

Abstract

Future power production in Europe is expected to include large shares of variable wind and solar power production. Norway, with approximately half of the hydropower reservoir capacity in Europe, can contribute to balance the variability. The aim of this paper is to assess [...] Read more.

Future power production in Europe is expected to include large shares of variable wind and solar power production. Norway, with approximately half of the hydropower reservoir capacity in Europe, can contribute to balance the variability. The aim of this paper is to assess how such a role may impact the Norwegian hydropower system in terms of production pattern of the plants, changes in reservoir level and water values. The study uses a stochastic optimization and simulation model and analyses an eHighway2050 scenario combined with increases in the hydropower production capacities in Norway. The capacity increases from ca. 31 GW in the present system to 42 and 50 GW respectively. The study uses 75 years with stochastic wind, solar radiation, temperature and inflow data. The results show that the hydropower system is able to partly balance the variable production and significantly reduce the power prices for the analyzed case. The paper shows that some of the power plants utilize their increased capacity, while other plants do not due to hydrological constraints and model limitations. The paper discusses how the modelling can be further improved in order to quantify more of the potential impacts on the future power system. Full article

(This article belongs to the Special Issue Hydropower 2017)

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Open AccessArticle

A Security Level Classification Method for Power Systems under N-1 Contingency

by Zhigang Lu, Liangce He, Dan Zhang, Boxuan Zhao, Jiangfeng Zhang and Hao Zhao

Energies 2017, 10(12), 2055; https://doi.org/10.3390/en10122055 - 5 Dec 2017

Cited by 12 | Viewed by 6402

Abstract

Security assessment is crucial for the reliable and secure operation of power systems. This paper proposes a security level classification (SLC) method to analyze the security level of power systems both qualitatively and quantitatively. In this SLC method, security levels are graded according [...] Read more.

Security assessment is crucial for the reliable and secure operation of power systems. This paper proposes a security level classification (SLC) method to analyze the security level of power systems both qualitatively and quantitatively. In this SLC method, security levels are graded according to a comprehensive safety index (CSI), which is defined by integrating the system margin index (SMI) and load entropy. The SMI depends on the operating load and the total supply capacity (TSC) under N-1 contingency, and the load entropy reflects the heterogeneity of load distribution calculated from entropy theory. In order to calculate the TSC under N-1 contingency considering both of the computational accuracy and speed, the TSC is converted into an extended conic quadratic programming (ECQP) model. In addition, the load boundary vector (LBV) model is established to obtain the capacity limit of each load bus, and thus detect potential risks of power systems. Finally, two modified practical power systems and the IEEE 118-bus test system are studied to validate the feasibility of the proposed SLC method. Full article

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2011 KiB

Open AccessArticle

Multiscale Modeling of a Packed Bed Chemical Looping Reforming (PBCLR) Reactor

by Arpit Singhal, Schalk Cloete, Rosa Quinta-Ferreira and Shahriar Amini

Energies 2017, 10(12), 2056; https://doi.org/10.3390/en10122056 - 5 Dec 2017

Cited by 6 | Viewed by 3794

Abstract

Packed bed reactors are broadly used in industry and are under consideration for novel reactor concepts such as packed bed chemical looping reforming (PBCLR). Mass and heat transfer limitations in and around the particles in packed bed reactors strongly affect the behavior of [...] Read more.

Packed bed reactors are broadly used in industry and are under consideration for novel reactor concepts such as packed bed chemical looping reforming (PBCLR). Mass and heat transfer limitations in and around the particles in packed bed reactors strongly affect the behavior of these units. This study employs a multiscale modeling methodology to simulate a PBCLR reactor. Specifically, small-scale particle-resolved direct numerical simulation is utilized to improve large-scale mass transfer models for use in an industrial scale 1D model. Existing intra-particle mass transfer models perform well for simple first order reactions, but several model enhancements were required to model the more complex steam methane reforming reaction system. Three specific aspects required enhanced modeling: the generation of additional gas volume by the reforming reactions, the lack of clear reaction orders in the equilibrium reactions, and the diffusion of multiple reactant species into the particle. Large-scale simulations of the PBCLR reactor with the enhanced 1D model showed that the highly reactive Ni-based catalyst/oxygen carrier employed allows for the use of large particle sizes and high gas flowrates, offering potential for process intensification. 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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Open AccessArticle

Experimental Analysis and Evaluation of the Numerical Prediction of Wake Characteristics of Tidal Stream Turbine

by Yuquan Zhang, Jisheng Zhang, Yuan Zheng, Chunxia Yang, Wei Zang and E. Fernandez-Rodriguez

Energies 2017, 10(12), 2057; https://doi.org/10.3390/en10122057 - 5 Dec 2017

Cited by 25 | Viewed by 3032

Abstract

It is important to understand tidal stream turbine performance and flow field, if tidal energy is to advance. The operating condition of a tidal stream turbine with a supporting structure has a significant impact on its performance and wake recovery. The aim of [...] Read more.

It is important to understand tidal stream turbine performance and flow field, if tidal energy is to advance. The operating condition of a tidal stream turbine with a supporting structure has a significant impact on its performance and wake recovery. The aim of this work is to provide an understanding of turbine submerged depth that governs the downstream wake structure and its recovery to the free-stream velocity profile. An experimentally validated numerical model, based on a computational fluid dynamics (CFD) tool, was present to obtain longitudinal, transverse and vertical velocity profiles. Wake characteristics measurements have been carried out in an open channel at Hohai University. The results indicate that varying the turbine proximity to the water surface introduces differential mass flow rate around the rotor that could make the wake persist differently downstream. CFD shows the same predicted wake recovery tendency with the experiments, and an agreement from CFD and experiments is good in the far-wake region. The results presented demonstrate that CFD is a good tool to simulate the performance of tidal turbines particularly in the far-wake region and that the turbine proximity to the water surface has an effect on the wake recovery. Full article

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Open AccessArticle

Improving the Performance Attributes of Plug-in Hybrid Electric Vehicles in Hot Climates through Key-Off Battery Cooling

by Sina Shojaei, Andrew McGordon, Simon Robinson and James Marco

Energies 2017, 10(12), 2058; https://doi.org/10.3390/en10122058 - 5 Dec 2017

Cited by 9 | Viewed by 5457

Abstract

Ambient conditions can have a significant impact on the average and maximum temperature of the battery of electric and plug-in hybrid electric vehicles. Given the sensitivity of the ageing mechanisms of typical battery cells to temperature, a significant variability in battery lifetime has [...] Read more.

Ambient conditions can have a significant impact on the average and maximum temperature of the battery of electric and plug-in hybrid electric vehicles. Given the sensitivity of the ageing mechanisms of typical battery cells to temperature, a significant variability in battery lifetime has been reported with geographical location. In addition, high battery temperature and the associated cooling requirements can cause poor passenger thermal comfort, while extreme battery temperatures can negatively impact the power output of the battery, limiting the available electric traction torque. Avoiding such issues requires enabling battery cooling even when the vehicle is parked and not plugged in (key-off), but the associated extra energy requirements make applying key-off cooling a non-trivial decision. In this paper, a representative plug-in parallel hybrid electric vehicle model is used to simulate a typical 24-h duty cycle to quantify the impact of hot ambient conditions on three performance attributes of the vehicle: the battery lifetime, passenger thermal comfort and fuel economy. Key-off cooling is defined as an optimal control problem in view of the duty cycle of the vehicle. The problem is then solved using the dynamic programming method. Controlling key-off cooling through this method leads to significant improvements in the battery lifetime, while benefiting the fuel economy and thermal comfort attributes. To further improve the battery lifetime, partial charging of the battery is considered. An algorithm is developed that determines the optimum combination of key-off cooling and the level of battery charge. Simulation results confirm the benefits of the proposed method. Full article

(This article belongs to the Special Issue Thermal Energy Storage and Thermal Management (TESM2017))

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Open AccessArticle

Solid-Liquid Interfacial Effects on Residual Oil Distribution Utilizing Three-Dimensional Micro Network Models

by Weiyao Zhu, Bingbing Li, Yajing Liu, Hongqing Song and Xiaofeng Wang

Energies 2017, 10(12), 2059; https://doi.org/10.3390/en10122059 - 5 Dec 2017

Cited by 7 | Viewed by 3602

Abstract

A number of experiments on fluid flow at the micro/nano-scale have demonstrated that flow velocity obviously deviates from the classical Poiseuille’s law due to the micro forces between the wall and the fluid. Based on an oil–water two-phase network simulation model, a three-dimensional [...] Read more.

A number of experiments on fluid flow at the micro/nano-scale have demonstrated that flow velocity obviously deviates from the classical Poiseuille’s law due to the micro forces between the wall and the fluid. Based on an oil–water two-phase network simulation model, a three-dimensional pore-scale micro network model with solid–liquid interfacial effects was established. The influences of solid–liquid interface effects including van der Waals force and wettability on the residual oil distribution and relative permeability were investigated through microscopic simulation. The effects of pore radius, pore–throat size ratio, shaping factor, and coordination number on the residual oil distribution were analyzed at the same time. The results showed that the oil recovery would be overestimated by about 4% without van der Waals force in a water-wet reservoir. The impact of van der Waals force on water-wet reservoirs was significantly obvious in contrast with oil-wet reservoirs. In addition, the residual oil distribution was significantly influenced by pore radius in water-wet reservoir, comparatively influenced by pore–throat size ratio in oil-wet reservoir. The present study illustrates the successful application of three-dimensional micro network models considering solid–liquid interfacial effects, and provides new insights for oil recovery enhancement. Full article

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Open AccessArticle

Impact of Efficient Driving in Professional Bus Fleets

by Roberto Garcia, Gabriel Diaz, Xabiel G. Pañeda, Alejandro G. Tuero, Laura Pozueco, David Melendi, Jose A. Sanchez, Victor Corcoba and Alejandro G. Pañeda

Energies 2017, 10(12), 2060; https://doi.org/10.3390/en10122060 - 5 Dec 2017

Cited by 1 | Viewed by 3023

Abstract

Diesel engines of the vehicles in the transport sector are responsible for most of the CO₂ emissions into the environment. An alternative to reduce fuel consumption is to promote efficient driving techniques. The aim of this paper is to assess the impact [...] Read more.

Diesel engines of the vehicles in the transport sector are responsible for most of the CO₂ emissions into the environment. An alternative to reduce fuel consumption is to promote efficient driving techniques. The aim of this paper is to assess the impact of efficient driving on fuel consumption in professional fleets. Data captured from the engine control unit (ECU) of the vehicles are complemented with external information from weather stations and context data from the transport companies. The paper proposes linear and quadratic models in order to quantify the impact of all the terms influencing energy consumption. The analysis was made from the traces captured from a passenger transport company in Spain with more than 50 bus routes. 20 vehicles of five different models were monitored and 58 drivers participated in the study. The results indicate that efficient driving has significant influence on fuel consumption, which confirms efficient driving as a valid and economical option for reducing consumption and therefore emissions of harmful particles into the atmosphere. According to the proposed model, in average external conditions, a driver that increases efficiency from 25% to 75% can reach savings in fuel consumption of up to 16 L/100 km in the analysed bus fleet, which is a significant improvement considering the long distances covered by professionals of the transport sector. Full article

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Open AccessEditor’s ChoiceArticle

Spray Combustion Characteristics and Soot Emission Reduction of Hydrous Ethanol Diesel Emulsion Fuel Using Color-Ratio Pyrometry

by Xiaoqing Zhang, Tie Li, Pengfei Ma and Bin Wang

Energies 2017, 10(12), 2062; https://doi.org/10.3390/en10122062 - 5 Dec 2017

Cited by 19 | Viewed by 4647

Abstract

To elucidate the relationship between physicochemical properties, spray characteristics, and combustion performance, a series of experiments have been conducted in a constant volume vessel with injection of hydrous ethanol diesel emulsion and regular diesel. HE30 (emulsion with 30% volume fraction of 20% water-containing [...] Read more.

To elucidate the relationship between physicochemical properties, spray characteristics, and combustion performance, a series of experiments have been conducted in a constant volume vessel with injection of hydrous ethanol diesel emulsion and regular diesel. HE30 (emulsion with 30% volume fraction of 20% water-containing ethanol and 70% volume fraction of 0# diesel) is developed using Shah’s technique and regular diesel is also employed for comparison. Firstly, the physicochemical properties of two kinds of fuels are investigated. Then, the non-evaporating and evaporating spray characteristics are examined through the high-speed shadowgraphs. Finally, spray combustion experiments under different ambient oxygen concentrations are carried out, and color-ratio pyrometry (CRP) is applied to measure the flame temperature and soot concentration (KL) distributions. The results indicate that the physicochemical properties, such as density, surface tension, kinematic viscosity, cetane number, and oxygen content, have significant impact on the spray mixture formation and combustion performance. HE30 exhibits lower soot emissions than that of regular diesel. Further analysis supports the standpoint that the hydrous ethanol diesel emulsion can suppress the soot and NO_x simultaneously. Therefore, the hydrous ethanol diesel emulsion has great potential to be an alternative clean energy resource. Full article

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Open AccessArticle

Performance Evaluation and Durability Enhancement of FEP-Based Gas Diffusion Media for PEM Fuel Cells

by Saverio Latorrata, Paola Gallo Stampino, Cinzia Cristiani and Giovanni Dotelli

Energies 2017, 10(12), 2063; https://doi.org/10.3390/en10122063 - 5 Dec 2017

Cited by 14 | Viewed by 5130

Abstract

Nowadays, micro-porous layers (MPLs) for polymer electrolyte membrane fuel cells (PEMFCs) are commonly deposited onto gas diffusion layer (GDL) substrates starting from hydrophobic carbon-based dispersions. In this work, different quantities of fluorinated ethylene propylene (FEP), a fluorinated copolymer proven to be superior to [...] Read more.

Nowadays, micro-porous layers (MPLs) for polymer electrolyte membrane fuel cells (PEMFCs) are commonly deposited onto gas diffusion layer (GDL) substrates starting from hydrophobic carbon-based dispersions. In this work, different quantities of fluorinated ethylene propylene (FEP), a fluorinated copolymer proven to be superior to polytetrafluoroethylene (PTFE) for a proper water management, were used to make both GDL and MPL hydrophobic. After the identification of the optimal amount of FEP, carboxymethylcellulose (CMC) was also added to gas diffusion media (GDM) to reduce overall ohmic resistance of the whole device and adhesion of MPLs to GDLs. Ex-situ chemical and mechanical accelerated stress tests (ASTs) were carried out to accelerate degradation of materials aiming to assess their durability. The highest quantity of FEP in GDMs led to the best electrochemical and diffusive properties. The presence of CMC allowed reducing overall ohmic resistance due to a better electrolyte hydration. A satisfactory durability was proven since the fundamental properties related to gas diffusion medium, such as wettability, ohmic and mass transport resistances, revealed to be quasi-stable upon ASTs. Full article

(This article belongs to the Special Issue Polymer Electrolyte Membrane Fuel Cells 2017)

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Open AccessCommunication

A New Model for Describing the Rheological Behavior of Heavy and Extra Heavy Crude Oils in the Presence of Nanoparticles

by Esteban A. Taborda, Camilo A. Franco, Vladimir Alvarado and Farid B. Cortés

Energies 2017, 10(12), 2064; https://doi.org/10.3390/en10122064 - 5 Dec 2017

Cited by 5 | Viewed by 3546

Abstract

The present work proposes for the first time a mathematical model for describing the rheological behavior of heavy and extra-heavy crude oils in the presence of nanoparticles. This model results from the combination of two existing mathematical models. The first one applies to [...] Read more.

The present work proposes for the first time a mathematical model for describing the rheological behavior of heavy and extra-heavy crude oils in the presence of nanoparticles. This model results from the combination of two existing mathematical models. The first one applies to the rheology of pseudoplastic substances, i.e., the Herschel-Bulkley model. The second one was previously developed by our research group to model the rheology of suspensions, namely the modified Pal and Rhodes model. The proposed model is applied to heavy and extra heavy crude oils in the presence of nanoparticles, considering the effects of nanoparticles concentration and surface chemical nature, temperature, and crude oil type. All the experimental data evaluated exhibited compelling goodness of fitting, and the physical parameters in the model follow correlate well with variations in viscosity. The new model is dependent of share rate and opens new possibilities for phenomenologically understanding viscosity reduction in heavy crude by adding solid nanoparticles and favoring the scale-up in enhanced oil recovery (EOR) and/or improved oil recovery (IOR) process. Full article

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

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Open AccessEditor’s ChoiceArticle

Towards Efficient Energy Management of Smart Buildings Exploiting Heuristic Optimization with Real Time and Critical Peak Pricing Schemes

by Sheraz Aslam, Zafar Iqbal, Nadeem Javaid, Zahoor Ali Khan, Khursheed Aurangzeb and Syed Irtaza Haider

Energies 2017, 10(12), 2065; https://doi.org/10.3390/en10122065 - 5 Dec 2017

Cited by 113 | Viewed by 8173

Abstract

The smart grid plays a vital role in decreasing electricity cost through Demand Side Management (DSM). Smart homes, a part of the smart grid, contribute greatly to minimizing electricity consumption cost via scheduling home appliances. However, user waiting time increases due to the [...] Read more.

The smart grid plays a vital role in decreasing electricity cost through Demand Side Management (DSM). Smart homes, a part of the smart grid, contribute greatly to minimizing electricity consumption cost via scheduling home appliances. However, user waiting time increases due to the scheduling of home appliances. This scheduling problem is the motivation to find an optimal solution that could minimize the electricity cost and Peak to Average Ratio (PAR) with minimum user waiting time. There are many studies on Home Energy Management (HEM) for cost minimization and peak load reduction. However, none of the systems gave sufficient attention to tackle multiple parameters (i.e., electricity cost and peak load reduction) at the same time as user waiting time was minimum for residential consumers with multiple homes. Hence, in this work, we propose an efficient HEM scheme using the well-known meta-heuristic Genetic Algorithm (GA), the recently developed Cuckoo Search Optimization Algorithm (CSOA) and the Crow Search Algorithm (CSA), which can be used for electricity cost and peak load alleviation with minimum user waiting time. The integration of a smart Electricity Storage System (ESS) is also taken into account for more efficient operation of the Home Energy Management System (HEMS). Furthermore, we took the real-time electricity consumption pattern for every residence, i.e., every home has its own living pattern. The proposed scheme is implemented in a smart building; comprised of thirty smart homes (apartments), Real-Time Pricing (RTP) and Critical Peak Pricing (CPP) signals are examined in terms of electricity cost estimation for both a single smart home and a smart building. In addition, feasible regions are presented for single and multiple smart homes, which show the relationship among the electricity cost, electricity consumption and user waiting time. Experimental results demonstrate the effectiveness of our proposed scheme for single and multiple smart homes in terms of electricity cost and PAR minimization. Moreover, there exists a tradeoff between electricity cost and user waiting. Full article

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

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Open AccessArticle

The General Regression Neural Network Based on the Fruit Fly Optimization Algorithm and the Data Inconsistency Rate for Transmission Line Icing Prediction

by Dongxiao Niu, Haichao Wang, Hanyu Chen and Yi Liang

Energies 2017, 10(12), 2066; https://doi.org/10.3390/en10122066 - 5 Dec 2017

Cited by 35 | Viewed by 5092

Abstract

Accurate and stable prediction of icing thickness on transmission lines is of great significance for ensuring the safe operation of the power grid. In order to improve the accuracy and stability of icing prediction, an innovative prediction model based on the generalized regression [...] Read more.

Accurate and stable prediction of icing thickness on transmission lines is of great significance for ensuring the safe operation of the power grid. In order to improve the accuracy and stability of icing prediction, an innovative prediction model based on the generalized regression neural network (GRNN) and the fruit fly optimization algorithm (FOA) is proposed. Firstly, a feature selection method based on the data inconsistency rate (IR) is adopted to select the optimal feature, which aims to reduce redundant input vectors. Then, the fruit FOA is utilized for optimization of smoothing factor for the GRNN. Lastly, the icing forecasting method FOA-IR-GRNN is established. Two cases in different locations and different months are selected to validate the proposed model. The results indicate that the new hybrid FOA-IR-GRNN model presents better accuracy, robustness, and generality in icing forecasting. Full article

(This article belongs to the Special Issue Hybrid Advanced Optimization Methods with Evolutionary Computation Techniques in Energy Forecasting)

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Open AccessArticle

A Novel Method of Statistical Line Loss Estimation for Distribution Feeders Based on Feeder Cluster and Modified XGBoost

by Shouxiang Wang, Pengfei Dong and Yingjie Tian

Energies 2017, 10(12), 2067; https://doi.org/10.3390/en10122067 - 5 Dec 2017

Cited by 55 | Viewed by 4949

Abstract

The estimation of losses of distribution feeders plays a crucial guiding role for the planning, design, and operation of a distribution system. This paper proposes a novel estimation method of statistical line loss of distribution feeders using the feeder cluster technique and modified [...] Read more.

The estimation of losses of distribution feeders plays a crucial guiding role for the planning, design, and operation of a distribution system. This paper proposes a novel estimation method of statistical line loss of distribution feeders using the feeder cluster technique and modified eXtreme Gradient Boosting (XGBoost) algorithm that is based on the characteristic data of feeders that are collected in the smart power distribution and utilization system. In order to enhance the applicability and accuracy of the estimation model, k-medoids algorithm with weighting distance for clustering distribution feeders is proposed. Meanwhile, a variable selection method for clustering distribution feeders is discussed, considering the correlation and validity of variables. This paper next modifies the XGBoost algorithm by adding a penalty function in consideration of the effect of the theoretical value to the loss function for the estimation of statistical line loss of distribution feeders. The validity of the proposed methodology is verified by 762 distribution feeders in the Shanghai distribution system. The results show that the XGBoost method has higher accuracy than decision tree, neural network, and random forests by comparison of Root Mean Square Error (RMSE), Mean Absolute Percentage Error (MAPE), and Absolute Percentage Error (APE) indexes. In particular, the theoretical value can significantly improve the reasonability of estimated results. Full article

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

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Open AccessArticle

A Novel Digital Control Method of a Single-Phase Grid-Connected Inverter Based on a Virtual Closed-Loop Circuit and Complex Vector Representation

by Kun Xie, Gangyi Hu, Hong Yi, Zhibi Lyu and Yangxiao Xiang

Energies 2017, 10(12), 2068; https://doi.org/10.3390/en10122068 - 6 Dec 2017

Cited by 5 | Viewed by 5041

Abstract

With the rapid development of renewable energy generation, single-phase grid-connected inverters have been widely applied in modern power systems. Since the power output of the renewable sources is continuously changing, independent active/reactive power control and a rapid current tracking performance is supposed to [...] Read more.

With the rapid development of renewable energy generation, single-phase grid-connected inverters have been widely applied in modern power systems. Since the power output of the renewable sources is continuously changing, independent active/reactive power control and a rapid current tracking performance is supposed to be achieved in a single-phase grid-connected inverter. However, the poor orthogonal-axis-constructing strategy and the ineffective decoupling in some widely-used controllers have severely weakened the dynamic performance of the single-phase inverter. To deal with the challenges above, this study proposes a comprehensive control strategy for current control in a single-phase grid-connected inverter. In the proposed control strategy, a virtual closed-loop is constructed to improve the dynamic performance and realize independent power control under a synchronous frame. Then, complex vector theory is used to model the virtual closed-loop based single-phase inverter, and a novel digital controller is designed based on zero-pole cancellation and minimum beat control to completely decouple the active/reactive components and achieve a supreme current tracking performance. Experimental results are shown to validate the feasibility of the proposed current controller. Full article

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

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8665 KiB

Open AccessArticle

Integration Design and Optimization Control of a Dynamic Vibration Absorber for Electric Wheels with In-Wheel Motor

by Mingchun Liu, Feihong Gu, Juhua Huang, Changjiang Wang and Ming Cao

Energies 2017, 10(12), 2069; https://doi.org/10.3390/en10122069 - 5 Dec 2017

Cited by 41 | Viewed by 6198

Abstract

This paper presents an integration design scheme and an optimization control strategy for electric wheels to suppress the in-wheel vibration and improve vehicle ride comfort. The in-wheel motor is considered as a dynamic vibration absorber (DVA), which is isolated from the unsprung mass [...] Read more.

This paper presents an integration design scheme and an optimization control strategy for electric wheels to suppress the in-wheel vibration and improve vehicle ride comfort. The in-wheel motor is considered as a dynamic vibration absorber (DVA), which is isolated from the unsprung mass by using a spring and a damper. The proposed DVA system is applicable for both the inner-rotor motor and outer-rotor motor. Parameters of the DVA system are optimized for the typical conditions, by using the particle swarm optimization (PSO) algorithm, to achieve an acceptable vibration performance. Further, the DVA actuator force is controlled by using the alterable-domain-based fuzzy control method, to adaptively suppress the wheel vibration and reduce the wallop acting on the in-wheel motor (IWM) as well. In addition, a suspension actuator force is also controlled, by using the linear quadratic regulator (LQR) method, to enhance the suspension performance and meanwhile improve vehicle ride comfort. Simulation results demonstrate that the proposed DVA system effectively suppresses the wheel vibration and simultaneously reduces the wallop acting on the IWM. Also, the alterable-domain-based fuzzy control method performs better than the conventional ones, and the LQR-based suspension exhibits excellent performance in vehicle ride comfort. Full article

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

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Open AccessArticle

Latching and Declutching Control of the Solo Duck Wave-Energy Converter with Different Load Types

by Jinming Wu, Yingxue Yao, Liang Zhou and Malin Göteman

Energies 2017, 10(12), 2070; https://doi.org/10.3390/en10122070 - 6 Dec 2017

Cited by 10 | Viewed by 3630

Abstract

The solo duck wave-energy converter (WEC) captures power in a point absorber manner, hence it exhibits high power-capture efficiency within only a narrow bandwidth. Passive control is characterized by a unidirectional power flow, and thus its engineering implementation can be simplified. In this [...] Read more.

The solo duck wave-energy converter (WEC) captures power in a point absorber manner, hence it exhibits high power-capture efficiency within only a narrow bandwidth. Passive control is characterized by a unidirectional power flow, and thus its engineering implementation can be simplified. In this paper, two typical passive control strategies, latching and declutching control, are applied to the solo duck WEC to improve its power-capture performance at wave periods larger and smaller than the natural period of the WEC, respectively. Special attention is paid to the peak value of instantaneous WEC performance parameters, including the peak motion excursion, the peak power take-off (PTO) moment, and the peak-to-average power ratio, when the captured power is maximized. Performance differences between the linear and coulomb loads are also investigated. Results show that both latching and declutching control can effectively improve captured power, but also incidentally increase the peak motion excursion and peak-to-average power ratio. When under latching and declutching control, the coulomb load leads to the same maximum relative capture width and peak motion excursion as the linear load, but presents smaller peak PTO moment and peak-to-average power ratio than the linear load, hence making the coulomb load the better choice for the solo duck WEC. Full article

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Adaptive Marginal Costs-Based Distributed Economic Control of Microgrid Clusters Considering Line Loss

by Xiaoqian Zhou, Qian Ai and Hao Wang

Energies 2017, 10(12), 2071; https://doi.org/10.3390/en10122071 - 6 Dec 2017

Cited by 12 | Viewed by 3136

Abstract

When several microgrids (MG) are interconnected into microgrid clusters (MGC), they have great potential to improve their reliability. Traditional droop control tends to make the total operating costs higher as the power is distributed by capacity ratios of distributed energy resources (DERs). This [...] Read more.

When several microgrids (MG) are interconnected into microgrid clusters (MGC), they have great potential to improve their reliability. Traditional droop control tends to make the total operating costs higher as the power is distributed by capacity ratios of distributed energy resources (DERs). This paper proposes an adaptive distributed economic control for islanded microgrids which considers line loss, specifically, an interesting marginal costs-based economic droop control is proposed, and consensus-based adaptive controller is applied, to deal with power limits and capacity constraints for storage. The whole expense can be effectively lowered by achieving identical marginal costs for DERs in MGC. Specially, the capacity constraints only for storages are also included to do further optimization. Moreover, consensus-based distributed secondary controllers are used to rapidly restore system frequency and voltage magnitudes. The above controllers only need to interact with neighbor DERs by a sparse communication network, eliminating the necessity of a central controller and enhancing the stability. A MGC, incorporating three microgrids, is used to verify the effectiveness of the proposed methods. Full article

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

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Open AccessArticle

Determination of the Most Optimal On-Shore Wind Farm Site Location Using a GIS-MCDM Methodology: Evaluating the Case of South Korea

by Sajid Ali, Sang-Moon Lee and Choon-Man Jang

Energies 2017, 10(12), 2072; https://doi.org/10.3390/en10122072 - 6 Dec 2017

Cited by 48 | Viewed by 5502

Abstract

Optimum wind farm site selection is a quite complicated and iterative process, as it depends upon various parameters and so called “site selection criteria”. Determining the relative weight of each criterion, which is a multi-criteria decision making (MCDM) process, is very critical during [...] Read more.

Optimum wind farm site selection is a quite complicated and iterative process, as it depends upon various parameters and so called “site selection criteria”. Determining the relative weight of each criterion, which is a multi-criteria decision making (MCDM) process, is very critical during this process. The current study deals with the optimum site selection for on-shore wind farm development in the territory of South Korea using a geographic information system (GIS). Seven different site selection criteria, including the slope of the land, the distance to roads and wind potential are considered. Similarly, seven different types of land zones where it is impossible to build a wind farm, commonly known as restricted areas, such as military zones, wetlands, etc., were also considered and excluded from the study area. The analytical hierarchy process (AHP) coupled with fuzzy triangular numbers (FTN) was utilized as a MCDM tool to get criterion weights and making the optimum site selection decision. Wind farm suitability maps were prepared under six different scenarios, and it was found that the eastern part of the country has relatively higher feasibility for on-shore wind farm development in the near future. According to the wind farm suitability scale (1 to 8 where 8 being top sites) developed in this study, it was determined that under each scenario the total area of scale 8 sites i.e., “the most suitable sites” account for less than one percent of the total area of South Korea. Apart from the wind farm suitability maps, the top five sites were also determined according to each scenario and the values of important parameters such as latitude (°) & longitude (°), the area of the site (km²) and the average values of all seven criterions were also estimated for each of the top five sites. Full article

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

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Open AccessArticle

Numerical Simulation about Reconstruction of the Boundary Layer

by Yan Li, Chuan Li, Yajie Wu, Cong Liu, Han Yuan and Ning Mei

Energies 2017, 10(12), 2074; https://doi.org/10.3390/en10122074 - 6 Dec 2017

Viewed by 3608

Abstract

In this paper, the reconstruction mechanism of the boundary layer in the channel is studied using the lattice Boltzmann method (LBM). By comparing the distribution of velocity in the channel, the conclusion that LBM has feasibility and superiority is obtained. Based on this, [...] Read more.

In this paper, the reconstruction mechanism of the boundary layer in the channel is studied using the lattice Boltzmann method (LBM). By comparing the distribution of velocity in the channel, the conclusion that LBM has feasibility and superiority is obtained. Based on this, a physical model of square cylinders is set up to simulate the velocity distribution and the effect on the thickness of boundary layer. When the square cylinder moves at a certain speed, the velocity distribution in the flow field changes drastically. As well, it is found that the thickness of the boundary layer decreases with the cylinders’ height increasing in the given range. Furthermore, double cylinders model is also set up, and the results show that the optimal interval distance of the cylinders is between 90 and 140 lattice units. It is found that the moving cylinders have a significant effect on the thickness of the boundary layer, which will change the fluid flow and enhance the heat transfer. 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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An Emulated PV Source Based on an Unilluminated Solar Panel and DC Power Supply

by Zhongfu Zhou and John Macaulay

Energies 2017, 10(12), 2075; https://doi.org/10.3390/en10122075 - 6 Dec 2017

Cited by 22 | Viewed by 9999

Abstract

This paper provides a review on various PV simulator technologies as well as presents a novel equivalent photovoltaic (PV) source that was constructed by using un-illuminated solar panels and a DC power supply that operates in current source mode. The constructed PV source [...] Read more.

This paper provides a review on various PV simulator technologies as well as presents a novel equivalent photovoltaic (PV) source that was constructed by using un-illuminated solar panels and a DC power supply that operates in current source mode. The constructed PV source was used for testing photovoltaic converters and various maximum power point tracking (MPPT) algorithms required for capturing the maximum possible output power. The mathematical model and electrical characteristics of the constructed PV source were defined and analyzed in detail in the paper. The constructed PV source has the advantages of high bandwidth over the switching circuit based PV simulators. The constructed PV source has been used for testing various power electronics converters and various control techniques effectively in laboratory environments for researchers and university students. Full article

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Open AccessArticle

A Method of Abnormal States Detection Based on Adaptive Extraction of Transformer Vibro-Acoustic Signals

by Liang Zou, Yongkang Guo, Han Liu, Li Zhang and Tong Zhao

Energies 2017, 10(12), 2076; https://doi.org/10.3390/en10122076 - 7 Dec 2017

Cited by 18 | Viewed by 3478

Abstract

State monitoring is very important for the safe operation of high-voltage transformers. A non-contact vibro-acoustic detection method based on the Blind Source Separation (BSS) was proposed in this paper to promote the development of transformer on-line monitoring technology. Firstly, the algorithm of Sparse [...] Read more.

State monitoring is very important for the safe operation of high-voltage transformers. A non-contact vibro-acoustic detection method based on the Blind Source Separation (BSS) was proposed in this paper to promote the development of transformer on-line monitoring technology. Firstly, the algorithm of Sparse Component Analysis (SCA) was applied for the adaptive extraction of vibro-acoustic signals, which utilizes the sorted local maximum values of the potential function. Then, the operating states of the transformer were detected by analyzing the vibro-acoustic signal eigenvectors. Different conditions including running normally, increasing of transformer vibro-acoustic amplitude and changing of frequency component of transformer vibro-acoustic were simulated. Moreover, experiments were carried out in a 220 kV substation. The research results show that the number of mixed noise sources can be estimated and the transformer vibro-acoustic signal was always ranked first in the separation signals. The source signals were effectively separated from the mixed signals while all of the correlation coefficients are more than 0.98 and the quadratic residuals are less than −32 dB. As for the experiments, the vibro-acoustic signal was separated out successfully from two voice signals and two interference signals. The acoustic signal reflection is considered as the main cause of the signal interference, and the transformer volume source model is considered as the main reason of unstable vibro-acoustic signal amplitude. Finally, the simulated abnormal states of the transformer were well recognized and the state of the tested transformer was judged to be normal. Full article

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Open AccessArticle

Experimental Evaluation of a Switching Matrix Applied in a Bank of Supercapacitors

by Maria Guadalupe Reveles-Miranda, Manuel Israel Flota-Bañuelos, Freddy Chan-Puc and Daniella Pacheco-Catalán

Energies 2017, 10(12), 2077; https://doi.org/10.3390/en10122077 - 7 Dec 2017

Cited by 6 | Viewed by 3129

Abstract

Distributed power generation systems (DPGSs) integrate power sources that tend to be smaller than the typical utility scale, such as for renewable energy sources and other applications. Storage systems that incorporate supercapacitors (SCs) have been proposed to extend the life of batteries and [...] Read more.

Distributed power generation systems (DPGSs) integrate power sources that tend to be smaller than the typical utility scale, such as for renewable energy sources and other applications. Storage systems that incorporate supercapacitors (SCs) have been proposed to extend the life of batteries and to increase the power capacity of the DPGSs, guaranteeing maximum efficiency. The extraction of energy in SCs is more demanding than in the case of batteries; when SCs have delivered only 75% of their energy, their voltage has already decreased to 50%. Beyond this value, the banks fail to meet the requirements demanded by loads that require a minimum voltage to operate correctly, leaving 25% of the energy unused, thereby limiting the deep charge/discharge cycles that occur. This paper presents a model of a switching matrix applied in a bank of SCs. The model allows the use of a simpler circuit to achieve a large number of serial/parallel-configuration connections (levels), improving the utilization of energy to obtain deep discharge cycles in each SC; therefore, by increasing the average energy extracted from each SC, it extends the power delivery time in the storage bank. The efficiency was verified by experimental results obtained using a bank of six SCs. Full article

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

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Open AccessArticle

Experimental Study on the Mechanical Properties of CH₄ and CO₂ Hydrate Remodeling Cores in Qilian Mountain

by Tingting Luo, Yanghui Li, Weiguo Liu, Xiang Sun and Shi Shen

Energies 2017, 10(12), 2078; https://doi.org/10.3390/en10122078 - 7 Dec 2017

Cited by 10 | Viewed by 3871

Abstract

The CH₄-CO₂ replacement method has attracted global attention as a new promising method for methane hydrate exploitation. In the replacement process, the mechanical stabilities of CH₄ and CO₂ hydrate-bearing sediments have become problems requiring attention. In this paper, [...] Read more.

The CH₄-CO₂ replacement method has attracted global attention as a new promising method for methane hydrate exploitation. In the replacement process, the mechanical stabilities of CH₄ and CO₂ hydrate-bearing sediments have become problems requiring attention. In this paper, considering the hydrate characteristics and burial conditions of hydrate-bearing cores, sediments matrices were formed by a mixture of kaolin clay and quartz sand, and an experimental study was focused on the failure strength of CH₄ and CO₂ hydrate-bearing sediments under different conditions to verify the mechanical reliability of CH₄-CO₂ replacement in permafrost-associated natural gas deposits. A series of triaxial shear tests were conducted on the CH₄ and CO₂ hydrate-bearing sediments under temperatures of −20, −10, and −5 °C, confining pressures of 2.5, 3.75, 5, 7.5, and 10 MPa, and a strain rate of 1.0 mm/min. The results indicated that the failure strength of the CO₂ hydrate-bearing sediments was higher than that of the CH₄ hydrate-bearing sediments under different confining pressures and temperatures; the failure strength of the CH₄ and CO₂ hydrate-bearing sediments increased with an increase in confining pressure at a low confining pressure state. Besides that, the failure strength of all hydrate-bearing sediments decreased with an increase in temperature; all the failure strengths of the CO₂ hydrate-bearing sediments were higher than those of the CH₄ hydrate-bearing sediments in different sediment matrices. The experiments proved that the hydrate-bearing sediments would be more stable than that before CH₄-CO₂ replacement. Full article

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Open AccessArticle

Design and Selection of Innovative Primary Circulation Pumps for GEN-IV Lead Fast Reactors

by Walter Borreani, Alessandro Alemberti, Guglielmo Lomonaco, Fabrizio Magugliani and Paolo Saracco

Energies 2017, 10(12), 2079; https://doi.org/10.3390/en10122079 - 7 Dec 2017

Cited by 7 | Viewed by 5739

Abstract

Although Lead-cooled Fast Reactor (LFR) is not a new concept, it continues to be an example of innovation in the nuclear field. Recently, there has been strong interest in liquid lead (Pb) or liquid lead–bismuth eutectic (LBE) both critical and subcritical systems in [...] Read more.

Although Lead-cooled Fast Reactor (LFR) is not a new concept, it continues to be an example of innovation in the nuclear field. Recently, there has been strong interest in liquid lead (Pb) or liquid lead–bismuth eutectic (LBE) both critical and subcritical systems in a relevant number of Countries, including studies performed in the frame of GENERATION-IV initiative. In this paper, the theoretical and computational findings for three different designs of Primary Circulation Pump (PCP) evolving liquid lead (namely the jet pump, the Archimedean pump and the blade pump) are presented with reference to the ALFRED (Advanced Lead Fast Reactor European Demonstrator) design. The pumps are first analyzed from the theoretical point of view and then modeled with a 3D CFD code. Required design performance of the pumps are approximatively around an effective head of 2 bar with a mass flow rate of 5000 kg/s. Taking into account the geometrical constraints of the reactor and the fluid dynamics characteristics of the molten lead, the maximum design velocity for molten lead fluid flow of 2 m/s may be exceeded giving rise to unacceptable erosion phenomena of the blade or rotating component of the primary pumping system. For this reason a deep investigation of non-conventional axial pumps has been performed. The results presented shows that the design of the jet pump looks like beyond the current technological feasibility while, once the mechanical challenges of the Archimedean (screw) pump and the fluid-dynamic issues of the blade pump will be addressed, both could represent viable solutions as PCP for ALFRED. Particularly, the blade pump shows the best performance in terms of pressure head generated in normal operation conditions as well as pressure drop in locked rotor conditions. Further optimizations (mainly for what the geometrical configuration is concerned) are still necessary. Full article

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

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Open AccessArticle

The Future of the European Electricity Grid Is Bright: Cost Minimizing Optimization Shows Solar with Storage as Dominant Technologies to Meet European Emissions Targets to 2050

by Zack Norwood, Joel Goop and Mikael Odenberger

Energies 2017, 10(12), 2080; https://doi.org/10.3390/en10122080 - 7 Dec 2017

Cited by 8 | Viewed by 3662

Abstract

The European roadmap for the power sector dictates an 80–95% cut of existing levels of carbon dioxide emissions is needed by the year 2050 to meet climate goals. This article describes results from a linear cost optimization investment model, ELIN, coupled with a [...] Read more.

The European roadmap for the power sector dictates an 80–95% cut of existing levels of carbon dioxide emissions is needed by the year 2050 to meet climate goals. This article describes results from a linear cost optimization investment model, ELIN, coupled with a solar technology model, Distributed Concentrating Solar Combined Heat and Power (DCS-CHP), using published investment costs for a comprehensive suite of renewable and conventional electricity generation technologies, to compare possible scenarios for the future electricity grid. The results of these model runs and sensitivity analyses indicate that: (1) solar photovoltaics (PV) with battery storage will likely play a very large role in meeting European targets; (2) concentrating solar power (CSP) with thermal energy storage is at a slight economic disadvantage with respect to PV to compete economically; (3) the economic potential of wind power is only comparable with solar PV if high wind penetration levels are allowed in the best wind sites in Europe; and (4) carbon capture and nuclear technologies are unlikely to compete economically with renewable technologies in creating a low-carbon future grid. Full article

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

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Open AccessArticle

Large Eddy Simulation Analysis on Confined Swirling Flows in a Gas Turbine Swirl Burner

by Tao Liu, Fuqiang Bai, Zixuan Zhao, Yuzhen Lin, Qing Du and Zhijun Peng

Energies 2017, 10(12), 2081; https://doi.org/10.3390/en10122081 - 7 Dec 2017

Cited by 15 | Viewed by 8417

Abstract

This paper describes a Large Eddy Simulation (LES) investigation into flow fields in a model gas turbine combustor equipped with a swirl burner. A probability density function was used to describe the interaction physics of chemical reaction and turbulent flow as liquid fuel [...] Read more.

This paper describes a Large Eddy Simulation (LES) investigation into flow fields in a model gas turbine combustor equipped with a swirl burner. A probability density function was used to describe the interaction physics of chemical reaction and turbulent flow as liquid fuel was directly injected into the combustion chamber and rapidly mixed with the swirling air. Simulation results showed that heat release during combustion accelerated the axial velocity motion and made the recirculation zone more compact. As the combustion was taking place under lean burn conditions, NO emissions was less than 10 ppm. Finally, the effects of outlet contraction on swirling flows and combustion instability were investigated. Results suggest that contracted outlet can enhance the generation of a Central Vortex Core (CVC) flow structure. As peak RMS of velocity fluctuation profiles at center-line suggested the turbulent instability can be enhanced by CVC motion, the Power Spectrum Density (PSD) amplitude also explained that the oscillation at CVC position was greater than other places. Both evidences demonstrated that outlet contraction can increase the instability of the central field. Full article

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

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Modelling the Small Throw Fault Effect on the Stability of a Mining Roadway and Its Verification by In Situ Investigation

by Małkowski Piotr, Ostrowski Łukasz and Bachanek Piotr

Energies 2017, 10(12), 2082; https://doi.org/10.3390/en10122082 - 7 Dec 2017

Cited by 34 | Viewed by 3219

Abstract

The small throw fault zones cause serious problems for mining engineers. The knowledge about the range of fractured zone around the roadway and about roadway’s contour deformations helps a lot with the right support design or its reinforcement. The paper presents the results [...] Read more.

The small throw fault zones cause serious problems for mining engineers. The knowledge about the range of fractured zone around the roadway and about roadway’s contour deformations helps a lot with the right support design or its reinforcement. The paper presents the results of numerical analysis of the effect of a small throw fault zone on the convergence of the mining roadway and the extent of the fracturing induced around the roadway. The computations were performed on a dozen physical models featuring various parameters of rock mass and support for the purpose to select the settings that reflects most suitably the behavior of tectonically disturbed and undisturbed rocks around the roadway. Finally, the results of the calculations were verified by comparing them with in situ convergence measurements carried out in the maingate D-2 in the “Borynia-Zofiówka-Jastrzębie” coal mine. Based on the results of measurements it may be concluded that the rock mass displacements around a roadway section within a fault zone during a year were four times in average greater than in the section tectonically unaffected. The results of numerical calculations show that extent of the yielding zone in the roof reaches two times the throw of the fault, in the floor 3 times the throw, and horizontally approx. 1.5 to 1.8 times the width of modelled fault zone. Only a few elasto-plastic models or models with joints between the rock beds can be recommended for predicting the performance of a roadway which is within a fault zone. It is possible, using these models, to design the roadway support of sufficient load bearing capacity at the tectonically disturbed section. Full article

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

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Core Abilities Evaluation Index System Exploration and Empirical Study on Distributed PV-Generation Projects

by Lin He, Chang-Ling Li, Qing-Yun Nie, Yan Men, Hai Shao and Jiang Zhu

Energies 2017, 10(12), 2083; https://doi.org/10.3390/en10122083 - 7 Dec 2017

Cited by 14 | Viewed by 3560

Abstract

In line with the constraints of environmental problems and economic development, large-scale renewable-generation projects have been planned and constructed in recent years. In order to achieve sustainable power development and improve the power supply structure, China’s government has focused on distributed photovoltaic (PV) [...] Read more.

In line with the constraints of environmental problems and economic development, large-scale renewable-generation projects have been planned and constructed in recent years. In order to achieve sustainable power development and improve the power supply structure, China’s government has focused on distributed photovoltaic (PV) generation projects due to their advantages of clean emission and local consumption. However, their unstable output power still brings a series of problems concerning reliability, investment income, and available substitution proportion to traditional power, and so on. Therefore, it is imperative to understand the competitive development abilities of distributed PV generation projects and measure them effectively. First, through various investigation methods such as literature reviews, feasibility report analysis and expert interviews, the factors that influence the core abilities of distributed PV-generation projects were explored based on the micro-grid structure. Then, with the indexed exploration results, the factors were classified into 6 dimensions, i.e., investment and earning ability, production and operation ability, power-grid coordination ability, energy-conservation and emission-reduction ability, sustainable development ability, and society-serving ability. Meanwhile, an evaluation index system for core abilities of distributed PV-generation project was constructed using all quantitative indicators. Third, for examining the availability of the evaluation index system, combination weighting and techniques for order preference by similarity to an ideal solution (TOPSIS) methods were adopted to assess the practical distributed PV-generation projects. The case study results showed that installed capacity, local economy development, and grid-connected power quantity will influence the core abilities of distributed PV-generation project, obviously. The conclusions of the evaluation analysis on core abilities can provide useful references to operate and manage distributed PV-generation projects and promote their sustainable and health advantages. The proposed evaluation index system can also be used to assess power-generation projects in other types of energy, such as wind power and hydropower. Full article

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Open AccessArticle

Low Temperature Selective Catalytic Reduction Using Molding Catalysts Mn-Ce/FA and Mn-Ce/FA-30%TiO₂

by Xiang Gou, Yating Wang, Chunfei Wu, Shian Liu, Dong Zhao, Yamei Li and Saima Iram

Energies 2017, 10(12), 2084; https://doi.org/10.3390/en10122084 - 8 Dec 2017

Cited by 6 | Viewed by 3152

Abstract

Mn-Ce/FA (M) and Mn-Ce/FA-TiO₂ (M), using fly ash (FA) with and without TiO₂ as the carriers, were prepared by an integral molding technique. With the increase of TiO₂ content, the rates of NO conversion and denitration of Mn-Ce/FA-TiO₂ (M) [...] Read more.

Mn-Ce/FA (M) and Mn-Ce/FA-TiO₂ (M), using fly ash (FA) with and without TiO₂ as the carriers, were prepared by an integral molding technique. With the increase of TiO₂ content, the rates of NO conversion and denitration of Mn-Ce/FA-TiO₂ (M) increased, and the NO₂ and N₂O formation rates decreased. It is found that TiO₂ could effectively inhibit the excessive oxidation of NO and the generation of N₂O. The effects of space velocity, oxygen concentration and ammonia nitrogen ratio on three types of nitrogen oxides (NO, NO₂, N₂O) and denitration rates of the Mn-Ce/FA (M) and Mn-Ce/FA-30%TiO₂ (M) were further investigated. In addition, it is demonstrated that Mn-Ce/FA (M) and Mn-Ce/FA-30%TiO₂ (M) were more suitable to be used in the environment of low sulfur and less water. Full article

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Open AccessArticle

Floor Heave Mechanism of Gob-Side Entry Retaining with Fully-Mechanized Backfilling Mining

by Peng Gong, Zhanguo Ma, Xiaoyan Ni and Ray Ruichong Zhang

Energies 2017, 10(12), 2085; https://doi.org/10.3390/en10122085 - 8 Dec 2017

Cited by 47 | Viewed by 6449

Abstract

Serious floor heave in gob-side entry retaining (GER) with fully-mechanized gangue backfilling mining affects the transportation and ventilation safety of the mine. A theoretical mechanical model for the floor of gob-backfilled GER was established. The effects of the mechanical properties of floor strata, [...] Read more.

Serious floor heave in gob-side entry retaining (GER) with fully-mechanized gangue backfilling mining affects the transportation and ventilation safety of the mine. A theoretical mechanical model for the floor of gob-backfilled GER was established. The effects of the mechanical properties of floor strata, the granular compaction of backfilling area (BFA), the vertical support of roadside support body (RSB), and the stress concentration of the solid coal on the floor heave of the gob-backfilled GER were studied. The results show that the floor heave increases with the increase of the coal seam buried depth, and decreases with the increase of the floor rock elastic modulus. The development depth of the plastic zone decreases with the increase of the c and φ value of the floor rock, and increases with the increase of the stress concentration factor of the solid coal. The development depth of the plastic zone in the test mine reached 2.68 m. The field test and monitoring results indicate that the comprehensive control scheme of adjusting backfilling pressure, deep grouting reinforcement, shallow opening stress relief slots, and surface pouring can effectively control the floor heave. The roof-floor displacement is reduced by 73.8% compared to that with the original support scheme. The roadway section meets the design and application requirements when the deformation stabilizes, demonstrating the rationality of the mechanical model. The research results overcome the technical bottleneck of floor heave control of fully-mechanized backfilling GER, providing a reliable basis for the design of a floor heave control scheme. Full article

(This article belongs to the Collection Bioenergy and Biofuel)

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Open AccessArticle

Analysis of Heating Expenses in a Large Social Housing Stock Using Artificial Neural Networks

by Shaker Zabada and Isam Shahrour

Energies 2017, 10(12), 2086; https://doi.org/10.3390/en10122086 - 8 Dec 2017

Cited by 6 | Viewed by 3078

Abstract

This paper presents an analysis of heating expenses in a large social housing stock in the North of France. An artificial neural network (ANN) approach is taken for the analysis of heating consumption data collected over four years in 84 social housing residences [...] Read more.

This paper presents an analysis of heating expenses in a large social housing stock in the North of France. An artificial neural network (ANN) approach is taken for the analysis of heating consumption data collected over four years in 84 social housing residences containing 13,179 dwellings that use collective heating. Analysis provides an understanding of the influence of both physical and socio-economic parameters on heating expenses and proposes a predictive model for these expenses. The model shows that the heating expenses are influenced by both the buildings’ physical parameters and social indicators. Concerning the physical parameters, the most important indicators are the area of the dwellings, followed by the building age and the DPE (energy performance diagnostic). The family size as well as tenant age and income have an important influence on heating expense. The model is then used for establishing a data-based strategy for social housing stock renovation. Full article

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Open AccessArticle

Harmonic Analyzing of the Double PWM Converter in DFIG Based on Mathematical Model

by Jing Liu and Zhigang Liu

Energies 2017, 10(12), 2087; https://doi.org/10.3390/en10122087 - 8 Dec 2017

Cited by 6 | Viewed by 3098

Abstract

Harmonic pollution of double fed induction generators (DFIGs) has become a vital concern for its undesirable effects on power quality issues of wind generation systems and grid-connected system, and the double pulse width modulation (PWM)converter is one of the main harmonic sources in [...] Read more.

Harmonic pollution of double fed induction generators (DFIGs) has become a vital concern for its undesirable effects on power quality issues of wind generation systems and grid-connected system, and the double pulse width modulation (PWM)converter is one of the main harmonic sources in DFIGs. Thus the harmonic analysis of the converter in DFIGs is a necessary step to evaluate their harmonic pollution of DFIGs. This paper proposes a detailed harmonic modeling method to discuss the main harmonic components in a converter. In general the harmonic modeling could be divided into the low-order harmonic part (up to 30th order) and the high-order harmonic part (greater than order 30) parts in general. The low-order harmonics are produced by the circuit topology and control algorithm, and the harmonic component will be different if the control strategy changes. The high-order harmonics are produced by the modulation of the switching function to the dc variable. In this paper, the low-order harmonic modeling is established according to the directions of power flow under the vector control (VC), and the high-order harmonic modeling is established by the switching function of space vector PWM and dc currents. Meanwhile, the simulations of harmonic a components in a converter are accomplished in a real time digital simulation system. The results indicate that the proposed modeling could effectively show the harmonics distribution of the converter in DFIGs. Full article

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Open AccessArticle

Combination of Compensations and Multi-Parameter Coil for Efficiency Optimization of Inductive Power Transfer System

by Guozhen Hu, Junkun Zhang, Junhua Wang, Zhijian Fang, Changsong Cai and Zhongzheng Lin

Energies 2017, 10(12), 2088; https://doi.org/10.3390/en10122088 - 8 Dec 2017

Cited by 3 | Viewed by 4618

Abstract

A loosely coupled inductive power transfer (IPT) system for industrial track applications has been researched in this paper. The IPT converter using primary Inductor-Capacitor-Inductor (LCL) network and secondary parallel-compensations is analyzed combined coil design for optimal operating efficiency. Accurate mathematical analytical model and [...] Read more.

A loosely coupled inductive power transfer (IPT) system for industrial track applications has been researched in this paper. The IPT converter using primary Inductor-Capacitor-Inductor (LCL) network and secondary parallel-compensations is analyzed combined coil design for optimal operating efficiency. Accurate mathematical analytical model and expressions of self-inductance and mutual inductance are proposed to achieve coil parameters. Furthermore, the optimization process is performed combined with the proposed resonant compensations and coil parameters. The results are evaluated and discussed using finite element analysis (FEA). Finally, an experimental prototype is constructed to verify the proposed approach and the experimental results show that the optimization can be better applied to industrial track distributed IPT system. Full article

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

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Economic Feasibility Analysis for Renewable Energy Project Using an Integrated TFN–AHP–DEA Approach on the Basis of Consumer Utility

by Lu Gan, Dirong Xu, Lin Hu and Lei Wang

Energies 2017, 10(12), 2089; https://doi.org/10.3390/en10122089 - 9 Dec 2017

Cited by 14 | Viewed by 6217

Abstract

A renewable energy (RE) project has been brought into focus in recent years. Although there is quite a lot of research to assist investors in assessing the economic feasibility of the project, because of the lack of consideration of consumer utility, the existing [...] Read more.

A renewable energy (RE) project has been brought into focus in recent years. Although there is quite a lot of research to assist investors in assessing the economic feasibility of the project, because of the lack of consideration of consumer utility, the existing approaches may still cause a biased result. In order to promote further development, this study focuses on the economic feasibility analysis of the RE project on the basis of consumer utility in the whole life cycle. Therefore, an integrated approach is proposed, which consists of triangular fuzzy numbers (TFNs), an analytic hierarchy process (AHP) and data envelopment analysis (DEA). The first step is to determine the comprehensive cost index weights of DEA by TFN–AHP. Secondly, to solve the problem, the first DEA model, which is proposed by A. Charnes, W. W. Cooper and E. Rhodes (C²R), is established to calculate the DEA effectiveness. Then, the third task involves designing a computer-based intelligent interface (CBII) to simplify realistic application and ensure performance efficiency. Finally, a solar water heater case study is demonstrated to validate the effectiveness of the entire method’s system. The study shows that this could make investors’ lives easier by using the CBII scientifically, reasonably and conveniently. Moreover, the research results could be easily extended to more complex real-world applications. Full article

(This article belongs to the Special Issue Energy Efficient and Smart Cities)

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Open AccessArticle

Environmental and Economic Benefit Analysis of an Integrated Heating System with Geothermal Energy—A Case Study in Xi’an China

by Qingyou Yan and Chao Qin

Energies 2017, 10(12), 2090; https://doi.org/10.3390/en10122090 - 9 Dec 2017

Cited by 11 | Viewed by 4433

Abstract

Due to the increase in environmental problems and air pollution during the heating period, it is important to promote clean heating in cold regions, thereby meeting the heating demand in a green manner. In order to allocate resources more effectively and facilitate the [...] Read more.

Due to the increase in environmental problems and air pollution during the heating period, it is important to promote clean heating in cold regions, thereby meeting the heating demand in a green manner. In order to allocate resources more effectively and facilitate the consumption of renewable energy, this paper designs an integrated heating system that incorporates geothermal energy into the framework of an integrated energy system of electricity, heating, and gas. An analysis of the environmental and economic benefits indicates that the system reduces pollutant emissions and decreases the cost of urban heating. Using an example of central heating of residential buildings in Xi’an, the paper conducts a scenario analysis based on the gas peak-shaving ratio and the ratio of geothermal heating loads to basic heating loads. The results demonstrate that the environmental and economic benefits of the integrated heating system are higher compared to central heating using coal-fired boilers. In addition, this paper conducts a sensitivity analysis of the heat source to the price factors and the load ratios. The results show that the operating costs of the integrated heating system are most sensitive to the natural gas price and the gas peak-shaving ratio. Therefore, an optimum natural gas peak-shaving ratio can be determined. Full article

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

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Open AccessArticle

LED Uniform Illumination Using Double Linear Fresnel Lenses for Energy Saving

by Ngoc Hai Vu, Thanh Tuan Pham and Seoyong Shin

Energies 2017, 10(12), 2091; https://doi.org/10.3390/en10122091 - 11 Dec 2017

Cited by 17 | Viewed by 12268

Abstract

We present a linear Fresnel lens design for light-emitting diode (LED) uniform illumination applications. The LED source is an array of LEDs. An array of collimating lens is applied to collimate output from the LED array. Two linear Fresnel lenses are used to [...] Read more.

We present a linear Fresnel lens design for light-emitting diode (LED) uniform illumination applications. The LED source is an array of LEDs. An array of collimating lens is applied to collimate output from the LED array. Two linear Fresnel lenses are used to redistribute the collimated beam along two dimensions in the illumination area. Collimating lens and linear Fresnel lens surfaces are calculated by geometrical optics and nonimaging optics. The collimated beam output from the collimating lens array is divided into many fragments. Each fragment is refracted by a segment of Fresnel lens and distributed over the illumination area, so that the total beam can be distributed to the illumination target uniformly. The simulation results show that this design has a compact structure, high optical efficiency of 82% and good uniformity of 76.9%. Some consideration of the energy savings and optical performance are discussed by comparison with other typical light sources. The results show that our proposed LED lighting system can reduce energy consumption five-times in comparison to using a conventional fluorescent lamp. Our research is a strong candidate for low cost, energy savings for indoor and outdoor lighting applications. Full article

(This article belongs to the Special Issue Solid State Lighting)

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Open AccessArticle

Optimal Power Assignment of Energy Storage Systems to Improve the Energy Storage Efficiency for Frequency Regulation

by Sung-Min Cho and Sang-Yun Yun

Energies 2017, 10(12), 2092; https://doi.org/10.3390/en10122092 - 9 Dec 2017

Cited by 18 | Viewed by 3726

Abstract

Losses in energy storage systems (ESSs) are considered operational costs and it is critical to improve efficiency in order to expand their use. We proposed a method of improving efficiency through the operation algorithm of an ESS, consisting of multiple energy storage units [...] Read more.

Losses in energy storage systems (ESSs) are considered operational costs and it is critical to improve efficiency in order to expand their use. We proposed a method of improving efficiency through the operation algorithm of an ESS, consisting of multiple energy storage units (ESUs). Since the ESS used for frequency adjustment maintains a fast response characteristics, we have created a lookup table of efficient ESU operating combinations using genetic algorithms in advance to maintain a fast response time. In addition, the charge/discharge energy balance between the plurality of ESUs is maintained, and the deterioration is prevented from being concentrated in some ESUs. The proposed algorithm was reviewed based on three case studies. The first case study examined whether the lookup table obtained using the genetic algorithm well identified the optimal solution. The second compared the system that optimally distributes the output to ESUs to achieve ESS efficiency for frequency regulation with the system that uniformly distributes the output to ESUs. The third analyzed the impact of efficiency enhancement on the operation of an ESS for frequency regulation through a one-month simulation. The findings confirmed that when the entire system output is optimally allocated to the ESUs, the system’s economic efficiency can be improved by reducing the loss while maintaining the accumulative charge/discharge balance. Full article

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

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Functional Expression of the Arachis hypogaea L. Acyl-ACP Thioesterases AhFatA and AhFatB Enhances Fatty Acid Production in Synechocystis sp. PCC6803

by Gao Chen, Jun Chen, Qingfang He, Yan Zhang, Zhenying Peng, Zhongxue Fan, Fei Bian, Jinhui Yu and Song Qin

Energies 2017, 10(12), 2093; https://doi.org/10.3390/en10122093 - 9 Dec 2017

Cited by 13 | Viewed by 5190

Abstract

Palmitoleic acid (C16:1) and stearic acid (C18:0) are precursors of polyunsaturated fatty acids, which are the focus of intensive global research due to their nutritional value, medicinal applications, and potential use as biofuel. Acyl-acyl carrier protein (ACP) thioesterases are intraplastidial enzymes that determine [...] Read more.

Palmitoleic acid (C16:1) and stearic acid (C18:0) are precursors of polyunsaturated fatty acids, which are the focus of intensive global research due to their nutritional value, medicinal applications, and potential use as biofuel. Acyl-acyl carrier protein (ACP) thioesterases are intraplastidial enzymes that determine the types and amounts of fatty acids produced in plants and release fatty acids into the cytosol to be incorporated into glycerolipids. Based on amino acid sequence identity and substrate specificity, these enzymes are classified into two families, FatA and FatB. In this study, we cloned FatA and FatB thioesterases from Arachis hypogaea L. seeds and functionally expressed these genes, both individually and in tandem, in a blue-green alga Synechocystis sp. PCC6803. The heterologous expression of these genes in Synechocystis altered the fatty acid composition of lipids, resulting in a 29.5–31.6% increase in palmitoleic acid production and a 22.5–35.5% increase in stearic acid production. Moreover, the transgenic Synechocystis cells also showed significant increases in levels of oleic acid (C18:1, OA), linoleic acid (C18:2, LA), and α-linolenic acid (C18:3n3, ALA). These results suggest that the fatty acid profile of algae can be significantly improved by the heterologous expression of exogenous genes. This study not only provides insight into fatty acid biosynthesis, but also lays the foundation for manipulating the fatty acid content of cyanobacteria. Full article

(This article belongs to the Special Issue Algae Fuel 2017)

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Open AccessArticle

Efficient Low Temperature Hydrothermal Carbonization of Chinese Reed for Biochar with High Energy Density

by Chang Liu, Xin Huang and Lingzhao Kong

Energies 2017, 10(12), 2094; https://doi.org/10.3390/en10122094 - 11 Dec 2017

Cited by 17 | Viewed by 4675

Abstract

Hydrothermal carbonization (HTC), as an environmental friendly process, presents wide potential applicability for converting biomass to biochar with high energy density. Reed, a major energy crop, was converted by a HTC process in a batch reactor at 200–280 °C for 0.5 to 4 [...] Read more.

Hydrothermal carbonization (HTC), as an environmental friendly process, presents wide potential applicability for converting biomass to biochar with high energy density. Reed, a major energy crop, was converted by a HTC process in a batch reactor at 200–280 °C for 0.5 to 4 h. Biochar mass yield changed from 66.7% to 19.2% and high heating value (HHV) from 20.0 kJ/g to 28.3 kJ/g, respectively, by increasing the carbonization temperature from 200 °C to 280 °C and decreasing the residence time from 2 h to 1 h. The Fourier Transform infrared spectroscopy (FTIR), X-ray Diffraction (XRD), and Scanning Electron Microscope (SEM) results indicated the lignocellulosic crosslink structure of reed is broken and biochar having a high energy density is obtained with the increase of temperature. The microcrystal features of reed are destroyed and biochar contained mainly lignin fractions. The HTC of biocrude is carried out at 200–280 °C for 2.0 h and the results showed that the obtained biochar has uniform particles filled with carbon microspheres. Full article

(This article belongs to the Special Issue Biomass Chars: Elaboration, Characterization and Applications Ⅱ)

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Open AccessArticle

A Multicriteria GIS-Based Assessment to Optimize Biomass Facility Sites with Parallel Environment—A Case Study in Spain

by Jin Su Jeong and Álvaro Ramírez-Gómez

Energies 2017, 10(12), 2095; https://doi.org/10.3390/en10122095 - 11 Dec 2017

Cited by 38 | Viewed by 4975

Abstract

Optimizing a biomass facility site is a critical concern that is currently receiving an increased attention because of geographically spread biomass feedstock. This research presents a multicriteria GIS assessment with Weighted Linear Combination (WLC) (most suitable areas) and a sensitivity analysis (implementation strategies) [...] Read more.

Optimizing a biomass facility site is a critical concern that is currently receiving an increased attention because of geographically spread biomass feedstock. This research presents a multicriteria GIS assessment with Weighted Linear Combination (WLC) (most suitable areas) and a sensitivity analysis (implementation strategies) applied to various disciplines using suitable criteria to optimize a biomass facility location in the context of renewable energies respecting the environment. The analyses of results with twelve criteria show the most suitable areas (9.25%) and constraints in a case study in Extremadura (Spain), where forest and agriculture are typical for land uses. Thus, the sensitivity analysis demonstrates the insight of the most influential criteria for supporting energy planning decisions. Therefore, this assessment could be used in studies to verify suitable biomass plants sites with corresponding geographical and spatial circumstances and available spatial data necessary in various governmental and industrial sectors. 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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Open AccessArticle

Performance Comparison of Grid-Faulty Control Schemes for Inverter-Based Industrial Microgrids

by Antonio Camacho, Miguel Castilla, Franco Canziani, Carlos Moreira, Paulo Coelho, Mario Gomes and Pedro E. Mercado

Energies 2017, 10(12), 2096; https://doi.org/10.3390/en10122096 - 11 Dec 2017

Cited by 8 | Viewed by 4395

Abstract

Several control schemes specifically designed to operate inverter-based industrial microgrids during voltage sags have been recently proposed. This paper first classifies these control schemes in three categories and then performs a comparative analysis of them. Representative control schemes of each category are selected, [...] Read more.

Several control schemes specifically designed to operate inverter-based industrial microgrids during voltage sags have been recently proposed. This paper first classifies these control schemes in three categories and then performs a comparative analysis of them. Representative control schemes of each category are selected, described and used to identify the main features and performance of the considered category. The comparison is based on the evaluation of several indexes, which measure the power quality of the installation and utility grid during voltage sags, including voltage regulation, reactive current injection and transient response. The paper includes selected simulation results from a 500 kVA industrial microgrid to validate the expected features of the considered control schemes. Finally, in view of the obtained results, the paper proposes an alternative solution to cope with voltage sags, which includes the use of a static compensator in parallel with the microgrid. The novelty of this proposal is the suitable selection of the control schemes for both the microgrid and the static compensator. The superior performance of the proposal is confirmed by the analysis of the quality indexes. Its practical limitations are also revealed, showing that the topic studied in this paper is still open for further research. Full article

(This article belongs to the Special Issue Control and Communication in Distributed Generation Systems)

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Open AccessArticle

Directionality Effects of Aligned Wind and Wave Loads on a Y-Shape Semi-Submersible Floating Wind Turbine under Rated Operational Conditions

by Shengtao Zhou, Baohua Shan, Yiqing Xiao, Chao Li, Gang Hu, Xiaoping Song, Yongqing Liu and Yimin Hu

Energies 2017, 10(12), 2097; https://doi.org/10.3390/en10122097 - 11 Dec 2017

Cited by 12 | Viewed by 4850

Abstract

The Y-shape (triangular) semi-submersible foundation has been adopted by most of the built full-scale floating wind turbines, such as Windfloat, Fukushima Mirai and Shimpuu. Considering the non-fully-symmetrical shape and met-ocean condition, the foundation laying angle relative to wind/wave directions will not only influence [...] Read more.

The Y-shape (triangular) semi-submersible foundation has been adopted by most of the built full-scale floating wind turbines, such as Windfloat, Fukushima Mirai and Shimpuu. Considering the non-fully-symmetrical shape and met-ocean condition, the foundation laying angle relative to wind/wave directions will not only influence the downtime and power efficiency of the floating turbine, but also the strength and fatigue safety of the whole structure. However, the dynamic responses induced by various aligned wind and wave load directions have scarcely been investigated comparatively before. In our study, the directionality effects are investigated by means of combined wind and wave tests and coupled multi-body simulations. By comparing the measured data in three load directions, it is found that the differences of platform motions are mainly derived from the wave loads and larger pitch motion can always be observed in one of the directions. To make certain the mechanism underlying the observed phenomena, a coupled multi-body dynamic model of the floating wind turbine is established and validated. The numerical results demonstrate that the second-order hydrodynamic forces contribute greatly to the directionality distinctions for surge and pitch, and the first-order hydrodynamic forces determine the variations of tower base bending moments and nacelle accelerations. These findings indicate the directionality effects should be predetermined comprehensively before installation at sea, which is important for the operation and maintenance of the Y-shape floating wind turbines. Full article

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

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Open AccessArticle

A Hierarchical Transactive Energy Management System for Energy Sharing in Residential Microgrids

by Most Nahida Akter, Md Apel Mahmud and Amanullah Maung Than Oo

Energies 2017, 10(12), 2098; https://doi.org/10.3390/en10122098 - 11 Dec 2017

Cited by 33 | Viewed by 4798

Abstract

This paper presents an analytical framework to develop a hierarchical energy management system (EMS) for energy sharing among neighbouring households in residential microgrids. The houses in residential microgrids are categorized into three different types, traditional, proactive and enthusiastic, based on the inclusion of [...] Read more.

This paper presents an analytical framework to develop a hierarchical energy management system (EMS) for energy sharing among neighbouring households in residential microgrids. The houses in residential microgrids are categorized into three different types, traditional, proactive and enthusiastic, based on the inclusion of solar photovoltaic (PV) systems and battery energy storage systems (BESSs). Each of these three houses has an individual EMS, which is defined as the primary EMS. Two other EMSs (secondary and tertiary) are also considered in the proposed hierarchical energy management framework for the purpose of effective energy sharing. The intelligences of each EMS are presented in this paper for the purpose of energy sharing in a residential microgrid along with the priorities. The effectiveness of the proposed hierarchical framework is evaluated on a residential microgrid in Australia. The analytical results clearly reflect that the proposed scheme effectively and efficiently shares the energy among neighbouring houses in a residential microgrid. Full article

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

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Open AccessArticle

A Case Study of Surface Borehole Wall Dislocation Induced by Top-Coal Longwall Mining

by Jinfeng Ju, Jialin Xu and Jingmin Xu

Energies 2017, 10(12), 2100; https://doi.org/10.3390/en10122100 - 11 Dec 2017

Cited by 8 | Viewed by 3373

Abstract

Underground coal extraction causes failure and movement of overlying strata, which could also result in the dislocation of vertical surface boreholes. Investigating the correlation between the dislocation of surface boreholes and the broken of overlying strata is of great significance in deducing the [...] Read more.

Underground coal extraction causes failure and movement of overlying strata, which could also result in the dislocation of vertical surface boreholes. Investigating the correlation between the dislocation of surface boreholes and the broken of overlying strata is of great significance in deducing the mining-induced dynamic movement of overlying strata, which cannot be seen inside the ‘black box’. Field measurement, laboratory experiment and theoretical analysis were employed to study the mechanism of the mining-induced dislocation of surface boreholes, and its relationship with the movement of overlying strata. Due to different deflection angles of adjacent strata, the horizontal movement of strata varies, and this contributes primarily to the dislocation of borehole wall. As the development of strata movement from the mining level towards surface, the position of borehole dislocation also occurred upwards, and the highest borehole dislocation occurred at the same position of overlying Key Stratum (KS). In other words, when a KS breaks, borehole dislocation will occur and develop from the bottom of this KS until the bottom of an upper KS. These key findings can provide a theoretical basis for deducing the mining-induced movement of overlying strata, determining the KS position and assessing the water conductivity of broken strata. Full article

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Analyses of Wind and Photovoltaic Energy Integration from the Promoting Scheme Point of View: Study Case of Romania

by Simona-Vasilica Oprea and Adela Bâra

Energies 2017, 10(12), 2101; https://doi.org/10.3390/en10122101 - 11 Dec 2017

Cited by 8 | Viewed by 3782

Abstract

The integration of renewable energy sources (RES) has several complex technical and economic aspects, such as: grid reinforcement, tertiary power reserves required for intermittent operation of RES, promoting or support scheme, etc. In this paper, the focus will be given to wind and [...] Read more.

The integration of renewable energy sources (RES) has several complex technical and economic aspects, such as: grid reinforcement, tertiary power reserves required for intermittent operation of RES, promoting or support scheme, etc. In this paper, the focus will be given to wind and photovoltaic energy integration from the promoting scheme point of view, with a special emphasis on the case of Romania. In this respect, we propose a model that shows the relation between wind and photovoltaic energy integration and support scheme in Romania. Due to the green certificates (GC) support scheme design that is related to several elements such as total consumption forecast, installed power of the plants based on each type of RES and their full load hours that are expected to vary, we also perform several sensitivity analyses. The GC support scheme implemented in Romania provides interesting insights regarding the installed power based on the primary energy source that could benefit from the GC for RES investors, policy and decision makers. Full article

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

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Open AccessArticle

Towards a New Generation of Building Envelope Calibration

by Carlos Fernández Bandera and Germán Ramos Ruiz

Energies 2017, 10(12), 2102; https://doi.org/10.3390/en10122102 - 11 Dec 2017

Cited by 36 | Viewed by 3515

Abstract

Building energy performance (BEP) is an ongoing point of reflection among researchers and practitioners. The importance of buildings as one of the largest activators in climate change mitigation was illustrated recently at the United Nations Framework Convention on Climate Change 21st Conference of [...] Read more.

Building energy performance (BEP) is an ongoing point of reflection among researchers and practitioners. The importance of buildings as one of the largest activators in climate change mitigation was illustrated recently at the United Nations Framework Convention on Climate Change 21st Conference of the Parties (COP21). Continuous technological improvements make it necessary to revise the methodology for energy calculations in buildings, as has recently happened with the new international standard ISO 52016-1 on Energy Performance of Buildings. In this area, there is a growing need for advanced tools like building energy models (BEMs). BEMs should play an important role in this process, but until now there has no been international consensus on how these models should reconcile the gap between measurement and simulated data in order to make them more reliable and affordable. Our proposal is a new generation of models that reconcile the traditional data-driven (inverse) modelling and law-driven (forward) modelling in a single type that we have called law-data-driven models. This achievement has greatly simplified past methodologies, and is a step forward in the search for a standard in the process of calibrating a building energy model. Full article

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

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Dynamic Analysis of Load Operations of Two-Stage SOFC Stacks Power Generation System

by Paulina Pianko-Oprych and S. M. Hosseini

Energies 2017, 10(12), 2103; https://doi.org/10.3390/en10122103 - 11 Dec 2017

Cited by 35 | Viewed by 4371

Abstract

The main purpose of this paper was to develop a complete dynamic model of a power generation system based on two serially connected solid oxide fuel cell stacks. The uniqueness of this study lies in a different number of fuel cells in the [...] Read more.

The main purpose of this paper was to develop a complete dynamic model of a power generation system based on two serially connected solid oxide fuel cell stacks. The uniqueness of this study lies in a different number of fuel cells in the stacks. The model consists of the electrochemical model, mass and energy balance equations implemented in MATLAB Simulink environment. Particular attention has been paid to the analysis of the transient response of the reformers, fuel cells and the burner. The dynamic behavior of the system during transient conditions was investigated by load step changing. The model evaluates electrical and thermal responses of the system at variable drawn current. It was found that a decrease of 40% in the 1st stage and 2nd solid oxide fuel cell (SOFC) stacks drawn current caused both stacks temperature to drop by 2%. An increase of the cell voltage for the 1st and 2nd SOFC stacks led to very fast steam reformer response combined with a slight decrease in reformer temperature, while a considerable burner temperature increase of 70 K can be observed. Predictions of the model provide the basic insight into the operation of the power generation-based SOFC system during various transients and support its further design modifications. Full article

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

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14458 KiB

Open AccessArticle

A Study of Spill Control Characteristics of JP-8 and Conventional Diesel Fuel with a Common Rail Direct Injection System

by Seomoon Yang, Hoonyoung Moon and Changhee Lee

Energies 2017, 10(12), 2104; https://doi.org/10.3390/en10122104 - 11 Dec 2017

Cited by 8 | Viewed by 4353

Abstract

Diversification of energy sources is a key task for decreasing environmental impacts and global emission of gases. JP-8, a fuel derived from natural gas, coal, biomass, and waste plastics, is a bright prospect. JP-8 is considered a multi-source multi-purpose fuel, with several applications. [...] Read more.

Diversification of energy sources is a key task for decreasing environmental impacts and global emission of gases. JP-8, a fuel derived from natural gas, coal, biomass, and waste plastics, is a bright prospect. JP-8 is considered a multi-source multi-purpose fuel, with several applications. A preliminary characterization of the JP-8 injection rate and injection quantity behavior was investigated based on the high-pressure common rail injection system used in a heavy-duty engine. According to the spill injection and injection pressure, a trade-off trend between injection rate and injection quantity was observed. As expected, pilot injection of JP-8 aviation fuel and diesel fuel affects the spray quantity and injection evolution of the subsequent operation without pilot injection. The difference in spilling between diesel and JP-8 aviation fuel is greater than the difference in injection amount per time; in the process of controlling the injector solenoid through ECU (Electric Control Units), the oil pressure valve and the needle valve operate to a higher extent in order to maintain the diesel fuel’s injection quantity volume. It was found that the total injection quantity was decreased by adding 20% pilot injection duration. Because the pilot injection quantity causes solenoid response, loss and needle lift stroke friction loss. Full article

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

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6176 KiB

Open AccessArticle

Positioning and Imaging Detection of Corona Discharge in Air with Double Helix Acoustic Sensors Array

by Ming Dong, Ao Ma, Ming Ren, Chongxing Zhang, Jiacheng Xie and Ricardo Albarracín

Energies 2017, 10(12), 2105; https://doi.org/10.3390/en10122105 - 11 Dec 2017

Cited by 13 | Viewed by 4063

Abstract

Corona discharge could be a serious hazard to the outdoor insulation of a high-voltage (HV) system and also is an important detection issue for insulation status diagnosis. In this study, a double-helix-ultrasonic-array (DHUA) sensor was developed for corona positioning, which showed a good [...] Read more.

Corona discharge could be a serious hazard to the outdoor insulation of a high-voltage (HV) system and also is an important detection issue for insulation status diagnosis. In this study, a double-helix-ultrasonic-array (DHUA) sensor was developed for corona positioning, which showed a good sensitivity to the ultrasonic signal originating from corona discharge and a satisfied directional response in static beam patterns. Based on the matting-based image fusion method, the acoustic intensity matrix was fused to a visual scene in real-time. This ultrasonic visualization technology was then evaluated with a simulation test and performed in a real air insulated substation (AIS), and showed a satisfied performance in terms of sensitivity and spatial location resolution. Full article

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

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7552 KiB

Open AccessArticle

Development of Numerical Heat Transfer and the Structural Model to Design Slim and Translucent Vacuum Layer Type Insulation Panels to Retrofitting Insulation in Existing Buildings

by Zhang Yang, Takao Katsura, Masahiro Aihara, Makoto Nakamura and Katsunori Nagano

Energies 2017, 10(12), 2108; https://doi.org/10.3390/en10122108 - 11 Dec 2017

Cited by 9 | Viewed by 4534

Abstract

The authors develop slim and light-weight vacuum insulation panels (VIPs) by producing vacuum layers with spacers and plastic plates. The developed VIPs have the advantages of a low cost and easy installation, thus facilitating retrofitting insulation of existing buildings. In addition, one of [...] Read more.

The authors develop slim and light-weight vacuum insulation panels (VIPs) by producing vacuum layers with spacers and plastic plates. The developed VIPs have the advantages of a low cost and easy installation, thus facilitating retrofitting insulation of existing buildings. In addition, one of the developed VIPs is slim and translucent so it can be easily used for windows in an internal installation. In this paper, the authors first propose a vacuum layer type slim translucent VIP and focus on a reasonable design method. Next, the authors introduce the design process in which the structural design is obtained with element mechanical analysis and a three-dimensional analysis is conducted for the VIP element. In the study, a heat transfer model is used to predict the insulation performance through finite element analysis (FEA). Subsequently, the authors perform an experiment to measure the thermal conductivity in a guarded hot plate apparatus to validate the performance prediction. Finally, case studies are performed to confirm how the different design conditions affect the insulation performance. The optimum design of the vacuum layer type slim and translucent VIP will have a sufficient structural strength to hold and maintain the vacuum layer. The thermal conductivity is approximately 0.007

W / (m \cdot K)

, which can effectively improve the insulation performance in applications. Full article

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6583 KiB

Open AccessArticle

Optimal Design of a Multi-Carrier Microgrid (MCMG) Considering Net Zero Emission

by Vahid Amir, Shahram Jadid and Mehdi Ehsan

Energies 2017, 10(12), 2109; https://doi.org/10.3390/en10122109 - 12 Dec 2017

Cited by 17 | Viewed by 3887

Abstract

In this paper, a two-stage optimum planning and design method for a multi-carrier microgrid (MCMG) is presented in the targeted operation period considering energy purchasing and the component’s maintenance costs. An MCMG is most likely owned by a community or small group of [...] Read more.

In this paper, a two-stage optimum planning and design method for a multi-carrier microgrid (MCMG) is presented in the targeted operation period considering energy purchasing and the component’s maintenance costs. An MCMG is most likely owned by a community or small group of public and private sectors comprising loads and distributed energy resources (DERs) with the ability of self-supply to regulate the flows of various energies to local consumers. The operation cost is undoubtedly reduced by selecting the proper components. In the proposed model, the investment and operation and maintenance costs of MCMG are simultaneously carried out in order to choose the right component and its size in the given period. Moreover, in this innovative model, net zero emission (NZE) is regarded as an environmental constraint. The genetic algorithm of MATLAB and the mixed-integer nonlinear programming (MINLP) technique of GAMS (general algebraic modeling system) software are used to solve the optimization problem. Illustrative examples show the efficiency of the proposed model. Full article

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1467 KiB

Open AccessArticle

Chance-Constrained Real-Time Dispatch with Renewable Uncertainty Based on Dynamic Load Flow

by Pei Bie, Buhan Zhang, Hang Li, Yong Wang, Le Luan, Guoyan Chen and Guojun Lu

Energies 2017, 10(12), 2111; https://doi.org/10.3390/en10122111 - 12 Dec 2017

Cited by 4 | Viewed by 2873

Abstract

In this paper, a comprehensive real-time dispatch model considering renewable uncertainty based on dynamic load flow (DLF) is proposed. Through DLF, the primary and secondary frequency regulation amount caused by the variation of renewable energy as well as the line flow when primary [...] Read more.

In this paper, a comprehensive real-time dispatch model considering renewable uncertainty based on dynamic load flow (DLF) is proposed. Through DLF, the primary and secondary frequency regulation amount caused by the variation of renewable energy as well as the line flow when primary and secondary regulation are deployed can be obtained easily. Not only the frequency constraints, but also the regular constraints like generator production limits and line flow limits are respected under both primary and secondary frequency regulation. To solve the dispatch problem with renewable uncertainty, chance-constrained programming based on cumulants and Cornish-fisher expansions (CCP-CMCF) is adopted to get the probability of holding the chance constraints and then the real-time dispatch model can be transformed into a quadratic programming. The simulation results show that the dispatch model proposed in this paper can deal with both primary and secondary regulation well and has a fast computation speed. Full article

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

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1236 KiB

Open AccessArticle

Bioethanol Production from Cachaza as Hydrogen Feedstock: Effect of Ammonium Sulfate during Fermentation

by Nestor Sanchez, Ruth Yolanda Ruiz, Nicolas Infante and Martha Cobo

Energies 2017, 10(12), 2112; https://doi.org/10.3390/en10122112 - 12 Dec 2017

Cited by 13 | Viewed by 3829

Abstract

Cachaza is a type of non-centrifugal sugarcane press-mud that, if it is not employed efficiently, generates water pollution, soil eutrophication, and the spread of possible pathogens. This biomass can be fermented to produce bioethanol. Our intention is to obtain bioethanol that can be [...] Read more.

Cachaza is a type of non-centrifugal sugarcane press-mud that, if it is not employed efficiently, generates water pollution, soil eutrophication, and the spread of possible pathogens. This biomass can be fermented to produce bioethanol. Our intention is to obtain bioethanol that can be catalytically reformed to produce hydrogen (H₂) for further use in fuel cells for electricity production. However, some impurities could negatively affect the catalyst performance during the bioethanol reforming process. Hence, the aim of this study was to assess the fermentation of Cachaza using ammonium sulfate ((NH₄)₂SO₄) loadings and Saccharomyces cerevisiae strain to produce the highest ethanol concentration with the minimum amount of impurities in anticipation of facilitating further bioethanol purification and reforming for H₂ production. The results showed that ethanol production from Cachaza fermentation was about 50 g·L⁻¹ and the (NH₄)₂SO₄ addition did not affect its production. However, it significantly reduced the production of branched alcohols. When a 160 mg·L⁻¹ (NH₄)₂SO₄ was added to the fermentation culture, 2-methyl-1-propanol was reduced by 41% and 3-methyl-1-butanol was reduced by 6%, probably due to the repression of the catabolic nitrogen mechanism. Conversely, 1-propanol doubled its concentration likely due to the higher threonine synthesis promoted by the reducing sugar presence. Afterwards, we employed the modified Gompertz model to fit the ethanol, 2M1P, 3M1B, and 1-propanol production, which provided acceptable fits (R² > 0.881) for the tested compounds during Cachaza fermentation. To the best of our knowledge, there are no reports of the modelling of aliphatic production during fermentation; this model will be employed to calculate yields with further scaling and for life cycle assessment. Full article

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

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4663 KiB

Open AccessArticle

Reducing WCET Overestimations by Correcting Errors in Loop Bound Constraints

by Fanqi Meng and Xiaohong Su

Energies 2017, 10(12), 2113; https://doi.org/10.3390/en10122113 - 12 Dec 2017

Cited by 3 | Viewed by 3324

Abstract

In order to reduce overestimations of worst-case execution time (WCET), in this article, we firstly report a kind of specific WCET overestimation caused by non-orthogonal nested loops. Then, we propose a novel correction approach which has three basic steps. The first step is [...] Read more.

In order to reduce overestimations of worst-case execution time (WCET), in this article, we firstly report a kind of specific WCET overestimation caused by non-orthogonal nested loops. Then, we propose a novel correction approach which has three basic steps. The first step is to locate the worst-case execution path (WCEP) in the control flow graph and then map it onto source code. The second step is to identify non-orthogonal nested loops from the WCEP by means of an abstract syntax tree. The last step is to recursively calculate the WCET errors caused by the loose loop bound constraints, and then subtract the total errors from the overestimations. The novelty lies in the fact that the WCET correction is only conducted on the non-branching part of WCEP, thus avoiding potential safety risks caused by possible WCEP switches. Experimental results show that our approach reduces the specific WCET overestimation by an average of more than 82%, and 100% of corrected WCET is no less than the actual WCET. Thus, our approach is not only effective but also safe. It will help developers to design energy-efficient and safe real-time systems. Full article

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

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16107 KiB

Open AccessArticle

The Effect of Wind Forcing on Modeling Coastal Circulation at a Marine Renewable Test Site

by Lei Ren, Diarmuid Nagle, Michael Hartnett and Stephen Nash

Energies 2017, 10(12), 2114; https://doi.org/10.3390/en10122114 - 12 Dec 2017

Cited by 6 | Viewed by 4518

Abstract

The hydrodynamic circulation in estuaries is primarily driven by tides, river inflows and surface winds. While tidal and river data can be quite easily obtained for input to hydrodynamic models, sourcing accurate surface wind data is problematic. Inaccurate wind data can lead to [...] Read more.

The hydrodynamic circulation in estuaries is primarily driven by tides, river inflows and surface winds. While tidal and river data can be quite easily obtained for input to hydrodynamic models, sourcing accurate surface wind data is problematic. Inaccurate wind data can lead to inaccuracies in the surface currents computed by three-dimensional hydrodynamic models. In this research, a high-resolution wind model was coupled with a three-dimensional hydrodynamic model of Galway Bay, a semi-enclosed estuary on the west coast of Ireland, to investigate the effect of wind forcing on model accuracy. Two wind-forcing conditions were investigated: (1) using wind data measured onshore on the NUI Galway campus (NUIG) and (2) using offshore wind data provided by a high resolution wind model (HR). A scenario with no wind forcing (NW) was also assessed. The onshore wind data varied with time but the speed and direction were applied across the full model domain. The modeled offshore wind fields varied with both time and space. The effect of wind forcing on modeled hydrodynamics was assessed via comparison of modeled surface currents with surface current measurements obtained from a High-Frequency (HF) radar Coastal Ocean Dynamics Applications Radar (CODAR) observation system. Results indicated that winds were most significant in simulating the north-south surface velocity component. The model using high resolution temporally- and spatially-varying wind data achieved better agreement with the CODAR surface currents than the model using the onshore wind measurements and the model without any wind forcing. 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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9081 KiB

Open AccessArticle

A Modified Version of the RNG k–ε Turbulence Model for the Scale-Resolving Simulation of Internal Combustion Engines

by Vesselin Krassimirov Krastev, Luca Silvestri and Giacomo Falcucci

Energies 2017, 10(12), 2116; https://doi.org/10.3390/en10122116 - 13 Dec 2017

Cited by 29 | Viewed by 4334

Abstract

The unsteady and random character of turbulent flow motion is a key aspect of the multidimensional modeling of internal combustion engines (ICEs). A typical example can be found in the prediction of the cycle-to-cycle variability (CCV) in modern, highly downsized gasoline direct injection [...] Read more.

The unsteady and random character of turbulent flow motion is a key aspect of the multidimensional modeling of internal combustion engines (ICEs). A typical example can be found in the prediction of the cycle-to-cycle variability (CCV) in modern, highly downsized gasoline direct injection (GDI) engines, which strongly depends on the accurate simulation of turbulent in-cylinder flow structures. The current standard for turbulence modeling in ICEs is still represented by the unsteady form of Reynold-averaged Navier Stokes equations (URANS), which allows the simulation of full engine cycles at relatively low computational costs. URANS-based methods, however, are only able to return a statistical description of turbulence, as the effects of all scales of motion are entirely modeled. Therefore, during the last decade, scale-resolving methods such as large eddy simulation (LES) or hybrid URANS/LES approaches are gaining increasing attention among the engine-modeling community. In the present paper, we propose a scale-resolving capable modification of the popular RNG k–

ε

URANS model. The modification is based on a detached-eddy simulation (DES) framework and allows one to explicitly set the behavior (URANS, DES or LES) of the model in different zones of the computational domain. The resulting zonal formulation has been tested on two reference test cases, comparing the numerical predictions with the available experimental data sets and with previous computational studies. Overall, the scale-resolved part of the computed flow has been found to be consistent with the expected flow physics, thus confirming the validity of the proposed simulation methodology. Full article

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

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445 KiB

Open AccessArticle

Environmental Impact of End-of-Life Tires: Life Cycle Assessment Comparison of Three Scenarios from a Case Study in Valle Del Cauca, Colombia

by Oscar O. Ortíz-Rodríguez, William Ocampo-Duque and Laura I. Duque-Salazar

Energies 2017, 10(12), 2117; https://doi.org/10.3390/en10122117 - 13 Dec 2017

Cited by 33 | Viewed by 6661

Abstract

Life Cycle Assessment methodology has been applied to estimate diverse environmental impacts of different usage alternatives for worn-out tires at the end of their useful life in a case study at the Department of Valle del Cauca, Colombia. Different real scenarios were compared, [...] Read more.

Life Cycle Assessment methodology has been applied to estimate diverse environmental impacts of different usage alternatives for worn-out tires at the end of their useful life in a case study at the Department of Valle del Cauca, Colombia. Different real scenarios were compared, which allowed for the assessment of the best environmental option for the management of worn-out tires. A method developed in the Institute of Environmental Sciences at University of Leiden, better known as CML-2001, was used to calculate the environmental impact indicators. The results show that the incineration of whole tires in cement plants, and the activities of grinding and floor manufacturing from granulated rubber, exhibited the best indicators, especially in terms of environmental load avoidance through the recovery of materials. Finally, the categories of depletion of the ozone layer, acidification, global warming potential, depletion of abiotic resources, and photochemical ozone formation revealed that the strongest environmental impacts are associated with retreading and the production of multipart asphalt. This is due to the use of synthetic rubber in the former alternative, and of liquid asphalt, gravel, and diesel consumption in the latter. Full article

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

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5106 KiB

Open AccessArticle

Distribution and Presence of Polymers in Porous Media

by Juan Zhao, Hongfu Fan, Qing You and Yi Jia

Energies 2017, 10(12), 2118; https://doi.org/10.3390/en10122118 - 13 Dec 2017

Cited by 17 | Viewed by 3317

Abstract

In order to better utilize the residual polymers formed after polymer flooding, the distribution and the presence of the polymers after polymer flooding were studied. This paper studied the vertical and plane distribution of the hydrophobically-associating polymer in addition to measuring the parameters [...] Read more.

In order to better utilize the residual polymers formed after polymer flooding, the distribution and the presence of the polymers after polymer flooding were studied. This paper studied the vertical and plane distribution of the hydrophobically-associating polymer in addition to measuring the parameters after polymer flooding, which is important for numerical reservoir simulation. The results showed that the polymers mainly enter into the high permeability zone and distribute in the mainstream line area with only a small portion in the wing area. Based on the comparison of various experimental methods, double-slug experiments were chosen to measure the inaccessible pore volume and retention, which is considered to be the most accurate, most time-consuming and most complex method. Following this, we improved the processing method of experimental data by reducing it to one experiment with two parameters. At the same time, we further enhanced the accuracy of the experimental results. The results show that at 1750 mg/L, the inaccessible pore volume of the polymer is 25.8%. When the detention is 68.2 µg/g, the inaccessible pore volume constituted 22% of the total polymer, with the other 77.7% being the dissolved polymer. Moreover, the static adsorption and dynamic detention were measured, with the results showing that the static adsorption is larger than dynamic detention. Therefore, in the numerical reservoir simulation, using the static adsorption capacity instead of the dynamic detention is unreasonable. The double-slug method was chosen since it is more accurate for the determination of various parameters. Meanwhile, in order to enhance the accuracy of results, we improved the treatment of data. Full article

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3329 KiB

Open AccessArticle

Potential of Tropical Fruit Waste Biomass for Production of Bio-Briquette Fuel: Using Indonesia as an Example

by Anna Brunerová, Hynek Roubík, Milan Brožek, David Herák, Vladimír Šleger and Jana Mazancová

Energies 2017, 10(12), 2119; https://doi.org/10.3390/en10122119 - 13 Dec 2017

Cited by 38 | Viewed by 28807

Abstract

Within developing countries, there is an appeal to use waste biomass for energy generation in the form of bio-briquettes. This study investigated the potential use of bio-briquettes that are produced from the waste biomass of the following tropical fruits: durian (Durio zibethinus [...] Read more.

Within developing countries, there is an appeal to use waste biomass for energy generation in the form of bio-briquettes. This study investigated the potential use of bio-briquettes that are produced from the waste biomass of the following tropical fruits: durian (Durio zibethinus), coconut (Cocos nucifera), coffee (Coffea arabica), cacao (Theobroma cacao), banana (Musa acuminata) and rambutan (Nephelium lappaceum). All fruit waste biomass samples exhibited an extremely high level of initial moisture content (78.22% in average). Fruit samples with the highest proportion of fruit waste biomass (of total unprocessed fruit mass) were represented by cacao (83.82%), durian (62.56%) and coconut (56.83%). Highest energy potentials (calorific value) of fruit waste biomass were observed in case of coconut (18.22 MJ∙kg⁻¹), banana (17.79 MJ∙kg⁻¹) and durian (17.60 MJ∙kg⁻¹) fruit samples, whereas fruit waste biomass with the lowest level of ash content originated from the rambutan (3.67%), coconut (4.52%), and durian (5.05%) fruit samples. When investigating the energy demands to produce bio-briquettes from such feedstock materials, the best results (lowest amount of required deformation energy in combination with highest level of bio-briquette bulk density) were achieved by the rambutan, durian and banana fruit waste biomass samples. Finally, all investigated bio-briquette samples presented satisfactory levels of bulk density (>1050 kg∙m⁻³). In conclusion, our results indicated the practicability and viability of such bio-briquette fuel production, as well as supporting the fact that bio-briquettes from tropical fruit waste biomass can offer a potentially attractive energy source with many benefits, especially in rural areas. Full article

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

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338 KiB

Open AccessArticle

Measuring Renewable Energy Development in the Eastern Bloc of the European Union

by Daniela Cristina Momete

Energies 2017, 10(12), 2120; https://doi.org/10.3390/en10122120 - 13 Dec 2017

Cited by 12 | Viewed by 4817

Abstract

This paper aims to investigate the energy development in terms of renewable energy in the Eastern Bloc European Union member states. Energy is a topic of planetary implications and the analysis of the development of renewable energy sources (RES) in parts of the [...] Read more.

This paper aims to investigate the energy development in terms of renewable energy in the Eastern Bloc European Union member states. Energy is a topic of planetary implications and the analysis of the development of renewable energy sources (RES) in parts of the world where the fossil fuels are scarce is of tremendous importance. In the first section, the paper concisely explores the energy landscape of the European Union (EU), revealing important concerns. The second section introduces an index of renewable energy development (IRED) which captures the complexity of the development of RES and is based on two components, each containing three factors built on efforts and outcomes in RES development. IRED is further applied on a cross-country analysis based on the Eastern Bloc of the EU member states for 2005–2015 interval, revealing the best and worst performers. The application of IRED might contribute to a better understanding of the needed efforts required by different countries in their quest towards energy security, efficient energy use and emissions control. The findings of this paper might conduct to the identification of the best practices which could be spread throughout EU and might contribute to a more rigorous development of policymaking in the energy area. Full article

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

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Open AccessArticle

Effect on Vehicle Turbocharger Exhaust Gas Energy Utilization for the Performance of Centrifugal Compressors under Plateau Conditions

by Hong Zhang, Hang Zhang and Zhuo Wang

Energies 2017, 10(12), 2121; https://doi.org/10.3390/en10122121 - 13 Dec 2017

Cited by 6 | Viewed by 4965

Abstract

This paper is focused on the performance of centrifugal compressors for vehicle turbochargers operating at high altitude. The reasons for turbocharged diesel engine power loss increases and bad economy performance caused by exhaust gas energy utilization are investigated. The atmosphere’s impact on the [...] Read more.

This paper is focused on the performance of centrifugal compressors for vehicle turbochargers operating at high altitude. The reasons for turbocharged diesel engine power loss increases and bad economy performance caused by exhaust gas energy utilization are investigated. The atmosphere’s impact on the turbocharger centrifugal compressor’s energy distribution characteristics under the plateau is discussed. The key parameters that affect compressor characteristics are concluded in a theoretical method. A simulation calculation model is established to accurately predict compressor performance at high altitude. By comparing the experimental results, the calculation results are validated. The details of the internal flow fields analysis, including critical parameters of a compressor operating at high altitude, are analyzed. The results show that with the increase of altitude from 0 m to 4500 m, the peak efficiency of the compressor is reduced by 2.4%, while the peak pressure ratio is increased by 7%. The main influence characters of the plateau environment on the turbocharger centrifugal compressor performance, such as blade loads, exergy utilization and entropy distribution are concluded. The key factors for compressor performance and compressor energy flow control design method operated at high altitude are obtained. Full article

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

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Open AccessArticle

An Improved Lubrication Model between Piston Rings and Cylinder Liners with Consideration of Liner Dynamic Deformations

by Guoxing Li, Fengshou Gu, Tie Wang, Xingchen Lu, Li Zhang, Chunfeng Zhang and Andrew Ball

Energies 2017, 10(12), 2122; https://doi.org/10.3390/en10122122 - 13 Dec 2017

Cited by 15 | Viewed by 7883

Abstract

The friction pair of piston rings and cylinder liner is one of the most important friction couplings in an internal combustion engine. It influences engine efficiency and service life. Under the excitation of piston slaps, the dynamic deformation of cylinder liner is close [...] Read more.

The friction pair of piston rings and cylinder liner is one of the most important friction couplings in an internal combustion engine. It influences engine efficiency and service life. Under the excitation of piston slaps, the dynamic deformation of cylinder liner is close to the surface roughness magnitudes, which can affect the friction and lubrication performance between the piston rings and cylinder assemblies. To investigate the potential influences of structural deformations to tribological behaviours of cylinder assemblies, the dynamic deformation of the inner surface due to pistons slaps is obtained by dynamic simulations, and then coupled into an improved lubrication model. Different from the traditional lubrication model which takes the pressure stress factor and shear stress factor to be constant, the model proposed in this paper calculated these factors in real time using numerical integration to achieve a more realistic simulation. Based on the improved piston rings and cylinder liner lubrication model, the minimum oil film thickness and friction force curves are obtained for an entire work cycle. It shows that the friction force obtained from the improved model manifests clear oscillations in each stoke, which is different from the smoothed profiles predicted traditionally. Moreover, the average amplitude of the friction forces also shows clear reduction. Full article

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Open AccessArticle

Chip Temperature-Based Workload Allocation for Holistic Power Minimization in Air-Cooled Data Center

by Yan Bai and Lijun Gu

Energies 2017, 10(12), 2123; https://doi.org/10.3390/en10122123 - 13 Dec 2017

Cited by 10 | Viewed by 3379

Abstract

Minimizing the energy consumption is a dominant problem in data center design and operation. To cope with this issue, the common approach is to optimize the data center layout and the workload distribution among servers. Previous works have mainly adopted the temperature at [...] Read more.

Minimizing the energy consumption is a dominant problem in data center design and operation. To cope with this issue, the common approach is to optimize the data center layout and the workload distribution among servers. Previous works have mainly adopted the temperature at the server inlet as the optimization constraint. However, the inlet temperature does not properly characterize the server’s thermal state. In this paper, a chip temperature-based workload allocation strategy (CTWA-MTP) is proposed to reduce the holistic power consumption in data centers. Our method adopts an abstract heat-flow model to describe the thermal environment in data centers and uses a thermal resistance model to describe the convective heat transfer of the server. The core optimizes the workload allocation with respect to the chip temperature threshold. In addition, the temperature-dependent leakage power of the server has been considered in our model. The proposed method is described as a constrained nonlinear optimization problem to find the optimal solution by a genetic algorithm (GA). We applied the method to a sample data center constructed with computational fluid dynamics (CFD) software. By comparing the simulation results with other different workload allocation strategies, the proposed method prevents the servers from overcooling and achieves a substantial energy saving by optimizing the workload allocation in an air-cooled data center. Full article

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13619 KiB

Open AccessArticle

Power Swing Generated in Francis Turbines by Part Load and Overload Instabilities

by David Valentín, Alexandre Presas, Eduard Egusquiza, Carme Valero, Mònica Egusquiza and Matias Bossio

Energies 2017, 10(12), 2124; https://doi.org/10.3390/en10122124 - 13 Dec 2017

Cited by 67 | Viewed by 5557

Abstract

Hydropower plays a key role in the actual energy market due to its fast response and regulation capacity. In that way, hydraulic turbines are increasingly demanded to work at off-design conditions, where complex flow patterns and cavitation appear, especially in Francis turbines. The [...] Read more.

Hydropower plays a key role in the actual energy market due to its fast response and regulation capacity. In that way, hydraulic turbines are increasingly demanded to work at off-design conditions, where complex flow patterns and cavitation appear, especially in Francis turbines. The draft tube cavitation surge is a hydraulic phenomenon that appears in Francis turbines below and above its Best Efficiency Point (BEP). It is a low frequency phenomenon consisting of a vortex rope in the runner outlet and draft tube, which can become unstable when its frequency coincides with a natural frequency of the hydraulic circuit. At this situation, the output power can significantly swing, endangering the electrical grid stability. This study is focused on the detection of these instabilities in Francis turbines and their relationship with the output power swings. To do so, extensive experimental tests for different operating conditions have been carried out in a large prototype Francis turbine (444 MW of rated power) within the frame of the European Project Hyperbole (FP7-ENERGY-2013-1). Several sensors have been installed in the hydraulic circuit (pressure sensors in the draft tube, spiral casing, and penstock), in the rotating and static structures (vibration sensors, proximity probes, and strain gauges in the runner and in the shaft), as well as in the electrical side (output power, intensity, and voltage). Moreover, a numerical Finite Element Method (FEM) has been also used to relate the hydraulic excitation with the output power swing. Full article

(This article belongs to the Special Issue Hydropower 2017)

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Boolean Network-Based Sensor Selection with Application to the Fault Diagnosis of a Nuclear Plant

by Zhe Dong

Energies 2017, 10(12), 2125; https://doi.org/10.3390/en10122125 - 13 Dec 2017

Cited by 12 | Viewed by 3245

Abstract

Fault diagnosis is crucial for the operation of energy systems such as nuclear plants, and heavily relies on various types of sensors for temperature, pressure, concentration, etc. Due to the redundancy of sensors in each energy system, the sensor selection scheme can deeply [...] Read more.

Fault diagnosis is crucial for the operation of energy systems such as nuclear plants, and heavily relies on various types of sensors for temperature, pressure, concentration, etc. Due to the redundancy of sensors in each energy system, the sensor selection scheme can deeply influence the diagnostic efficiency. In this paper, a Boolean network (BN) with its linear representation is proposed for describing the fault propagation among sensors. Both the sufficient condition of fault detectability and that of fault discriminability are given. Then, a sensor selection method for fault detection and discrimination is proposed. Finally, the theoretic result is applied to realize the diagnosis oriented sensor selection for a nuclear steam supply system based on a modular high temperature gas-cooled reactor (MHTGR). The computation and simulation results verify the correctness of the theoretical results. Full article

(This article belongs to the Special Issue 2017 Prognostics and System Health Management Conference)

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A Wind Power Plant with Thermal Energy Storage for Improving the Utilization of Wind Energy

by Chang Liu, Mao-Song Cheng, Bing-Chen Zhao and Zhi-Min Dai

Energies 2017, 10(12), 2126; https://doi.org/10.3390/en10122126 - 14 Dec 2017

Cited by 26 | Viewed by 10269

Abstract

The development of the wind energy industry is seriously restricted by grid connection issues and wind energy generation rejections introduced by the intermittent nature of wind energy sources. As a solution of these problems, a wind power system integrating with a thermal energy [...] Read more.

The development of the wind energy industry is seriously restricted by grid connection issues and wind energy generation rejections introduced by the intermittent nature of wind energy sources. As a solution of these problems, a wind power system integrating with a thermal energy storage (TES) system for district heating (DH) is designed to make best use of the wind power in the present work. The operation and control of the system are described in detail. A one-dimensional system model of the system is developed based on a generic model library using the object-oriented language Modelica for system modeling. Validations of the main components of the TES module are conducted against experimental results and indicate that the models can be used to simulate the operation of the system. The daily performance of the integrated system is analyzed based on a seven-day operation. And the influences of system configurations on the performance of the integrated system are analyzed. The numerical results show that the integrated system can effectively improve the utilization of total wind energy under great wind power rejection. Full article

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

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Sliding Surface in Consensus Problem of Multi-Agent Rigid Manipulators with Neural Network Controller

by Thang Nguyen Trong and Minh Nguyen Duc

Energies 2017, 10(12), 2127; https://doi.org/10.3390/en10122127 - 14 Dec 2017

Cited by 7 | Viewed by 4197

Abstract

Based on Lyapunov theory, this research demonstrates the stability of the sliding surface in the consensus problem of multi-agent systems. Each agent in this system is represented by the dynamically uncertain robot, unstructured disturbances, and nonlinear friction, especially when the dynamic function of [...] Read more.

Based on Lyapunov theory, this research demonstrates the stability of the sliding surface in the consensus problem of multi-agent systems. Each agent in this system is represented by the dynamically uncertain robot, unstructured disturbances, and nonlinear friction, especially when the dynamic function of agent is unknown. All system states use neural network online weight tuning algorithms to compensate for the disturbance and uncertainty. Each agent in the system has a different position, and their trajectory approach to the same target is from each distinct orientation. In this research, we analyze the design of the sliding surface for this model and demonstrate which type of sliding surface is the best for the consensus problem. Lastly, simulation results are presented to certify the correctness and the effectiveness of the proposed control method. Full article

(This article belongs to the Special Issue Advanced Electric Devices and Technologies for Electric-Drive Robotics)

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Open AccessArticle

Seven Operation Modes and Simulation Models of Solar Heating System with PCM Storage Tank

by Juan Zhao, Yasheng Ji, Yanping Yuan, Zhaoli Zhang and Jun Lu

Energies 2017, 10(12), 2128; https://doi.org/10.3390/en10122128 - 14 Dec 2017

Cited by 20 | Viewed by 4292

Abstract

A physical model and dynamic simulation models of a solar phase-change heat storage heating system with a plate solar collector, phase-change material (PCM) storage tank, plate heat exchanger, and auxiliary heat sources were established. A control strategy and numerical models for each of [...] Read more.

A physical model and dynamic simulation models of a solar phase-change heat storage heating system with a plate solar collector, phase-change material (PCM) storage tank, plate heat exchanger, and auxiliary heat sources were established. A control strategy and numerical models for each of seven different operation modes that cover the entire heating season of the system were developed for the first time. The seven proposed operation modes are Mode 1: free cooling; Mode 2: reservation of heat absorbed by the solar collector in the PCM storage tank when there is no heating demand; Mode 3: direct supply of the heating demand by the solar collector; Mode 4: use of the heat absorbed by the solar collector to meet the heating demands, with the excess heat stored in the PCM storage tank; Mode 5: use of heat stored in the PCM storage tank to meet the heating demands, Mode 6: combined use of heat stored in the PCM storage tank and the auxiliary heating sources to meet the heating demands; and Mode 7: exclusive use of the auxiliary heat sources in order to meet the heating demands. Mathematical models were established for each of the above seven operation modes, taking into consideration the effects of the outdoor meteorological parameters and terminal load on the heating system. The real-time parameters for the entire heating season of the system with respect to the different operation modes can be obtained by solving the simulation models, and used as reference for the optimal design and operation of the actual system. Full article

(This article belongs to the Special Issue Solar Technologies for Buildings)

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Near State Vector Selection-Based Model Predictive Control with Common Mode Voltage Mitigation for a Three-Phase Four-Leg Inverter

by Abdul Mannan Dadu, Saad Mekhilef, Tey Kok Soon, Mehdi Seyedmahmoudian and Ben Horan

Energies 2017, 10(12), 2129; https://doi.org/10.3390/en10122129 - 14 Dec 2017

Cited by 7 | Viewed by 4804

Abstract

A high computational burden is required in conventional model predictive control, as all of the voltage vectors of a power inverter are used to predict the future behavior of the system. Apart from that, the common mode voltage (CMV) of a three-phase four-leg [...] Read more.

A high computational burden is required in conventional model predictive control, as all of the voltage vectors of a power inverter are used to predict the future behavior of the system. Apart from that, the common mode voltage (CMV) of a three-phase four-leg inverter utilizes up to half of the DC-link voltage due to the use of all of the available voltage vectors. Thus, this paper proposes a near state vector selection-based model predictive control (NSV-MPC) scheme to mitigate the CMV and reduce computational burden. In the proposed technique, only six active voltage vectors are used in the predictive model, and the vectors are selected based on the position of the future reference vector. In every sampling period, the position of the reference current is used to detect the voltage vectors surrounding the reference voltage vector. Besides the six active vectors, one of the zero vectors is also used. The proposed technique is compared with the conventional control scheme in terms of execution time, CMV variation, and load current ripple in both simulation and an experimental setup. The LabVIEW Field programmable gate array rapid prototyping controller is used to validate the proposed control scheme experimentally, and demonstrate that the CMV can be bounded within one-fourth of the DC-link voltage. Full article

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Wide Area Coordinated Control of Multi-FACTS Devices to Damp Power System Oscillations

by Shiyun Xu, Ying Yang, Kaixiang Peng, Linlin Li, Tasawar Hayat and Ahmed Alsaedi

Energies 2017, 10(12), 2130; https://doi.org/10.3390/en10122130 - 14 Dec 2017

Cited by 4 | Viewed by 3890

Abstract

Aiming at damping the inter-area oscillations of power systems, the present study proposes a wide-area decentralized coordinated control framework, where the upper-level controller is designed to coordinate the lower-level multiple FACTS devices. Based on the polytopic differential inclusion method, the derived controller adopts [...] Read more.

Aiming at damping the inter-area oscillations of power systems, the present study proposes a wide-area decentralized coordinated control framework, where the upper-level controller is designed to coordinate the lower-level multiple FACTS devices. Based on the polytopic differential inclusion method, the derived controller adopts a decentralized structure and it is guaranteed to be robust to meet the demand of operation under multiple operating conditions. Since time delay of wide area signal transmission is inevitable, in what follows, the quantum evolution algorithm (QEA) method is introduced to find an optimal solution of the time-delay coordinated controller. In this regard, the stability of the system with a prescribed time delay is guaranteed and the system damping ratio is increased. Effectiveness and applicability of the proposed controller design methods have been demonstrated through numerical simulations. 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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Does Dynamic Efficiency of Public Policy Promote Export Prformance? Evidence from Bioenergy Technology Sector

by Bongsuk Sung and Woo-Yong Song

Energies 2017, 10(12), 2131; https://doi.org/10.3390/en10122131 - 14 Dec 2017

Cited by 4 | Viewed by 3494

Abstract

This study examines how the dynamic efficiency of public policy influences the export performance of bioenergy technologies in the short and long run using panel data over the 1995–2012 period for 16 countries that are members of the OECD. Various dynamic panel framework [...] Read more.

This study examines how the dynamic efficiency of public policy influences the export performance of bioenergy technologies in the short and long run using panel data over the 1995–2012 period for 16 countries that are members of the OECD. Various dynamic panel framework tests to check data characteristics are performed. The study found evidence of co-movement among the series, and set up the panel vector error correction mechanism to evaluate the short- and long-run Granger-causality between the following variables: dynamic efficiency of public policy, export, and environmental policy stringency. This study highlighted positive effects of the dynamic efficiency of public policy and environmental policy efforts on exports in both the short and long run. This study proposes policy considerations based on its results. 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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Energy Efficiency and Network Performance: A Reality Check in SDN-Based 5G Systems

by Adriana Fernández-Fernández, Cristina Cervelló-Pastor and Leonardo Ochoa-Aday

Energies 2017, 10(12), 2132; https://doi.org/10.3390/en10122132 - 14 Dec 2017

Cited by 19 | Viewed by 4611

Abstract

The increasing power consumption and related environmental implications currently generated by large data networks have become a major concern over the last decade. Given the drastic traffic increase expected in 5G dense environments, the energy consumption problem becomes even more concerning and challenging. [...] Read more.

The increasing power consumption and related environmental implications currently generated by large data networks have become a major concern over the last decade. Given the drastic traffic increase expected in 5G dense environments, the energy consumption problem becomes even more concerning and challenging. In this context, Software-Defined Networks (SDN), a key technology enabler for 5G systems, can be seen as an attractive solution. In these programmable networks, an energy-aware solution could be easily implemented leveraging the capabilities provided by control and data plane separation. This paper investigates the impact of energy-aware routing on network performance. To that end, we propose a novel energy-aware mechanism that reduces the number of active links in SDN with multiple controllers, considering in-band control traffic. The proposed strategy exploits knowledge of the network topology combined with traffic engineering techniques to reduce the overall power consumption. Therefore, two heuristic algorithms are designed: a static network configuration and a dynamic energy-aware routing. Significant values of switched-off links are reached in the simulations where real topologies and demands data are used. Moreover, the obtained results confirm that crucial network parameters such as control traffic delay, data path latency, link utilization and Ternary Content Addressable Memory (TCAM) occupation are affected by the performance-agnostic energy-aware model. Full article

(This article belongs to the Special Issue Energy-Efficient Computing and Networking in the 5G Era)

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A Two-Level Optimal Scheduling Strategy for Central Air-Conditioners Based on Metal Model with Comprehensive State-Queueing Control Models

by Yebai Qi, Dan Wang, Yu Lan, Hongjie Jia, Chengshan Wang, Kaixin Liu, Qing’e Hu and Menghua Fan

Energies 2017, 10(12), 2133; https://doi.org/10.3390/en10122133 - 14 Dec 2017

Cited by 6 | Viewed by 3064

Abstract

Unlike some thermostatically controlled appliances (TCAs) with small capacities, Central Air-conditioner (CAC) has huge potential for demand response because of its large capacity. This paper presents a new CAC control strategy under multiple constraints. The CAC is modeled by three main modules: CAC [...] Read more.

Unlike some thermostatically controlled appliances (TCAs) with small capacities, Central Air-conditioner (CAC) has huge potential for demand response because of its large capacity. This paper presents a new CAC control strategy under multiple constraints. The CAC is modeled by three main modules: CAC central unit, water pumps, and temperature simulation of terminal users. The CAC’s power consumption is mainly determined by users’ load ratio. As the information and communication system have become the central nervous system of the smart grid, big data analysis is of great significance. Assuming that reliable two-way communication systems are preset, an integrated parameter priority list (IPPL) control strategy is used to control and monitor CAC. A new intelligent algorithm, Space Exploration and Unimodal Region Elimination (SEUMRE) algorithm, is introduced for solving the optimization problem of demand response targets generation under multiple constraints with the help of big data analysis. In this paper, influences and constrain factors, such as price and users’ comfortable levels are taken into account to satisfy the need of actual situation. Simulation results show that the proposed approach, when comparing with other typical optimization algorithms, yields better performances and efficiency. Full article

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Comparative Performance Analysis of Optimal PID Parameters Tuning Based on the Optics Inspired Optimization Methods for Automatic Generation Control

by Mahmut Temel ÖZDEMİR and Dursun ÖZTÜRK

Energies 2017, 10(12), 2134; https://doi.org/10.3390/en10122134 - 14 Dec 2017

Cited by 51 | Viewed by 4546

Abstract

The Optics Inspired Optimization (OIO) algorithm is a new metaheuristic optimization method. In this paper, the OIO algorithm was proposed for automatic production control parameters in electrical power systems. The performance of the proposed algorithm was realized on two power systems that have [...] Read more.

The Optics Inspired Optimization (OIO) algorithm is a new metaheuristic optimization method. In this paper, the OIO algorithm was proposed for automatic production control parameters in electrical power systems. The performance of the proposed algorithm was realized on two power systems that have different structures. The first structure is a two-area interconnected thermal reheat power system and the other one is a two-area interconnected multi-unit hydro-thermal power system. The results obtained with the proposed algorithm were compared with an artificial bee colony and particle swarm optimization, initial values are randomly defined that are commonly used in literature. The results were examined using four different cost functions based on area control error. Considering the obtained results, the proposed algorithm reached to the global minimum value with less number of iterations and is more suitable for online optimization. According to the results obtained with this novel method, it has a better performance for maximum overshoot and settling time values when the test systems are implemented. Full article

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

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Ageing and Water-Based Processing of LiFeMnPO₄ Secondary Agglomerates and Its Effects on Electrochemical Characteristics

by Benjamin Starke, Stefan Seidlmayer, Oleksandr Dolotko, Ralph Gilles and Karl-Heinz Pettinger

Energies 2017, 10(12), 2135; https://doi.org/10.3390/en10122135 - 15 Dec 2017

Cited by 9 | Viewed by 5196

Abstract

LiFeMnPO₄ secondary agglomerates have been aged under different temperature and moisture conditions. The aged and pristine powder samples were then processed to water- and solvent-based cathodes. Structural studies by means of neutron and X-ray diffraction revealed that neither ageing nor water-based processing [...] Read more.

LiFeMnPO₄ secondary agglomerates have been aged under different temperature and moisture conditions. The aged and pristine powder samples were then processed to water- and solvent-based cathodes. Structural studies by means of neutron and X-ray diffraction revealed that neither ageing nor water-based processing significantly modified the crystal structure of LiFeMnPO₄ secondary agglomerates. Electrochemical characterization was carried out with full-cells. It was found that long-term cycling is similar independent of the solvent used for slurry preparation. Full-cells assembled with water-based cathodes show a better C-rate capability due to a more homogeneous distribution of cathode constituents compared to solvent-based ones. In no case was any negative effect of initial active material ageing on the electrochemical performance found. During ageing and processing, LiFeMnPO₄ is effectively protected by carbon coating and water can be completely removed by drying since it is only reversibly bound. This contribution shows that LiFeMnPO₄ secondary agglomerates allow simplified active material handling and have a high potential for sustainable water-based electrode manufacturing. Full article

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

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Estimating Human Health Impacts and Costs Due to Iranian Fossil Fuel Power Plant Emissions through the Impact Pathway Approach

by Mojtaba Jorli, Steven Van Passel, Hossein Sadeghi, Alireza Nasseri and Lotfali Agheli

Energies 2017, 10(12), 2136; https://doi.org/10.3390/en10122136 - 15 Dec 2017

Cited by 23 | Viewed by 6127

Abstract

Air pollutants from fossil fuel fired power plants harm the environment and human health. More than 91% of Iran’s electricity production is from thermal power plants that use natural gas, diesel, and fuel oil. We apply the impact pathway approach to estimate the [...] Read more.

Air pollutants from fossil fuel fired power plants harm the environment and human health. More than 91% of Iran’s electricity production is from thermal power plants that use natural gas, diesel, and fuel oil. We apply the impact pathway approach to estimate the health impacts arising from Iranian fossil-based electricity generation emission, and in a next step, we calculate monetary costs of the estimated damages, for a one-year period starting from 20 March 2016 through 2017. We use the new version of SIMPACTS (International Atomic Energy Agency, Vienna, Austria) to investigate the health effects from 61 major Iran fossil-based power plants separately. The selected plants represent 95.6% of total Iran fossil-based power generation. Using the individual and different power plant estimates, we avoid extrapolation and our results can be considered more reliable, taking into account spatial differences. The total damage cost is 723.42 million USD (2000). The damage cost per generated electricity varies from 0.06 to 22.41 USD/MWh and average plant damage cost is 2.85 USD/MWh. Accounting for these external costs indicates the actual costs of fossil energy. The results are useful for policy makers to compare the health costs from these plants and to decide on cleaner energy sources and to take measures to increase benefits for society. Full article

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

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Multi-Objective Coordinated Planning of Distributed Generation and AC/DC Hybrid Distribution Networks Based on a Multi-Scenario Technique Considering Timing Characteristics

by Yongchun Yang, Xiaodan Wang, Jingjing Luo, Jie Duan, Yajing Gao, Hong Li and Xiangning Xiao

Energies 2017, 10(12), 2137; https://doi.org/10.3390/en10122137 - 15 Dec 2017

Cited by 18 | Viewed by 3706

Abstract

With increased direct current (DC) load density and the penetration of a large number of distributed generation (DG) units in alternating current (AC) distribution networks (DNs); a planning approach that considers transforming some of the AC lines into DC lines and building the [...] Read more.

With increased direct current (DC) load density and the penetration of a large number of distributed generation (DG) units in alternating current (AC) distribution networks (DNs); a planning approach that considers transforming some of the AC lines into DC lines and building the DC network is proposed. Considering the DG output uncertainty and the load fluctuation, a planning model for an AC/DC hybrid distribution network (DN) with the DG based on the construction of multi-scenario technology with timing characteristics is built. In the DG configuration planning model, the lines to be transformed into DC form the access location and the decision regarding the DC or AC form of the newly built lines are considered optimizing variables. The DG investment, the network and converters of the DG and load, the active power loss and the voltage stability are considered in the objective functions. An improved adaptive niche genetic algorithm based on the fuzzy degree of membership and variance weighting is used to solve the nested model. Finally, considering the improved electrical and electronic engineers 33 (IEEE33) node system as an example, the correctness and effectiveness of the proposed planning method are verified. Compared to the plan without transforming some of the AC lines into DC lines and building a DC network, more DG can be admitted, and the economic cost of the AC/DC hybrid DN is notably decreased when planning to transform some of the AC lines into DC lines and build a DC network. The active power network loss and the voltage stability index are similarly further optimized. Full article

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Stochastic Dynamic AC Optimal Power Flow Based on a Multivariate Short-Term Wind Power Scenario Forecasting Model

by Wenlei Bai, Duehee Lee and Kwang Y. Lee

Energies 2017, 10(12), 2138; https://doi.org/10.3390/en10122138 - 15 Dec 2017

Cited by 24 | Viewed by 4149

Abstract

The deterministic methods generally used to solve DC optimal power flow (OPF) do not fully capture the uncertainty information in wind power, and thus their solutions could be suboptimal. However, the stochastic dynamic AC OPF problem can be used to find an optimal [...] Read more.

The deterministic methods generally used to solve DC optimal power flow (OPF) do not fully capture the uncertainty information in wind power, and thus their solutions could be suboptimal. However, the stochastic dynamic AC OPF problem can be used to find an optimal solution by fully capturing the uncertainty information of wind power. That uncertainty information of future wind power can be well represented by the short-term future wind power scenarios that are forecasted using the generalized dynamic factor model (GDFM)—a novel multivariate statistical wind power forecasting model. Furthermore, the GDFM can accurately represent the spatial and temporal correlations among wind farms through the multivariate stochastic process. Fully capturing the uncertainty information in the spatially and temporally correlated GDFM scenarios can lead to a better AC OPF solution under a high penetration level of wind power. Since the GDFM is a factor analysis based model, the computational time can also be reduced. In order to further reduce the computational time, a modified artificial bee colony (ABC) algorithm is used to solve the AC OPF problem based on the GDFM forecasting scenarios. Using the modified ABC algorithm based on the GDFM forecasting scenarios has resulted in better AC OPF’ solutions on an IEEE 118-bus system at every hour for 24 h. Full article

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

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An Experimental Study on the Radiation Noise Characteristics of a Centrifugal Pump with Various Working Conditions

by Chang Guo, Ming Gao, Dongyue Lu and Kun Wang

Energies 2017, 10(12), 2139; https://doi.org/10.3390/en10122139 - 15 Dec 2017

Cited by 11 | Viewed by 3997

Abstract

To investigate the radiation noise characteristics of a centrifugal pump under various working conditions, a noise measurement system is established; afterwards, the distribution of different points and intervals, as well as the overall level of noise, are studied. The total sound pressure level [...] Read more.

To investigate the radiation noise characteristics of a centrifugal pump under various working conditions, a noise measurement system is established; afterwards, the distribution of different points and intervals, as well as the overall level of noise, are studied. The total sound pressure level distribution for different points manifests the dipole and asymmetric directivity characteristics. Additionally, the acoustic energy is introduced to compare the noise of different intervals to reveal the asymmetric characteristics, and it is found that variation in working conditions has little impact on the acoustic energy distribution, and the ratio of the acoustic energy in the direction facing the tongue, as well as that in the direction against the tongue, to total acoustic energy fluctuate around 0.410 and 0.160, respectively, under various working conditions. Also, the A-weighted average sound pressure level (L_pA) is applied to describe the overall level of noise, and L_pA increases gradually with the growth of rotational speed, but the growth slope decreases. While in the operation of throttling regulation, L_pA shows the trend that first increases, then remains stable, and increases again with the growth of flow rate. This study could provide guidance for optimizing the operating conditions and noise control of centrifugal pumps. Full article

(This article belongs to the Special Issue Engineering Fluid Dynamics 2018)

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Optimal Design of a Novel Hybrid Electric Powertrain for Tracked Vehicles

by Zhaobo Qin, Yugong Luo, Keqiang Li and Huei Peng

Energies 2017, 10(12), 2141; https://doi.org/10.3390/en10122141 - 15 Dec 2017

Cited by 11 | Viewed by 4119

Abstract

Tracked vehicles have been widely used in construction, agriculture, and the military. Major problems facing the industry, however, are high emissions and fuel consumption. Hybrid electric tracked vehicles have thus become increasingly popular because of their improved fuel economy and reduced emissions. While [...] Read more.

Tracked vehicles have been widely used in construction, agriculture, and the military. Major problems facing the industry, however, are high emissions and fuel consumption. Hybrid electric tracked vehicles have thus become increasingly popular because of their improved fuel economy and reduced emissions. While the series hybrid system has drawn the most attention and has been applied in most cases, the low efficiency caused by energy conversion losses and large propulsion motors has limited its development. A novel multi-mode powertrain with two output shafts controlling each side of the track independently is first proposed. The powertrain is a three-planetary-gear power-split system with one engine, three motors, and an ultracapacitor pack. Compared with the existing technologies, the proposed powertrain can realize skid steering without an extra steering mechanism, and significantly improve the overall efficiency. To demonstrate the advantages of the novel powertrain, a topology-control-size integrated optimization problem is solved based on drivability, fuel economy, and cost. Final simulation results show that the optimized design with downsized components can produce about a 30% improvement in drivability and a 15% improvement in fuel economy compared with the commonly used series hybrid benchmark. Moreover, the optimized design is verified to be much more economical taking cumulative cost into account, which is very attractive for potential industrial applications in the future. Full article

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

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Electrical-Loss Analysis of Power-Split Hybrid Electric Vehicles

by Andrea Bonfiglio, Damiano Lanzarotto, Mario Marchesoni, Massimiliano Passalacqua, Renato Procopio and Matteo Repetto

Energies 2017, 10(12), 2142; https://doi.org/10.3390/en10122142 - 15 Dec 2017

Cited by 18 | Viewed by 4670

Abstract

The growing development of hybrid electric vehicles (HEVs) has seen the spread of architectures with transmission based on planetary gear train, realized thanks to two electric machines. This architecture, by continuously regulating the transmission ratio, allows the internal combustion engine (ICE) [...] Read more.

The growing development of hybrid electric vehicles (HEVs) has seen the spread of architectures with transmission based on planetary gear train, realized thanks to two electric machines. This architecture, by continuously regulating the transmission ratio, allows the internal combustion engine (ICE) to work in optimal conditions. On the one hand, the average ICE efficiency is increased thanks to better loading situations, while, on the other hand, electrical losses are introduced due to the power circulation between the two electrical machines mentioned above. The aim of this study is then to accurately evaluate electrical losses and the average ICE efficiency in various operating conditions and over different road missions. The models used in this study are presented for both the Continuously Variable Transmission (CVT) architecture and the Discontinuously Variable Transmission (DVT) architecture. In addition, efficiency maps of the main components are shown. Finally, the simulation results are presented to point out strengths and weaknesses of the CVT architecture. Full article

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Brexit and Article 50 of the Treaty of the European Union: Implications for UK Energy Policy and Security

by Augustine O. Ifelebuegu, Kenneth E. Aidelojie and Elijah Acquah-Andoh

Energies 2017, 10(12), 2143; https://doi.org/10.3390/en10122143 - 15 Dec 2017

Cited by 7 | Viewed by 5393

Abstract

This paper articulates the potential implications of Brexit on energy policy and security in the United Kingdom (UK). Given the uncertainties associated with the decision to leave the European Union (EU), the need to consider its potential effects on the UK’s energy sector [...] Read more.

This paper articulates the potential implications of Brexit on energy policy and security in the United Kingdom (UK). Given the uncertainties associated with the decision to leave the European Union (EU), the need to consider its potential effects on the UK’s energy sector becomes even more pertinent. Through the lens of a few widely reviewed trade regimes in the light of Brexit, it can be observed that while UK energy policies are unlikely to change drastically, Brexit nevertheless threatens the UK’s capacity to safeguard its energy supply. The uncertainties following Brexit could arguably starve the UK’s upstream petroleum, electricity, and renewable energy sectors of their required investments. Both short and long-term impacts could result in UK residents paying more per unit of energy consumed in a “hard Brexit” scenario, where the UK exits the Internal Energy Market (IEM) and must trade with the EU under World Trade Organisation rules. While a hard Brexit could aid the growth of the nascent shale gas industry, a negotiated withdrawal that includes some form of access to the IEM (a “soft Brexit”) would be more beneficial for the future of energy security in the UK. Full article

(This article belongs to the Special Issue Energy Market Transitions)

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Multi-Objective Optimized Aggregation of Demand Side Resources Based on a Self-organizing Map Clustering Algorithm Considering a Multi-Scenario Technique

by Yajing Gao, Yanping Sun, Xiaodan Wang, Feifan Chen, Ali Ehsan, Hongmei Li and Hong Li

Energies 2017, 10(12), 2144; https://doi.org/10.3390/en10122144 - 15 Dec 2017

Cited by 15 | Viewed by 3497

Abstract

To fully investigate the characteristics and the complementarities of demand side resources (DSRs), and to achieve efficient utilization of resources, the aggregation of DSRs is studied in this paper. Considering the uncertainty of DSRs, the characteristics analysis and the selection of relevant daily [...] Read more.

To fully investigate the characteristics and the complementarities of demand side resources (DSRs), and to achieve efficient utilization of resources, the aggregation of DSRs is studied in this paper. Considering the uncertainty of DSRs, the characteristics analysis and the selection of relevant daily feature corresponding to various types of DSR are carried out. Then a multi-scenario model based on quarter division and self-organizing map (SOM) neural network algorithm is proposed. In the model, the clustering feature vector is selected as the input vector of the SOM algorithm to perform DSR clustering analysis to get the different scenarios. In addition, to obtain the resource aggregation (RA) with good load characteristics, response characteristics and distributed generation (DG) consumption, a multi-scenario objective optimization aggregation model of DSR based on scenario partition is established, and an the model is solved by an improved niche evolutionary multi-objective immune algorithm. Finally, the case studies are given to verify the validity of the model. Full article

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Open AccessArticle

Adaptive State Feedback—Theory and Application for Wind Turbine Control

by Kaman Thapa Magar, Mark Balas, Susan Frost and Nailu Li

Energies 2017, 10(12), 2145; https://doi.org/10.3390/en10122145 - 15 Dec 2017

Cited by 4 | Viewed by 3393

Abstract

A class of adaptive disturbance tracking controllers (ADTCs) is augmented with disturbance and state estimation and adaptive state feedback, in which a controller and estimator, which are designed on the basis of a lower-order model, are used to control a higher-order nonlinear plant. [...] Read more.

A class of adaptive disturbance tracking controllers (ADTCs) is augmented with disturbance and state estimation and adaptive state feedback, in which a controller and estimator, which are designed on the basis of a lower-order model, are used to control a higher-order nonlinear plant. The ADTC requires that the plant be almost strict positive real (ASPR) to ensure stability. In this paper, we show that the ASPR property of a plant is retained with the addition of disturbance and state estimation and state feedback, thereby ensuring the stability of the augmented system. The proposed adaptive controller with augmentation is presented in the context of maximum power extraction from a wind turbine in a low-wind-speed operation region. A simulation and comparative study on the National Renewable Energy Laboratory’s (NREL’s) 5 MW nonlinear wind turbine model with an existing baseline Proportional-Integral-Derivative(PID) controller shows that the proposed controller is more effective than the existing baseline PID controller. Full article

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

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4855 KiB

Open AccessArticle

Emission Characteristics for a Homogeneous Charged Compression Ignition Diesel Engine with Exhaust Gas Recirculation Using Split Injection Methodology

by Changhee Lee, Jaewoo Chung and Kihyung Lee

Energies 2017, 10(12), 2146; https://doi.org/10.3390/en10122146 - 15 Dec 2017

Cited by 10 | Viewed by 4893

Abstract

Due to the serious issues caused by air pollution and global warming, emission regulations are becoming stricter. New technologies that reduce NO_x and PM emissions are needed. To cope with these social exhaust gas regulation demands, many advanced countries are striving to [...] Read more.

Due to the serious issues caused by air pollution and global warming, emission regulations are becoming stricter. New technologies that reduce NO_x and PM emissions are needed. To cope with these social exhaust gas regulation demands, many advanced countries are striving to develop eco-friendly vehicles in order to respond to stricter emissions regulations. The homogeneous charged compression ignition engine (HCCI) incorporates a multi-stage combustion engine with multiple combustion modes, catalyst, direct fuel injection and partial mixing combustion. In this study, the HCCI combustion was applied to analyze and review the results of engines applying HCCI combustion without altering the conventional engine specifications. The optimization of exhaust gas recirculation (EGR) and compression ratio changes provides an optimal fuel economy. In this study, potential for optimum economy within the range of IMEP 0.8 MPa has been evaluated. Full article

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3442 KiB

Open AccessArticle

Estimation of Conservation Voltage Reduction Factors Using Measurement Data of KEPCO System

by Kwan-Shik Shim, Seok-Il Go, Sang-Yun Yun, Joon-Ho Choi, Won Nam-Koong, Chang-Hoon Shin and Seon-Ju Ahn

Energies 2017, 10(12), 2148; https://doi.org/10.3390/en10122148 - 15 Dec 2017

Cited by 8 | Viewed by 3971

Abstract

This paper describes a method to estimate conservation voltage reduction (CVR) factors using data measured in power distribution systems. A direct method is proposed to estimate CVR factors using only data measured at the moment of the transformer tap change. The mean absolute [...] Read more.

This paper describes a method to estimate conservation voltage reduction (CVR) factors using data measured in power distribution systems. A direct method is proposed to estimate CVR factors using only data measured at the moment of the transformer tap change. The mean absolute deviation (MAD) direct method is proposed to consider direct methods and load variations. The proposed methods do not necessitate intentional tap changes for testing purposes. Instead, the voltage and load changes that occur when the tap changes, for voltage regulation purposes, are measured and utilized in the CVR factor calculation. The proposed methods were tested using data obtained from the Korea Electric Power Corporation (KEPCO) system, and the results revealed that CVR factors for both active power and reactive power could be estimated using data measured in power distribution systems. Results of the CVR factor estimation for the active power revealed that the highest CVR factors occurred in winter, during which a large quantity of heating loads exist. In addition, the estimated CVR factors for the reactive power were higher than the estimated CVR factors for the active power because reactive power is more sensitive to voltage changes. Full article

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

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2269 KiB

Open AccessArticle

Lightning Surge Analysis on a Large Scale Grid-Connected Solar Photovoltaic System

by Nur Hazirah Zaini, Mohd Zainal Abidin Ab. Kadir, Mohd Amran Mohd Radzi, Mahdi Izadi, Norhafiz Azis, Nor Izzati Ahmad and Mohd Solehin Mohd Nasir

Energies 2017, 10(12), 2149; https://doi.org/10.3390/en10122149 - 15 Dec 2017

Cited by 42 | Viewed by 8209

Abstract

Solar photovoltaic (PV) farms currently play a vital role in the generation of electrical power in different countries, such as Malaysia, which is moving toward the use of renewable energy. Malaysia is one of the countries with abundant sunlight and thus can use [...] Read more.

Solar photovoltaic (PV) farms currently play a vital role in the generation of electrical power in different countries, such as Malaysia, which is moving toward the use of renewable energy. Malaysia is one of the countries with abundant sunlight and thus can use solar PV farms as alternative sources for electricity generation. However, lightning strikes frequently occur in the country. Being installed in open and flat areas, solar PV farms, especially their electronic components, are at great risk of damage caused by lightning. In this paper, the effects of lightning currents with different peak currents and waveshapes on grid-connected solar PV farms were determined to approximate the level of transient effect that can damage solar PV modules, inverters and transformers. Depending on the location of the solar PV farm, engineer can obtain information on the peak current and median current of the site from the lightning location system (LLS) and utilise the results obtained in this study to appropriately assign an SPD to protect the solar panel, inverter and the main panel that connected to the grid. Therefore, the simulation results serve as the basis for controlling the effects of lightning strikes on electrical equipment and power grids where it provides proper justification on the ‘where to be installed’ and ‘what is the rating’ of the SPD. This judgment and decision will surely reduce the expensive cost of repair and replacement of electrical equipment damages due to the lightning. Full article

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Open AccessArticle

A Digitally Controlled Power Converter for an Electrostatic Precipitator

by Pedro J. Villegas, Juan A. Martín-Ramos, Juan Díaz, Juan Á. Martínez, Miguel J. Prieto and Alberto M. Pernía

Energies 2017, 10(12), 2150; https://doi.org/10.3390/en10122150 - 15 Dec 2017

Cited by 7 | Viewed by 3787

Abstract

Electrostatic precipitators (ESPs) are devices used in industry to eliminate polluting particles in gases. In order to supply them, an interface must be included between the three-phase main line and the required high DC voltage of tens of kilovolts. This paper describes an [...] Read more.

Electrostatic precipitators (ESPs) are devices used in industry to eliminate polluting particles in gases. In order to supply them, an interface must be included between the three-phase main line and the required high DC voltage of tens of kilovolts. This paper describes an 80-kW power supply for such an application. Its structure is based on the series parallel resonant converter with a capacitor as output filter (PRC-LCC), which can adequately cope with the parasitic elements of the step-up transformer involved. The physical implementation of the prototype includes the use of silicon carbide—SiC—semiconductors, which provide better switching capabilities than their traditional silicon—Si—counterparts. As a result, a new control strategy results as a better alternative in which the resonant current is maintained in phase with the first harmonic of the inverter voltage. Although this operation mode imposes hard switching in one of the inverter legs, it minimizes the reactive energy that circulates through the resonant tank, the resonant current amplitude itself and the switching losses. Overall efficiency of the converter benefits from this. These ideas are supported mathematically using the steady state and dynamic models of the topology. They are confirmed with experimental measurements that include waveforms, Bode plots and thermal behavior. The experimental setup delivers 80 kW with an estimated efficiency of 98%. Full article

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353 KiB

Open AccessArticle

The (R)evolution of China: Offshore Wind Diffusion

by Thomas Poulsen and Charlotte Bay Hasager

Energies 2017, 10(12), 2153; https://doi.org/10.3390/en10122153 - 16 Dec 2017

Cited by 11 | Viewed by 12649

Abstract

This research presents an industry level gap analysis for Chinese offshore wind, which serves as a way to illuminate how China may fast track industry evolution. The research findings provide insight into how the Chinese government strongly and systematically decrees state-owned Chinese firms [...] Read more.

This research presents an industry level gap analysis for Chinese offshore wind, which serves as a way to illuminate how China may fast track industry evolution. The research findings provide insight into how the Chinese government strongly and systematically decrees state-owned Chinese firms to expand into overseas markets to speed up learning efforts. Insights are offered regarding the nation-level strategic plans and institutional support policies mobilized by China in order to be able to conquer market shares internationally by building a strong home market and then facilitating an end-to-end and fully financed export solution. This is interesting in itself and in particular so because it now also includes complex billion-dollar megaprojects such as turnkey offshore wind farm assets with an expected lifespan of 30+ years. Research findings are provided on how European and Chinese firms may successfully forge long-term alliances also for future Chinese wind energy export projects. Examples of past efforts of collaboration not yielding desired results have been included as well. At policy level, recommendations are provided on how the evolution of the Chinese offshore wind power industry can be fast-tracked to mirror the revolutionary pace, volume, and velocity which the Chinese onshore wind power industry has mustered. Full article

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

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Open AccessArticle

Gas Hydrate and Free Gas Concentrations in Two Sites inside the Chilean Margin (Itata and Valdivia Offshores)

by Vargas-Cordero Iván, Tinivella Umberta and Villar-Muñoz Lucía

Energies 2017, 10(12), 2154; https://doi.org/10.3390/en10122154 - 16 Dec 2017

Cited by 19 | Viewed by 4274

Abstract

Two sectors, Itata and Valdivia, which are located in the Chilean margin were analysed by using seismic data with the main purpose to characterize the gas hydrate concentration. Strong lateral velocity variations are recognised, showing a maximum value in Valdivia offshore (2380 ms [...] Read more.

Two sectors, Itata and Valdivia, which are located in the Chilean margin were analysed by using seismic data with the main purpose to characterize the gas hydrate concentration. Strong lateral velocity variations are recognised, showing a maximum value in Valdivia offshore (2380 ms⁻¹ above the BSR) and a minimum value in the Itata offshore (1380 m·s⁻¹ below the BSR). In both of the sectors, the maximum hydrate concentration reaches 17% of total volume, while the maximum free gas concentration is located Valdivia offshore (0.6% of total volume) in correspondence of an uplift sector. In the Itata offshore, the geothermal gradient that is estimated is variable and ranges from 32 °C·km⁻¹ to 87 °C·km⁻¹, while in Valdivia offshore it is uniform and about 35 °C·km⁻¹. When considering both sites, the highest hydrate concentration is located in the accretionary prism (Valdivia offshore) and highest free gas concentration is distributed upwards, which may be considered as a natural pathway for lateral fluid migration. The results that are presented here contribute to the global knowledge of the relationship between hydrate/free gas presence and tectonic features, such as faults and folds, and furnishes a piece of the regional hydrate potentiality Chile offshore. Full article

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

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Open AccessArticle

Electromagnetic Vibration Simulation of a 250-MW Large Hydropower Generator with Rotor Eccentricity and Rotor Deformation

by Ruhai Li, Chaoshun Li, Xuanlin Peng and Wei Wei

Energies 2017, 10(12), 2155; https://doi.org/10.3390/en10122155 - 17 Dec 2017

Cited by 26 | Viewed by 6377

Abstract

The electromagnetic vibration caused by electromagnetic force on the stator has threatened large hydro generators operating safely and stably. At the Zhexi hydropower station, the hydro generator was beset by electromagnetic vibration for a long time. Therefore, the paper provided a new method [...] Read more.

The electromagnetic vibration caused by electromagnetic force on the stator has threatened large hydro generators operating safely and stably. At the Zhexi hydropower station, the hydro generator was beset by electromagnetic vibration for a long time. Therefore, the paper provided a new method to help to find the vibration source and detect the hydro generator fault, through the combination of simulation and experiments. In this paper, the 3D stator pack structure model and the 2D hydro generator electromagnetic models under rotor eccentricity and rotor ellipse deformation conditions were built. Then, electromagnetism simulations were conducted to study the characteristics of the electromagnetic flux and electromagnetic force under different conditions by using the finite element method (FEM). Lastly, the vibration testing experiments and harmonic response simulations of stator frame were performed to present the characteristics of vibration distribution in frequency conditions. The simulation results were compared with the generator measured data to try to find out the main vibration source and guide the overhaul. Full article

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Open AccessArticle

Research on Energy-Saving Operation Strategy for Multiple Trains on the Urban Subway Line

by Jianqiang Liu and Nan Zhao

Energies 2017, 10(12), 2156; https://doi.org/10.3390/en10122156 - 17 Dec 2017

Cited by 19 | Viewed by 4610

Abstract

Energy consumption for multiple trains on the urban subway line is predominantly affected by the operation strategy. This paper proposed an energy-saving operation strategy for multiple trains, which is suitable for various line conditions and complex train schedules. The model and operation modes [...] Read more.

Energy consumption for multiple trains on the urban subway line is predominantly affected by the operation strategy. This paper proposed an energy-saving operation strategy for multiple trains, which is suitable for various line conditions and complex train schedules. The model and operation modes of the strategy are illustrated in detail, aiming to take full use of regenerative braking energy in complex multi-train systems with different departure intervals and dwell times. The computing method is proposed by means of the heuristic algorithm to obtain the optimum operation curve for each train. The simulation result based on a real urban subway line is provided to verify the correctness and effectiveness of the proposed energy-saving operation strategy. Full article

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

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6149 KiB

Open AccessArticle

Design and Analysis of a New Torque Vectoring System with a Ravigneaux Gearset for Vehicle Applications

by Yu-Fan Chen, I-Ming Chen, Joshua Chang and Tyng Liu

Energies 2017, 10(12), 2157; https://doi.org/10.3390/en10122157 - 17 Dec 2017

Cited by 12 | Viewed by 6295

Abstract

The purpose of this research is to develop a new torque vectoring differential (TVD) for vehicle applications and investigate its effect on vehicle dynamic control. TVD is a technology that is able to distribute the engine torque to the left and right driving [...] Read more.

The purpose of this research is to develop a new torque vectoring differential (TVD) for vehicle applications and investigate its effect on vehicle dynamic control. TVD is a technology that is able to distribute the engine torque to the left and right driving wheels at different ratios so that the yaw motion control can be realized. Attention has been paid to this technology in recent years because of its potential to improve the vehicle performance and driving safety. In this study, a new TVD design with a Ravigneaux gearset was developed. This new design is able to use only one pair of gearsets to generate two different speed ratios, and the weight and volume of the system can be reduced. To execute the research, current TVD designs were analyzed and their design principles were clarified. Next, a new TVD design with Ravigneaux gearset was proposed. Then the connecting manner and the gear ratio of the Ravigneaux gearset were discussed. The dynamic equation of the system was then derived and the operation of the system was simulated in a MATLAB program. Further simulation was performed with a vehicle dynamic model in SimulationX to demonstrate the effect of the new system. The results of this study show the potential of building a new TVD with a Ravigneaux gearset and can be helpful for further system development. Full article

(This article belongs to the Special Issue Methods to Improve Energy Use in Road Vehicles)

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3192 KiB

Open AccessArticle

Renewable Energy Potential by the Application of a Building Integrated Photovoltaic and Wind Turbine System in Global Urban Areas

by Jaewook Lee, Jeongsu Park, Hyung-Jo Jung and Jiyoung Park

Energies 2017, 10(12), 2158; https://doi.org/10.3390/en10122158 - 17 Dec 2017

Cited by 15 | Viewed by 6731

Abstract

Globally, maintaining equilibrium between energy supply and demand is critical in urban areas facing increasing energy consumption and high-speed economic development. As an alternative, the large-scale application of renewable energy, such as solar and wind power, might be a long-term solution in an [...] Read more.

Globally, maintaining equilibrium between energy supply and demand is critical in urban areas facing increasing energy consumption and high-speed economic development. As an alternative, the large-scale application of renewable energy, such as solar and wind power, might be a long-term solution in an urban context. This study assessed the overall utilization potential of a building-integrated photovoltaic and wind turbine (BIPvWt) system, which can be applied to a building skin in global urban areas. The first step of this study was to reorganize the large volume of global annual climate data. The data were analyzed by computational fluid dynamic analysis and an energy simulation applicable to the BIPvWt system, which can generate a P_max 300 Wp/module with a 15% conversion efficiency from a photovoltaic (PV) system and a 0.149 power coefficient/module from wind turbines in categorized urban contexts and office buildings in specific cities; it was constructed to evaluate and optimize the ratio that can cover the current energy consumption. A diagram of the distribution of the solar and wind energy potential and design guidelines for a building skin were developed. The perspective of balancing the increasing energy consumption using renewable energy in urban areas can be visualized positively in the near future. Full article

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3042 KiB

Open AccessArticle

Power Decoupling Method Based on the Diagonal Compensating Matrix for VSG-Controlled Parallel Inverters in the Microgrid

by Bin Li and Lin Zhou

Energies 2017, 10(12), 2159; https://doi.org/10.3390/en10122159 - 17 Dec 2017

Cited by 40 | Viewed by 4911

Abstract

The thought of the virtual synchronous generator (VSG) for controlling the grid-connected inverters and providing virtual inertia to the microgrid is emerging as a wide extension of the droop control, power coupling that always exists in the low-voltage microgrid, which may deteriorate the [...] Read more.

The thought of the virtual synchronous generator (VSG) for controlling the grid-connected inverters and providing virtual inertia to the microgrid is emerging as a wide extension of the droop control, power coupling that always exists in the low-voltage microgrid, which may deteriorate the dynamic response and the stability of the system. In this paper, the principle of VSG control is introduced first. As an important issue of VSG control, the mechanism of the power coupling in the low-voltage microgrid is analyzed and the small-signal equivalent model of the power transmission loop is established. Subsequently, a power decoupling method based on the diagonal compensating matrix for VSG is proposed, which can realize the power decoupling with no impact on the original control channel. Meanwhile, the feasibility analysis of the decoupling method and the improved approach for reactive power sharing are also discussed. Simulation results verify the effectiveness of the decoupling strategy for VSGs. Full article

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2951 KiB

Open AccessArticle

A Combined Electro-Thermal Breakdown Model for Oil-Impregnated Paper

by Meng Huang, Yuanxiang Zhou, Zhongliu Zhou and Bo Qi

Energies 2017, 10(12), 2160; https://doi.org/10.3390/en10122160 - 18 Dec 2017

Cited by 13 | Viewed by 4514

Abstract

The breakdown property of oil-impregnated paper is a key factor for converter transformer design and operation, but it is not well understood. In this paper, breakdown voltages of oil-impregnated paper were measured at different temperatures. The results showed that with the increase of [...] Read more.

The breakdown property of oil-impregnated paper is a key factor for converter transformer design and operation, but it is not well understood. In this paper, breakdown voltages of oil-impregnated paper were measured at different temperatures. The results showed that with the increase of temperature, electrical, electro-thermal and thermal breakdown occurred successively. An electro-thermal breakdown model was proposed based on the heat equilibrium and space charge transport, and negative differential mobility was introduced to the model. It was shown that carrier mobility determined whether it was electrical or thermal breakdown, and the model can effectively explain the temperature-dependent breakdown. Full article

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

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1248 KiB

Open AccessArticle

Battery Storage Systems as Grid-Balancing Measure in Low-Voltage Distribution Grids with Distributed Generation

by Bernhard Faessler, Michael Schuler, Markus Preißinger and Peter Kepplinger

Energies 2017, 10(12), 2161; https://doi.org/10.3390/en10122161 - 18 Dec 2017

Cited by 30 | Viewed by 5068

Abstract

Due to the promoted integration of renewable sources, a further growth of strongly transient, distributed generation is expected. Thus, the existing electrical grid may reach its physical limits. To counteract this, and to fully exploit the viable potential of renewables, grid-balancing measures are [...] Read more.

Due to the promoted integration of renewable sources, a further growth of strongly transient, distributed generation is expected. Thus, the existing electrical grid may reach its physical limits. To counteract this, and to fully exploit the viable potential of renewables, grid-balancing measures are crucial. In this work, battery storage systems are embedded in a grid simulation to evaluate their potential for grid balancing. The overall setup is based on a real, low-voltage distribution grid topology, real smart meter household load profiles, and real photovoltaics load data. An autonomous optimization routine, driven by a one-way communicated incentive, determines the prospective battery operation mode. Different battery positions and incentives are compared to evaluate their impact. The configurations incorporate a baseline simulation without storage, a single, central battery storage or multiple, distributed battery storages which together have the same power and capacity. The incentives address either market conditions, grid balancing, optimal photovoltaic utilization, load shifting, or self-consumption. Simulations show that grid-balancing incentives result in lowest peak-to-average power ratios, while maintaining negligible voltage changes in comparison to a reference case. Incentives reflecting market conditions for electricity generation, such as real-time pricing, negatively influence the power quality, especially with respect to the peak-to-average power ratio. A central, feed-in-tied storage performs better in terms of minimizing the voltage drop/rise and shows lower distribution losses, while distributed storages attached at nodes with electricity generation by photovoltaics achieve lower peak-to-average power ratios. Full article

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

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Open AccessArticle

A Kriging Model Based Optimization of Active Distribution Networks Considering Loss Reduction and Voltage Profile Improvement

by Dan Wang, Qing’e Hu, Jia Tang, Hongjie Jia, Yun Li, Shuang Gao and Menghua Fan

Energies 2017, 10(12), 2162; https://doi.org/10.3390/en10122162 - 18 Dec 2017

Cited by 7 | Viewed by 4063

Abstract

Optimal operation of the active distribution networks (ADN) is essential to keep its safety, reliability and economy. With the integration of multiple controllable resources, the distribution networks are facing more challenges in which the optimization strategy is the key. This paper establishes the [...] Read more.

Optimal operation of the active distribution networks (ADN) is essential to keep its safety, reliability and economy. With the integration of multiple controllable resources, the distribution networks are facing more challenges in which the optimization strategy is the key. This paper establishes the optimal operation model of the ADN considering a diversity of controllable resources including energy storage devices, distributed generators, voltage regulators and switchable capacitor banks. The objective functions contain reducing the power losses and improving the voltage profiles. To solve the optimization problem, the Kriging model based Improved Surrogate Optimization-Mixed-Integer (ISO-MI) algorithm is proposed in this paper. The Kriging model is applied to approximate the complicated distribution networks, which speeds up the solving process. Finally, the accuracy of the Kriging model is validated and the efficiency among the proposed method, genetic algorithm (GA) and particle swarm optimization (PSO) is compared in an unbalanced IEEE-123 nodes test feeder. The results demonstrate that the proposed method has better performance than GA and PSO. Full article

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

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Open AccessArticle

Numerical Investigation of the Air-Steam Biomass Gasification Process Based on Thermodynamic Equilibrium Model

by Qitai Eri, Wenzhen Wu and Xinjun Zhao

Energies 2017, 10(12), 2163; https://doi.org/10.3390/en10122163 - 18 Dec 2017

Cited by 18 | Viewed by 4703

Abstract

In the present work, the air-steam biomass gasification model with tar has been developed based on the equilibrium constants. The simulation results based on two different models (with and without tar) have been validated by the experimental data. The model with tar can [...] Read more.

In the present work, the air-steam biomass gasification model with tar has been developed based on the equilibrium constants. The simulation results based on two different models (with and without tar) have been validated by the experimental data. The model with tar can well predict the tar content in gasification; meanwhile, the predicted gas yield (GY), based on the model with tar, is much closer to the experimental data. The energy exchange between the gasifier and the surrounding has been studied based on the dimensionless heat transfer ratio (DHTR), and the relationship between DHTR and the process parameters is given by a formula. The influence of process parameters on the syngas composition, tar content, GY, lower heating value (LHV), and exergy efficiency have been researched. Full article

(This article belongs to the Special Issue Biofuel and Bioenergy Technology)

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Open AccessEditor’s ChoiceArticle

Flow Adjustment Inside and Around Large Finite-Size Wind Farms

by Ka Ling Wu and Fernando Porté-Agel

Energies 2017, 10(12), 2164; https://doi.org/10.3390/en10122164 - 18 Dec 2017

Cited by 72 | Viewed by 10295

Abstract

In this study, large-eddy simulations are performed to investigate the flow inside and around large finite-size wind farms in conventionally-neutral atmospheric boundary layers. Special emphasis is placed on characterizing the different farm-induced flow regions, including the induction, entrance and development, fully-developed, exit and [...] Read more.

In this study, large-eddy simulations are performed to investigate the flow inside and around large finite-size wind farms in conventionally-neutral atmospheric boundary layers. Special emphasis is placed on characterizing the different farm-induced flow regions, including the induction, entrance and development, fully-developed, exit and farm wake regions. The wind farms extend 20 km in the streamwise direction and comprise 36 wind turbine rows arranged in aligned and staggered configurations. Results show that, under weak free-atmosphere stratification (

Γ = 1

K/km), the flow inside and above both wind farms, and thus the turbine power, do not reach the fully-developed regime even though the farm length is two orders of magnitude larger than the boundary layer height. In that case, the wind farm induction region, affected by flow blockage, extends upwind about 0.8 km and leads to a power reduction of 1.3% and 3% at the first row of turbines for the aligned and staggered layouts, respectively. The wind farm wake leads to velocity deficits at hub height of around 3.5% at a downwind distance of 10 km for both farm layouts. Under stronger stratification (

Γ = 5

K/km), the vertical deflection of the subcritical flow induced by the wind farm at its entrance and exit regions triggers standing gravity waves whose effects propagate upwind. They, in turn, induce a large decelerating induction region upwind of the farm leading edge, and an accelerating exit region upwind of the trailing edge, both extending about 7 km. As a result, the turbine power output in the entrance region decreases more than 35% with respect to the weakly stratified case. It increases downwind as the flow adjusts, reaching the fully-developed regime only for the staggered layout at a distance of about 8.5 km from the farm edge. The flow acceleration in the exit region leads to an increase of the turbine power with downwind distance in that region, and a relatively fast (compared with the weakly stratified case) recovery of the farm wake, which attains its inflow hub height speed at a downwind distance of 5 km. Full article

(This article belongs to the Collection Wind Turbines)

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Open AccessArticle

Hydro Power Reservoir Aggregation via Genetic Algorithms

by Markus Löschenbrand and Magnus Korpås

Energies 2017, 10(12), 2165; https://doi.org/10.3390/en10122165 - 18 Dec 2017

Cited by 14 | Viewed by 3712

Abstract

Electrical power systems with a high share of hydro power in their generation portfolio tend to display distinct behavior. Low generation cost and the possibility of peak shaving create a high amount of flexibility. However, stochastic influences such as precipitation and external market [...] Read more.

Electrical power systems with a high share of hydro power in their generation portfolio tend to display distinct behavior. Low generation cost and the possibility of peak shaving create a high amount of flexibility. However, stochastic influences such as precipitation and external market effects create uncertainty and thus establish a wide range of potential outcomes. Therefore, optimal generation scheduling is a key factor to successful operation of hydro power dominated systems. This paper aims to bridge the gap between scheduling on large-scale (e.g., national) and small scale (e.g., a single river basin) levels, by applying a multi-objective master/sub-problem framework supported by genetic algorithms. A real-life case study from southern Norway is used to assess the validity of the method and give a proof of concept. The introduced method can be applied to efficiently integrate complex stochastic sub-models into Virtual Power Plants and thus reduce the computational complexity of large-scale models whilst minimizing the loss of information. Full article

(This article belongs to the Special Issue Hydropower 2017)

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Open AccessArticle

Performance Recovery of Natural Draft Dry Cooling Systems by Combined Air Leading Strategies

by Weijia Wang, Lei Chen, Xianwei Huang, Lijun Yang and Xiaoze Du

Energies 2017, 10(12), 2166; https://doi.org/10.3390/en10122166 - 18 Dec 2017

Cited by 11 | Viewed by 4550

Abstract

The cooling efficiency of natural draft dry cooling system (NDDCS) are vulnerable to ambient winds, so the implementation of measures against the wind effects is of great importance. This work presents the combined air leading strategies to recover the flow and heat transfer [...] Read more.

The cooling efficiency of natural draft dry cooling system (NDDCS) are vulnerable to ambient winds, so the implementation of measures against the wind effects is of great importance. This work presents the combined air leading strategies to recover the flow and heat transfer performances of NDDCS. Following the energy balance among the exhaust steam, circulating water, and cooling air, numerical models of natural draft dry cooling systems with the combined air leading strategies are developed. The cooling air streamlines, volume effectiveness, thermal efficiency and outlet water temperature for each cooling delta of the large-scale heat exchanger are obtained. The overall volume effectiveness, average outlet water temperature of NDDCS and steam turbine back pressure are calculated. The results show that with the air leading strategies inside or outside the dry-cooling tower, the thermo-flow performances of natural draft dry cooling system are improved under all wind conditions. The combined inner and outer air leading strategies are superior to other single strategy in the performance recovery, thus can be recommended for NDDCS in power generating units. Full article

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Open AccessArticle

Influence of the Periodicity of Sinusoidal Boundary Condition on the Unsteady Mixed Convection within a Square Enclosure Using an Ag–Water Nanofluid

by Azharul Karim, M. Masum Billah, M. T. Talukder Newton and M. Mustafizur Rahman

Energies 2017, 10(12), 2167; https://doi.org/10.3390/en10122167 - 18 Dec 2017

Cited by 12 | Viewed by 5083

Abstract

A numerical study of the unsteady mixed convection heat transfer characteristics of an Ag–water nanofluid confined within a square shape lid-driven cavity has been carried out. The Galerkin weighted residual of the finite element method has been employed to investigate the effects of [...] Read more.

A numerical study of the unsteady mixed convection heat transfer characteristics of an Ag–water nanofluid confined within a square shape lid-driven cavity has been carried out. The Galerkin weighted residual of the finite element method has been employed to investigate the effects of the periodicity of sinusoidal boundary condition for a wide range of Grashof numbers (Gr) (10⁵ to 10⁷) with the parametric variation of sinusoidal even and odd frequency, N, from 1 to 6 at different instants (for τ = 0.1 and 1). It has been observed that both the Grashof number and the sinusoidal even and odd frequency have a significant influence on the streamlines and isotherms inside the cavity. The heat transfer rate enhanced by 90% from the heated surface as the Grashof number (Gr) increased from 10⁵ to 10⁷ at sinusoidal frequency N = 1 and τ = 1. Full article

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

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2323 KiB

Open AccessArticle

Adjusting the Parameters of Metal Oxide Gapless Surge Arresters’ Equivalent Circuits Using the Harmony Search Method

by Christos A. Christodoulou, Vasiliki Vita, Georgios Perantzakis, Lambros Ekonomou and George Milushev

Energies 2017, 10(12), 2168; https://doi.org/10.3390/en10122168 - 18 Dec 2017

Cited by 11 | Viewed by 4540

Abstract

The appropriate circuit modeling of metal oxide gapless surge arresters is critical for insulation coordination studies. Metal oxide arresters present a dynamic behavior for fast front surges; namely, their residual voltage is dependent on the peak value, as well as the duration of [...] Read more.

The appropriate circuit modeling of metal oxide gapless surge arresters is critical for insulation coordination studies. Metal oxide arresters present a dynamic behavior for fast front surges; namely, their residual voltage is dependent on the peak value, as well as the duration of the injected impulse current, and should therefore not only be represented by non-linear elements. The aim of the current work is to adjust the parameters of the most frequently used surge arresters’ circuit models by considering the magnitude of the residual voltage, as well as the dissipated energy for given pulses. In this aim, the harmony search method is implemented to adjust parameter values of the arrester equivalent circuit models. This functions by minimizing a defined objective function that compares the simulation outcomes with the manufacturer’s data and the results obtained from previous methodologies. Full article

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

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3102 KiB

Open AccessArticle

Nuclear Power Learning and Deployment Rates; Disruption and Global Benefits Forgone

by Peter A. Lang

Energies 2017, 10(12), 2169; https://doi.org/10.3390/en10122169 - 18 Dec 2017

Cited by 11 | Viewed by 48532

Abstract

This paper presents evidence of the disruption of a transition from fossil fuels to nuclear power, and finds the benefits forgone as a consequence are substantial. Learning rates are presented for nuclear power in seven countries, comprising 58% of all power reactors ever [...] Read more.

This paper presents evidence of the disruption of a transition from fossil fuels to nuclear power, and finds the benefits forgone as a consequence are substantial. Learning rates are presented for nuclear power in seven countries, comprising 58% of all power reactors ever built globally. Learning rates and deployment rates changed in the late-1960s and 1970s from rapidly falling costs and accelerating deployment to rapidly rising costs and stalled deployment. Historical nuclear global capacity, electricity generation and overnight construction costs are compared with the counterfactual that pre-disruption learning and deployment rates had continued to 2015. Had the early rates continued, nuclear power could now be around 10% of its current cost. The additional nuclear power could have substituted for 69,000–186,000 TWh of coal and gas generation, thereby avoiding up to 9.5 million deaths and 174 Gt CO₂ emissions. In 2015 alone, nuclear power could have replaced up to 100% of coal-generated and 76% of gas-generated electricity, thereby avoiding up to 540,000 deaths and 11 Gt CO₂. Rapid progress was achieved in the past and could be again, with appropriate policies. Research is needed to identify impediments to progress, and policy is needed to remove them. Full article

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

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3360 KiB

Open AccessArticle

Spatial Distribution of the Baltic Sea Near-Shore Wave Power Potential along the Coast of Klaipėda, Lithuania

by Egidijus Kasiulis, Jens Peter Kofoed, Arvydas Povilaitis and Algirdas Radzevičius

Energies 2017, 10(12), 2170; https://doi.org/10.3390/en10122170 - 19 Dec 2017

Cited by 5 | Viewed by 3863

Abstract

Wave power is an abundant source of energy that can be utilized to produce electricity. Therefore, assessments of wave power resources are being carried out worldwide. An overview of the recent assessments is presented in this paper, revealing the global distribution of these [...] Read more.

Wave power is an abundant source of energy that can be utilized to produce electricity. Therefore, assessments of wave power resources are being carried out worldwide. An overview of the recent assessments is presented in this paper, revealing the global distribution of these resources. Additionally, a study, which aims to assess the spatial distribution of the Baltic Sea near-shore wave power potential along the coast of Klaipėda (Lithuania), is introduced in this paper. The impacts of the wave propagation direction and decreasing depth on wave power resources were examined using the numerical wind-wave model MIKE 21 NSW. The wave height loss of the design waves propagating to shore was modelled, and the wave power fluxes in the studied depths were calculated using the JONSWAP wave spectrum modified for the Baltic Sea. The results revealed that all waves that propagate to the shore in the Baltic Sea near-shore area along the coast of Klaipėda from 30 m depth to 5 m depth lose at least 30% of their power. Still, most common waves in this area are low, and therefore, they start to lose their power while propagating to the shore at relatively low (10–14 m) depths. To turn this into an advantage the wave power converter would have to work efficiently under low power conditions. Full article

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2011 KiB

Open AccessArticle

Decoupling Weather Influence from User Habits for an Optimal Electric Load Forecast System

by Luca Massidda and Marino Marrocu

Energies 2017, 10(12), 2171; https://doi.org/10.3390/en10122171 - 19 Dec 2017

Cited by 15 | Viewed by 3556

Abstract

The balance between production and consumption in a smart grid with high penetration of renewable sources and in the presence of energy storage systems benefits from an accurate load prediction. A general approach to load forecasting is not possible because of the additional [...] Read more.

The balance between production and consumption in a smart grid with high penetration of renewable sources and in the presence of energy storage systems benefits from an accurate load prediction. A general approach to load forecasting is not possible because of the additional complication due to the increasing presence of distributed and usually unmeasured photovoltaic production. Various methods are proposed in the literature that can be classified into two classes: those that predict by separating the portion of load due to consumption habits from the part of production due to local weather conditions, and those that attempt to predict the load as a whole. The characteristic that should lead to a preference for one approach over another is obviously the percentage of penetration of distributed production. The study site discussed in this document is the grid of Borkum, an island located in the North Sea. The advantages in terms of reducing forecasting errors for the electrical load, which can be obtained by using weather information, are explained. In particular, when comparing the results of different approaches gradually introducing weather forecasts, it is clear that the correct functional dependency of production has to be taken into account in order to obtain maximum yield from the available information. Where possible, this approach can significantly improve the quality of the forecasts, which in turn can improve the balance of a network—especially if energy storage systems are in place. Full article

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

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2742 KiB

Open AccessArticle

Effects of Mixture Stratification on Combustion and Emissions of Boosted Controlled Auto-Ignition Engines

by Jacek Hunicz, Aymen Tmar and Paweł Krzaczek

Energies 2017, 10(12), 2172; https://doi.org/10.3390/en10122172 - 19 Dec 2017

Cited by 16 | Viewed by 6025

Abstract

The stratification of in-cylinder mixtures appears to be an effective method for managing the combustion process in controlled auto-ignition (CAI) engines. Stratification can be achieved and controlled using various injection strategies such as split fuel injection and the introduction of a portion of [...] Read more.

The stratification of in-cylinder mixtures appears to be an effective method for managing the combustion process in controlled auto-ignition (CAI) engines. Stratification can be achieved and controlled using various injection strategies such as split fuel injection and the introduction of a portion of fuel directly before the start of combustion. This study investigates the effect of injection timing and the amount of fuel injected for stratification on the combustion and emissions in CAI engine. The experimental research was performed on a single cylinder engine with direct gasoline injection. CAI combustion was achieved using negative valve overlap and exhaust gas trapping. The experiments were performed at constant engine fueling. Intake boost was applied to control the excess air ratio. The results show that the application of the late injection strategy has a significant effect on the heat release process. In general, the later the injection is and the more fuel is injected for stratification, the earlier the auto-ignition occurs. However, the experimental findings reveal that the effect of stratification on combustion duration is much more complex. Changes in combustion are reflected in NO_X emissions. The attainable level of stratification is limited by the excessive emission of unburned hydrocarbons, CO and soot. Full article

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22729 KiB

Open AccessArticle

Investigation of the Magnetic Circuit and Performance of Less-Rare-Earth Interior Permanent-Magnet Synchronous Machines Used for Electric Vehicles

by Ping Zheng, Weinan Wang, Mingqiao Wang, Yong Liu and Zhenxing Fu

Energies 2017, 10(12), 2173; https://doi.org/10.3390/en10122173 - 19 Dec 2017

Cited by 8 | Viewed by 4399

Abstract

The less-rare-earth interior permanent-magnet synchronous machines (LRE-IPMSMs), which have the advantages of high power density, high efficiency, and low cost, are promising candidates for electric vehicles (EVs). In this paper, the equivalent magnetic circuit (EMC) of LRE-IPMSM is established and analyzed to investigate [...] Read more.

The less-rare-earth interior permanent-magnet synchronous machines (LRE-IPMSMs), which have the advantages of high power density, high efficiency, and low cost, are promising candidates for electric vehicles (EVs). In this paper, the equivalent magnetic circuit (EMC) of LRE-IPMSM is established and analyzed to investigate the machine design principles, and then the performance of an optimized machine is analyzed. Firstly, the equivalent magnetic circuits of the LRE-IPMSM are established by taking the saturation effect into consideration. Secondly, the effects of geometric parameters, such as the permanent-magnet (PM) width, the PM thickness, the flux barrier thickness, the flux barrier span angle, and the bridge width, on no-load flux, q-axis flux, and d-axis flux are investigated, respectively. The results calculated by the EMC method and finite-element analysis (FEA) are analyzed and compared, which proves the effectiveness of the EMC method. Finally, an optimized design of LRE-IPMSM obtained by the magnetic circuit analyses is proposed. The electromagnetic performances and mechanical strength of the optimized LRE-IPMSM are analyzed and verified, respectively. Full article

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4140 KiB

Open AccessArticle

Comparison of Lithium-Ion Anode Materials Using an Experimentally Verified Physics-Based Electrochemical Model

by Rujian Fu, Xuan Zhou, Hengbin Fan, Douglas Blaisdell, Ajay Jagadale, Xi Zhang and Rui Xiong

Energies 2017, 10(12), 2174; https://doi.org/10.3390/en10122174 - 19 Dec 2017

Cited by 23 | Viewed by 5921

Abstract

Researchers are in search of parameters inside Li-ion batteries that can be utilized to control their external behavior. Physics-based electrochemical model could bridge the gap between Li+ transportation and distribution inside battery and battery performance outside. In this paper, two commercially available Li-ion [...] Read more.

Researchers are in search of parameters inside Li-ion batteries that can be utilized to control their external behavior. Physics-based electrochemical model could bridge the gap between Li+ transportation and distribution inside battery and battery performance outside. In this paper, two commercially available Li-ion anode materials: graphite and Lithium titanate (Li₄Ti₅O₁₂ or LTO) were selected and a physics-based electrochemical model was developed based on half-cell assembly and testing. It is found that LTO has a smaller diffusion coefficient (D_s) than graphite, which causes a larger overpotential, leading to a smaller capacity utilization and, correspondingly, a shorter duration of constant current charge or discharge. However, in large current applications, LTO performs better than graphite because its effective particle radius decreases with increasing current, leading to enhanced diffusion. In addition, LTO has a higher activation overpotential in its side reactions; its degradation rate is expected to be much smaller than graphite, indicating a longer life span. Full article

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

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8155 KiB

Open AccessArticle

Experimental and Finite Element Analysis to Investigate the Vibration of Oblique-Stud Stator Frame in a Large Hydropower Generator Unit

by Jianzhong Zhou, Xuanlin Peng, Ruhai Li, Yanhe Xu, Han Liu and Diyi Chen

Energies 2017, 10(12), 2175; https://doi.org/10.3390/en10122175 - 19 Dec 2017

Cited by 13 | Viewed by 6018

Abstract

This paper presents an investigation on the undesirable vibration of an oblique-stud stator frame in a large hydropower generator by means of experimental and finite element (FE) analysis. First, field experimental tests were performed, and the results indicate that the main vibration component [...] Read more.

This paper presents an investigation on the undesirable vibration of an oblique-stud stator frame in a large hydropower generator by means of experimental and finite element (FE) analysis. First, field experimental tests were performed, and the results indicate that the main vibration component comes from electromagnetic factors. Then, a 2D-magnetic and 3D-mechanical FE model was developed to investigate the vibration of the stator frame under the action of electromagnetic forces. A set of contrast models was established to study the effects of different kinds of eccentricity and different structures. Based on the comparative analysis between the results of simulations and experimental tests, it can be inferred that the abnormal vibration is generated because of the lack of stiffness in the upper part of structure and the existence of dynamic eccentricity in the rotor–stator system. In addition, the structural simulation analysis shows that the flexible designed oblique-stud stator frame is relatively vulnerable against the electromagnetic forces. Full article

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2807 KiB

Open AccessArticle

Modeling and Stability Analysis of a Single-Phase Two-Stage Grid-Connected Photovoltaic System

by Liying Huang, Dongyuan Qiu, Fan Xie, Yanfeng Chen and Bo Zhang

Energies 2017, 10(12), 2176; https://doi.org/10.3390/en10122176 - 19 Dec 2017

Cited by 21 | Viewed by 6009

Abstract

The stability issue of a single-phase two-stage grid-connected photovoltaic system is complicated due to the nonlinear v-i characteristic of the photovoltaic array as well as the interaction between power converters. Besides, even though linear system theory is widely used in stability [...] Read more.

The stability issue of a single-phase two-stage grid-connected photovoltaic system is complicated due to the nonlinear v-i characteristic of the photovoltaic array as well as the interaction between power converters. Besides, even though linear system theory is widely used in stability analysis of balanced three-phase systems, the application of the same theory to single-phase systems meets serious challenges, since single-phase systems cannot be transformed into linear time-invariant systems simply using Park transformation as balanced three-phase systems. In this paper, (1) the integrated mathematical model of a single-phase two-stage grid-connected photovoltaic system is established, in which both DC-DC converter and DC-AC converter are included also the characteristic of the PV array is considered; (2) an observer-pattern modeling method is used to eliminate the time-varying variables; and (3) the stability of the system is studied using eigenvalue sensitivity and eigenvalue loci plots. Finally, simulation results are given to validate the proposed model and stability analysis. Full article

(This article belongs to the Special Issue PV System Design and Performance)

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4993 KiB

Open AccessArticle

Analysis of the Influence of Compensation Capacitance Errors of a Wireless Power Transfer System with SS Topology

by Yi Wang, Fei Lin, Zhongping Yang and Zhiyuan Liu

Energies 2017, 10(12), 2177; https://doi.org/10.3390/en10122177 - 19 Dec 2017

Cited by 8 | Viewed by 4623

Abstract

In this study, in order to determine the reasonable accuracy of the compensation capacitances satisfying the requirements on the output characteristics for a wireless power transfer (WPT) system, taking the series-series (SS) compensation structure as an example, the calculation formulas of the output [...] Read more.

In this study, in order to determine the reasonable accuracy of the compensation capacitances satisfying the requirements on the output characteristics for a wireless power transfer (WPT) system, taking the series-series (SS) compensation structure as an example, the calculation formulas of the output characteristics, such as the power factor, output power, coil transfer efficiency, and capacitors’ voltage stress, are given under the condition of incomplete compensation according to circuit theory. The influence of compensation capacitance errors on the output characteristics of the system is then analyzed. The Taylor expansions of the theoretical formulas are carried out to simplify the formulas. The influence degrees of compensation capacitance errors on the output characteristics are calculated according to the simplified formulas. The reasonable error ranges of the compensation capacitances are then determined according to the requirements of the output characteristics of the system in the system design. Finally, the validity of the theoretical analysis and the simplified processing is verified through experiments. The proposed method has a certain guiding role for practical engineering design, especially in mass production. Full article

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

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4466 KiB

Open AccessArticle

Extension of Operating Range in Pump-Turbines. Influence of Head and Load

by Carme Valero, Mònica Egusquiza, Eduard Egusquiza, Alexandre Presas, David Valentin and Matias Bossio

Energies 2017, 10(12), 2178; https://doi.org/10.3390/en10122178 - 19 Dec 2017

Cited by 31 | Viewed by 5205

Abstract

Due to the increasing share of new renewable energies like wind and solar in the generation of electricity the need for power regulation and energy storage is becoming of paramount importance. One of the systems to store huge amounts of energy is pumped [...] Read more.

Due to the increasing share of new renewable energies like wind and solar in the generation of electricity the need for power regulation and energy storage is becoming of paramount importance. One of the systems to store huge amounts of energy is pumped storage using reversible hydropower units. The machines used in these power plants are pump-turbines, which can operate as a pump and as a turbine. The surplus of electrical energy during low consumption hours can be converted into potential hydraulic energy by pumping water to a higher level. The stored energy can be converted into electricity again by operating the runner as a turbine. Due to new regulation requirements machines have to extend the operating range in order to match energy generation with consumption for the grid stability. In this paper the consequences of extending the operating range in existing pump-turbines have been studied. For that purpose, the data obtained after two years of condition monitoring were analyzed. Vibrations and pressure fluctuations of two pump-turbines of 85 MW each have been studied during pump and turbine operation. For turbine operation the effects of extending the operating range from the standard range of 45–85 MW to and increased range of 20–85 MW were analyzed. The change in vibration levels and signatures at very low load are presented with the identification of the phenomena that occur under these conditions. The influence of head in the vibration behavior is also presented. The appearance of fluid instabilities generated at part load that may produce power swing is also presented. Finally, the effect of head on the vibration levels for pump operation is shown and analyzed. Full article

(This article belongs to the Special Issue Hydropower 2017)

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1960 KiB

Open AccessArticle

A Probabilistically Constrained Approach for the Energy Procurement Problem

by Patrizia Beraldi, Antonio Violi, Maria Elena Bruni and Gianluca Carrozzino

Energies 2017, 10(12), 2179; https://doi.org/10.3390/en10122179 - 19 Dec 2017

Cited by 15 | Viewed by 3698

Abstract

The definition of the electric energy procurement plan represents a fundamental problem that any consumer has to deal with. Bilateral contracts, electricity market and self-production are the main supply sources that should be properly combined to satisfy the energy demand over a given [...] Read more.

The definition of the electric energy procurement plan represents a fundamental problem that any consumer has to deal with. Bilateral contracts, electricity market and self-production are the main supply sources that should be properly combined to satisfy the energy demand over a given time horizon at the minimum cost. The problem is made more complex by the presence of uncertainty, mainly related to the energy requirements and electricity market prices. Ignoring the uncertain nature of these elements can lead to the definition of procurement plans which are infeasible or overly expensive in a real setting. In this paper, we deal with the procurement problem under uncertainty by adopting the paradigm of joint chance constraints to define reliable plans that are feasible with a high probability level. Moreover, the proposed model includes in the objective function a risk measure to control undesirable effects caused by the random variations of the electricity market prices. The proposed model is applied to a real test case. The results show the benefit deriving from the stochastic optimization approach and the effect of considering different levels of risk aversion. 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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4970 KiB

Open AccessArticle

Hybrid Chaotic Quantum Bat Algorithm with SVR in Electric Load Forecasting

by Ming-Wei Li, Jing Geng, Shumei Wang and Wei-Chiang Hong

Energies 2017, 10(12), 2180; https://doi.org/10.3390/en10122180 - 19 Dec 2017

Cited by 37 | Viewed by 5075

Abstract

Hybridizing evolutionary algorithms with a support vector regression (SVR) model to conduct the electric load forecasting has demonstrated the superiorities in forecasting accuracy improvements. The recently proposed bat algorithm (BA), compared with classical GA and PSO algorithm, has greater potential in forecasting accuracy [...] Read more.

Hybridizing evolutionary algorithms with a support vector regression (SVR) model to conduct the electric load forecasting has demonstrated the superiorities in forecasting accuracy improvements. The recently proposed bat algorithm (BA), compared with classical GA and PSO algorithm, has greater potential in forecasting accuracy improvements. However, the original BA still suffers from the embedded drawbacks, including trapping in local optima and premature convergence. Hence, to continue exploring possible improvements of the original BA and to receive more appropriate parameters of an SVR model, this paper applies quantum computing mechanism to empower each bat to possess quantum behavior, then, employs the chaotic mapping function to execute the global chaotic disturbance process, to enlarge bat’s search space and to make the bat jump out from the local optima when population is over accumulation. This paper presents a novel load forecasting approach, namely SVRCQBA model, by hybridizing the SVR model with the quantum computing mechanism, chaotic mapping function, and BA, to receive higher forecasting accuracy. The numerical results demonstrate that the proposed SVRCQBA model is superior to other alternative models in terms of forecasting accuracy. Full article

(This article belongs to the Special Issue Hybrid Advanced Optimization Methods with Evolutionary Computation Techniques in Energy Forecasting)

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Review

Jump to: Editorial, Research, Other

1633 KiB

Open AccessFeature PaperReview

Lithium-Sulfur Battery Technology Readiness and Applications—A Review

by Abbas Fotouhi, Daniel J. Auger, Laura O’Neill, Tom Cleaver and Sylwia Walus

Energies 2017, 10(12), 1937; https://doi.org/10.3390/en10121937 - 23 Nov 2017

Cited by 143 | Viewed by 13353

Abstract

Lithium Sulfur (Li-S) battery is generally considered as a promising technology where high energy density is required at different applications. Over the past decade, there has been an ever increasing volume of Li-S academic research spanning materials development, fundamental understanding and modelling, and [...] Read more.

Lithium Sulfur (Li-S) battery is generally considered as a promising technology where high energy density is required at different applications. Over the past decade, there has been an ever increasing volume of Li-S academic research spanning materials development, fundamental understanding and modelling, and application-based control algorithm development. In this study, the Li-S battery technology, its advantages and limitations from the fundamental perspective are firstly discussed. In the second part of this study, state-of-the-art Li-S cell modelling and state estimation techniques are reviewed with a focus on practical applications. The existing studies on Li-S cell equivalent-circuit-network modelling and state estimation techniques are then discussed. A number of challenges in control of Li-S battery are also explained such as the flat open-circuit-voltage curve and high sensitivity of Li-S cell’s behavior to temperature variation. In the last part of this study, current and future applications of Li-S battery are mentioned. Full article

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

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7842 KiB

Open AccessReview

Operational Range of Several Interface Algorithms for Different Power Hardware-In-The-Loop Setups

by Ron Brandl

Energies 2017, 10(12), 1946; https://doi.org/10.3390/en10121946 - 23 Nov 2017

Cited by 41 | Viewed by 4960

Abstract

The importance of Power Hardware-in-the-Loop (PHIL) experiments is rising more and more over the last decade in the field of power system and components testing. Due to the bidirectional exchange between virtual and physical systems, a true-to-reality interface is essential; however, linking several [...] Read more.

The importance of Power Hardware-in-the-Loop (PHIL) experiments is rising more and more over the last decade in the field of power system and components testing. Due to the bidirectional exchange between virtual and physical systems, a true-to-reality interface is essential; however, linking several dynamic systems, stability issues can challenge the experiments, the components under test, and the individuals performing the experiments. Over the time, several interface algorithms (IA) have been developed and analyzed, each having different advantages and disadvantages in view of combining virtual simulations with physical power systems. Finally, IA are very specific to the kind of PHIL experiment. This paper investigates the operational range of several IA for specific PHIL setups by calculations, simulations, and measurements. Therefore, a selection of the mainly used respectively optimized IA is mathematically described. The operational range is verified in a PHIL system testing environment. Furthermore, in order to study the influence of different PHIL setups, according to software and hardware impedance, different tests using linear and switching amplifiers are performed. Full article

(This article belongs to the Special Issue Methods and Concepts for Designing and Validating Smart Grid Systems)

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Open AccessReview

A Review of Design Optimization Methods for Electrical Machines

by Gang Lei, Jianguo Zhu, Youguang Guo, Chengcheng Liu and Bo Ma

Energies 2017, 10(12), 1962; https://doi.org/10.3390/en10121962 - 24 Nov 2017

Cited by 164 | Viewed by 14020

Abstract

Electrical machines are the hearts of many appliances, industrial equipment and systems. In the context of global sustainability, they must fulfill various requirements, not only physically and technologically but also environmentally. Therefore, their design optimization process becomes more and more complex as more [...] Read more.

Electrical machines are the hearts of many appliances, industrial equipment and systems. In the context of global sustainability, they must fulfill various requirements, not only physically and technologically but also environmentally. Therefore, their design optimization process becomes more and more complex as more engineering disciplines/domains and constraints are involved, such as electromagnetics, structural mechanics and heat transfer. This paper aims to present a review of the design optimization methods for electrical machines, including design analysis methods and models, optimization models, algorithms and methods/strategies. Several efficient optimization methods/strategies are highlighted with comments, including surrogate-model based and multi-level optimization methods. In addition, two promising and challenging topics in both academic and industrial communities are discussed, and two novel optimization methods are introduced for advanced design optimization of electrical machines. First, a system-level design optimization method is introduced for the development of advanced electric drive systems. Second, a robust design optimization method based on the design for six-sigma technique is introduced for high-quality manufacturing of electrical machines in production. Meanwhile, a proposal is presented for the development of a robust design optimization service based on industrial big data and cloud computing services. Finally, five future directions are proposed, including smart design optimization method for future intelligent design and production of electrical machines. Full article

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

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1719 KiB

Open AccessReview

Lithium Ion Battery Models and Parameter Identification Techniques

by Simone Barcellona and Luigi Piegari

Energies 2017, 10(12), 2007; https://doi.org/10.3390/en10122007 - 1 Dec 2017

Cited by 108 | Viewed by 14991

Abstract

Nowadays, battery storage systems are very important in both stationary and mobile applications. In particular, lithium ion batteries are a good and promising solution because of their high power and energy densities. The modeling of these devices is very crucial to correctly predict [...] Read more.

Nowadays, battery storage systems are very important in both stationary and mobile applications. In particular, lithium ion batteries are a good and promising solution because of their high power and energy densities. The modeling of these devices is very crucial to correctly predict their state of charge (SoC) and state of health (SoH). The literature shows that numerous battery models and parameters estimation techniques have been developed and proposed. Moreover, surveys on their electric, thermal, and aging modeling are also reported. This paper presents a more complete overview of the different proposed battery models and estimation techniques. In particular, a method for classifying the proposed models based on their approaches is proposed. For this classification, the models are divided in three categories: mathematical models, physical models, and circuit models. Full article

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3566 KiB

Open AccessReview

Control Algorithms of Shunt Active Power Filter for Harmonics Mitigation: A Review

by Yap Hoon, Mohd Amran Mohd Radzi, Mohd Khair Hassan and Nashiren Farzilah Mailah

Energies 2017, 10(12), 2038; https://doi.org/10.3390/en10122038 - 3 Dec 2017

Cited by 132 | Viewed by 10792

Abstract

Current harmonics is one of the most significant power quality issues which has attracted tremendous research interest. Shunt active power filter (SAPF) is the best solution to minimize harmonic contamination, but its effectiveness is strictly dependent on how quickly and accurately its control [...] Read more.

Current harmonics is one of the most significant power quality issues which has attracted tremendous research interest. Shunt active power filter (SAPF) is the best solution to minimize harmonic contamination, but its effectiveness is strictly dependent on how quickly and accurately its control algorithms can perform. This manuscript reviews various types of existing control algorithms which have been employed for controlling operation of SAPF. Harmonic extraction, DC-link capacitor voltage regulation, current control and synchronizer algorithms are examined and discussed. The most relevant techniques which have been applied for each control algorithm are described and contrasted in an organized manner to identify their respective strengths and weaknesses. It is found that the applied control algorithms differ in two conditions: (1) the condition where harmonic current distortion is treated by the SAPF in the presence of non-ideal source voltage; and (2) the condition where multilevel inverter is employed as the circuit topology of SAPF. Full article

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9222 KiB

Open AccessReview

Characterisation of Ground Thermal and Thermo-Mechanical Behaviour for Shallow Geothermal Energy Applications

by Ana Vieira, Maria Alberdi-Pagola, Paul Christodoulides, Saqib Javed, Fleur Loveridge, Frederic Nguyen, Francesco Cecinato, João Maranha, Georgios Florides, Iulia Prodan, Gust Van Lysebetten, Elsa Ramalho, Diana Salciarini, Aleksandar Georgiev, Sandrine Rosin-Paumier, Rumen Popov, Stanislav Lenart, Søren Erbs Poulsen and Georgia Radioti

Energies 2017, 10(12), 2044; https://doi.org/10.3390/en10122044 - 3 Dec 2017

Cited by 80 | Viewed by 11979

Abstract

Increasing use of the ground as a thermal reservoir is expected in the near future. Shallow geothermal energy (SGE) systems have proved to be sustainable alternative solutions for buildings and infrastructure conditioning in many areas across the globe in the past decades. Recently [...] Read more.

Increasing use of the ground as a thermal reservoir is expected in the near future. Shallow geothermal energy (SGE) systems have proved to be sustainable alternative solutions for buildings and infrastructure conditioning in many areas across the globe in the past decades. Recently novel solutions, including energy geostructures, where SGE systems are coupled with foundation heat exchangers, have also been developed. The performance of these systems is dependent on a series of factors, among which the thermal properties of the soil play a major role. The purpose of this paper is to present, in an integrated manner, the main methods and procedures to assess ground thermal properties for SGE systems and to carry out a critical review of the methods. In particular, laboratory testing through either steady-state or transient methods are discussed and a new synthesis comparing results for different techniques is presented. In situ testing including all variations of the thermal response test is presented in detail, including a first comparison between new and traditional approaches. The issue of different scales between laboratory and in situ measurements is then analysed in detail. Finally, the thermo-hydro-mechanical behaviour of soil is introduced and discussed. These coupled processes are important for confirming the structural integrity of energy geostructures, but routine methods for parameter determination are still lacking. Full article

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6003 KiB

Open AccessReview

Insertion of Mono- vs. Bi- vs. Trivalent Atoms in Prospective Active Electrode Materials for Electrochemical Batteries: An ab Initio Perspective

by Vadym V. Kulish, Daniel Koch and Sergei Manzhos

Energies 2017, 10(12), 2061; https://doi.org/10.3390/en10122061 - 5 Dec 2017

Cited by 9 | Viewed by 5905

Abstract

Rational design of active electrode materials is important for the development of advanced lithium and post-lithium batteries. Ab initio modeling can provide mechanistic understanding of the performance of prospective materials and guide design. We review our recent comparative ab initio studies of lithium, [...] Read more.

Rational design of active electrode materials is important for the development of advanced lithium and post-lithium batteries. Ab initio modeling can provide mechanistic understanding of the performance of prospective materials and guide design. We review our recent comparative ab initio studies of lithium, sodium, potassium, magnesium, and aluminum interactions with different phases of several actively experimentally studied electrode materials, including monoelemental materials carbon, silicon, tin, and germanium, oxides TiO₂ and V_xO_y as well as sulphur-based spinels MS₂ (M = transition metal). These studies are unique in that they provided reliable comparisons, i.e., at the same level of theory and using the same computational parameters, among different materials and among Li, Na, K, Mg, and Al. Specifically, insertion energetics (related to the electrode voltage) and diffusion barriers (related to rate capability), as well as phononic effects, are compared. These studies facilitate identification of phases most suitable as anode or cathode for different types of batteries. We highlight the possibility of increasing the voltage, or enabling electrochemical activity, by amorphization and p-doping, of rational choice of phases of oxides to maximize the insertion potential of Li, Na, K, Mg, Al, as well as of rational choice of the optimum sulfur-based spinel for Mg and Al insertion, based on ab initio calculations. Some methodological issues are also addressed, including construction of effective localized basis sets, applications of Hubbard correction, generation of amorphous structures, and the use of a posteriori dispersion corrections. Full article

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11974 KiB

Open AccessReview

Cross-Layer Energy Optimization for IoT Environments: Technical Advances and Opportunities

by Kirshna Kumar, Sushil Kumar, Omprakash Kaiwartya, Yue Cao, Jaime Lloret and Nauman Aslam

Energies 2017, 10(12), 2073; https://doi.org/10.3390/en10122073 - 6 Dec 2017

Cited by 44 | Viewed by 8107

Abstract

Energy efficiency is a significant characteristic of battery-run devices such as sensors, RFID and mobile phones. In the present scenario, this is the most prominent requirement that must be served while introducing a communication protocol for an IoT environment. IoT network success and [...] Read more.

Energy efficiency is a significant characteristic of battery-run devices such as sensors, RFID and mobile phones. In the present scenario, this is the most prominent requirement that must be served while introducing a communication protocol for an IoT environment. IoT network success and performance enhancement depend heavily on optimization of energy consumption that enhance the lifetime of IoT nodes and the network. In this context, this paper presents a comprehensive review on energy efficiency techniques used in IoT environments. The techniques proposed by researchers have been categorized based on five different layers of the energy architecture of IoT. These five layers are named as sensing, local processing and storage, network/communication, cloud processing and storage, and application. Specifically, the significance of energy efficiency in IoT environments is highlighted. A taxonomy is presented for the classification of related literature on energy efficient techniques in IoT environments. Following the taxonomy, a critical review of literature is performed focusing on major functional models, strengths and weaknesses. Open research challenges related to energy efficiency in IoT are identified as future research directions in the area. The survey should benefit IoT industry practitioners and researchers, in terms of augmenting the understanding of energy efficiency and its IoT-related trends and issues. Full article

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2406 KiB

Open AccessReview

Structural Reliability Analysis of Wind Turbines: A Review

by Zhiyu Jiang, Weifei Hu, Wenbin Dong, Zhen Gao and Zhengru Ren

Energies 2017, 10(12), 2099; https://doi.org/10.3390/en10122099 - 11 Dec 2017

Cited by 88 | Viewed by 13789

Abstract

The paper presents a detailed review of the state-of-the-art research activities on structural reliability analysis of wind turbines between the 1990s and 2017. We describe the reliability methods including the first- and second-order reliability methods and the simulation reliability methods and show the [...] Read more.

The paper presents a detailed review of the state-of-the-art research activities on structural reliability analysis of wind turbines between the 1990s and 2017. We describe the reliability methods including the first- and second-order reliability methods and the simulation reliability methods and show the procedure for and application areas of structural reliability analysis of wind turbines. Further, we critically review the various structural reliability studies on rotor blades, bottom-fixed support structures, floating systems and mechanical and electrical components. Finally, future applications of structural reliability methods to wind turbine designs are discussed. Full article

(This article belongs to the Collection Wind Turbines)

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1342 KiB

Open AccessReview

State-Of-The-Art and Prospects for Peer-To-Peer Transaction-Based Energy System

by Olamide Jogunola, Augustine Ikpehai, Kelvin Anoh, Bamidele Adebisi, Mohammad Hammoudeh, Sung-Yong Son and Georgina Harris

Energies 2017, 10(12), 2106; https://doi.org/10.3390/en10122106 - 11 Dec 2017

Cited by 104 | Viewed by 9805

Abstract

Transaction-based energy (TE) management and control has become an increasingly relevant topic, attracting considerable attention from industry and the research community alike. As a result, new techniques are emerging for its development and actualization. This paper presents a comprehensive review of TE involving [...] Read more.

Transaction-based energy (TE) management and control has become an increasingly relevant topic, attracting considerable attention from industry and the research community alike. As a result, new techniques are emerging for its development and actualization. This paper presents a comprehensive review of TE involving peer-to-peer (P2P) energy trading and also covering the concept, enabling technologies, frameworks, active research efforts and the prospects of TE. The formulation of a common approach for TE management modelling is challenging given the diversity of circumstances of prosumers in terms of capacity, profiles and objectives. This has resulted in divergent opinions in the literature. The idea of this paper is therefore to explore these viewpoints and provide some perspectives on this burgeoning topic on P2P TE systems. This study identified that most of the techniques in the literature exclusively formulate energy trade problems as a game, an optimization problem or a variational inequality problem. It was also observed that none of the existing works has considered a unified messaging framework. This is a potential area for further investigation. Full article

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1535 KiB

Open AccessEditor’s ChoiceReview

Lithium-Ion Battery Storage for the Grid—A Review of Stationary Battery Storage System Design Tailored for Applications in Modern Power Grids

by Holger C. Hesse, Michael Schimpe, Daniel Kucevic and Andreas Jossen

Energies 2017, 10(12), 2107; https://doi.org/10.3390/en10122107 - 11 Dec 2017

Cited by 538 | Viewed by 46311

Abstract

Battery energy storage systems have gained increasing interest for serving grid support in various application tasks. In particular, systems based on lithium-ion batteries have evolved rapidly with a wide range of cell technologies and system architectures available on the market. On the application [...] Read more.

Battery energy storage systems have gained increasing interest for serving grid support in various application tasks. In particular, systems based on lithium-ion batteries have evolved rapidly with a wide range of cell technologies and system architectures available on the market. On the application side, different tasks for storage deployment demand distinct properties of the storage system. This review aims to serve as a guideline for best choice of battery technology, system design and operation for lithium-ion based storage systems to match a specific system application. Starting with an overview to lithium-ion battery technologies and their characteristics with respect to performance and aging, the storage system design is analyzed in detail based on an evaluation of real-world projects. Typical storage system applications are grouped and classified with respect to the challenges posed to the battery system. Publicly available modeling tools for technical and economic analysis are presented. A brief analysis of optimization approaches aims to point out challenges and potential solution techniques for system sizing, positioning and dispatch operation. For all areas reviewed herein, expected improvements and possible future developments are highlighted. In order to extract the full potential of stationary battery storage systems and to enable increased profitability of systems, future research should aim to a holistic system level approach combining not only performance tuning on a battery cell level and careful analysis of the application requirements, but also consider a proper selection of storage sub-components as well as an optimized system operation strategy. Full article

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

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4463 KiB

Open AccessReview

Utilization of Microalgal Biofractions for Bioethanol, Higher Alcohols, and Biodiesel Production: A Review

by Marwa M. El-Dalatony, El-Sayed Salama, Mayur B. Kurade, Sedky H. A. Hassan, Sang-Eun Oh, Sunjoon Kim and Byong-Hun Jeon

Energies 2017, 10(12), 2110; https://doi.org/10.3390/en10122110 - 12 Dec 2017

Cited by 56 | Viewed by 7785

Abstract

Biomass is a crucial energy resource used for the generation of electricity and transportation fuels. Microalgae exhibit a high content of biocomponents which makes them a potential feedstock for the generation of ecofriendly biofuels. Biofuels derived from microalgae are suitable carbon-neutral replacements for [...] Read more.

Biomass is a crucial energy resource used for the generation of electricity and transportation fuels. Microalgae exhibit a high content of biocomponents which makes them a potential feedstock for the generation of ecofriendly biofuels. Biofuels derived from microalgae are suitable carbon-neutral replacements for petroleum. Fermentation is the major process for metabolic conversion of microalgal biocompounds into biofuels such as bioethanol and higher alcohols. In this review, we explored the use of all three major biocomponents of microalgal biomass including carbohydrates, proteins, and lipids for maximum biofuel generation. Application of several pretreatment methods for enhancement the bioavailability of substrates (simple sugar, amino acid, and fatty acid) was discussed. This review goes one step further to discuss how to direct these biocomponents for the generation of various biofuels (bioethanol, higher alcohol, and biodiesel) through fermentation and transesterification processes. Such an approach would result in the maximum utilization of biomasses for economically feasible biofuel production. Full article

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

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Graphical abstract

3402 KiB

Open AccessFeature PaperReview

Rare Earth Borohydrides—Crystal Structures and Thermal Properties

by Christoph Frommen, Magnus H. Sørby, Michael Heere, Terry D. Humphries, Jørn E. Olsen and Bjørn C. Hauback

Energies 2017, 10(12), 2115; https://doi.org/10.3390/en10122115 - 12 Dec 2017

Cited by 42 | Viewed by 5262

Abstract

Rare earth (RE) borohydrides have received considerable attention during the past ten years as possible hydrogen storage materials due to their relatively high gravimetric hydrogen density. This review illustrates the rich chemistry, structural diversity and thermal properties of borohydrides containing RE [...] Read more.

Rare earth (RE) borohydrides have received considerable attention during the past ten years as possible hydrogen storage materials due to their relatively high gravimetric hydrogen density. This review illustrates the rich chemistry, structural diversity and thermal properties of borohydrides containing RE elements. In addition, it highlights the decomposition and rehydrogenation properties of composites containing RE-borohydrides, light-weight metal borohydrides such as LiBH₄ and additives such as LiH. Full article

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501 KiB

Open AccessReview

Evaluating Energy Policies through the Use of a Hybrid Quantitative Indicator-Based Approach: The Case of Mercosur

by Thauan Santos, Amaro Olímpio Pereira Júnior and Emilio Lèbre La Rovere

Energies 2017, 10(12), 2140; https://doi.org/10.3390/en10122140 - 15 Dec 2017

Cited by 6 | Viewed by 3015

Abstract

This paper evaluates the performance of energy policies in the Southern Common Market (Mercosur), a regional initiative consisting of Argentina, Brazil, Paraguay and Uruguay, but also considering Venezuela (full member since mid-2012) and Bolivia (full participation under negotiation since 2015). The methodology is [...] Read more.

This paper evaluates the performance of energy policies in the Southern Common Market (Mercosur), a regional initiative consisting of Argentina, Brazil, Paraguay and Uruguay, but also considering Venezuela (full member since mid-2012) and Bolivia (full participation under negotiation since 2015). The methodology is based on a qualitative-quantitative approach. First, we provide a critical review of the literature on energy security. Then, we carry out a comparative analysis of energy policies in Mercosur countries, concluding that there is no harmonization between them. Next, we offer the new concept of socio-environmental-energy security (SEES) as a more suitable approach to deal with current challenges, providing a hybrid quantitative indicator-based approach to the SEES index. Ergo, after defining the indicators, selecting the data, carrying out a normalization process, assigning weights and aggregating data points, the SEES composite index is generated. We suggest that energy integration can contribute to better regional performance in terms of energy policies and that the SEES index can guide policy makers and investments, replacing the old-fashioned concept of energy security. Full article

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

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1473 KiB

Open AccessReview

The Impact of Urban Design Descriptors on Outdoor Thermal Environment: A Literature Review

by Pingying Lin, Zhonghua Gou, Stephen Siu-Yu Lau and Hao Qin

Energies 2017, 10(12), 2151; https://doi.org/10.3390/en10122151 - 15 Dec 2017

Cited by 79 | Viewed by 7580

Abstract

This paper presents a literature review on urban design indicators addressing the impact of urban geometry and vegetation on the outdoor thermal environment at the pedestrian level, as urban geometry and vegetation have been regarded as the most influential urban design factors that [...] Read more.

This paper presents a literature review on urban design indicators addressing the impact of urban geometry and vegetation on the outdoor thermal environment at the pedestrian level, as urban geometry and vegetation have been regarded as the most influential urban design factors that affect outdoor microclimate. The thermal balance concept is first introduced to elaborate how each component of energy fluxes is affected by the urban built environment, which helps to explore the underlying thermophysical mechanisms of how urban design modifies the outdoor thermal environment. The literature on numerous urban design descriptors addressing urban geometric characteristics is categorized into five groups in this paper according to the design features that the parameters entail, including land use intensity, building form, canyon geometry, space enclosure and descriptive characteristics. The literature on urban vegetation descriptors is reviewed together, followed by the combined effect of urban geometry and vegetation. This paper identifies a series of important urban design parameters and shows that the impact of design parameters on thermal environment varies with time, season, local climate and urban contexts. Contradictory impacts often occur between daytime and nighttime, or different seasons, which requests trade-offs to be achieved when proposing design strategies. Full article

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6080 KiB

Open AccessReview

LNG Regasification Terminals: The Role of Geography and Meteorology on Technology Choices

by Randeep Agarwal, Thomas J. Rainey, S. M. Ashrafur Rahman, Ted Steinberg, Robert K. Perrons and Richard J. Brown

Energies 2017, 10(12), 2152; https://doi.org/10.3390/en10122152 - 16 Dec 2017

Cited by 37 | Viewed by 9198

Abstract

Liquefied natural gas (LNG) projects are regulated by host countries, but policy and regulation should depend on geography and meteorology. Without considering the role of geography and meteorology, sub-optimal design choices can result, leading to energy conversion efficiency and capital investment decisions that [...] Read more.

Liquefied natural gas (LNG) projects are regulated by host countries, but policy and regulation should depend on geography and meteorology. Without considering the role of geography and meteorology, sub-optimal design choices can result, leading to energy conversion efficiency and capital investment decisions that are less than ideal. A key step in LNG is regasification, which transforms LNG back from liquid to the gaseous state and requires substantial heat input. This study investigated different LNG regasification technologies used around the world and benchmarked location and meteorology-related factors, such as seawater temperatures, ambient air temperatures, wind speeds and relative humidity. Seawater vaporizers are used for more than 95% of locations subject to water quality. Ambient air conditions are relatively better for South America, India, Spain and other Asian countries (Singapore, Taiwan, Indonesia, and Thailand) and provide a much cleaner regasification technology option for natural and forced draft systems and air-based intermediate fluid vaporizers. On a global basis, cold energy utilization currently represents <1% of the total potential, but this approach could deliver nearly 12 Gigawatt (GW) per annum. Overall, climate change is expected to have a positive financial impact on the LNG regasification industry, but the improvement could be unevenly distributed. Full article

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

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Jump to: Editorial, Research, Review

14017 KiB

Open AccessTechnical Note

A New Thin Seam Backfill Mining Technology and Its Application

by Hengjie Luan, Yujing Jiang, Huili Lin and Yahua Wang

Energies 2017, 10(12), 2023; https://doi.org/10.3390/en10122023 - 1 Dec 2017

Cited by 23 | Viewed by 4184

Abstract

Backfill mining is an effective way to control ground subsidence and govern gangue. To solve the problem of thin coal seam mining under villages, a new thin seam backfill mining technology was proposed. This paper investigated a reasonable proportion of filling materials by [...] Read more.

Backfill mining is an effective way to control ground subsidence and govern gangue. To solve the problem of thin coal seam mining under villages, a new thin seam backfill mining technology was proposed. This paper investigated a reasonable proportion of filling materials by experiments, designed the filling system and introduced key technologies for thin seam working face filling. Finally, an industrial test of thin seam backfill mining technology was carried out in the C1661 working face, Beixu Coal Mine. The results show that the developed filling material meets both the pumping liquidity and strength requirements of the filling body during the early and late stages. The design and equipment selection of the paste filling system were reasonable. By using the key technologies for thin seam working face filling, the time needed for working face filling, the connection and disconnection of the filling pipeline and gob-side entry retaining were all greatly shortened. The labor intensity of the workers was reduced, and the mechanization level of the mine was improved. A fill mining length of 480 m was successfully completed. With effective roof subsidence control, the ground subsidence can be reduced, and good results can be achieved. This study can contribute to the development of backfill mining in thin coal seams. Full article

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548 KiB

Open AccessObituary

Professor Doctor Jan Szargut—Obituary

by Enrico Sciubba

Energies 2017, 10(12), 2032; https://doi.org/10.3390/en10122032 - 2 Dec 2017

Cited by 1 | Viewed by 3615

Abstract

n/a Full article

9391 KiB

Open AccessConference Report

Oil Impregnated Pressboard Barrier Systems Based on Ester Fluids for an Application in HVDC Insulation Systems

by Patrick Rumpelt and Frank Jenau

Energies 2017, 10(12), 2147; https://doi.org/10.3390/en10122147 - 15 Dec 2017

Cited by 3 | Viewed by 4089

Abstract

Ester-based insulation fluids are being increasingly used in high-voltage insulation systems. The reasons are the advantages in the area of ecological compatibility and resource-saving provision. The intention to use ester-based insulation fluids in high voltage direct current (HVDC) equipment is new. The major [...] Read more.

Ester-based insulation fluids are being increasingly used in high-voltage insulation systems. The reasons are the advantages in the area of ecological compatibility and resource-saving provision. The intention to use ester-based insulation fluids in high voltage direct current (HVDC) equipment is new. The major challenge in designing the HVDC insulation system is, that the systems do not only experience an alternating voltage, but also a direct voltage Offset. This presents a challenge to predict the electric field distribution. For this purpose, basic investigations are carried out in the form of conductivity investigations for various insulation barrier systems. In addition, a mineral oil serves as a reference oil for estimating existing insights. The results show the influence of the ester-based insulating liquids on the direct current (DC) conductivity for basic arrangements, consisting of pressboard barriers and mixed insulations. Full article

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

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