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Energies, Volume 10, Issue 4 (April 2017) – 170 articles

Cover Story (view full-size image): Optimized component behavior, for instance of check valves, turned out to be crucial for good energetic performance of a hydraulic stepper converter. Despite their simple mechanical design, check valves have very complicated dynamical behavior due to different flow regimes which interact in a highly nonlinear way with the check valve’s plate motion. A model in the free CFD software OpenFOAM was able to simulate quite accurately this coupled fluid and solid body mechanics. The insight into the flow and motion details allowed an optimized design of the fast-check valves. View this paper

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20 pages, 7251 KiB

Open AccessArticle

Optimal Energy Management Strategy for a Plug-in Hybrid Electric Vehicle Based on Road Grade Information

by Yonggang Liu, Jie Li, Ming Ye, Datong Qin, Yi Zhang and Zhenzhen Lei

Energies 2017, 10(4), 412; https://doi.org/10.3390/en10040412 - 23 Mar 2017

Cited by 32 | Viewed by 6130

Energy management strategies (EMSs) are critical for the improvement of fuel economy of plug-in hybrid electric vehicles (PHEVs). However, conventional EMSs hardly consider the influence of uphill terrain on the fuel economy and battery life, leaving vehicles with insufficient battery power for continuous [...] Read more.

Energy management strategies (EMSs) are critical for the improvement of fuel economy of plug-in hybrid electric vehicles (PHEVs). However, conventional EMSs hardly consider the influence of uphill terrain on the fuel economy and battery life, leaving vehicles with insufficient battery power for continuous uphill terrains. Hence, in this study, an optimal control strategy for a PHEV based on the road grade information is proposed. The target state of charge (SOC) is estimated based on the road grade information as well as the predicted driving cycle on uphill road obtained from the GPS/GIS system. Furthermore, the trajectory of the SOC is preplanned to ensure sufficient electricity for the uphill terrain in the charge depleting (CD) and charge sustaining (CS) modes. The genetic algorithm is applied to optimize the parameters of the control strategy to maintain the SOC of battery in the CD mode. The pre-charge mode is designed to charge the battery in the CS mode from a reasonable distance before the uphill terrain. Finally, the simulation model of the powertrain system for the PHEV is established using MATLAB/Simulink platform. The results show that the proposed control strategy based on road-grade information helps successfully achieve better fuel economy and longer battery life. Full article

(This article belongs to the Special Issue Advanced Energy Storage Technologies and Their Applications (AESA))

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26 pages, 3389 KiB

Open AccessArticle

Small Scale Organic Rankine Cycle (ORC): A Techno-Economic Review

by Lorenzo Tocci, Tamas Pal, Ioannis Pesmazoglou and Benjamin Franchetti

Energies 2017, 10(4), 413; https://doi.org/10.3390/en10040413 - 23 Mar 2017

Cited by 161 | Viewed by 16880

The Organic Rankine Cycle (ORC) is widely considered as a promising technology to produce electrical power output from low-grade thermal sources. In the last decade, several power plants have been installed worldwide in the MW range. However, despite its market potential, the commercialization [...] Read more.

The Organic Rankine Cycle (ORC) is widely considered as a promising technology to produce electrical power output from low-grade thermal sources. In the last decade, several power plants have been installed worldwide in the MW range. However, despite its market potential, the commercialization of ORC power plants in the kW range did not reach a high level of maturity, for several reasons. Firstly, the specific price is still too high to offer an attractive payback period, and secondly, potential costumers for small-scale ORCs are typically SMEs (Small-Medium Enterprises), generally less aware of the potential savings this technology could lead to. When it comes to small-scale plants, additional design issues arise that still limit the widespread availability of the technology. This review paper presents the state of the art of the technology, from a technical and economic perspective. Working fluid selection and expander design are illustrated in detail, as they represent the bottleneck of the ORC technology for small-scale power production. In addition, a European market analysis is presented, which constitutes a useful instrument to understand the future evolution of the technology. Full article

(This article belongs to the Special Issue Recent Advances in Organic Rankine Cycle Technology for Stationary Applications)

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12 pages, 6654 KiB

Open AccessArticle

Characterization of the Diamond Wire Sawing Process for Monocrystalline Silicon by Raman Spectroscopy and SIREX Polarimetry

by Sindy Würzner, Martin Herms, Thomas Kaden, Hans Joachim Möller and Matthias Wagner

Energies 2017, 10(4), 414; https://doi.org/10.3390/en10040414 - 23 Mar 2017

Cited by 21 | Viewed by 5873

A detailed approach to evaluate the sub-surface damage of diamond wire-sawn monocrystalline silicon wafers relating to the sawing process is presented. Residual stresses, the presence of amorphous silicon and microcracks are considered and related to diamond wire velocity and cutting ability. In particular, [...] Read more.

A detailed approach to evaluate the sub-surface damage of diamond wire-sawn monocrystalline silicon wafers relating to the sawing process is presented. Residual stresses, the presence of amorphous silicon and microcracks are considered and related to diamond wire velocity and cutting ability. In particular, the degree of amorphization of the wafer surface is analyzed, as it may affect the etching performance (texturing) during solar cell manufacture. Raman spectroscopy and Scanning Infrared Stress Explorer (SIREX) measurements are used independently as non-destructive, contactless optical characterization methods to provide stress imaging with high spatial resolution. Raman mappings show that amorphous silicon layers can occur inhomogeneously across the surface of diamond wire-sawn wafers. The Raman and SIREX results reveal a connection between a higher fraction of the amorphous phase, a more inhomogeneous stress distribution and a lower peak maximum of the stress difference on wafers, depending on both the wire wear and the wire velocity. SIREX line scans of the in-plane difference of the principal stress components ∆σ taken across the sawing grooves show significant differences in magnitude and periodicity. Furthermore, the results are compared with the microcrack depth from the same investigation areas. The possibility to optimize the diamond wire sawing processes by analyzing the sub-surface stress of the wafers is offered by complementary use of both Raman and SIREX measurements. Full article

(This article belongs to the Special Issue Crystalline Silicon Solar Cells: Fundamentals and Technologies)

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15 pages, 6284 KiB

Open AccessArticle

Image Recognition of Icing Thickness on Power Transmission Lines Based on a Least Squares Hough Transform

by Jingjing Wang, Junhua Wang, Jianwei Shao and Jiangui Li

Energies 2017, 10(4), 415; https://doi.org/10.3390/en10040415 - 23 Mar 2017

Cited by 51 | Viewed by 5346

In view of the shortcomings of current image detection methods for icing thickness on power transmission lines, an image measuring method for icing thickness based on remote online monitoring was proposed. In this method, a Canny operator is used to get the image [...] Read more.

In view of the shortcomings of current image detection methods for icing thickness on power transmission lines, an image measuring method for icing thickness based on remote online monitoring was proposed. In this method, a Canny operator is used to get the image edge, in addition, a Hough transform and least squares are combined to solve the problems of traditional Hough transform in the parameter space whereby it is easily disturbed by the image background and noises, and eventually the edges of iced power transmission lines and un-iced power transmission lines are accurately detected in images which have low contrast, complex grayscale, and many noises. Furthermore, based on the imaging principle of the camera, a new geometric calculation model for icing thickness is established by using the radius of power transmission line as a reference, and automatic calculation of icing thickness is achieved. The results show that proposed image recognition method is rarely disturbed by noises and background, the image recognition results show good agreement with the real edges of iced power transmission lines and un-iced power transmission lines, and is simple and easy to program, which suggests that the method can be used for image recognition and calculation of icing thickness. Full article

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15 pages, 3012 KiB

Open AccessArticle

Robust Operation of Energy Storage System with Uncertain Load Profiles

by Jangkyum Kim, Yohwan Choi, Seunghyoung Ryu and Hongseok Kim

Energies 2017, 10(4), 416; https://doi.org/10.3390/en10040416 - 23 Mar 2017

Cited by 28 | Viewed by 5737

In this paper, we propose novel techniques to reduce total cost and peak load of factories from a customer point of view. We control energy storage system (ESS) to minimize the total electricity bill under the Korea commercial and industrial (KCI) tariff, which [...] Read more.

In this paper, we propose novel techniques to reduce total cost and peak load of factories from a customer point of view. We control energy storage system (ESS) to minimize the total electricity bill under the Korea commercial and industrial (KCI) tariff, which both considers peak load and time of use (ToU). Under the KCI tariff, the average peak load, which is the maximum among all average power consumptions measured every 15 min for the past 12 months, determines the monthly base cost, and thus peak load control is extremely critical. We aim to leverage ESS for both peak load reduction based on load prediction as well as energy arbitrage exploiting ToU. However, load prediction inevitably has uncertainty, which makes ESS operation challenging with KCI tariff. To tackle it, we apply robust optimization to minimize risk in a real environment. Our approach significantly reduces the peak load by 49.9% and the total cost by 10.8% compared to the case that does not consider load uncertainty. In doing this we also consider battery degradation cost and validate the practical use of the proposed techniques. Full article

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

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17 pages, 8990 KiB

Open AccessArticle

Analyzing the Impacts of System Parameters on MPC-Based Frequency Control for a Stand-Alone Microgrid

by Thai-Thanh Nguyen, Hyeong-Jun Yoo and Hak-Man Kim

Energies 2017, 10(4), 417; https://doi.org/10.3390/en10040417 - 23 Mar 2017

Cited by 26 | Viewed by 4989

Model predictive control (MPC) has been widely studied for regulating frequency in stand-alone microgrids (MGs), owing to the advantages of MPC such as fast response and robustness against the parameter uncertainties. Understanding the impacts of system parameters on the control performance of MPC [...] Read more.

Model predictive control (MPC) has been widely studied for regulating frequency in stand-alone microgrids (MGs), owing to the advantages of MPC such as fast response and robustness against the parameter uncertainties. Understanding the impacts of system parameters on the control performance of MPC could be useful for the designing process of the controller to achieve better performance. This study analyzes the impact of system parameters on the control performance of MPC for frequency regulation in a stand-alone MG. The typical stand-alone MG, which consists of a diesel engine generator, an energy storage system (ESS), a wind turbine generator, and a load, is considered in this study. The diesel engine generator is in charge of primary frequency control whereas the ESS is responsible for secondary frequency control. The stand-alone MG is linearized to obtain the dynamic model that is used for designing MPC-based secondary frequency control. The robustness of MPC against the variation of system parameters is also analyzed in this study. A comparison study of MPC and proportional–integral (PI) control is presented. Simulation results show that MPC has a faster response time and lower overshoot compared to PI control. In addition, the robustness of MPC against the system uncertainties is stronger than conventional PI control. Full article

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

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20 pages, 5289 KiB

Open AccessArticle

A High-Frequency Isolated Online Uninterruptible Power Supply (UPS) System with Small Battery Bank for Low Power Applications

by Muhammad Aamir, Wajahat Ullah Tareen, Kafeel Ahmed Kalwar, Mudasir Ahmed Memon and Saad Mekhilef

Energies 2017, 10(4), 418; https://doi.org/10.3390/en10040418 - 23 Mar 2017

Cited by 3 | Viewed by 6976

Uninterruptible power supplies (UPSs) are widely used to deliver reliable and high quality power to critical loads under all grid conditions. This paper proposes a high-frequency isolated online UPS system for low power applications. The proposed UPS consists of a single-stage AC-DC converter, [...] Read more.

Uninterruptible power supplies (UPSs) are widely used to deliver reliable and high quality power to critical loads under all grid conditions. This paper proposes a high-frequency isolated online UPS system for low power applications. The proposed UPS consists of a single-stage AC-DC converter, boost DC-DC converter, and an inverter. The single-stage AC-DC converter provides galvanic isolation, input power factor correction, and continuous conduction of both input and output current. The low battery bank voltage is stepped up to high dc-link voltage by employing a high voltage gain boost converter, thus allows the reduction of battery bank to only 24 V parallel connected batteries. Operating batteries in parallel improves the battery performance and resolves the issues related to conventional battery banks that arrange the batteries in series combination. The inverter provides regulated output voltage to the load. A new cascaded slide mode (SM) and proportional-resonant (PR) control for the inverter has been proposed, which regulates the output voltage for both linear and non-linear loads. The controller shows excellent performance during load transients and step changes. Besides, the controller for boost converter and AC-DC converter is presented. Operating principle and experimental results of 1 kVA laboratory setup have been presented for the validation of proposed system. Full article

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15 pages, 1576 KiB

Open AccessArticle

A Novel Multi-Objective Optimal Approach for Wind Power Interval Prediction

by Mengyue Hu, Zhijian Hu, Jingpeng Yue, Menglin Zhang and Meiyu Hu

Energies 2017, 10(4), 419; https://doi.org/10.3390/en10040419 - 23 Mar 2017

Cited by 35 | Viewed by 4521

Numerous studies on wind power forecasting show that random errors found in the prediction results cause uncertainty in wind power prediction and cannot be solved effectively using conventional point prediction methods. In contrast, interval prediction is gaining increasing attention as an effective approach [...] Read more.

Numerous studies on wind power forecasting show that random errors found in the prediction results cause uncertainty in wind power prediction and cannot be solved effectively using conventional point prediction methods. In contrast, interval prediction is gaining increasing attention as an effective approach as it can describe the uncertainty of wind power. A wind power interval forecasting approach is proposed in this article. First, the original wind power series is decomposed into a series of subseries using variational mode decomposition (VMD); second, the prediction model is established through kernel extreme learning machine (KELM). Three indices are taken into account in a novel objective function, and the improved artificial bee colony algorithm (IABC) is used to search for the best wind power intervals. Finally, when compared with other competitive methods, the simulation results show that the proposed approach has much better performance. Full article

(This article belongs to the Special Issue Sustainable Energy Technologies)

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13 pages, 2534 KiB

Open AccessArticle

Improved Separation and Collection of Charge Carriers in Micro-Pyramidal-Structured Silicon/PEDOT:PSS Hybrid Solar Cells

by Yuuki Sugano, Keisuke Sato, Naoki Fukata and Kenji Hirakuri

Energies 2017, 10(4), 420; https://doi.org/10.3390/en10040420 - 23 Mar 2017

Cited by 14 | Viewed by 6007

Silicon (Si)/organic polymer hybrid solar cells have great potential for becoming cost-effective and efficient energy-harvesting devices. We report herein on the effects of polymer coverage and the rear electrode on the device performance of Si/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hybrid solar cells with micro-pyramidal structures. These [...] Read more.

Silicon (Si)/organic polymer hybrid solar cells have great potential for becoming cost-effective and efficient energy-harvesting devices. We report herein on the effects of polymer coverage and the rear electrode on the device performance of Si/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hybrid solar cells with micro-pyramidal structures. These hybrid solar cells provided adequate generation of charge carriers owing to the suppression of reflectance to below 13%. Additionally, the separation of the photogenerated charge carriers at the micro-pyramidal-structured Si/PEDOT:PSS interface regions and their collection at the electrodes were dramatically improved by tuning the adhesion areas of the PEDOT:PSS layer and the rear electrode materials, thereby attaining a power conversion efficiency of 8.25%. These findings suggest that it is important to control the PEDOT:PSS coverage and to optimize the rear electrode materials in order to achieve highly efficient separation of the charge carriers and their effective collection in micro-textured hybrid solar cells. Full article

(This article belongs to the Special Issue Solar Photovoltaics Trilemma: Efficiency, Stability and Cost Reduction 2017)

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23 pages, 3319 KiB

Open AccessFeature PaperEditor’s ChoiceReview

A Review of Smart Cities Based on the Internet of Things Concept

by Saber Talari, Miadreza Shafie-khah, Pierluigi Siano, Vincenzo Loia, Aurelio Tommasetti and João P. S. Catalão

Energies 2017, 10(4), 421; https://doi.org/10.3390/en10040421 - 23 Mar 2017

Cited by 486 | Viewed by 38658

With the expansion of smart meters, like the Advanced Metering Infrastructure (AMI), and the Internet of Things (IoT), each smart city is equipped with various kinds of electronic devices. Therefore, equipment and technologies enable us to be smarter and make various aspects of [...] Read more.

With the expansion of smart meters, like the Advanced Metering Infrastructure (AMI), and the Internet of Things (IoT), each smart city is equipped with various kinds of electronic devices. Therefore, equipment and technologies enable us to be smarter and make various aspects of smart cities more accessible and applicable. The goal of the current paper is to provide an inclusive review on the concept of the smart city besides their different applications, benefits, and advantages. In addition, most of the possible IoT technologies are introduced, and their capabilities to merge into and apply to the different parts of smart cities are discussed. The potential application of smart cities with respect to technology development in the future provides another valuable discussion in this paper. Meanwhile, some practical experiences all across the world and the key barriers to its implementation are thoroughly expressed. Full article

(This article belongs to the Special Issue Innovative Methods for Smart Grids Planning and Management)

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9 pages, 3608 KiB

Open AccessArticle

A 3-D Coupled Magneto-Fluid-Thermal Analysis of a 220 kV Three-Phase Three-Limb Transformer under DC Bias

by Ruohan Gong, Jiangjun Ruan, Jingzhou Chen, Yu Quan, Jian Wang and Shuo Jin

Energies 2017, 10(4), 422; https://doi.org/10.3390/en10040422 - 23 Mar 2017

Cited by 14 | Viewed by 4786

This paper takes a typical 220 kV three-phase three-limb oil-immersed transformer as an example, this paper building transient field-circuit coupled model and 3D coupled magneto -fluid-thermal model. Considering a nonlinear B–H curve, the magneto model uses the field-circuit coupled finite element method (FEM) [...] Read more.

This paper takes a typical 220 kV three-phase three-limb oil-immersed transformer as an example, this paper building transient field-circuit coupled model and 3D coupled magneto -fluid-thermal model. Considering a nonlinear B–H curve, the magneto model uses the field-circuit coupled finite element method (FEM) to calculate the magnetic flux distribution of the core and the current distribution of the windings when the transformer is at a rated current and under direct current (DC) bias. Taking the electric power losses of the core and windings as a heat source, the temperature inside the transformer and the velocity of the transformer oil are analyzed by the finite volume method (FVM) in a fluid-thermal field. In order to improve the accuracy of the calculation results, the influence of temperature on the electrical resistivity of the windings and the physical parameter of the transformer oil are taken into account in the paper. Meanwhile, the convective heat transfer coefficient of the FVM model boundary is determined by its temperature. By iterative computations, the model is updated according to the thermal field calculation result until the maximum difference in hot spot temperature between the two adjacent steps is less than 0.01 K. The result calculated by the coupling method agrees well with the empirical equation result according to IEC 60076-7. Full article

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13 pages, 2815 KiB

Open AccessArticle

Coordinated Control and Fault Protection Investigation of a Renewable Energy Integration Facility with Solar PVs and a Micro-Turbine

by Jiefeng Hu

Energies 2017, 10(4), 423; https://doi.org/10.3390/en10040423 - 23 Mar 2017

Cited by 3 | Viewed by 3983

In this paper, a renewable energy integration facility (REIF) with photovoltaic (PV) distributed generation resources for micro-grid applications is studied. In grid-tied operation, the PV system together with the grid supply the power to the local loads while the surplus energy is fed [...] Read more.

In this paper, a renewable energy integration facility (REIF) with photovoltaic (PV) distributed generation resources for micro-grid applications is studied. In grid-tied operation, the PV system together with the grid supply the power to the local loads while the surplus energy is fed back to the grid. In stand-alone mode, a gas micro-turbine is operated as a master to establish the common AC bus voltage to which the PV inverters can synchronize The experimental results demonstrate the stable operation of the REIF under various generation and load conditions. The power quality can meet the IEEE Standard 1547. Furthermore, the responses of the REIF under different fault conditions are investigated. Relevant protection mechanisms are then developed, providing insights into the fault protection for the future grid. Full article

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12 pages, 7505 KiB

Open AccessArticle

Scale-Dependent Light Scattering Analysis of Textured Structures on LED Light Extraction Enhancement Using Hybrid Full-Wave Finite-Difference Time-Domain and Ray-Tracing Methods

by Tsung-Xian Lee and Ching-Chia Chou

Energies 2017, 10(4), 424; https://doi.org/10.3390/en10040424 - 23 Mar 2017

Cited by 12 | Viewed by 6559

A multiscale model that enables quantitative understanding and prediction of the size effect on the scattering properties of micro- and nanostructures is crucial for the design of light-emitting diode (LED) surface textures optimized for high light extraction efficiency (LEE). In this paper, a [...] Read more.

A multiscale model that enables quantitative understanding and prediction of the size effect on the scattering properties of micro- and nanostructures is crucial for the design of light-emitting diode (LED) surface textures optimized for high light extraction efficiency (LEE). In this paper, a hybrid process for combining full-wave finite-difference time-domain simulation and a ray-tracing technique based on a bidirectional scattering distribution function model is proposed. We apply this method to study the influence of different pattern sizes of a patterned sapphire substrate on GaN-based LED light extraction from the micro-scale to the nano-scale. The results show that near-wavelength–scale patterns with strong diffraction are not expected to enhance the LEE. By contrast, micro-scale patterns with optical diffusion behavior have the highest LEE at a specific aspect ratio, and subwavelength-scale patterns that have antireflection properties show a marked enhancement of the LEE for a wide range of aspect ratios. Full article

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

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20 pages, 5207 KiB

Open AccessArticle

The EU Electricity Security Decision-Analytic Framework: Status and Perspective Developments

by Gianluca Fulli, Marcelo Masera, Catalin Felix Covrig, Francesco Profumo, Ettore Bompard and Tao Huang

Energies 2017, 10(4), 425; https://doi.org/10.3390/en10040425 - 23 Mar 2017

Cited by 9 | Viewed by 5476

Electricity security, generally referring to a system’s capability to provide electricity to its users, is a multi-faceted problem attracting mounting attention from policy makers and scientists around the world. Electricity security encompasses largely different properties based upon the time/geographical scales of the factors [...] Read more.

Electricity security, generally referring to a system’s capability to provide electricity to its users, is a multi-faceted problem attracting mounting attention from policy makers and scientists around the world. Electricity security encompasses largely different properties based upon the time/geographical scales of the factors affecting electricity delivery; it is challenged by threats surfacing in spheres far beyond the physical one; it involves a myriad of stakeholders spanning manifold disciplines and with considerably different expectations from the electricity commodity or services; it can be studied as a complicated techno-economic problem or as a complex socio-economic problem. All the above reasons, in a framework of changing European Union (EU) and global energy scenarios, render electricity security ever more challenging to assess and critical to safeguard. Against this background, this work presents recommendations to bring science and policy making closer towards evaluating and handling EU electricity security. More in detail, this is done by:

Characterising electricity security via features at the cross-roads of policy and science.
Reviewing the electricity security modelling and assessment approaches across sectors.
Proposing elements for a novel electricity security decision-analytic framework for the EU.
Contextualising the proposed framework in EU’s Energy Union grid design initiatives.

Full article

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20 pages, 1011 KiB

Open AccessArticle

Pareto-Efficient Capacity Planning for Residential Photovoltaic Generation and Energy Storage with Demand-Side Load Management

by Somi Jung and Dongwoo Kim

Energies 2017, 10(4), 426; https://doi.org/10.3390/en10040426 - 23 Mar 2017

Cited by 15 | Viewed by 3645

Optimal sizing of residential photovoltaic (PV) generation and energy storage (ES) systems is a timely issue since government polices aggressively promote installing renewable energy sources in many countries, and small-sized PV and ES systems have been recently developed for easy use in residential [...] Read more.

Optimal sizing of residential photovoltaic (PV) generation and energy storage (ES) systems is a timely issue since government polices aggressively promote installing renewable energy sources in many countries, and small-sized PV and ES systems have been recently developed for easy use in residential areas. We in this paper investigate the problem of finding the optimal capacities of PV and ES systems in the context of home load management in smart grids. Unlike existing studies on optimal sizing of PV and ES that have been treated as a part of designing hybrid energy systems or polygeneration systems that are stand-alone or connected to the grid with a fixed energy price, our model explicitly considers the varying electricity price that is a result of individual load management of the customers in the market. The problem we have is formulated by a D-day capacity planning problem, the goal of which is to minimize the overall expense paid by each customer for the planning period. The overall expense is the sum of expenses to buy electricity and to install PV and ES during D days. Since each customer wants to minimize his/her own monetary expense, their objectives look conflicting, and we first regard the problem as a multi-objective optimization problem. Additionally, we secondly formulate the problem as a D-day noncooperative game between customers, which can be solved in a distributed manner and, thus, is better fit to the pricing practice in smart grids. In order to have a converging result of the best-response game, we use the so-called proximal point algorithm. With numerical investigation, we find Pareto-efficient trajectories of the problem, and the converged game-theoretic solution is shown to be mostly worse than the Pareto-efficient solutions. Full article

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21 pages, 4538 KiB

Open AccessArticle

Modeling and Analysis of a DC Electrical System and Controllers for Implementation of a Grid-Interactive Building

by Youngjin Kim

Energies 2017, 10(4), 427; https://doi.org/10.3390/en10040427 - 23 Mar 2017

Cited by 7 | Viewed by 6450

As the penetration of photovoltaic (PV) systems on building rooftops increases, the accumulated effect of the rooftop PV power outputs on electric network operation is no longer negligible. Energy storage resources (ESRs) have been used to smooth PV power outputs, particularly when building [...] Read more.

As the penetration of photovoltaic (PV) systems on building rooftops increases, the accumulated effect of the rooftop PV power outputs on electric network operation is no longer negligible. Energy storage resources (ESRs) have been used to smooth PV power outputs, particularly when building load becomes low. In commercial buildings, the batteries of plug-in electric vehicles (PEVs) can be regarded as distributed ESRs. This paper proposes a DC electrical system in a commercial building that enables PEVs to compensate for rooftop PV power fluctuation and participate in tracking signals for grid frequency regulation (GFR). The proposed building system and associated controllers are modeled considering steady-state and dynamic operations of the PV system and PEV batteries. Simulation case studies are conducted to demonstrate the performance of the proposed building system under various conditions, determined by such factors as the maximum voltage, minimum state-of-charge, and desired charging end-time of PEVs batteries. Full article

(This article belongs to the Special Issue DC Systems)

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11 pages, 2715 KiB

Open AccessArticle

Predictive Direct Flux Control—A New Control Method of Voltage Source Inverters in Distributed Generation Applications

by Jiefeng Hu

Energies 2017, 10(4), 428; https://doi.org/10.3390/en10040428 - 23 Mar 2017

Cited by 2 | Viewed by 3655

Voltage source inverters (VSIs) have been widely utilized in electric drives and distributed generations (DGs), where electromagnetic torque, currents and voltages are usually the control objectives. The inverter flux, defined as the integral of the inverter voltage, however, is seldom studied. Although a [...] Read more.

Voltage source inverters (VSIs) have been widely utilized in electric drives and distributed generations (DGs), where electromagnetic torque, currents and voltages are usually the control objectives. The inverter flux, defined as the integral of the inverter voltage, however, is seldom studied. Although a conventional flux control approach has been developed, it presents major drawbacks of large flux ripples, leading to distorted inverter output currents and large power ripples. This paper proposes a new control strategy of VSIs by controlling the inverter flux. To improve the system’s steady-state and transient performance, a predictive control scheme is adopted. The flux amplitude and flux angle can be well regulated by choosing the optimum inverter control action according to formulated selection criteria. Hence, the inverter flux can be controlled to have a specified magnitude and a specified position relative to the grid flux with less ripples. This results in a satisfactory line current performance with a fast transient response. The proposed predictive direct flux control (PDFC) method is tested in a 3 MW high-power grid-connected VSI system in the MATLAB/Simulink environment, and the results demonstrate its effectiveness. Full article

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17 pages, 2279 KiB

Open AccessArticle

A Solar Energy Solution for Sustainable Third Generation Mobile Networks

by Mohammed H. Alsharif

Energies 2017, 10(4), 429; https://doi.org/10.3390/en10040429 - 24 Mar 2017

Cited by 18 | Viewed by 5628

The energy consumption of cellular networks has become increasingly important to cellular network operators, due to the significant economic and ecological influence of these networks in the future. The development of alternative energy technologies has resulted in the consideration of a solar powered [...] Read more.

The energy consumption of cellular networks has become increasingly important to cellular network operators, due to the significant economic and ecological influence of these networks in the future. The development of alternative energy technologies has resulted in the consideration of a solar powered base station (BS) as a long-term solution for the mobile cellular network industry, to reduce the operational expenditures and CO₂ footprints of cellular networks. This study addresses the deployment and operational issues of a solar powered universal mobile telecommunications system (UMTS; a third generation mobile cellular system) BS (i.e., Node B) that is currently deployed (i.e., UMTS Node B 2/2/2 and UMTS Node B 4/4/4). In addition, this study employs a hybrid optimization model for an electric renewable software simulator developed by the American National Renewable Energy Laboratory. Four key aspects are discussed in this study: optimal solar system architecture, energy production, the cash flow of the solar powered UMTS Node B project, and the economic feasibility of a solar powered system compared with traditional sources. Simulation results show that the proposed solution ensures 100% energy autonomy and long-term energy balance for the UMTS Node B, with cost effectiveness. Full article

(This article belongs to the Special Issue Contemporary Environmental Paradigms and the Renewable Energy in Rural Economies)

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20 pages, 2485 KiB

Open AccessArticle

Financial Appraisal of Small Hydro-Power Considering the Cradle-to-Grave Environmental Cost: A Case from Greece

by Adamantia Zoi Vougioukli, Eleni Didaskalou and Dimitrios Georgakellos

Energies 2017, 10(4), 430; https://doi.org/10.3390/en10040430 - 28 Mar 2017

Cited by 12 | Viewed by 5956

In the last decades increasing attention to environmental issues has come to the fore due to the looming issue of climate change. The growing demand for energy, coupled with the increasing greenhouse gas (GHG) emissions, have forced the study and development of energy [...] Read more.

In the last decades increasing attention to environmental issues has come to the fore due to the looming issue of climate change. The growing demand for energy, coupled with the increasing greenhouse gas (GHG) emissions, have forced the study and development of energy plants that use renewable energy sources (RES), as electricity generation is one of the major contributors to anthropogenic emissions. Small hydropower plants are of particular interest as their potential is assumed to be high. The aim of this study is to provide a comprehensive assessment of the environmental impacts of small hydropower plants (SHPs) using Life Cycle Assessment (LCA) methodology. The main parameter set for our simplified LCA model was the weight of the components used to construct and operate the plant: concrete, aggregates and steel. Through LCA, air pollutant externalities were associated with the life cycle of SHPs. This was accomplished by applying the NEEDS framework. The results are given per impact type (human health, loss of biodiversity, crop yield, material damage and climate change). The spearhead of the study is that the environmental cost must be a parameter of the total investment cost, which may affect the indexes of the financial evaluation of the project. Full article

(This article belongs to the Special Issue Contemporary Environmental Paradigms and the Renewable Energy in Rural Economies)

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16 pages, 5569 KiB

Open AccessArticle

Comparison of Impulse Wave and Sweep Frequency Response Analysis Methods for Diagnosis of Transformer Winding Faults

by Qing Yang, Peiyu Su and Yong Chen

Energies 2017, 10(4), 431; https://doi.org/10.3390/en10040431 - 28 Mar 2017

Cited by 25 | Viewed by 7878

Monitoring of winding faults is the most important item used to determine the maintenance status of a transformer. Commonly used methods for winding-fault diagnosis require the transformer to exit operation before testing and an external exciting signal, whether the transformer is malfunctioning or [...] Read more.

Monitoring of winding faults is the most important item used to determine the maintenance status of a transformer. Commonly used methods for winding-fault diagnosis require the transformer to exit operation before testing and an external exciting signal, whether the transformer is malfunctioning or not. However, if an overvoltage signal can be regarded as a broadband excitation source for fault diagnosis, then the interference caused by signal injection can be eliminated without the need for additional pulse or impulse signals. In this paper, a tapped transformer is designed and test platforms are built to compare winding diagnoses using the impulse wave and sweep frequency response analysis methods by recording voltage responses on both the high- and low-voltage sides and calculating the respective transfer functions. Based on comparison of statistical indicators, it is found that the sensitivities of both methods are similar for detecting conditions of winding-ground and winding-interlayer short circuits. It is concluded that it is feasible to use a transient overvoltage monitoring system for winding-fault diagnosis. Full article

(This article belongs to the Special Issue Electric Power Systems Research 2017)

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18 pages, 2990 KiB

Open AccessArticle

Multi-Scale Parameter Identification of Lithium-Ion Battery Electric Models Using a PSO-LM Algorithm

by Wen-Jing Shen and Han-Xiong Li

Energies 2017, 10(4), 432; https://doi.org/10.3390/en10040432 - 27 Mar 2017

Cited by 19 | Viewed by 4785

This paper proposes a multi-scale parameter identification algorithm for the lithium-ion battery (LIB) electric model by using a combination of particle swarm optimization (PSO) and Levenberg-Marquardt (LM) algorithms. Two-dimensional Poisson equations with unknown parameters are used to describe the potential and current density [...] Read more.

This paper proposes a multi-scale parameter identification algorithm for the lithium-ion battery (LIB) electric model by using a combination of particle swarm optimization (PSO) and Levenberg-Marquardt (LM) algorithms. Two-dimensional Poisson equations with unknown parameters are used to describe the potential and current density distribution (PDD) of the positive and negative electrodes in the LIB electric model. The model parameters are difficult to determine in the simulation due to the nonlinear complexity of the model. In the proposed identification algorithm, PSO is used for the coarse-scale parameter identification and the LM algorithm is applied for the fine-scale parameter identification. The experiment results show that the multi-scale identification not only improves the convergence rate and effectively escapes from the stagnation of PSO, but also overcomes the local minimum entrapment drawback of the LM algorithm. The terminal voltage curves from the PDD model with the identified parameter values are in good agreement with those from the experiments at different discharge/charge rates. Full article

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14 pages, 2726 KiB

Open AccessArticle

Stability Analysis of DC Distribution Systems with Droop-Based Charge Sharing on Energy Storage Devices

by Despoina I. Makrygiorgou and Antonio T. Alexandridis

Energies 2017, 10(4), 433; https://doi.org/10.3390/en10040433 - 27 Mar 2017

Cited by 22 | Viewed by 5946

Direct current (DC) distribution systems and DC microgrids are becoming a reliable and efficient alternative energy system, compatible with the DC nature of most of the distributed energy resources (DERs), storage devices and loads. The challenging problem of redesigning an autonomous DC-grid system [...] Read more.

Direct current (DC) distribution systems and DC microgrids are becoming a reliable and efficient alternative energy system, compatible with the DC nature of most of the distributed energy resources (DERs), storage devices and loads. The challenging problem of redesigning an autonomous DC-grid system in view of using energy storage devices to balance the power produced and absorbed, by applying simple decentralized controllers on the electronic power interfaces, is investigated in this paper. To this end, a complete nonlinear DC-grid model has been deployed that includes different DC-DERs, two controlled parallel battery branches, and different varying DC loads. Since many loads in modern distribution systems are connected through power converters, both constant power loads and simple resistive loads are considered in parallel. Within this system, suitable cascaded controllers on the DC/DC power converter interfaces to the battery branches are proposed, in a manner that ensures stability and charge sharing between the two branches at the desired ratio. To achieve this task, inner-loop current controllers are combined with outer-loop voltage, droop-based controllers. The proportional-integral (PI) inner-loop current controllers include damping terms and are fully independent from the system parameters. The controller scheme is incorporated into the system model and a globally valid nonlinear stability analysis is conducted; this differs from small-signal linear methods that are valid only for specific systems, usually via eigenvalue investigations. In the present study, under the virtual cost of applying advanced Lyapunov techniques on the entire nonlinear system, a rigorous analysis is formulated to prove stability and convergence to the desired operation, regardless of the particular system characteristics. The theoretical results are evaluated by detailed simulations, with the system performance being very satisfactory. Full article

(This article belongs to the Special Issue Microgrids 2016)

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24 pages, 6528 KiB

Open AccessArticle

A High-Efficiency Isolated-Type Three-Port Bidirectional DC/DC Converter for Photovoltaic Systems

by Yu-En Wu and Pin-Nan Chiu

Energies 2017, 10(4), 434; https://doi.org/10.3390/en10040434 - 25 Mar 2017

Cited by 16 | Viewed by 7090

This paper proposes a novel high-efficiency isolated three-port bidirectional DC/DC device for photovoltaic (PV) systems. The device contains a high step-up converter for PV modules to supply power to the DC bus, and a bidirectional charge/discharge control circuit for the battery with an [...] Read more.

This paper proposes a novel high-efficiency isolated three-port bidirectional DC/DC device for photovoltaic (PV) systems. The device contains a high step-up converter for PV modules to supply power to the DC bus, and a bidirectional charge/discharge control circuit for the battery with an improved boost-flyback converter. When the PV modules supply sufficient energy, their output can be stepped up and energy supply to the DC bus and charging of the battery can be achieved simultaneously. However, when the energy supplied is insufficient, the battery provides energy to the DC bus. When the proposed converter is operated in the step-down mode, the DC-blocking capacitor on the high-voltage side is used to reduce the voltage on the transformer and achieve high step-down performance. Moreover, to improve the overall efficiency of the system, the energy stored in the leakage inductance is recycled and supplied to the DC-blocking capacitor during operation in the step-up mode. Finally, to verify the feasibility and practicability of the proposed devices, a 500 W three-port bidirectional DC/DC devices was implemented. The highest efficiencies achieved for operation in different modes were as follows: high step-up mode for the PV modules, 95.2%; battery step-up mode, 94.2%; and step-down mode, 97.6%. Full article

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14 pages, 5733 KiB

Open AccessArticle

GeroMAG: In-House Prototype of an Innovative Sealed, Compact and Non-Shaft-Driven Gerotor Pump with Magnetically-Driving Outer Rotor

by Pedro Javier Gamez-Montero, Robert Castilla, Esteve Codina, Javier Freire, Joan Morató, Enric Sanchez-Casas and Ivan Flotats

Energies 2017, 10(4), 435; https://doi.org/10.3390/en10040435 - 26 Mar 2017

Cited by 30 | Viewed by 8431

The technology of gerotor pumps is progressing towards cutting-edge applications in emerging sectors, which are more demanding for pump performance. Moreover, recent environmental standards are heading towards leakage-free and noiseless hydraulic systems. Hence, in order to respond to these demands, this study, which [...] Read more.

The technology of gerotor pumps is progressing towards cutting-edge applications in emerging sectors, which are more demanding for pump performance. Moreover, recent environmental standards are heading towards leakage-free and noiseless hydraulic systems. Hence, in order to respond to these demands, this study, which will be referred to as the GeroMAG concept, aims to make a leap from the standard gerotor pump technology: a sealed, compact, non-shaft-driven gerotor pump with a magnetically-driving outer rotor. The GeroMAG pump is conceived as a variable-flow pump to accomplish a standard volumetric flow rate at low rotational speed with satisfactory volumetric efficiency. By following the authors’ methodology based on a catalogue of best-practice rules, a custom trochoidal gear set is designed. Then, two main technological challenges are encountered: how to generate the rotational movement of the driving outer rotor and how to produce the guide of rotation of the gear set once there is no drive shaft. To confront them, a quiet magnet brushless motor powers the driving outer rotor through pole pieces placed in its external sideway and the rotational movement is guided by the inner edgewise pads carved on it. Subsequently, GeroMAG pump architecture, prototype, housing, methodology, materials and manufacture will be presented. As a principal conclusion, the GeroMAG proof of concept and pump prototype are feasible, which is corroborated by experimental results and performance indexes. Full article

(This article belongs to the Special Issue Energy Efficiency and Controllability of Fluid Power Systems)

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20 pages, 4454 KiB

Open AccessArticle

Optimizing the Energy-Efficient Metro Train Timetable and Control Strategy in Off-Peak Hours with Uncertain Passenger Demands

by Jia Feng, Xiamiao Li, Haidong Liu, Xing Gao and Baohua Mao

Energies 2017, 10(4), 436; https://doi.org/10.3390/en10040436 - 29 Mar 2017

Cited by 14 | Viewed by 5273

How to reduce the energy consumption of metro trains by optimizing both the timetable and control strategy is a major focus. Due to the complexity and difficulty of the combinatorial operation problem, the commonly-used method to optimize the train operation problem is based [...] Read more.

How to reduce the energy consumption of metro trains by optimizing both the timetable and control strategy is a major focus. Due to the complexity and difficulty of the combinatorial operation problem, the commonly-used method to optimize the train operation problem is based on an unchanged dwelling time for all trains at a specific station. Here, we develop a simulation-based method to design an energy-efficient train control strategy under the optimized timetable constraints, which assign the dwelling time margin to the running time. This time margin is caused by dynamically uncertain passenger demands in off-peak hours. Firstly, we formulate a dwelling time calculation model to minimize the passenger boarding and alighting time. Secondly, we design an optimal train control strategy with fixed time and develop a time-based model to describe mass-belt train movement. Finally, based on this simulation module, we present numerical examples based on the real-world operation data from the Beijing metro Line 2, in which the energy consumption of one train can be reduced by 21.9%. These results support the usefulness of the proposed approach. Full article

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18 pages, 11711 KiB

Open AccessArticle

Design Methodology of a Power Split Type Plug-In Hybrid Electric Vehicle Considering Drivetrain Losses

by Hanho Son, Kyusik Park, Sungho Hwang and Hyunsoo Kim

Energies 2017, 10(4), 437; https://doi.org/10.3390/en10040437 - 25 Mar 2017

Cited by 15 | Viewed by 7558

This paper proposes a design methodology for a power split type plug-in hybrid electric vehicle (PHEV) by considering drivetrain losses. Selecting the input split type PHEV with a single planetary gear as the reference topology, the locations of the engine, motor and generators [...] Read more.

This paper proposes a design methodology for a power split type plug-in hybrid electric vehicle (PHEV) by considering drivetrain losses. Selecting the input split type PHEV with a single planetary gear as the reference topology, the locations of the engine, motor and generators (MGs), on the speed lever were determined by using the mechanical point considering the system efficiency. Based on the reference topology, feasible candidates were selected by considering the operation conditions of the engine, MG1, and a redundant element. To evaluate the fuel economy of the selected candidates, the loss models of the power electronic system and drivetrain components were obtained from the mathematical governing equation and the experimental results. Based on the component loss model, a comparative analysis was performed using a dynamic programming approach under the presence or absence of the drivetrain losses. It was found that the selection of the operating mode and the operation time of each mode vary since the drivetrain loss affects the system efficiency. In addition, even if the additional modes provide the flexibility of selecting the operating mode that results in a higher system efficiency for the given driving condition, additional drivetrain elements for realizing the modes can deteriorate the fuel economy due to their various losses. Full article

(This article belongs to the Special Issue Energy Management, Control, and System Architectures for Electric Vehicle Applications)

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13 pages, 4494 KiB

Open AccessArticle

Combustion Characteristics and Slagging during Co-Combustion of Rice Husk and Sewage Sludge Blends

by Hao Rong, Teng Wang, Min Zhou, Hao Wang, Haobo Hou and Yongjie Xue

Energies 2017, 10(4), 438; https://doi.org/10.3390/en10040438 - 30 Mar 2017

Cited by 41 | Viewed by 5024

In this work, the thermal behavior of rice husk, sewage sludge, and their blends during combustion processes was investigated by means of thermogravimetric analysis (TGA), and the slagging characteristics were studied through X-ray fluorescence (XRF) and melting temperature. The effects of the proportion [...] Read more.

In this work, the thermal behavior of rice husk, sewage sludge, and their blends during combustion processes was investigated by means of thermogravimetric analysis (TGA), and the slagging characteristics were studied through X-ray fluorescence (XRF) and melting temperature. The effects of the proportion of rice husk and sewage sludge blends on the combustion process, ignition and burnout characteristics were also studied. The blends had rice husk percentages of 30, 50, 70 and 100%. The results indicate that there are four main stages of the material burning processes: dehydration, volatile oxidation, and decomposition/oxidation. The reactivity of the blends improved with increasing amounts of rice husk and the results suggest synergistic interactions between rice husk and sewage sludge during the co-combustion process. All co-combustion ashes showed a lower slagging potential owing to their high amorphous SiO₂ content. On the basis of combustion properties and slagging characteristics of ash, the ratio of sewage sludge in the blends should not exceed 30%. Full article

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15 pages, 2708 KiB

Open AccessArticle

Battery Pack Grouping and Capacity Improvement for Electric Vehicles Based on a Genetic Algorithm

by Zheng Chen, Ningyuan Guo, Xiaoyu Li, Jiangwei Shen, Renxin Xiao and Siqi Li

Energies 2017, 10(4), 439; https://doi.org/10.3390/en10040439 - 31 Mar 2017

Cited by 16 | Viewed by 5802

This paper proposes an optimal grouping method for battery packs of electric vehicles (EVs). Based on modeling the vehicle powertrain, analyzing the battery degradation performance and setting up the driving cycle of an EV, a genetic algorithm (GA) is applied to optimize the [...] Read more.

This paper proposes an optimal grouping method for battery packs of electric vehicles (EVs). Based on modeling the vehicle powertrain, analyzing the battery degradation performance and setting up the driving cycle of an EV, a genetic algorithm (GA) is applied to optimize the battery grouping topology with the objective of minimizing the total cost of ownership (TCO). The battery capacity and the serial and parallel amounts of the pack can thus be determined considering the influence of battery degradation. The results show that the optimized pack grouping can be solved by GA within around 9 min. Compared with the results of maximum discharge efficiency within a fixed lifetime, the proposed method can not only achieve a higher discharge efficiency, but also reduce the TCO by 2.29%. To enlarge the applications of the proposed method, the sensitivity to driving conditions is also analyzed to further prove the feasibility of the proposed method. Full article

(This article belongs to the Special Issue Energy Management, Control, and System Architectures for Electric Vehicle Applications)

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21 pages, 3626 KiB

Open AccessFeature PaperArticle

Numerical Analysis of an Organic Rankine Cycle with Adjustable Working Fluid Composition, a Volumetric Expander and a Recuperator

by Peter Collings and Zhibin Yu

Energies 2017, 10(4), 440; https://doi.org/10.3390/en10040440 - 27 Mar 2017

Cited by 11 | Viewed by 5870

Conventional Organic Rankine Cycles (ORCs) using ambient air as their coolant cannot fully utilize the greater temperature differential available to them during the colder months. However, changing the working fluid composition so its boiling temperature matches the ambient temperature as it changes has [...] Read more.

Conventional Organic Rankine Cycles (ORCs) using ambient air as their coolant cannot fully utilize the greater temperature differential available to them during the colder months. However, changing the working fluid composition so its boiling temperature matches the ambient temperature as it changes has been shown to have potential to increase year-round electricity generation. Previous research has assumed that the cycle pressure ratio is able to vary without a major loss in the isentropic efficiency of the turbine. This paper investigates if small scale ORC systems that normally use positive-displacement expanders with fixed expansion ratios could also benefit from this new concept. A numerical model was firstly established, based on which a comprehensive analysis was then conducted. The results showed that it can be applied to systems with positive-displacement expanders and improve their year-round electricity generation. However, such an improvement is less than that of the systems using turbine expanders with variable expansion ratios. Furthermore, such an improvement relies on heat recovery via the recuperator. This is because expanders with a fixed expansion ratio have a relatively constant pressure ratio between their inlet and outlet. The increase of pressure ratio between the evaporator and condenser by tuning the condensing temperature to match colder ambient condition in winter cannot be utilised by such expanders. However, with the recuperator in place, the higher discharging temperature of the expander could increase the heat recovery and consequently reduce the heat input at the evaporator, increasing the thermal efficiency and the specific power. The higher the amount of heat energy transferred in the recuperator, the higher the efficiency improvement. Full article

(This article belongs to the Special Issue Recent Advances in Organic Rankine Cycle Technology for Stationary Applications)

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21 pages, 2188 KiB

Open AccessArticle

Data-Driven Predictive Torque Coordination Control during Mode Transition Process of Hybrid Electric Vehicles

by Jing Sun, Guojing Xing and Chenghui Zhang

Energies 2017, 10(4), 441; https://doi.org/10.3390/en10040441 - 1 Apr 2017

Cited by 19 | Viewed by 4989

Torque coordination control significantly affects the mode transition quality during the mode transition dynamic process of hybrid electric vehicles (HEV). Most of the existing torque coordination control methods are based on the mechanism model, whose control effect heavily depends on the modeling accuracy [...] Read more.

Torque coordination control significantly affects the mode transition quality during the mode transition dynamic process of hybrid electric vehicles (HEV). Most of the existing torque coordination control methods are based on the mechanism model, whose control effect heavily depends on the modeling accuracy of the HEV powertrain. However, the powertrain structure is so complex, that it is difficult to establish its precise mechanism model. In this paper, a torque coordination control strategy using the data-driven predictive control (DDPC) technique is proposed to overcome the shortcomings of mechanism model-based control methods for a clutch-enabled HEV. The proposed control strategy is only based on the measured input-output data in the HEV powertrain, and no mechanism model is needed. The conflicting control requirements of comfortability and economy are included in the cost function. The actual physical constraints of actuators are also explicitly taken into account in the solving process of the data-driven predictive controller. The co-simulation results in Cruise and Simulink validate the effectiveness of the proposed control strategy and demonstrate that the DDPC method can achieve less vehicle jerk, faster mode transition and smaller clutch frictional losses compared with the traditional model predictive control (MPC) method. Full article

(This article belongs to the Special Issue Advanced Energy Storage Technologies and Their Applications (AESA))

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13 pages, 888 KiB

Open AccessArticle

Research on Optimal Planning of Access Location and Access Capacity of Large-Scale Integrated Wind Power Plants

by Hui Li, Gengyin Li, Siwei Liu, Yuning Wang, Zhidong Wang, Jiaming Wang and Ning Zhang

Energies 2017, 10(4), 442; https://doi.org/10.3390/en10040442 - 1 Apr 2017

Cited by 3 | Viewed by 4313

This paper proposes a multi-objective optimal planning model of access location and access capacity for large-scale integrated wind power generation considering the mutual restriction between the planning of large-scale wind power plants and the planning of power system network. In this model, the [...] Read more.

This paper proposes a multi-objective optimal planning model of access location and access capacity for large-scale integrated wind power generation considering the mutual restriction between the planning of large-scale wind power plants and the planning of power system network. In this model, the power flow equilibrium degree, investment costs and active network loss are taken as the optimization goals. The improved differential evolution (IDE) algorithm is applied to calculate the Pareto optimal solution set of wind power’s access planning. With the solution results described by the Pareto pattern, all the alternative solutions are then ranked based on the entropy weight method and the final compromised solution is selected by the method of technique for order preference by similarity to ideal (TOPSIS). And the proposed optimal planning model is tested based on a practical planning need of large-scale integrated wind power generation in an actual power grid of China in 2020. The simulation results show that applied with the proposed optimization model and matching algorithm, the planning scheme of large-scale wind power’s access location and access capacity under complex and practical power system circumstances has been successfully optimized. Full article

(This article belongs to the Special Issue Techniques of Control for Energy Optimization in Actuators, Motors and Power Generation Systems)

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19 pages, 1934 KiB

Open AccessArticle

Wind Power Potentials in Cameroon and Nigeria: Lessons from South Africa

by Abdullahi Abubakar Mas’ud, Asan Vernyuy Wirba, Jorge Alfredo Ardila-Rey, Ricardo Albarracín, Firdaus Muhammad-Sukki, Álvaro Jaramillo Duque, Nurul Aini Bani and Abu Bakar Munir

Energies 2017, 10(4), 443; https://doi.org/10.3390/en10040443 - 27 Mar 2017

Cited by 28 | Viewed by 9645

Wind energy has seen a tremendous growth for electricity generation worldwide and reached 456 GW by the end of June 2016. According to the World Wind Energy Association, global wind power will reach 500 GW by the end of 2016. Africa is a [...] Read more.

Wind energy has seen a tremendous growth for electricity generation worldwide and reached 456 GW by the end of June 2016. According to the World Wind Energy Association, global wind power will reach 500 GW by the end of 2016. Africa is a continent that possesses huge under-utilized wind potentials. Some African countries, e.g., Morocco, Egypt, Tunisia and South Africa, have already adopted wind as an alternative power generation source in their energy mix. Among these countries, South Africa has invested heavily in wind energy with operational wind farms supplying up to 26,000 GWh annually to the national grid. However, two African countries, i.e., Cameroon and Nigeria, have vast potentials, but currently are lagging behind in wind energy development. For Nigeria, there is slow implementation of renewable energy policy, with no visible operational wind farms; while Cameroon does not have any policy plan for wind power. These issues are severely hindering both direct foreign and local investments into the electricity sector. Cameroon and Nigeria have huge wind energy potentials with similar climatic conditions and can benefit greatly from the huge success recorded in South Africa in terms of policy implementation, research, development and technical considerations. Therefore, this paper reviews the wind energy potentials, policies and future renewable energy road-maps in Cameroon and Nigeria and identifies their strength and weakness, as well as providing necessary actions for future improvement that South Africa has already adopted. Full article

(This article belongs to the Special Issue Sustainable Energy Technologies)

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10 pages, 3494 KiB

Open AccessArticle

A Dual Half-Bridge Converter with Adaptive Energy Storage to Achieve ZVS over Full Range of Operation Conditions

by Lei Zhao, Chuangyu Xu, Xuemei Zheng and Haoyu Li

Energies 2017, 10(4), 444; https://doi.org/10.3390/en10040444 - 28 Mar 2017

Cited by 6 | Viewed by 6419

The phase-shifted full-bridge (PSFB) converter is widely employed in high-power applications. However, circulating current, duty-cycle loss, secondary voltage oscillation, and narrow zero-voltage-switching (ZVS) range are the main drawbacks of the conventional PSFB converter. This paper proposes a novel full-bridge converter to improve the [...] Read more.

The phase-shifted full-bridge (PSFB) converter is widely employed in high-power applications. However, circulating current, duty-cycle loss, secondary voltage oscillation, and narrow zero-voltage-switching (ZVS) range are the main drawbacks of the conventional PSFB converter. This paper proposes a novel full-bridge converter to improve the performance of the conventional PSFB converter. The proposed converter contains two paralleled half-bridge inverters and an auxiliary inductor on the primary side. The rectifier stage is composed of six diodes connected with the form of full-bridge rectification. This structure allows the stored energy for ZVS operation to change adaptively with duty-cycle. The power can be transferred from the primary side to the secondary side during the whole period. Therefore, the requirement of output filter inductance is reduced and the circulating current is removed. The proposed converter is a good candidate for high power, high voltage and variable input voltage applications. The operation principle and performance are verified on a laboratory prototype. Full article

(This article belongs to the Collection Smart Grid)

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21 pages, 4901 KiB

Open AccessArticle

Performance of an Energy Efficient Low Power Stepper Converter

by Christoph Gradl and Rudolf Scheidl

Energies 2017, 10(4), 445; https://doi.org/10.3390/en10040445 - 28 Mar 2017

Cited by 8 | Viewed by 6200

This paper presents the development of an energy efficient low power stepper converter. A prototype with a hydraulic output power of ≈600 W was designed, manufactured, investigated and improved. The converter consists of a hydraulic cylinder piston unit controlled by a fast switching [...] Read more.

This paper presents the development of an energy efficient low power stepper converter. A prototype with a hydraulic output power of ≈600 W was designed, manufactured, investigated and improved. The converter consists of a hydraulic cylinder piston unit controlled by a fast switching valve to displace a defined fluid quantum by the limited forward stroke of the piston in its cylinder. The displaced fluid generates a precise, incremental motion of a load cylinder which should be controlled. Energy saving is achieved by storing the pressure surplus intermediately in the kinetic energy of the piston to displace a part of the fluid quantum without hydraulic energy from the supply line. Energy recuperation can be done in a similar way. Simulations and experiments showed two main efficiency improvement measures of the first converter prototype. The weak points were the commercially available check valves and the used guidance system for the pistons. The second part of the paper reports about the development of a fast check valve and of a combined hydrostatic hydrodynamic bearing system based on the elastic deformation of plastics. The theoretical and experimental results show a significant improvement of the energy efficiency, the potential of this drive technology and further improvement potential. Expressed in terms of numbers an energy efficiency increase compared to a resistance control up to 30% and a maximum recuperation energy efficiency over 60% were measured. Full article

(This article belongs to the Special Issue Energy Efficiency and Controllability of Fluid Power Systems)

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23 pages, 18700 KiB

Open AccessArticle

An Isolated Three-Port Bidirectional DC-DC Converter with Enlarged ZVS Region for HESS Applications in DC Microgrids

by Cheng-Shan Wang, Wei Li, Yi-Feng Wang, Fu-Qiang Han, Zhun Meng and Guo-Dong Li

Energies 2017, 10(4), 446; https://doi.org/10.3390/en10040446 - 1 Apr 2017

Cited by 25 | Viewed by 5140

In this paper, a two-stage three-port isolated bidirectional DC-DC converter (BDC) for hybrid energy storage system (HESS) applications in DC microgrids is proposed. It has an enlarged zero-voltage-switching (ZVS) region and reduced power circulation loss. A front-end three-phase interleaved BDC is introduced to [...] Read more.

In this paper, a two-stage three-port isolated bidirectional DC-DC converter (BDC) for hybrid energy storage system (HESS) applications in DC microgrids is proposed. It has an enlarged zero-voltage-switching (ZVS) region and reduced power circulation loss. A front-end three-phase interleaved BDC is introduced to the supercapacitor (SC) channel to compensate voltage variations of SC. Consequently, wide ZVS range and reduced circulation power loss for SC and DC bus ports are achieved under large-scale fluctuating SC voltage. Furthermore, a novel modified pulse-width-modulation (PWM) and phase-shift (PHS) hybrid control method with two phase-shift angles is proposed for BA port. And it contributes to an increasing number of switches operating in ZVS mode with varying battery (BA) voltage. Phase shift control with fixed driving frequency is applied to manage power flow. The ZVS range as well as the current stress of resonant tanks under varying port voltages is analyzed in detail. Finally, a 1 kW prototype with peak efficiency of 94.9% is built, and the theoretical analysis and control method are verified by experiments. Full article

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22 pages, 3494 KiB

Open AccessArticle

Hybridising Human Judgment, AHP, Grey Theory, and Fuzzy Expert Systems for Candidate Well Selection in Fractured Reservoirs

by Fanhui Zeng, Xiaozhao Cheng, Jianchun Guo, Liang Tao and Zhangxin Chen

Energies 2017, 10(4), 447; https://doi.org/10.3390/en10040447 - 1 Apr 2017

Cited by 46 | Viewed by 4930

The selection of appropriate wells for hydraulic fracturing is one of the most important decisions faced by oilfield engineers. It has significant implications for the future development of an oilfield in terms of its productivity and economics. In this study, we developed a [...] Read more.

The selection of appropriate wells for hydraulic fracturing is one of the most important decisions faced by oilfield engineers. It has significant implications for the future development of an oilfield in terms of its productivity and economics. In this study, we developed a fuzzy model for well selection that combines the major objective criteria with the subjective judgments of decision makers. This was done by fusing the analytic hierarchy process (AHP) method, grey theory and an advanced version of fuzzy logic theory (FLT). The AHP component was used to identify the relevant criteria involved in selecting wells for hydraulic fracturing. Grey theory was used to determine the relative importance of those criteria. Then a fuzzy expert system was applied to fuzzily process the aggregated inputs using a Type-2 fuzzy logic system. This undertakes approximate reasoning and generates recommendations for candidate wells. These techniques and technologies were hybridized by using an intercommunication job-sharing method that integrates human judgment. The proposed method was tested on data from an oilfield in Western China and finally the most appropriate candidate wells for hydraulic fracturing were ranked in order of their projected output after fracturing. Full article

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

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11 pages, 1615 KiB

Open AccessArticle

Active, Reactive and Harmonic Control for Distributed Energy Micro-Storage Systems in Smart Communities Homes

by Maria-Isabel Milanes-Montero, Fermin Barrero-Gonzalez, Jaime Pando-Acedo, Eva Gonzalez-Romera, Enrique Romero-Cadaval and Antonio Moreno-Munoz

Energies 2017, 10(4), 448; https://doi.org/10.3390/en10040448 - 1 Apr 2017

Cited by 10 | Viewed by 4042

This paper aims to provide control strategies for distributed micro-storage energy systems at the residential level to contribute to smart grid goals. A simulation model of an energy storage system (ESS) charger has been implemented to test these proposed control strategies. The smart [...] Read more.

This paper aims to provide control strategies for distributed micro-storage energy systems at the residential level to contribute to smart grid goals. A simulation model of an energy storage system (ESS) charger has been implemented to test these proposed control strategies. The smart community energy management system (SCEMS), acting as an aggregator of resources in the community according to the expected demand and production, sends to each individual home the active and reactive power set-points. Besides, in case the ESS has available capacity, once the SCEMS requirements are satisfied, it is used to absorb the harmonic current components demanded by the household circuitry. It allows a local improvement in the power quality of the demanded current, and thus contributes to the global power quality consumption of the community. Simulation results showing the operation of a local ESS at a home in a Smart Community are presented to validate the proposed control strategies. Full article

(This article belongs to the Special Issue Selected Papers from 16 IEEE International Conference on Environment and Electrical Engineering (EEEIC 2016))

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15 pages, 4663 KiB

Open AccessArticle

Enhancement of Power System Stability Using a Novel Power System Stabilizer with Large Critical Gain

by Ziquan Liu, Wei Yao and Jinyu Wen

Energies 2017, 10(4), 449; https://doi.org/10.3390/en10040449 - 1 Apr 2017

Cited by 16 | Viewed by 5987

Power system stabilizers (PSSs) are widely used for suppressing low frequency oscillations in practical power systems. However, according to the requirement of the “guide for setting test of power system stabilizer” of China, PSS gain is limited to no more than 1/3 of [...] Read more.

Power system stabilizers (PSSs) are widely used for suppressing low frequency oscillations in practical power systems. However, according to the requirement of the “guide for setting test of power system stabilizer” of China, PSS gain is limited to no more than 1/3 of its critical gain. As a result, PSSs may not provide enough damping to the inter-area mode oscillations. Through analyzing the Heffron-Phillips (H-P) model of the generator with PSS, it is found that exciter mode will become unstable when PSS exceeds its critical gain. This exciter mode is formed by the natural characteristic of the exciter-PSS loop. To address this problem, a novel PSS with a parallel component added to the conventional PSS is proposed to improve its critical gain. Therefore, large gain can be chosen for the proposed PSS to meet the critical gain requirements of the guide and provide enough damping to the inter-area modes simultaneously. Simulation results on the Ximeng coal power station of China verify the effectiveness of the proposed PSS. Full article

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

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20 pages, 3449 KiB

Open AccessArticle

Aggregators’ Optimal Bidding Strategy in Sequential Day-Ahead and Intraday Electricity Spot Markets

by Xiaolin Ayón, María Ángeles Moreno and Julio Usaola

Energies 2017, 10(4), 450; https://doi.org/10.3390/en10040450 - 1 Apr 2017

Cited by 42 | Viewed by 6748

This paper proposes a probabilistic optimization method that produces optimal bidding curves to be submitted by an aggregator to the day-ahead electricity market and the intraday market, considering the flexible demand of his customers (based in time dependent resources such as batteries and [...] Read more.

This paper proposes a probabilistic optimization method that produces optimal bidding curves to be submitted by an aggregator to the day-ahead electricity market and the intraday market, considering the flexible demand of his customers (based in time dependent resources such as batteries and shiftable demand) and taking into account the possible imbalance costs as well as the uncertainty of forecasts (market prices, demand, and renewable energy sources (RES) generation). The optimization strategy aims to minimize the total cost of the traded energy over a whole day, taking into account the intertemporal constraints. The proposed formulation leads to the solution of different linear optimization problems, following the natural temporal sequence of electricity spot markets. Intertemporal constraints regarding time dependent resources are fulfilled through a scheduling process performed after the day-ahead market clearing. Each of the different problems is of moderate dimension and requires short computation times. The benefits of the proposed strategy are assessed comparing the payments done by an aggregator over a sample period of one year following different deterministic and probabilistic strategies. Results show that probabilistic strategy reports better benefits for aggregators participating in power markets. Full article

(This article belongs to the Special Issue Distributed Energy Resources Management)

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21 pages, 2207 KiB

Open AccessArticle

Power-to-Steel: Reducing CO₂ through the Integration of Renewable Energy and Hydrogen into the German Steel Industry

by Alexander Otto, Martin Robinius, Thomas Grube, Sebastian Schiebahn, Aaron Praktiknjo and Detlef Stolten

Energies 2017, 10(4), 451; https://doi.org/10.3390/en10040451 - 1 Apr 2017

Cited by 204 | Viewed by 19377

This paper analyses some possible means by which renewable power could be integrated into the steel manufacturing process, with techniques such as blast furnace gas recirculation (BF-GR), furnaces that utilize carbon capture, a higher share of electrical arc furnaces (EAFs) and the use [...] Read more.

This paper analyses some possible means by which renewable power could be integrated into the steel manufacturing process, with techniques such as blast furnace gas recirculation (BF-GR), furnaces that utilize carbon capture, a higher share of electrical arc furnaces (EAFs) and the use of direct reduced iron with hydrogen as reduction agent (H-DR). It is demonstrated that these processes could lead to less dependence on—and ultimately complete independence from—coal. This opens the possibility of providing the steel industry with power and heat by coupling to renewable power generation (sector coupling). In this context, it is shown using the example of Germany that with these technologies, reductions of 47–95% of CO₂ emissions against 1990 levels and 27–95% of primary energy demand against 2008 can be achieved through the integration of 12–274 TWh of renewable electrical power into the steel industry. Thereby, a substantial contribution to reducing CO₂ emissions and fuel demand could be made (although it would fall short of realizing the German government’s target of a 50% reduction in power consumption by 2050). Full article

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

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15 pages, 16000 KiB

Open AccessFeature PaperArticle

A Comprehensive Study on the Avalanche Breakdown Robustness of Silicon Carbide Power MOSFETs

by Asad Fayyaz, Gianpaolo Romano, Jesus Urresti, Michele Riccio, Alberto Castellazzi, Andrea Irace and Nick Wright

Energies 2017, 10(4), 452; https://doi.org/10.3390/en10040452 - 1 Apr 2017

Cited by 40 | Viewed by 12802

This paper presents an in-depth investigation into the avalanche breakdown robustness of commercial state-of-the-art silicon carbide (SiC) power MOSFETs comprising of functional as well as structural characterization and the corresponding underlying physical mechanisms responsible for device failure. One aspect of robustness for power [...] Read more.

This paper presents an in-depth investigation into the avalanche breakdown robustness of commercial state-of-the-art silicon carbide (SiC) power MOSFETs comprising of functional as well as structural characterization and the corresponding underlying physical mechanisms responsible for device failure. One aspect of robustness for power MOSFETs is determined by its ability to withstand energy during avalanche breakdown. Avalanche energy (E_AV) is an important figure of merit for all applications requiring load dumping and/or to benefit from snubber-less converter design. 2D TCAD electro-thermal simulations were performed to get important insight into the failure mechanism of SiC power MOSFETs during avalanche breakdown. Full article

(This article belongs to the Special Issue Semiconductor Power Devices)

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18 pages, 2274 KiB

Open AccessArticle

Energy Management with Support of PV Partial Shading Modelling in Micro Grid Environments

by Marco Severini, Emanuele Principi, Marco Fagiani, Stefano Squartini and Francesco Piazza

Energies 2017, 10(4), 453; https://doi.org/10.3390/en10040453 - 1 Apr 2017

Cited by 7 | Viewed by 4356

Although photovoltaic power plants are suitable local energy sources in Micro Grid environments, when large plants are involved, partial shading and inaccurate modelling of the plant can affect both the design of the Micro Grid as well as the energy management process that [...] Read more.

Although photovoltaic power plants are suitable local energy sources in Micro Grid environments, when large plants are involved, partial shading and inaccurate modelling of the plant can affect both the design of the Micro Grid as well as the energy management process that allows for lowering the overall Micro Grid demand towards the main grid. To investigate the issue, a Photovoltaic Plant simulation model, based on a real life power plant, and an energy management system, based on a real life Micro Grid environment, have been integrated to evaluate the performance of a Micro Grid under partial shading conditions. Using a baseline energy production model as a reference, the energy demand of the Micro Grid has been computed in sunny and partial shading conditions. The experiments reveal that an estimation based on a simplified PV model can exceed by 65% the actual production. With regards to Micro Grid design, on sunny days, the expected costs, based on a simplified PV model, can be 5.5% lower than the cost based on the double inverter model. In single cloud scenarios, the underrating can reach 28.3%. With regard to the management process, if the energy yield is estimated by means of a simplified PV model, the actual cost can be from 17.1% to 21.5% higher than the theoretical cost expected at design time. Full article

(This article belongs to the Special Issue Selected Papers from 16 IEEE International Conference on Environment and Electrical Engineering (EEEIC 2016))

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19 pages, 6536 KiB

Open AccessArticle

The Performance of Polymer Flooding in Heterogeneous Type II Reservoirs—An Experimental and Field Investigation

by Huiying Zhong, Weidong Zhang, Jing Fu, Jun Lu and Hongjun Yin

Energies 2017, 10(4), 454; https://doi.org/10.3390/en10040454 - 1 Apr 2017

Cited by 40 | Viewed by 5864

The polymer flooding process has already been applied to the medium permeability type II reservoirs of the Daqing Oilfield (China) to enhance oil recovery. However, this process faces a number of challenges, such as the flooding efficiency, high injection pressure, formation blockage and [...] Read more.

The polymer flooding process has already been applied to the medium permeability type II reservoirs of the Daqing Oilfield (China) to enhance oil recovery. However, this process faces a number of challenges, such as the flooding efficiency, high injection pressure, formation blockage and damage, unbalanced absorption ratio, and economical justification. In this study, single-phase and two-phase flow experiments are performed to investigate polymer injection adaptability with natural cores of type II reservoirs. The enhanced oil recovery (EOR) effects of the polymer are studied by physical simulation experiments, and the results of application in an actual field are also presented. The results indicate that the flow characteristics and injection capability are dominated by the reservoir permeability in polymer flooding. Moreover, the adsorption of polymer molecules and the injection pressure gradient, which reflect formation damage, are affected more significantly by the concentration than by the molecular weight in type II reservoirs. Using the matching relationship, the injection-production process is stable, and additional oil recoveries of 10%–15% can be obtained in heterogeneous type II reservoirs with a high water saturation. This work is significant in that it further accelerates the application of polymer flooding EOR in medium permeability heterogeneous oilfields with high water saturation. Full article

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

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19 pages, 1943 KiB

Open AccessArticle

A New Method for Distribution Network Reconfiguration Analysis under Different Load Demands

by Firas M. F. Flaih, Xiangning Lin, Mohammed Kdair Abd, Samir M. Dawoud, Zhengtian Li and Owolabi Sunday Adio

Energies 2017, 10(4), 455; https://doi.org/10.3390/en10040455 - 1 Apr 2017

Cited by 36 | Viewed by 5472

The strategies of distribution network reconfiguration are applicable for minimizing power loss and saving electrical energy in the distribution system. Network reconfiguration is usually represented by constant load demand so ignoring the variability of load demand causes uncertainty and misleading results in the [...] Read more.

The strategies of distribution network reconfiguration are applicable for minimizing power loss and saving electrical energy in the distribution system. Network reconfiguration is usually represented by constant load demand so ignoring the variability of load demand causes uncertainty and misleading results in the minimization of power loss. This paper consists of two parts: first, the reconfiguration was accomplished using an optimization framework based on constant load to find sets of optimal switches. The minimization of active power loss was taken as an objective function while bus voltage, branch current and system radiality were taken as system constraints. The study was applied to a 33-bus test distribution network, which is exceedingly used as test examples for solving reconfiguration problems. Second, lists of the configurations set obtained from the first part, as well as other different optimization methods proposed earlier under constant load demand were taken as test switches. Additionally, the network in the presence of distributed generators was taken to analyze the reconfiguration under an active network. Two types of load demands; the variable load and voltage-dependent load, are proposed to represent the practical load demands. This paper presents a new method for good analysis as it defines the effect of loading levels and loading patterns on a distribution system performance for passive and active networks. The proposed approach tries to find the actual power loss under different characteristics of loads. Therefore, the probable benefit of this approach is the contribution to providing more flexibility for electrical utilities in terms of distribution system operation, while also opening new prospects in the automation of smart distribution systems. Full article

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19 pages, 16905 KiB

Open AccessArticle

Methodology Applied to the Evaluation of Natural Ventilation in Residential Building Retrofits: A Case Study

by Alberto Meiss, Miguel A. Padilla-Marcos and Jesús Feijó-Muñoz

Energies 2017, 10(4), 456; https://doi.org/10.3390/en10040456 - 1 Apr 2017

Cited by 12 | Viewed by 6222

The primary objective of this paper is to present the use of a steady model that is able to qualify and quantify available natural ventilation flows applied to the energy retrofitting of urban residential districts. In terms of air quality, natural ventilation presents [...] Read more.

The primary objective of this paper is to present the use of a steady model that is able to qualify and quantify available natural ventilation flows applied to the energy retrofitting of urban residential districts. In terms of air quality, natural ventilation presents more efficient solutions compared to active systems. This method combines numeric simulations, through the utilization of Ansys Fluent R15.0^® and Engineering Equation Solver EES^®, with on-site pressurization tests. Testing consists of the application of the seasonal pressure gradient on the building’s envelope and the calculation of the ventilation flows in three climatic representative conditions (summer, winter, and annual average). Through the implementation of this methodology to existing buildings it is possible to evaluate the influence of the built environment, as well as key parameters (relative height of the dwelling, number of vertical ventilation ducts, and airtightness of windows) of available natural ventilation. Full article

(This article belongs to the Special Issue Energy Conservation in Infrastructures 2016)

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15 pages, 11257 KiB

Open AccessArticle

A Cubature Particle Filter Algorithm to Estimate the State of the Charge of Lithium-Ion Batteries Based on a Second-Order Equivalent Circuit Model

by Bizhong Xia, Zhen Sun, Ruifeng Zhang and Zizhou Lao

Energies 2017, 10(4), 457; https://doi.org/10.3390/en10040457 - 1 Apr 2017

Cited by 100 | Viewed by 6096

The state of charge (SOC) is the residual capacity of a battery. The SOC value indicates the mileage endurance, and an accurate SOC value is required to ensure the safe use of the battery to prevent over- and over-discharging. However, unlike [...] Read more.

The state of charge (SOC) is the residual capacity of a battery. The SOC value indicates the mileage endurance, and an accurate SOC value is required to ensure the safe use of the battery to prevent over- and over-discharging. However, unlike size and weight, battery power is not easily determined. As a consequence, we can only estimate the SOC value based on the external characteristics of the battery. In this paper, a cubature particle filter (CPF) based on the cubature Kalman filter (CKF) and the particle filter (PF) is presented for accurate and reliable SOC estimation. The CPF algorithm combines the CKF and PF algorithms to generate a suggested density function for the PF algorithm based on the CKF. The second-order resistor-capacitor (RC) equivalent circuit model was used to approximate the dynamic performance of the battery, and the model parameters were identified by fitting. A dynamic stress test (DST) was used to separately estimate the accuracy and robustness of the CKF and the CPF algorithms. The experimental results show that the CPF algorithm exhibited better accuracy and robustness than the CKF algorithm. Full article

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12 pages, 2821 KiB

Open AccessArticle

Combustion and Emission Characteristics of Coconut-Based Biodiesel in a Liquid Fuel Burner

by Muhammad Syahiran Abdul Malik, Ashrul Ishak Mohamad Shaiful, Mohd Shuisma Mohd. Ismail, Mohammad Nazri Mohd Jaafar and Amirah Mohamad Sahar

Energies 2017, 10(4), 458; https://doi.org/10.3390/en10040458 - 1 Apr 2017

Cited by 26 | Viewed by 5779

This paper presents an investigation on the combustion performance of different Coconut Methyl Ester (CME) biodiesel blends with Conventional Diesel Fuel (CDF) under B5 (5% CME, 95% CDF), B15 (15% CME, 85% CDF), and B25 (25% CME, 75% CDF) conditions. The performances of [...] Read more.

This paper presents an investigation on the combustion performance of different Coconut Methyl Ester (CME) biodiesel blends with Conventional Diesel Fuel (CDF) under B5 (5% CME, 95% CDF), B15 (15% CME, 85% CDF), and B25 (25% CME, 75% CDF) conditions. The performances of these fuels were evaluated based on the temperature profiles of the combustor wall and emission concentration of Oxides of Nitrogen (NO_x), Sulphur Dioxide (SO₂), and Carbon Monoxide (CO). The fuel properties of the CME biodiesel blends were measured and compared with CDF. All tested fuels were combusted using an open-ended combustion chamber at three different equivalence ratios, i.e., lean fuel to air mixture (Ф = 0.8), stoichiometry (Ф = 1.0), and rich fuel to air mixture (Ф =1.2), using a standard solid spray fuel nozzle. The results indicated that CME biodiesel blends combust at a lower temperature and produce less emission in comparison with CDF for all equivalence ratios. Moreover, the increase of CME content in biodiesel blends reduced the temperature of the combustor wall and the emission concentration. Results also proved that the utilization of biodiesel is beneficial to various industrial applications, especially in the transportation sector due to it being environmentally friendly, and serves as an alternative to petroleum diesel fuel. Full article

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22 pages, 4541 KiB

Open AccessArticle

A Novel Remaining Useful Life Prediction Approach for Superbuck Converter Circuits Based on Modified Grey Wolf Optimizer-Support Vector Regression

by Li Wang, Jiguang Yue, Yongqing Su, Feng Lu and Qiang Sun

Energies 2017, 10(4), 459; https://doi.org/10.3390/en10040459 - 2 Apr 2017

Cited by 21 | Viewed by 5150

The reliability of power packs is very important for the performance of electronic equipment and ensuring the reliability of power electronic circuits is especially vital for equipment security. An alteration in the converter component parameter can lead to the decline of the power [...] Read more.

The reliability of power packs is very important for the performance of electronic equipment and ensuring the reliability of power electronic circuits is especially vital for equipment security. An alteration in the converter component parameter can lead to the decline of the power supply quality. In order to effectively prevent failure and estimate the remaining useful life (RUL) of superbuck converters, a circuit failure prognostics framework is proposed in this paper. We employ the average value and ripple value of circuit output voltage as a feature set to calculate the Mahalanobis distance (MD) in order to reflect the health status of the circuit. Time varying MD sets form the circuit state time series. According to the working condition time series that have been obtained, we can predict the later situation with support vector regression (SVR). SVR has been improved by a modified grey wolf optimizer (MGWO) algorithm before estimating the RUL. This is the first attempt to apply the modified version of the grey wolf optimizer (GWO) to circuit prognostics and system health management (PHM). Subsequently, benchmark functions have been used to validate the performance of the MGWO. Finally, the simulation results of comparative experiments demonstrate that MGWO-SVR can predict the RUL of circuits with smaller error and higher prediction precision. Full article

(This article belongs to the Special Issue DC Systems)

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17 pages, 7859 KiB

Open AccessArticle

A Method for Energy and Resource Assessment of Waves in Finite Water Depths

by Wanan Sheng and Hui Li

Energies 2017, 10(4), 460; https://doi.org/10.3390/en10040460 - 2 Apr 2017

Cited by 46 | Viewed by 5638

This paper presents a new method for improving the assessment of energy and resources of waves in the cases of finite water depths in which the historical and some ongoing sea wave measurements are simply given in forms of scatter diagrams or the [...] Read more.

This paper presents a new method for improving the assessment of energy and resources of waves in the cases of finite water depths in which the historical and some ongoing sea wave measurements are simply given in forms of scatter diagrams or the forms of (significant) wave heights and the relevant statistical wave periods, whilst the detailed spectrum information has been discarded, thus no longer available for the purpose of analysis. As a result of such simplified wave data, the assessment for embracing the effects of water depths on wave energy and resources becomes either difficult or inaccurate. In many practical cases, the effects of water depths are simply ignored because the formulas for deep-water waves are frequently employed. This simplification may cause large energy under-estimations for the sea waves in finite water depths. To improve the wave energy assessment for such much-simplified wave data, an approximate method is proposed for approximating the effect of water depth in this research, for which the wave energy period or the calculated peak period can be taken as the reference period for implementing the approximation. The examples for both theoretical and measured spectra show that the proposed method can significantly reduce the errors on wave energy assessment due to the approximations and inclusions of the effects of finite water depths. Full article

(This article belongs to the Special Issue Numerical Modelling of Wave and Tidal Energy)

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24 pages, 8091 KiB

Open AccessArticle

A Multiple Data Fusion Approach to Wheel Slip Control for Decentralized Electric Vehicles

by Dejun Yin, Nan Sun, Danfeng Shan and Jia-Sheng Hu

Energies 2017, 10(4), 461; https://doi.org/10.3390/en10040461 - 2 Apr 2017

Cited by 17 | Viewed by 6175

Currently, active safety control methods for cars, i.e., the antilock braking system (ABS), the traction control system (TCS), and electronic stability control (ESC), govern the wheel slip control based on the wheel slip ratio, which relies on the information from non-driven wheels. However, [...] Read more.

Currently, active safety control methods for cars, i.e., the antilock braking system (ABS), the traction control system (TCS), and electronic stability control (ESC), govern the wheel slip control based on the wheel slip ratio, which relies on the information from non-driven wheels. However, these methods are not applicable in the cases without non-driven wheels, e.g., a four-wheel decentralized electric vehicle. Therefore, this paper proposes a new wheel slip control approach based on a novel data fusion method to ensure good traction performance in any driving condition. Firstly, with the proposed data fusion algorithm, the acceleration estimator makes use of the data measured by the sensor installed near the vehicle center of mass (CM) to calculate the reference acceleration of each wheel center. Then, the wheel slip is constrained by controlling the acceleration deviation between the actual wheel and the reference wheel center. By comparison with non-control and model following control (MFC) cases in double lane change tests, the simulation results demonstrate that the proposed control method has significant anti-slip effectiveness and stabilizing control performance. Full article

(This article belongs to the Special Issue Advances in Electric Vehicles and Plug-in Hybrid Vehicles 2017)

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19 pages, 5332 KiB

Open AccessArticle

Energy Demand Modeling Methodology of Key State Transitions of Turning Processes

by Shun Jia, Qinghe Yuan, Dawei Ren and Jingxiang Lv

Energies 2017, 10(4), 462; https://doi.org/10.3390/en10040462 - 2 Apr 2017

Cited by 13 | Viewed by 4064

Energy demand modeling of machining processes is the foundation of energy optimization. Energy demand of machining state transition is integral to the energy requirements of the machining process. However, research focus on energy modeling of state transition is scarce. To fill this gap, [...] Read more.

Energy demand modeling of machining processes is the foundation of energy optimization. Energy demand of machining state transition is integral to the energy requirements of the machining process. However, research focus on energy modeling of state transition is scarce. To fill this gap, an energy demand modeling methodology of key state transitions of the turning process is proposed. The establishment of an energy demand model of state transition could improve the accuracy of the energy model of the machining process, which also provides an accurate model and reliable data for energy optimization of the machining process. Finally, case studies were conducted on a CK6153i CNC lathe, the results demonstrating that predictive accuracy with the proposed method is generally above 90% for the state transition cases. Full article

(This article belongs to the Special Issue Energy Efficient Manufacturing)

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16 pages, 3115 KiB

Open AccessArticle

Power Loss Analysis for Wind Power Grid Integration Based on Weibull Distribution

by Ahmed Al Ameri, Aouchenni Ounissa, Cristian Nichita and Aouzellag Djamal

Energies 2017, 10(4), 463; https://doi.org/10.3390/en10040463 - 2 Apr 2017

Cited by 23 | Viewed by 7467

The growth of electrical demand increases the need of renewable energy sources, such as wind energy, to meet that need. Electrical power losses are an important factor when wind farm location and size are selected. The capitalized cost of constant power losses during [...] Read more.

The growth of electrical demand increases the need of renewable energy sources, such as wind energy, to meet that need. Electrical power losses are an important factor when wind farm location and size are selected. The capitalized cost of constant power losses during the life of a wind farm will continue to high levels. During the operation period, a method to determine if the losses meet the requirements of the design is significantly needed. This article presents a Simulink simulation of wind farm integration into the grid; the aim is to achieve a better understanding of wind variation impact on grid losses. The real power losses are set as a function of the annual variation, considering a Weibull distribution. An analytical method has been used to select the size and placement of a wind farm, taking into account active power loss reduction. It proposes a fast linear model estimation to find the optimal capacity of a wind farm based on DC power flow and graph theory. The results show that the analytical approach is capable of predicting the optimal size and location of wind turbines. Furthermore, it revealed that the annual variation of wind speed could have a strong effect on real power loss calculations. In addition to helping to improve utility efficiency, the proposed method can develop specific designs to speeding up integration of wind farms into grids. Full article

(This article belongs to the Collection Wind Turbines)

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28 pages, 2298 KiB

Open AccessArticle

The Role of Logistics in Practical Levelized Cost of Energy Reduction Implementation and Government Sponsored Cost Reduction Studies: Day and Night in Offshore Wind Operations and Maintenance Logistics

by Thomas Poulsen, Charlotte Bay Hasager and Christian Munk Jensen

Energies 2017, 10(4), 464; https://doi.org/10.3390/en10040464 - 2 Apr 2017

Cited by 23 | Viewed by 18308

This paper reveals that logistics make up at least 17% of annual operational expenditure costs for offshore wind farms. Annual operational expenditure is found to vary by a factor of 9.5, making its share of levelized cost of energy for offshore wind range [...] Read more.

This paper reveals that logistics make up at least 17% of annual operational expenditure costs for offshore wind farms. Annual operational expenditure is found to vary by a factor of 9.5, making its share of levelized cost of energy for offshore wind range from 13% to 57%. These are key findings of a 20-month research project targeting cost reduction initiatives for offshore wind systems. The findings reveal that cost-out measures are difficult to implement due to cultural differences. Implementation efforts are rendered by personnel located offshore in a harsh sea environment which is in stark contrast to the shore-based office personnel who develop studies directing cost reduction efforts. This paper details the company motivation to join industry-wide cost reduction initiatives. A business case for offshore wind operations and maintenance logistics yielding 1% savings in levelized cost of energy is included on how to expand working hours from daytime to also work at night. Full article

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

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19 pages, 4577 KiB

Open AccessArticle

A Time-Efficient Approach for Modelling and Simulation of Aggregated Multiple Photovoltaic Microinverters

by Sungmin Park, Weiqiang Chen, Ali M. Bazzi and Sung-Yeul Park

Energies 2017, 10(4), 465; https://doi.org/10.3390/en10040465 - 31 Mar 2017

Cited by 2 | Viewed by 4172

This paper presents a time-efficient modeling and simulation strategy for aggregated microinverters in large-scale photovoltaic systems. As photovoltaic microinverter systems are typically comprised of multiple power electronic converters, a suitable modeling and simulation strategy that can be used for rapid prototyping is required. [...] Read more.

This paper presents a time-efficient modeling and simulation strategy for aggregated microinverters in large-scale photovoltaic systems. As photovoltaic microinverter systems are typically comprised of multiple power electronic converters, a suitable modeling and simulation strategy that can be used for rapid prototyping is required. Dynamic models incorporating switching action may induce significant computational burdens and long simulation durations. This paper introduces a single-matrix-form approach using the average model of a basic microinverter with two power stages consisting of a dc-dc and dc-ac converter. The proposed methodology using a common or intermediate source between two average models of cascaded converters to find the overall average model is introduced and is applicable to many other converter topologies and combinations. It provides better flexibility and simplicity when investigating various power topologies in system-level studies of microinverter and other power electronic systems. A 200 W prototype microinverter is tested to verify the proposed average and dynamic models. Furthermore, MATLAB/Simulink (2010a, Mathworks, Natick, MA, USA) is used to show the improved simulation speed and maintained accuracy of the multiple microinverter configurations when the derived average model is compared to a dynamic switching simulation model. Full article

(This article belongs to the Special Issue Power Electronics and Power Quality)

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14 pages, 1714 KiB

Open AccessArticle

Fatigue Reliability Analysis of Wind Turbine Cast Components

by Hesam Mirzaei Rafsanjani, John Dalsgaard Sørensen, Søren Fæster and Asger Sturlason

Energies 2017, 10(4), 466; https://doi.org/10.3390/en10040466 - 2 Apr 2017

Cited by 4 | Viewed by 4717

The fatigue life of wind turbine cast components, such as the main shaft in a drivetrain, is generally determined by defects from the casting process. These defects may reduce the fatigue life and they are generally distributed randomly in components. The foundries, cutting [...] Read more.

The fatigue life of wind turbine cast components, such as the main shaft in a drivetrain, is generally determined by defects from the casting process. These defects may reduce the fatigue life and they are generally distributed randomly in components. The foundries, cutting facilities and test facilities can affect the verification of properties by testing. Hence, it is important to have a tool to identify which foundry, cutting and/or test facility produces components which, based on the relevant uncertainties, have the largest expected fatigue life or, alternatively, have the largest reliability to be used for decision-making if additional cost considerations are added. In this paper, a statistical approach is presented based on statistical hypothesis testing and analysis of covariance (ANCOVA) which can be applied to compare different groups (manufacturers, suppliers, test facilities, etc.) and to quantify the relevant uncertainties using available fatigue tests. Illustrative results are presented as obtained by statistical analysis of a large set of fatigue data for casted test components typically used for wind turbines. Furthermore, the SN curves (fatigue life curves based on applied stress) for fatigue assessment are estimated based on the statistical analyses and by introduction of physical, model and statistical uncertainties used for the illustration of reliability assessment. Full article

(This article belongs to the Collection Wind Turbines)

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16 pages, 1126 KiB

Open AccessArticle

Experimental Investigations of Physical and Chemical Properties for Microalgae HTL Bio-Crude Using a Large Batch Reactor

by Farhad M. Hossain, Jana Kosinkova, Richard J. Brown, Zoran Ristovski, Ben Hankamer, Evan Stephens and Thomas J. Rainey

Energies 2017, 10(4), 467; https://doi.org/10.3390/en10040467 - 5 Apr 2017

Cited by 49 | Viewed by 6937

As a biofuel feedstock, microalgae has good scalability and potential to supply a significant proportion of world energy compared to most types of biofuel feedstock. Hydrothermal liquefaction (HTL) is well-suited to wet biomass (such as microalgae) as it greatly reduces the energy requirements [...] Read more.

As a biofuel feedstock, microalgae has good scalability and potential to supply a significant proportion of world energy compared to most types of biofuel feedstock. Hydrothermal liquefaction (HTL) is well-suited to wet biomass (such as microalgae) as it greatly reduces the energy requirements associated with dewatering and drying. This article presents experimental analyses of chemical and physical properties of bio-crude oil produced via HTL using a high growth-rate microalga Scenedesmus sp. in a large batch reactor. The overarching goal was to investigate the suitability of microalgae HTL bio-crude produced in a large batch reactor for direct application in marine diesel engines. To this end we characterized the chemical and physical properties of the bio-crudes produced. HTL literature mostly reports work using very small batch reactors which are preferred by researchers, so there are few experimental and parametric measurements for bio-crude physical properties, such as viscosity and density. In the course of this study, a difference between traditionally calculated values and measured values was noted. In the parametric study, the bio-crude viscosity was significantly closer to regular diesel and biodiesel standards than transesterified (FAME) microalgae biodiesel. Under optimised conditions, HTL bio-crude’s high density (0.97–1.04 kg·L⁻¹) and its high viscosity (70.77–73.89 mm²·s⁻¹) had enough similarity to marine heavy fuels. although the measured higher heating value, HHV, was lower (29.8 MJ·kg⁻¹). The reaction temperature was explored in the range 280–350 °C and bio-crude oil yield and HHV reached their maxima at the highest temperature. Slurry concentration was explored between 15% and 30% at this temperature and the best HHV, O:C, and N:C were found to occur at 25%. Two solvents (dichloromethane and n-hexane) were used to recover the bio-crude oil, affecting the yield and chemical composition of the bio-crude. Full article

(This article belongs to the Collection Bioenergy and Biofuel)

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17 pages, 593 KiB

Open AccessArticle

Determining the Minimal Power Capacity of Energy Storage to Accommodate Renewable Generation

by Xingning Han, Shiwu Liao, Xiaomeng Ai, Wei Yao and Jinyu Wen

Energies 2017, 10(4), 468; https://doi.org/10.3390/en10040468 - 2 Apr 2017

Cited by 28 | Viewed by 4077

The increasing penetration of renewable generation increases the need for flexibility to accommodate for growing uncertainties. The level of flexibility is measured by the available power that can be provided by flexible resources, such as dispatachable generators, in a certain time period under [...] Read more.

The increasing penetration of renewable generation increases the need for flexibility to accommodate for growing uncertainties. The level of flexibility is measured by the available power that can be provided by flexible resources, such as dispatachable generators, in a certain time period under the constraint of transmission capacity. In addition to conventional flexible resources, energy storage is also expected as a supplementary flexible resource for variability accommodation. To aid the cost-effective planning of energy storage in power grids with intensive renewable generation, this study proposed an approach to determine the minimal requirement of power capacity and the appropriate location for the energy storage. In the proposed approach, the variation of renewable generation is limited within uncertainty sets, then a linear model is proposed for dispatchable generators and candidate energy storage to accommodate the variation in renewable generation under the power balance and transmission network constraints. The target of the proposed approach is to minimize the total power capacity of candidate energy storage facilities when the availability of existing flexible resources is maximized. After that, the robust linear optimization method is employed to convert and solve the proposed model with uncertainties. Case studies are carried out in a modified Garver 6-bus system and the Liaoning provincial power system in China. Simulation results well demonstrate the proposed optimization can provide the optimal location of energy storage with small power capacities. The minimal power capacity of allocated energy storage obtained from the proposed approach only accounts for 1/30 of the capacity of the particular transmission line that is required for network expansion. Besides being adopted for energy storage planning, the proposed approach can also be a potential tool for identifying the sufficiency of flexibility when a priority is given to renewable generation. Full article

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

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12 pages, 3289 KiB

Open AccessArticle

Thermal Properties of Biochars Derived from Waste Biomass Generated by Agricultural and Forestry Sectors

by Xing Yang, Hailong Wang, Peter James Strong, Song Xu, Shujuan Liu, Kouping Lu, Kuichuan Sheng, Jia Guo, Lei Che, Lizhi He, Yong Sik Ok, Guodong Yuan, Ying Shen and Xin Chen

Energies 2017, 10(4), 469; https://doi.org/10.3390/en10040469 - 2 Apr 2017

Cited by 95 | Viewed by 9825

Waste residues produced by agricultural and forestry industries can generate energy and are regarded as a promising source of sustainable fuels. Pyrolysis, where waste biomass is heated under low-oxygen conditions, has recently attracted attention as a means to add value to these residues. [...] Read more.

Waste residues produced by agricultural and forestry industries can generate energy and are regarded as a promising source of sustainable fuels. Pyrolysis, where waste biomass is heated under low-oxygen conditions, has recently attracted attention as a means to add value to these residues. The material is carbonized and yields a solid product known as biochar. In this study, eight types of biomass were evaluated for their suitability as raw material to produce biochar. Material was pyrolyzed at either 350 °C or 500 °C and changes in ash content, volatile solids, fixed carbon, higher heating value (HHV) and yield were assessed. For pyrolysis at 350 °C, significant correlations (p < 0.01) between the biochars’ ash and fixed carbon content and their HHVs were observed. Masson pine wood and Chinese fir wood biochars pyrolyzed at 350 °C and the bamboo sawdust biochar pyrolyzed at 500 °C were suitable for direct use in fuel applications, as reflected by their higher HHVs, higher energy density, greater fixed carbon and lower ash contents. Rice straw was a poor substrate as the resultant biochar contained less than 60% fixed carbon and a relatively low HHV. Of the suitable residues, carbonization via pyrolysis is a promising technology to add value to pecan shells and Miscanthus. Full article

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

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14 pages, 2445 KiB

Open AccessArticle

Impedance Decoupling in DC Distributed Systems to Maintain Stability and Dynamic Performance

by Ahmed Aldhaheri and Amir Etemadi

Energies 2017, 10(4), 470; https://doi.org/10.3390/en10040470 - 2 Apr 2017

Cited by 18 | Viewed by 5511

DC distributed systems are highly reliable and efficient means of delivering DC power or adopting renewable energy resources. However, DC distributed systems are prone to instability and dynamic performance degradation due to the negative incremental input impedance of DC-DC converts. In this paper, [...] Read more.

DC distributed systems are highly reliable and efficient means of delivering DC power or adopting renewable energy resources. However, DC distributed systems are prone to instability and dynamic performance degradation due to the negative incremental input impedance of DC-DC converts. In this paper, we propose a generic method to eliminate the impact of the negative input impedance on DC systems by shaping the source output impedance such that its bode-plot is restricted in the area that is contained below the product of the source’s duty ratio and its characteristic impedance. The performance deterioration originates whenever the output impedance of the source exceeds, in magnitude, the input impedance of the load converter due to deficiency in stability margins. Hence, confining the impedance in the proposed region helps decouple the interaction between the converters and preserve their own dynamic performances. The proposed method was proven by analytical analysis, time-based simulation, and practical experiments. All of their outcomes were in agreement, proving the effectiveness of the proposed method in preserving the dynamic performance of distributed systems. Full article

(This article belongs to the Special Issue Distribution Power Systems and Power Quality)

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16 pages, 6705 KiB

Open AccessArticle

Effects of Lean Zones on Steam-Assisted Gravity Drainage Performance

by Jinze Xu, Zhangxin Chen, Xiaohu Dong and Wei Zhou

Energies 2017, 10(4), 471; https://doi.org/10.3390/en10040471 - 3 Apr 2017

Cited by 19 | Viewed by 5822

A thorough understanding of the effects of lean zones and the improvement of steam-assisted gravity drainage (SAGD) operations with such heterogeneities is critically important for reducing the disadvantages of lean zones. The numerical model shows: (1) SAGD is most influenced by the single-layer [...] Read more.

A thorough understanding of the effects of lean zones and the improvement of steam-assisted gravity drainage (SAGD) operations with such heterogeneities is critically important for reducing the disadvantages of lean zones. The numerical model shows: (1) SAGD is most influenced by the single-layer lean zone with the above-injector (AI) location; with the decrease of interval distance and increase of thickness and water saturation in lean zones, the detrimental effect of single-layer lean zones on SAGD performance increases; (2) with the increase of period and decrease of connate and initial water saturations in lean zones, the detrimental effect of multiple-layer lean zones on SAGD performance increases; (3) reducing the injection pressure properly improves SAGD performance in leaky oil sands. The field-scale study indicates: (1) well pair 1 is most affected by lean zones in the studied pad due to the widest distribution of lean zones above its injector, and a hybrid cyclic steam stimulation (CSS)/SAGD method is proposed to overcome the practical problem of a low injection pressure in this area; (2) simulation results prove that the hybrid CSS/SAGD method is better than the conventional SAGD method in leaky oil sands. Full article

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

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33 pages, 2240 KiB

Open AccessArticle

System Identification of a Heaving Point Absorber: Design of Experiment and Device Modeling

by Giorgio Bacelli, Ryan G. Coe, David Patterson and David Wilson

Energies 2017, 10(4), 472; https://doi.org/10.3390/en10040472 - 3 Apr 2017

Cited by 69 | Viewed by 11257

Empirically based modeling is an essential aspect of design for a wave energy converter. Empirically based models are used in structural, mechanical and control design processes, as well as for performance prediction. Both the design of experiments and methods used in system identification [...] Read more.

Empirically based modeling is an essential aspect of design for a wave energy converter. Empirically based models are used in structural, mechanical and control design processes, as well as for performance prediction. Both the design of experiments and methods used in system identification have a strong impact on the quality of the resulting model. This study considers the system identification and model validation process based on data collected from a wave tank test of a model-scale wave energy converter. Experimental design and data processing techniques based on general system identification procedures are discussed and compared with the practices often followed for wave tank testing. The general system identification processes are shown to have a number of advantages, including an increased signal-to-noise ratio, reduced experimental time and higher frequency resolution. The experimental wave tank data is used to produce multiple models using different formulations to represent the dynamics of the wave energy converter. These models are validated and their performance is compared against one another. While most models of wave energy converters use a formulation with surface elevation as an input, this study shows that a model using a hull pressure measurement to incorporate the wave excitation phenomenon has better accuracy. Full article

(This article belongs to the Special Issue Marine Energy)

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19 pages, 4392 KiB

Open AccessReview

Recent Progress and Novel Applications in Enzymatic Conversion of Carbon Dioxide

by Nguyen Van Duc Long, Jintae Lee, Kee-Kahb Koo, Patricia Luis and Moonyong Lee

Energies 2017, 10(4), 473; https://doi.org/10.3390/en10040473 - 3 Apr 2017

Cited by 61 | Viewed by 12647

Turning carbon dioxide (CO₂) into fuels and chemicals using chemical, photochemical, electrochemical, and enzymatic methods could be used to recycle large quantities of carbon. The enzymatic method, which is inspired by cellular CO₂ metabolism, has attracted considerable attention for efficient [...] Read more.

Turning carbon dioxide (CO₂) into fuels and chemicals using chemical, photochemical, electrochemical, and enzymatic methods could be used to recycle large quantities of carbon. The enzymatic method, which is inspired by cellular CO₂ metabolism, has attracted considerable attention for efficient CO₂ conversion due to improved selectivity and yields under mild reaction conditions. In this review, the research progress of green and potent enzymatic conversion of CO₂ into useful fuels and chemicals was discussed. Furthermore, applications of the enzymatic conversion of CO₂ to assist in CO₂ capture and sequestration were highlighted. A summary including the industrial applications, barriers, and some perspectives on the research and development of the enzymatic approach to convert CO₂ were introduced. Full article

(This article belongs to the Special Issue CO₂ Capture)

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13 pages, 4026 KiB

Open AccessArticle

A Novel High Controllable Voltage Gain Push-Pull Topology for Wireless Power Transfer System

by Qichang Duan, Yanling Li, Xin Dai and Tao Zou

Energies 2017, 10(4), 474; https://doi.org/10.3390/en10040474 - 1 Apr 2017

Cited by 8 | Viewed by 4124

Wireless Power Transfer (WPT) is commonly used to transmit power from a transmitting coil to various movable power devices. In the WPT system, due to a resonant tank inherent characteristic, the system cannot achieve a high output voltage gain. This paper proposes a [...] Read more.

Wireless Power Transfer (WPT) is commonly used to transmit power from a transmitting coil to various movable power devices. In the WPT system, due to a resonant tank inherent characteristic, the system cannot achieve a high output voltage gain. This paper proposes a novel current-fed push–pull circuit to realize high output voltage gain by adding a bi-directional switch between the resonant network and inverter. To obtain a high voltage gain, this paper proposes energy storage and energy injection mode to realize an energy boost function. A duty cycle control method for mode switching is also proposed. The proposed method allows the converter to operate with a variable voltage gain over a wide range with high efficiency. Experimental validation shows that the system gain of a proposed circuit can achieve a variable gain from 2 to 7 of which the converter can be two times higher than the classical system with the same condition. Full article

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

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16 pages, 3079 KiB

Open AccessArticle

Risk-Based Dynamic Security Assessment for Power System Operation and Operational Planning

by Emanuele Ciapessoni, Diego Cirio, Stefano Massucco, Andrea Morini, Andrea Pitto and Federico Silvestro

Energies 2017, 10(4), 475; https://doi.org/10.3390/en10040475 - 1 Apr 2017

Cited by 28 | Viewed by 5309

Assessment of dynamic stability in a modern power system (PS) is becoming a stringent requirement both in operational planning and in on-line operation, due to the increasingly complex dynamics of a PS. Further, growing uncertainties in forecast state and in the response to [...] Read more.

Assessment of dynamic stability in a modern power system (PS) is becoming a stringent requirement both in operational planning and in on-line operation, due to the increasingly complex dynamics of a PS. Further, growing uncertainties in forecast state and in the response to disturbances suggests the adoption of risk-based approaches in Dynamic Security Assessment (DSA). The present paper describes a probabilistic risk-based DSA, which provides instability risk indicators by combining an innovative probabilistic hazard/vulnerability analysis with the assessment of contingency impacts via time domain simulation. The tool implementing the method can be applied to both current and forecast PS states, the latter characterized in terms of renewable and load forecast uncertainties, providing valuable results for operation and operational planning contexts. Some results from a real PS model are discussed. Full article

(This article belongs to the Special Issue Advances in Power System Operations and Planning)

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13 pages, 1443 KiB

Open AccessArticle

A Novel Caving Model of Overburden Strata Movement Induced by Coal Mining

by Dongjing Xu, Suping Peng, Shiyao Xiang and Yunlan He

Energies 2017, 10(4), 476; https://doi.org/10.3390/en10040476 - 1 Apr 2017

Cited by 30 | Viewed by 4666

The broken pattern of the overburden strata induced by mining has a non-ignorable effect on overlying strata movement, failure, and safety in mining production. To study the caving pattern of overlying strata and determine the calculation method of fracture pathway parameters due to [...] Read more.

The broken pattern of the overburden strata induced by mining has a non-ignorable effect on overlying strata movement, failure, and safety in mining production. To study the caving pattern of overlying strata and determine the calculation method of fracture pathway parameters due to roof caving induced by coal mining, the trapezoidal broken models were developed to explain and prevent water leakage, and even water inrush, during the mining process. By incorporating the variation of the volume expansion coefficient, a connection among the parameters of the fracture pathways and fracture angles, face width, and mining height could be established, which shows that the larger the degree of the fracture angle is, the smaller the value of the volume expansion coefficient and face width is with a relatively larger mining height. This relationship was also used to determine the eventual evolution configuration of the trapezoidal broken model. The presented approaches may help us to better understand the movement of overburden strata and provide an idea to help settle conflicts related to fracture space calculations induced by coal mining. Full article

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14 pages, 2443 KiB

Open AccessArticle

Measurement of Line-to-Ground Capacitance in Distribution Network Considering Magnetizing Impedance’s Frequency Characteristic

by Qing Yang, Bo Zhang, Jiaquan Ran, Song Chen, Yanxiao He and Jian Sun

Energies 2017, 10(4), 477; https://doi.org/10.3390/en10040477 - 3 Apr 2017

Cited by 8 | Viewed by 5319

Signal injection method (SIM) is widely applied to the insulation parameters’ measurement in distribution network for its convenience and safety. It can be divided into two kinds of patterns: injecting a specific frequency signal or several frequencies’ groups, and scanning frequency in a [...] Read more.

Signal injection method (SIM) is widely applied to the insulation parameters’ measurement in distribution network for its convenience and safety. It can be divided into two kinds of patterns: injecting a specific frequency signal or several frequencies’ groups, and scanning frequency in a scheduled frequency scope. In order to avoid the disadvantages in related researches, improved signal injection method (ISIM), in which the frequency characteristic of the transformer magnetizing impedance is taken into consideration, is proposed. In addition, optimization for signal injection position has been accomplished, and the corresponding three calculation methods of line-to-ground capacitance has been derived. Calculations are carried out through the vector information (vector calculation method), the amplitude information (amplitude calculation method), the phase information (phase calculation method) of voltage and current in signal injecting port, respectively. The line-to-ground capacitance is represented by lumped parameter capacitances in high-voltage simulation test. Eight different sinusoidal signals are injected into zero-sequence circuit, and then line-to-ground capacitance is calculated with the above-mentioned vector calculation method based on the voltage and the current data of the injecting port. The results obtained by the vector calculation method show that ISIM has a wider application frequency range compared with signal injection method with rated parameters (RSIM) and SIM. The RSIM is calculated with the rated transformer parameters of magnetizing impedance, and the SIM based on the ideal transformer model, and the relative errors of calculation results of ISIM are smaller than that for other methods in general. The six groups of two-frequency set are chosen in a specific scope which is recommended by vector calculation results. Based on ISIM, the line-to-ground capacitance calculations through the amplitude calculation method and phase calculation method are compared, and then its application frequency range, which can work as a guidance for line-to-ground capacitance measurement, is concluded. Full article

(This article belongs to the Special Issue Electric Power Systems Research 2017)

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14 pages, 5970 KiB

Open AccessArticle

Numerical Simulations of a VAWT in the Wake of a Moving Car

by Wenlong Tian, Zhaoyong Mao and Yukai Li

Energies 2017, 10(4), 478; https://doi.org/10.3390/en10040478 - 3 Apr 2017

Cited by 18 | Viewed by 9374

Wind energy generated from the wake of moving cars has a large energy potential that has not yet been utilized. In this study, a vertical axis wind turbine (VAWT) was used to recover energy from the wakes of moving cars. The turbine was [...] Read more.

Wind energy generated from the wake of moving cars has a large energy potential that has not yet been utilized. In this study, a vertical axis wind turbine (VAWT) was used to recover energy from the wakes of moving cars. The turbine was designed to be planted by the side of the car lane and driven by the wake produced by the car. Transient computational fluid dynamics (CFD) simulations were performed to evaluate the performance of the VAWT. The influence of two main factors on the performance of the VAWT, the velocity of the car and the gap between the car and the rotor, were studied. The simulations confirmed the feasibility of this plan, and in the tested cases, the VAWT was able to generate a maximum energy output of 100.49 J from the wake of a car. The results also showed that the performance of the VAWT decreased with the velocity of the car, and the increased gap between the car and the VAWT. Full article

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

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10 pages, 2678 KiB

Open AccessArticle

Analysis of the Average Annual Consumption of Water in the Hospitals of Extremadura (Spain)

by Justo Garcia-Sanz-Calcedo, Fernando Lopez-Rodriguez, Talal Yusaf and Awf Al-Kassir

Energies 2017, 10(4), 479; https://doi.org/10.3390/en10040479 - 3 Apr 2017

Cited by 16 | Viewed by 6738

The aim of this paper is to quantity the annual average consumption of water in 13 public hospitals in Extremadura (Spain). An analytical study in order to reduce water demand was conducted from 2010 to 2014 in the above-mentioned hospitals. The study concluded [...] Read more.

The aim of this paper is to quantity the annual average consumption of water in 13 public hospitals in Extremadura (Spain). An analytical study in order to reduce water demand was conducted from 2010 to 2014 in the above-mentioned hospitals. The study concluded that, in order to determine the average annual water consumption, a fixed ratio is not the appropriate tool. A parametric type related to the built surface area and/or number of beds by hospital should be used instead. The average annual consumption of cold water for human consumption (CWHC) was 262.82 m3 (102.10) per bed and 1.65 m3 (0.46) per built surface area. The mean annual consumption of domestic hot water (DHW) was 92.96 m3 (35.72) per bed and 0.59 m3 (0.18) per built surface area. The ratio between DHW and CWHC was 35.62% (5.53). The time period of greatest demand was between 12 p.m. and 6 p.m. Considering B as the number of hospital beds and S its built surface area, to calculate the average annual cold water for human consumption in a hospital, the equation 165B + 12,100 (m3) or 1.568S + 2400 (m3) should be used. Similarly, in terms of hot domestic water, the average annual consumption in m3 corresponds to either 53.65B + 5170 (m3) or 0.53S + 1400 (m3). Full article

(This article belongs to the Special Issue Energy and Water, Current and Future Crisis)

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15 pages, 807 KiB

Open AccessArticle

Automatic J–A Model Parameter Tuning Algorithm for High Accuracy Inrush Current Simulation

by Xishan Wen, Jingzhuo Zhang and Hailiang Lu

Energies 2017, 10(4), 480; https://doi.org/10.3390/en10040480 - 4 Apr 2017

Cited by 5 | Viewed by 4495

Inrush current simulation plays an important role in many tasks of the power system, such as power transformer protection. However, the accuracy of the inrush current simulation can hardly be ensured. In this paper, a Jiles–Atherton (J–A) theory based model is proposed to [...] Read more.

Inrush current simulation plays an important role in many tasks of the power system, such as power transformer protection. However, the accuracy of the inrush current simulation can hardly be ensured. In this paper, a Jiles–Atherton (J–A) theory based model is proposed to simulate the inrush current of power transformers. The characteristics of the inrush current curve are analyzed and results show that the entire inrush current curve can be well featured by the crest value of the first two cycles. With comprehensive consideration of both of the features of the inrush current curve and the J–A parameters, an automatic J–A parameter estimation algorithm is proposed. The proposed algorithm can obtain more reasonable J–A parameters, which improve the accuracy of simulation. Experimental results have verified the efficiency of the proposed algorithm. Full article

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

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22 pages, 9016 KiB

Open AccessArticle

Co-Production Performance Evaluation of a Novel Solar Combi System for Simultaneous Pure Water and Hot Water Supply in Urban Households of UAE

by Nutakki Tirumala Uday Kumar and Andrew R. Martin

Energies 2017, 10(4), 481; https://doi.org/10.3390/en10040481 - 4 Apr 2017

Cited by 19 | Viewed by 6750

Water is the most desirable and sparse resource in Gulf cooperation council (GCC) region. Utilization of point-of-use (POU) water treatment devices has been gaining huge market recently due to increase in knowledge of urban population on health related issues over contaminants in decentralized [...] Read more.

Water is the most desirable and sparse resource in Gulf cooperation council (GCC) region. Utilization of point-of-use (POU) water treatment devices has been gaining huge market recently due to increase in knowledge of urban population on health related issues over contaminants in decentralized water distribution networks. However, there is no foolproof way of knowing whether the treated water is free of contaminants harmful for drinking and hence reliance on certified bottled water has increased worldwide. The bottling process right from treatment to delivery is highly unsustainable due to huge energy demand along the supply chain. As a step towards sustainability, we investigated various ways of coupling of membrane distillation (MD) process with solar domestic heaters for co-production of domestic heat and pure water. Performance dynamics of various integration techniques have been evaluated and appropriate configuration has been identified for real scale application. A solar combi MD (SCMD) system is experimentally tested for single household application for production 20 L/day of pure water and 250 L/day of hot water simultaneously without any auxiliary heating device. The efficiency of co-production system is compared with individual operation of solar heaters and solar membrane distillation. Full article

(This article belongs to the Special Issue Integration of Renewable Technologies in Water, Electricity, Heating and Cooling Networks)

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27 pages, 3493 KiB

Open AccessArticle

A Highly Relevant Method for Incorporation of Shunt Connected FACTS Device into Multi-Machine Power System to Dampen Electromechanical Oscillations

by Le Van Dai, Doan Duc Tung and Le Cao Quyen

Energies 2017, 10(4), 482; https://doi.org/10.3390/en10040482 - 4 Apr 2017

Cited by 10 | Viewed by 5794

A number of techniques have been proposed to dampen the power system oscillations in the electric power systems. Flexible alternating current transmission system (FACTS) devices are becoming one of them. Among the FACTS family, the static synchronous compensator (STATCOM), a shunt connected FACTS [...] Read more.

A number of techniques have been proposed to dampen the power system oscillations in the electric power systems. Flexible alternating current transmission system (FACTS) devices are becoming one of them. Among the FACTS family, the static synchronous compensator (STATCOM), a shunt connected FACTS device, has been widely used to provide smooth and rapid steady state, limit transient voltage, and improve the power system stability and performance by absorbing or injecting reactive power. However, the influence ability depends on its placement, control signal, and place of receiving-signal in the network. In order to satisfy these issues, this paper proposes a method for optimal setting and signal position of the STATCOM into the multi-machine power systems with the aim for damping the electromechanical oscillations. This method is developed from the energy approach based on Gramian matrices considering multiple tasks on the Lyapunov equation, in which the observability Gramian matrix is used to seek an optimal location for STATCOM placement. The another is the controllability one used to determine the best local input signal placement that is chosen as a feedback signal for the power oscillation damping (POD) of STATCOM. In addition, the Krylov-based model reduction method is introduced to shorten the calculation time. The proposed method has been verified on the IEEE 24-bus system by analyzing the small-signal stability to search several feasible placements, and then the transient stability is analyzed to compare and determine an optimal placement through testing various cases. The obtained result is also compared with other optimal method. Full article

(This article belongs to the Special Issue Electric Power Systems Research 2017)

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17 pages, 2807 KiB

Open AccessArticle

Optimal Charging Schedule Planning and Economic Analysis for Electric Bus Charging Stations

by Rong-Ceng Leou and Jeng-Jiun Hung

Energies 2017, 10(4), 483; https://doi.org/10.3390/en10040483 - 5 Apr 2017

Cited by 82 | Viewed by 7984

The battery capacity of electric buses (EB) used for public transportation is greater than that of electric cars, and the charging power is also several times greater than that used in electric cars; this can result in high energy consumption and negatively impact [...] Read more.

The battery capacity of electric buses (EB) used for public transportation is greater than that of electric cars, and the charging power is also several times greater than that used in electric cars; this can result in high energy consumption and negatively impact power distribution networks. This paper proposes a framework to determine the optimal contracted power capacity and charging schedule of an EB charging station in such a way that energy costs can be reduced. A mathematical model of controlled charging, which includes the capacity and energy charges of the station, was developed to minimize costs. The constraints of the model include the charging characteristics of an EB and the operational guidelines of the bus company. A practical EB charging station was used to verify the proposed model. The financial viability of this EB charging station is also studied in this paper. The economic analysis model for this charging station considers investment and operational costs, and the operational revenue. Sensitivity analyses with respect to some key parameters are also performed in this paper. Based on actual operational routes and EB charging schemes, test results indicate that the EB charging station investment is feasible, and the planning model proposed can be used to determine optimal station power capacity and minimize energy costs. Full article

(This article belongs to the Special Issue Advances in Electric Vehicles and Plug-in Hybrid Vehicles 2017)

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18 pages, 5143 KiB

Open AccessArticle

Analysis of Low Frequency Oscillation Using the Multi-Interval Parameter Estimation Method on a Rolling Blackout in the KEPCO System

by Kwan-Shik Shim, Seon-Ju Ahn, Sang-Yun Yun and Joon-Ho Choi

Energies 2017, 10(4), 484; https://doi.org/10.3390/en10040484 - 4 Apr 2017

Cited by 6 | Viewed by 3466

This paper describes a multiple time interval (“multi-interval”) parameter estimation method. The multi-interval parameter estimation method estimates a parameter from a new multi-interval prediction error polynomial that can simultaneously consider multiple time intervals. The root of the multi-interval prediction error polynomial includes the [...] Read more.

This paper describes a multiple time interval (“multi-interval”) parameter estimation method. The multi-interval parameter estimation method estimates a parameter from a new multi-interval prediction error polynomial that can simultaneously consider multiple time intervals. The root of the multi-interval prediction error polynomial includes the effect on each time interval, and the important mode can be estimated by solving one polynomial for multiple time intervals or signals. The algorithm of the multi-interval parameter estimation method proposed in this paper is applied to the test function and the data measured from a PMU (phasor measurement unit) installed in the KEPCO (Korea Electric Power Corporation) system. The results confirm that the proposed multi-interval parameter estimation method accurately and reliably estimates important parameters. Full article

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

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17 pages, 3677 KiB

Open AccessArticle

A Novel Optimal Control Method for Islanded Microgrids Based on Droop Control Using the ICA-GA Algorithm

by Hamed Moazami Goodarzi and Mohammad Hosein Kazemi

Energies 2017, 10(4), 485; https://doi.org/10.3390/en10040485 - 4 Apr 2017

Cited by 14 | Viewed by 4763

Microgrids are small scale power systems with local resources for generation; consumption and storage, that can operate connected to the main grid or islanded. For the islanding operation of microgrids, two important tasks are to share the load demand and maintain the voltage [...] Read more.

Microgrids are small scale power systems with local resources for generation; consumption and storage, that can operate connected to the main grid or islanded. For the islanding operation of microgrids, two important tasks are to share the load demand and maintain the voltage and frequency stabilities. In order to achieve this goal, a hierarchical control structure can be employed. This research presents a solution technique for finding the optimal site, production and droop coefficients of distributed generation (DG) units in microgrids. In this paper, three main factors are scrutinized through a multi-objective optimization approach. These factors include fuel consumption cost, stability and variations of voltage. To solve this optimization problem, an Imperialist Competitive Algorithm-Genetic Algorithm (ICA-GA) is presented. A fuzzy approach is used to search in non-dominated outcomes and to find the best answer. To show the effectiveness of the proposed method, it is implemented on 33-buses IEEE test systems. The simulation results exhibit the ability and efficiency of the proposed scheme to find the optimal solutions. Full article

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

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14 pages, 2241 KiB

Open AccessArticle

A Decoupled Design Parameter Analysis for Free-Piston Engine Generators

by Boru Jia, Zhengxing Zuo, Andrew Smallbone, Huihua Feng and Anthony Paul Roskilly

Energies 2017, 10(4), 486; https://doi.org/10.3390/en10040486 - 4 Apr 2017

Cited by 9 | Viewed by 4659

The free-piston engine generator (FPEG) is a novel power generation device with an estimated brake efficiency (energy contained in the fuel that is transformed into useful work) of up to 46%, compared to the 25–35% reported in conventional reciprocating engines. This paper seeks [...] Read more.

The free-piston engine generator (FPEG) is a novel power generation device with an estimated brake efficiency (energy contained in the fuel that is transformed into useful work) of up to 46%, compared to the 25–35% reported in conventional reciprocating engines. This paper seeks to address a major challenge in the development of new and complex technologies—how do we effectively communicate and understand the influence of key design parameters on its operating performance? In this paper, the FPEG is described using a simple numerical model, a model which is reduced to a forced mass-spring vibration system under external excitation, enabling all the major input parameters to be decoupled. It proved that the engine piston position as a function of time and output power could be predicted directly from the input parameters with acceptable accuracy. The influence of the key FPEG design parameters on the piston oscillation characteristics and electric power output can be characterised with respect to one another and summarised. Key design parameters include piston mass, compression stroke length, piston cross sectional area, and electric load. Compared with previous and more complex numerical models, the presented methods can be used to simply describe the sensitivity of key design parameters on the FPEG performance. It will provide useful general guidance for the FPEG hardware design process. Full article

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19 pages, 7825 KiB

Open AccessArticle

Operating Energy Savings of a Liquid Desiccant and Evaporative Cooling-Assisted Air-Handling System in Marine Applications

by Joon-Young Park and Jae-Weon Jeong

Energies 2017, 10(4), 487; https://doi.org/10.3390/en10040487 - 4 Apr 2017

Cited by 7 | Viewed by 4419

The aim of this study is to analyze the operating energy savings of a liquid desiccant and an indirect and direct evaporative cooling-assisted 100% outdoor air system (LD-IDECOAS) for marine applications. The LD-IDECOAS comprises a liquid desiccant (LD) unit and indirect and direct [...] Read more.

The aim of this study is to analyze the operating energy savings of a liquid desiccant and an indirect and direct evaporative cooling-assisted 100% outdoor air system (LD-IDECOAS) for marine applications. The LD-IDECOAS comprises a liquid desiccant (LD) unit and indirect and direct evaporative coolers (IEC and DEC) to meet the target supply air (SA) conditions. In this study, seawater was used as the cooling source and the waste heat reclaimed from the engine was used as the heating source in the proposed system. The operating energy of the LD-IDECOAS was determined based on detailed energy simulations conducted on two cabins with an area of 16.5 m², which was compared to a conventional system. The thermal loads on the cabins were estimated using design weather data under various oceanic climate conditions (normal, extremely hot, and extremely cold climates), by adhering to the ISO-7547 standard. The operating energy consumption of the LD-IDECOAS was calculated by modeling the proposed system with a commercial equation solver program (i.e., EES). The results were then compared to those of a conventional constant air volume (CAV) system. The operating energy consumption of the proposed system was reduced by 57–70% in cooling operations and 39% in heating operations under normal climate conditions. In the extremely hot climate regions, the energy consumed by the proposed system was reduced by 56–63% for cooling applications and 39% for heating applications. Full article

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16 pages, 3149 KiB

Open AccessEditor’s ChoiceArticle

Improvement of Transient Stability in a Hybrid Power Multi-System Using a Designed NIDC (Novel Intelligent Damping Controller)

by Ting-Chia Ou, Kai-Hung Lu and Chiou-Jye Huang

Energies 2017, 10(4), 488; https://doi.org/10.3390/en10040488 - 5 Apr 2017

Cited by 115 | Viewed by 8046

This paper endeavors to apply a novel intelligent damping controller (NIDC) for the static synchronous compensator (STATCOM) to reduce the power fluctuations, voltage support and damping in a hybrid power multi-system. In this paper, we discuss the integration of an offshore wind farm [...] Read more.

This paper endeavors to apply a novel intelligent damping controller (NIDC) for the static synchronous compensator (STATCOM) to reduce the power fluctuations, voltage support and damping in a hybrid power multi-system. In this paper, we discuss the integration of an offshore wind farm (OWF) and a seashore wave power farm (SWPF) via a high-voltage, alternating current (HVAC) electric power transmission line that connects the STATCOM and the 12-bus hybrid power multi-system. The hybrid multi-system consists of a battery energy storage system (BESS) and a micro-turbine generation (MTG). The proposed NIDC consists of a designed proportional–integral–derivative (PID) linear controller, an adaptive critic network and a proposed functional link-based novel recurrent fuzzy neural network (FLNRFNN). Test results show that the proposed controller can achieve better damping characteristics and effectively stabilize the network under unstable conditions. Full article

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20 pages, 3759 KiB

Open AccessArticle

Impact of Copper Loading on NH₃-Selective Catalytic Reduction, Oxidation Reactions and N₂O Formation over Cu/SAPO-34

by Kirsten Leistner, Florian Brüsewitz, Kurnia Wijayanti, Ashok Kumar, Krishna Kamasamudram and Louise Olsson

Energies 2017, 10(4), 489; https://doi.org/10.3390/en10040489 - 5 Apr 2017

Cited by 33 | Viewed by 6681

We developed a procedure for aqueous ion exchange to obtain different Cu loadings of Cu/SAPO-34 (between 0 and 2.6 wt %.) The catalysts were washcoated on monoliths and characterised with respect to their activity and selectivity under standard selective catalytic reduction (SCR), fast [...] Read more.

We developed a procedure for aqueous ion exchange to obtain different Cu loadings of Cu/SAPO-34 (between 0 and 2.6 wt %.) The catalysts were washcoated on monoliths and characterised with respect to their activity and selectivity under standard selective catalytic reduction (SCR), fast SCR, NH₃ oxidation and NO oxidation reactions. They were further characterised using X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), H₂-temperature programmed reduction (H₂-TPR), ultraviolet (UV)-vis spectroscopy and NH₃ adsorption. As expected, activity of all reactions increased with copper loading, due to increased number of active sites. However, the N₂O formation during standard and fast SCR yielded interesting mechanistic information. We observed that N₂O formation at low temperature increased with copper loading for the standard SCR reaction, while it decreased for fast SCR. The low-temperature N₂O formation during fast SCR thus occurs predominantly over Brønsted sites. Species responsible for N₂O formation during standard SCR, on the other hand, are formed on the copper sites. We further found that the fast SCR reaction occurs to a significant extent even over the H/SAPO-34 form. The Brønsted sites in SAPO-34 are thus active for the fast SCR reaction. Full article

(This article belongs to the Special Issue Automotive Engines Emissions and Control)

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27 pages, 3834 KiB

Open AccessArticle

Research and Application of Hybrid Forecasting Model Based on an Optimal Feature Selection System—A Case Study on Electrical Load Forecasting

by Yunxuan Dong, Jianzhou Wang, Chen Wang and Zhenhai Guo

Energies 2017, 10(4), 490; https://doi.org/10.3390/en10040490 - 5 Apr 2017

Cited by 12 | Viewed by 4770

The process of modernizing smart grid prominently increases the complexity and uncertainty in scheduling and operation of power systems, and, in order to develop a more reliable, flexible, efficient and resilient grid, electrical load forecasting is not only an important key but is [...] Read more.

The process of modernizing smart grid prominently increases the complexity and uncertainty in scheduling and operation of power systems, and, in order to develop a more reliable, flexible, efficient and resilient grid, electrical load forecasting is not only an important key but is still a difficult and challenging task as well. In this paper, a short-term electrical load forecasting model, with a unit for feature learning named Pyramid System and recurrent neural networks, has been developed and it can effectively promote the stability and security of the power grid. Nine types of methods for feature learning are compared in this work to select the best one for learning target, and two criteria have been employed to evaluate the accuracy of the prediction intervals. Furthermore, an electrical load forecasting method based on recurrent neural networks has been formed to achieve the relational diagram of historical data, and, to be specific, the proposed techniques are applied to electrical load forecasting using the data collected from New South Wales, Australia. The simulation results show that the proposed hybrid models can not only satisfactorily approximate the actual value but they are also able to be effective tools in the planning of smart grids. Full article

(This article belongs to the Special Issue Innovative Methods for Smart Grids Planning and Management)

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21 pages, 3468 KiB

Open AccessFeature PaperArticle

Experimental and Numerical Analyses of a Flat Plate Photovoltaic/Thermal Solar Collector

by Francesco Calise, Rafal Damian Figaj and Laura Vanoli

Energies 2017, 10(4), 491; https://doi.org/10.3390/en10040491 - 6 Apr 2017

Cited by 42 | Viewed by 6231

This paper presents a one-dimensional finite-volume model of an unglazed photovoltaic/thermal (PVT) solar collector. The unit consists of a conventional solar photovoltaic (PV) collector coupled with a suitable heat exchanger. In particular, the collector includes a roll bond heat exchanger and it is [...] Read more.

This paper presents a one-dimensional finite-volume model of an unglazed photovoltaic/thermal (PVT) solar collector. The unit consists of a conventional solar photovoltaic (PV) collector coupled with a suitable heat exchanger. In particular, the collector includes a roll bond heat exchanger and it is not equipped with back and frame insulation. The system is discretized along the flow direction (longitudinal) of the cogenerative collector. For each finite-volume element of the discretized computational domain, mass and energy balances are implemented. The collector geometry and materials parameters are taken from a commercially available device. An on-field experimental investigation is performed in order to validate the proposed model. The model is used to evaluate both electrical and thermodynamic parameters for each element of the domain and for fixed operating conditions. Finally, a sensitivity analysis is also performed in order to investigate the energetic performance of the cogenerative collector as a function of the main design/environmental parameters. Full article

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

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18 pages, 14364 KiB

Open AccessArticle

Heat Transfer and Flow of Nanofluids in a Y-Type Intersection Channel with Multiple Pulsations: A Numerical Study

by Wei-Tao Wu, Mehrdad Massoudi and Hongbin Yan

Energies 2017, 10(4), 492; https://doi.org/10.3390/en10040492 - 6 Apr 2017

Cited by 10 | Viewed by 4253

In this paper, we study pulsed flow and heat transfer in water-Al₂O₃ nanofluids in a Y-type intersection channel with two inlets and one outlet. At the two inlets, two sinusoidal velocities with a phase difference of π are applied. We [...] Read more.

In this paper, we study pulsed flow and heat transfer in water-Al₂O₃ nanofluids in a Y-type intersection channel with two inlets and one outlet. At the two inlets, two sinusoidal velocities with a phase difference of π are applied. We assume that the shear viscosity and the thermal conductivity of the nanofluids depend on the nanoparticles concentration. The motion of the nanoparticles is modeled by a convention-diffusion equation, where the effects of the Brownian motion, thermophoretic diffusion, etc., are included. The effects of pulse frequency, pulse amplitude and nanoparticles concentration on the heat transfer are explored numerically at various Reynolds numbers. The results show that the application of the pulsed flow improves the heat transfer efficiency (Nusselt number) for most of the cases studied. Amongst the four factors considered, the effect of the frequency seems to be the most important. Full article

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

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18 pages, 9902 KiB

Open AccessArticle

Analytical Calculation of the Magnetic Field Distribution in a Linear and Rotary Machine with an Orthogonally Arrayed Permanent Magnet

by Lei Xu, Mingyao Lin, Xinghe Fu, Kai Liu and Baocheng Guo

Energies 2017, 10(4), 493; https://doi.org/10.3390/en10040493 - 6 Apr 2017

Cited by 9 | Viewed by 4649

In this paper, an analytical model is proposed to analyze and predict the characteristics of a double stator linear and rotary permanent magnet machine (DSLRPMM). In order to simplify the magnetic field calculation, the DSLRPMM is cut along the axial direction (z [...] Read more.

In this paper, an analytical model is proposed to analyze and predict the characteristics of a double stator linear and rotary permanent magnet machine (DSLRPMM). In order to simplify the magnetic field calculation, the DSLRPMM is cut along the axial direction (z direction) and transferred into a planar one. Hence, an analytical model of the machine considered the orthogonal effect (OE) is proposed based on the combined solution of Maxwell’s equation, conformal mapping, and equivalent magnetic circuit model (EMCM). The magnetic field distributions of the DSLRPMM are calculated with and without considering the OE, and some important electromagnetic parameters, including the back electromotive force (EMF), detent force, cogging torque, and output torque and thrust, are also predicted and compared to the 3D finite element analysis (FEA). The results show that the errors between the proposed analytical model and the 3D FEA results are less than 0.2% and even less than 0.1% for certain parameters, that is, the results obtained from the proposed analytical model agree well with that of the FEA. Moreover, the analyzed and predicted results are also verified by the experimental results on the prototype of the DSLRPMM. Full article

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12 pages, 2300 KiB

Open AccessArticle

Low Temperature Aqueous Solution-Processed ZnO and Polyethylenimine Ethoxylated Cathode Buffer Bilayer for High Performance Flexible Inverted Organic Solar Cells

by Hailong You, Junchi Zhang, Zeyulin Zhang, Chunfu Zhang, Zhenhua Lin, Jingjing Chang, Genquan Han, Jincheng Zhang, Gang Lu and Yue Hao

Energies 2017, 10(4), 494; https://doi.org/10.3390/en10040494 - 6 Apr 2017

Cited by 15 | Viewed by 5935

High performance flexible inverted organic solar cells (OSCs) employing the low temperature cathode buffer bilayer combining the aqueous solution-processed ZnO and polyethylenimine ethoxylated (PEIE) are investigated based on Poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C₆₁-butryric acid methyl ester (P3HT:PC₆₁BM) and Poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexy)carbonyl]thieno[3,4-b]thiophenediyl}):[6,6]-phenyl-C₇₁-butyric acid methyl [...] Read more.

High performance flexible inverted organic solar cells (OSCs) employing the low temperature cathode buffer bilayer combining the aqueous solution-processed ZnO and polyethylenimine ethoxylated (PEIE) are investigated based on Poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C₆₁-butryric acid methyl ester (P3HT:PC₆₁BM) and Poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexy)carbonyl]thieno[3,4-b]thiophenediyl}):[6,6]-phenyl-C₇₁-butyric acid methyl ester (PTB-7:PC₇₁BM) material systems. It is found that, compared with pure ZnO or PEIE cathode buffer layer (CBL), the proper combination of low-temperature processed ZnO and PEIE as the CBL enhanced the short circuit current density (J_SC), resulting in better device performance. The increased J_SC results from the enhanced electron collection ability from the active layer to the cathode. By using the ZnO/PEIE CBL, a power conversion efficiency (PCE) as high as 4.04% for the P3HT:PC₆₁BM flexible device and a PCE as high as 8.12% for the PTB-7:PC₇₁BM flexible device are achieved, which are higher than the control devices with the pure ZnO CBL or pure PEIE CBL. The flexible inverted OSC also shows a superior mechanical property and it can keep 92.9% of its initial performance after 1000 bending cycles with a radius of 0.8 cm. These results suggest that the combination of the low temperature aqueous solution processed ZnO and PEIE can be a promising cathode buffer bilayer for flexible inverted OSCs. Full article

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25 pages, 11796 KiB

Open AccessFeature PaperArticle

Semiconductor Devices in Solid-State/Hybrid Circuit Breakers: Current Status and Future Trends

by Chunyang Gu, Pat Wheeler, Alberto Castellazzi, Alan J. Watson and Francis Effah

Energies 2017, 10(4), 495; https://doi.org/10.3390/en10040495 - 6 Apr 2017

Cited by 44 | Viewed by 14097

Circuit breakers (CBs) are the main protection devices for both alternating current (AC) and direct current (DC) power systems, ranging from tens of watts up to megawatts. This paper reviews the current status for solid-state circuit breakers (SSCBs) as well as hybrid circuit [...] Read more.

Circuit breakers (CBs) are the main protection devices for both alternating current (AC) and direct current (DC) power systems, ranging from tens of watts up to megawatts. This paper reviews the current status for solid-state circuit breakers (SSCBs) as well as hybrid circuit breakers (HCBs) with semiconductor power devices. A few novel SSCB and HCB concepts are described in this paper, including advantage and limitation discussions of wide-band-gap (WBG) devices in basic SSCB/HCB configuration by simulation and 360 V/150 A experimental verifications. Novel SSCB/HCB configurations combining ultra-fast switching and high efficiency at normal operation are proposed. Different types of power devices are installed in these circuit breakers to achieve adequate performance. Challenges and future trends of semiconductor power devices in SSCB/HCB with different voltage/power levels and special performance requirements are clarified. Full article

(This article belongs to the Special Issue Semiconductor Power Devices)

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15 pages, 8853 KiB

Open AccessArticle

Rapid Reserve Generation from a Francis Turbine for System Frequency Control

by Dean R. Giosio, Alan D. Henderson, Jessica M. Walker and Paul A. Brandner

Energies 2017, 10(4), 496; https://doi.org/10.3390/en10040496 - 7 Apr 2017

Cited by 10 | Viewed by 4693

The increase in contributions from non base load renewables, such as wind and solar, can have adverse effects on the stability of an electrical grid. In this study, the possibility of rapidly loading a Francis turbine from a tail water depression (TWD) mode [...] Read more.

The increase in contributions from non base load renewables, such as wind and solar, can have adverse effects on the stability of an electrical grid. In this study, the possibility of rapidly loading a Francis turbine from a tail water depression (TWD) mode for providing additional system frequency control is investigated. Based on the analysis of full-scale TWD test results and key findings from the transient testing of a micro-hydro scale turbine unit, a detailed description of the TWD transition process is given. The formulation of an improved turbine model for use in one-dimensional hydro-electric plant models is presented with simulation results compared to full-scale data. The analytical model, which calculates output power according to the conservation of angular momentum and identified sources of loss, is used in parallel with full-scale and model scale test observations to elucidate the events and mechanisms occurring during this proposed transition. The output response, in terms of active power, was found to be highly dependent on guide vane opening rate in both full-scale and model tests. For an approximate doubling in opening rate, the duration of the reverse power flow was reduced by 38% and 21%, for full-scale and model units, while the low pressure transient increased by 16% and 8%, respectively. The analytical model was shown to capture the general response characteristic in all cases tested; however, output power response was over predicted due to two identified model assumptions made, while, for the more rapid opening, the penstock pressure was under predicted by approximately 15%. Full article

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

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21 pages, 9794 KiB

Open AccessArticle

Experimental Studies of Turbulent Intensity around a Tidal Turbine Support Structure

by Stuart Walker and Lorenzo Cappietti

Energies 2017, 10(4), 497; https://doi.org/10.3390/en10040497 - 7 Apr 2017

Cited by 11 | Viewed by 8654

Tidal stream energy is a low-carbon energy source. Tidal stream turbines operate in a turbulent environment, and the effect of the structure between the turbine and seabed on this environment is not fully understood. An experimental study using 1:72 scale models based on [...] Read more.

Tidal stream energy is a low-carbon energy source. Tidal stream turbines operate in a turbulent environment, and the effect of the structure between the turbine and seabed on this environment is not fully understood. An experimental study using 1:72 scale models based on a commercial turbine design was carried out to study the support structure influence on turbulent intensity around the turbine blades. The study was conducted using the wave-current tank at the Laboratory of Maritime Engineering (LABIMA), University of Florence. A realistic flow environment (ambient turbulent intensity = 11%) was established. Turbulent intensity was measured upstream and downstream of a turbine mounted on two different support structures (one resembling a commercial design, the other the same with an additional vertical element), in order to quantify any variation in turbulence and performance between the support structures. Turbine drive power was used to calculate power generation. Acoustic Doppler velocimetry (ADV) was used to record and calculate upstream and downstream turbulent intensity. In otherwise identical conditions, performance variation of only 4% was observed between two support structures. Turbulent intensity at 1, 3 and 5 blade diameters, both upstream and downstream, showed variation up to 21% between the two cases. The additional turbulent structures generated by the additional element of the second support structure appears to cause this effect, and the upstream propagation of turbulent intensity is believed to be permitted by surface waves. This result is significant for the prediction of turbine array performance. Full article

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

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18 pages, 5548 KiB

Open AccessArticle

Combined Conformal Strongly-Coupled Magnetic Resonance for Efficient Wireless Power Transfer

by Matjaz Rozman, Michael Fernando, Bamidele Adebisi, Khaled M. Rabie, Rupak Kharel, Augustine Ikpehai and Haris Gacanin

Energies 2017, 10(4), 498; https://doi.org/10.3390/en10040498 - 7 Apr 2017

Cited by 19 | Viewed by 9371

This paper proposes a hybrid circuit between a conformal strongly-coupled magnetic resonance (CSCMR) and a strongly-coupled magnetic resonance (SCMR), for better wireless power transmission (WPT). This combination promises to enhance the flexibility of the proposed four-loop WPT system. The maximum efficiency at various [...] Read more.

This paper proposes a hybrid circuit between a conformal strongly-coupled magnetic resonance (CSCMR) and a strongly-coupled magnetic resonance (SCMR), for better wireless power transmission (WPT). This combination promises to enhance the flexibility of the proposed four-loop WPT system. The maximum efficiency at various distances is achieved by combining coupling-matching between the source and transmitting coils along with the coupling factor between the transmitting and receiving coils. Furthermore, the distance between transmitting and receiving coils is investigated along with the distance relationship between the source loop and transmission coil, in order to achieve the maximum efficiency of the proposed hybrid WPT system. The results indicate that the proposed approach can be effectively employed at distances comparatively smaller than the maximum distance without frequency matching. The achievable efficiency can be as high as 84% for the whole working range of the transmitter. In addition, the proposed hybrid system allows more spatial freedom compared to existing chargers. Full article

(This article belongs to the Special Issue Wireless Power Transfer 2016)

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19 pages, 1762 KiB

Open AccessFeature PaperArticle

Examining the Feasibilities of Industry 4.0 for the Hospitality Sector with the Lens of Management Practice

by Saqib Shamim, Shuang Cang, Hongnian Yu and Yun Li

Energies 2017, 10(4), 499; https://doi.org/10.3390/en10040499 - 7 Apr 2017

Cited by 113 | Viewed by 15648

Industry 4.0 and its impact in the manufacturing sector are well documented. However, the service sector is understudied, and it is also facing the challenges of mass customization, digital enhancement, smart work environment, and efficient supply chain. The aim of this study is [...] Read more.

Industry 4.0 and its impact in the manufacturing sector are well documented. However, the service sector is understudied, and it is also facing the challenges of mass customization, digital enhancement, smart work environment, and efficient supply chain. The aim of this study is to fill this research gap by exploring the issues of Industry 4.0 in the service sector, with cases in the hospitality industry. All the challenges of Industry 4.0 require continuous innovation and learning, which is dependent on people and the enterprise’s capabilities. Appropriate management approaches can play a vital role in the development of dynamic capabilities, and an effective learning and innovation environment. This paper proposes a framework of management practices which can promote the environment of innovation and learning in an organization, and hence facilitate business to match the pace of Industry 4.0 by facilitating technology acceptance e.g., digital enhancements and implementation of cyber physical systems (CPS). This study integrates the literature with logical beliefs to suggest the appropriate management practices for Industry 4.0. It represents one of the initial attempts to draw research attention towards the important role of management practices in Industry 4.0, as most of the recent studies have been restricted to the technological aspects. Semi-structured interviews of hospitality employees are conducted to explore the management practices suitable for meeting the challenges of Industry 4.0, specifically for informing the service sector. Full article

(This article belongs to the Special Issue Smart Design, Smart Manufacturing and Industry 4.0)

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14 pages, 8371 KiB

Open AccessArticle

Experimental Investigation on the Strength and Failure Behavior of Coal and Synthetic Materials under Plane-Strain Biaxial Compression

by Hongwei Zhang, Zhijun Wan, Dan Ma, Yuan Zhang, Jingyi Cheng and Qi Zhang

Energies 2017, 10(4), 500; https://doi.org/10.3390/en10040500 - 7 Apr 2017

Cited by 14 | Viewed by 4599

An evaluation of the failures of coal under variable conditions in relation to the stability of coal pillars is an important issue for coal mining. This paper presents the results of an experimental investigation of the mechanical behavior of brittle coal under plane-strain [...] Read more.

An evaluation of the failures of coal under variable conditions in relation to the stability of coal pillars is an important issue for coal mining. This paper presents the results of an experimental investigation of the mechanical behavior of brittle coal under plane-strain biaxial stress state (PSBSS) compression. The synthetic specimens were meant to test the ductile properties. Modified surface instability detection apparatus was setup to carry out the tests. The results show that the stress-strain curves of coal and synthetic specimens under the PSBSS can be divided into four typical stages, namely original microcrack closure, elastic deformation, sudden stress drop, and residual behavior. The stress-strain curve of coal under PSBSS compression showed periodic stress drops during the post-peak phase, while the curve of the synthetic specimen presented a moderate decrease during the post-peak stage. The remarkable residual strengths of the coal and composites can be observed using these curves, which is vital to the stability of specimens after the failure strength is exceeded. Strain rates have a significant effect on the strength of coal samples under PSBSS compression. Specifically, a higher strain rate indicates a greater peak strength. The failure modes for coal and synthetic specimens are different. During PSBSS compressive tests, coal showed a split failure under different strain rates. For flexible composites, the failure pattern is conjugate shear failure. The study indicated that the Modified Lade and Modified Wiebols-Cook criteria are competent for estimating the defined strength coefficient, which is a ratio proposed to estimate the PSBSS peak strength. Full article

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

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47 pages, 4067 KiB

Open AccessReview

Smart Distribution Networks: A Review of Modern Distribution Concepts from a Planning Perspective

by Syed Ali Abbas Kazmi, Muhammad Khuram Shahzad, Akif Zia Khan and Dong Ryeol Shin

Energies 2017, 10(4), 501; https://doi.org/10.3390/en10040501 - 7 Apr 2017

Cited by 84 | Viewed by 10991

Smart grids (SGs), as an emerging grid modernization concept, is spreading across diverse research areas for revolutionizing power systems. SGs realize new key concepts with intelligent technologies, maximizing achieved objectives and addressing critical issues that are limited in conventional grids. The SG modernization [...] Read more.

Smart grids (SGs), as an emerging grid modernization concept, is spreading across diverse research areas for revolutionizing power systems. SGs realize new key concepts with intelligent technologies, maximizing achieved objectives and addressing critical issues that are limited in conventional grids. The SG modernization is more noticeable at the distribution grid level. Thus, the transformation of the traditional distribution network (DN) into an intelligent one, is a vital dimension of SG research. Since future DNs are expected to be interconnected in nature and operation, hence traditional planning methods and tools may no longer be applicable. In this paper, the smart distribution network (SDN) concept under the SG paradigm, has presented and reviewed from the planning perspective. Also, developments in the SDN planning process have been surveyed on the basis of SG package (SGP). The package presents a SDN planning foundation via major SG-enabling technologies (SGTF), anticipated functionalities (SGAF), new consumption models (MDC) as potential SDN candidates, associated policies and pilot projects and multi-objective planning (MOP) as a real-world optimization problem. In addition, the need for an aggregated SDN planning model has also been highlighted. The paper discusses recent notable related works, implementation activities, various issues/challenges and potential future research directions; all aiming at SDN planning. Full article

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

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11 pages, 3750 KiB

Open AccessArticle

Dielectric Properties of Biomass/Biochar Mixtures at Microwave Frequencies

by Candice Ellison, Murat Sean McKeown, Samir Trabelsi and Dorin Boldor

Energies 2017, 10(4), 502; https://doi.org/10.3390/en10040502 - 9 Apr 2017

Cited by 60 | Viewed by 8322

Material dielectric properties are important for understanding their response to microwaves. Carbonaceous materials are considered good microwave absorbers and can be mixed with dry biomasses, which are otherwise low-loss materials, to improve the heating efficiency of biomass feedstocks. In this study, dielectric properties [...] Read more.

Material dielectric properties are important for understanding their response to microwaves. Carbonaceous materials are considered good microwave absorbers and can be mixed with dry biomasses, which are otherwise low-loss materials, to improve the heating efficiency of biomass feedstocks. In this study, dielectric properties of pulverized biomass and biochar mixtures are presented from 0.5 GHz to 20 GHz at room temperature. An open-ended coaxial-line dielectric probe and vector network analyzer were used to measure dielectric constant and dielectric loss factor. Results show a quadratic increase of dielectric constant and dielectric loss with increasing biochar content. In measurements on biochar, a strong dielectric relaxation is observed at 8 GHz as indicated by a peak in dielectric loss factor at that frequency. Biochar is found to be a good microwave absorber and mixtures of biomass and biochar can be utilized to increase microwave heating rates for high temperature microwave processing of biomass feedstocks. These data can be utilized for design, scale-up and simulation of microwave heating processes of biomass, biochar, and their mixtures. Full article

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

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16 pages, 3076 KiB

Open AccessArticle

Evaluation Method for Real-Time Dynamic Line Ratings Based on Line Current Variation Model for Representing Forecast Error of Intermittent Renewable Generation

by Hideharu Sugihara, Tsuyoshi Funaki and Nobuyuki Yamaguchi

Energies 2017, 10(4), 503; https://doi.org/10.3390/en10040503 - 8 Apr 2017

Cited by 25 | Viewed by 5006

Due the high penetration of intermittent renewable energy sources (IRESs), transmission line currents show large fluctuations and thus significant uncertainty. This makes it difficult to operate a power system without violating transmission capacity constraints. This paper evaluates the dynamic line ratings (DLRs) of [...] Read more.

Due the high penetration of intermittent renewable energy sources (IRESs), transmission line currents show large fluctuations and thus significant uncertainty. This makes it difficult to operate a power system without violating transmission capacity constraints. This paper evaluates the dynamic line ratings (DLRs) of overhead lines based on changes in the line current owing to the high penetration of intermittent renewable energy sources. In particular, by focusing on extremely large (but rare) forecasting errors in the intermittent renewable energy source output, which are generally inevitable in most forecasting methods, a model for representing the forecasting error in line with current variation due to intermittent renewable energy source output is developed. The model is based on a shape parameter that represents the equivalent current variation required for the same temperature increase as that due to the extremely large forecasting error. Finally, based on the annual minute-by-minute irradiance data, preventive control of the transmission network with dynamic line ratings is evaluated using worst-case parameter values. Full article

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

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20 pages, 5971 KiB

Open AccessFeature PaperArticle

Output Voltage Quality Evaluation of Stand-alone Four-Leg Inverters Using Linear and Non-Linear Controllers

by Ricardo Luís, José Fernando Silva and José Carlos Quadrado

Energies 2017, 10(4), 504; https://doi.org/10.3390/en10040504 - 9 Apr 2017

Cited by 7 | Viewed by 6019

This paper presents the design and experimental voltage quality evaluation of controllers for the output voltages of 3-phase four-leg voltage source inverters. These inverters are needed in stand-alone power systems to supply linear and non-linear, balanced or unbalanced loads with constant RMS value [...] Read more.

This paper presents the design and experimental voltage quality evaluation of controllers for the output voltages of 3-phase four-leg voltage source inverters. These inverters are needed in stand-alone power systems to supply linear and non-linear, balanced or unbalanced loads with constant RMS value voltages at fixed frequency. Comparisons include closed loop outer voltage controllers based on predictive, sliding mode and decoupled proportional-integral controllers in dqo synchronous space, fitted with an inner hysteretic current loop vector controller in

α β γ

space. The 3-phase four-leg VSI output voltages waveform quality is analysed under unbalanced and non-linear loads. Full article

(This article belongs to the Special Issue Power Electronics in Power Quality)

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20 pages, 11412 KiB

Open AccessArticle

Sensitivity of Risk-Based Maintenance Planning of Offshore Wind Turbine Farms

by Simon Ambühl and John Dalsgaard Sørensen

Energies 2017, 10(4), 505; https://doi.org/10.3390/en10040505 - 8 Apr 2017

Cited by 25 | Viewed by 6306

Inspection and maintenance expenses cover a considerable part of the cost of energy from offshore wind turbines. Risk-based maintenance planning approaches are a powerful tool to optimize maintenance and inspection actions and decrease the total maintenance expenses. Risk-based planning is based on many [...] Read more.

Inspection and maintenance expenses cover a considerable part of the cost of energy from offshore wind turbines. Risk-based maintenance planning approaches are a powerful tool to optimize maintenance and inspection actions and decrease the total maintenance expenses. Risk-based planning is based on many input parameters, which are in reality often not completely known. This paper will assess the cost impact of this incomplete knowledge based on a case study following risk-based maintenance planning. The sensitivity study focuses on weather forecast uncertainties, incomplete knowledge about the needed repair time on the site as well as uncertainties about the operational range of the boat and helicopter used to access the broken wind turbine. The cost saving potential is estimated by running Crude Monte Carlo simulations. Furthermore, corrective and preventive (scheduled and condition-based) maintenance strategies are implemented. The considered case study focuses on a wind farm consisting of ten 6 MW turbines placed 30 km off the Danish North Sea coast. The results show that the weather forecast is the uncertainty source dominating the maintenance expenses increase when considering risk-based decision-making uncertainties. The overall maintenance expenses increased by 70% to 140% when considering uncertainties directly related with risk-based maintenance planning. Full article

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

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14 pages, 4844 KiB

Open AccessArticle

Effect of Nanoparticles on Spontaneous Imbibition of Water into Ultraconfined Reservoir Capillary by Molecular Dynamics Simulation

by Xiao Wang, Senbo Xiao, Zhiliang Zhang and Jianying He

Energies 2017, 10(4), 506; https://doi.org/10.3390/en10040506 - 8 Apr 2017

Cited by 20 | Viewed by 7849

Imbibition is one of the key phenomena underlying processes such as oil recovery and others. In this paper, the influence of nanoparticles on spontaneous water imbibition into ultraconfined channels is investigated by molecular dynamics simulation. By combining the dynamic process of imbibition, the [...] Read more.

Imbibition is one of the key phenomena underlying processes such as oil recovery and others. In this paper, the influence of nanoparticles on spontaneous water imbibition into ultraconfined channels is investigated by molecular dynamics simulation. By combining the dynamic process of imbibition, the water contact angle in the capillary and the relationship of displacement (l) and time (t), a competitive mechanism of nanoparticle effects on spontaneous imbibition is proposed. The results indicate that the addition of nanoparticles decreases the displacement of fluids into the capillary dramatically, and the relationship between displacement and time can be described by l(t) ~ t^1/2. Based on the analysis of the dynamic contact angle and motion behavior of nanoparticles, for water containing hydrophobic nanoparticles, the displacement decreases with the decrease of hydrophobicity, and the properties of fluids, such as viscosity and surface tension, play a major role. While for hydrophilic nanoparticles, the displacement of fluids increases slightly with the increase of hydrophilicity in the water-wet capillary and simulation time, which can be ascribed to disjoining pressure induced by “sticking nanoparticles”. This study provides new insights into the complex interactions between nanoparticles and other components in nanofluids in the spontaneous imbibition, which is crucially important to enhanced oil recovery. Full article

(This article belongs to the Special Issue Nanotechnology for Oil and Gas Applications)

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13 pages, 2864 KiB

Open AccessArticle

Design and Research of the Movable Hybrid Photovoltaic-Thermal (PVT) System

by Lian Zhang and Zi Jian Chen

Energies 2017, 10(4), 507; https://doi.org/10.3390/en10040507 - 8 Apr 2017

Cited by 11 | Viewed by 5266

In recent years, with the development of photovoltaic system and photo-thermal system technology, hybrid photovoltaic-thermal (PVT) technology has been a breakthrough in many aspects. This paper describes the movable hybrid PVT system from the aspects of appearance structure, energy flow, and control circuit. [...] Read more.

In recent years, with the development of photovoltaic system and photo-thermal system technology, hybrid photovoltaic-thermal (PVT) technology has been a breakthrough in many aspects. This paper describes the movable hybrid PVT system from the aspects of appearance structure, energy flow, and control circuit. The system is equipped with rolling wheels and the simulated light sources also can be removed so that the system can be used in the outdoor conditions. The movable system is also suitable for the PVT system and its related applications without any external power supply. This system combines two technologies: photovoltaic power generation and photo-thermal utilization. The first part of the power supply is for the systems own output power supply, and the second part is for generating thermal energy. The two separate parts can be controlled and monitored respectively through the control circuits and the touch screens. The experimental results show that the system can generate 691 kWh electric energy and 3047.8 kWh thermal energy each year under normal working conditions. The efficiency of the proposed movable hybrid PVT system is calculated to be approximately 42.82% using the revised equations that are proposed in this paper. Therefore, the movable hybrid PVT system can meet the daily demands of hot water and electricity power in remote areas or islands and other non-grid areas. It also can be used to conduct experiment tests for the PVT system. Full article

(This article belongs to the Special Issue Solar Photovoltaics Trilemma: Efficiency, Stability and Cost Reduction 2017)

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20 pages, 8864 KiB

Open AccessArticle

Hysteresis Analysis and Control of a Metal-Polymer Hybrid Soft Actuator

by Manuel Schimmack, Eduardo E. Feistauer, Sergio T. Amancio-Filho and Paolo Mercorelli

Energies 2017, 10(4), 508; https://doi.org/10.3390/en10040508 - 8 Apr 2017

Cited by 9 | Viewed by 5108

The number of applications of stimulus-responsive polymers is growing at an impressive rate. The motivation of this contribution is to use a commercially available low-budget silver-coated polyamide (PA6) as a thermo-responsive metal-polymer hybrid soft actuator. Polyamide is a hygroscopic polymer; therefore, its mechanical [...] Read more.

The number of applications of stimulus-responsive polymers is growing at an impressive rate. The motivation of this contribution is to use a commercially available low-budget silver-coated polyamide (PA6) as a thermo-responsive metal-polymer hybrid soft actuator. Polyamide is a hygroscopic polymer; therefore, its mechanical and physical-chemical properties are affected by exposition to humidity or immersion in water. The effect of water absorption content on the PA6 and silver-coated PA6 monofilament properties, such as mass change and resistance, were evaluated. Moreover, the influence of swelling and shrinking effects on the surface morphology, caused by variations of moisture and water immersion, was investigated. Based on these variations, the dynamics of the resistance of the hybrid material were analyzed in the context of the proposed hysteresis model. An identification procedure of the hysteresis is presented along with an approximation of the upper and lower bound based on a constrained least square approach. A switching logic algorithm for this hybrid dynamic system is introduced, which makes it possible to structure the non-linear function in a switching mode. Finally, a non-linear integral sliding manifold is proposed and tested to control the resulting force of the actuator.hysteresis model. An identification procedure of the hysteresis is presented along with an approximation of the upper and lower bound based on a constrained least square approach. A switching logic algorithm for this hybrid dynamic system is introduced, which makes it possible to structure the non-linear function in a switching mode. Finally, a non-linear integral sliding manifold is proposed and tested to control the resulting force of the actuator. Full article

(This article belongs to the Special Issue Techniques of Control for Energy Optimization in Actuators, Motors and Power Generation Systems)

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15 pages, 2907 KiB

Open AccessArticle

Condition Assessment of Paper Insulation in Oil-Immersed Power Transformers Based on the Iterative Inversion of Resistivity

by Jiangjun Ruan, Shuo Jin, Zhiye Du, Yiming Xie, Lin Zhu, Yu Tian, Ruohan Gong, Guannan Li and Min Xiong

Energies 2017, 10(4), 509; https://doi.org/10.3390/en10040509 - 10 Apr 2017

Cited by 14 | Viewed by 5230

The resistivity of oil impregnated paper will decrease during its aging process. This paper takes paper resistivity as an assessment index to evaluate the insulation condition of oil impregnated paper in power transformer. The feasibility of this method are discussed in two aspects: [...] Read more.

The resistivity of oil impregnated paper will decrease during its aging process. This paper takes paper resistivity as an assessment index to evaluate the insulation condition of oil impregnated paper in power transformer. The feasibility of this method are discussed in two aspects: reliability and sensitivity. Iterative inversion of paper resistivity was combined with finite element simulation. Both the bisection method and Newton’s method were used as iterative methods. After the analysis and comparison, Newton’s method was selected as the first option of paper resistivity iteration for its faster convergence. In order to consider the spatial distribution characteristic of paper aging and enhance the calculation accuracy, the resistivity calculation is expanded to a multivariate iteration based on Newton’s method, in order to consider the spatial distribution characteristic of paper aging and improve the calculation accuracy. This paper presents an exploratory research on condition assessment of oil impregnated paper insulation, and provides some reference to the security and economy operation of power transformers. Full article

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15 pages, 3651 KiB

Open AccessArticle

Molecular Structure and Electronic Properties of Triolein Molecule under an External Electric Field Related to Streamer Initiation and Propagation

by Yachao Wang, Feipeng Wang, Jian Li, Zhengyong Huang, Suning Liang and Jinghan Zhou

Energies 2017, 10(4), 510; https://doi.org/10.3390/en10040510 - 10 Apr 2017

Cited by 29 | Viewed by 5257

Natural ester has been widely studied as an alternative dielectric liquid to mineral oil in recent years. Unsaturated triacylglycerol molecules are the main components of natural ester; therefore, in this paper, we investigate the molecular structure and electronic properties of the triolein molecule, [...] Read more.

Natural ester has been widely studied as an alternative dielectric liquid to mineral oil in recent years. Unsaturated triacylglycerol molecules are the main components of natural ester; therefore, in this paper, we investigate the molecular structure and electronic properties of the triolein molecule, an oleic-type triacylglycerol molecule, as a representative component of natural ester oils. The effects of external electric fields at the electric field intensity related to streamer initiation and propagation on the bond lengths, dipole moment, total energy, infrared spectra, and orbital energy of the triolein molecule are investigated using density functional theory (DFT). In addition, the excitation energies, transition wavelengths, and oscillator strengths of the first eight excited states of the triolein molecule under external electric fields are calculated by time-dependent DFT. The results show that the bond lengths, dipole moments, total energy, and infrared spectra change obviously under external electric fields. With increasing external electric field intensity, the energy of the highest occupied molecular orbital increases, and the gap between that and the energy of the lowest unoccupied molecular orbital decreases, which make the molecule susceptible to excitation. The calculations contribute to an understanding of the causes behind the degradation of the insulation properties of natural ester oils. Full article

(This article belongs to the Special Issue Selected Papers from 2016 IEEE International Conference on High Voltage Engineering (ICHVE 2016))

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17 pages, 5834 KiB

Open AccessArticle

Comparative Study of Breakdown Voltage of Mineral, Synthetic and Natural Oils and Based Mineral Oil Mixtures under AC and DC Voltages

by Abderrahmane Beroual, Usama Khaled, Phanuel Seraphine Mbolo Noah and Henry Sitorus

Energies 2017, 10(4), 511; https://doi.org/10.3390/en10040511 - 10 Apr 2017

Cited by 81 | Viewed by 9825

This paper deals with a comparative study of AC and DC breakdown voltages of based mineral oil mixtures with natural and synthetic esters mainly used in high voltage power transformers. The goal was to analyze the performances of oil mixtures from the dielectric [...] Read more.

This paper deals with a comparative study of AC and DC breakdown voltages of based mineral oil mixtures with natural and synthetic esters mainly used in high voltage power transformers. The goal was to analyze the performances of oil mixtures from the dielectric withstand point of view and to predict the behavior of transformers originally filled with mineral oil and re-filled with synthetic or natural ester oils when emptied for maintenance. The study concerns mixtures based on 20%, 50%, and 80% of natural and synthetic ester oils. AC breakdown voltages were measured using a sphere-sphere electrode system according to IEC 60156 specifications; the same specification was adopted for DC measurements since there is no standard specifications for this voltage waveform. A statistical analysis of the mean values, standard deviations, and histograms of breakdown voltage data was carried out. The Normal and Weibull distribution functions were used to analyze the experimental data and the best function that the data followed was used to estimate the breakdown voltage with risk of 1%, 10%, and 50% probability. It was shown that whatever the applied voltage waveforms, ester oils always have a significantly higher breakdown voltage than mineral oil. The addition of only 20% of natural or synthetic ester oil was sufficient to considerably increase the breakdown voltage of mineral oil. The dielectric strength of such a mixture is much higher than that of mineral oil alone and can reach that of ester oils. From the point of view of dielectric strength, the mixtures constitute an option for improving the performance of mineral oil. Thus, re-filling of transformers containing up to 20% mineral oil residues with ester oils, does not present any problem; it is even advantageous when considering only the breakdown voltage. Under AC, the mixtures with natural ester always follow the behavior of vegetable oil alone. With the exception of the 20% mixture of natural ester in DC, the breakdown voltage values of all the tested mixtures were in accordance with the normal distribution, which made it possible to define the breakdown voltages for the risk levels of 1%, 10%, and 50% of probability. Full article

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

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18 pages, 3262 KiB

Open AccessArticle

An Online SOC and SOH Estimation Model for Lithium-Ion Batteries

by Shyh-Chin Huang, Kuo-Hsin Tseng, Jin-Wei Liang, Chung-Liang Chang and Michael G. Pecht

Energies 2017, 10(4), 512; https://doi.org/10.3390/en10040512 - 10 Apr 2017

Cited by 153 | Viewed by 26582

The monitoring and prognosis of cell degradation in lithium-ion (Li-ion) batteries are essential for assuring the reliability and safety of electric and hybrid vehicles. This paper aims to develop a reliable and accurate model for online, simultaneous state-of-charge (SOC) and state-of-health (SOH) estimations [...] Read more.

The monitoring and prognosis of cell degradation in lithium-ion (Li-ion) batteries are essential for assuring the reliability and safety of electric and hybrid vehicles. This paper aims to develop a reliable and accurate model for online, simultaneous state-of-charge (SOC) and state-of-health (SOH) estimations of Li-ion batteries. Through the analysis of battery cycle-life test data, the instantaneous discharging voltage (V) and its unit time voltage drop, V′, are proposed as the model parameters for the SOC equation. The SOH equation is found to have a linear relationship with 1/V′ times the modification factor, which is a function of SOC. Four batteries are tested in the laboratory, and the data are regressed for the model coefficients. The results show that the model built upon the data from one single cell is able to estimate the SOC and SOH of the three other cells within a 5% error bound. The derived model is also proven to be robust. A random sampling test to simulate the online real-time SOC and SOH estimation proves that this model is accurate and can be potentially used in an electric vehicle battery management system (BMS). Full article

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13 pages, 2676 KiB

Open AccessArticle

Pyrolysis of Polyolefins Using Rotating Arc Plasma Technology for Production of Acetylene

by Ming Zhang, Jie Ma, Baogen Su, Guangdong Wen, Qiwei Yang and Qilong Ren

Energies 2017, 10(4), 513; https://doi.org/10.3390/en10040513 - 10 Apr 2017

Cited by 14 | Viewed by 5320

Polyolefin, as one of the most widely used macromolecule materials, has been one of the most serious threats to the environment. Current treatment methods of waste polyolefin including landfill, incineration, and thermal degradation have suffered from severe problems such as secondary pollution and [...] Read more.

Polyolefin, as one of the most widely used macromolecule materials, has been one of the most serious threats to the environment. Current treatment methods of waste polyolefin including landfill, incineration, and thermal degradation have suffered from severe problems such as secondary pollution and the generation of other toxic substances. In this article, we report for the first time a high-efficiency method to produce high-value C₂H₂ from polyolefins using a rotating direct current arc plasma reactor, using polyethylene and polypropylene as feedstocks. The essence of this method is that a reductive atmosphere of pyrolysis enables a thermodynamic preference to C₂H₂ over other carbon-containing gas and the rotating direct current arc plasma reactor allows for a uniform distribution of high temperature to ensure high conversion of polymers. Thermodynamic simulation of product composition was performed, and the effect of plasma input power, polyolefin feed rate, and working gas flow rate on the pyrolysis results was experimentally investigated. It was found that, with proper parameter control, approximately complete conversion of carbon in polyolefin could be obtained, with a C₂H₂ selectivity higher than 80% and a C₂H₂ yield higher than 70%. These results not only create new opportunities for the reuse of polymer waste, but are also instructive for the green production of C₂H₂. Full article

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

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17 pages, 2085 KiB

Open AccessArticle

Generalized Energy Flow Analysis Considering Electricity Gas and Heat Subsystems in Local-Area Energy Systems Integration

by Jiaqi Shi, Ling Wang, Yingrui Wang and Jianhua Zhang

Energies 2017, 10(4), 514; https://doi.org/10.3390/en10040514 - 10 Apr 2017

Cited by 30 | Viewed by 7444

To alleviate environmental pollution and improve the efficient use of energy, energy systems integration (ESI)—covering electric power systems, heat systems and natural gas systems—has become an important trend in energy utilization. The traditional power flow calculation method, with the object as the power [...] Read more.

To alleviate environmental pollution and improve the efficient use of energy, energy systems integration (ESI)—covering electric power systems, heat systems and natural gas systems—has become an important trend in energy utilization. The traditional power flow calculation method, with the object as the power system, will prove difficult in meeting the requirements of the coupled energy flow analysis. This paper proposes a generalized energy flow (GEF) analysis method which is suitable for an ESI containing electricity, heat and gas subsystems. First, the models of electricity, heat, and natural gas networks in the ESI are established. In view of the complexity of the conventional method to solve the gas network including the compressor, an improved practical equivalent method was adopted based on different control modes. On this basis, a hybrid method combining homotopy and the Newton-Raphson algorithm was executed to compute the nonlinear equations of GEF, and the Jacobi matrix reflecting the coupling relationship of multi-energy was derived considering the grid connected mode and island modes of the power system in the ESI. Finally, the validity of the proposed method in multi-energy flow calculation and the analysis of interacting characteristics was verified using practical cases. Full article

(This article belongs to the Special Issue Energy Production Systems)

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14 pages, 3617 KiB

Open AccessArticle

Predictive Control of Power Electronics Converters in Renewable Energy Systems

by Jiefeng Hu and Ka Wai Eric Cheng

Energies 2017, 10(4), 515; https://doi.org/10.3390/en10040515 - 10 Apr 2017

Cited by 27 | Viewed by 5184

Predictive control has attracted much attention and has been widely used in power electronics and electric drives. However, further developments for applications in the field of renewable energy systems are still under investigation. In this paper, the principles of predictive control are studied [...] Read more.

Predictive control has attracted much attention and has been widely used in power electronics and electric drives. However, further developments for applications in the field of renewable energy systems are still under investigation. In this paper, the principles of predictive control are studied with a focus on model predictive control (MPC) and vector-sequence-based predictive control (VPC). Based on these techniques, two control strategies for flexible power supply are developed. They are implemented in the most promising renewable energy systems, namely solar photovoltaic (PV) systems and wind generators, respectively. The experimental results based on a laboratory prototype show that the active and reactive powers supplied by the PV and wind generator can be controlled flexibly with excellent steady-state and transient performance. As the penetration level of the renewable energy sources in electricity network continues to rise, predictive control tends to be an attractive and powerful technique for power electronics converters in renewable energy systems. Full article

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

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16 pages, 4100 KiB

Open AccessFeature PaperArticle

CO₂ Foam Stability Improvement Using Polyelectrolyte Complex Nanoparticles Prepared in Produced Water

by Negar Nazari, Jyun-Syung Tsau and Reza Barati

Energies 2017, 10(4), 516; https://doi.org/10.3390/en10040516 - 11 Apr 2017

Cited by 34 | Viewed by 5543

Despite the increasing interest in CO₂ foam flooding for enhanced oil recovery applications, it is challenging to have a successful field operation as the performance of the surfactant is often affected by the presence of crude oil and salinity of the water. [...] Read more.

Despite the increasing interest in CO₂ foam flooding for enhanced oil recovery applications, it is challenging to have a successful field operation as the performance of the surfactant is often affected by the presence of crude oil and salinity of the water. It is also challenging to dispose of huge amounts of water associated with the field operation. Due to the incompatibility of the produced water with chemicals used in the foam system, the produced water cannot be used as an injecting fluid. The objective of this project is to design a chemical system compatible with produced water which may fully utilize the oil field produced water as an injecting fluid and make the foam injection economically viable and environmentally friendly. In this study, we investigate the performance of a foam system with a surfactant and the addition of polyelectrolyte and polyelectrolyte complex nanoparticles (PECNP) in various salinities of produced water. A recipe is developed to prepare a nanoparticle solution that is sustainable in high salinity produced water. The rheological property of the foam, the stability, and durability of the foam with and without the presence of crude oil are measured and compared as the water salinity is changed. It is found that foam stability and durability deteriorated when water salinity increased. However, by the addition of polyelectrolyte and PECNP in the system, the foam stability and durability was improved even in high salinity water with or without the presence of crude oil. Full article

(This article belongs to the Special Issue Nanotechnology for Oil and Gas Applications)

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22 pages, 13184 KiB

Open AccessArticle

High Robustness Control for Robotic Wireless Power Transfer Systems with Multiple Uncertain Parameters Using a Virtual Buck Converter

by Yanling Li, Qichang Duan and Yang Zou

Energies 2017, 10(4), 517; https://doi.org/10.3390/en10040517 - 11 Apr 2017

Cited by 7 | Viewed by 4578

Aiming at achieving high robustness performance in Wireless Power Transfer (WPT) systems for moving robot power supply, this paper proposes a H_∞ robust control method with multiple parameters that vary randomly, including the mutual inductance, load parameter, and operating frequency. These uncertain [...] Read more.

Aiming at achieving high robustness performance in Wireless Power Transfer (WPT) systems for moving robot power supply, this paper proposes a H_∞ robust control method with multiple parameters that vary randomly, including the mutual inductance, load parameter, and operating frequency. These uncertain parameters make the system control extremely difficult. A composite Upper Linear Fractional Transformation (LFT) method is proposed to deal with the system uncertainty, particularly for the mutual inductance detachment, which is very unique and important for WPT systems. A suboptimal H_∞ controller design method is proposed based on Generalized State Space Averaging (GSSA) model in order to simplify the system structure. In controller implementation, a virtual buck converter for phase shifted regulation is proposed to replace real input buck converter. The proposed H_∞ control method is easy to implement because only the output voltage of the WPT system needs to be sampled, and based on which a simple DSP control algorithm is developed. Simulation and experimental results have demonstrated that the proposed control method can achieve less than 15 ms response speed with 70% mutual inductance variation and 50% load variation tolerance respectively. Full article

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

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13 pages, 3257 KiB

Open AccessArticle

How Smart LEDs Lighting Benefit Color Temperature and Luminosity Transformation

by Yu-Sheng Huang, Wei-Cheng Luo, Hsiang-Chen Wang, Shih-Wei Feng, Chie-Tong Kuo and Chia-Mei Lu

Energies 2017, 10(4), 518; https://doi.org/10.3390/en10040518 - 11 Apr 2017

Cited by 21 | Viewed by 6198

Luminosity and correlated color temperature (CCT) have gradually become two of the most important factors in the evaluation of the performance of light sources. However, although most color performance evaluation metrics are highly correlated with CCT, these metrics often do not account for [...] Read more.

Luminosity and correlated color temperature (CCT) have gradually become two of the most important factors in the evaluation of the performance of light sources. However, although most color performance evaluation metrics are highly correlated with CCT, these metrics often do not account for light sources with different CCTs. This paper proposes the existence of a relationship between luminosity and CCT to remove the effects of CCT and to allow for a fairer judgment of light sources under the current color performance evaluation metrics. This paper utilizes the Hyper-Spectral Imaging (HSI) technique to recreate images of a standard color checker under different luminosities, CCT, and light sources. The images are then analyzed and transformed into interpolation figures and equal color difference curves. This paper utilizes statistic tools and symmetry properties to determine an exponential relationship between luminosity and CCT in red-green-blue (RGB) LED and OLED light sources. Such a relationship presents an option to remove the effects of CCT in color evaluation standards, as well as provide a guide line for adjusting visual experience solely by adjusting luminosity when creating a lighting system. Full article

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

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18 pages, 18400 KiB

Open AccessArticle

Research on a Multiple-Receiver Inductively Coupled Power Transfer System for Mooring Buoy Applications

by Jiayi Xu, Xingfei Li, Ziming Xie, Huilin Zhang, Tengfei Wu and Cheng Fang

Energies 2017, 10(4), 519; https://doi.org/10.3390/en10040519 - 12 Apr 2017

Cited by 11 | Viewed by 5777

Inductively coupled power transfer (ICPT) systems, which are superior to batteries due to their real-time power supplycapacity have been used in mooring buoys for the purpose of long-term measurements. A multiple-receiver ICPT system for mooring buoys, which contains a mooring cable for transmitting [...] Read more.

Inductively coupled power transfer (ICPT) systems, which are superior to batteries due to their real-time power supplycapacity have been used in mooring buoys for the purpose of long-term measurements. A multiple-receiver ICPT system for mooring buoys, which contains a mooring cable for transmitting power, is proposed in this paper to obtain the corresponding profile parameters. Series compensation is applied to all three sections, including the transmitter, the mooring cable and multiple receivers. The voltage of an underwater system with arbitrary load can be stabilized. On that basis, high efficiency can be obtained. By adopting Wolfram Mathematica a detailed analysis of both double-receiver and multiple-receiver ICPT systems for mooring buoys is presented. Finally, a prototype ICPT system with three receivers mounted on a 30 m mooring cable was built to verify the theoretical analysis. Experimental results show that the power transfer efficiency exceeds 45%. Both theoretical analysis and experiments indicate that this system is appropriate for measuring ocean profile parameters. Full article

(This article belongs to the Special Issue Advanced Power Electronics and Control for Wireless Power Transfer Systems)

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19 pages, 1684 KiB

Open AccessArticle

Supercapacitor State Based Control and Optimization for Multiple Energy Storage Devices Considering Current Balance in Urban Rail Transit

by Zhongping Yang, Zhihong Yang, Huan Xia, Fei Lin and Feiqin Zhu

Energies 2017, 10(4), 520; https://doi.org/10.3390/en10040520 - 12 Apr 2017

Cited by 19 | Viewed by 6243

The use of supercapacitors (SCs) to store regenerative braking energy from urban rail trains is able to achieve a good energy saving effect. This paper analyzes the current balance method of stationary energy storage devices (ESDs). At the beginning of the paper, the [...] Read more.

The use of supercapacitors (SCs) to store regenerative braking energy from urban rail trains is able to achieve a good energy saving effect. This paper analyzes the current balance method of stationary energy storage devices (ESDs). At the beginning of the paper, the mathematical model of the DC traction power system, which includes trains, ESDs and traction substations, is established. Next, based on this, the SC state-based control strategy (SCSCS) is proposed, which can adjust the charging voltage of the ESD according to the SC voltage and current, then the charging current of the ESD can be reasonably distributed under the voltage difference of ESDs, and the SC voltage and current stress can be reduced. In order to determine the optimal controlling parameters, the optimization model is proposed and solved by the genetic algorithm. The analysis of the case study also shows the effectiveness of the proposed control strategy and optimization algorithm. Finally, the rationality of the proposed strategy is verified by experiments. Full article

(This article belongs to the Special Issue Advanced Electric Devices and Technologies for Electric-Drive Robotics)

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19 pages, 11762 KiB

Open AccessArticle

EMTP Model of a Bidirectional Cascaded Multilevel Solid State Transformer for Distribution System Studies

by Jacinto Martin-Arnedo, Francisco González-Molina, Juan A. Martinez-Velasco and Mohammad Ebrahim Adabi

Energies 2017, 10(4), 521; https://doi.org/10.3390/en10040521 - 12 Apr 2017

Cited by 9 | Viewed by 6724

Abstract: This paper presents a time-domain model of a MV/LV bidirectional solid state transformer (SST). A multilevel converter configuration of the SST MV side is obtained by cascading a single-phase cell made of the series connection of an H bridge and a [...] Read more.

Abstract: This paper presents a time-domain model of a MV/LV bidirectional solid state transformer (SST). A multilevel converter configuration of the SST MV side is obtained by cascading a single-phase cell made of the series connection of an H bridge and a dual active bridge (dc-dc converter); the aim is to configure a realistic SST design suitable for MV levels. A three-phase four-wire converter has been used for the LV side, allowing the connection of both load/generation. The SST model, including the corresponding controllers, has been built and encapsulated as a custom-made model in the ATP version of the EMTP for application in distribution system studies. Several case studies have been carried out in order to evaluate the behavior of the proposed SST design under different operating conditions and check its impact on power quality. Full article

(This article belongs to the Special Issue Electric Power Systems Research 2017)

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23 pages, 16385 KiB

Open AccessArticle

Research on Stochastic Optimal Operation Strategy of Active Distribution Network Considering Intermittent Energy

by Fei Chen, Dong Liu and Xiaofang Xiong

Energies 2017, 10(4), 522; https://doi.org/10.3390/en10040522 - 12 Apr 2017

Cited by 22 | Viewed by 3839

Active distribution networks characterized by high flexibility and controllability are an important development mode of future smart grids to be interconnected with large scale distributed generation sources including intermittent energies. However, the uncertainty of intermittent energy and the diversity of controllable devices make [...] Read more.

Active distribution networks characterized by high flexibility and controllability are an important development mode of future smart grids to be interconnected with large scale distributed generation sources including intermittent energies. However, the uncertainty of intermittent energy and the diversity of controllable devices make the optimal operation of distribution network a challenging issue. In this paper, we propose a stochastic optimal operation strategy for distribution networks with the objective function considering the operation state of the distribution network. Both distributed generations and flexible loads are taken into consideration in our strategy. The uncertainty of the intermittent energy is considered in this paper to obtain an optimized operation and an efficient utilization of intermittent energy under the worst scenario. Then, Benders decomposition is used in this paper to solve the two-stage max-min problem for stochastic optimal operation. Finally, we test the effectiveness of our strategy under different scenarios of the demonstration project of active distribution network located in Guizhou, China. Full article

(This article belongs to the Special Issue Electric Power Systems Research 2017)

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22 pages, 3299 KiB

Open AccessArticle

Modelling and Optimization in Microgrids

by Tobias Porsinger, Przemyslaw Janik, Zbigniew Leonowicz and Radomir Gono

Energies 2017, 10(4), 523; https://doi.org/10.3390/en10040523 - 12 Apr 2017

Cited by 34 | Viewed by 5761

The expansion of renewable energies is progressing strongly. The influence on the power supply networks by the variability of the infeed must be met with new concepts. In this paper, we investigate the possibilities of integrating microgrids as a cooperating unit in the [...] Read more.

The expansion of renewable energies is progressing strongly. The influence on the power supply networks by the variability of the infeed must be met with new concepts. In this paper, we investigate the possibilities of integrating microgrids as a cooperating unit in the power supply network to support further expansion of renewable energy sources (RES) power plants. In this paper, a differentiation of microgrids from similar network structures is established, and a classification of proposed groups is made. Then, after the description of the simulation of the components in a microgrid, with practical advice, an example model is shown, which aids the dimensioning of the components within a microgrid to achieve a specified goal. Full article

(This article belongs to the Special Issue Selected Papers from 16 IEEE International Conference on Environment and Electrical Engineering (EEEIC 2016))

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15 pages, 2331 KiB

Open AccessArticle

A Method to Facilitate Uncertainty Analysis in LCAs of Buildings

by Francesco Pomponi, Bernardino D’Amico and Alice M. Moncaster

Energies 2017, 10(4), 524; https://doi.org/10.3390/en10040524 - 13 Apr 2017

Cited by 65 | Viewed by 6105

Life cycle assessment (LCA) is increasingly becoming a common technique to assess the embodied energy and carbon of buildings and their components over their life cycle. However, the vast majority of existing LCAs result in very definite, deterministic values which carry a false [...] Read more.

Life cycle assessment (LCA) is increasingly becoming a common technique to assess the embodied energy and carbon of buildings and their components over their life cycle. However, the vast majority of existing LCAs result in very definite, deterministic values which carry a false sense of certainty and can mislead decisions and judgments. This article tackles the lack of uncertainty analysis in LCAs of buildings by addressing the main causes for not undertaking this important activity. The research uses primary data for embodied energy collected from European manufacturers as a starting point. Such robust datasets are used as inputs for the stochastic modelling of uncertainty through Monte Carlo algorithms. Several groups of random samplings between 10¹ and 10⁷ are tested under two scenarios: data are normally distributed (empirically verified) and data are uniformly distributed. Results show that the hypothesis on the data no longer influences the results after a high enough number of random samplings (10⁴). This finding holds true both in terms of mean values and standard deviations and is also independent of the size of the life cycle inventory (LCI): it occurs in both large and small datasets. Findings from this research facilitate uncertainty analysis in LCA. By reducing significantly the amount of data necessary to infer information about uncertainty, a more widespread inclusion of uncertainty analysis in LCA can be encouraged in assessments from practitioners and academics alike. Full article

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16 pages, 4943 KiB

Open AccessArticle

A Bi-Level Coordinated Optimization Strategy for Smart Appliances Considering Online Demand Response Potential

by Jia Ning, Yi Tang, Qian Chen, Jianming Wang, Jianhua Zhou and Bingtuan Gao

Energies 2017, 10(4), 525; https://doi.org/10.3390/en10040525 - 13 Apr 2017

Cited by 20 | Viewed by 3861

Demand response (DR) is counted as an effective method when there is a large-capacity power shortage in the power system, which may lead to peak loads or a rapid ramp. This paper proposes a bi-level coordinated optimization strategy by quantitating the DR potential [...] Read more.

Demand response (DR) is counted as an effective method when there is a large-capacity power shortage in the power system, which may lead to peak loads or a rapid ramp. This paper proposes a bi-level coordinated optimization strategy by quantitating the DR potential (DRP) of smart appliances to descend the steep ramp and balance the power energy. Based on dynamic characteristics of the smart appliances, the mathematic models of online DRP are presented. In the upper layer, a multi-agent coordinated distribution method is proposed to allocate the demand limit to each agent from the dispatching center considering the online DRP. In the lower layer, an optimal smart appliances-controlling strategy is presented to guarantee the total household power consumption of each agent below its demand limit considering the consumers’ comfort and response times. Simulation results indicate the feasibility of the proposed strategy. Full article

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

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15 pages, 3654 KiB

Open AccessArticle

Unsynchronized Phasor-Based Protection Method for Single Line-to-Ground Faults in an Ungrounded Offshore Wind Farm with Fully-Rated Converters-Based Wind Turbines

by Liuming Jing, Dae-Hee Son, Sang-Hee Kang and Soon-Ryul Nam

Energies 2017, 10(4), 526; https://doi.org/10.3390/en10040526 - 13 Apr 2017

Cited by 2 | Viewed by 5974

This paper proposes a protection method for single line-to-ground (SLG) faults in an ungrounded offshore wind farm with fully-rated converter-based wind turbines. The proposed method uses the unsynchronized current phasors measured by unit protections installed at the connection point of the fully-rated converter [...] Read more.

This paper proposes a protection method for single line-to-ground (SLG) faults in an ungrounded offshore wind farm with fully-rated converter-based wind turbines. The proposed method uses the unsynchronized current phasors measured by unit protections installed at the connection point of the fully-rated converter (FRC)-based wind turbines (WTs). Each unit protection collects the unsynchronized current phasors from two adjacent nodes and synchronizes them by aligning the positive-sequence current to the same phase angle. The faulted section is identified by comparing the phase angles of the synchronized zero-sequence currents from adjacent nodes. Simulations of an ungrounded offshore wind farm with relay models were carried out using power system computer-aided design (PSCAD)/ electromagnetic transients including direct current (EMTDC). Full article

(This article belongs to the Special Issue Electric Power Systems Research 2017)

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15 pages, 6183 KiB

Open AccessArticle

Experimental Investigation of Stress Rate and Grain Size on Gas Seepage Characteristics of Granular Coal

by Dan Ma, Qiang Li, Matthew R. Hall and Yu Wu

Energies 2017, 10(4), 527; https://doi.org/10.3390/en10040527 - 13 Apr 2017

Cited by 33 | Viewed by 4875

Coal seam gas, held within the inner pores of unmineable coal, is an important energy resource. Gas release largely depends on the gas seepage characteristics and their evolution within granular coal. To monitor this evolution, a series of experiments were conducted to study [...] Read more.

Coal seam gas, held within the inner pores of unmineable coal, is an important energy resource. Gas release largely depends on the gas seepage characteristics and their evolution within granular coal. To monitor this evolution, a series of experiments were conducted to study the effects of applied compressive stress and original grain size distribution (GSD) on the variations in the gas seepage characteristics of granular coal samples. Grain crushing under higher stress rates was observed to be more intense. Isolated fractures in the larger diameter fractions transformed from self–extending to inter-connecting pathways at a critical compressive stress. Grain crushing was mainly caused by compression and high-speed impact. Based on the test results of the original GSD effect, the overall process of porosity and permeability evolution during compression can be divided into three different phases: (1) rapid reduction in the void ratio; (2) continued reduction in the void ratio and large particle crushing; and (3) continued crushing of large particles. Void size reduction and particle crushing were mainly attributed to the porosity and permeability decreases that occurred. The performance of an empirical model, for porosity and permeability evolution, was also investigated. The predictive results indicate that grain crushing caused permeability increases during compression, and that this appeared to be the main cause for the predictive values being lower than those obtained from the experimental tests. The predictive accuracy would be the same for samples under different stress rates and the lowest for the sample with the highest proportion of large grain diameters. Full article

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

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17 pages, 10522 KiB

Open AccessArticle

IEC 61850 Configuration Solution to Distributed Intelligence in Distribution Grid Automation

by Zhengyi Zhu, Bingyin Xu, Christoph Brunner, Tony Yip and Yu Chen

Energies 2017, 10(4), 528; https://doi.org/10.3390/en10040528 - 13 Apr 2017

Cited by 19 | Viewed by 6998

To solve the configuration issue when using International Electrotechnical Commission (IEC) 61850 for distributed intelligence in Distribution Automation Systems (DAS), this paper proposes the configuration solution in terms of semantic models and processing methods. Firstly, the special requirements of the DAS configuration are [...] Read more.

To solve the configuration issue when using International Electrotechnical Commission (IEC) 61850 for distributed intelligence in Distribution Automation Systems (DAS), this paper proposes the configuration solution in terms of semantic models and processing methods. Firstly, the special requirements of the DAS configuration are analyzed, consisting of the system boundary of a configuration project, the topology configuration for distributed applications, and the automatic identification of the Intelligent Electronic Devices (IED). The new models of Process, Line, and other elements are then presented based on the System Configuration Language (SCL) to describe the distribution network topology. The planned contents are allocated into a new format of the Configured IED Description (CID) file to realize the distributed applications. A register service is designed, which fulfills the automatic identification of IEDs when they are remotely placed into a DAS. The service checks the configuration status in real-time and automates the whole configuration engineering process. The case study shows that the proposed solution allows an IED to detect the real-time topology and re-establish the data flow configuration with peer IEDs independently from the master station; thus the distributed applications can be performed more autonomously and efficiently. Full article

(This article belongs to the Special Issue ICT for Energy)

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11 pages, 12136 KiB

Open AccessArticle

Comparison of the 60Sn40Pb and 62Sn2Ag36Pb Solders for a PV Ribbon Joint in Photovoltaic Modules Using the Thermal Shock Test

by Min-Soo Kang, Yu-Jae Jeon, Do-Seok Kim and Young-Eui Shin

Energies 2017, 10(4), 529; https://doi.org/10.3390/en10040529 - 13 Apr 2017

Cited by 10 | Viewed by 7718

In this study, the characteristics of a photovoltaic (PV) ribbon (t = 0.25 mm) joint with 60Sn40Pb and 62Sn2Ag36Pb solders were evaluated using thermal shock tests. The thermal shock tests were performed under three conditions: −40–65 °C, −40–85 °C, and −40–105 °C. [...] Read more.

In this study, the characteristics of a photovoltaic (PV) ribbon (t = 0.25 mm) joint with 60Sn40Pb and 62Sn2Ag36Pb solders were evaluated using thermal shock tests. The thermal shock tests were performed under three conditions: −40–65 °C, −40–85 °C, and −40–105 °C. The results of these tests were analyzed using electroluminescence (EL) and cross-sectional images. Following testing, broken metal fingers (MFs) were confirmed near the solder joint. PV module degradation was attributed to the broken finger ratio (BFR) based on quantitative analysis of the dark rectangular (DR) regions on the EL images. In addition, the activation energy of the broken MFs was calculated from the increasing BFR. Thermal characteristic variations due to the added Ag in the PV ribbon solder joints were evaluated through observation of solder micro-structure changes following thermal shock tests. Full article

(This article belongs to the Special Issue Solar Photovoltaics Trilemma: Efficiency, Stability and Cost Reduction 2017)

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14 pages, 3697 KiB

Open AccessArticle

Design and Evaluation of an Efficient Three-Phase Four-Leg Voltage Source Inverter with Reduced IGBTs

by Yixiao Luo, Chunhua Liu, Feng Yu and Christopher H.T. Lee

Energies 2017, 10(4), 530; https://doi.org/10.3390/en10040530 - 13 Apr 2017

Cited by 8 | Viewed by 5638

This paper presents a new three-phase four-leg voltage source inverter (VSI), which achieves a high cost effectiveness for mega-watt level system applications. The proposed four-leg inverter adopts the integrated topology with thyristors and insulated-gate bipolar transistors (IGBTs), which aims to reduce the number [...] Read more.

This paper presents a new three-phase four-leg voltage source inverter (VSI), which achieves a high cost effectiveness for mega-watt level system applications. The proposed four-leg inverter adopts the integrated topology with thyristors and insulated-gate bipolar transistors (IGBTs), which aims to reduce the number of IGBTs. In order to handle the zero sequence current, a neutral leg via incorporating IGBTs is artfully integrated with the regular phase legs. Furthermore, the modelling principles are elaborated and analyzed, which emphasizes switching states and voltage vectors in six segments based on the states of thyristors. Finally, by using the carrier-based pulse width modulation (PWM) method, the closed-loop current control of the proposed inverter is verified by both simulation and experimentation. Full article

(This article belongs to the Special Issue Power Electronics and Power Quality)

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16 pages, 3208 KiB

Open AccessArticle

Analysis of the Physical Properties of Hydrate Sediments Recovered from the Pearl River Mouth Basin in the South China Sea: Preliminary Investigation for Gas Hydrate Exploitation

by Bin Wang, Peng Huo, Tingting Luo, Zhen Fan, Fanglan Liu, Bo Xiao, Mingjun Yang, Jiafei Zhao and Yongchen Song

Energies 2017, 10(4), 531; https://doi.org/10.3390/en10040531 - 13 Apr 2017

Cited by 44 | Viewed by 5083

Laboratory based research on the physical properties of gas hydrate hosting sediment matrix was carried out on the non-pressurized hydrate-bearing sediment samples from the Chinese Guangzhou Marine Geological Survey 2 (GMGS2) drilling expedition in the Pearl River Mouth (PRM) basin. Measurements of index [...] Read more.

Laboratory based research on the physical properties of gas hydrate hosting sediment matrix was carried out on the non-pressurized hydrate-bearing sediment samples from the Chinese Guangzhou Marine Geological Survey 2 (GMGS2) drilling expedition in the Pearl River Mouth (PRM) basin. Measurements of index properties, surface characteristics, and thermal and mechanical properties were performed on ten sediment cores. The grains were very fine with a mean grain size ranging from 7 to 11 μm throughout all intervals, which provide guidance for the option of a screen system. Based on X-ray Computed Tomography (CT) and SEM images, bioclasts, which could promote hydrate formation, were not found in the PRM basin. However, the flaky clay might be conducive to hydrate formation in pore spaces. The measured sediment thermal conductivities are relatively low compared to those measured at other mines, ranging from 1.3 to 1.45 W/(m·K). This suggests that thermal stimulation may not be a good option for gas production from hydrate-bearing sediments in the PRM basin, and depressurization could exacerbate the problems of gas hydrate reformation and/or ice generation. Therefore, the heat transfer problem needs to be considered when exploiting the natural gas hydrate resource within these areas. In addition, the results of testing the mechanical property indicate the stability of hydrate-bearing sediments decreases with hydrate dissociation, suggesting that a holistic approach should be considered when establishing a drilling platform. Both the heat-transfer characteristic and mechanical property provide the foundation for the establishment of a safe and efficient production technology for utilizing the hydrate resource. Full article

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28 pages, 7684 KiB

Open AccessFeature PaperArticle

Exergoeconomic Performance Comparison and Optimization of Single-Stage Absorption Heat Transformers

by S. Mohammad S. Mahmoudi, Sina Salehi, Mortaza Yari and Marc A. Rosen

Energies 2017, 10(4), 532; https://doi.org/10.3390/en10040532 - 14 Apr 2017

Cited by 24 | Viewed by 4792

Three single-stage absorption heat transformer (SSHT) configurations are modeled, analyzed and compared from the viewpoints of thermodynamics and economics, using the Engineering Equation Solver (EES) software. In addition, a multi-objective optimization is carried out for the three configurations to specify the optimal design [...] Read more.

Three single-stage absorption heat transformer (SSHT) configurations are modeled, analyzed and compared from the viewpoints of thermodynamics and economics, using the Engineering Equation Solver (EES) software. In addition, a multi-objective optimization is carried out for the three configurations to specify the optimal design point considering the second law efficiency and the product unit cost as two objective functions. The configurations differ from one another considering the number of heat exchangers used in them. The results show that the coefficient of performance (COP) and exergy coefficient of performance (ECOP) for configuration 3 are around 35% and 30% higher than the corresponding values for configuration 1, respectively. Also, configuration 2 is found to be more economic with a product unit cost of about 21% and 5% lower than those for configurations 1 and 3, respectively. Furthermore, it is observed that relatively higher absorber temperatures can be achieved by configurations 2 and 3 compared to configuration 1. It is concluded from the multi-objective optimization that the conditions at which the evaporator, condenser and absorber temperatures are 86.51 °C, 39.03 °C and 123.1 °C, respectively, represents an optimal solution. Full article

(This article belongs to the Special Issue Applied Energy System Modeling 2016)

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17 pages, 18295 KiB

Open AccessArticle

Impact of Silicon Carbide Devices on the Powertrain Systems in Electric Vehicles

by Xiaofeng Ding, Jiawei Cheng and Feida Chen

Energies 2017, 10(4), 533; https://doi.org/10.3390/en10040533 - 14 Apr 2017

Cited by 25 | Viewed by 10022

The DC/DC converters and DC/AC inverters based on silicon carbide (SiC) devices as battery interfaces, motor drives, etc., in electric vehicles (EVs) benefit from their low resistances, fast switching speed, high temperature tolerance, etc. Such advantages could improve the power density and efficiency [...] Read more.

The DC/DC converters and DC/AC inverters based on silicon carbide (SiC) devices as battery interfaces, motor drives, etc., in electric vehicles (EVs) benefit from their low resistances, fast switching speed, high temperature tolerance, etc. Such advantages could improve the power density and efficiency of the converter and inverter systems in EVs. Furthermore, the total powertrain system in EVs is also affected by the converter and inverter system based on SiC, especially the capacity of the battery and the overall system efficiency. Therefore, this paper investigates the impact of SiC on the powertrain systems in EVs. First, the characteristics of SiC are evaluated by a double pulse test (DPT). Then, the power losses of the DC/DC converter, DC/AC inverter, and motor are measured. The measured results are assigned into a powertrain model built in the Advanced Vehicle Simulator (ADVISOR) software in order to explore a direct correlation between the SiC and the performance of the powertrain system in EVs, which are then compared with the conventional powertrain system based on silicon (Si). The test and simulation results demonstrate that the efficiency of the overall powertrain is significantly improved and the capacity of the battery can be remarkably reduced if the Si is replaced by SiC in the powertrain system. Full article

(This article belongs to the Special Issue Advanced Energy Storage Technologies and Their Applications (AESA))

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21 pages, 3422 KiB

Open AccessArticle

Developing an Input-Output Based Method to Estimate a National-Level Energy Return on Investment (EROI)

by Lina I. Brand-Correa, Paul E. Brockway, Claire L. Copeland, Timothy J. Foxon, Anne Owen and Peter G. Taylor

Energies 2017, 10(4), 534; https://doi.org/10.3390/en10040534 - 14 Apr 2017

Cited by 31 | Viewed by 11134

Concerns have been raised that declining energy return on energy investment (EROI) from fossil fuels, and low levels of EROI for alternative energy sources, could constrain the ability of national economies to continue to deliver economic growth and improvements in social wellbeing while [...] Read more.

Concerns have been raised that declining energy return on energy investment (EROI) from fossil fuels, and low levels of EROI for alternative energy sources, could constrain the ability of national economies to continue to deliver economic growth and improvements in social wellbeing while undertaking a low-carbon transition. However, in order to test these concerns on a national scale, there is a conceptual and methodological gap in relation to calculating a national-level EROI and analysing its policy implications. We address this by developing a novel application of an Input-Output methodology to calculate a national-level indirect energy investment, one of the components needed for calculating a national-level EROI. This is a mixed physical and monetary approach using Multi-Regional Input-Output data and an energy extension. We discuss some conceptual and methodological issues relating to defining EROI for a national economy, and describe in detail the methodology and data requirements for the approach. We obtain initial results for the UK for the period 1997–2012, which show that the country’s EROI has been declining since the beginning of the 21st Century. We discuss the policy relevance of measuring national-level EROI and propose avenues for future research. Full article

(This article belongs to the Special Issue Low Carbon Economy)

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28 pages, 3835 KiB

Open AccessArticle

A Framework for Real-Time Optimal Power Flow under Wind Energy Penetration

by Erfan Mohagheghi, Aouss Gabash and Pu Li

Energies 2017, 10(4), 535; https://doi.org/10.3390/en10040535 - 14 Apr 2017

Cited by 40 | Viewed by 5536

Developing a suitable framework for real-time optimal power flow (RT-OPF) is of utmost importance for ensuring both optimality and feasibility in the operation of energy distribution networks (DNs) under intermittent wind energy penetration. The most challenging issue thereby is that a large-scale complex [...] Read more.

Developing a suitable framework for real-time optimal power flow (RT-OPF) is of utmost importance for ensuring both optimality and feasibility in the operation of energy distribution networks (DNs) under intermittent wind energy penetration. The most challenging issue thereby is that a large-scale complex optimization problem has to be solved in real-time. Online simultaneous optimization of the wind power curtailments of wind stations and the discrete reference values of the slack bus voltage which leads to a mixed-integer nonlinear programming (MINLP) problem, in addition to considering variable reverse power flow, make the optimization problem even much more complicated. To address these difficulties, a two-phase solution approach to RT-OPF is proposed in this paper. In the prediction phase, a number of MINLP OPF problems corresponding to the most probable scenarios of the wind energy penetration in the prediction horizon, by taking its forecasted value and stochastic distribution into account, are solved in parallel. The solution provides a lookup table for optional control strategies for the current prediction horizon which is further divided into a certain number of short time intervals. In the realization phase, one of the control strategies is selected from the lookup table based on the actual wind power and realized to the grid in the current time interval, which will proceed from one interval to the next, till the end of the current prediction horizon. Then, the prediction phase for the next prediction horizon will be activated. A 41-bus medium-voltage DN is taken as a case study to demonstrate the proposed RT-OPF approach. Full article

(This article belongs to the Special Issue Selected Papers from 16 IEEE International Conference on Environment and Electrical Engineering (EEEIC 2016))

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16 pages, 3064 KiB

Open AccessArticle

Validation of the Measurement Characteristics in an Instrument for Power Quality Estimation—A Case Study

by Romuald Masnicki

Energies 2017, 10(4), 536; https://doi.org/10.3390/en10040536 - 15 Apr 2017

Cited by 10 | Viewed by 4755

An acceptable quality of electrical energy is seen today as an important component of ecology. Several instruments for estimating the quality of electrical power have been elaborated. Each supplier assures that the instrument meets the applicable standards and that the uncertainty of the [...] Read more.

An acceptable quality of electrical energy is seen today as an important component of ecology. Several instruments for estimating the quality of electrical power have been elaborated. Each supplier assures that the instrument meets the applicable standards and that the uncertainty of the measurement results obtained using the instrument does not exceed the established levels. The accuracy of the measurement results depends on a couple of things, e.g., the correctness of the measurement algorithms implemented in the instrument and the quality of its calibration. In this paper, the basic features of an “estimator/analyzer” (E/A) instrument, as well as the calibration methods of the instrument, the verification of its measurement algorithms, and also the obtained exemplary results, are shown. The proposal of the strategy of the reliable validation of embedded measurement algorithms for the identification of parameters characterizing electrical power quality in the power grid is discussed. Full article

(This article belongs to the Special Issue Selected Papers from 16 IEEE International Conference on Environment and Electrical Engineering (EEEIC 2016))

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27 pages, 2369 KiB

Open AccessArticle

Strategic Choices of China’s New Energy Vehicle Industry: An Analysis Based on ANP and SWOT

by Xiaojia Wang, Chenggong Li, Jennifer Shang, Changhui Yang, Bingli Zhang and Xinsheng Ke

Energies 2017, 10(4), 537; https://doi.org/10.3390/en10040537 - 16 Apr 2017

Cited by 36 | Viewed by 13381

This goal of this paper is to provide a framework by which China should accelerate the development and production of new energy vehicles, which should effectively address current energy and environmental pressures, while promoting the sustainable development of the automotive industry, which is [...] Read more.

This goal of this paper is to provide a framework by which China should accelerate the development and production of new energy vehicles, which should effectively address current energy and environmental pressures, while promoting the sustainable development of the automotive industry, which is an urgent task. In addition, this paper provides guidelines that seek to transform China’s auto industry while developing a new economic growth point to gain an international competitive advantage with strategic initiatives. This study aims to provide an ANP-SWOT (Analytic Network Process and Strength-Weakness-Opportunity-Threat analysis) approach for an interdependency analysis and to prioritize the new energy automobile industry in China. Firstly, a SWOT model is used to analyze the internal and external factors surrounding the development of the new energy automobile industry in China. Secondly, four types of development strategies are proposed by means of the SWOT matrix according to the conclusions of the factor analysis. Finally, the ANP network structure is designed to measure the effects of influential sub-factors, and then to define a strategic plan for China’s new energy automobile industry. The results of this study show that the optimal short-term development strategy for China’s new energy automotive industry is to increase the construction of new energy vehicle-related facilities, while the best long-term development strategy is to use local advantages and resources, through cost control measures which increase competition within the local new energy automotive industry. Full article

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21 pages, 3773 KiB

Open AccessArticle

Load Signature Formulation for Non-Intrusive Load Monitoring Based on Current Measurements

by Aggelos S. Bouhouras, Paschalis A. Gkaidatzis, Konstantinos C. Chatzisavvas, Evangelos Panagiotou, Nikolaos Poulakis and Georgios C. Christoforidis

Energies 2017, 10(4), 538; https://doi.org/10.3390/en10040538 - 16 Apr 2017

Cited by 33 | Viewed by 5752

In this paper we present a new methodology for the formulation of efficient load signatures towards the implementation of a near-real time Non-Intrusive Load Monitoring (NILM) approach. The purpose of this work relies on defining representative current values regarding the 1st, 3rd and [...] Read more.

In this paper we present a new methodology for the formulation of efficient load signatures towards the implementation of a near-real time Non-Intrusive Load Monitoring (NILM) approach. The purpose of this work relies on defining representative current values regarding the 1st, 3rd and 5th harmonic orders to be utilized in the load signatures formulation. A measurement setup has been developed and steady-state measurements have been performed in a Low Voltage residence. A data processing methodology is proposed aiming to depict representative current values for each harmonic order in order to keep the load signature short and simple. In addition, a simple disaggregation scheme is proposed under linear equations for the disaggregation mode in order to examine the near-real time application of the methodology. The analysis indicates that the developed load signatures could be efficient for a per second application rate of the NILM algorithm. The results show that the higher harmonic currents facilitate the identification performance. Finally, the analysis concludes that for combinations that include appliances with intense harmonic content, the phase angle of the higher for harmonic currents should also be considered to the load signatures formulation. Full article

(This article belongs to the Special Issue Selected Papers from 16 IEEE International Conference on Environment and Electrical Engineering (EEEIC 2016))

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18 pages, 1212 KiB

Open AccessArticle

Energy Recovery from Waste Incineration—The Importance of Technology Data and System Boundaries on CO₂ Emissions

by Ola Eriksson and Göran Finnveden

Energies 2017, 10(4), 539; https://doi.org/10.3390/en10040539 - 15 Apr 2017

Cited by 51 | Viewed by 11532

Previous studies on waste incineration as part of the energy system show that waste management and energy supply are highly dependent on each other, and that the preconditions for the energy system setup affects the avoided emissions and thereby even sometimes the total [...] Read more.

Previous studies on waste incineration as part of the energy system show that waste management and energy supply are highly dependent on each other, and that the preconditions for the energy system setup affects the avoided emissions and thereby even sometimes the total outcome of an environmental assessment. However, it has not been previously shown explicitly which key parameters are most crucial, how much each parameter affects results and conclusions and how different aspects depend on each other. The interconnection between waste incineration and the energy system is elaborated by testing parameters potentially crucial to the result: design of the incineration plant, avoided energy generation, degree of efficiency, electricity efficiency in combined heat and power plants (CHP), avoided fuel, emission level of the avoided electricity generation and avoided waste management. CO₂ emissions have been calculated for incineration of 1 kWh mixed combustible waste. The results indicate that one of the most important factors is the electricity efficiency in CHP plants in combination with the emission level of the avoided electricity generation. A novel aspect of this study is the plant by plant comparison showing how different electricity efficiencies associated with different types of fuels and plants influence results. Since waste incineration typically have lower power to fuel ratios, this has implications for further analyses of waste incineration compared to other waste management practises and heat and power production technologies. New incineration capacity should substitute mixed landfill disposal and recovered energy should replace energy from inefficient high polluting plants. Electricity generation must not be lost, as it has to be compensated for by electricity production affecting the overall results. Full article

(This article belongs to the Special Issue Energy and Waste Management)

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34 pages, 8779 KiB

Open AccessReview

Nano-Based Drilling Fluids: A Review

by Zisis Vryzas and Vassilios C. Kelessidis

Energies 2017, 10(4), 540; https://doi.org/10.3390/en10040540 - 15 Apr 2017

Cited by 224 | Viewed by 20391

Nanomaterials are engineered materials with at least one dimension in the range of 1–100 nm. Nanofluids—nanoscale colloidal suspensions containing various nanomaterials—have distinctive properties and offer unprecedented potential for various sectors such as the energy, cosmetic, aerospace and biomedical industries. Due to their unique [...] Read more.

Nanomaterials are engineered materials with at least one dimension in the range of 1–100 nm. Nanofluids—nanoscale colloidal suspensions containing various nanomaterials—have distinctive properties and offer unprecedented potential for various sectors such as the energy, cosmetic, aerospace and biomedical industries. Due to their unique physico-chemical properties, nanoparticles are considered as very good candidates for smart drilling fluid formulation, i.e., fluids with tailor-made rheological and filtration properties. However, due to the great risk of adapting new technologies, their application in oil and gas industry is not, to date, fully implemented. Over the last few years, several researchers have examined the use of various nanoparticles, from commercial to custom made particles, to formulate drilling fluids with enhanced properties that can withstand extreme downhole environments, particularly at high pressure and high temperature (HP/HT) conditions. This article summarizes the recent progress made on the use of nanoparticles as additives in drilling fluids in order to give such fluids optimal rheological and filtration characteristics, increase shale stability and achieve wellbore strengthening. Type, size and shape of nanoparticles, volumetric concentration, addition of different surfactants and application of an external magnetic field are factors that are critically evaluated and are discussed in this article. The results obtained from various studies show that nanoparticles have a great potential to be used as drilling fluid additives in order to overcome stern drilling problems. However, there are still challenges that should be addressed in order to take full advantage of the capabilities of such particles. Finally the paper identifies and discusses opportunities for future research. Full article

(This article belongs to the Special Issue Nanotechnology for Oil and Gas Applications)

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13 pages, 5399 KiB

Open AccessArticle

A Glowworm Swarm Optimization-Based Maximum Power Point Tracking for Photovoltaic/Thermal Systems under Non-Uniform Solar Irradiation and Temperature Distribution

by Yi Jin, Wenhui Hou, Guiqiang Li and Xiao Chen

Energies 2017, 10(4), 541; https://doi.org/10.3390/en10040541 - 15 Apr 2017

Cited by 37 | Viewed by 5966

The output power of a photovoltaic (PV) system depends on the external solar irradiation and its own temperature. In order to obtain more power from the PV system, the maximum power point tracking (MPPT) is necessary. However, when the PV is partially shaded, [...] Read more.

The output power of a photovoltaic (PV) system depends on the external solar irradiation and its own temperature. In order to obtain more power from the PV system, the maximum power point tracking (MPPT) is necessary. However, when the PV is partially shaded, there will be multiple peaks in the power-current (P-I) curve. The conventional MPPT methods may be invalid due to falling into the local peak. In addition, in a photovoltaic-thermal (PV/T) system, the non-uniform temperature distribution on PV will also occur, which complicates the situation. This paper presents a MPPT method with glowworm swarm optimization (GSO) for PV in a PV/T system under non-uniform solar irradiation and temperature distribution. In order to study the performance of the proposed method, the conventional methods including the perturbation and observe algorithm (P and O), and the fractional open-circuit voltage technique (FOCVT) are compared with it in this paper. Simulation results show that the proposed method can rapidly track the real maximum power point (MPP) under different conditions, such as the gradient temperature distribution, the fast variable solar irradiation and the variable partial shading. The outcome indicates the proposed method has obvious advantages, especially the performance being superior to the conventional methods under the partial shading condition. Full article

(This article belongs to the Special Issue Solar Photovoltaics Trilemma: Efficiency, Stability and Cost Reduction 2017)

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11 pages, 3528 KiB

Open AccessArticle

Dependence of the Microporosity of Activated Carbons on the Lignocellulosic Composition of the Precursors

by Silvia Román, Beatriz Ledesma, Andrés Álvarez-Murillo, Awf Al-Kassir and Talal Yusaf

Energies 2017, 10(4), 542; https://doi.org/10.3390/en10040542 - 15 Apr 2017

Cited by 19 | Viewed by 3897

A series of activated carbons were prepared by physical steam gasification under identical experimental conditions to compare the pore development from almond tree pruning chars and walnut shell activated carbons. The results obtained showed that steam gasification yields microporous carbons in both cases, [...] Read more.

A series of activated carbons were prepared by physical steam gasification under identical experimental conditions to compare the pore development from almond tree pruning chars and walnut shell activated carbons. The results obtained showed that steam gasification yields microporous carbons in both cases, and the rise in temperature causes an increase of the pore volumes of the activated carbons, up to a certain degree of burn-off. This effect was more marked for walnut shell, which gave rise to activated carbons with apparent surface values of up to 1434 m² g⁻¹. Also, a slight widening of porosity was found at low burn-off degrees. This pore widening was more marked in the case of activated carbons from almond tree pruning, which also have a high macropore volume. It was found that the lignocellulosic and porosity properties of the raw materials can cause this different behavior towards activation processes. Full article

(This article belongs to the Special Issue Recent development in the field of biofuels from agricultural industry)

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26 pages, 1809 KiB

Open AccessArticle

Surrogate Measures for the Robust Scheduling of Stochastic Job Shop Scheduling Problems

by Shichang Xiao, Shudong Sun and Jionghua (Judy) Jin

Energies 2017, 10(4), 543; https://doi.org/10.3390/en10040543 - 16 Apr 2017

Cited by 15 | Viewed by 4854

This study focuses on surrogate measures (SMs) of robustness for the stochastic job shop scheduling problems (SJSSP) with uncertain processing times. The objective is to provide the robust predictive schedule to the decision makers. The mathematical model of SJSSP is formulated by considering [...] Read more.

This study focuses on surrogate measures (SMs) of robustness for the stochastic job shop scheduling problems (SJSSP) with uncertain processing times. The objective is to provide the robust predictive schedule to the decision makers. The mathematical model of SJSSP is formulated by considering the railway execution strategy, which defined that the starting time of each operation cannot be earlier than its predictive starting time. Robustness is defined as the expected relative deviation between the realized makespan and the predictive makespan. In view of the time-consuming characteristic of simulation-based robustness measure (RMsim), this paper puts forward new SMs and investigates their performance through simulations. By utilizing the structure of schedule and the available information of stochastic processing times, two SMs on the basis of minimizing the robustness degradation on the critical path and the non-critical path are suggested. For this purpose, a hybrid estimation of distribution algorithm (HEDA) is adopted to conduct the simulations. To analyze the performance of the presented SMs, two computational experiments are carried out. Specifically, the correlation analysis is firstly conducted by comparing the coefficient of determination between the presented SMs and the corresponding simulation-based robustness values with those of the existing SMs. Secondly, the effectiveness and the performance of the presented SMs are further validated by comparing with the simulation-based robustness measure under different uncertainty levels. The experimental results demonstrate that the presented SMs are not only effective for assessing the robustness of SJSSP no matter the uncertainty levels, but also require a tremendously lower computational burden than the simulation-based robustness measure. Full article

(This article belongs to the Special Issue Smart Design, Smart Manufacturing and Industry 4.0)

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23 pages, 4641 KiB

Open AccessArticle

Simulation and Performance Analysis of Organic Rankine Systems for Stationary Compressed Natural Gas Engine

by Songsong Song, Hongguang Zhang, Rui Zhao, Fanxiao Meng, Hongda Liu, Jingfu Wang and Baofeng Yao

Energies 2017, 10(4), 544; https://doi.org/10.3390/en10040544 - 17 Apr 2017

Cited by 13 | Viewed by 4852

The organic Rankine cycle (ORC) can be used to recover the waste heat from a stationary compressed natural gas (CNG) engine. However, the exhaust energy rate varies with engine load, which can influence the operating performance of the ORC system, therefore, it is [...] Read more.

The organic Rankine cycle (ORC) can be used to recover the waste heat from a stationary compressed natural gas (CNG) engine. However, the exhaust energy rate varies with engine load, which can influence the operating performance of the ORC system, therefore, it is necessary to study the running state of the ORC system. In this paper, first, the numerical simulation model of the ORC system is built by using GT-Suite software, with R245fa selected as the working fluid of the ORC system. The boundary conditions of the numerical simulation model are specified according to the measured data obtained by the stationary CNG engine test. Subsequently, the power output and dynamic characteristics of expander are analyzed to determine the running state of the ORC system. Investigations indicate that the fluctuation of refrigerant mass flow rate in the expander is obvious in the engine’s low-load regions (from 20% engine load to 40% engine load). The performances of ORC system and stationary CNG engine-ORC combined system (combined system) are finally investigated, respectively. The results show that the thermal efficiency of the combined system can be increased by a maximum 5.0% (at the engine rated condition), while the brake specific fuel consumption (BSFC) can be reduced by a maximum 4.0% (at the engine rated condition). Full article

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25 pages, 1811 KiB

Open AccessFeature PaperReview

Development of Heterogeneous Catalysts for Thermo-Chemical Conversion of Lignocellulosic Biomass

by Jacek Grams and Agnieszka M. Ruppert

Energies 2017, 10(4), 545; https://doi.org/10.3390/en10040545 - 17 Apr 2017

Cited by 45 | Viewed by 7636

Lignocellulosic biomass is one of the most attractive renewable resources that can be used for the production of biofuels and valuable chemicals. However, problems associated with the low efficiency of its conversion and poor selectivity to desired products remain. Therefore, in recent years [...] Read more.

Lignocellulosic biomass is one of the most attractive renewable resources that can be used for the production of biofuels and valuable chemicals. However, problems associated with the low efficiency of its conversion and poor selectivity to desired products remain. Therefore, in recent years researchers have focused on the design of highly active and stable catalysts, enabling an increase in the effectiveness of lignocellulosic biomass processing. This work is devoted to the presentation of the latest trends in the studies of the heterogeneous catalysts used in thermo-chemical conversion of such feedstock. The systems applied for the production of both bio-oil and hydrogen-rich gas are discussed. Zeolites, mesoporous materials, metal oxides, supported metal catalysts, and modifications of their structure are described. Moreover, the impact of the physicochemical properties of the presented catalyst on their catalytic performance in the mentioned processes is demonstrated. Full article

(This article belongs to the Special Issue Thermo-Chemical Conversion of Waste Biomass)

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14 pages, 2733 KiB

Open AccessArticle

Comparison of Biodiesel Obtained from Virgin Cooking Oil and Waste Cooking Oil Using Supercritical and Catalytic Transesterification

by Jeeban Poudel, Sujeeta Karki, Nawaraj Sanjel, Malesh Shah and Sea Cheon Oh

Energies 2017, 10(4), 546; https://doi.org/10.3390/en10040546 - 17 Apr 2017

Cited by 19 | Viewed by 8916

Comparative analysis of transesterification of virgin cooking oil (VCO) and waste cooking oil (WCO) in catalyzed and supercritical transesterification process using methanol and ethanol as solvents has been conducted in this study. The luminous point of this research was the direct comparison of [...] Read more.

Comparative analysis of transesterification of virgin cooking oil (VCO) and waste cooking oil (WCO) in catalyzed and supercritical transesterification process using methanol and ethanol as solvents has been conducted in this study. The luminous point of this research was the direct comparison of catalytic and supercritical process using the ester composition obtained from virgin cooking oil and waste cooking oil transesterification. Oil to alcohol molar ratio of 1:6 and reaction condition of 65 °C and 1 bar pressure were considered for the catalytic process, while 260 °C and high pressure (65 and 75 bar for methanol and ethanol, respectively) were accounted for the supercritical process. Distinct layer separation was observed for both processes. Ester, fatty acid and glycerol composition was studied for both the upper and lower layers separately, from which 100% ester composition in the upper layer and a mixture of ester and other composition in the lower layer was obtained for the catalytic process owing to succeeding filtration and washing. However, mixture of ester (>75%) and other composition was obtained in both layers for the supercritical process where purification process was not implemented. The similarity in the result obtained demonstrates the superiority of waste cooking oil compared to virgin cooking oil, taking cost into consideration. Full article

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

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23 pages, 408 KiB

Open AccessFeature PaperArticle

A Comparison of Organic and Steam Rankine Cycle Power Systems for Waste Heat Recovery on Large Ships

by Jesper Graa Andreasen, Andrea Meroni and Fredrik Haglind

Energies 2017, 10(4), 547; https://doi.org/10.3390/en10040547 - 17 Apr 2017

Cited by 79 | Viewed by 9480

This paper presents a comparison of the conventional dual pressure steam Rankine cycle process and the organic Rankine cycle process for marine engine waste heat recovery. The comparison was based on a container vessel, and results are presented for a high-sulfur (3 wt [...] Read more.

This paper presents a comparison of the conventional dual pressure steam Rankine cycle process and the organic Rankine cycle process for marine engine waste heat recovery. The comparison was based on a container vessel, and results are presented for a high-sulfur (3 wt %) and low-sulfur (0.5 wt %) fuel case. The processes were compared based on their off-design performance for diesel engine loads in the range between 25% and 100%. The fluids considered in the organic Rankine cycle process were MM(hexamethyldisiloxane), toluene, n-pentane, i-pentane and c-pentane. The results of the comparison indicate that the net power output of the steam Rankine cycle process is higher at high engine loads, while the performance of the organic Rankine cycle units is higher at lower loads. Preliminary turbine design considerations suggest that higher turbine efficiencies can be obtained for the ORC unit turbines compared to the steam turbines. When the efficiency of the c-pentane turbine was allowed to be 10% points larger than the steam turbine efficiency, the organic Rankine cycle unit reaches higher net power outputs than the steam Rankine cycle unit at all engine loads for the low-sulfur fuel case. The net power production from the waste heat recovery units is generally higher for the low-sulfur fuel case. The steam Rankine cycle unit produces 18% more power at design compared to the high-sulfur fuel case, while the organic Rankine cycle unit using MM produces 33% more power. Full article

(This article belongs to the Special Issue Waste Heat Recovery)

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28 pages, 6458 KiB

Open AccessArticle

Dynamic Simulation of an Organic Rankine Cycle—Detailed Model of a Kettle Boiler

by Roberto Pili, Hartmut Spliethoff and Christoph Wieland

Energies 2017, 10(4), 548; https://doi.org/10.3390/en10040548 - 17 Apr 2017

Cited by 13 | Viewed by 7279

Organic Rankine Cycles (ORCs) are nowadays a valuable technology to produce electricity from low and medium temperature heat sources, e.g., in geothermal, biomass and waste heat recovery applications. Dynamic simulations can help improve the flexibility and operation of such plants, and guarantee a [...] Read more.

Organic Rankine Cycles (ORCs) are nowadays a valuable technology to produce electricity from low and medium temperature heat sources, e.g., in geothermal, biomass and waste heat recovery applications. Dynamic simulations can help improve the flexibility and operation of such plants, and guarantee a better economic performance. In this work, a dynamic model for a multi-pass kettle evaporator of a geothermal ORC power plant has been developed and its dynamics have been validated against measured data. The model combines the finite volume approach on the tube side and a two-volume cavity on the shell side. To validate the dynamic model, a positive and a negative step function in heat source flow rate is applied. The simulation model performed well in both cases. The liquid level appeared the most challenging quantity to simulate. A better agreement in temperature was achieved by increasing the volume flow rate of the geothermal brine by 2% over the entire simulation. Measurement errors, discrepancies in working fluid and thermal brine properties and uncertainties in heat transfer correlations can account for this. In the future, the entire geothermal power plant will be simulated, and suggestions to improve its dynamics and control by means of simulations will be provided. Full article

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35 pages, 3364 KiB

Open AccessEditor’s ChoiceArticle

An Optimized Home Energy Management System with Integrated Renewable Energy and Storage Resources

by Adnan Ahmad, Asif Khan, Nadeem Javaid, Hafiz Majid Hussain, Wadood Abdul, Ahmad Almogren, Atif Alamri and Iftikhar Azim Niaz

Energies 2017, 10(4), 549; https://doi.org/10.3390/en10040549 - 17 Apr 2017

Cited by 249 | Viewed by 18952

Traditional power grid and its demand-side management (DSM) techniques are centralized and mainly focus on industrial consumers. The ignorance of residential and commercial sectors in DSM activities degrades the overall performance of a conventional grid. Therefore, the concept of DSM and demand response [...] Read more.

Traditional power grid and its demand-side management (DSM) techniques are centralized and mainly focus on industrial consumers. The ignorance of residential and commercial sectors in DSM activities degrades the overall performance of a conventional grid. Therefore, the concept of DSM and demand response (DR) via residential sector makes the smart grid (SG) superior over the traditional grid. In this context, this paper proposes an optimized home energy management system (OHEMS) that not only facilitates the integration of renewable energy source (RES) and energy storage system (ESS) but also incorporates the residential sector into DSM activities. The proposed OHEMS minimizes the electricity bill by scheduling the household appliances and ESS in response to the dynamic pricing of electricity market. First, the constrained optimization problem is mathematically formulated by using multiple knapsack problems, and then solved by using the heuristic algorithms; genetic algorithm (GA), binary particle swarm optimization (BPSO), wind driven optimization (WDO), bacterial foraging optimization (BFO) and hybrid GA-PSO (HGPO) algorithms. The performance of the proposed scheme and heuristic algorithms is evaluated via MATLAB simulations. Results illustrate that the integration of RES and ESS reduces the electricity bill and peak-to-average ratio (PAR) by 19.94% and 21.55% respectively. Moreover, the HGPO algorithm based home energy management system outperforms the other heuristic algorithms, and further reduces the bill by 25.12% and PAR by 24.88%. Full article

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20 pages, 2745 KiB

Open AccessArticle

Optimal Charging and Discharging Scheduling for Electric Vehicles in a Parking Station with Photovoltaic System and Energy Storage System

by Leehter Yao, Zolboo Damiran and Wei Hong Lim

Energies 2017, 10(4), 550; https://doi.org/10.3390/en10040550 - 17 Apr 2017

Cited by 100 | Viewed by 10573

The economic and environmental benefits brought by electric vehicles (EVs) cannot be fully delivered unless these vehicles are fully or partially charged by renewable energy sources (RES) such as photovoltaic system (PVS). Nevertheless, the EV charging management problem of a parking station integrated [...] Read more.

The economic and environmental benefits brought by electric vehicles (EVs) cannot be fully delivered unless these vehicles are fully or partially charged by renewable energy sources (RES) such as photovoltaic system (PVS). Nevertheless, the EV charging management problem of a parking station integrated with RES is challenging due to the uncertain nature of local RES generation. This paper aims to address these difficulties by deploying an energy storage system (ESS) in parking stations and exploiting the charging and discharging scheduling of EVs to achieve better utilization of intermittent PVS for EV charging. A real-time charging optimization scheme is also formulated, using mixed-integer linear programming (MILP) to coordinate the charging or discharging power of EVs along with the power dispatches of power grid and ESS based on the vehicles’ charging or discharging priorities and electricity price preferences. Extensive simulations show that the proposed approach not only maximizes the satisfaction of EV owners in terms of fulfilling all charging and discharging requests, but also minimizes the overall operational cost of the parking station by prioritizing the utilization of energy from PVS, ESS, and scheduling of every EV’s charging and discharging. Full article

(This article belongs to the Special Issue Energy Management, Control, and System Architectures for Electric Vehicle Applications)

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14 pages, 1611 KiB

Open AccessArticle

Optimal Design of the Rotor Structure of a HSPMSM Based on Analytic Calculation of Eddy Current Losses

by Yanan Yu, Deliang Liang and Xing Liu

Energies 2017, 10(4), 551; https://doi.org/10.3390/en10040551 - 17 Apr 2017

Cited by 6 | Viewed by 4485

The rotor eddy current losses of a high-speed permanent magnet synchronous motor reduce the efficiency of the motor and increase the temperature rise of the rotor. In severe cases, the permanent magnet of the rotor can be demagnetized, affecting the safe operation of [...] Read more.

The rotor eddy current losses of a high-speed permanent magnet synchronous motor reduce the efficiency of the motor and increase the temperature rise of the rotor. In severe cases, the permanent magnet of the rotor can be demagnetized, affecting the safe operation of the motor. In this paper, an analytical model of rotor eddy current losses calculation based on Maxwell equations is introduced. The eddy current losses of rotor structures, e.g., protection sleeve, shield layer and permanent magnets, are analyzed. The calculation results of rotor eddy current losses are compared with two-dimensional (2D) finite element analysis. The comparison verifies the accuracy and versatility of analytical calculation. Finally, the influences of the variables on eddy current losses in the derived model are analyzed. Based on the principle of minimizing eddy current losses, an optimized structure with copper layers covering both inner and outer surfaces of the protective sleeve is proposed. Furthermore, the optimized distribution parameter of copper film thickness is obtained. Full article

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16 pages, 15677 KiB

Open AccessArticle

A Fast-Acting Diagnostic Algorithm of Insulated Gate Bipolar Transistor Open Circuit Faults for Power Inverters in Electric Vehicles

by Lei Yu, Youtong Zhang, Wenqing Huang and Khaled Teffah

Energies 2017, 10(4), 552; https://doi.org/10.3390/en10040552 - 18 Apr 2017

Cited by 13 | Viewed by 7001

To improve the diagnostic detection speed in electric vehicles, a novel diagnostic algorithm of insulated gate bipolar transistor (IGBT) open circuit faults for power inverters is proposed in this paper. The average of the difference between the actual three-phase current and referential three-phase [...] Read more.

To improve the diagnostic detection speed in electric vehicles, a novel diagnostic algorithm of insulated gate bipolar transistor (IGBT) open circuit faults for power inverters is proposed in this paper. The average of the difference between the actual three-phase current and referential three-phase current values over one electrical period is used as the diagnostic variable. The normalization method based on the amplitude of the d-q axis referential current is applied to the diagnostic variables to improve the response speed of diagnosis, and to avoid the noise and the delay caused by signal acquisition. In the parameter discretization process, the variable parameter moving average method (VPMAM) is adopted to solve the variation of the average value over a period with the speed of the motor; hence, the diagnostic reliability of the system is improved. This algorithm is robust, independent of load variations, and has a high resistivity against false alarms. Since only the three-phase current of the motor is utilized for calculations in the time domain, a fast diagnostic detection speed can be achieved, which is significantly essential for real-time control in electric vehicles. The effectiveness of the proposed algorithm is verified by both simulation and experimental results. Full article

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

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14 pages, 3176 KiB

Open AccessArticle

Maximum Boost Control Method for Single-Phase Quasi-Switched-Boost and Quasi-Z-Source Inverters

by Minh-Khai Nguyen and Youn-Ok Choi

Energies 2017, 10(4), 553; https://doi.org/10.3390/en10040553 - 18 Apr 2017

Cited by 21 | Viewed by 7260

The maximum boost control method for a single-phase switched-boost inverter (SBI) and single-phase Z-source inverter (ZSI) is proposed in this paper. In the proposed method, the low frequency voltage is added to the constant voltage for generating the variable shoot-through time intervals. For [...] Read more.

The maximum boost control method for a single-phase switched-boost inverter (SBI) and single-phase Z-source inverter (ZSI) is proposed in this paper. In the proposed method, the low frequency voltage is added to the constant voltage for generating the variable shoot-through time intervals. For improving the AC output quality of the inverter, an active power switch is used to replace one of the diodes in the single-phase SBI. The operating principles and circuit analysis using the proposed maximum boost control method for single-phase inverters are presented. Laboratory prototypes are built to verify the operation of the proposed pulse-width modulation (PWM) control method for both single-phase quasi-ZSI and single-phase quasi-SBI. Full article

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

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19 pages, 2858 KiB

Open AccessArticle

A Unified Trading Model Based on Robust Optimization for Day-Ahead and Real-Time Markets with Wind Power Integration

by Yuewen Jiang, Meisen Chen and Shi You

Energies 2017, 10(4), 554; https://doi.org/10.3390/en10040554 - 18 Apr 2017

Cited by 16 | Viewed by 4162

In a conventional electricity market, trading is conducted based on power forecasts in the day-ahead market, while the power imbalance is regulated in the real-time market, which is a separate trading scheme. With large-scale wind power connected into the power grid, power forecast [...] Read more.

In a conventional electricity market, trading is conducted based on power forecasts in the day-ahead market, while the power imbalance is regulated in the real-time market, which is a separate trading scheme. With large-scale wind power connected into the power grid, power forecast errors increase in the day-ahead market which lowers the economic efficiency of the separate trading scheme. This paper proposes a robust unified trading model that includes the forecasts of real-time prices and imbalance power into the day-ahead trading scheme. The model is developed based on robust optimization in view of the undefined probability distribution of clearing prices of the real-time market. For the model to be used efficiently, an improved quantum-behaved particle swarm algorithm (IQPSO) is presented in the paper based on an in-depth analysis of the limitations of the static character of quantum-behaved particle swarm algorithm (QPSO). Finally, the impacts of associated parameters on the separate trading and unified trading model are analyzed to verify the superiority of the proposed model and algorithm. Full article

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

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13 pages, 4843 KiB

Open AccessArticle

Power-Smoothing Scheme of a DFIG Using the Adaptive Gain Depending on the Rotor Speed and Frequency Deviation

by Hyewon Lee, Min Hwang, Eduard Muljadi, Poul Sørensen and Yong Cheol Kang

Energies 2017, 10(4), 555; https://doi.org/10.3390/en10040555 - 18 Apr 2017

Cited by 8 | Viewed by 4609

In an electric power grid that has a high penetration level of wind, the power fluctuation of a large-scale wind power plant (WPP) caused by varying wind speeds deteriorates the system frequency regulation. This paper proposes a power-smoothing scheme of a doubly-fed induction [...] Read more.

In an electric power grid that has a high penetration level of wind, the power fluctuation of a large-scale wind power plant (WPP) caused by varying wind speeds deteriorates the system frequency regulation. This paper proposes a power-smoothing scheme of a doubly-fed induction generator (DFIG) that significantly mitigates the system frequency fluctuation while preventing over-deceleration of the rotor speed. The proposed scheme employs an additional control loop relying on the system frequency deviation that operates in combination with the maximum power point tracking control loop. To improve the power-smoothing capability while preventing over-deceleration of the rotor speed, the gain of the additional loop is modified with the rotor speed and frequency deviation. The gain is set to be high if the rotor speed and/or frequency deviation is large. The simulation results based on the IEEE 14-bus system clearly demonstrate that the proposed scheme significantly lessens the output power fluctuation of a WPP under various scenarios by modifying the gain with the rotor speed and frequency deviation, and thereby it can regulate the frequency deviation within a narrow range. Full article

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16 pages, 1997 KiB

Open AccessArticle

Decomposition Characteristics of SF₆ and Partial Discharge Recognition under Negative DC Conditions

by Ju Tang, Xu Yang, Gaoxiang Ye, Qiang Yao, Yulong Miao and Fuping Zeng

Energies 2017, 10(4), 556; https://doi.org/10.3390/en10040556 - 18 Apr 2017

Cited by 21 | Viewed by 5482

Four typical types of artificial defects are designed in conducting the decomposition experiments of SF₆ gas to obtain and understand the decomposition characteristics of SF₆ gas-insulated medium under different types of negative DC partial discharge (DC-PD), and use the obtained decomposition [...] Read more.

Four typical types of artificial defects are designed in conducting the decomposition experiments of SF₆ gas to obtain and understand the decomposition characteristics of SF₆ gas-insulated medium under different types of negative DC partial discharge (DC-PD), and use the obtained decomposition characteristics of SF₆ in diagnosing the type and severity of insulation fault in DC SF₆ gas-insulated equipment. Experimental results show that the negative DC partial discharges caused by the four defects decompose the SF₆ gas and generate five stable decomposed components, namely, CF₄, CO₂, SO₂F₂, SOF₂, and SO₂. The concentration, effective formation rate, and concentration ratio of SF₆ decomposed components can be associated with the PD types. Furthermore, back propagation neural network algorithm is used to recognize the PD types. The recognition results show that compared with the concentrations of SF₆ decomposed components, their concentration ratios are more suitable as the characteristic quantities for PD recognition, and using those concentration ratios in recognizing the PD types can obtain a good effect. Full article

(This article belongs to the Special Issue Selected Papers from 2016 IEEE International Conference on High Voltage Engineering (ICHVE 2016))

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20 pages, 15679 KiB

Open AccessEditor’s ChoiceArticle

Deformation Behavior of Hard Roofs in Solid Backfill Coal Mining Using Physical Models

by Nan Zhou, Jixiong Zhang, Hao Yan and Meng Li

Energies 2017, 10(4), 557; https://doi.org/10.3390/en10040557 - 18 Apr 2017

Cited by 49 | Viewed by 5833

Solid backfill coal mining technology has been widely applied in coal seams that are at risk of hard roof. Using actual measured strain–stress curves of the backfill body and the similarity theory, this study designed and employed four experimental models for physical simulation, [...] Read more.

Solid backfill coal mining technology has been widely applied in coal seams that are at risk of hard roof. Using actual measured strain–stress curves of the backfill body and the similarity theory, this study designed and employed four experimental models for physical simulation, corresponding to roof-controlled backfilling ratios of 0%, 40%, 82.5% and 97% using the geological conditions of Face No. 6304 in the Jining No. 3 coal mine—a solid backfill coal mining face under a hard roof. A non-contact strain measurement system and pressure sensors were used to monitor the deformation of the overlying strata and changes in abutment stress ahead of the face during mining of the models for varying roof-controlled backfilling ratios. The results indicated that the solid backfill body was able to support the roof. As the roof-controlled backfilling ratio was increased, the maximum subsidence of the roof and the maximum height of the cracks decreased. When the roof-controlled backfilling ratio was 82.5% or higher, the working face did not display any obvious initial fractures or periodic fractures, and both the value and the impact range of the abutment stress ahead of the face decreased. Full article

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11 pages, 2453 KiB

Open AccessArticle

Synchronization of Low-Frequency Oscillation in Power Systems

by Kwan-Shik Shim, Seon-Ju Ahn and Joon-Ho Choi

Energies 2017, 10(4), 558; https://doi.org/10.3390/en10040558 - 19 Apr 2017

Cited by 12 | Viewed by 5868

This paper presents the well-documented concept of synchronization of low frequency oscillation occurring in power systems and describes the characteristics of sync occurring in basic electrical circuits. The theory of sync, observed in basic circuits, is extended to analyze the dynamic characteristics of [...] Read more.

This paper presents the well-documented concept of synchronization of low frequency oscillation occurring in power systems and describes the characteristics of sync occurring in basic electrical circuits. The theory of sync, observed in basic circuits, is extended to analyze the dynamic characteristics of low-frequency oscillation in power systems. Full article

(This article belongs to the Special Issue Advances in Power System Operations and Planning)

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21 pages, 4483 KiB

Open AccessArticle

Frequency Control Ancillary Service Provided by Efficient Power Plants Integrated in Queuing-Controlled Domestic Water Heaters

by Yebai Qi, Dan Wang, Xuyang Wang, Hongjie Jia, Tianjiao Pu, Naishi Chen and Kaixin Liu

Energies 2017, 10(4), 559; https://doi.org/10.3390/en10040559 - 19 Apr 2017

Cited by 12 | Viewed by 4690

Frequency is an important parameter of a power system. It is of great significance to maintain its stability, especially in the current development scenario of large-scale interconnected power systems. Thermostatically controlled appliances (TCAs) are good controllable resources for demand response owing to their [...] Read more.

Frequency is an important parameter of a power system. It is of great significance to maintain its stability, especially in the current development scenario of large-scale interconnected power systems. Thermostatically controlled appliances (TCAs) are good controllable resources for demand response owing to their rapid response capabilities and relatively wide controllable ranges. In this study, domestic water heaters, which have wider deadbands compared with other typical TCAs, such as heat pumps, are used as frequency regulation resources. The main contribution of this paper is that it proposes a queuing-controlled strategy with lock-on and off constraints for controlling an efficient power plant consisting of water heaters (EPP-WH). The queuing-controlled strategy enables TCAs to provide frequency regulation ancillary service for the normal operation of the power system. The thermal dynamic process of the water heater and the formation of the EPP-WH are first discussed. Based on the developed model, a series of strategies are proposed, including load shedding calculation, top layer optimization, and improved temperature priority list (TPL) strategy with lock-on and off constraints. Finally, typical case studies are discussed to illustrate the frequency regulation effects and the effects of two characteristic parameters—users’ willingness and lock time limits. Reasonable targets are generated based on various consideration from top layer optimization module. The results indicate that using the model and proposed strategies, the EPP-WH has good frequency regulation performance. Full article

(This article belongs to the Special Issue Energy Management Control)

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21 pages, 16730 KiB

Open AccessArticle

Flow Behavior and Displacement Mechanisms of Nanoparticle Stabilized Foam Flooding for Enhanced Heavy Oil Recovery

by Teng Lu, Zhaomin Li and Yan Zhou

Energies 2017, 10(4), 560; https://doi.org/10.3390/en10040560 - 20 Apr 2017

Cited by 33 | Viewed by 6931

In this study, nanoparticle stabilized foam experiments were performed in bulk tests, micromodels, and sandpacks at elevated temperatures and pressures to investigate the flow behavior and displacement mechanisms for enhanced heavy oil recovery. The results from the bulk tests showed that the stability [...] Read more.

In this study, nanoparticle stabilized foam experiments were performed in bulk tests, micromodels, and sandpacks at elevated temperatures and pressures to investigate the flow behavior and displacement mechanisms for enhanced heavy oil recovery. The results from the bulk tests showed that the stability of the foam and oil in water (O/W) emulsion improved when silica nanoparticles (SiO₂) were added, compared with the anionic surfactant alone. Also, the SiO₂ nanoparticles increased the dilatational viscoelasticity of the gas-water interface, which is an important fluid property and mechanism for improving heavy oil recovery. The micromodel studies demonstrated that several gas bubbles and oil droplets were stably dispersed during the nanoparticle stabilized foam flooding. The gas bubbles and oil droplets plug pores through capture-plugging and bridge-plugging, thereby increasing the sweep efficiency. The trapped residual oil is gradually pushed to the pores by the elastic forces of bubbles. Subsequently, the residual oil is pulled into oil threads by the flowing gas bubbles. Then, a greater improvement in displacement efficiency is obtained. The sandpack tests showed that the tertiary oil recovery of nanoparticle stabilized foam flooding can reach about 27% using 0.5 wt % SiO₂ nanoparticles. The foam slug size of 0.3 pore volume (PV) and the gas liquid ratio (GLR) of 3:1 were found to be the optimum conditions in terms of heavy oil recovery by nanoparticle stabilized foam flooding in this study. A continuous nanoparticle dispersion and N₂ could be more effective compared with the cyclic injection pattern. Full article

(This article belongs to the Special Issue Nanotechnology for Oil and Gas Applications)

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13 pages, 1849 KiB

Open AccessArticle

Methane Hydrate Formation in Marine Sediment from South China Sea with Different Water Saturations

by Yu Zhang, Xiaosen Li, Yi Wang, Zhaoyang Chen and Gang Li

Energies 2017, 10(4), 561; https://doi.org/10.3390/en10040561 - 20 Apr 2017

Cited by 18 | Viewed by 5020

The kinetics of methane hydrate formation in marine sediments with different water saturations are important to assess the feasibility of the hydrate production and understand the process of the secondary hydrate formation in the gas production from hydrate reservoir. In this paper, the [...] Read more.

The kinetics of methane hydrate formation in marine sediments with different water saturations are important to assess the feasibility of the hydrate production and understand the process of the secondary hydrate formation in the gas production from hydrate reservoir. In this paper, the behaviors of methane hydrate formation in marine sediments from the South China Sea at different water saturation levels were experimentally studied in isobaric conditions. The marine sediments used in the experiments have the mean pore diameter of 12.178 nm, total pore volume of 4.997 × 10⁻² mL/g and surface area of 16.412 m²/g. The volume fraction of water in the marine sediments ranges from 30% to 50%. The hydrate formation rate and the final water conversion increase with the decrease of the formation temperature at the water saturation of 40%. At the same experimental conditions, the hydrate formation rate decreases with the increase of the water saturation from 40% to 50% due to the reduction of the gas diffusion speed. At the water saturation of 30%, the hydrate formation rate is lower than that at the water saturation of 40% due to the effect of the equilibrium hydrate formation pressure, which increases with the decrease of the water saturation. The final water conversion is shown to increase with the increase of the water saturation, even the formation process at higher water did not end. The experiments at low water saturation show a better repeatability than that at high water saturation. Full article

(This article belongs to the Special Issue Methane Hydrate Research and Development)

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15 pages, 2869 KiB

Open AccessArticle

Evaluating Heat Flux Profiles in Aluminum Reheating Furnace with Regenerative Burner

by Hang Zhang and Shengxiang Deng

Energies 2017, 10(4), 562; https://doi.org/10.3390/en10040562 - 20 Apr 2017

Cited by 3 | Viewed by 6738

Properly understanding heat flux characteristics is a crucial prerequisite to efficiently applying a regenerative burner in an aluminum reheating furnace. A series of experiments was conducted in this study in order to establish a database of the best available burners according to furnace [...] Read more.

Properly understanding heat flux characteristics is a crucial prerequisite to efficiently applying a regenerative burner in an aluminum reheating furnace. A series of experiments was conducted in this study in order to establish a database of the best available burners according to furnace temperature, excess air ratio, and flame combustion mode as they affect heat flux characteristics at the burner plane (Z = 0 mm). A heat flux model was developed to estimate heat transfer in the furnace, and the heat flux proportions of the other two horizontal levels (Z = 400 mm and Z = 750 mm) were investigated. The contour profile of heat flux indicates that total heat flux (THF) and radiation heat flux (RHF) increases with furnace temperature increment (900–1100 °C). Low excess air ratio (1.2–1.3, at furnace temperature 1100 °C) not only reduced the heat flux gradient, but also contributed to enlarge high THF areas and the maximum RHF. The flameless combustion mode displayed larger average THF and RHF uniformity than that of conventional combustion mode. Therefore, the burning effect of operating condition 1 (gas velocity, 90 m/s; excess air ratio, 1.2; flameless combustion) is better than the other conditions. A change of furnace temperature and excess air ratio had mildly effect on convection coefficient, but combustion mode was in contrast. The estimated heat flux distribution from the measured heat flux at the whole burner plane was in agreement with the fitted line of the axis of burner B. Although the intercept of the simulated equation was slightly underestimated, the error can be eliminated by improving the experimental conditions. The results presented here similarly apply to all regenerative burners. A comparison of heat flux among the three horizontal levels indicated that the RHF proportion comprised about 80% of the THF at each level, and a slightly increase (21.1 kW/m²) of THF in the high level from the low levels. Full article

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

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17 pages, 5100 KiB

Open AccessArticle

Jointed Surrounding Rock Mass Stability Analysis on an Underground Cavern in a Hydropower Station Based on the Extended Key Block Theory

by Chao Jia, Yong Li, Mingyuan Lian and Xiaoyong Zhou

Energies 2017, 10(4), 563; https://doi.org/10.3390/en10040563 - 20 Apr 2017

Cited by 23 | Viewed by 4978

The jointed surrounding rock mass stability is of utmost importance to integral stability during the construction and long-term safety operation of the underground caverns in hydropower stations. The key blocks play a significant role in the integral stability of the jointed surrounding rock [...] Read more.

The jointed surrounding rock mass stability is of utmost importance to integral stability during the construction and long-term safety operation of the underground caverns in hydropower stations. The key blocks play a significant role in the integral stability of the jointed surrounding rock mass, therefore it is critical to determine the location, size, and failure mode of random key blocks. This paper proposes an improved method combining the traditional key block theory (KBT) and the force transfer algorithm to accurately calculate the safety factors of probabilistic key blocks in the surrounding rock mass. The force transfer algorithm can consider the interactions between the internal blocks. After the probabilistic characteristics of the joint fissures are obtained, the stereographic projection method is employed to determine the locations of dangerous joints. Then the vector analysis method is used to search the random blocks, determine the sliding directions of random blocks, and calculate the block sizes and safety factors near the free surface of the underground cavern, which can be used to comprehensively evaluate the surrounding rock mass stability. The above numerical results have provided powerful guidance for developing a reinforcement system for the surrounding rock mass. Full article

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32 pages, 3112 KiB

Open AccessArticle

Assessment of the Usability and Accuracy of Two-Diode Models for Photovoltaic Modules

by Vincenzo Franzitta, Aldo Orioli and Alessandra Di Gangi

Energies 2017, 10(4), 564; https://doi.org/10.3390/en10040564 - 20 Apr 2017

Cited by 34 | Viewed by 4669

Many diode-based equivalent circuits for simulating the electrical behaviour of photovoltaic (PV) cells and panels are reported in the scientific literature. Two-diode equivalent circuits, which require more complex procedures to calculate the seven model parameters, are less numerous. The model parameters are generally [...] Read more.

Many diode-based equivalent circuits for simulating the electrical behaviour of photovoltaic (PV) cells and panels are reported in the scientific literature. Two-diode equivalent circuits, which require more complex procedures to calculate the seven model parameters, are less numerous. The model parameters are generally calculated using the data extracted from the datasheets issued by the PV panel manufactures and adopting simplifying hypotheses and numerical solving techniques. A criterion for rating both the usability and accuracy of two-diode models is proposed in this paper with the aim of supporting researchers and designers, working in the area of PV systems, to select and use a model that may be fit for purpose. The criterion adopts a three-level rating scale that considers the ease of finding the data used by the analytical procedure, the simplicity of the mathematical tools needed to perform calculations and the accuracy achieved in calculating the current and power. The analytical procedures, the simplifying hypotheses and the operative steps to calculate the parameters of the most famous two-diode equivalent circuits are exhaustively described in this paper. The accuracy of the models is tested by comparing the characteristics issued by the PV panel manufacturers with the current-voltage (I-V) curves, at constant solar irradiance and/or cell temperature, calculated with the analysed models with. The results of the study show that the two-diode models recently proposed reach accuracies that are comparable with the values derived from the one-diode models. Full article

(This article belongs to the Special Issue Solar Photovoltaics Trilemma: Efficiency, Stability and Cost Reduction 2017)

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23 pages, 4204 KiB

Open AccessArticle

Simultaneous Robust Coordinated Damping Control of Power System Stabilizers (PSSs), Static Var Compensator (SVC) and Doubly-Fed Induction Generator Power Oscillation Dampers (DFIG PODs) in Multimachine Power Systems

by Jian Zuo, Yinhong Li, Dongyuan Shi and Xianzhong Duan

Energies 2017, 10(4), 565; https://doi.org/10.3390/en10040565 - 20 Apr 2017

Cited by 28 | Viewed by 6424

The potential of utilizing doubly-fed induction generator (DFIG)-based wind farms to improve power system damping performance and to enhance small signal stability has been proposed by many researchers. However, the simultaneous coordinated tuning of a DFIG power oscillation damper (POD) with other damping [...] Read more.

The potential of utilizing doubly-fed induction generator (DFIG)-based wind farms to improve power system damping performance and to enhance small signal stability has been proposed by many researchers. However, the simultaneous coordinated tuning of a DFIG power oscillation damper (POD) with other damping controllers is rarely involved. A simultaneous robust coordinated multiple damping controller design strategy for a power system incorporating power system stabilizer (PSS), static var compensator (SVC) POD and DFIG POD is presented in this paper. This coordinated damping control design strategy is addressed as an eigenvalue-based optimization problem to increase the damping ratios of oscillation modes. Both local and inter-area electromechanical oscillation modes are intended in the optimization design process. Wide-area phasor measurement unit (PMU) signals, selected by the joint modal controllability/ observability index, are utilized as SVC and DFIG POD feedback modulation signals to suppress inter-area oscillation modes. The robustness of the proposed coordinated design strategy is achieved by simultaneously considering multiple power flow situations and operating conditions. The recently proposed Grey Wolf optimizer (GWO) algorithm is adopted to efficiently optimize the parameter values of multiple damping controllers. The feasibility and effectiveness of the proposed coordinated design strategy are demonstrated through frequency-domain eigenvalue analysis and nonlinear time-domain simulation studies in two modified benchmark test systems. Moreover, the dynamic response simulation results also validate the robustness of the recommended coordinated multiple damping controllers under various system operating conditions. Full article

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

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17 pages, 532 KiB

Open AccessArticle

Optimal Energy Scheduling and Transaction Mechanism for Multiple Microgrids

by Boram Kim, Sunghwan Bae and Hongseok Kim

Energies 2017, 10(4), 566; https://doi.org/10.3390/en10040566 - 21 Apr 2017

Cited by 25 | Viewed by 5057

In this paper, we propose a framework for optimal energy scheduling combined with a transaction mechanism to enable multiple microgrids to exchange their energy surplus/deficit with others while the distributed networks of microgrids remain secure. Our framework is based on two layers: a [...] Read more.

In this paper, we propose a framework for optimal energy scheduling combined with a transaction mechanism to enable multiple microgrids to exchange their energy surplus/deficit with others while the distributed networks of microgrids remain secure. Our framework is based on two layers: a distributed network layer and a market layer. In the distributed network layer, we first solve optimal power flow (OPF) using a predictor corrector proximal multiplier algorithm to optimally dispatch diesel generation considering renewable energy and power loss within a microgrid. Then, in the market layer, the agent of microgrid behaves either as a load agent or generator agent so that the auctioneer sets a reasonable transaction price for both agents by using the naive auction-inspired algorithm. Finally, energy surplus/deficit is traded among microgrids at a determined transaction price while the main grid balances the transaction. We implement the proposed mechanism in MATLAB (Matlab Release 15, The MathWorks Inc., Natick, MA, USA) using an optimization solver, CVX. In the case studies, we compare four scenarios depending on whether OPF and/or energy transaction is performed or not. Our results show that the joint consideration of OPF and energy transaction achieves as minimal a cost as the ideal case where all microgrids are combined into a single microgrid (or called grand-microgrid) and OPF is performed. We confirm that, even though microgrids are operated by private owners who are not collaborated, a transaction-based mechanism can mimic the optimal operation of a grand-microgrid in a scalable way. Full article

(This article belongs to the Special Issue Smart Microgrids: Developing the Intelligent Power Grid of Tomorrow)

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16 pages, 2168 KiB

Open AccessArticle

Thermal-Flow Analysis of a Simple LTD (Low-Temperature-Differential) Heat Engine

by Yeongmin Kim, Wongee Chun and Kuan Chen

Energies 2017, 10(4), 567; https://doi.org/10.3390/en10040567 - 21 Apr 2017

Cited by 8 | Viewed by 4640

A combined thermal and flow analysis was carried out to study the behavior and performance of a simple, commercial LTD (low-temperature-differential) heat engine. Laminar-flow solutions for annulus and channel flows were employed to estimate the viscous drags on the piston and the displacer, [...] Read more.

A combined thermal and flow analysis was carried out to study the behavior and performance of a simple, commercial LTD (low-temperature-differential) heat engine. Laminar-flow solutions for annulus and channel flows were employed to estimate the viscous drags on the piston and the displacer, and the pressure difference across the displacer. Temperature correction factors were introduced in the thermal analysis to account for the departures from the ideal heat transfer processes. The flow analysis results indicate that the work required to overcome the viscous drags on engine moving parts is very small for engine speeds below 10 RPS (revolutions per second). The work required to move the displacer due to the pressure difference across the displacer is also one-to-two orders of magnitude smaller than the moving-boundary work of the piston for temperature differentials in the neighborhood of 20 °C and engine speeds below 10 RPS. A comparison with experimental data reveals large degradations from the ideal heat transfer processes inside the engine. Full article

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

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19 pages, 3928 KiB

Open AccessArticle

Simulations of Melting of Encapsulated CaCl₂·6H₂O for Thermal Energy Storage Technologies

by Antonio M. Puertas, Manuel S. Romero-Cano, Francisco Javier De Las Nieves, Sabina Rosiek and Francisco J. Batlles

Energies 2017, 10(4), 568; https://doi.org/10.3390/en10040568 - 21 Apr 2017

Cited by 8 | Viewed by 4528

We present in this work simulations using the finite difference approximation in 2D for the melting of an encapsulated phase-change material suitable for heat storage applications; in particular, we study CaCl₂·6H₂O in a cylindrical encapsulation of internal radius 8 [...] Read more.

We present in this work simulations using the finite difference approximation in 2D for the melting of an encapsulated phase-change material suitable for heat storage applications; in particular, we study CaCl₂·6H₂O in a cylindrical encapsulation of internal radius 8 mm. We choose this particular salt hydrate due to its availability and economic feasibility in high thermal mass building walls or storage. Considering only heat conduction, a thermostat is placed far from the capsule, providing heat for the melting of the phase-change material (PCM), which is initially frozen in a water bath. The difference in density between the solid and liquid phases is taken into account by considering a void in the solid PCM. A simple theoretical model is also presented, based on solving the heat equation in the steady state. The kinetics of melting is monitored by the total solid fraction and temperatures in the inner and outer surfaces of the capsule. The effect of different parameters is presented (thermostat temperature, capsule thickness, capsule conductivity and natural convection in the bath), showing the potential application of the method to select materials or geometries of the capsule. Full article

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

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21 pages, 3465 KiB

Open AccessArticle

Development of Novel Robust Regulator for Maximum Wind Energy Extraction Based upon Perturbation and Observation

by Bo Li, Wenhu Tang, Kaishun Xiahou and Qinghua Wu

Energies 2017, 10(4), 569; https://doi.org/10.3390/en10040569 - 21 Apr 2017

Cited by 8 | Viewed by 4718

This paper develops a robust regulator design approach to maximum power point tracking (MPPT) of a variable-speed wind energy conversion system (WECS) under the concept of perturbation and observation. The proposed perturb and observe regulators (PORs) rooted on the sliding mode method employs [...] Read more.

This paper develops a robust regulator design approach to maximum power point tracking (MPPT) of a variable-speed wind energy conversion system (WECS) under the concept of perturbation and observation. The proposed perturb and observe regulators (PORs) rooted on the sliding mode method employs the optimal power curve (OPC) to realize MPPT operations by continuously adjusting rotor speeds and the duty cycles, which can ensure control performance against system parameter variations. The proposed PORs can detect sudden wind speed changes indirectly through the mechanical power coefficient, which is used to acquire the rotor speed reference by comparing it with the optimal power constant. For the speed and duty cycle regulation, two novel controllers based on the proposed POR, i.e., an MPPT controller and a speed controller, are devised in this research. Moreover, by applying the small-signal analysis on a nonlinear wind turbine system, the convergence of the proposed speed controller is proven for the first time based on the Lyapunov theory, and meanwhile, a single-pole transfer function, to describe the effect of duty cycle variations on rotor speeds, is designed to ensure its stability. The proposed strategy is verified by simulation cases operated in MATLAB/Simulink and experimental results performed from a 0.5-kW wind turbine generator simulator. Full article

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16 pages, 1973 KiB

Open AccessArticle

Performance Evaluation of Waste Heat Recovery Systems Based on Semiconductor Thermoelectric Generators for Hypersonic Vehicles

by Kunlin Cheng, Yu Feng, Chuanwen Lv, Silong Zhang, Jiang Qin and Wen Bao

Energies 2017, 10(4), 570; https://doi.org/10.3390/en10040570 - 22 Apr 2017

Cited by 21 | Viewed by 5471

The types and the characteristics of the waste heat on hypersonic vehicles and the application feasibility of thermoelectric generators (TEGs) for hypersonic aircraft are discussed in this paper. Two thermoelectric generator schemes with an isothermal heat source and a variable temperature heat source [...] Read more.

The types and the characteristics of the waste heat on hypersonic vehicles and the application feasibility of thermoelectric generators (TEGs) for hypersonic aircraft are discussed in this paper. Two thermoelectric generator schemes with an isothermal heat source and a variable temperature heat source were proposed, and the corresponding models were developed to predict the performance of the waste heat recovery systems on a hypersonic vehicle with different heat sources. The thermoelectric efficiency variation with electric current, the temperature distribution of fuel and junctions, and the distribution of the thermoelectric figure of merit (ZT value) are described by diagrams. Besides, some improvements for a better performance are analyzed. The results indicate that the maximum values of thermoelectric efficiency are 5% and 2.5% for the isothermal heat source and the variable temperature heat source, respectively, and the thermoelectric efficiency improves with the temperature of the hot junction. The performance of the TEGs with variable temperature heat source is worse than that of the other TEGs under the same highest hot junction temperature conditions, and the former has a better conversion efficiency than the latter when the average temperatures are identical. Full article

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

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23 pages, 7402 KiB

Open AccessArticle

Research on the Common Rail Pressure Overshoot of Opposed-Piston Two-Stroke Diesel Engines

by Yi Lu, Changlu Zhao, Zhe Zuo, Fujun Zhang and Shuanlu Zhang

Energies 2017, 10(4), 571; https://doi.org/10.3390/en10040571 - 21 Apr 2017

Cited by 3 | Viewed by 7055

The common rail pressure has a direct influence on the working stability of Opposed-Piston Two-Stroke (OP2S) diesel engines, especially on performance indexes such as power, economy and emissions. Meanwhile, the rail pressure overshoot phenomenon occurs frequently due to the operating characteristics of OP2S [...] Read more.

The common rail pressure has a direct influence on the working stability of Opposed-Piston Two-Stroke (OP2S) diesel engines, especially on performance indexes such as power, economy and emissions. Meanwhile, the rail pressure overshoot phenomenon occurs frequently due to the operating characteristics of OP2S diesel engines, which could lead to serious consequences. In order to solve the rail pressure overshoot problem of OP2S diesel engines, a nonlinear concerted algorithm adding a speed state feedback was investigated. First, the nonlinear Linear Parameter Varying (LPV) model was utilized to describe the coupling relationship between the engine speed and the rail pressure. The Linear Quadratic Regulator (LQR) optimal control algorithm was applied to design the controller by the feedback of speed and rail pressure. Second, cooperating with the switching characteristics of injectors, the co-simulation of MATLAB/Simulink and GT-Power was utilized to verify the validity of the control algorithm and analyze workspaces for both normal and special sections. Finally, bench test results showed that the accuracy of the rail pressure control was in the range of ±1 MPa, in the condition of sudden 600 r/min speed increases. In addition, the fuel mass was reduced 76.3% compared with the maximum fuel supply quantity and the rail pressure fluctuation was less than 20 MPa. The algorithm could also be appropriate for other types of common rail system thanks to its universality. Full article

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21 pages, 5838 KiB

Open AccessArticle

PTC Self-Heating Experiments and Thermal Modeling of Lithium-Ion Battery Pack in Electric Vehicles

by Chengning Zhang, Xin Jin and Junqiu Li

Energies 2017, 10(4), 572; https://doi.org/10.3390/en10040572 - 22 Apr 2017

Cited by 39 | Viewed by 7256

This paper proposes a positive temperature coefficient (PTC) self-heating method, in which EVs can be operated independently of external power source at low temperature, with a lithium-ion battery (LIB) pack discharging electricity to provide PTC material with power. Three comparative heating experiments have [...] Read more.

This paper proposes a positive temperature coefficient (PTC) self-heating method, in which EVs can be operated independently of external power source at low temperature, with a lithium-ion battery (LIB) pack discharging electricity to provide PTC material with power. Three comparative heating experiments have been carried out respectively. With charge/discharge tests implemented, results demonstrate the superiority of the self-heating method, proving that the discharge capability, especially the discharge capacity of the self-heated pack is better than that of the external power heated pack. In order to evaluate the heating effect of this method, further studies are conducted on temperature distribution uniformity in the heated pack. Firstly, a geometric model is established, and heat-generation rate of PTC materials and LIB are calculated. Then, thermal characteristics of the self-heating experiment processes are numerically simulated, validating the accuracy of our modeling and confirming that temperature distributions inside the pack after heating are kept in good uniformity. Therefore, the PTC self-heating method is verified to have a significant effect on the improvement of performance of LIB at low temperature. Full article

(This article belongs to the Special Issue Advanced Energy Storage Technologies and Their Applications (AESA))

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16 pages, 2177 KiB

Open AccessArticle

Primary and Albedo Solar Energy Sources for High Altitude Persistent Air Vehicle Operation

by Tim Smith, Michele Trancossi, Dean Vucinic, Chris Bingham and Paul Stewart

Energies 2017, 10(4), 573; https://doi.org/10.3390/en10040573 - 22 Apr 2017

Cited by 7 | Viewed by 6725

A new class of the all electric airship to globally transport both passengers and freight using a ‘feeder-cruiser’ concept, and powered by renewable electric energy, is considered. Specific focus is given to photo-electric harvesting as the primary energy source and the associated hydrogen-based [...] Read more.

A new class of the all electric airship to globally transport both passengers and freight using a ‘feeder-cruiser’ concept, and powered by renewable electric energy, is considered. Specific focus is given to photo-electric harvesting as the primary energy source and the associated hydrogen-based energy storage systems. Furthermore, it is shown that the total PV output may be significantly increased by utilising cloud albedo effects. Appropriate power architectures and energy audits required for life support, and the propulsion and ancillary loads to support the continuous daily operation of the primary airship (cruiser) at stratospheric altitudes (circa 18 km), are also considered. The presented solution is substantially different from those of conventional aircraft due to the airship size and the inherent requirement to harvest and store sufficient energy during “daylight” operation, when subject to varying seasonal conditions and latitudes, to ensure its safe and continued operation during the corresponding varying “dark hours”. This is particularly apparent when the sizing of the proposed electrolyser is considered, as its size and mass increase nonlinearly with decreasing day-night duty. As such, a Unitized Regenerative Fuel Cell is proposed. For the first time the study also discusses the potential benefits of integrating the photo-voltaic cells into airship canopy structures utilising TENSAIRITY®-based elements in order to eliminate the requirements for separate inter-PV array wiring and the transport of low pressure hydrogen between fuel cells. Full article

(This article belongs to the Special Issue Next-Generation Low-Carbon Power and Energy Systems)

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15 pages, 4761 KiB

Open AccessArticle

Automatic Tracking of the Modal Parameters of an Offshore Wind Turbine Drivetrain System

by Mahmoud El-Kafafy, Christof Devriendt, Patrick Guillaume and Jan Helsen

Energies 2017, 10(4), 574; https://doi.org/10.3390/en10040574 - 22 Apr 2017

Cited by 16 | Viewed by 5639

An offshore wind turbine (OWT) is a complex structure that consists of different parts (e.g., foundation, tower, drivetrain, blades, et al.). The last decade, there has been continuous trend towards larger machines with the goal of cost reduction. Modal behavior is an important [...] Read more.

An offshore wind turbine (OWT) is a complex structure that consists of different parts (e.g., foundation, tower, drivetrain, blades, et al.). The last decade, there has been continuous trend towards larger machines with the goal of cost reduction. Modal behavior is an important design aspect. For tackling noise, vibration, and harshness (NVH) issues and validating complex simulation models, it is of high interest to continuously track the vibration levels and the evolution of the modal parameters (resonance frequencies, damping ratios, mode shapes) of the fundamental modes of the turbine. Wind turbines are multi-physical machines with significant interaction between their subcomponents. This paper will present the possibility of identifying and automatically tracking the structural vibration modes of the drivetrain system of an instrumented OWT by using signals (e.g., acceleration responses) measured on the drivetrain system. The experimental data has been obtained during a measurement campaign on an OWT in the Belgian North Sea where the OWT was in standstill condition. The drivetrain, more specifically the gearbox and generator, is instrumented with a dedicated measurement set-up consisting of 17 sensor channels with the aim to continuously track the vibration modes. The consistency of modal parameter estimates made at consequent 10-min intervals is validated, and the dominant drivetrain modal behavior is identified and automatically tracked. Full article

(This article belongs to the Collection Wind Turbines)

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17 pages, 10079 KiB

Open AccessArticle

Aerodynamic Analysis of a Helical Vertical Axis Wind Turbine

by Qian Cheng, Xiaolan Liu, Ho Seong Ji, Kyung Chun Kim and Bo Yang

Energies 2017, 10(4), 575; https://doi.org/10.3390/en10040575 - 22 Apr 2017

Cited by 53 | Viewed by 14244

Vertical axis wind turbines (VAWTs) are gradually receiving more and more interest due to their lower sensitivity to the yawed wind direction. Compared with straight blades VAWT, blades with a certain helicity show a better aerodynamic performance and less noise emission. Nowadays computational [...] Read more.

Vertical axis wind turbines (VAWTs) are gradually receiving more and more interest due to their lower sensitivity to the yawed wind direction. Compared with straight blades VAWT, blades with a certain helicity show a better aerodynamic performance and less noise emission. Nowadays computational fluid dynamics technology is frequently applied to VAWTs and gives results that can reflect real flow phenomena. In this paper, a 2D flow field simulation of a helical vertical axis wind turbine (HVAWT) with four blades has been carried out by means of a large eddy simulation (LES). The power output and fluctuation at each azimuthal position are studied with different tip speed ratio (TSR). The result shows that the variation of angle of attack (AOA) and blade-wake interaction under different TSR conditions are the two main reasons for the effects of TSR on power output. Furthermore, in order to understand the characteristics of the HVAWT along the spanwise direction, the 3D full size flow field has also been studied by the means of unsteady Reynold Averaged Navier-Stokes (U-RANS) and 3D effects on the turbine performance can be observed by the spanwise pressure distribution. It shows that tip vortex near blade tips and second flow in the spanwise direction also play a major role on the performance of VAWTs. Full article

(This article belongs to the Special Issue Wind Turbine 2017)

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16 pages, 4688 KiB

Open AccessArticle

Enhancing Oil Recovery from Chalk Reservoirs by a Low-Salinity Water Flooding Mechanism and Fluid/Rock Interactions

by Aly A. Hamouda and Sachin Gupta

Energies 2017, 10(4), 576; https://doi.org/10.3390/en10040576 - 22 Apr 2017

Cited by 22 | Viewed by 5734

Different Low Salinity Waters (LSWs) are investigated in this work to understand the role of some ions, which were recognized from our previous work and the literature for their effect on wettability alteration. Different flooding stages were followed. The primary stage was by [...] Read more.

Different Low Salinity Waters (LSWs) are investigated in this work to understand the role of some ions, which were recognized from our previous work and the literature for their effect on wettability alteration. Different flooding stages were followed. The primary stage was by injecting synthetic seawater (SSW) and the secondary stage was with SSW diluted by 10 (LSW 1:10) and 50 (LSW 1:50) times, single and two salt brines, such as Na₂SO₄, MgCl₂, and NaCl+MgCl₂ at 70 °C. The flooding sequence was due to that most of the fields in the North Sea were flooded with seawater. Two flooding rates were followed, 4 PV/day (PV = Pore Volume) and 16 PV/day in all the experiments. One of the observations was the increase of the pH during the flooding with LSW and single salt brines. The increase of the pH was attributed to mineral precipitation/dissolution as the results of ionic interactions. The effluent ion concentrations measured to understand the most likely oil recovery mechanisms. The results showed that the higher the SSW dilution the slower the oil recovery response. In presence of SO₄²⁻, Ca/Mg, higher oil recovery. The exchange between Ca/Mg, was in line with field observations. A geochemical simulation was done for a comparison with the experimental data. Full article

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

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20 pages, 7122 KiB

Open AccessArticle

Performance Comparison between Selected Evaporative Air Coolers

by Demis Pandelidis, Sergey Anisimov and Paweł Drąg

Energies 2017, 10(4), 577; https://doi.org/10.3390/en10040577 - 22 Apr 2017

Cited by 9 | Viewed by 4891

The aim of this study is to determine which of the heat exchangers is characterized by the highest efficiency in different applications. Various types of evaporative air coolers were compared: a typical counter-flow unit, the same unit operating as a heat recovery exchanger, [...] Read more.

The aim of this study is to determine which of the heat exchangers is characterized by the highest efficiency in different applications. Various types of evaporative air coolers were compared: a typical counter-flow unit, the same unit operating as a heat recovery exchanger, a regenerative unit and a novel, modified regenerative exchanger. The analysis includes comparing the work of evaporative heat exchangers during summer and winter season. The analysis is based on the original mathematical models. The numerical models are based on the modified ε-NTU (number of heat transfer units) method. It was established that selected arrangements of the presented exchangers are characterized by the different efficiency in different air-conditioning applications. The analysis faces the main construction aspects of those evaporative coolers and also compares two above-mentioned devices with modified regenerative air cooler, which can partly operate on cooled outdoor airflow and on the exhaust air from conditioned spaces. This solution can be applied in any climate and it is less dependent on the outdoor conditions. The second part of the study focuses on winter season and the potential of recovering heat with the same exchangers, but with dry working air channels. This allows establishing their total potential of generating energy savings during the annual operation. Full article

(This article belongs to the Special Issue The 1st “The Belt and Road Initiative” International Conference on Sustainable Refrigeration and Air Conditioning)

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18 pages, 1654 KiB

Open AccessFeature PaperReview

Heat Roadmap Europe: Large-Scale Electric Heat Pumps in District Heating Systems

by Andrei David, Brian Vad Mathiesen, Helge Averfalk, Sven Werner and Henrik Lund

Energies 2017, 10(4), 578; https://doi.org/10.3390/en10040578 - 22 Apr 2017

Cited by 219 | Viewed by 22507

The Heat Roadmap Europe (HRE) studies estimated a potential increase of the district heating (DH) share to 50% of the entire heat demand by 2050, with approximately 25–30% of it being supplied using large-scale electric heat pumps. This study builds on this potential [...] Read more.

The Heat Roadmap Europe (HRE) studies estimated a potential increase of the district heating (DH) share to 50% of the entire heat demand by 2050, with approximately 25–30% of it being supplied using large-scale electric heat pumps. This study builds on this potential and aims to document that such developments can begin now with technologies currently available. We present a database and the status of the technology and its ability of expansion to other European locations by reviewing experiences aimed at further research or application in the heating industry. This is based on a survey of the existing capacity of electric large-scale heat pumps with more than 1 MW thermal output, operating in European DH systems. The survey is the first database of its kind containing the technical characteristics of these heat pumps, and provides the basis for the analysis of this paper. By quantifying the heat sources, refrigerants, efficiency and types of operation of 149 units with 1580 MW of thermal output, the study further uses this data to analyze if the deployment of this technology on a large-scale is possible in other locations in Europe. It finally demonstrates that the technical level of the existing heat pumps is mature enough to make them suitable for replication in other locations in Europe. Full article

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16 pages, 3553 KiB

Open AccessArticle

Multi-Objective History Matching with a Proxy Model for the Characterization of Production Performances at the Shale Gas Reservoir

by Jaejun Kim, Joe M. Kang, Changhyup Park, Yongjun Park, Jihye Park and Seojin Lim

Energies 2017, 10(4), 579; https://doi.org/10.3390/en10040579 - 23 Apr 2017

Cited by 13 | Viewed by 8790

This paper presents a fast, reliable multi-objective history-matching method based on proxy modeling to forecast the production performances of shale gas reservoirs for which all available post-hydraulic-fracturing production data, i.e., the daily gas rate and cumulative-production volume until the given date, are honored. [...] Read more.

This paper presents a fast, reliable multi-objective history-matching method based on proxy modeling to forecast the production performances of shale gas reservoirs for which all available post-hydraulic-fracturing production data, i.e., the daily gas rate and cumulative-production volume until the given date, are honored. The developed workflow consists of distance-based generalized sensitivity analysis (DGSA) to determine the spatiotemporal-parameter significance, fast marching method (FMM) as a proxy model, and a multi-objective evolutionary algorithm to integrate the dynamic data. The model validation confirms that the FMM is a sound surrogate model working within an error of approximately 2% for the estimated ultimate recovery (EUR), and it is 11 times faster than a full-reservoir simulation. The predictive accuracy on future production after matching 1.5-year production histories is assessed to examine the applicability of the proposed method. The DGSA determines the effective parameters with respect to the gas rate and the cumulative volume, including fracture permeability, fracture half-length, enhanced permeability in the stimulated reservoir volume, and average post-fracturing porosity. A comparison of the prediction accuracy for single-objective optimization shows that the proposed method accurately estimates the recoverable volume as well as the production profiles to within an error of 0.5%, while the single-objective consideration reveals the scale-dependency problem with lesser accuracy. The results of this study are useful to overcome the time-consuming effort of using a multi-objective evolutionary algorithm and full-scale reservoir simulation as well as to conduct a more-realistic prediction of the shale gas reserves and the corresponding production performances. Full article

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17 pages, 2671 KiB

Open AccessArticle

Influences of Winding MMF Harmonics on Torque Characteristics in Surface-Mounted Permanent Magnet Vernier Machines

by Daekyu Jang and Junghwan Chang

Energies 2017, 10(4), 580; https://doi.org/10.3390/en10040580 - 23 Apr 2017

Cited by 11 | Viewed by 5831

This paper presents the influences of winding magneto-motive force (MMF) harmonics on the torque characteristics in surface-mounted permanent magnet vernier (SPMV) machines. Based on the magnetic gearing effects, the armature magnetic field of the SPMV machines is modulated by flux modulation poles (FMPs). [...] Read more.

This paper presents the influences of winding magneto-motive force (MMF) harmonics on the torque characteristics in surface-mounted permanent magnet vernier (SPMV) machines. Based on the magnetic gearing effects, the armature magnetic field of the SPMV machines is modulated by flux modulation poles (FMPs). In the modulated magnetic field, a working harmonic which corresponds to the number of the rotor pole pairs generates torque. Unlike regular PM machines, the winding MMF harmonics in the SPMV machines can produce the working harmonic by adjusting the FMP shapes. In order to investigate the effects of the winding MMF harmonics, the operating principle of the SPMV machines is elaborated by an analytical method using the winding MMF distribution and air-gap permeance function. After that, the design method of the FMP shapes that can improve the output torque by using the winding MMF harmonics is proposed. For the SPMV machine having 6 slots and 24 FMPs, the effects of the winding MMF harmonics and the validity of the proposed design method are confirmed by the finite element analysis method. It is shown that the proposed design method can improve the performances of the SPMV machine in terms of the torque density, induced electromagnetic force, and efficiency. Full article

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

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