Energies

21 pages, 1303 KiB

Open AccessArticle

A Dedicated Mixture Model for Clustering Smart Meter Data: Identification and Analysis of Electricity Consumption Behaviors

by Fateh Nassim Melzi^1,*, Allou Same², Mohamed Haykel Zayani¹ and Latifa Oukhellou²

¹ IRT SystemX, 8 Avenue de la Vauve, 91120 Palaiseau, Paris Saclay, France

² IFSTTAR, 14-20 Boulevard Newton, 77420 Champs-sur-Marne, France

Energies 2017, 10(10), 1446; https://doi.org/10.3390/en10101446 - 21 Sep 2017

Cited by 37 | Viewed by 6797

Abstract

The large amount of data collected by smart meters is a valuable resource that can be used to better understand consumer behavior and optimize electricity consumption in cities. This paper presents an unsupervised classification approach for extracting typical consumption patterns from data generated [...] Read more.

The large amount of data collected by smart meters is a valuable resource that can be used to better understand consumer behavior and optimize electricity consumption in cities. This paper presents an unsupervised classification approach for extracting typical consumption patterns from data generated by smart electric meters. The proposed approach is based on a constrained Gaussian mixture model whose parameters vary according to the day type (weekday, Saturday or Sunday). The proposed methodology is applied to a real dataset of Irish households collected by smart meters over one year. For each cluster, the model provides three consumption profiles that depend on the day type. In the first instance, the model is applied on the electricity consumption of users during one month to extract groups of consumers who exhibit similar consumption behaviors. The clustering results are then crossed with contextual variables available for the households to show the close links between electricity consumption and household socio-economic characteristics. At the second instance, the evolution of the consumer behavior from one month to another is assessed through variations of cluster sizes over time. The results show that the consumer behavior evolves over time depending on the contextual variables such as temperature fluctuations and calendar events. Full article

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

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13 pages, 218 KiB

Open AccessReview

A Review of the Methane Hydrate Program in Japan

by Ai Oyama^*

and Stephen M. Masutani

Hawaii Natural Energy Institute, University of Hawaii, Honolulu, HI 96822, USA

Energies 2017, 10(10), 1447; https://doi.org/10.3390/en10101447 - 21 Sep 2017

Cited by 71 | Viewed by 7832

Abstract

In this paper, methane hydrate R&D in Japan was examined in the context of Japan’s evolving energy policies. Methane hydrates have been studied extensively in Japanese national R&D programs since 1993, with the goal of utilizing them as an energy resource. Currently, the [...] Read more.

In this paper, methane hydrate R&D in Japan was examined in the context of Japan’s evolving energy policies. Methane hydrates have been studied extensively in Japanese national R&D programs since 1993, with the goal of utilizing them as an energy resource. Currently, the Research Consortium for Methane Hydrate Resources in Japan (MH 21) is in the third phase of a project that began in early 2002. Based on publicly available reports and other publications, and presentations made at the ten International Workshops for Methane Hydrate Research and Development, we have attempted to provide a timeline and a succinct summary of the major technical accomplishments of MH 21 during project Phases 1, 2, and 3. Full article

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

21 pages, 5161 KiB

Open AccessArticle

Stability Analysis and Trigger Control of LLC Resonant Converter for a Wide Operational Range

by Zhijian Fang¹

, Junhua Wang^1,*

, Shanxu Duan², Jianwei Shao¹ and Guozheng Hu³

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

² State Key Laboratory of Advanced Electromagnetic Engineering and Technology, School of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan 430074, China

³ School of Electrical and Electronic Engineering, Hubei Polytechnic University, Huangshi 435003, China

Energies 2017, 10(10), 1448; https://doi.org/10.3390/en10101448 - 21 Sep 2017

Cited by 8 | Viewed by 6246

Abstract

The gain of a LLC resonant converter can vary with the loads that can be used to improve the efficiency and power density for some special applications, where the maximum gain does not apply at the heaviest loads. However, nonlinear gain characteristics can [...] Read more.

The gain of a LLC resonant converter can vary with the loads that can be used to improve the efficiency and power density for some special applications, where the maximum gain does not apply at the heaviest loads. However, nonlinear gain characteristics can make the converters unstable during a major disturbance. In this paper, the stability of an LLC resonant converter during a major disturbance is studied and a trigger control scheme is proposed to improve the converter’s stability by extending the converter’s operational range. Through in-depth analysis of the gain curve of the LLC resonant converter, we find that the switching frequency range is one of the key factors determining the system’s stability performance. The same result is also obtained from a mathematical point of view by utilizing the mixed potential function method. Then a trigger control method is proposed to make the LLC resonant converter stable even during a major disturbance, which can be used to extend the converter’s operational range. Finally, experimental results are given to verify the analysis and proposed control scheme. Full article

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

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16 pages, 1693 KiB

Open AccessArticle

A Scatter Search Heuristic for the Optimal Location, Sizing and Contract Pricing of Distributed Generation in Electric Distribution Systems

by Andrés Felipe Pérez Posada¹, Juan G. Villegas²

and Jesús M. López-Lezama^3,*

¹ Celsia S.A. E.S.P., Carrera 43A No. 1sur-143, Medellín 050022, Colombia

² Supply Chains Management and Innovation Research Group (INCAS), Department of Industrial Engineering, Universidad de Antioquia, 67th Street, No. 53-108, Medellín 050110, Colombia

³ Research Group in Efficient Energy Management (GIMEL), Department of Electrical Engineering, Universidad de Antioquia, 67th Street, No. 53-108, Medellín 050110, Colombia

Energies 2017, 10(10), 1449; https://doi.org/10.3390/en10101449 - 21 Sep 2017

Cited by 24 | Viewed by 4082

Abstract

In this paper we present a scatter search (SS) heuristic for the optimal location, sizing and contract pricing of distributed generation (DG) in electric distribution systems. The proposed optimization approach considers the interaction of two agents: (i) the potential investor and owner of [...] Read more.

In this paper we present a scatter search (SS) heuristic for the optimal location, sizing and contract pricing of distributed generation (DG) in electric distribution systems. The proposed optimization approach considers the interaction of two agents: (i) the potential investor and owner of the DG, and (ii) the Distribution Company (DisCo) in charge of the operation of the network. The DG owner seeks to maximize his profits from selling energy to the DisCo, while the DisCo aims at minimizing the cost of serving the network demand, while meeting network constraints. To serve the expected demand the DisCo is able to purchase energy, through long-term bilateral contracts, from the wholesale electricity market and from the DG units within the network. The interaction of both agents leads to a bilevel programming problem that we solve through a SS heuristic. Computational experiments show that SS outperforms a genetic algorithm hybridized with local search both in terms of solution quality and computational time. Full article

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

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27 pages, 1190 KiB

Open AccessArticle

Low-Load Limit in a Diesel-Ignited Gas Engine

by Richard Hutter^*,†, Johannes Ritzmann, Philipp Elbert and Christopher Onder

¹ Institute for Dynamic Systems and Control, ETH Zurich, 8092 Zurich, Switzerland

^† Current address: Sonneggstrasse 3, 8092 Zurich, Switzerland.

Energies 2017, 10(10), 1450; https://doi.org/10.3390/en10101450 - 21 Sep 2017

Cited by 27 | Viewed by 5930

Abstract

The lean-burn capability of the Diesel-ignited gas engine combined with its potential for high efficiency and low CO

_{2}

emissions makes this engine concept one of the most promising alternative fuel converters for passenger cars. Instead of using a spark plug, the ignition [...] Read more.

The lean-burn capability of the Diesel-ignited gas engine combined with its potential for high efficiency and low CO

_{2}

emissions makes this engine concept one of the most promising alternative fuel converters for passenger cars. Instead of using a spark plug, the ignition relies on the compression-ignited Diesel fuel providing ignition centers for the homogeneous air-gas mixture. In this study the amount of Diesel is reduced to the minimum amount required for the desired ignition. The low-load operation of such an engine is known to be challenging, as hydrocarbon (HC) emissions rise. The objective of this study is to develop optimal low-load operation strategies for the input variables equivalence ratio and exhaust gas recirculation (EGR) rate. A physical engine model helps to investigate three important limitations, namely maximum acceptable HC emissions, minimal CO

_{2}

reduction, and minimal exhaust gas temperature. An important finding is the fact that the high HC emissions under low-load and lean conditions are a consequence of the inability to raise the gas equivalence ratio resulting in a poor flame propagation. The simulations on the various low-load strategies reveal the conflicting demand of lean combustion with low CO

_{2}

emissions and stoichiometric operation with low HC emissions, as well as the minimal feasible dual-fuel load of

3.2

bar brake mean effective pressure. Full article

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

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15 pages, 1189 KiB

Open AccessArticle

Airflow Sensitivity Assessment Based on Underground Mine Ventilation Systems Modeling

by Wacław Dziurzyński^*, Andrzej Krach and Teresa Pałka

Strata Mechanics Institute of the Polish Academy of Sciences, 27 Reymonta Street, Krakow 30-059, Poland

Energies 2017, 10(10), 1451; https://doi.org/10.3390/en10101451 - 21 Sep 2017

Cited by 34 | Viewed by 6105

Abstract

This paper presents a method for determining the sensitivity of the main air flow directions in ventilation subnetworks to changes in aerodynamic resistance and air density in mine workings. The authors have developed formulae for determining the sensitivity of the main subnetwork air [...] Read more.

This paper presents a method for determining the sensitivity of the main air flow directions in ventilation subnetworks to changes in aerodynamic resistance and air density in mine workings. The authors have developed formulae for determining the sensitivity of the main subnetwork air flows by establishing the degree of dependency of the air volume stream in a given working on the variations in resistance or air density of other workings of the network. They have been implemented in the Ventgraph mine ventilation network simulator. This software, widely used in Polish collieries, provides an extended possibility to predict the process of ventilation, air distribution and, in the case of underground fire, the spread of combustion gasses. The new method facilitates an assessment by mine ventilation services of the stability of ventilation systems in exploitation areas and determines the sensitivity of the main subnetwork air flow directions to changes in aerodynamic resistance and air density. Recently in some Polish collieries new longwalls are developed in seams located deeper than the bottom of the intake shaft. Such a solution is called “exploitation below the level of access” or “sublevel”. The new approach may be applied to such developments to assess the potential of changes in direction and air flow rates. In addition, an interpretation of the developed sensitivity indicator is presented. While analyzing air distributions for sublevel exploitation, the application of current numerical models for calculations of the distribution results in tangible benefits, such as the evaluation of the safety or risk levels for such exploitation. Application of the Ventgraph computer program, and particularly the module POŻAR (fire) with the newly developed options, allows for an additional approach to the sensitivity indicator in evaluating air flow safety levels for the risks present during exploitation below the level of the intake shaft. The analyses performed and examples presented enabled useful conclusions for mining practice to be drawn. Full article

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17 pages, 3114 KiB

Open AccessArticle

Directional Overcurrent Relays Coordination Problems in Distributed Generation Systems

by Jakub Ehrenberger^*

and Jan Švec

Department of Electrical Power Engineering, Faculty of Electrical Engineering, Czech Technical University in Prague, 166 27 Prague 6, Czech Republic

Energies 2017, 10(10), 1452; https://doi.org/10.3390/en10101452 - 21 Sep 2017

Cited by 19 | Viewed by 6475

Abstract

This paper proposes a new approach to the distributed generation system protection coordination based on directional overcurrent protections with inverse-time characteristics. The key question of protection coordination is the determination of correct values of all inverse-time characteristics coefficients. The coefficients must be correctly [...] Read more.

This paper proposes a new approach to the distributed generation system protection coordination based on directional overcurrent protections with inverse-time characteristics. The key question of protection coordination is the determination of correct values of all inverse-time characteristics coefficients. The coefficients must be correctly chosen considering the sufficiently short tripping times and the sufficiently long selectivity times. In the paper a new approach to protection coordination is designed, in which not only some, but all the required types of short-circuit contributions are taken into account. In radial systems, if the pickup currents are correctly chosen, protection coordination for maximum contributions is enough to ensure selectivity times for all the required short-circuit types. In distributed generation systems, due to different contributions flowing through the primary and selective protections, coordination for maximum contributions is not enough, but all the short-circuit types must be taken into account, and the protection coordination becomes a complex problem. A possible solution to the problem, based on an appropriately designed optimization, has been proposed in the paper. By repeating a simple optimization considering only one short-circuit type, the protection coordination considering all the required short-circuit types has been achieved. To show the importance of considering all the types of short-circuit contributions, setting optimizations with one (the highest) and all the types of short-circuit contributions have been performed. Finally, selectivity time values are explored throughout the entire protected section, and both the settings are compared. Full article

(This article belongs to the Special Issue Control and Communication in Distributed Generation Systems)

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15 pages, 1452 KiB

Open AccessArticle

Forecasting of Chinese Primary Energy Consumption in 2021 with GRU Artificial Neural Network

by Bingchun Liu¹, Chuanchuan Fu¹, Arlene Bielefield² and Yan Quan Liu^1,2,*

¹ Research Institute of Circular Economy, Tianjin University of Technology, Tianjin 300384, China

² Department of Information and Library Science, Southern Connecticut State University, New Haven, CT 06514, USA

Energies 2017, 10(10), 1453; https://doi.org/10.3390/en10101453 - 21 Sep 2017

Cited by 82 | Viewed by 8023

Abstract

The forecasting of energy consumption in China is a key requirement for achieving national energy security and energy planning. In this study, multi-variable linear regression (MLR) and support vector regression (SVR) were utilized with a gated recurrent unit (GRU) artificial neural network of [...] Read more.

The forecasting of energy consumption in China is a key requirement for achieving national energy security and energy planning. In this study, multi-variable linear regression (MLR) and support vector regression (SVR) were utilized with a gated recurrent unit (GRU) artificial neural network of Chinese energy to establish a forecasting model. The derived model was validated through four economic variables; the gross domestic product (GDP), population, imports, and exports. The performance of various forecasting models was assessed via MAPE and RMSE, and three scenarios were configured based on different sources of variable data. In predicting Chinese energy consumption from 2015 to 2021, results from the established GRU model of the highest predictive accuracy showed that Chinese energy consumption would be likely to fluctuate from 2954.04 Mtoe to 5618.67 Mtoe in 2021. Full article

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26 pages, 5279 KiB

Open AccessArticle

DC Grids for Smart LED-Based Lighting: The EDISON Solution

by Steffen Thielemans^1,2

, Dario Di Zenobio³, Abdellah Touhafi³, Philippe Lataire⁴ and Kris Steenhaut^1,2,3,*

¹ Department of Electronics and Informatics (ETRO), Vrije Universiteit Brussel (VUB), Pleinlaan 2, B1050 Brussels, Belgium

² Interuniversity Microelectronics Centre (IMEC), Kapeldreef 75, B3001 Leuven, Belgium

³ Department of Engineering Technology (INDI), Vrije Universiteit Brussel (VUB), Pleinlaan 2, B1050 Brussels, Belgium

⁴ Department of Electric Engineering and Energy Technology (ETEC), Vrije Universiteit Brussel (VUB), Pleinlaan 2, B1050 Brussels, Belgium

Energies 2017, 10(10), 1454; https://doi.org/10.3390/en10101454 - 21 Sep 2017

Cited by 14 | Viewed by 6413

Abstract

This paper highlights the benefits and possible drawbacks of a DC-based lighting infrastructure for powering Light Emitting Diode (LED)-lamps. It also evaluates the efforts needed for integrating the so called smart lighting and other sensor/actuator based control systems, and compares existing and emerging [...] Read more.

This paper highlights the benefits and possible drawbacks of a DC-based lighting infrastructure for powering Light Emitting Diode (LED)-lamps. It also evaluates the efforts needed for integrating the so called smart lighting and other sensor/actuator based control systems, and compares existing and emerging solutions. It reviews and discusses published work in this field with special focus on the intelligent DC-based infrastructure named EDISON that is primarily dedicated to lighting, but is applicable to building automation in general. The EDISON “PowerLAN” consists of a DC-based infrastructure that offers telecommunication abilities and can be applied to lighting retrofitting scenarios for buildings. Its infrastructure allows simple and efficient powering of DC-oriented devices like LED lamps, sensors and microcontrollers, while offering a wired communication channel. This paper motivates the design choices for organizing DC lighting grids and their associated communication possibilities. It also shows how the EDISON based smart lighting solution is evolving today to include new communication technologies and to further integrate other parts of building management solutions through the OneM2M (Machine to Machine) service bus. Full article

(This article belongs to the Special Issue DC Systems)

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14 pages, 2130 KiB

Open AccessFeature PaperArticle

How Wood Fuels’ Quality Relates to the Standards: A Class-Modelling Approach

by Michela Zanetti^1,*

, Corrado Costa^2,*

, Rosa Greco¹, Stefano Grigolato¹

, Giovanna Ottaviani Aalmo³ and Raffaele Cavalli¹

¹ Università degli Studi di Padova, Department of Land, Environment, Agriculture and Forestry, Laboratorio Analisi BioCombustibili, Viale dell’Università 16, 35020 Legnaro, Padova, Italy

² Consiglio per la ricerca in agricoltura e l’analisi dell’economia agraria (CREA), Centro di Ricerca per l’Ingegneria e le Trasformazioni Agro-alimentari (CREA-IT), Via della Pascolare 16, 00015 Monterotondo Scalo, Rome, Italy

³ Norwegian Institute of Bioeconomy Research, Pb 115, NO-1431 Ås, Norway

Energies 2017, 10(10), 1455; https://doi.org/10.3390/en10101455 - 21 Sep 2017

Cited by 15 | Viewed by 4444

Abstract

The quality requirements of wood biofuels are regulated by a series of harmonized international standards. These standards define the technical parameter limits that influence the quality of solid biomass as a fuel. In 2014 the European reference standard for solid biofuel was replaced [...] Read more.

The quality requirements of wood biofuels are regulated by a series of harmonized international standards. These standards define the technical parameter limits that influence the quality of solid biomass as a fuel. In 2014 the European reference standard for solid biofuel was replaced by the International ISO standard. In the case of wood chips, the main difference between the European and International standards is the definition of particle size distribution classes. In this context, this study analyses the quality of wood chips and its variation over the years according to the “former” (EN 14691-4) and “in force” (ISO 17225-4) standards. A Soft Independent Modelling of Class Analogy (SIMCA) model was built to predict the best quality of wood chips and to clarify the relationship between quality and standard parameters, time and changes in the standard regulations. The results show that, compared to the EN standards, classification with the ISO standards increases the samples belonging to the best quality classes and decreases the not classified samples. Furthermore, all the SIMCA models have a high sensitivity (>90%), reflect the differences introduced to the quality standards and are therefore suitable for monitoring the quality of wood chips and their changes. Full article

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

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19 pages, 6274 KiB

Open AccessArticle

Analysis of Voltage Variation in Silicon Carbide MOSFETs during Turn-On and Turn-Off

by Hui Li, Xinglin Liao^*, Yaogang Hu, Zhangjian Huang and Kun Wang

State Key Laboratory of Power Transmission Equipment & System Security and New Technology, School of Electrical Engineering, Chongqing University, No.174, Shazhengjie Road, Shapingba, Chongqing 400044, China

Energies 2017, 10(10), 1456; https://doi.org/10.3390/en10101456 - 21 Sep 2017

Cited by 21 | Viewed by 7954

Abstract

Due to our limited knowledge about silicon carbide metal–oxide–semiconductor field-effect transistors (SiC MOSFETs), the theoretical analysis and change regularity in terms of the effects of temperature on their switching characteristics have not been fully characterized and understood. An analysis of variation in voltage [...] Read more.

Due to our limited knowledge about silicon carbide metal–oxide–semiconductor field-effect transistors (SiC MOSFETs), the theoretical analysis and change regularity in terms of the effects of temperature on their switching characteristics have not been fully characterized and understood. An analysis of variation in voltage (dV_DS/dt) for SiC MOSFET during turn-on and turn-off has been performed theoretically and experimentally in this paper. Turn-off variation in voltage is not a strong function of temperature, whereas the turn-on variation in voltage has a monotonic relationship with temperature. The temperature dependence is a result of the competing effects between the positive temperature coefficient of the intrinsic carrier concentration and the negative temperature coefficient of the effective mobility of the electrons in SiC MOSFETs. The relationship between variation in voltage and supply voltage, load current, and gate resistance are also discussed. A temperature-based analytical model of dV_DS/dt for SiC MOSFETs was derived in terms of internal parasitic capacitances during the charging and discharging processes at the voltage fall period during turn-on, and the rise period during turn-off. The calculation results were close to the experimental measurements. These results provide a potential junction temperature estimation approach for SiC MOSFETs. In SiC MOSFET-based practical applications, if the turn on dV_DS/dt is sensed, the device temperature can be estimated from the relationship curve of turn on dV_DS/dt versus temperature drawn in advance. Full article

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

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10 pages, 1150 KiB

Open AccessArticle

Analysis of Porous Structure Parameters of Biomass Chars Versus Bituminous Coal and Lignite Carbonized at High Pressure and Temperature—A Chemometric Study

by Adam Smoliński

and Natalia Howaniec^*

Department of Energy Saving and Air Protection, Central Mining Institute, Pl. Gwarków 1, 40-166 Katowice, Poland

Energies 2017, 10(10), 1457; https://doi.org/10.3390/en10101457 - 21 Sep 2017

Cited by 26 | Viewed by 4719

Abstract

The characteristics of the porous structure of carbonized materials affect their physical properties, such as density or strength, their sorption capacity, and their reactivity in thermochemical processing, determining both their applicability as fuels or sorbents and their efficiency in various processes. The porous [...] Read more.

The characteristics of the porous structure of carbonized materials affect their physical properties, such as density or strength, their sorption capacity, and their reactivity in thermochemical processing, determining both their applicability as fuels or sorbents and their efficiency in various processes. The porous structure of chars is shaped by the combined effects of physical and chemical properties of a carbonaceous material and the operating parameters applied in the carbonization process. In the study presented, the experimental dataset covering parameters of various fuels, ranging from biomass through lignite to bituminous coal, and chars produced at 1273 K and under the pressure of 1, 2, 3, and 4 MPa was analyzed with the application of the advanced method of data exploration. The principal component analysis showed that the sample of the highest coal rank was characterized by lower values of parameters reflecting the development of the porous structure of chars. A negative correlation was also observed between the carbon content in a fuel and the evolution of the porous structure of chars at high pressure. The highest total pore volume of chars produced under 1 and 3 MPa and the highest micropore surface area under 3 MPa were reported for a carbonized fuel sample of the highest moisture content. Full article

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

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18 pages, 6298 KiB

Open AccessArticle

Magnet-Sleeve-Sealed Mini Trochoidal-Gear Pump Prototype with Polymer Composite Gear

by Pedro Javier Gamez-Montero^1,*

, Piotr Antoniak², Robert Castilla¹

, Javier Freire³

, Justyna Krawczyk², Jaroslaw Stryczek² and Esteve Codina¹

¹ LABSON, Department of Fluid Mechanics, Universitat Politecnica de Catalunya, Campus Terrassa, Colom 11, 08222 Terrassa, Spain

² Fluid Power Research Group, Faculty of Machine Design Fundamentals and Tribology, Mechanical Engineering Department, Wrocław University of Technology, Ul. Łukasiewicza 7/9, 50-371 Wrocław, Poland

³ LABSON, Mechanical Engineering Department, Universitat Politecnica de Catalunya, Campus Terrassa, Colom 11, 08222 Terrassa, Spain

Energies 2017, 10(10), 1458; https://doi.org/10.3390/en10101458 - 21 Sep 2017

Cited by 21 | Viewed by 6844

Abstract

The trochoidal-gear technology has been growing in groundbreaking fields. Forthcoming applications are demanding to this technology a step forward in the conceiving stage of positive displacement machines. The compendium of the qualities and the inherent characteristics of trochoidal-gear technology, especially towards the gerotor [...] Read more.

The trochoidal-gear technology has been growing in groundbreaking fields. Forthcoming applications are demanding to this technology a step forward in the conceiving stage of positive displacement machines. The compendium of the qualities and the inherent characteristics of trochoidal-gear technology, especially towards the gerotor pump, together with scale/size factor and magnetic-driven transmission has led to the idea of a magnet-sleeve-sealed variable flow mini trochoidal-gear pump. From its original concept, to the last phase of the design development, the proof of concept, this new product will intend to overcome problems such as noise, vibration, maintenance, materials, and dimensions. The paper aims to show the technological path followed from the concept, design, and model, to the manufacture of the first prototype, where the theoretical and numerical approaches are not always directly reflected in the prototype performance results. Early in the design process, from a standard-commercial sintered metal mini trochoidal-gear unit, fundamental characteristics and dimensional limitations have been evaluated becoming the strategic parameters that led to its configuration. The main technical challenge to confront is being sealed with non-exterior driveshaft, ensuring that the whole interior is filled and wetted with working fluid and helping the hydrodynamic film formation, the pumping effect, and the heat dissipation. Subsequently, the mini pump architecture, embodiment, methodology, materials, and manufacture are presented. The trend of applications of polymer composite materials and their benefits wanted to be examined with this new mini pump prototype, and a pure polyoxymethylene mini trochoidal-gear set has been designed and manufactured. Finally, both the sintered and the polymer trochoidal-gear units have been experimentally tested in an in-house full-instrumented mini test bench. Although the main goal of the presented work is the development of a new mini trochoidal-gear pump prototype rather than a numerical study, the results have been compared with numerical simulation. Subsequently, the prototype of the mini trochoidal-gear pump is a feasible proof of concept supported by functional indexes and the experimental results. Full article

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

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18 pages, 7476 KiB

Open AccessArticle

Case Studies of Environmental Visualization

by Panagiotis Patlakas^1,*, Georgios Koronaios², Rokia Raslan³, Gareth Neighbour¹

and Hasim Altan⁴

¹ School of Engineering and the Built Environment, Birmingham City University, 15 Bartholomew Row, Birmingham B5 5JU, UK

² Hodkinson Consultancy, 59-65 Lowlands Road, Harrow HA1 3AW, UK

³ Institute for Environmental Design and Engineering (IEDE), University College London, 14 Upper Woburn Place, London WC1H 0NN, UK

⁴ Department of Architectural Engineering, University of Sharjah, P. O. Box 27272 Sharjah, UAE

Energies 2017, 10(10), 1459; https://doi.org/10.3390/en10101459 - 21 Sep 2017

Cited by 5 | Viewed by 4943

Abstract

The performance gap between simulation and reality has been identified as a major challenge to achieving sustainability in the Built Environment. While Post-Occupancy Evaluation (POE) surveys are an integral part of better understanding building performance, and thus addressing this issue, the importance of [...] Read more.

The performance gap between simulation and reality has been identified as a major challenge to achieving sustainability in the Built Environment. While Post-Occupancy Evaluation (POE) surveys are an integral part of better understanding building performance, and thus addressing this issue, the importance of POE remains relatively unacknowledged within the wider Built Environment community. A possible reason that has been highlighted is that POE survey data is not easily understood and utilizable by non-expert stakeholders, including designers. A potential method by which to address this is the visualization method, which has well established benefits for communication of big datasets. This paper presents two case studies where EnViz (short for “Environmental Visualization”), a prototype software application developed for research purposes, was utilized and its effectiveness tested via a range of analysis tasks. The results are discussed and compared with those of previous work that utilized variations of the methods presented here. The paper concludes by presenting the lessons drawn from the five-year period of EnViz, emphasizing the potential of environmental visualization for decision support in environmental design and engineering for the built environment, and suggests directions for future development. Full article

(This article belongs to the Special Issue Selected Papers from ZEMCH 2016: Building Energy Performance Evaluation/Simulation)

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16 pages, 5089 KiB

Open AccessArticle

A Novel Optimal Current Trajectory Control Strategy of IPMSM Considering the Cross Saturation Effects

by Huimin Li, Jian Gao^*, Shoudao Huang and Peng Fan

College of Electrical and Information Engineering, Hunan University, Changsha 410082, China

Energies 2017, 10(10), 1460; https://doi.org/10.3390/en10101460 - 21 Sep 2017

Cited by 4 | Viewed by 3522

Abstract

Abstract: The nonlinearity and uncertain variation of machine parameters are always caused by cross coupling and magnetic saturation effects, which are easily neglected in the conventional control strategy. In this paper, a current trajectory control strategy (CTCS) is proposed to take the [...] Read more.

Abstract: The nonlinearity and uncertain variation of machine parameters are always caused by cross coupling and magnetic saturation effects, which are easily neglected in the conventional control strategy. In this paper, a current trajectory control strategy (CTCS) is proposed to take the cross coupling and magnetic saturation effects into account under voltage and current constraints. It can be considered as a calculating method considering parameter variation and separating among each iteration step which treats the calculated result of the former step as the initial value of the next step. At first, the torque command is translated into the current reference. Then, the increments between the target value and real value of the torque and the voltage are respectively calculated, which are subsequently converted into the current modification vector in di_d, di_q framework for further analysis. In order to take the influence caused by cross coupling and magnetic saturation effects on the CTCS into consideration, self and mutual inductances are analyzed by finite element analysis (FEA). The results of the simulation and experiment show that the rapid response and robustness on reference speed variation could be achieved by employing the proposed CTCS, and the seamless switching between the constant torque and flux-weakening operation can also be realized. Full article

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

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11 pages, 2156 KiB

Open AccessArticle

The Energy Footprint of China’s Textile Industry: Perspectives from Decoupling and Decomposition Analysis

by Laili Wang^1,2,*, Yi Li²

and Wanwen He¹

¹ Fashion Institute, Zhejiang Sci-Tech University, Hangzhou 310018, China

² Ecological Civilization Research Center of Zhejiang Province, Zhejiang Sci-Tech University, Hangzhou 310018, China

Energies 2017, 10(10), 1461; https://doi.org/10.3390/en10101461 - 22 Sep 2017

Cited by 27 | Viewed by 8638

Abstract

Energy is the essential input for operations along the industrial manufacturing chain of textiles. China’s textile industry is facing great pressure on energy consumption reduction. This paper presents an analysis of the energy footprint (EFP) of China’s textile industry from 1991 [...] Read more.

Energy is the essential input for operations along the industrial manufacturing chain of textiles. China’s textile industry is facing great pressure on energy consumption reduction. This paper presents an analysis of the energy footprint (EFP) of China’s textile industry from 1991 to 2015. The relationship between EFP and economic growth in the textile industry was investigated with a decoupling index approach. The logarithmic mean Divisia index approach was applied for decomposition analysis on how changes in key factors influenced the EFP of China’s textile industry. Results showed that the EFP of China’s textile industry increased from 41.1 Mt in 1991 to 99.6 Mt in 2015. EFP increased fastest in the period of 1996–2007, with an average annual increasing rate of 7.7 percent, especially from 2001 to 2007 (8.5 percent). Manufacture of textile sector consumed most (from 58 percent to 76 percent) of the energy among the three sub-sectors, as it has lots of energy-intensive procedures. EFP and economic growth were in a relative decoupling state for most years of the researched period. Their relationship showed a clear tendency toward decoupling. Industrial scale was the most important factor that led to the increase of EFP, while decreasing energy intensity contributed significantly to reducing the EFP. The promoting effect of the factors was larger than the inhibiting effect on EFP in most years from 1991 to 2015. Full article

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

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23 pages, 9777 KiB

Open AccessArticle

A High-Frequency Isolation (HFI) Charging DC Port Combining a Front-End Three-Level Converter with a Back-End LLC Resonant Converter

by Guowei Cai^*, Duolun Liu, Chuang Liu, Wei Li and Jiajun Sun

School of Electrical Engineering, Northeast Electric Power University, Jilin 132012, China

Energies 2017, 10(10), 1462; https://doi.org/10.3390/en10101462 - 22 Sep 2017

Cited by 7 | Viewed by 10363

Abstract

The high-frequency isolation (HFI) charging DC port can serve as the interface between unipolar/bipolar DC buses and electric vehicles (EVs) through the two-power-stage system structure that combines the front-end three-level converter with the back-end logical link control (LLC) resonant converter. The DC output [...] Read more.

The high-frequency isolation (HFI) charging DC port can serve as the interface between unipolar/bipolar DC buses and electric vehicles (EVs) through the two-power-stage system structure that combines the front-end three-level converter with the back-end logical link control (LLC) resonant converter. The DC output voltage can be maintained within the desired voltage range by the front-end converter. The electrical isolation can be realized by the back-end LLC converter, which has the bus converter function. According to the three-level topology, the low-voltage rating power devices can be adapted for half-voltage stress of the total DC grid, and the PWM phase-shift control can double the equivalent switching frequency to greatly reduce the filter volume. LLC resonant converters have advance characteristics of inverter-side zero-voltage-switching (ZVS) and rectifier-side zero-current switching (ZCS). In particular, it can achieve better performance under quasi-resonant frequency mode. Additionally, the magnetizing current can be modified following different DC output voltages, which have the self-adaptation ZVS condition for decreasing the circulating current. Here, the principles of the proposed topology are analyzed in detail, and the design conditions of the three-level output filter and high-frequency isolation transformer are explored. Finally, a 20 kW prototype with the 760 V input and 200–500 V output are designed and tested. The experimental results are demonstrated to verify the validity and performance of this charging DC port system structure. Full article

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

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27 pages, 8313 KiB

Open AccessArticle

Comparison of Different Solar-Assisted Air Conditioning Systems for Australian Office Buildings

by Yunlong Ma^1,*

, Suvash C. Saha^1,*, Wendy Miller¹

and Lisa Guan²

¹ School of Chemistry, Physics, and Mechanical Engineering, Queensland University of Technology (QUT), 2 George Street, GPO Box 2434, Brisbane QLD 4001, Australia

² University of Technology Sydney, Faculty of Design Architecture and Building, Ultimo NSW 2007, Australia

Energies 2017, 10(10), 1463; https://doi.org/10.3390/en10101463 - 22 Sep 2017

Cited by 41 | Viewed by 8317

Abstract

This study has investigated the feasibility of three different solar-assisted air conditioning systems for typical medium-sized office buildings in all eight Australian capital cities using the whole building energy simulation software EnergyPlus. The studied solar cooling systems include: solar desiccant-evaporative cooling (SDEC) system, [...] Read more.

This study has investigated the feasibility of three different solar-assisted air conditioning systems for typical medium-sized office buildings in all eight Australian capital cities using the whole building energy simulation software EnergyPlus. The studied solar cooling systems include: solar desiccant-evaporative cooling (SDEC) system, hybrid solar desiccant-compression cooling (SDCC) system, and solar absorption cooling (SAC) system. A referenced conventional vapor compression variable-air-volume (VAV) system has also been investigated for comparison purpose. The technical, environmental, and economic performances of each solar cooling system have been evaluated in terms of solar fraction (SF), system coefficient of performance (COP), annual HVAC (heating, ventilation, and air conditioning) electricity consumption, annual CO₂ emissions reduction, payback period (PBP), and net present value (NPV). The results demonstrate that the SDEC system consumes the least energy in Brisbane and Darwin, achieving 56.9% and 82.1% annual energy savings, respectively, compared to the conventional VAV system, while for the other six cities, the SAC system is the most energy efficient. However, from both energy and economic aspects, the SDEC system is more feasible in Adelaide, Brisbane, Darwin, Melbourne, Perth, and Sydney because of high annual SF and COP, low yearly energy consumption, short PBP and positive NPV, while for Canberra and Hobart, although the SAC system achieves considerable energy savings, it is not economically beneficial due to high initial cost. Therefore, the SDEC system is the most economically beneficial for most of Australian cities, especially in hot and humid climates. The SAC system is also energy efficient, but is not as economic as the SDEC system. However, for Canberra and Hobart, reducing initial cost is the key point to achieve economic feasibility of solar cooling applications. Full article

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

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23 pages, 3760 KiB

Open AccessArticle

Zonal Voltage Control Combined Day-Ahead Scheduling and Real-Time Control for Distribution Networks with High Proportion of PVs

by Chuanliang Xiao^1,*, Bo Zhao², Ming Ding¹, Zhihao Li² and Xiaohui Ge²

¹ School of Electrical Engineering and Automation, Hefei University of Technology, Hefei 230009, China

² State Grid Zhejiang Electric Power Research Institute, Hangzhou 310014, China

Energies 2017, 10(10), 1464; https://doi.org/10.3390/en10101464 - 22 Sep 2017

Cited by 17 | Viewed by 4216

Abstract

Considering the possible overvoltage caused by the high proportion of photovoltaic systems (PVs) accessing distribution networks in the future, traditional centralized control methods will be too complex to satisfy the control response time demands. To solve this problem this paper presents a two-level [...] Read more.

Considering the possible overvoltage caused by the high proportion of photovoltaic systems (PVs) accessing distribution networks in the future, traditional centralized control methods will be too complex to satisfy the control response time demands. To solve this problem this paper presents a two-level voltage control method. At the day-ahead level, based on the PV-output and load-demand forecast, a community detection algorithm using an improved modularity index is introduced to divide the distribution network into clusters; a day-ahead optimal scheduling is drawn up on the basis of the network partition, and the objective is to minimize the operation costs of the distribution networks. At the real-time level, under the day-ahead optimal scheduling and network partition of the upper level, a real-time optimal voltage control algorithm is proposed based on the real-time operation data of the distribution networks, and the objective is to correct the day-ahead optimal scheduling through modifications. Thus, the algorithm realizes the combination of day-ahead scheduling and real-time control and achieves complete zonal voltage control for future distribution networks with high proportion of PVs. The proposed method can not only optimize the tap operation of an on-load tap changer (OLTC), improving the PV hosting capacity of the distribution network for a high proportion of PVs, but can also reduce the number of control nodes and simplify the control process to reduce the optimization time. The proposed approach is applied to a real, practical, 10 kV, 62-node feeder in Zhejiang Province of China to verify its feasibility and effectiveness. Full article

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18 pages, 3023 KiB

Open AccessArticle

Demand Response Unit Commitment Problem Solution for Maximizing Generating Companies’ Profit

by K. Selvakumar^*

, K. Vijayakumar

and C. S. Boopathi

Department of EEE, SRM University, Chennai 603203, India

Energies 2017, 10(10), 1465; https://doi.org/10.3390/en10101465 - 22 Sep 2017

Cited by 16 | Viewed by 5492

Abstract

Over the recent years there has been an immense growth in load consumption due to which, Load Management (LM) has become more significant. Energy providers around the world apply different load management concepts and techniques to improve the load profile. In order to [...] Read more.

Over the recent years there has been an immense growth in load consumption due to which, Load Management (LM) has become more significant. Energy providers around the world apply different load management concepts and techniques to improve the load profile. In order to reduce the stress over the load management, Demand Response Unit Commitment (DRUC), a new concept, has been implemented in this paper. The main feature of this concept is that both the energy providers and consumers must participate in order to get mutual benefits hence maximizing each of their profits. In this paper we discuss the time-based Demand Response Program since there is no penalty observed in this program. When the Demand Response was combined with Unit Commitment and compiled it was observed that a satisfactory solution resulted, which is proved to be mutually beneficial for both Generating Companies (GENCOs) and their customers. Here, we have used a Cat Swarm Optimization (CSO) technique to find the solution for the DRUC problem. The results are obtained using CSO technique for UC problem with and without DR program. This is compared with the results obtained using other conventional methods. The test system considered for the study is IEEE39 bus system. Full article

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

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15 pages, 2738 KiB

Open AccessArticle

Relationship between Creep Property and Loading-Rate Dependence of Strength of Artificial Methane-Hydrate-Bearing Toyoura Sand under Triaxial Compression

by Kuniyuki Miyazaki^1,*, Norio Tenma² and Tsutomu Yamaguchi³

¹ Institute for Geo-Resources and Environment, National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8567, Japan

² Research Institute of Energy Frontier, National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8569, Japan

³ Department of Environmental Science, Toho University, Funabashi 274-8510, Japan

Energies 2017, 10(10), 1466; https://doi.org/10.3390/en10101466 - 22 Sep 2017

Cited by 27 | Viewed by 4700

Abstract

Methane hydrate is anticipated to be a promising energy resource. It is essential to consider the mechanical properties of a methane hydrate reservoir to ensure sustainable production, since its mechanical behavior may affect the integrity of the production well, the occurrence of geohazards, [...] Read more.

Methane hydrate is anticipated to be a promising energy resource. It is essential to consider the mechanical properties of a methane hydrate reservoir to ensure sustainable production, since its mechanical behavior may affect the integrity of the production well, the occurrence of geohazards, and gas productivity. In particular, the creep property of methane-hydrate-bearing sediment is thought to have great significance in the long-term prediction of the mechanical behaviors of a reservoir. In earlier studies, triaxial compression tests were conducted on artificial methane-hydrate-bearing Toyoura sand under three axial-loading conditions, i.e., constant-strain-rate test, constant-stress-rate test, and creep (constant-stress) test. In this paper, the time-dependent properties of the methane-hydrate-bearing Toyoura sand observed in these tests were quantitatively discussed and found to be almost in agreement. The creep life obtained from the creep tests had a reasonably strong correlation with the loading-rate dependencies of strength, obtained from the constant-strain-rate tests and constant-stress-rate tests based on a simple hypothesis. The findings are expected to be used to develop a constitutive model considering the time-dependent behaviors of hydrate-bearing soil in future studies, and to improve the reliability of long-term prediction of the geomechanical response to gas extraction from a reservoir. Full article

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2 pages, 163 KiB

Open AccessEditorial

Engineering Fluid Dynamics

by Bjørn H. Hjertager

Department of Mechanical and Structural Engineering and Materials Science, University of Stavanger, N-4016 Stavanger, Norway

Energies 2017, 10(10), 1467; https://doi.org/10.3390/en10101467 - 22 Sep 2017

Cited by 1 | Viewed by 3469

Abstract

Over the last few decades, the use of computational fluid dynamics (CFD) and experimental fluid dynamics (EFD) methods has penetrated into all fields of engineering. [...] Full article

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

28 pages, 3080 KiB

Open AccessArticle

Designing a Model for the Global Energy System—GENeSYS-MOD: An Application of the Open-Source Energy Modeling System (OSeMOSYS)

by Konstantin Löffler^1,2,*

, Karlo Hainsch¹, Thorsten Burandt¹

, Pao-Yu Oei^1,2,3, Claudia Kemfert^2,3,4 and Christian Von Hirschhausen^1,2

¹ Workgroup for Infrastructure and Policy, TU Berlin, Straße des 17. Juni 135, 10623 Berlin, Germany

² Energy, Transport, and Environment, DIW Berlin, Mohrenstraße 58, 10117 Berlin, Germany

³ German Advisory Council on Environment, SRU, Luisenstraße 46, 10117 Berlin, Germany

⁴ Energy Economics and Sustainability, Hertie School of Governance, Friedrichstraße 180, 10117 Berlin, Germany

Energies 2017, 10(10), 1468; https://doi.org/10.3390/en10101468 - 22 Sep 2017

Cited by 165 | Viewed by 25296

Abstract

This paper develops a path for the global energy system up to 2050, presenting a new application of the open-source energy modeling system (OSeMOSYS) to the community. It allows quite disaggregate energy and emission analysis: Global Energy System Model (GENeSYS-MOD) uses a system [...] Read more.

This paper develops a path for the global energy system up to 2050, presenting a new application of the open-source energy modeling system (OSeMOSYS) to the community. It allows quite disaggregate energy and emission analysis: Global Energy System Model (GENeSYS-MOD) uses a system of linear equations of the energy system to search for lowest-cost solutions for a secure energy supply, given externally defined constraints, mainly in terms of CO₂-emissions. The general algebraic modeling system (GAMS) version of OSeMOSYS is updated to the newest version and, in addition, extended and enhanced to include e.g., a modal split for transport, an improved trading system, and changes to storages. The model can be scaled from small-scale applications, e.g., a company, to cover the global energy system. The paper also includes an application of GENeSYS-MOD to analyze decarbonization scenarios at the global level, broken down into 10 regions. Its main focus is on interdependencies between traditionally segregated sectors: electricity, transportation, and heating; which are all included in the model. Model calculations suggests that in order to achieve the 1.5–2 °C target, a combination of renewable energy sources provides the lowest-cost solution, solar photovoltaic being the dominant source. Average costs of electricity generation in 2050 are about 4 €cents/kWh (excluding infrastructure and transportation costs). Full article

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

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15 pages, 9636 KiB

Open AccessArticle

A Novel Algorithm for Establishing a Balanced Synchronization Hierarchy with Spare Masters (BSHSM) for the IEEE 1588 Precision Time Protocol

by Nguyen Xuan Tien

and Jong Myung Rhee^*

Department of Information and Communications Engineering, Myongji University, 116 Myongji-ro, Yongin, Gyeonggi 17058, Korea

Energies 2017, 10(10), 1469; https://doi.org/10.3390/en10101469 - 22 Sep 2017

Cited by 2 | Viewed by 5168

Abstract

The best master clock (BMC) algorithm is currently used to establish the master-slave hierarchy for the IEEE 1588 Precision Time Protocol (PTP). However, the BMC algorithm may create an unbalanced hierarchy that contains several boundary clocks with a large number of slaves in [...] Read more.

The best master clock (BMC) algorithm is currently used to establish the master-slave hierarchy for the IEEE 1588 Precision Time Protocol (PTP). However, the BMC algorithm may create an unbalanced hierarchy that contains several boundary clocks with a large number of slaves in comparison to other clocks. The unbalanced hierarchy can cause problems, such as high communication load and high bandwidth consumption in boundary clocks. Additionally, the BMC algorithm does not provide any fast recovery mechanism in the case of a master failure. In this paper, we propose a novel balanced synchronization hierarchy with spare masters (BSHSM) algorithm to establish a balanced master-slave hierarchy and to provide a fast recovery mechanism in the case of master failures for the PTP. The BSHSM algorithm establishes the master-slave hierarchy with boundary clocks that have a balanced number of slaves. In doing so, it solves the problems caused by the unbalanced master-slave hierarchy. Additionally, the BSHSM algorithm provides a fast recovery mechanism by selecting a spare master for each boundary clock; this allows a boundary clock to immediately select a new master clock when its current master has failed or is disconnected. The fast recovery mechanism reduces the period of running freely and clock drift in clocks, improving the synchronization quality of the PTP. Various simulations were conducted using the network simulation OMNeT++ v4.6 to analyze, evaluate, and compare the performance of the BSHSM and BMC algorithms. The simulation results show that the synchronization hierarchy of the BSHSM algorithm is much more balanced than the BMC algorithm, and it also has a shorter period of recovery. Full article

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

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18 pages, 1729 KiB

Open AccessArticle

Trends in Data Centre Energy Consumption under the European Code of Conduct for Data Centre Energy Efficiency

by Maria Avgerinou, Paolo Bertoldi and Luca Castellazzi^*

European Commission, Joint Research Centre (JRC), Directorate C-Energy, Transport and Climate, Via E. Fermi 2749, I-21027 Ispra (VA), Italy

Energies 2017, 10(10), 1470; https://doi.org/10.3390/en10101470 - 22 Sep 2017

Cited by 247 | Viewed by 23260

Abstract

Climate change is recognised as one of the key challenges humankind is facing. The Information and Communication Technology (ICT) sector including data centres generates up to 2% of the global CO₂ emissions, a number on par to the aviation sector contribution, and [...] Read more.

Climate change is recognised as one of the key challenges humankind is facing. The Information and Communication Technology (ICT) sector including data centres generates up to 2% of the global CO₂ emissions, a number on par to the aviation sector contribution, and data centres are estimated to have the fastest growing carbon footprint from across the whole ICT sector, mainly due to technological advances such as the cloud computing and the rapid growth of the use of Internet services. There are no recent estimations of the total energy consumption of the European data centre and of their energy efficiency. The aim of this paper is to evaluate, analyse and present the current trends in energy consumption and efficiency in data centres in the European Union using the data submitted by companies participating in the European Code of Conduct for Data Centre Energy Efficiency programme, a voluntary initiative created in 2008 in response to the increasing energy consumption in data centres and the need to reduce the related environmental, economic and energy supply security impacts. The analysis shows that the average Power Usage Effectiveness (PUE) of the facilities participating in the programme is declining year after year. This confirms that voluntary approaches could be effective in addressing climate and energy issue. Full article

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15 pages, 7480 KiB

Open AccessArticle

Integrating Embedded Discrete Fracture and Dual-Porosity, Dual-Permeability Methods to Simulate Fluid Flow in Shale Oil Reservoirs

by Weirong Li^1,*, Zhenzhen Dong^2,* and Gang Lei^1,*

¹ Beijing Innovation Center for Engineering Science and Advanced Technology (BIC-ESAT), Peking University, Beijing 100193, China

² Petroleum Department, Xi’an Shiyou University, Xi’an 710065, China

Energies 2017, 10(10), 1471; https://doi.org/10.3390/en10101471 - 23 Sep 2017

Cited by 24 | Viewed by 5642

Abstract

The oil recovery factor from shale oil remains low, about 5 to 7% of the oil in place. How to increase oil recovery from shale oil reservoirs is attracting more and more attention. CO₂ huff-and-puff was historically considered one of the best [...] Read more.

The oil recovery factor from shale oil remains low, about 5 to 7% of the oil in place. How to increase oil recovery from shale oil reservoirs is attracting more and more attention. CO₂ huff-and-puff was historically considered one of the best approaches to improve the oil rate. Most previous simulation studies have been based on dual porosity, but simulation results from dual-porosity models have not been as accurate as discrete fracture models in composition modeling. This study proposes a new model that integrates the embedded discrete fracture model and the dual-porosity, dual-permeability model (DPDP). The newly developed method could explicitly describe large-scale fractures as flow conduits by embedded discrete fracture modeling and could model the flow in small- and medium-length fractures by DPDP modeling. In this paper, we first introduce four different non-neighboring connections and the way to calculate the transmissibility among different media in the new model. Then, the paper compares the performance of the new method, discrete fracture modeling, DPDP modeling, and embedded discrete fracture modeling for production from oil reservoirs. Following, the paper carries out a series of simulations to analyze the effects of hydraulic fracture stages, hydraulic fracture permeabilities, and natural fracture permeabilities on the CO₂ huff-and-puff process based on the new method. In addition, the injection cycle and soaking time are investigated to optimize CO₂ huff-and-puff performance. This study is the first to integrate embedded discrete fracture modeling with DPDP modeling to simulate the CO₂ huff-and-puff process in a shale oil reservoir with natural fractures. This paper also provides detailed discussions and comparisons on the integrated strategy, embedded discrete fracture modeling, discrete fracture modeling, and dual-porosity, dual-permeability modeling in the context of fracture simulation with a compositional model. Most importantly, this study answers the question regarding how fractures affect CO₂ huff-and-puff and how to optimize the CO₂ huff-and-puff process in a reservoir with natural fractures. Full article

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

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16 pages, 1363 KiB

Open AccessArticle

Study on Nested-Structured Load Shedding Method of Thermal Power Stations Based on Output Fluctuations

by Liping Wang, Minghao Liu^*, Boquan Wang, Jiajie Wu and Chuangang Li

Renewable Energy School, North China Electric Power University, Beijing 102206, China

Energies 2017, 10(10), 1472; https://doi.org/10.3390/en10101472 - 23 Sep 2017

Cited by 2 | Viewed by 4063

Abstract

The balance of electric power and energy is important for designing power stations’ load distribution, capacity allocation, and future operation plans, and is thus of vital significance for power design and planning departments. In this paper, we analyzed the correlation between the output [...] Read more.

The balance of electric power and energy is important for designing power stations’ load distribution, capacity allocation, and future operation plans, and is thus of vital significance for power design and planning departments. In this paper, we analyzed the correlation between the output fluctuations of power stations and the load fluctuations of the power system in order to study the load change of the power system within a year/month/day, and the output variation amongst the power stations in operation. Reducing the output of hydropower stations or increasing the output of thermal power stations (TPS) could keep the monthly adjustment coefficient of the power system within a certain range, and thus balance the power system’s electric power and energy. The method for calculating the balance of electric power and energy of TPS is also improved. The nested-structured load shedding method (NSLSM), which is based on the calculation principle of the load shedding method, is put forward to iteratively calculate the peak shaving capacity and non-peak shaving capacity of every single thermal power station. In this way, the output process of each thermal power station can be obtained. According to the results and analysis of an example, the proposed methods of calculating monthly adjustment coefficients and the balance of electric power and energy of a thermal power station are validated in terms of correctness, feasibility, and effectiveness. Full article

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

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14 pages, 2925 KiB

Open AccessArticle

Evaluating the Effect of Distributed Generation on Power Supply Capacity in Active Distribution System Based on Sensitivity Analysis

by Yajing Gao^1,*, Wenhai Yang¹, Jing Zhu^2,*, Jiafeng Ren¹ and Peng Li¹

¹ School of Electrical and Electronic Engineering, North China Electric Power University, Baoding 071003, China

² Maintenance Branch Company of State Grid Fujian Electric Power Co., Ltd, Xiamen 361000, China

Energies 2017, 10(10), 1473; https://doi.org/10.3390/en10101473 - 23 Sep 2017

Cited by 5 | Viewed by 3818

Abstract

In active distribution system (ADS), the access of distributed generation (DG) can effectively improve the power supply capacity (PSC). In order to explore the effect of DG on the PSC, the influence of accessed DG on the power supply of ADS has been [...] Read more.

In active distribution system (ADS), the access of distributed generation (DG) can effectively improve the power supply capacity (PSC). In order to explore the effect of DG on the PSC, the influence of accessed DG on the power supply of ADS has been studied based on generalized sensitivity analysis (SA). On the basis of deriving and obtaining the sensitivity of the evaluation indexes of the PSC to the parameters of connected DG, seeking for the DG access instruction for the purpose of improving the PSC, PSC evaluation model with inserted DG is established based on SA. The change degrees and trends of the PSC and its evaluation indexes caused by the slight increase of DG are calculated rapidly, which provides reference for the planning and operation of ADS. Finally, the feasibility and validity of the proposed theory are validated via IEEE 14-node case study. Full article

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

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18 pages, 5687 KiB

Open AccessArticle

Global Gust Climate Evaluation and Its Influence on Wind Turbines

by Christopher Jung^*, Dirk Schindler, Alexander Buchholz and Jessica Laible

Environmental Meteorology, University of Freiburg, 79085 Freiburg, Germany

Energies 2017, 10(10), 1474; https://doi.org/10.3390/en10101474 - 23 Sep 2017

Cited by 28 | Viewed by 6185

Abstract

Strong gusts negatively affect wind turbines in many ways. They (1) harm their structural safety; (2) reduce their wind energy output; and (3) lead to a shorter wind turbine rotor blade fatigue life. Therefore, the goal of this study was to provide a [...] Read more.

Strong gusts negatively affect wind turbines in many ways. They (1) harm their structural safety; (2) reduce their wind energy output; and (3) lead to a shorter wind turbine rotor blade fatigue life. Therefore, the goal of this study was to provide a global assessment of the gust climate, considering its influence on wind turbines. The gust characteristics analyzed were: (1) the gust speed return values for 30, 50 and 100 years; (2) the share of gust speed exceedances of cut-out speed; and (3) the gust factor. In order to consider the seasonal variation of gust speed, gust characteristics were evaluated on a monthly basis. The global monthly wind power density was simulated and geographical restrictions were applied to highlight gust characteristics in areas that are generally suitable for wind turbine installation. Gust characteristics were computed based on ERA-interim data on a 1° × 1° spatial resolution grid. After comprehensive goodness-of-fit evaluation of 12 theoretical distributions, Wakeby distribution was used to compute gust speed return values. Finally, the gust characteristics were integrated into the newly developed wind turbine gust index. It was found that the Northeastern United States and Southeast Canada, Newfoundland, the southern tip of South America, and Northwestern Europe are most negatively affected by the impacts of gusts. In regions where trade winds dominate, such as eastern Brazil, the Sahara, southern parts of Somalia, and southeastern parts of the Arabian Peninsula, the gust climate is well suitable for wind turbine installation. Full article

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

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20 pages, 3670 KiB

Open AccessArticle

Wind Power Ramps Driven by Windstorms and Cyclones

by Madalena Lacerda^*, António Couto

and Ana Estanqueiro

Unidade de Energias Renováveis e Integração de Sistemas de Energia, Laboratório Nacional de Energia e Geologia, I.P. (LNEG), 1649-038 Lisbon, Portugal

Energies 2017, 10(10), 1475; https://doi.org/10.3390/en10101475 - 23 Sep 2017

Cited by 7 | Viewed by 4055

Abstract

The increase in the wind power predictability assumes a very important role for secure power system operation at minimum costs, especially in situations with severe changes in wind power production. In order to improve the forecast of such events, also known as “wind [...] Read more.

The increase in the wind power predictability assumes a very important role for secure power system operation at minimum costs, especially in situations with severe changes in wind power production. In order to improve the forecast of such events, also known as “wind power ramp events”, the underlying role of some severe meteorological phenomena in triggering wind power ramps must be clearly understood. In this paper, windstorm and cyclone detection algorithms are implemented using historical reanalysis data allowing the identification of key characteristics (e.g., location, intensity and trajectories) of the events with the highest impact on the wind power ramp events in Portugal. The results show a strong association between cyclones/windstorms and wind power ramp events. Moreover, the results highlight that it is possible to use some features of these meteorological phenomena to detect, in an early stage, severe wind power ramps thus creating the possibility to develop operational decision tools in order to support the security of power systems with high amounts of wind power generation. Full article

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13 pages, 811 KiB

Open AccessArticle

A Novel Sliding Mode Control Scheme for a PMSG-Based Variable Speed Wind Energy Conversion System

by Florentino Chavira^1,†, S. Ortega-Cisneros^2,*,†

and Jorge Rivera^3,†

¹ University Center for Exact Sciences and Engineering, University of de Guadalajara, Guadalajara 44430, Mexico

² Advanced Studies and Research Center (CINVESTAV), National Polytechnic Institute (IPN), Guadalajara Campus, Zapopan 45015, Mexico

³ CONACYT–Advanced Studies and Research Center (CINVESTAV), National Polytechnic Institute (IPN), Guadalajara Campus, Zapopan 45015, Mexico

^† These authors contributed equally to this work.

Energies 2017, 10(10), 1476; https://doi.org/10.3390/en10101476 - 24 Sep 2017

Cited by 9 | Viewed by 4595

Abstract

This work proposes a novel control scheme for a variable speed wind turbine system based on the permanent magnet synchronous generator. Regions II and III for a wind speed profile are considered, hence the control is designed for maximizing the generated power from [...] Read more.

This work proposes a novel control scheme for a variable speed wind turbine system based on the permanent magnet synchronous generator. Regions II and III for a wind speed profile are considered, hence the control is designed for maximizing the generated power from the wind turbine when the wind speed is below the nominal wind speed, and to saturate the generated power when the wind speed is above its nominal value in order to avoid damage to the system. Based on nonlinear models, the control scheme is also designed for introducing robustness to the closed-loop system. The pitch angle reference signal is also designed based on a mathematical model of the system, yielding in that way to a great performance of the wind turbine as predicted by the numeric simulations. Full article

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

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20 pages, 374 KiB

Open AccessArticle

Optimal Allocation of Photovoltaic Systems and Energy Storage Systems based on Vulnerability Analysis

by Ryusuke Konishi^1,3 and Masaki Takahashi^2,3,*

¹ Graduate School of Science and Technology, Keio University, Yokohama 223-0061, Japan

² Faculty of Science and Technology, Keio University, Yokohama 223-0061, Japan

³ Japan Science and Technology Agency (JST), CREST, Kawaguchi 332-0012, Japan

Energies 2017, 10(10), 1477; https://doi.org/10.3390/en10101477 - 24 Sep 2017

Cited by 9 | Viewed by 4244

Abstract

There is a growing need to connect renewable energy systems (REs), such as photovoltaic systems (PVs), to the power grid for solving environmental problems such as global warming. However, an electricity grid with RE is vulnerable to problems of power shortage and surplus [...] Read more.

There is a growing need to connect renewable energy systems (REs), such as photovoltaic systems (PVs), to the power grid for solving environmental problems such as global warming. However, an electricity grid with RE is vulnerable to problems of power shortage and surplus owing to the uncertainty of RE outputs and grid failures. Energy storage systems (ESSs) can be used to solve supply reliability problems, but their installation should be minimized considering their high costs. This study proposes a method to optimize the allocations of PVs and ESSs based on vulnerability analysis, and utilizes our proposed concept of “slow” and “fast” ESSs, which can reflect the influences of both uncertainties: PV outputs and grid failures. Accordingly, this paper demonstrates an optimal allocation of PVs and ESSs that minimizes the amount of ESSs while satisfying the PV installation target and the constraints on supply reliability indices for power shortage and power surplus in the event of a grid failure. Full article

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

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13 pages, 3853 KiB

Open AccessArticle

Flexibility-Based Reserve Scheduling of Pumped Hydroelectric Energy Storage in Korea

by Chang-Gi Min and Mun-Kyeom Kim^*

Department of Energy System Engineering, Chung-Ang University, 84 Heukseok-ro, Dongjak-gu, Seoul 06974, Korea

Energies 2017, 10(10), 1478; https://doi.org/10.3390/en10101478 - 24 Sep 2017

Cited by 14 | Viewed by 4356

Abstract

The high penetration of renewable energy resources has made it harder to secure a flexible power system. Accordingly, this has become an issue in operating power systems. As a possible solution, pumped hydroelectric energy storage (PHES) has received much attention because of its [...] Read more.

The high penetration of renewable energy resources has made it harder to secure a flexible power system. Accordingly, this has become an issue in operating power systems. As a possible solution, pumped hydroelectric energy storage (PHES) has received much attention because of its fast start-up and ramp characteristics. This study proposes a flexibility-based reserve scheduling method for PHES. In this method, the reserve scheduling of PHES was conducted to improve flexibility; the associated risk index was termed the ramping capability shortage expectation (RSE). The peak-load days in 2016 and 2029 were selected to examine the applicability and performance of the proposed method. Results indicate that the proposed method can improve the flexibility by 4.45% for 2016 and 0.9% for 2029, respectively. Full article

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

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16 pages, 9045 KiB

Open AccessArticle

Modeling and Static Analysis of Primary Consequent-Pole Tubular Transverse-Flux Flux-Reversal Linear Machine

by Dingfeng Dong^1,2,*, Wenxin Huang^1,*, Feifei Bu¹, Qi Wang¹, Wen Jiang¹ and Xiaogang Lin¹

¹ College of Automation Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 211106, Jiangsu, China

² ESTUN AUTOMATION TECHNOLOGY Co., LTD, Nanjing 211106, Jiangsu, China

Energies 2017, 10(10), 1479; https://doi.org/10.3390/en10101479 - 24 Sep 2017

Cited by 5 | Viewed by 4824

Abstract

A novel primary consequent-pole tubular transverse-flux flux-reversal linear machine (TTFFRLM) is proposed in this paper. The permanent magnets (PMs) of the machine are located on the inner surface of the short teeth of the primary iron cores for reducing the amount of PM [...] Read more.

A novel primary consequent-pole tubular transverse-flux flux-reversal linear machine (TTFFRLM) is proposed in this paper. The permanent magnets (PMs) of the machine are located on the inner surface of the short teeth of the primary iron cores for reducing the amount of PM in long stroke drive systems, and the primary is easily manufactured. The structure and principle of this machine are analyzed in detail. Based on the unit machine, a no-load equivalent magnetic circuit model is established by using the magnetic circuit method. Then, the equations of the no-load back electromotive force (back-EMF) and the electromagnetic thrust force are deduced. The simulation models of the unit machine are established by equivalent 2D finite element method (FEM) for saving computation time, and the static characteristics, including the flux field, the no-load back-EMF, and the electromagnetic thrust force, are analyzed. Detailed simulation and experimental results of a three-phase 4-poles 12-slots machine are given. The results verify the correctness and effectiveness of topology, model, and analysis method of the proposed TTFFRLM. Compared with the conventional TTFFRLM, the proposed prototype has the advantages of a lower cost and smaller electromagnetic thrust force ripple. Full article

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

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22 pages, 3522 KiB

Open AccessArticle

Dependence of Total Production Costs on Production and Infrastructure Parameters in the Polish Hard Coal Mining Industry

by Izabela Jonek-Kowalska^* and Marian Turek

Faculty of Organization and Management, Silesian University of Technology, Roosevelt 26 Street, 41-800 Zabrze, Poland

Energies 2017, 10(10), 1480; https://doi.org/10.3390/en10101480 - 25 Sep 2017

Cited by 22 | Viewed by 4703

Abstract

European hard coalmining is a declining industry, despite the use of hard coal for energy in several countries. Industry restructuring and public subsidies have failed to stop this industry’s decline. The largest hard coalmining sector, the Polish sector, has faced an obstacle to [...] Read more.

European hard coalmining is a declining industry, despite the use of hard coal for energy in several countries. Industry restructuring and public subsidies have failed to stop this industry’s decline. The largest hard coalmining sector, the Polish sector, has faced an obstacle to its survival: How to reduce production costs to compete with less expensive imported hard coal? This article aims to identify and analyze the dependence of the total production costs representing production and infrastructure parameters of the Polish hard coalmining industry. The parameters are divided into three groups: (1) the cost of employees and the production volume; (2) the number of longwalls, the length of a longwall, the daily longwall advance and the preparatory work advance; and (3) the number of levels in exploitation, the number of layers in exploitation and the number of shafts. The findings indicate that, even in well-functioning coalmines, there are many economically irrational relationships, especially regarding employment and infrastructure size. This study shows that employment, which is a significant cost component of the production and infrastructure parameters of the examined Polish hard coalmines, is not economically rational in terms of its proportion to the total production costs. As a result, even a considerable reduction in employment or infrastructure does not influence the unit costs of mining production, which could only be partially explained by the high level of fixed costs. There are also no appropriate relationships between infrastructure parameters and the total production cost. Under these irrational conditions, a reduction in the production costs of hard coalmining enterprises is difficult, but unproductive costly activities could prevent an improvement in production efficiency. Only restoring the proper relationship between economic and infrastructure parameters and the total production costs can ensure a return to price competitiveness. Those actions are crucial for the Polish hard coalmining industry, because the research focused on successful hard coalmines that were not declining indicate it should be able to implement cost improvements. Full article

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16 pages, 3774 KiB

Open AccessArticle

An Improved Commutation Prediction Algorithm to Mitigate Commutation Failure in High Voltage Direct Current

by Xinnian Li^1,*, Fengqi Li², Shuyong Chen³, Yanan Li⁴, Qiang Zou⁵, Ziping Wu⁶ and Shaobo Lin³

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

² State Grid Operation Company, Beijing 100052, China

³ State Key Laboratory of Power Grid Safety and Energy Conservation (China Electric Power Research Institute), Beijing 100192, China

⁴ State Power Economic Research Institute, Beijing 102209, China

⁵ NR Electric Co., Ltd., Nanjing 211102, China

⁶ Information Trust Institute, University of Illinois at Urbana-Champaign, Champaign, IL 61801, USA

Energies 2017, 10(10), 1481; https://doi.org/10.3390/en10101481 - 25 Sep 2017

Cited by 26 | Viewed by 4973

Abstract

Commutation failure is a common fault for line-commutated converters in the inverter. To reduce the possibility of commutation failure, many prediction algorithms based on alternating current (AC) voltage detection have already been implemented in high voltage direct current (HVDC) control and protection systems. [...] Read more.

Commutation failure is a common fault for line-commutated converters in the inverter. To reduce the possibility of commutation failure, many prediction algorithms based on alternating current (AC) voltage detection have already been implemented in high voltage direct current (HVDC) control and protection systems. Nevertheless, there are currently no effective methods to prevent commutation failure due to transformer excitation surge current. In this paper, an improved commutation failure prediction algorithm based on the harmonic characteristics of the converter bus voltage during transformer charging is proposed. Meanwhile, a sliding-window iterative algorithm of discrete Fourier transformation (DFT) is developed for detecting the voltage harmonic in real time. This method is proved to be an effective solution, which prevents commutation failure in cases of excitation surge current, through experimental analysis. This method is already implemented into TianShan-ZhongZhou (TianZhong) ± 800 kV ultra high voltage direct current (UHVDC) system. Full article

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

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16 pages, 4340 KiB

Open AccessArticle

Battery Equalization by Fly-Back Transformers with Inductance, Capacitance and Diode Absorbing Circuits

by Xintian Liu¹, Yafei Sun¹, Yao He^1,*, Xinxin Zheng¹, Guojian Zeng¹ and Jiangfeng Zhang²

¹ Intelligent Manufacturing Institute, Hefei University of Technology, 193 Tunxi Road, Hefei 230000, China

² School of Electrical and Data Engineering, University of Technology Sydney, 81 Broadway, Sydney, NSW 2007, Australia

Energies 2017, 10(10), 1482; https://doi.org/10.3390/en10101482 - 25 Sep 2017

Cited by 18 | Viewed by 4821

Abstract

Battery equalization can increase batteries’ life cycle, utilization, and reliability. Compared with battery equalization topologies based on resistance or energy storage components, the topologies based on transformers have the advantages of high balancing current and efficiency. However, the existence of switching losses will [...] Read more.

Battery equalization can increase batteries’ life cycle, utilization, and reliability. Compared with battery equalization topologies based on resistance or energy storage components, the topologies based on transformers have the advantages of high balancing current and efficiency. However, the existence of switching losses will reduce the reliability and service life span of the equalization circuit. Aiming at resolving this problem, a new battery equalization topology by fly-back transformer with an absorbing circuit is proposed in this paper. Compared with other transformer-based topologies, it can decrease switching losses because the voltage/current spike is solved by the absorbing circuit which is composed of inductance, capacitance and diode (LCD), and it can also maintain a high balancing current of about 1.8 A and high efficiency of about 89%, while the balancing current and efficiency of other topologies were usually 1.725 A/1.5 A and 80%/80.4%. The working principle of the balancing topology and the process of soft switching are analyzed and calculated in the frequency domain. Due to the addition of the LCD absorbing circuit, soft switching can be realized to reduce the switching losses while the high equalization speed and efficiency are still maintained. The corresponding control strategy of the balancing topology is also proposed and the timely balancing is achieved. The theoretical analysis is verified by simulation and experimental results. Full article

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

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17 pages, 5528 KiB

Open AccessReview

Wearable Biomechanical Energy Harvesting Technologies

by Young-Man Choi

, Moon Gu Lee and Yongho Jeon^*

Department of Mechanical Engineering, Ajou University, Suwon 16499, Korea

Energies 2017, 10(10), 1483; https://doi.org/10.3390/en10101483 - 25 Sep 2017

Cited by 171 | Viewed by 25852

Abstract

Energy harvesting has been attracting attention as a technology that is capable of replacing or supplementing a battery with the development of various mobile electronics. In environments where stable electrical supply is not possible, energy harvesting technology can guarantee an increased leisure and [...] Read more.

Energy harvesting has been attracting attention as a technology that is capable of replacing or supplementing a battery with the development of various mobile electronics. In environments where stable electrical supply is not possible, energy harvesting technology can guarantee an increased leisure and safety for human beings. Harvesting with several watts of power is essential for directly driving or efficiently charging mobile electronic devices such as laptops or cell phones. In this study, we reviewed energy harvesting technologies that harvest biomechanical energy from human motion such as foot strike, joint motion, and upper limb motion. They are classified based on the typical principle of kinetic energy harvesting: piezoelectric, triboelectric, and electromagnetic energy harvesting. We focused on the wearing position of high-power wearable biomechanical energy harvesters (WBEHs) generating watt-level power. In addition, the features and future trends of the watt-level WBEHs are discussed. Full article

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

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16 pages, 3278 KiB

Open AccessArticle

Optimal Operation of Microgrids Considering Auto-Configuration Function Using Multiagent System

by Van-Hai Bui¹, Akhtar Hussain¹

and Hak-Man Kim^1,2,*

¹ Department of Electrical Engineering, Incheon National University, 12-1 Songdo-dong, Yeonsu-gu, Incheon 406840, Korea

² Research Institute for Northeast Asian Super Grid, Incheon National University, 12-1 Songdo-dong, Yeonsu-gu, Incheon 406840, Korea

Energies 2017, 10(10), 1484; https://doi.org/10.3390/en10101484 - 25 Sep 2017

Cited by 29 | Viewed by 4966

Abstract

Monitoring the status of existing devices and identification of newly added devices is required in microgrids to adjust the operation schedule followed by any event or integration of a new device. Therefore, in this paper, automatic reconfiguration of microgrids is considered after the [...] Read more.

Monitoring the status of existing devices and identification of newly added devices is required in microgrids to adjust the operation schedule followed by any event or integration of a new device. Therefore, in this paper, automatic reconfiguration of microgrids is considered after the addition of a new device or change in the operation status of an existing device by using a multiagent system. This capability of the microgrid is named as auto-configuration function, which is performed by the auto-configurator agent. In case of addition of a new device, the auto-configurator agent is responsible for authorization and registration of the newly added device. In case of change in status of any existing device, the status information is updated. After integration of a new device or change in status of an existing device, re-optimization is carried out by the energy management system (EMS) agent. Agent communication language (ACL) is used to develop a modified contract net protocol (MCNP) for communication among different agents. EMS agent and auto-configurator agent exchange information for economic rescheduling of the microgrid components. Simulation results have shown that the proposed method can be used for optimal operation of microgrids when the configuration changes due to the addition/removal of a device. Full article

(This article belongs to the Special Issue Control and Communication in Distributed Generation Systems)

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18 pages, 3105 KiB

Open AccessArticle

An Improved Flexible Solar Thermal Energy Integration Process for Enhancing the Coal-Based Energy Efficiency and NO_x Removal Effectiveness in Coal-Fired Power Plants under Different Load Conditions

by Yu Han^1,2, Cheng Xu^1,*, Gang Xu^1,*, Yuwen Zhang²

and Yongping Yang¹

¹ Beijing Key Laboratory of Emission Surveillance and Control for Thermal Power Generation, North China Electric Power University, Beijing 102206, China

² Department of Mechanical & Aerospace Engineering, University of Missouri, Columbia, MO 65211, USA

Energies 2017, 10(10), 1485; https://doi.org/10.3390/en10101485 - 25 Sep 2017

Cited by 16 | Viewed by 6021

Abstract

An improved flexible solar-aided power generation system (SAPG) for enhancing both selective catalytic reduction (SCR) de-NO_x efficiency and coal-based energy efficiency of coal-fired power plants is proposed. In the proposed concept, the solar energy injection point is changed for different power plant [...] Read more.

An improved flexible solar-aided power generation system (SAPG) for enhancing both selective catalytic reduction (SCR) de-NO_x efficiency and coal-based energy efficiency of coal-fired power plants is proposed. In the proposed concept, the solar energy injection point is changed for different power plant loads, bringing about different benefits for coal-fired power generation. For partial/low load, solar energy is beneficially used to increase the flue gas temperature to guarantee the SCR de-NO_x effectiveness as well as increase the boiler energy input by reheating the combustion air. For high power load, solar energy is used for saving steam bleeds from turbines by heating the feed water. A case study for a typical 1000 MW coal-fired power plant using the proposed concept has been performed and the results showed that, the SCR de-NO_x efficiency of proposed SAPG could increase by 3.1% and 7.9% under medium load and low load conditions, respectively, as compared with the reference plant. The standard coal consumption rate of the proposed SAPG could decrease by 2.68 g/kWh, 4.05 g/kWh and 6.31 g/kWh for high, medium and low loads, respectively, with 0.040 USD/kWh of solar generated electricity cost. The proposed concept opens up a novel solar energy integration pattern in coal-fired power plants to improve the pollutant removal effectiveness and decrease the coal consumption of the power plant. Full article

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

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17 pages, 2502 KiB

Open AccessArticle

Improved State of Charge Estimation for High Power Lithium Ion Batteries Considering Current Dependence of Internal Resistance

by Cunxue Wu^1,2,*

, Rujian Fu³, Zhongming Xu¹ and Yang Chen³

¹ College of Automotive Engineering, Chongqing University, Chongqing 40044, China

² China Chang’an Automotive Engineering Institute, Chongqing 401120, China

³ A123 Systems, LLC., Livonia, MI 48377, USA

Energies 2017, 10(10), 1486; https://doi.org/10.3390/en10101486 - 25 Sep 2017

Cited by 14 | Viewed by 5263

Abstract

For high power Li-ion batteries, an important approach to improve the accuracy of modeling and algorithm development is to consider the current dependence of internal resistance, especially for large current applications in mild/median hybrid electric vehicles (MHEV). For the first time, the work [...] Read more.

For high power Li-ion batteries, an important approach to improve the accuracy of modeling and algorithm development is to consider the current dependence of internal resistance, especially for large current applications in mild/median hybrid electric vehicles (MHEV). For the first time, the work has experimentally captured the decrease of internal resistance at an increasing current of up to the C-rate of 25 and developed an equivalent circuit model (ECM) with current dependent parameters. The model is integrated to extended Kalman filter (EKF) to improve SOC estimation, which is validated by experimental data collected in dynamic stress testing (DST). Results show that EKF with current dependent parameters is capable of estimating SOC with a higher accuracy when it is compared to EKF without current dependent parameters. Full article

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

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16 pages, 2526 KiB

Open AccessArticle

Economic Microgrid Planning Algorithm with Electric Vehicle Charging Demands

by Sung-Guk Yoon^* and Seok-Gu Kang

Department of Electrical Engineering, Soongsil University, Seoul 06978, Korea

Energies 2017, 10(10), 1487; https://doi.org/10.3390/en10101487 - 25 Sep 2017

Cited by 34 | Viewed by 5389

Abstract

Two of the most important technologies for future power systems to reduce greenhouse gas are electric vehicles (EVs) and renewable generation. When EVs become more common, the overall demand of electricity will significantly increase because EVs consume a large amount of electricity. Also, [...] Read more.

Two of the most important technologies for future power systems to reduce greenhouse gas are electric vehicles (EVs) and renewable generation. When EVs become more common, the overall demand of electricity will significantly increase because EVs consume a large amount of electricity. Also, a daily load curve with EVs heavily depends on how much electricity EVs consume and when electricity is consumed. The microgrid is an important technology to promote renewable generation, and the increased demand and changed load curve should be considered in the microgrid planning stage to install robust and economical microgrids. In this paper, we propose an algorithm for microgrid planning with EV charging demand to find the most economical configuration through which to maximally utilize renewable generation. The algorithm uses a renewable generation-following EV charging scheme and HOMER. Through simulations, it is shown that the microgrid constructed by the proposed algorithm reduces the investment cost and CO₂ emission. Full article

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

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22 pages, 16059 KiB

Open AccessArticle

PV Hosting Capacity Analysis and Enhancement Using High Resolution Stochastic Modeling

by Emilio J. Palacios-Garcia^1,*

, Antonio Moreno-Muñoz¹

, Isabel Santiago¹

, Isabel M. Moreno-Garcia¹

and María I. Milanés-Montero²

¹ Departamento de Arquitectura de Computadores, Electrónica y Tecnología Electrónica, Escuela Politécnica Superior, Universidad de Córdoba, Campus de Rabanales, Edificio Leonardo da Vinci, E-14071 Córdoba, Spain

² Power Electrical and Electronic Systems Research Group, Escuela de Ingenierías Industriales, Universidad de Extremadura, Avda. de Elvas, s/n, E-06006 Badajoz, Spain

Energies 2017, 10(10), 1488; https://doi.org/10.3390/en10101488 - 26 Sep 2017

Cited by 28 | Viewed by 6294

Abstract

Reduction of CO₂ emissions is a main target in the future smart grid. This goal is boosting the installation of renewable energy resources (RES), as well as a major consumer engagement that seeks for a more efficient utilization of these resources toward [...] Read more.

Reduction of CO₂ emissions is a main target in the future smart grid. This goal is boosting the installation of renewable energy resources (RES), as well as a major consumer engagement that seeks for a more efficient utilization of these resources toward the figure of ‘prosumers’. Nevertheless, these resources present an intermittent nature, which requires the presence of an energy storage system and an energy management system (EMS) to ensure an uninterrupted power supply. Moreover, network-related issues might arise due to the increasing power of renewable resources installed in the grid, the storage systems also being capable of contributing to the network stability. However, to assess these future scenarios and test the control strategies, a simulation system is needed. The aim of this paper is to analyze the interaction between residential consumers with high penetration of PV generation and distributed storage and the grid by means of a high temporal resolution simulation scenario based on a stochastic residential load model and PV production records. Results of the model are presented for different PV power rates and storage capacities, as well as a two-level charging strategy as a mechanism for increasing the hosting capacity (HC) of the network. Full article

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

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15 pages, 4379 KiB

Open AccessArticle

Performance Analysis of Thermoelectric Based Automotive Waste Heat Recovery System with Nanofluid Coolant

by Zhi Li^1,2, Wenhao Li^1,3,* and Zhen Chen⁴

¹ Hubei Key Laboratory of Advanced Technology for Automotive Components, Wuhan University of Technology, Wuhan 430070, China

² Institute of Power Machinery and Vehicular Engineering, Zhejiang University, Hangzhou 310027, China

³ Hubei Collaborative Innovation Center for Automotive Components Technology, Wuhan University of Technology, Wuhan 430070, China

⁴ School of Mechanical and Electronic Engineering, Wuhan University of Technology, Wuhan 430070, China

Energies 2017, 10(10), 1489; https://doi.org/10.3390/en10101489 - 26 Sep 2017

Cited by 21 | Viewed by 4809

Abstract

Output performance of a thermoelectric-based automotive waste heat recovery system with a nanofluid coolant is analyzed in this study. Comparison between Cu-Ethylene glycol (Cu-EG) nanofluid coolant and ethylene glycol with water (EG-W) coolant under equal mass flow rate indicates that Cu-EG nanofluid as [...] Read more.

Output performance of a thermoelectric-based automotive waste heat recovery system with a nanofluid coolant is analyzed in this study. Comparison between Cu-Ethylene glycol (Cu-EG) nanofluid coolant and ethylene glycol with water (EG-W) coolant under equal mass flow rate indicates that Cu-EG nanofluid as a coolant can effectively improve power output and thermoelectric conversion efficiency for the system. Power output enhancement for a 3% concentration of nanofluid is 2.5–8 W (12.65–13.95%) compared to EG-Water when inlet temperature of exhaust varies within 500–710 K. The increase of nanofluid concentration within a realizable range (6%) has positive effect on output performance of the system. Study on the relationship between total area of thermoelectric modules (TEMs) and output performance of the system indicates that optimal total area of TEMs exists for maximizing output performance of the system. Cu-EG nanofluid as coolant can decrease optimal total area of TEMs compared with EG-W, which will bring significant advantages for the optimization and arrangement of TEMs whether the system space is sufficient or not. Moreover, power output enhancement under Cu-EG nanofluid coolant is larger than that of EG-W coolant due to the increase of hot side heat transfer coefficient of TEMs. Full article

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

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14 pages, 2298 KiB

Open AccessArticle

Probing Temperature-Dependent Recombination Kinetics in Polymer:Fullerene Solar Cells by Electric Noise Spectroscopy

by Giovanni Landi¹, Carlo Barone^2,*

, Costantino Mauro², Antonietta De Sio³, Giovanni Carapella², Heinz Christoph Neitzert¹ and Sergio Pagano²

¹ Dipartimento di Ingegneria Industriale, Università di Salerno, I-84084 Fisciano, Salerno, Italy

² Dipartimento di Fisica “E.R. Caianiello” and CNR-SPIN Salerno, Università di Salerno, I-84084 Fisciano, Salerno, Italy

³ Institute of Physics, Carl von Ossietzky University of Oldenburg, 26111 Oldenburg, Germany

Energies 2017, 10(10), 1490; https://doi.org/10.3390/en10101490 - 26 Sep 2017

Cited by 8 | Viewed by 3741

Abstract

The influence of solvent additives on the temperature behavior of both charge carrier transport and recombination kinetics in bulk heterojunction solar cells has been investigated by electric noise spectroscopy. The observed differences in charge carrier lifetime and mobility are attributed to a different [...] Read more.

The influence of solvent additives on the temperature behavior of both charge carrier transport and recombination kinetics in bulk heterojunction solar cells has been investigated by electric noise spectroscopy. The observed differences in charge carrier lifetime and mobility are attributed to a different film ordering and donor-acceptor phase segregation in the blend. The measured temperature dependence indicates that bimolecular recombination is the dominant loss mechanism in the active layer, affecting the device performance. Blend devices prepared with a high-boiling-point solvent additive show a decreased recombination rate at the donor-acceptor interface as compared to the ones prepared with the reference solvent. A clear correlation between the device performance and the morphological properties is discussed in terms of the temperature dependence of the mobility-lifetime product. Full article

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

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20 pages, 3013 KiB

Open AccessFeature PaperArticle

A Decentralized Multi-Agent-Based Approach for Low Voltage Microgrid Restoration

by Ebrahim Rokrok¹, Miadreza Shafie-khah¹

, Pierluigi Siano^2,*

and João P. S. Catalão^1,3,4,*

¹ Centre for Mechanical and Aerospace Science and Technologies (C-MAST), University of Beira Interior, R. Fonte do Lameiro, 6201-001 Covilhã, Portugal

² Department of Industrial Engineering, University of Salerno, 84084 Fisciano (SA), Italy

³ Institute for Systems and Computer Engineering, Technology and Science (INESC TEC), Faculty of Engineering, University of Porto, 4200-465 Porto, Portugal

⁴ Institute for Systems and Computer Engineering, Research and Development (INESC-ID), Instituto Superior Técnico, University of Lisbon, Av. Rovisco Pais, 1049-001 Lisbon, Portugal

Energies 2017, 10(10), 1491; https://doi.org/10.3390/en10101491 - 27 Sep 2017

Cited by 20 | Viewed by 6693

Abstract

Although a well-organized power system is less subject to blackouts, the existence of a proper restoration plan is nevertheless still essential. The goal of a restoration plan is to bring the power system back to its normal operating conditions in the shortest time [...] Read more.

Although a well-organized power system is less subject to blackouts, the existence of a proper restoration plan is nevertheless still essential. The goal of a restoration plan is to bring the power system back to its normal operating conditions in the shortest time after a blackout occurs and to minimize the impact of the blackout on society. This paper presents a decentralized multi-agent system (MAS)-based restoration method for a low voltage (LV) microgrid (MG). In the proposed method, the MG local controllers are assigned to the specific agents who interact with each other to achieve a common decision in the restoration procedure. The evaluation of the proposed decentralized technique using a benchmark low-voltage MG network demonstrates the effectiveness of the proposed restoration plan. Full article

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

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12 pages, 3003 KiB

Open AccessArticle

Field-Weakening Performance Improvement of the Yokeless and Segmented Armature Axial Flux Motor for Electric Vehicles

by Xiaoyuan Wang^*, Sijia Xu, Chunpeng Li and Xiang Li

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

Energies 2017, 10(10), 1492; https://doi.org/10.3390/en10101492 - 26 Sep 2017

Cited by 11 | Viewed by 14594

Abstract

In order to avoid the unsafe operation and raise efficiency of yokeless and segmented armature axial flux motors at high speed, the control current of air gap flux is expected to be as small as possible with the same field-weakening effect. To reduce [...] Read more.

In order to avoid the unsafe operation and raise efficiency of yokeless and segmented armature axial flux motors at high speed, the control current of air gap flux is expected to be as small as possible with the same field-weakening effect. To reduce the control complexity, a new structure of module poles with a combination of permanent magnet and soft magnetic material is proposed, which has the characteristics of lower d-axis reluctance and a higher performance of yokeless and segmented armature axial flux motor with surface mounted permanent magnet. According to finite element analysis (FEA), the flux distributions of a rotor pole in no-load and demagnetization condition are contrasted, and under this new configuration, the derivative analytical models of back electromotive-force (EMF), electromagnetic torque, and air gap flux are validated, moreover, the influence of soft magnetic material of rotor poles on controlling the air gap flux is investigated in different load. Based on a particular objective function, the combination of permanent magnet and soft magnetic material is optimized. The results show that optimal solution of field-weakening performance of yokeless and segmented armature axial flux motors can be improved effectively and legitimately. Full article

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17 pages, 4428 KiB

Open AccessArticle

Coordinated Control Strategies for a Permanent Magnet Synchronous Generator Based Wind Energy Conversion System

by Ramji Tiwari¹

, Sanjeevikumar Padmanaban^2,*

and Ramesh Babu Neelakandan¹

¹ School of Electrical Engineering, VIT University, Vellore 632014, India

² Department of Electrical and Electronics Engineering, University of Johannesburg, Auckland Park 2006, South Africa

Energies 2017, 10(10), 1493; https://doi.org/10.3390/en10101493 - 28 Sep 2017

Cited by 39 | Viewed by 8050

Abstract

In this paper, a novel co-ordinated hybrid maximum power point tracking (MPPT)-pitch angle based on a radial basis function network (RBFN) is proposed for a variable speed variable pitch wind turbine. The proposed controller is used to maximise output power when the wind [...] Read more.

In this paper, a novel co-ordinated hybrid maximum power point tracking (MPPT)-pitch angle based on a radial basis function network (RBFN) is proposed for a variable speed variable pitch wind turbine. The proposed controller is used to maximise output power when the wind speed is low and optimise the power when the wind speed is high. The proposed controller provides robustness to the nonlinear characteristic of wind speed. It uses wind speed, generator speed, and generator power as input variables and utilises the duty cycle and the reference pitch angle as the output control variables. The duty cycle is used to control the converter so as to maximise the power output and the reference pitch angle is used to control the generator speed in order to control the generator output power in the above rated wind speed region. The effectiveness of the proposed controller was verified using MATLAB/Simulink software. Full article

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

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14 pages, 4133 KiB

Open AccessArticle

Heating Performance Characteristics of High-Voltage PTC Heater for an Electric Vehicle

by Myeong Hyeon Park

and Sung Chul Kim^*

School of Mechanical Engineering, Yeungnam University, 280 Daehak-ro, Gyeongsan-si, Gyeongbuk 712-749, Korea

Energies 2017, 10(10), 1494; https://doi.org/10.3390/en10101494 - 26 Sep 2017

Cited by 30 | Viewed by 9147

Abstract

High-voltage positive temperature coefficient (PTC) heaters have a high heating capacity and are fast acting; thus, they function as the actual main heating equipment in electric cars, and considerable research is devoted to improving their heating performance and efficiency. We evaluated the heating [...] Read more.

High-voltage positive temperature coefficient (PTC) heaters have a high heating capacity and are fast acting; thus, they function as the actual main heating equipment in electric cars, and considerable research is devoted to improving their heating performance and efficiency. We evaluated the heating performance of a high-voltage PTC heater for an electric car by building a closed-loop-type test system including an air channel, environment chamber, DC power supply, and data acquisition system, and designed an initial prototype with general characteristics. Using this test system, we analyzed the heating performance characteristics of the heater as a function of changes in the blower airflow, ambient temperature, and battery voltage. We changed the geometrical variables of the heater and conducted an analysis to improve the heating performance and output density of the initial prototype. Based on the heating performance of the initial prototype and its geometrical variables, we designed an improved prototype and compared its heating performance and output density with that of the initial prototype. As a result, we achieved a heating capacity of 5.52 kW, a pressure drop of 48.2 Pa, and an efficiency of 98%, whereas the output density was 3.45 kW/kg, which is a 24% improvement over the initial prototype. Full article

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

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24 pages, 6527 KiB

Open AccessArticle

Influence of Various Irradiance Models and Their Combination on Simulation Results of Photovoltaic Systems

by Martin Hofmann^1,2,*

and Gunther Seckmeyer²

¹ Valentin Software GmbH, Stralauer Platz 34, 10243 Berlin, Germany

² Institute for Meteorology and Climatology, Leibniz Universität Hannover, Herrenhäuser Straße 2, 30419 Hannover, Germany

Energies 2017, 10(10), 1495; https://doi.org/10.3390/en10101495 - 26 Sep 2017

Cited by 35 | Viewed by 4773

Abstract

We analyze the output of various state-of-the-art irradiance models for photovoltaic systems. The models include two sun position algorithms, three types of input data time series, nine diffuse fraction models and five transposition models (for tilted surfaces), resulting in 270 different model chains [...] Read more.

We analyze the output of various state-of-the-art irradiance models for photovoltaic systems. The models include two sun position algorithms, three types of input data time series, nine diffuse fraction models and five transposition models (for tilted surfaces), resulting in 270 different model chains for the photovoltaic (PV) system simulation. These model chains are applied to 30 locations worldwide and three different module tracking types, totaling in 24,300 simulations. We show that the simulated PV yearly energy output varies between −5% and +8% for fixed mounted PV modules and between −26% and +14% for modules with two-axis tracking. Model quality varies strongly between locations; sun position algorithms have negligible influence on the simulation results; diffuse fraction models add a lot of variability; and transposition models feature the strongest influence on the simulation results. To highlight the importance of irradiance with high temporal resolution, we present an analysis of the influence of input temporal resolution and simulation models on the inverter clipping losses at varying PV system sizing factors for Lindenberg, Germany. Irradiance in one-minute resolution is essential for accurately calculating inverter clipping losses. Full article

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11 pages, 2806 KiB

Open AccessArticle

Effect of Coil Configuration on Conversion Efficiency of EMAT on 7050 Aluminum Alloy

by Yunxin Wu^1,2,3,*, Lei Han^1,2,3, Hai Gong², Jiangang Yang² and Wei Li²

¹ Research Institute of Light Alloys, Central South University, Changsha 410083, China

² State Key Laboratory of High-Performance Complex Manufacturing, Central South University, Changsha 410083, China

³ Nonferrous Metal Oriented Advanced Structural Material and Manufacturing Cooperative Innovation Center, Central South University, Changsha 410083, China

Energies 2017, 10(10), 1496; https://doi.org/10.3390/en10101496 - 26 Sep 2017

Cited by 7 | Viewed by 4311

Abstract

Compared to traditional ultrasonic detection methods, the electromagnetic acoustic transducer (EMAT) technique can be applied in many hostile environments such as elevated temperatures, on-line inspections, etc. However, the EMAT technique has a low conversion efficiency. This paper develops a numerical model to study [...] Read more.

Compared to traditional ultrasonic detection methods, the electromagnetic acoustic transducer (EMAT) technique can be applied in many hostile environments such as elevated temperatures, on-line inspections, etc. However, the EMAT technique has a low conversion efficiency. This paper develops a numerical model to study the effects of the coil configurations on the conversion efficiency of shear-wave EMAT on 7050 aluminum alloy. The numerical model is fully validated by the experiment data. The effects of the configuration parameters, including the coil wires’ cross-sectional area, coil wires’ cross-sectional shape, and distance between coil wires, on the conversion efficiency are then discussed. The results indicate that after using the coil with a square cross-section, the conversion efficiency of EMAT is increased by 22.5%. In addition, the coil wires’ cross-sectional area and the distance between coil wires also have a significant effect on the conversion efficiency. Full article

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29 pages, 5244 KiB

Open AccessArticle

Application of a Simplified Thermal-Electric Model of a Sodium-Nickel Chloride Battery Energy Storage System to a Real Case Residential Prosumer

by Fabio Bignucolo^1,*

, Massimiliano Coppo¹

, Giorgio Crugnola² and Andrea Savio¹

¹ Department of Industrial Engineering, University of Padova, 35131 Padova, Italy

² FZSONICK SA, Via Laveggio 15, 6855 Stabio, Switzerland

Energies 2017, 10(10), 1497; https://doi.org/10.3390/en10101497 - 26 Sep 2017

Cited by 14 | Viewed by 4722

Abstract

Recently, power system customers have changed the way they interact with public networks, playing a more and more active role. End-users first installed local small-size generating units, and now they are being equipped with storage devices to increase the selfconsumption rate. By suitably [...] Read more.

Recently, power system customers have changed the way they interact with public networks, playing a more and more active role. End-users first installed local small-size generating units, and now they are being equipped with storage devices to increase the selfconsumption rate. By suitably managing local resources, the provision of ancillary services and aggregations among several end-users are expected evolutions in the near future. In the upcoming market of household-sized storage devices, sodium-nickel chloride technology seems to be an interesting alternative to lead-acid and lithium-ion batteries. To accurately investigate the operation of the NaNiCl₂ battery system at the residential level, a suitable thermoelectric model has been developed by the authors, starting from the results of laboratory tests. The behavior of the battery internal temperature has been characterized. Then, the designed model has been used to evaluate the economic profitability in installing a storage system in the case that end-users are already equipped with a photovoltaic unit. To obtain realistic results, real field measurements of customer consumption and solar radiation have been considered. A concrete interest in adopting the sodiumnickel chloride technology at the residential level is confirmed, taking into account the achievable benefits in terms of economic income, back-up supply, and increased indifference to the evolution of the electricity market. Full article

(This article belongs to the Special Issue Battery Energy Storage Applications in Smart Grid)

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6 pages, 1025 KiB

Open AccessFeature PaperCommunication

Analytical Derivation of Electrical-Side Maximum Power Line for Wind Generators

by Sergei Kolesnik¹ and Alon Kuperman^1,2,*

¹ Department of Electrical Engineering and Electronics, Ariel University of Samaria, Ariel 40700, Israel

² Department of Electrical and Computer Engineering, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel

Energies 2017, 10(10), 1498; https://doi.org/10.3390/en10101498 - 26 Sep 2017

Cited by 6 | Viewed by 3434

Abstract

In order to enhance the maximum power point tracking (MPPT) speed of solar generators, offline calculated maximum power line (MPL) is often used as a feed-forward signal added to the output of MPPT controller. MPL is nonlinear static electrical characteristic of renewable energy [...] Read more.

In order to enhance the maximum power point tracking (MPPT) speed of solar generators, offline calculated maximum power line (MPL) is often used as a feed-forward signal added to the output of MPPT controller. MPL is nonlinear static electrical characteristic of renewable energy generators connecting all the maximum power points for given temperature. In this letter, electrical side MPL is derived for a typical wind turbine generator (WTG). It is shown that MPLs of solar and wind generators possess similar structure, supporting the similarity between the two energy conversion processes. Full article

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

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21 pages, 26039 KiB

Open AccessArticle

Comparative Study on Uni- and Bi-Directional Fluid Structure Coupling of Wind Turbine Blades

by Mesfin Belayneh Ageze^1,2,*

, Yefa Hu¹ and Huachun Wu¹

¹ School of Mechanical and Electrical Engineering, Wuhan University of Technology, Wuhan 430070, China

² Department of Mechanical Engineering, Woldia University, Woldia, Ethiopia

Energies 2017, 10(10), 1499; https://doi.org/10.3390/en10101499 - 27 Sep 2017

Cited by 16 | Viewed by 6164

Abstract

The current trends of wind turbine blade designs are geared towards a longer and slender blade with high flexibility, exhibiting complex aeroelastic loadings and instability issues, including flutter; in this regard, fluid-structure interaction (FSI) plays a significant role. The present article will conduct [...] Read more.

The current trends of wind turbine blade designs are geared towards a longer and slender blade with high flexibility, exhibiting complex aeroelastic loadings and instability issues, including flutter; in this regard, fluid-structure interaction (FSI) plays a significant role. The present article will conduct a comparative study between uni-directional and bi-directional fluid-structural coupling models for a horizontal axis wind turbine. A full-scale, geometric copy of the NREL 5MW blade with simplified material distribution is considered for simulation. Analytical formulations of the governing relations with appropriate approximation are highlighted, including turbulence model, i.e., Shear Stress Transport (SST) k-ω. These analytical relations are implemented using Multiphysics package ANSYS employing Fluent module (Computational Fluid Dynamics (CFD)-based solver) for the fluid domain and Transient Structural module (Finite Element Analysis-based solver) for the structural domain. ANSYS system coupling module also is configured to model the two fluid-structure coupling methods. The rated operational condition of the blade for a full cycle rotation is considered as a comparison domain. In the bi-directional coupling model, the structural deformation alters the angle of attack from the designed values, and by extension the flow pattern along the blade span; furthermore, the tip deflection keeps fluctuating whilst it tends to stabilize in the uni-directional coupling model. Full article

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18 pages, 10337 KiB

Open AccessArticle

Performance Comparison of Conventional Synchronous Reluctance Machines and PM-Assisted Types with Combined Star–Delta Winding

by Mohamed Nabil Fathy Ibrahim^1,2,*, Essam Rashad³ and Peter Sergeant^1,4

¹ Department of Electrical Energy, Metals, Mechanical Constructions and Systems, Ghent University, 9000 Ghent, Belgium

² Electrical Engineering Department, Kafrelshiekh University, Kafr El-Sheikh 33511, Egypt

³ Electrical Power and Machines Department, Tanta University, Tanta 31527, Egypt

⁴ Flanders Make, The Strategic Research Center for the Manufacturing Industry, B-8500 Kortrijk, Belgium

Energies 2017, 10(10), 1500; https://doi.org/10.3390/en10101500 - 27 Sep 2017

Cited by 26 | Viewed by 7280

Abstract

This paper compares four prototype Synchronous Reluctance Motors (SynRMs) having an identical geometry of iron lamination stacks in the stator and rotor. Two different stator winding layouts are employed: a conventional three-phase star connection and a combined star–delta winding. In addition, two rotors [...] Read more.

This paper compares four prototype Synchronous Reluctance Motors (SynRMs) having an identical geometry of iron lamination stacks in the stator and rotor. Two different stator winding layouts are employed: a conventional three-phase star connection and a combined star–delta winding. In addition, two rotors are considered: a conventional rotor without magnets and a rotor with ferrite magnets. The performance of the four SynRMs is evaluated using a two-dimensional (2D) Finite Element Model (FEM). For the same copper volume and current, the combined star–delta-connected stator with Permanent Magnets (PMs) in the rotor corresponds to an approximately 22% increase in the output torque at rated current and speed compared to the conventional machine. This improvement is mainly thanks to adding ferrite PMs in the rotor as well as to the improved winding factor of the combined star–delta winding. The torque gain increases up to 150% for low current. Moreover, the rated efficiency is 93.60% compared to 92.10% for the conventional machine. On the other hand, the impact on the power factor and losses of SynRM when using the star–delta windings instead of the star windings is merely negligible. The theoretical results are experimentally validated using four identical prototype machines with identical lamination stacks but different rotors and winding layouts. Full article

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

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20 pages, 2186 KiB

Open AccessArticle

From Product to System Approaches in European Sustainable Product Policies: Analysis of the Package Concept of Heating Systems in Buildings

by Maria Calero-Pastor^1,2,*, Fabrice Mathieux¹

, Daniel Brissaud² and Luca Castellazzi³

¹ European Commission, Joint Research Centre, Directorate D—Sustainable Resources, Via E. Fermi, 2749, 21027 Ispra, Italy

² Université Grenoble Alpes, Centre National de la Recherche Scientifique, 46 Avenue Félix Viallet, 38000 Grenoble, France

³ European Commission, Joint Research Centre, Directorate C—Energy, Transport and Climate, Via E. Fermi, 2749, 21027 Ispra, Italy

Energies 2017, 10(10), 1501; https://doi.org/10.3390/en10101501 - 27 Sep 2017

Cited by 3 | Viewed by 3849

Abstract

Different policies with the goal of reducing energy consumption and other environmental impacts in the building sector coexist in Europe. Sustainable product polices, such as the Ecodesign and Energy Labelling Directives, have recently broadened the scope of their target product groups from a [...] Read more.

Different policies with the goal of reducing energy consumption and other environmental impacts in the building sector coexist in Europe. Sustainable product polices, such as the Ecodesign and Energy Labelling Directives, have recently broadened the scope of their target product groups from a strict product approach to extended product and system approaches. Indeed, there is a potential for greater savings when the focus is at a system level rather than on regulating individual products. Product policies for space and water heating systems have recently introduced and implemented the package label, which is a modular approach, standing between the extended product and the system approaches. This paper presents a systematic analysis of the different system approaches of various policies from an engineering perspective. It analyses in detail the package concept and its features through a practical application using a real case study. It focuses on how the package concept can support decisions made in the building design phase and, in particular, how can support the choice of appropriate components based on estimating system performances. This brings building engineers and regulators closer regarding the use of more consistent data on energy performance. Finally, this paper highlights the need to improve the alignment of the building-related product policies with the Energy Performance of Buildings Directive. Full article

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18 pages, 4121 KiB

Open AccessArticle

Design of a Fractional Order Frequency PID Controller for an Islanded Microgrid: A Multi-Objective Extremal Optimization Method

by Huan Wang^1,2, Guoqiang Zeng^2,*, Yuxing Dai^1,2, Daqiang Bi³, Jingliao Sun⁴ and Xiaoqing Xie²

¹ College of Electrical and Information Engineering, Hunan University, Changsha 410082, China

² National-Local Joint Engineering Laboratory of Digitalize Electrical Design Technology, Wenzhou University, Wenzhou 325035, China

³ State Key Laboratory of Power Systems and Department of Electrical Engineering, Tsinghua University, Beijing 100084, China

⁴ State Grid Wenzhou Electric Power Supply Company, Wenzhou 325000, China

Energies 2017, 10(10), 1502; https://doi.org/10.3390/en10101502 - 1 Oct 2017

Cited by 94 | Viewed by 6234

Abstract

Fractional order proportional-integral-derivative(FOPID) controllers have attracted increasing attentions recently due to their better control performance than the traditional integer-order proportional-integral-derivative (PID) controllers. However, there are only few studies concerning the fractional order control of microgrids based on evolutionary algorithms. From the perspective of [...] Read more.

Fractional order proportional-integral-derivative(FOPID) controllers have attracted increasing attentions recently due to their better control performance than the traditional integer-order proportional-integral-derivative (PID) controllers. However, there are only few studies concerning the fractional order control of microgrids based on evolutionary algorithms. From the perspective of multi-objective optimization, this paper presents an effective FOPID based frequency controller design method called MOEO-FOPID for an islanded microgrid by using a Multi-objective extremal optimization (MOEO) algorithm to minimize frequency deviation and controller output signal simultaneously in order to improve finally the efficient operation of distributed generations and energy storage devices. Its superiority to nondominated sorting genetic algorithm-II (NSGA-II) based FOPID/PID controllers and other recently reported single-objective evolutionary algorithms such as Kriging-based surrogate modeling and real-coded population extremal optimization-based FOPID controllers is demonstrated by the simulation studies on a typical islanded microgrid in terms of the control performance including frequency deviation, deficit grid power, controller output signal and robustness. Full article

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

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15 pages, 6119 KiB

Open AccessEditor’s ChoiceArticle

Design and Implementation of a Smart Lithium-Ion Battery System with Real-Time Fault Diagnosis Capability for Electric Vehicles

by Zuchang Gao¹, Cheng Siong Chin^2,*, Joel Hay King Chiew¹, Junbo Jia¹ and Caizhi Zhang³

¹ School of Engineering, Temasek Polytechnic, Singapore 529757, Singapore

² Faculty of Science, Agriculture and Engineering, Newcastle University, Newcastle upon Tyne NE1 7RU, UK

³ School of Automotive Engineering, Chongqing University, Chongqing 400044, China

Energies 2017, 10(10), 1503; https://doi.org/10.3390/en10101503 - 27 Sep 2017

Cited by 51 | Viewed by 10659

Abstract

Lithium-ion battery (LIB) power systems have been commonly used for energy storage in electric vehicles. However, it is quite challenging to implement a robust real-time fault diagnosis and protection scheme to ensure battery safety and performance. This paper presents a resilient framework for [...] Read more.

Lithium-ion battery (LIB) power systems have been commonly used for energy storage in electric vehicles. However, it is quite challenging to implement a robust real-time fault diagnosis and protection scheme to ensure battery safety and performance. This paper presents a resilient framework for real-time fault diagnosis and protection in a battery-power system. Based on the proposed system structure, the self-initialization scheme for state-of-charge (SOC) estimation and the fault-diagnosis scheme were tested and implemented in an actual 12-cell series battery-pack prototype. The experimental results validated that the proposed system can estimate the SOC, diagnose the fault and provide necessary protection and self-recovery actions under the load profile for an electric vehicle. Full article

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

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14 pages, 923 KiB

Open AccessFeature PaperArticle

Development of an Energy Biorefinery Model for Chestnut (Castanea sativa Mill.) Shells

by Alessandra Morana¹, Giuseppe Squillaci¹, Susana M. Paixão², Luís Alves², Francesco La Cara¹ and Patrícia Moura^2,*

¹ Institute of Agro-Environmental and Forest Biology, National Research Council of Italy, Via Pietro Castellino 111, 80131 Naples, Italy

² LNEG, Laboratório Nacional de Energia e Geologia, Unidade de Bioenergia, Estrada do Paço do Lumiar, 1649-038 Lisboa, Portugal

Energies 2017, 10(10), 1504; https://doi.org/10.3390/en10101504 - 27 Sep 2017

Cited by 42 | Viewed by 5015

Abstract

Chestnut shells (CS) are an agronomic waste generated from the peeling process of the chestnut fruit, which contain 2.7–5.2% (w/w) phenolic compounds and approximately 36% (w/w) polysaccharides. In contrast with current shell waste burning practices, [...] Read more.

Chestnut shells (CS) are an agronomic waste generated from the peeling process of the chestnut fruit, which contain 2.7–5.2% (w/w) phenolic compounds and approximately 36% (w/w) polysaccharides. In contrast with current shell waste burning practices, this study proposes a CS biorefinery that integrates biomass pretreatment, recovery of bioactive molecules, and bioconversion of the lignocellulosic hydrolyzate, while optimizing materials reuse. The CS delignification and saccharification produced a crude hydrolyzate with 12.9 g/L of glucose and xylose, and 682 mg/L of gallic acid equivalents. The detoxification of the crude CS hydrolyzate with 5% (w/v) activated charcoal (AC) and repeated adsorption, desorption and AC reuse enabled 70.3% (w/w) of phenolic compounds recovery, whilst simultaneously retaining the soluble sugars in the detoxified hydrolyzate. The phenols radical scavenging activity (RSA) of the first AC eluate reached 51.8 ± 1.6%, which is significantly higher than that of the crude CS hydrolyzate (21.0 ± 1.1%). The fermentation of the detoxified hydrolyzate by C. butyricum produced 10.7 ± 0.2 mM butyrate and 63.9 mL H₂/g of CS. Based on the obtained results, the CS biorefinery integrating two energy products (H₂ and calorific power from spent CS), two bioproducts (phenolic compounds and butyrate) and one material reuse (AC reuse) constitutes a valuable upgrading approach for this yet unexploited waste biomass. Full article

(This article belongs to the Special Issue Advances in Fermentative Hydrogen Production)

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23 pages, 5526 KiB

Open AccessArticle

Analysis of the Potential for Use of Floating PV Power Plant on the Skadar Lake for Electricity Supply of Aluminium Plant in Montenegro

by Vladan Durković^1,2,* and Željko Đurišić²

¹ Faculty of Electrical Engineering, University of Montenegro, 81000 Podgorica, Montenegro

² School of Electrical Engineering, University of Belgrade, 11000 Belgrade, Serbia

Energies 2017, 10(10), 1505; https://doi.org/10.3390/en10101505 - 29 Sep 2017

Cited by 52 | Viewed by 8020

Abstract

This paper deals with a conceptual solution for the supply of a part of electrical energy for the needs of Aluminium Plant Podgorica (KAP) in Montenegro from a large Floating Photovoltaic Power Plant (FPPP), that would be installed on the nearby lake. The [...] Read more.

This paper deals with a conceptual solution for the supply of a part of electrical energy for the needs of Aluminium Plant Podgorica (KAP) in Montenegro from a large Floating Photovoltaic Power Plant (FPPP), that would be installed on the nearby lake. The recommended FPPP, with an innovative azimuth angle control method and total installed power of 90 MWp, would consist of 18 power plants having an installed power of 5 MWp each. An analysis using the NREL solar insolation database ascertained that the recommended FPPP power plant can achieve a significantly higher production in comparison with previous solutions. An economic analysis has shown that the recommended power plant would yield positive economic indicators. Additionally, such a power plant would significantly contribute to the reduction of CO₂ emissions. Full article

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

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11 pages, 2471 KiB

Open AccessArticle

Energy Demand Reduction in the Residential Building Sector: A Case Study of Korea

by Kwon Sook Park¹

and Mi Jeong Kim^2,*

¹ Department of Architecture, Korea University, Seoul 02841, Korea

² Department of Housing and Interior Design, Kyung Hee University, Seoul 02447, Korea

Energies 2017, 10(10), 1506; https://doi.org/10.3390/en10101506 - 28 Sep 2017

Cited by 31 | Viewed by 4444

Abstract

This study sought to examine ways of reducing energy demands in the residential building sector by measuring energy usage and associated factors in Bundang District. This District represents the first phase of new towns in the Seoul metropolitan region to implement current polices [...] Read more.

This study sought to examine ways of reducing energy demands in the residential building sector by measuring energy usage and associated factors in Bundang District. This District represents the first phase of new towns in the Seoul metropolitan region to implement current polices directed at climate change. The majority of residential buildings in this district were constructed between 1991 and 1995, prior to the announcement of the integrated building design criteria directed at saving energy and intensifying thermal transmittance. The proportion of small households was increased by almost 40% from 2000 to 2010. Further, a number of weather records have been broken in the last two decades. These changes are strongly related to energy consumption patterns and trends; however, current polices, acts, and regulations do not sufficiently address these issues. This study suggests building energy-saving strategies that: (i) improve energy performance in existing buildings; (ii) strengthen building design criteria to address climate change issues, especially in relation to design and construction; and (iii) offer a framework to revitalize Korea’s energy-savings policies. Full article

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20 pages, 393 KiB

Open AccessArticle

Bi-Directional Coordination of Plug-In Electric Vehicles with Economic Model Predictive Control

by Yusuf A. Sha’aban

, Augustine Ikpehai, Bamidele Adebisi^*

and Khaled M. Rabie

School of Engineering, Manchester Metropolitan University, Manchester M1 5GD, UK

Energies 2017, 10(10), 1507; https://doi.org/10.3390/en10101507 - 28 Sep 2017

Cited by 21 | Viewed by 5612

Abstract

The emergence of plug-in electric vehicles (PEVs) is unveiling new opportunities to de-carbonise the vehicle parcs and promote sustainability in different parts of the globe. As battery technologies and PEV efficiency continue to improve, the use of electric cars as distributed energy resources [...] Read more.

The emergence of plug-in electric vehicles (PEVs) is unveiling new opportunities to de-carbonise the vehicle parcs and promote sustainability in different parts of the globe. As battery technologies and PEV efficiency continue to improve, the use of electric cars as distributed energy resources is fast becoming a reality. While the distribution network operators (DNOs) strive to ensure grid balancing and reliability, the PEV owners primarily aim at maximising their economic benefits. However, given that the PEV batteries have limited capacities and the distribution network is constrained, smart techniques are required to coordinate the charging/discharging of the PEVs. Using the economic model predictive control (EMPC) technique, this paper proposes a decentralised optimisation algorithm for PEVs during the grid-to-vehicle (G2V) and vehicle-to-grid (V2G) operations. To capture the operational dynamics of the batteries, it considers the state-of-charge (SoC) at a given time as a discrete state space and investigates PEVs performance in V2G and G2V operations. In particular, this study exploits the variability in the energy tariff across different periods of the day to schedule V2G/G2V cycles using real data from the university’s PEV infrastructure. The results show that by charging/discharging the vehicles during optimal time partitions, prosumers can take advantage of the price elasticity of supply to achieve net savings of about 63%. Full article

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15 pages, 3401 KiB

Open AccessArticle

The Potential of Activated Carbon Made of Agro-Industrial Residues in NO_x Immissions Abatement

by Imen Ghouma^1,2, Mejdi Jeguirim^1,*

, Uta Sager³

, Lionel Limousy¹

, Simona Bennici¹

, Eckhard Däuber³, Christof Asbach³, Roman Ligotski⁴, Frank Schmidt⁴ and Abdelmottaleb Ouederni²

¹ Institut de Sciences des Matériaux de Mulhouse, Université de Haute-Alsace, 15 Rue Jean Starcky, F-68057 Mulhouse, France

² Department of Chemical Engineering, National School of Engineers (ENIG), University of Gabes, Avenue Omar Ibn El Khattab, Gabes 6029, Tunisia

³ Institut für Energie-und Umwelttechnik e.V., Bliersheimer Str. 58-60, D-47229 Duisburg, Germany

⁴ Nanopartikel Prozesstechnik, Universität Duisburg-Essen, Lotharstr. 1, D-47057 Duisburg, Germany

Energies 2017, 10(10), 1508; https://doi.org/10.3390/en10101508 - 28 Sep 2017

Cited by 47 | Viewed by 6461

Abstract

The treatment of NO_x from automotive gas exhaust has been widely studied, however the presence of low concentrations of NO_x in confined areas is still under investigation. As an example, the concentration of NO₂ can approximate 0.15 ppmv inside vehicles [...] Read more.

The treatment of NO_x from automotive gas exhaust has been widely studied, however the presence of low concentrations of NO_x in confined areas is still under investigation. As an example, the concentration of NO₂ can approximate 0.15 ppmv inside vehicles when people are driving on highways. This interior pollution becomes an environmental problem and a health problem. In the present work, the abatement of NO₂ immission is studied at room temperature. Three activated carbons (ACs) prepared by physical (CO₂ or H₂O) or chemical activation (H₃PO₄) are tested as adsorbents. The novelty of this work consists in studying the adsorption of NO₂ at low concentrations that approach real life immission concentrations and is experimentally realizable. The ACs present different structural and textural properties as well as functional surface groups, which induce different affinities with NO₂. The AC prepared using water vapor activation presents the best adsorption capacity, which may originate from a more basic surface. The presence of a mesoporosity may also influence the diffusion of NO₂ inside the carbon matrix. The high reduction activity of the AC prepared from H₃PO₄ activation is explained by the important concentration of acidic groups on its surface. Full article

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

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21 pages, 4370 KiB

Open AccessArticle

Speed Control of Matrix Converter-Fed Five-Phase Permanent Magnet Synchronous Motors under Unbalanced Voltages

by Borzou Yousefi¹

, Soodabeh Soleymani^1,*, Babak Mozafari¹ and Seid Asghar Gholamian²

¹ Department of Electrical and Computer Engineering, Science and Research Branch, Islamic Azad University (IAU), Tehran 14778-93855, Iran

² Faculty of Electrical and Computer Engineering, Babol Noshirvani University of Technology, Babol 71167-47148, Iran

Energies 2017, 10(10), 1509; https://doi.org/10.3390/en10101509 - 28 Sep 2017

Cited by 5 | Viewed by 4247

Abstract

Five-phase permanent magnet synchronous motors (PMSM) have special applications in which highly accurate speed and torque control of the motor are a strong requirement. Direct Torque Control (DTC) is a suitable method for the driver structure of these motors. If in this method, [...] Read more.

Five-phase permanent magnet synchronous motors (PMSM) have special applications in which highly accurate speed and torque control of the motor are a strong requirement. Direct Torque Control (DTC) is a suitable method for the driver structure of these motors. If in this method, instead of using a common five-phase voltage source inverter, a three-phase to five-phase matrix converter is used, the low-frequency current harmonics and the high torque ripple are limited, and an improved input power factor is obtained. Because the input voltages of such converters are directly supplied by input three-phase supply voltages, an imbalance in the voltages will cause problems such as unbalanced stator currents and electromagnetic torque fluctuations. In this paper, a new method is introduced to remove speed and torque oscillator factors. For this purpose, motor torque equations were developed and the oscillation components created by the unbalanced source voltage, determined. Then, using the active and reactive power reference generator, the controller power reference was adjusted in such a way that the electromagnetic torque of the motor did not change. By this means, a number of features including speed, torque, and flux of the motor were improved in terms of the above-mentioned conditions. Simulations were analyzed using Matlab/Simulink software. Full article

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21 pages, 9608 KiB

Open AccessArticle

Development and Experimental Validation of a TRNSYS Dynamic Tool for Design and Energy Optimization of Ground Source Heat Pump Systems

by Félix Ruiz-Calvo, Carla Montagud^*, Antonio Cazorla-Marín

and José M. Corberán

IUIIE, Universitat Politècnica de València, Camino de Vera sn, 46022 Valencia, Spain

Energies 2017, 10(10), 1510; https://doi.org/10.3390/en10101510 - 28 Sep 2017

Cited by 30 | Viewed by 7886

Abstract

Ground source heat pump (GSHP) systems stand for an efficient technology for renewable heating and cooling in buildings. To optimize not only the design but also the operation of the system, a complete dynamic model becomes a highly useful tool, since it allows [...] Read more.

Ground source heat pump (GSHP) systems stand for an efficient technology for renewable heating and cooling in buildings. To optimize not only the design but also the operation of the system, a complete dynamic model becomes a highly useful tool, since it allows testing any design modifications and different optimization strategies without actually implementing them at the experimental facility. Usually, this type of systems presents strong dynamic operating conditions. Therefore, the model should be able to predict not only the steady-state behavior of the system but also the short-term response. This paper presents a complete GSHP system model based on an experimental facility, located at Universitat Politècnica de València. The installation was constructed in the framework of a European collaborative project with title GeoCool. The model, developed in TRNSYS, has been validated against experimental data, and it accurately predicts both the short- and long-term behavior of the system. Full article

(This article belongs to the Special Issue Low Enthalpy Geothermal Energy)

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13 pages, 1992 KiB

Open AccessArticle

Application of the Sensor Selection Approach in Polymer Electrolyte Membrane Fuel Cell Prognostics and Health Management

by Lei Mao^*

, Ben Davies and Lisa Jackson

Department of Aeronautical and Automotive Engineering, Loughborough University, Loughborough LE11 3RX, UK

Energies 2017, 10(10), 1511; https://doi.org/10.3390/en10101511 - 29 Sep 2017

Cited by 23 | Viewed by 4434

Abstract

In this paper, the sensor selection approach is investigated with the aim of using fewer sensors to provide reliable fuel cell diagnostic and prognostic results. The sensitivity of sensors is firstly calculated with a developed fuel cell model. With sensor sensitivities to different [...] Read more.

In this paper, the sensor selection approach is investigated with the aim of using fewer sensors to provide reliable fuel cell diagnostic and prognostic results. The sensitivity of sensors is firstly calculated with a developed fuel cell model. With sensor sensitivities to different fuel cell failure modes, the available sensors can be ranked. A sensor selection algorithm is used in the analysis, which considers both sensor sensitivity to fuel cell performance and resistance to noise. The performance of the selected sensors in polymer electrolyte membrane (PEM) fuel cell prognostics is also evaluated with an adaptive neuro-fuzzy inference system (ANFIS), and results show that the fuel cell voltage can be predicted with good quality using the selected sensors. Furthermore, a fuel cell test is performed to investigate the effectiveness of selected sensors in fuel cell fault diagnosis. From the results, different fuel cell states can be distinguished with good quality using the selected sensors. Full article

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

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56 pages, 12989 KiB

Open AccessReview

Marine Renewable Energy in the Mediterranean Sea: Status and Perspectives

by Takvor H. Soukissian^1,*

, Dimitra Denaxa¹, Flora Karathanasi^1,2

, Aristides Prospathopoulos¹

, Konstantinos Sarantakos¹, Athanasia Iona¹, Konstantinos Georgantas¹ and Spyridon Mavrakos^2,3

¹ Institute of Oceanography, Hellenic Center for Marine Research, 19013 Anavyssos, Greece

² Department of Naval Architecture and Marine Engineering, National Technical University of Athens, Zografos, 15780 Athens, Greece

³ Hellenic Center for Marine Research, 19013 Anavyssos, Greece

Energies 2017, 10(10), 1512; https://doi.org/10.3390/en10101512 - 29 Sep 2017

Cited by 131 | Viewed by 16353

Abstract

In this work, an extended overview of the marine renewable energy in the Mediterranean Sea is provided as regards current status, potential problems, challenges, and perspectives of development. An integrated and holistic approach is necessary for the economic viability and sustainability of marine [...] Read more.

In this work, an extended overview of the marine renewable energy in the Mediterranean Sea is provided as regards current status, potential problems, challenges, and perspectives of development. An integrated and holistic approach is necessary for the economic viability and sustainability of marine renewable energy projects; this approach comprises three different frameworks, not always aligned, i.e., geotechnical/engineering, socio-economic, and environmental/ecological frameworks. In this context, the geomorphological, climatological, socio-economic, and environmental/ecological particularities of the Mediterranean basin are discussed, as they constitute key issues of the spatial context in which marine renewable energy projects are to be implemented. General guidelines for the sustainable development of marine renewable energy in the Mediterranean are also provided. Full article

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

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14 pages, 5642 KiB

Open AccessArticle

Development of Sliding Mode Controller for a Modified Boost Ćuk Converter Configuration

by Sanjeevikumar Padmanaban^1,*

, Emre Ozsoy¹

, Viliam Fedák²

and Frede Blaabjerg³

¹ Department of Electrical and Electronics Engineering, University of Johannesburg, Auckland Park 2092, South Africa

² Department of Electrical Engineering and Mechatronics, FEI TU of Košice, Letná 9, 04200 Košice, Slovakia

³ Centre for Reliable Power Electronics (CORPE), Department of Energy Technology, Aalborg University, 9000 Aalborg, Denmark

Energies 2017, 10(10), 1513; https://doi.org/10.3390/en10101513 - 29 Sep 2017

Cited by 25 | Viewed by 5007

Abstract

This paper introduces a sliding mode control (SMC)-based equivalent control method to a novel high output gain Ćuk converter. An additional inductor and capacitor improves the efficiency and output gain of the classical Ćuk converter. Classical proportional integral (PI) controllers are widely used [...] Read more.

This paper introduces a sliding mode control (SMC)-based equivalent control method to a novel high output gain Ćuk converter. An additional inductor and capacitor improves the efficiency and output gain of the classical Ćuk converter. Classical proportional integral (PI) controllers are widely used in direct current to direct current (DC-DC) converters. However, it is a very challenging task to design a single PI controller operating in different loads and disturbances. An SMC-based equivalent control method which achieves a robust operation in a wide operation range is also proposed. Switching frequency is kept constant in appropriate intervals at different loading and disturbance conditions by implementing a dynamic hysteresis control method. Numerical simulations conducted in MATLAB/Simulink confirm the accuracy of analysis of high output gain modified Ćuk converter. In addition, the proposed equivalent control method is validated in different perturbations to demonstrate robust operation in wide operation range. Full article

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

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22 pages, 8088 KiB

Open AccessArticle

Seamless Grid Synchronization of a Proportional+Resonant Control-Based Voltage Controller Considering Non-Linear Loads under Islanded Mode

by Kyungbae Lim and Jaeho Choi^*

School of Electrical Engineering, Chungbuk National University, Chungbuk 28644, Korea

Energies 2017, 10(10), 1514; https://doi.org/10.3390/en10101514 - 29 Sep 2017

Cited by 15 | Viewed by 4950

Abstract

This paper proposes the grid synchronization method of inverter using a quasi Proportional+Multi Resonant (P+MR) control-based voltage controller a stationary reference frame. The inverter supplies a non-linear load under the islanded mode. In islanded mode, the inverter is defined as a voltage source [...] Read more.

This paper proposes the grid synchronization method of inverter using a quasi Proportional+Multi Resonant (P+MR) control-based voltage controller a stationary reference frame. The inverter supplies a non-linear load under the islanded mode. In islanded mode, the inverter is defined as a voltage source to supply the full local load demand without a connection to the grid. On the other hand, if the grid is restored from a previous fault or the strategic islanding is unnecessary, the inverter needs to be synchronized with the phase of the grid before the transfer from islanded mode to grid-connected mode. When the system is modeled and controlled based on the stationary reference frame control, the AC reference voltage, which has a constant voltage and frequency in islanded mode, is substituted to the AC grid voltage. Significant error can occur due to the large phase differences between the phase of reference and that of the measured value. This error also can cause severe voltage dynamic problems. In addition, if any nonlinear local load is connected to the output of the inverter, it becomes more serious due to the harmonics generated from the loads. In this paper, the PR control under a stationary reference frame is used for voltage control under islanded mode considering the harmonic effects from the nonlinear load. The seamless grid synchronization method based on this PR control is proposed to solve the aforementioned problems. The validity of the proposed seamless grid synchronization method is verified through PSiM simulations and experimental results. Full article

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

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14 pages, 1126 KiB

Open AccessArticle

Life Cycle Energy Consumption and Greenhouse Gas Emissions Analysis of Natural Gas-Based Distributed Generation Projects in China

by Hansi Liu, Sheng Zhou, Tianduo Peng and Xunmin Ou^*

Institute of Energy, Environment and Economy, Tsinghua University, Beijing 100084, China

Energies 2017, 10(10), 1515; https://doi.org/10.3390/en10101515 - 1 Oct 2017

Cited by 10 | Viewed by 7500

Abstract

In this paper, we used the life-cycle analysis (LCA) method to evaluate the energy consumption and greenhouse gas (GHG) emissions of natural gas (NG) distributed generation (DG) projects in China. We took the China Resources Snow Breweries (CRSB) NG DG project in Sichuan [...] Read more.

In this paper, we used the life-cycle analysis (LCA) method to evaluate the energy consumption and greenhouse gas (GHG) emissions of natural gas (NG) distributed generation (DG) projects in China. We took the China Resources Snow Breweries (CRSB) NG DG project in Sichuan province of China as a base scenario and compared its life cycle energy consumption and GHG emissions performance against five further scenarios. We found the CRSB DG project (all energy input is NG) can reduce GHG emissions by 22%, but increase energy consumption by 12% relative to the scenario, using coal combined with grid electricity as an energy input. The LCA also indicated that the CRSB project can save 24% of energy and reduce GHG emissions by 48% relative to the all-coal scenario. The studied NG-based DG project presents major GHG emissions reduction advantages over the traditional centralized energy system. Moreover, this reduction of energy consumption and GHG emissions can be expanded if the extra electricity from the DG project can be supplied to the public grid. The action of combining renewable energy into the NG DG system can also strengthen the dual merit of energy conservation and GHG emissions reduction. The marginal CO₂ abatement cost of the studied project is about 51 USD/ton CO₂ equivalent, which is relatively low. Policymakers are recommended to support NG DG technology development and application in China and globally to boost NG utilization and control GHG emissions. Full article

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

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14 pages, 1783 KiB

Open AccessArticle

Feature Selection for Partial Discharge Severity Assessment in Gas-Insulated Switchgear Based on Minimum Redundancy and Maximum Relevance

by Ju Tang¹, Miao Jin^1,*, Fuping Zeng¹, Siyuan Zhou¹, Xiaoxing Zhang¹

, Yi Yang² and Yan Ma²

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

² Shandong Electric Power Research Institute, State Grid Shandong Electric Power Company, Jinan 250002, China

Energies 2017, 10(10), 1516; https://doi.org/10.3390/en10101516 - 1 Oct 2017

Cited by 23 | Viewed by 5584

Abstract

Scientific evaluation of partial discharge (PD) severity in gas-insulation switchgear (GIS) can assist in mastering the insulation condition of in-service GIS. Limited theoretical research on the laws of PD deterioration leads to a finite number of evaluation features extracted and subjective features selected [...] Read more.

Scientific evaluation of partial discharge (PD) severity in gas-insulation switchgear (GIS) can assist in mastering the insulation condition of in-service GIS. Limited theoretical research on the laws of PD deterioration leads to a finite number of evaluation features extracted and subjective features selected for PD severity assessment. Therefore, this study proposes a minimum-redundancy maximum-relevance (mRMR) algorithm-based feature optimization selection method to realize the scientific and reasonable choice of PD severity features. PD ultra-high frequency data of varying severities are produced by simulating four typical insulation defects in GIS, which are then collected in the lab. A 16-dimension feature set describing PD original characteristics is abstracted in phase-resolved partial discharge (PRPD) mode, and the more informative evaluation feature set characterizing PD severity is further excavated by the mRMR method. Finally, a support vector machine (SVM) algorithm is employed as the classifier for intelligent evaluation to compare the evaluation effects of PD severity between the feature set selected by mRMR and the feature set is composed of discharge times, amplitude value, and time intervals obtained traditionally based on discharge change theory. The proposed comparison test showed the effectiveness of the mRMR method in informative feature selection and the accuracy of PD severity assessment for all defined defects. Full article

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

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14 pages, 4985 KiB

Open AccessArticle

Investigation of the Thermodynamic Process of the Refrigerator Compressor Based on the m-θ Diagram

by Tao Wang¹, Zhilong He^1,*

, Jun Guo² and Xueyuan Peng¹

¹ School of Energy and Power Engineering, Xi’an Jiaotong University, Xi’an 710049, China

² Nanjing Engineering Institute of Aircraft Systems, Shuige Road 33, Nanjing 211106, China

Energies 2017, 10(10), 1517; https://doi.org/10.3390/en10101517 - 1 Oct 2017

Cited by 12 | Viewed by 6921

Abstract

The variation of refrigerant mass in the cylinder of refrigerator compressor has a great influence on the compressor’s thermodynamic process. In this paper, the m-θ diagram, which represents the variation of refrigerant mass in compressor cylinder (m) and the crank angle ( [...] Read more.

The variation of refrigerant mass in the cylinder of refrigerator compressor has a great influence on the compressor’s thermodynamic process. In this paper, the m-θ diagram, which represents the variation of refrigerant mass in compressor cylinder (m) and the crank angle (θ), is proposed to investigate the thermodynamic process of the refrigerator compressor. Comparing with the traditional pressure-Volume (p-V) indicator diagram, the refrigerant’s backflow trigged by the delayed closure of valve can be clearly expressed in the m-θ diagram together with the mass flow rate. A typical m-θ diagram was obtained by experimental and theoretical investigations. To improve the thermodynamic model of the compressor, a 3D fluid-structure interaction (FSI) FEA model has been introduced to find out the effective flow area of the valves. Based on the m-θ diagram, the effect of rotating speed on the backflow through the valve, which depends on the movement of the valve, has been investigated. Specific to the compressor used in this study, the maximum backflow through the suction valve and discharge valve occur at 3500 r·min⁻¹ and 5500 r·min⁻¹, respectively. Full article

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

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13 pages, 1753 KiB

Open AccessArticle

Two-Tier Reactive Power and Voltage Control Strategy Based on ARMA Renewable Power Forecasting Models

by Jinling Lu¹, Bo Wang², Hui Ren¹, Daqian Zhao¹, Fei Wang^1,3,*

, Miadreza Shafie-khah⁴

and João P. S. Catalão^4,5,6,*

¹ State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University, Baoding 071003, China

² State Key Laboratory of Operation and Control of Renewable Energy & Storage Systems, China Electric Power Research Institute, Beijing 100192, China

³ Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA

⁴ C-MAST, University of Beira Interior, 6201-001 Covilhã, Portugal

⁵ INESC TEC and the Faculty of Engineering of the University of Porto, 4200-465 Porto, Portugal

⁶ INESC-ID, Instituto Superior Técnico, University of Lisbon, 1049-001 Lisbon, Portugal

Energies 2017, 10(10), 1518; https://doi.org/10.3390/en10101518 - 1 Oct 2017

Cited by 21 | Viewed by 4355

Abstract

To address the static voltage stability issue and suppress the voltage fluctuation caused by the increasing integration of wind farms and solar photovoltaic (PV) power plants, a two-tier reactive power and voltage control strategy based on ARMA power forecasting models for wind and [...] Read more.

To address the static voltage stability issue and suppress the voltage fluctuation caused by the increasing integration of wind farms and solar photovoltaic (PV) power plants, a two-tier reactive power and voltage control strategy based on ARMA power forecasting models for wind and solar plants is proposed in this paper. Firstly, ARMA models are established to forecast the output of wind farms and solar PV plants. Secondly, the discrete equipment is pre-regulated based on the single-step prediction information from ARMA forecasting models according to the optimization result. Thirdly, a multi-objective optimization model is presented and solved by particle swarm optimization (PSO) according to the measured data and the proposed static voltage stability index. Finally, the IEEE14 bus system including a wind farm and solar PV plant is utilized to test the effectiveness of the proposed strategy. The results show that the proposed strategy can suppress voltage fluctuation and improve the static voltage stability under the condition of high penetration of renewables including wind and solar power. Full article

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16 pages, 7145 KiB

Open AccessArticle

Partial Stray Inductance Modeling and Measuring of Asymmetrical Parallel Branches on the Bus-Bar of Electric Vehicles

by Chengfei Geng

, Fengyou He^*, Jingwei Zhang and Hongsheng Hu

School of Electrical and Power Engineering, China University of Mining and Technology, Xuzhou 221116, China

Energies 2017, 10(10), 1519; https://doi.org/10.3390/en10101519 - 1 Oct 2017

Cited by 16 | Viewed by 8685

Abstract

In order to increase the power rating of electric vehicles, insulated gate bipolar translator (IGBT) modules with multiple power terminals are usually adopted. The transient current sharing of the same polarity power terminals is related to the stray inductance in the branches of [...] Read more.

In order to increase the power rating of electric vehicles, insulated gate bipolar translator (IGBT) modules with multiple power terminals are usually adopted. The transient current sharing of the same polarity power terminals is related to the stray inductance in the branches of the bus-bar. Based on the laminated bus-bar of a three-phase inverter in the electric vehicles that consists of asymmetrical parallel branches, this paper investigates the transient current imbalance sharing caused by the asymmetrical stray inductance in the parallel branches of the bus-bar from the view of energy storing and releasing of stray inductance for the first time. Besides, the partial self-inductance and mutual-inductance model of the parallel branches is set up. Finally, a high-precision partial stray inductance measurement method is proposed, and the accuracy of the partial stray inductance model for asymmetrical parallel branches is verified by experimental tests. Full article

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

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17 pages, 1009 KiB

Open AccessArticle

Combining a Genetic Algorithm and Support Vector Machine to Study the Factors Influencing CO₂ Emissions in Beijing with Scenario Analysis

by Jinying Li, Binghua Zhang^* and Jianfeng Shi

Department of Economics and Management, North China Electric Power University, Baoding 071003, China

Energies 2017, 10(10), 1520; https://doi.org/10.3390/en10101520 - 2 Oct 2017

Cited by 19 | Viewed by 7776

Abstract

In recent years, Beijing has been facing serious environmental problems. As an important cause of environmental problems, a further study of the factors influencing CO₂ emissions in Beijing has important significance for the social and economic development of Beijing. In this paper, [...] Read more.

In recent years, Beijing has been facing serious environmental problems. As an important cause of environmental problems, a further study of the factors influencing CO₂ emissions in Beijing has important significance for the social and economic development of Beijing. In this paper, Cointegration and Granger causality test were proposed to select influencing factors of CO₂ emissions prediction in Beijing, the influencing factors with different leading lengths were checked as well, and the genetic algorithm (GA) was used to optimize the initial weight and threshold values of a support vector machine (SVM) and the new SVM optimized by GA (GA-SVM) was established to predict the CO₂ emissions of Beijing from 2016–2020 with scenario analysis. Through the comparison of 36 kinds of development scenarios, we found that economic growth, resident population growth and energy intensity enhancement were the major growth factors of carbon emissions, of which the contributions exceed 0.5% in all kinds of development scenarios. Finally, this paper put forward some reasonable policy recommendations for the control of CO₂ emissions. Full article

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14 pages, 2808 KiB

Open AccessArticle

Influence of Refrigerant Charge Amount and EEV Opening on the Performance of a Transcritical CO₂ Heat Pump Water Heater

by Ze Zhang¹

, Xiaojun Dong^1,2, Zheng Ren¹, Tianwei Lai^1,3 and Yu Hou^1,*

¹ State Key Laboratory of Multiphase Flow in Power Engineering, Xi’an Jiaotong University, Xi’an 710049, China

² Allfavor Circuits (Shenzhen) Co. Ltd., Shenzhen 518105, China

³ Xi’an Jiaotong University Suzhou Academy, Suzhou 215123, China

Energies 2017, 10(10), 1521; https://doi.org/10.3390/en10101521 - 3 Oct 2017

Cited by 19 | Viewed by 6533

Abstract

Besides compressor rotary speed and parameters of water flowing through gas cooler and evaporator, refrigerant charge amount and electronic expansion valve (EEV) opening are two important parameters that have significant effects on the performance of a transcritical CO₂ heat pump system. In [...] Read more.

Besides compressor rotary speed and parameters of water flowing through gas cooler and evaporator, refrigerant charge amount and electronic expansion valve (EEV) opening are two important parameters that have significant effects on the performance of a transcritical CO₂ heat pump system. In this study, the effects of refrigerant charge amount on the performance of a transcritical CO₂ heat pump water heater were investigated experimentally at different EEV openings. An optimal coefficient of performance (COP) was found that corresponded to a specific refrigerant charge and a specific EEV opening. Based on the experiment, the COP peaked at charge of 1.8 kg when EEV opening was 40% of full opening. The heating capacity and the COP increased at first, reached peaks and then decreased with increase of charge amount. The COP decreased 14.95% as the CO₂ charge amount was reduced by 22.2% from the optimal charge at 50% EEV opening. As EEV opening varied from 40% to 60% at the same charge amount, the heating capacity decreased more than 30%. Full article

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

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13 pages, 3466 KiB

Open AccessArticle

Using Random Forests to Select Optimal Input Variables for Short-Term Wind Speed Forecasting Models

by Hui Wang¹, Jingxuan Sun², Jianbo Sun¹ and Jilong Wang^1,*

¹ School of Economics and Management, North China Electric Power University, Changping District, Beijing 102206, China

² The Second High School Attached to Beijing Normal University, Xi Cheng District, Beijing 100088, China

Energies 2017, 10(10), 1522; https://doi.org/10.3390/en10101522 - 4 Oct 2017

Cited by 23 | Viewed by 4237

Abstract

Achieving relatively high-accuracy short-term wind speed forecasting estimates is a precondition for the construction and grid-connected operation of wind power forecasting systems for wind farms. Currently, most research is focused on the structure of forecasting models and does not consider the selection of [...] Read more.

Achieving relatively high-accuracy short-term wind speed forecasting estimates is a precondition for the construction and grid-connected operation of wind power forecasting systems for wind farms. Currently, most research is focused on the structure of forecasting models and does not consider the selection of input variables, which can have significant impacts on forecasting performance. This paper presents an input variable selection method for wind speed forecasting models. The candidate input variables for various leading periods are selected and random forests (RF) is employed to evaluate the importance of all variable as features. The feature subset with the best evaluation performance is selected as the optimal feature set. Then, kernel-based extreme learning machine is constructed to evaluate the performance of input variables selection based on RF. The results of the case study show that by removing the uncorrelated and redundant features, RF effectively extracts the most strongly correlated set of features from the candidate input variables. By finding the optimal feature combination to represent the original information, RF simplifies the structure of the wind speed forecasting model, shortens the training time required, and substantially improves the model’s accuracy and generalization ability, demonstrating that the input variables selected by RF are effective. Full article

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19 pages, 581 KiB

Open AccessArticle

Research on Risk Evaluation of Transnational Power Networking Projects Based on the Matter-Element Extension Theory and Granular Computing

by Jinying Li¹, Fan Wu^1,*, Jinchao Li² and Yunqi Zhao³

¹ Department of Economics and Management, North China Electric Power University, Baoding 071003, China

² School of Economics and Management, North China Electric Power University, Beijing 102206, China

³ State Grid Energy Research Institute, Beijing 102206, China

Energies 2017, 10(10), 1523; https://doi.org/10.3390/en10101523 - 5 Oct 2017

Cited by 17 | Viewed by 4027

Abstract

In project management, risk assessment is crucial for stakeholders to identify the risk factors during the whole life cycle of the project. A risk evaluation index system of a transnational networking project, which provides an effective way for the grid integration of clean [...] Read more.

In project management, risk assessment is crucial for stakeholders to identify the risk factors during the whole life cycle of the project. A risk evaluation index system of a transnational networking project, which provides an effective way for the grid integration of clean electricity and the sustainable development of the power industry, is constructed in this paper. Meanwhile, a combination of granular computing and order relation analysis (G1 method) is applied to determine the weight of each indicator and the matter-element extension evaluation model is also employed to seek the global optimal decision during the risk assessment. Finally, a case study is given to validate the index system and evaluation model established in this paper by assessing two different investment schemes of a transnational high voltage direct current (HVDC) transmission project. The result shows that the comprehensive risk level of Scheme 1 is “Low” and the level of Scheme 2 is “General”, which means Scheme 1 is better for the stakeholders from the angle of risk control. The main practical significance of this paper lies in that it can provide a reference and decision support for the government’s power sectors, investment companies and other stakeholders when carrying out related activities. Full article

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

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9 pages, 5101 KiB

Open AccessArticle

Enhanced Thermoelectric Properties of Cu₃SbSe₄ Compounds via Gallium Doping

by Degang Zhao^*, Di Wu and Lin Bo

School of Materials Science and Engineering, University of Jinan, Jinan 250022, China

Energies 2017, 10(10), 1524; https://doi.org/10.3390/en10101524 - 6 Oct 2017

Cited by 40 | Viewed by 4529

Abstract

In this study, the p-type Ga-doped Cu₃Sb_1−xGa_xSe₄ compounds were fabricated by melting, annealing, grinding, and spark plasma sintering (SPS). The transport properties of Ga-doped Cu₃Sb_1−xGa_xSe₄ compounds [...] Read more.

In this study, the p-type Ga-doped Cu₃Sb_1−xGa_xSe₄ compounds were fabricated by melting, annealing, grinding, and spark plasma sintering (SPS). The transport properties of Ga-doped Cu₃Sb_1−xGa_xSe₄ compounds were investigated. As Ga content increased, the hole concentration of Cu₃Sb_1−xGa_xSe₄ compounds increased, which led to an increase in electrical conductivity. Meanwhile, the Seebeck coefficient of the Cu₃Sb_1−xGa_xSe₄ compounds decreased as Ga content increased. The extra phonon scattering originating from Ga-doping effectively depressed the lattice thermal conductivity of the Cu₃Sb_1−xGa_xSe₄ compounds. The ZT value of Cu₃SbSe₄ markedly improved, which is primarily ascribed to the depressed lattice thermal conductivity and the increased electrical conductivity. The highest ZT value for the Cu₃Sb_0.985Ga_0.015Se₄ compound was 0.54 at 650 K, which is two times higher than that of a pure Cu₃SbSe₄ compound. Full article

(This article belongs to the Special Issue Thermoelectric Materials for Energy Conversion)

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20 pages, 1918 KiB

Open AccessEditor’s ChoiceArticle

Building Energy Consumption Prediction: An Extreme Deep Learning Approach

by Chengdong Li^1,*

, Zixiang Ding¹, Dongbin Zhao², Jianqiang Yi²

and Guiqing Zhang¹

¹ School of Information and Electrical Engineering, Shandong Jianzhu University, Jinan 250101, China

² Institute of Automation, Chinese Academy of Sciences, Beijing 100190, China

Energies 2017, 10(10), 1525; https://doi.org/10.3390/en10101525 - 7 Oct 2017

Cited by 260 | Viewed by 18356

Abstract

Building energy consumption prediction plays an important role in improving the energy utilization rate through helping building managers to make better decisions. However, as a result of randomness and noisy disturbance, it is not an easy task to realize accurate prediction of the [...] Read more.

Building energy consumption prediction plays an important role in improving the energy utilization rate through helping building managers to make better decisions. However, as a result of randomness and noisy disturbance, it is not an easy task to realize accurate prediction of the building energy consumption. In order to obtain better building energy consumption prediction accuracy, an extreme deep learning approach is presented in this paper. The proposed approach combines stacked autoencoders (SAEs) with the extreme learning machine (ELM) to take advantage of their respective characteristics. In this proposed approach, the SAE is used to extract the building energy consumption features, while the ELM is utilized as a predictor to obtain accurate prediction results. To determine the input variables of the extreme deep learning model, the partial autocorrelation analysis method is adopted. Additionally, in order to examine the performances of the proposed approach, it is compared with some popular machine learning methods, such as the backward propagation neural network (BPNN), support vector regression (SVR), the generalized radial basis function neural network (GRBFNN) and multiple linear regression (MLR). Experimental results demonstrate that the proposed method has the best prediction performance in different cases of the building energy consumption. Full article

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

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16 pages, 2324 KiB

Open AccessArticle

Grey Relational Analysis for Insulation Condition Assessment of Power Transformers Based Upon Conventional Dielectric Response Measurement

by Jiefeng Liu^1,2,†

, Hanbo Zheng^1,3,*,†

, Yiyi Zhang^1,*,†

, Hua Wei¹ and Ruijin Liao⁴

¹ Guangxi Key Laboratory of Power System Optimization and Energy Technology, Guangxi University, Nanning 530004, China

² Shijiazhuang Power Supply Branch of State Grid Electric Power Company, Shijiazhuang 050093, China

³ State Grid Henan Electric Power Research Institute, Zhengzhou 450052, China

⁴ State Key Laboratory of Power Transmission Equipment & System Security and New Technology, Chongqing University, Chongqing 400044, China

^† These authors contributed equally to this work.

Energies 2017, 10(10), 1526; https://doi.org/10.3390/en10101526 - 8 Oct 2017

Cited by 52 | Viewed by 5091

Abstract

Conventional dielectric response measurement techniques, for instance, recovery voltage measurement (RVM), frequency domain spectroscopy (FDS) and polarization–depolarization current (PDC) are effective nondestructive insulation monitoring techniques for oil-impregnated power transformers. Previous studies have focused mainly on some single type of dielectric measurement method. However, [...] Read more.

Conventional dielectric response measurement techniques, for instance, recovery voltage measurement (RVM), frequency domain spectroscopy (FDS) and polarization–depolarization current (PDC) are effective nondestructive insulation monitoring techniques for oil-impregnated power transformers. Previous studies have focused mainly on some single type of dielectric measurement method. However, the condition of oil paper insulation in transformer is affected by many factors, so it is difficult to predict the insulation status by means of a single method. In this paper, the insulation condition assessment is performed by grey relational analysis (GRA) technique after carefully investigating different dielectric response measurement data. The insulation condition sensitive parameters of samples with unknown insulation status are extracted from different dielectric response measurement data and then these are used to contrast with the standard insulation state vector models established in controlled laboratory conditions by using GRA technique for predicting insulation condition. The performance of the proposed approach is tested using both the laboratory samples and a power transformer to demonstrate that it can provide reliable and effective insulation diagnosis. Full article

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

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36 pages, 9540 KiB

Open AccessArticle

Dynamic Process Model Validation and Control of the Amine Plant at CO₂ Technology Centre Mongstad

by Rubén M. Montañés^1,*

, Nina E. Flø² and Lars O. Nord¹

¹ Department of Energy and Process Engineering, NTNU—Norwegian University of Science and Technology, NO-7491 Trondheim, Norway

² CO₂ Technology Center Mongstad, NO-5954 Mongstad, Norway

Energies 2017, 10(10), 1527; https://doi.org/10.3390/en10101527 - 1 Oct 2017

Cited by 33 | Viewed by 9266

Abstract

This paper presents a set of steady-state and transient data for dynamic process model validation of the chemical absorption process with monoethanolamine (MEA) for post-combustion CO₂ capture of exhaust gas from a natural gas-fired power plant. The data selection includes a wide [...] Read more.

This paper presents a set of steady-state and transient data for dynamic process model validation of the chemical absorption process with monoethanolamine (MEA) for post-combustion CO₂ capture of exhaust gas from a natural gas-fired power plant. The data selection includes a wide range of steady-state operating conditions and transient tests. A dynamic process model developed in the open physical modeling language Modelica is validated. The model is utilized to evaluate the open-loop transient performance at different loads of the plant, showing that pilot plant main process variables respond more slowly at lower operating loads of the plant, to step changes in main process inputs and disturbances. The performance of four decentralized control structures is evaluated, for fast load change transient events. Manipulation of reboiler duty to control CO₂ capture ratio at the absorber’s inlet and rich solvent flow rate to control the stripper bottom solvent temperature showed the best performance. Full article

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17 pages, 1491 KiB

Open AccessArticle

Integral Plus Resonant Sliding Mode Direct Power Control for VSC-HVDC Systems under Unbalanced Grid Voltage Conditions

by Weipeng Yang¹

, Aimin Zhang^1,*, Jungang Li², Guoqi Li³, Hang Zhang¹ and Jianhua Wang¹

¹ School of Electrical Engineering, Xi’an Jiaotong University, No. 28, West Xianning Road, Xi’an 710049, China

² Xuji Group Corporation, State Grid Corporation of China, No. 1298, Xuji Road, Xuchang 461000, China

³ Department of Precision Instrument, Tsinghua University, No. 30, Shuangqing Road, Beijing 100084, China

Energies 2017, 10(10), 1528; https://doi.org/10.3390/en10101528 - 1 Oct 2017

Cited by 11 | Viewed by 4307

Abstract

An integral plus resonant sliding mode direct power control (IRSMC DPC) strategy for voltage source converter high voltage direct current (VSC-HVDC) systems under unbalanced grid voltage conditions is proposed in this paper. Through detailed instantaneous power flow analysis, a generalized power compensation method, [...] Read more.

An integral plus resonant sliding mode direct power control (IRSMC DPC) strategy for voltage source converter high voltage direct current (VSC-HVDC) systems under unbalanced grid voltage conditions is proposed in this paper. Through detailed instantaneous power flow analysis, a generalized power compensation method, by which the ratio between the amplitude of active and reactive power ripples can be controlled continuously, is obtained. This enables the system to provide flexible power control, so that the desired performance of the system on both the ac and dc sides can be attained under different operating conditions. When the grid voltage is unbalanced, one or both of the active and reactive power terms contain ripples, oscillating at twice the grid frequency, to obtain non-distorted ac current. A power controller consisting of the proportional, integral and resonant control laws is designed using the sliding mode control approach, to achieve accurate power control objective. Simulation studies on a two-terminal VSC-HVDC system using MATLAB/SIMULINK (R2013b, Mathworks, Natick, MA, USA) are conducted to verify the effectiveness of the IRSMC DPC strategy. The results show that this strategy ensures satisfactory performance of the system over a wide range of operating conditions. Full article

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

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11 pages, 1689 KiB

Open AccessArticle

Gasification Performance of a Top-Lit Updraft Cook Stove

by Yogesh Mehta and Cecilia Richards^*

School of Mechanical and Materials Engineering, Washington State University, Pullman, WA 99164-2920, USA

Energies 2017, 10(10), 1529; https://doi.org/10.3390/en10101529 - 1 Oct 2017

Cited by 20 | Viewed by 5746

Abstract

This paper reports on an experimental study of a top-lit updraft cook stove with a focus on gasification. The reactor is operated with primary air only. The performance is studied for a variation in the primary airflow, as well as reactor geometry. Temperature [...] Read more.

This paper reports on an experimental study of a top-lit updraft cook stove with a focus on gasification. The reactor is operated with primary air only. The performance is studied for a variation in the primary airflow, as well as reactor geometry. Temperature in the reactor, air flow rate, fuel consumption rate, and producer gas composition were measured. From the measurements the superficial velocity, pyrolysis front velocity, peak bed temperature, air fuel ratio, heating value of the producer gas, and gasification rate were calculated. The results show that the producer gas energy content was maximized at a superficial velocity of 9 cm/s. The percent char remaining at the end of gasification decreased with increasing combustion chamber diameter. For a fixed superficial velocity, the gasification rate and producer gas energy content were found to scale linearly with diameter. The energy content of the producer gas was maximized at an air fuel (AF) ratio of 1.8 regardless of the diameter. Full article

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14 pages, 4551 KiB

Open AccessArticle

Effects of Nonlinearity in Input Filter on the Dynamic Behavior of an Interleaved Boost PFC Converter

by Yitao Liu^1,*

, Shan Yin², Xuewei Pan³, Huaizhi Wang¹, Guibin Wang¹ and Jianchun Peng¹

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

² Microsystem and Terahertz Research Center, China Academy of Engineering Physics, Chengdu 610200, China

³ School of Mechanical Engineering and Automation, Harbin Institute of Technology, Shenzhen 150001, China

Energies 2017, 10(10), 1530; https://doi.org/10.3390/en10101530 - 2 Oct 2017

Cited by 4 | Viewed by 4380

Abstract

A power factor correction (PFC) converter with interleaved multi-channel topology is gaining increasing attention due to its ability in reducing input and output current ripples, but an Electromagnetic Interference (EMI) noise filter is still required for suppressing the large high-frequency switching noise that [...] Read more.

A power factor correction (PFC) converter with interleaved multi-channel topology is gaining increasing attention due to its ability in reducing input and output current ripples, but an Electromagnetic Interference (EMI) noise filter is still required for suppressing the large high-frequency switching noise that could potentially degrade the input power quality of the supplying grid and cause malfunctions to other grid-connected systems. In this paper, a magnetic modeling of an interleaved PFC converter with an input differential mode (DM) EMI filter has been successfully implemented, which considers the nonlinear behavior of the inductive component in the EMI filter. The Jiles-Atherton (J-A) model is applied to describe the filtering inductor whose core displays saturation and hysteresis. The simulation results are verified with the experimental test. Full article

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

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16 pages, 3904 KiB

Open AccessArticle

On the Feasibility of Gap Detection of Power Transformer Partial Discharge UHF Signals: Gap Propagation Characteristics of Electromagnetic Waves

by Xiaoxing Zhang^1,*

, Guozhi Zhang¹, Yalong Li¹, Jian Zhang¹ and Rui Huang²

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

² Shandong Electric Power Research Institute, State Grid Shandong Electric Power Company, Jinan 250002, China

Energies 2017, 10(10), 1531; https://doi.org/10.3390/en10101531 - 2 Oct 2017

Cited by 17 | Viewed by 3165

Abstract

This study analyzed the transformer electromagnetic gap propagation characteristics. The influence of gap size is also analyzed, and the results experimentally verified. The obtained results indicated that the gap propagation characteristics of electromagnetic wave signals radiated by the partial discharge (PD) source in [...] Read more.

This study analyzed the transformer electromagnetic gap propagation characteristics. The influence of gap size is also analyzed, and the results experimentally verified. The obtained results indicated that the gap propagation characteristics of electromagnetic wave signals radiated by the partial discharge (PD) source in different directions are substantially different. The intensity of the electromagnetic wave in the gap reaches a maximum at a gap height of 1 cm; and inside the gap, the intensity of the electromagnetic wave depicted an increasing trend at the tail area of the gap. Finally, from the obtained results, some suggestions on where to install sensors in practical systems for ultra high frequency (UHF) PD signal detection in the transformer gap are provided. The obtained results confirmed the feasibility of using this approach. These results can be seen as a benchmark and a challenge for further research in this field. Full article

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

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17 pages, 4137 KiB

Open AccessArticle

A New Control Method for a Bi-Directional Phase-Shift-Controlled DC-DC Converter with an Extended Load Range

by Wenzheng Xu^1,2, Nelson Hon Lung Chan^1,2, Siu Wing Or^1,2,*

, Siu Lau Ho^1,2 and Ka Wing Chan¹

¹ Department of Electrical Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China

² Hong Kong Branch of National Rail Transit Electrification and Automation Engineering Technology Research Center, Hong Kong, China

Energies 2017, 10(10), 1532; https://doi.org/10.3390/en10101532 - 10 Oct 2017

Cited by 10 | Viewed by 6498

Abstract

Phase-shifted converters are practically important to provide high conversion efficiencies through soft-switching techniques. However, the limitation on a resonant inductor current in the converters often leads to a non-fulfillment of the requirement of minimum load current. This paper presents a new power electronics [...] Read more.

Phase-shifted converters are practically important to provide high conversion efficiencies through soft-switching techniques. However, the limitation on a resonant inductor current in the converters often leads to a non-fulfillment of the requirement of minimum load current. This paper presents a new power electronics control technique to enable the dual features of bi-directional power flow and an extended load range for soft-switching in phase-shift-controlled DC-DC converters. The proposed technique utilizes two identical full bridge converters and inverters in conjunction with a new control logic for gate-driving signals to facilitate both Zero Current Switching (ZCS) and Zero Voltage Switching (ZVS) in a single phase-shift-controlled DC-DC converter. The additional ZCS is designed for light load conditions at which the minimum load current cannot be attained. The bi-directional phase-shift-controlled DC-DC converter can implement the function of synchronous rectification. Its fast dynamic response allows for quick energy recovery during the regenerative braking of traction systems in electrified trains. Full article

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

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8 pages, 1793 KiB

Open AccessCommunication

Determining Coalbed Methane Production and Composition from Individual Stacked Coal Seams in a Multi-Zone Completed Gas Well

by Nino Ripepi^1,2, Kyle Louk², Joseph Amante², Charlies Schlosser², Xu Tang^2,*

and Ellen Gilliland^1,2

¹ Department of Mining and Minerals Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24060, USA

² Virginia Center for Coal and Energy Research Center, Virginia Polytechnic Institute and State University, Blacksburg, VA 24060, USA

Energies 2017, 10(10), 1533; https://doi.org/10.3390/en10101533 - 2 Oct 2017

Cited by 24 | Viewed by 5441

Abstract

This work proposes a novel and cost-effective approach to determine coalbed methane (CBM) production and composition from individual coal seams in a multi-zone completed CBM well. The novel method uses water to cover individual coal seams in a low pressure CBM well followed [...] Read more.

This work proposes a novel and cost-effective approach to determine coalbed methane (CBM) production and composition from individual coal seams in a multi-zone completed CBM well. The novel method uses water to cover individual coal seams in a low pressure CBM well followed by an Echometer fluid level survey to determine the water level. Corresponding gas flow measurements and natural gas chromatography analysis are used to determine gas production and composition from unique zones. A field test using this technology is conducted in Central Appalachia for a multi-zone CBM well containing 18 coal seams. Test results show that the shallow coal seams contribute the majority of the total CBM production in this multi-zone well, and the deeper coal seams contain more heavy hydrocarbons like ethane and propane. Full article

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

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13 pages, 1796 KiB

Open AccessArticle

An Electric Power Consumption Analysis System for the Installation of Electric Vehicle Charging Stations

by Seongpil Cheon and Suk-Ju Kang^*

Department of Electronic Engineering, Sogang University, Seoul 04107, Korea

Energies 2017, 10(10), 1534; https://doi.org/10.3390/en10101534 - 3 Oct 2017

Cited by 32 | Viewed by 7009

Abstract

With the rising demand for electric vehicles, the number of electric vehicle charging stations is increasing. Therefore, real-time monitoring of how the power consumption by charging stations affects the load on the peripheral power grid is important. However, related organizations generally do not [...] Read more.

With the rising demand for electric vehicles, the number of electric vehicle charging stations is increasing. Therefore, real-time monitoring of how the power consumption by charging stations affects the load on the peripheral power grid is important. However, related organizations generally do not provide actual power consumption data in real time, and only limited information, such as the charging time, is provided. Therefore, it is difficult to calculate and predict the power load in real time. In this paper, we propose a new model for estimating the electric power consumption from the supplied information, i.e., the charging time and the number of charging involved. The experimental results show that by displaying this information on a map, it is possible to visually monitor the electric power consumption of the charging stations with an accuracy rate of about 86%. Finally, the proposed system can be used to relocate and select the location of vehicle charging stations. Full article

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33 pages, 10446 KiB

Open AccessArticle

Detailed Modelling of the Deep Decarbonisation Scenarios with Demand Response Technologies in the Heating and Cooling Sector: A Case Study for Italy

by Francesco Calise¹

, Massimo Dentice D’Accadia¹

, Carlo Barletta¹, Vittoria Battaglia^1,*, Antun Pfeifer² and Neven Duic²

¹ Department of Industrial Engineering, University of Naples Federico II, 80040 Naples, Italy

² Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb,10000 Zagreb, Croatia

Energies 2017, 10(10), 1535; https://doi.org/10.3390/en10101535 - 3 Oct 2017

Cited by 40 | Viewed by 6097

Abstract

Energy policies accompanying the transition towards a sustainable development process must be supported by technical analyses in which future energy scenarios are modeled and evaluated. This paper analyzes possible decarbonization scenarios in Italy for the year 2050. They envisage high electrification of transports [...] Read more.

Energy policies accompanying the transition towards a sustainable development process must be supported by technical analyses in which future energy scenarios are modeled and evaluated. This paper analyzes possible decarbonization scenarios in Italy for the year 2050. They envisage high electrification of transports and residential buildings, high use of renewable energies, and a modal shift towards public transport. The energy scenarios are evaluated using a software program, EnergyPLAN, starting from a reference model developed for the year 2014. Special attention has been given to the modeling of data that are unavailable in the literature, such as the time profile of heating and cooling demands, obtained with the degree-days method and validated by elaborating the results of the modeling of the residential building stock, this latter was dynamically simulated in TRNSYS. The results show that to obtain a significant decrease of greenhouse gas emissions and fossil fuel consumption, it is necessary not only to promote a deeper penetration of renewable sources, but also their integration with other technologies (cogeneration, trigeneration, power-to-heat systems, thermal storage, vehicle-to-grid operations). In fact, renewables technologies alone can raise some critical issues, such as excess and/or shortage of electricity production and non-sustainable exploitation of biomass. Full article

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

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23 pages, 8502 KiB

Open AccessArticle

Probabilistic Load-Flow Analysis of Biomass-Fuelled Gas Engines with Electrical Vehicles in Distribution Systems

by Francisco J. Ruiz-Rodríguez¹

, Jesús C. Hernández^2,*

and Francisco Jurado²

¹ Electrical and Thermal Engineering Department, University of Huelva, 21004 Huelva, Spain

² Department of Electrical Engineering, University of Jaén, 23071 Jaén, Spain

Energies 2017, 10(10), 1536; https://doi.org/10.3390/en10101536 - 3 Oct 2017

Cited by 36 | Viewed by 4654

Abstract

Feeding biomass-fueled gas engines (BFGEs) with olive tree pruning residues offers new opportunities to decrease fossil fuel use in road vehicles and electricity generation. BFGEs, coupled to radial distribution systems (RDSs), provide renewable energy and power that can feed electric vehicle (EV) charging [...] Read more.

Feeding biomass-fueled gas engines (BFGEs) with olive tree pruning residues offers new opportunities to decrease fossil fuel use in road vehicles and electricity generation. BFGEs, coupled to radial distribution systems (RDSs), provide renewable energy and power that can feed electric vehicle (EV) charging stations. However, the combined impact of BFGEs and EVs on RDSs must be assessed to assure the technical constraint fulfilment. Because of the stochastic nature of source/load, it was decided that a probabilistic approach was the most viable option for this assessment. Consequently, this research developed an analytical technique to evaluate the technical constraint fulfilment in RDSs with this combined interaction. The proposed analytical technique (PAT) involved the calculation of cumulants and the linearization of load-flow equations, along with the application of the cumulant method, and Cornish-Fisher expansion. The uncertainties related to biomass stock and its heating value (HV) were important factors that were assessed for the first time. Application of the PAT in a Spanish RDS with BFGEs and EVs confirmed the feasibility of the proposal and its additional benefits. Specifically, BFGEs were found to clearly contribute to the voltage constraint fulfilment. The computational cost of the PAT was lower than that associated with Monte-Carlo simulations (MCSs). Full article

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

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17 pages, 3083 KiB

Open AccessArticle

Data-Driven Optimization of Incentive-based Demand Response System with Uncertain Responses of Customers

by Jimyung Kang^1,2 and Jee-Hyong Lee^1,*

¹ Department of Electrical and Computer Engineering, Sungkyunkwan University, 2006 Seobu-ro, Jangan-gu, Suwon 440-746, Korea

² Korea Electrotechnology Research Institute, 111 Hanggaul-ro, Sangnok-gu, Ansan 426-910, Korea

Energies 2017, 10(10), 1537; https://doi.org/10.3390/en10101537 - 4 Oct 2017

Cited by 9 | Viewed by 4836

Abstract

Demand response is nowadays considered as another type of generator, beyond just a simple peak reduction mechanism. A demand response service provider (DRSP) can, through its subcontracts with many energy customers, virtually generate electricity with actual load reduction. However, in this type of [...] Read more.

Demand response is nowadays considered as another type of generator, beyond just a simple peak reduction mechanism. A demand response service provider (DRSP) can, through its subcontracts with many energy customers, virtually generate electricity with actual load reduction. However, in this type of virtual generator, the amount of load reduction includes inevitable uncertainty, because it consists of a very large number of independent energy customers. While they may reduce energy today, they might not tomorrow. In this circumstance, a DSRP must choose a proper set of these uncertain customers to achieve the exact preferred amount of load curtailment. In this paper, the customer selection problem for a service provider that consists of uncertain responses of customers is defined and solved. The uncertainty of energy reduction is fully considered in the formulation with data-driven probability distribution modeling and stochastic programming technique. The proposed optimization method that utilizes only the observed load data provides a realistic and applicable solution to a demand response system. The performance of the proposed optimization is verified with real demand response event data in Korea, and the results show increased and stabilized performance from the service provider’s perspective. Full article

(This article belongs to the Collection Smart Grid)

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17 pages, 434 KiB

Open AccessArticle

Demand-Side Energy Management Based on Nonconvex Optimization in Smart Grid

by Kai Ma^1,*

, Yege Bai¹, Jie Yang^1,2, Yangqing Yu¹ and Qiuxia Yang¹

¹ School of Electrical Engineering, Yanshan University, Qinhuangdao 066004, China

² Key Laboratory of System Control and Information Processing, Ministry of Education, Shanghai Jiao Tong University, Shanghai 200240, China

Energies 2017, 10(10), 1538; https://doi.org/10.3390/en10101538 - 4 Oct 2017

Cited by 7 | Viewed by 4963

Abstract

Demand-side energy management is used for regulating the consumers’ energy usage in smart grid. With the guidance of the grid’s price policy, the consumers can change their energy consumption in response. The objective of this study is jointly optimizing the load status and [...] Read more.

Demand-side energy management is used for regulating the consumers’ energy usage in smart grid. With the guidance of the grid’s price policy, the consumers can change their energy consumption in response. The objective of this study is jointly optimizing the load status and electric supply, in order to make a tradeoff between the electric cost and the thermal comfort. The problem is formulated into a nonconvex optimization model. The multiplier method is used to solve the constrained optimization, and the objective function is transformed to the augmented Lagrangian function without constraints. Hence, the Powell direction acceleration method with advance and retreat is applied to solve the unconstrained optimization. Numerical results show that the proposed algorithm can achieve the balance between the electric supply and demand, and the optimization variables converge to the optimum. Full article

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

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12 pages, 5430 KiB

Open AccessArticle

Evaluation Method for the Firm Power Escalation of a Wind-Storage Hybrid Power System

by Sanli Zhu^1,*, Jiping Lu¹, Zheng Li¹ and Junyi Lin²

¹ State Key Laboratory of Power Transmission Equipment & System Security and New Technology, School of Electric Engineering of Chongqing University, Shapingba District, Chongqing 400000, China

² State Grid Chongqing Yongchuan Electric Power Supply Branch, Chongqing 400000, China

Energies 2017, 10(10), 1539; https://doi.org/10.3390/en10101539 - 5 Oct 2017

Viewed by 3013

Abstract

To improve the controllability of the electric power output and the economic performance of a large-scale wind farm, an auxiliary energy storage system is required. This paper deals with the rule of planning reasonable energy storage power and capacity based on the historical [...] Read more.

To improve the controllability of the electric power output and the economic performance of a large-scale wind farm, an auxiliary energy storage system is required. This paper deals with the rule of planning reasonable energy storage power and capacity based on the historical annual mean wind speed data, the probability density of the pulsating wind power output, and the warranted firm power provided by the wind farm. Specifically, the evaluation index of the fluctuation degree of the firm power is defined in order to optimize the planned energy storage capacity. After that, the firm power escalation affected by the energy storage power and the conversion rate of the storage device are quantitatively evaluated. All of these analyses contribute in a significant way towards determining the acceptable energy conversion rate with the condition of limited energy storage space of a wind-storage hybrid power system. The proposed evaluation method of the firm power escalation is verified by MatLab simulation results. Full article

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

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15 pages, 3925 KiB

Open AccessArticle

Advanced Reactive Power Reserve Management Scheme to Enhance LVRT Capability

by Hwanik Lee¹, Moonsung Bae² and Byongjun Lee^1,*

¹ School of Electrical Engineering, Korea University, Anam Campus, 145 Anam-ro, Seongbuk-gu, Seoul 02841, Korea

² Korea Electric Power Research Institute (KEPRI), Korea Electric Power Corporation (KEPCO), 105 Munji-Ro, Yuseong-Gu, Deajeon 305-760, Korea

Energies 2017, 10(10), 1540; https://doi.org/10.3390/en10101540 - 5 Oct 2017

Cited by 7 | Viewed by 5173

Abstract

Abstract: To increase the utilization of wind power in the power system, grid integration standards have been proposed for the stable integration of large-scale wind power plants. In particular, fault-ride-through capability, especially Low-Voltage-Ride-Through (LVRT), has been emphasized, as it is related to [...] Read more.

Abstract: To increase the utilization of wind power in the power system, grid integration standards have been proposed for the stable integration of large-scale wind power plants. In particular, fault-ride-through capability, especially Low-Voltage-Ride-Through (LVRT), has been emphasized, as it is related to tripping in wind farms. Therefore, this paper proposes the Wind power plant applicable-Effective Reactive power Reserve (Wa-ERPR), which combines both wind power plants and conventional generators at the Point of Interconnection (POI). The reactive power capability of the doubly-fed induction generator wind farm was considered to compute the total Wa-ERPR at the POI with reactive power capability of existing generators. By using the Wa-ERPR management algorithm, in case of a violation of the LVRT standards, the amount of reactive power compensation is computed using the Wa-ERPR management scheme. The proposed scheme calculates the Wa-ERPR and computes the required reactive power, reflecting the change of the system topology pre- and post-contingency, to satisfy the LVRT criterion when LVRT regulation is not satisfied at the POI. The static synchronous compensator (STATCOM) with the capacity corresponding to calculated amount of reactive power through the Wa-ERPR management scheme is applied to the POI. Therefore, it is confirmed that the wind power plant satisfies the LVRT criteria by securing the appropriate reactive power at the POI, by applying of the proposed algorithm. Full article

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

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17 pages, 5130 KiB

Open AccessArticle

Techniques for Reduction of the Cogging Torque in Claw Pole Machines with SMC Cores

by Chengcheng Liu^1,2

, Jiawei Lu^1,2, Youhua Wang^1,2,*, Gang Lei³

, Jianguo Zhu³ and Youguang Guo³

¹ State Key Laboratory of Reliability and Intelligence of Electrical Equipment, Hebei University of Technology, Tianjin 300131, China

² Key Laboratory of Electromagnetic Field and Electrical Apparatus Reliability of Hebei Province, Hebei University of Technology; Tianjin 300131, China

³ Schoolof Electrical, Mechanical and Mechatronic Systems University of Technology Sydney, Ultimo NSW 2007, Australia

Energies 2017, 10(10), 1541; https://doi.org/10.3390/en10101541 - 6 Oct 2017

Cited by 18 | Viewed by 6453

Abstract

As one of the main parasitic parameters in permanent magnet (PM) synchronous machines (PMSMs), cogging torque is the main component of the torque ripple, which has always been the handicap in the high-performance, low-speed drive systems. Over the last two decades, various methods [...] Read more.

As one of the main parasitic parameters in permanent magnet (PM) synchronous machines (PMSMs), cogging torque is the main component of the torque ripple, which has always been the handicap in the high-performance, low-speed drive systems. Over the last two decades, various methods have been proposed to decrease the cogging torque in both radial-flux and axial-flux PMSMs. Among these methods, stator slot skewing, stator tooth notching, permanent magnet (PM) skewing, PM shifting, and pole pairing are extensively investigated. However, little work has been done on reducing the cogging torque of the claw pole machine (CPM), whose cogging torque cannot be ignored. In this paper, the general methods that have been used to reduce the cogging torque in radial-flux and axial-flux PMSMs are developed and verified in a CPM with a soft magnetic composite (SMC) core. The 3-D finite element method (FEM) is used to calculate the cogging torque and PM flux linkage per turn. By comparing different cogging torque reduction technologies, it can be found that the magnet step skewing and unequal claw pole width are very suitable for CPM. Full article

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

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18 pages, 6857 KiB

Open AccessArticle

An Improved Forecasting Method for Photovoltaic Power Based on Adaptive BP Neural Network with a Scrolling Time Window

by Honglu Zhu^1,2,3

, Weiwei Lian², Lingxing Lu², Songyuan Dai^1,2,3 and Yang Hu^1,*

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

² School of Renewable Energy, North China Electric Power University, Changping District, Beijing 102206, China

³ Beijing Key Laboratory of New and Renewable Energy, North China Electric Power University, Changping District, Beijing 102206, China

Energies 2017, 10(10), 1542; https://doi.org/10.3390/en10101542 - 6 Oct 2017

Cited by 41 | Viewed by 4216

Abstract

Due to the large scale of grid-connected photovoltaic (PV) power generation installations, accurate PV power forecasting is critical to the safe and economic operation of the electric power system. In the paper, by analyzing the influence of external ambient factors and the changing [...] Read more.

Due to the large scale of grid-connected photovoltaic (PV) power generation installations, accurate PV power forecasting is critical to the safe and economic operation of the electric power system. In the paper, by analyzing the influence of external ambient factors and the changing characteristics of PV modules with time, it is found that PV power generation is a nonlinear and time-varying process. This suggests that a certain single forecasting model is inadequate for representing actual generation characteristics, and it is difficult to obtain an accurate forecasting result. An adaptive back propagation (BP) neural network model adopting scrolling time window is proposed to solve the problem. Via an update of the training data of BP neural network with the scrolling time window, the forecasting model adapts to time and a changing external environment with the required modeling precision. Meanwhile, through evaluation of the forecasting performance in different time windows, an optimized time window can be determined to guarantee accuracy. Finally, using the actual operation data of a PV plant in Beijing, the approach is validated as being applicable for PV power forecasting and is able to effectively respond to the dynamic change of the PV power generation process. This improves the forecasting accuracy and also reduces computation complexity as compared with the conventional BP neural network algorithm. Full article

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18 pages, 3953 KiB

Open AccessArticle

Modeling of HVDC System to Improve Estimation of Transient DC Current and Voltages for AC Line-to-Ground Fault—An Actual Case Study in Korea

by Dohoon Kwon¹, Youngjin Kim^2,*, Seungil Moon¹ and Chanki Kim³

¹ Department of Electrical and Computer Engineering, Seoul National University, 1 Gwanak-ro, Seoul, Korea

² Department of Electrical Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Gyungbuk 37673, Korea

³ Transmission & Distribution Lab., the R&D Center of Korea Electric Power Co., Daejeon 305-380, Korea

Energies 2017, 10(10), 1543; https://doi.org/10.3390/en10101543 - 6 Oct 2017

Cited by 17 | Viewed by 6454

Abstract

A new modeling method for high voltage direct current (HVDC) systems and associated controllers is presented for the power system simulator for engineering (PSS/E) simulation environment. The aim is to improve the estimation of the transient DC voltage and current in the event [...] Read more.

A new modeling method for high voltage direct current (HVDC) systems and associated controllers is presented for the power system simulator for engineering (PSS/E) simulation environment. The aim is to improve the estimation of the transient DC voltage and current in the event of an AC line-to-ground fault. The proposed method consists primary of three interconnected modules for (a) equation conversion; (b) control-mode selection; and (c) DC-line modeling. Simulation case studies were carried out using PSS/E and a power systems computer aided design/electromagnetic transients including DC (PSCAD/EMTDC) model of the Jeju– Haenam HVDC system in Korea. The simulation results are compared with actual operational data and the PSCAD/EMTDC simulation results for an HVDC system during single-phase and three-phase line-to-ground faults, respectively. These comparisons show that the proposed PSS/E modeling method results in the improved estimation of the dynamic variation in the DC voltage and current in the event of an AC network fault, with significant gains in computational efficiency, making it suitable for real-time analysis of HVDC systems. Full article

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

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15 pages, 9529 KiB

Open AccessArticle

Study of Anti-Sliding Stability of a Dam Foundation Based on the Fracture Flow Method with 3D Discrete Element Code

by Chong Shi^1,2

, Wenkun Yang^1,2,*

, Weijiang Chu³, Junliang Shen^1,3

and Yang Kong^1,2

¹ Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering, Hohai University, Nanjing 210098, China

² Institute of Geotechnical Research, Hohai University, Nanjing 210098, China

³ HydroChina-ITASCA R&D Center, ITASCA Consulting Group, Hangzhou 311122, China

Energies 2017, 10(10), 1544; https://doi.org/10.3390/en10101544 - 6 Oct 2017

Cited by 6 | Viewed by 4460

Abstract

Fractured seepage is an important factor affecting the interface stability of rock mass. It is closely related to fracture properties and hydraulic conditions. In this study, the law of seepage in a single fracture surface based on modified cubic law is described, and [...] Read more.

Fractured seepage is an important factor affecting the interface stability of rock mass. It is closely related to fracture properties and hydraulic conditions. In this study, the law of seepage in a single fracture surface based on modified cubic law is described, and the three-dimensional discrete element method is used to simulate the dam foundation structure of the Capulin San Pablo (Costa Rica) hydropower station. The effect of construction joints and developed structure on dam stability is studied, and its permeability law and sliding stability are also evaluated. It is found that the hydraulic-mechanical coupling with strength reduction method in DEM is more appropriate to use to study the seepage-related problems of fractured rock mass, which considers practical conditions, such as the roughness of and the width of fracture. The strength reduction method provides a more accurate safety factor of dam when considering the deformation coordination with bedrocks. It is an important method with which to study the stability of seepage conditions in complex structures. The discrete method also provided an effective and reasonable way of determining seepage control measures. Full article

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11 pages, 856 KiB

Open AccessArticle

Estimating the Value of Price Risk Reduction in Energy Efficiency Investments in Buildings

by Pekka Tuominen^1,* and Tuomas Seppänen²

¹ VTT Technical Research Centre of Finland Ltd., P.O. Box 1000, 02044 VTT Espoo, Finland

² OP Financial Group, P.O. Box 308, 00101 Helsinki, Finland

Energies 2017, 10(10), 1545; https://doi.org/10.3390/en10101545 - 8 Oct 2017

Cited by 4 | Viewed by 6537

Abstract

This paper presents a method for calculating the value of price risk reduction to a consumer that can be achieved with investments in energy efficiency. The value of price risk reduction is discussed to some length in general terms in the literature reviewed [...] Read more.

This paper presents a method for calculating the value of price risk reduction to a consumer that can be achieved with investments in energy efficiency. The value of price risk reduction is discussed to some length in general terms in the literature reviewed but, so far, no methodology for calculating the value has been presented. Here we suggest such a method. The problem of valuating price risk reduction is approached using a variation of the Black–Scholes model by considering a hypothetical financial instrument that a consumer would purchase to insure herself against unexpected price hikes. This hypothetical instrument is then compared with an actual energy efficiency investment that reaches the same level of price risk reduction. To demonstrate the usability of the method, case examples are calculated for typical single-family houses in Finland. The results show that the price risk entailed in household energy consumption can be reduced by a meaningful amount with energy efficiency investments, and that the monetary value of this reduction can be calculated. It is argued that this often-overlooked benefit of energy efficiency investments merits more consideration in future studies. Full article

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27 pages, 677 KiB

Open AccessArticle

Towards Cost and Comfort Based Hybrid Optimization for Residential Load Scheduling in a Smart Grid

by Nadeem Javaid^1,*

, Fahim Ahmed¹, Ibrar Ullah^1,2, Samia Abid¹, Wadood Abdul³

, Atif Alamri³

and Ahmad S. Almogren³

¹ COMSATS Institute of Information Technology, Islamabad 44000, Pakistan

² University of Engineering and Technology Peshawar, Bannu 28100, Pakistan

³ Pervasive and Mobile Computing, College of Computer and Information Sciences, King Saud University, Riyadh 11633, Saudi Arabia

Energies 2017, 10(10), 1546; https://doi.org/10.3390/en10101546 - 8 Oct 2017

Cited by 59 | Viewed by 6265

Abstract

In a smart grid, several optimization techniques have been developed to schedule load in the residential area. Most of these techniques aim at minimizing the energy consumption cost and the comfort of electricity consumer. Conversely, maintaining a balance between two conflicting objectives: energy [...] Read more.

In a smart grid, several optimization techniques have been developed to schedule load in the residential area. Most of these techniques aim at minimizing the energy consumption cost and the comfort of electricity consumer. Conversely, maintaining a balance between two conflicting objectives: energy consumption cost and user comfort is still a challenging task. Therefore, in this paper, we aim to minimize the electricity cost and user discomfort while taking into account the peak energy consumption. In this regard, we implement and analyse the performance of a traditional dynamic programming (DP) technique and two heuristic optimization techniques: genetic algorithm (GA) and binary particle swarm optimization (BPSO) for residential load management. Based on these techniques, we propose a hybrid scheme named GAPSO for residential load scheduling, so as to optimize the desired objective function. In order to alleviate the complexity of the problem, the multi dimensional knapsack is used to ensure that the load of electricity consumer will not escalate during peak hours. The proposed model is evaluated based on two pricing schemes: day-ahead and critical peak pricing for single and multiple days. Furthermore, feasible regions are calculated and analysed to develop a relationship between power consumption, electricity cost, and user discomfort. The simulation results are compared with GA, BPSO and DP, and validate that the proposed hybrid scheme reflects substantial savings in electricity bills with minimum user discomfort. Moreover, results also show a phenomenal reduction in peak power consumption. Full article

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

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25 pages, 2473 KiB

Open AccessArticle

Two-Stage Electricity Demand Modeling Using Machine Learning Algorithms

by Krzysztof Gajowniczek^*

and Tomasz Ząbkowski

Department of Informatics, Faculty of Applied Informatics and Mathematics, Warsaw University of Life Sciences, Nowoursynowska 159, 02-787 Warsaw, Poland

Energies 2017, 10(10), 1547; https://doi.org/10.3390/en10101547 - 8 Oct 2017

Cited by 40 | Viewed by 8345

Abstract

Forecasting of electricity demand has become one of the most important areas of research in the electric power industry, as it is a critical component of cost-efficient power system management and planning. In this context, accurate and robust load forecasting is supposed to [...] Read more.

Forecasting of electricity demand has become one of the most important areas of research in the electric power industry, as it is a critical component of cost-efficient power system management and planning. In this context, accurate and robust load forecasting is supposed to play a key role in reducing generation costs, and deals with the reliability of the power system. However, due to demand peaks in the power system, forecasts are inaccurate and prone to high numbers of errors. In this paper, our contributions comprise a proposed data-mining scheme for demand modeling through peak detection, as well as the use of this information to feed the forecasting system. For this purpose, we have taken a different approach from that of time series forecasting, representing it as a two-stage pattern recognition problem. We have developed a peak classification model followed by a forecasting model to estimate an aggregated demand volume. We have utilized a set of machine learning algorithms to benefit from both accurate detection of the peaks and precise forecasts, as applied to the Polish power system. The key finding is that the algorithms can detect 96.3% of electricity peaks (load value equal to or above the 99th percentile of the load distribution) and deliver accurate forecasts, with mean absolute percentage error (MAPE) of 3.10% and resistant mean absolute percentage error (r-MAPE) of 2.70% for the 24 h forecasting horizon. Full article

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

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17 pages, 1153 KiB

Open AccessArticle

Optimal Cold-Start Control of a Gasoline Engine

by Raffael Hedinger^*, Philipp Elbert and Christopher Onder

Institute for Dynamic Systems and Control, ETH Zurich, Sonneggstrasse 3, 8092 Zurich, Switzerland

Energies 2017, 10(10), 1548; https://doi.org/10.3390/en10101548 - 9 Oct 2017

Cited by 22 | Viewed by 4498

Abstract

This article analyzes the influence of the ignition retardation on the fuel consumption, the cumulative tailpipe hydrocarbon emissions, and the temperature inside the three-way catalytic converter in a gasoline direct injection engine operated under idling conditions. A dedicated cylinder-individual, model-based, multivariable controller was [...] Read more.

This article analyzes the influence of the ignition retardation on the fuel consumption, the cumulative tailpipe hydrocarbon emissions, and the temperature inside the three-way catalytic converter in a gasoline direct injection engine operated under idling conditions. A dedicated cylinder-individual, model-based, multivariable controller was used in experiments in order to isolate the effect of the ignition retardation on the hydrocarbon emissions as much as possible. An optimal control problem for a gasoline engine at a cold-start is formulated, which is used to interpret the experimental data obtained. The corresponding goal is to minimize the fuel consumption during an initial idling phase of a fixed duration while guaranteeing that the three-way catalytic converter reaches a sufficiently high final temperature and at the same time making sure that the cumulative hydrocarbon emissions stay below a given limit. The experimental data indicates that the engine should be operated with maximum ignition retardation in order to reach any temperature inside the three-way catalytic converter as quickly as possible concurrently with minimum tailpipe emissions and with the minimum possible fuel consumption. Full article

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23 pages, 7752 KiB

Open AccessArticle

Effect of Permeability Anisotropy on the Production of Multi-Scale Shale Gas Reservoirs

by Ting Huang^1,*, Zhengwu Tao², Erpeng Li², Qiqi Lyu¹ and Xiao Guo³

¹ Hubei Cooperative Innovation Center of Unconventional Oil and Gas, Yangtze University, Wuhan 430100, China

² Tarim Oilfield Company, PetroChina, Korla, Xinjiang 841000, China

³ State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, China

Energies 2017, 10(10), 1549; https://doi.org/10.3390/en10101549 - 9 Oct 2017

Cited by 23 | Viewed by 6148

Abstract

Shales or mudstones are fine grained and layered reservoirs, which leads to strong shale permeability anisotropy. Shale has a wide pore-size distribution, and pores with different diameters contribute differently to the apparent permeability of shales. Therefore, understanding the anisotropy of multiscale shale gas [...] Read more.

Shales or mudstones are fine grained and layered reservoirs, which leads to strong shale permeability anisotropy. Shale has a wide pore-size distribution, and pores with different diameters contribute differently to the apparent permeability of shales. Therefore, understanding the anisotropy of multiscale shale gas reservoirs is an important aspect to model and evaluate gas production from shales. In this paper, a novel model of permeability anisotropy for shale gas reservoirs is presented to calculate the permeability in an arbitrary direction in three dimensional space. A numerical model which is valid for the entire Knudsen’s range (continuum flow, slip flow, transition flow and free molecular flow) in shale gas reservoirs was developed, and the effect of gas-water flow and the simulation of hydraulic fracturing cracks were taken into consideration as well. The simulation result of the developed model was validated with field data. Effects of critical factors such as permeability anisotropy, relative permeability curves with different nanopore radii and initial water saturation in formation on the gas production rate of multi-stage fractured horizontal well were discussed. Besides, flow regimes of gas flow in shales were classified by Knudsen number, and the effect of various flow regimes on both apparent permeability of shales and then the gas production has been analyzed thoroughly. Full article

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

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20 pages, 979 KiB

Open AccessArticle

Evaluation of Economic, Social and Environmental Effects of Low-Emission Energy Technologies Development in Poland: A Multi-Criteria Analysis with Application of a Fuzzy Analytic Hierarchy Process (FAHP)

by Magdalena Ligus

Department of Corporate and Public Finance, Wroclaw University of Economics, Komandorska 118/120, 53-345 Wroclaw, Poland

Energies 2017, 10(10), 1550; https://doi.org/10.3390/en10101550 - 9 Oct 2017

Cited by 36 | Viewed by 5444

Abstract

The European Commission as well as the Polish government are promoting sustainable use of energy sources as a part of the dominating sustainable development paradigm. The development of low-emission energy sources engages the challenges of gradual depletion of coal, oil and natural gas [...] Read more.

The European Commission as well as the Polish government are promoting sustainable use of energy sources as a part of the dominating sustainable development paradigm. The development of low-emission energy sources engages the challenges of gradual depletion of coal, oil and natural gas reserves, as well as the intensification of the greenhouse effect. The energy policy should take into account development of low-emission energy technologies that contribute mostly to meeting the goals of sustainable development in three dimensions: economic, social and environmental. This study aims to assess the extent to which five low-emission energy technologies contribute to social welfare in the scope of the concept of sustainable development. Heuristic methods, including fuzzy analytic hierarchy process (FAHP) are used to resolve the multi-goal problem in order to achieve the aim of this research. Research results show that economic goal is still the most important to the development of various low-emission energy technologies in Poland, followed by the social and environmental goals. Secondly, renewable energy technologies should be utilized instead of nuclear energy to meet sustainable development policy goals. Photovoltaics, followed by biomass and biogas are perceived as the most suitable renewable energy sources. Wind on-shore and wind of-shore are on third and fourth place, respectively. Full article

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

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16 pages, 10134 KiB

Open AccessArticle

A Novel Design Method for the Geometric Shapes of Flux Modulation Poles in the Surface-Mounted Permanent Magnet Vernier Machines

by Daekyu Jang and Junghwan Chang^*

Mechatronics System Research Laboratory, Electrical Engineering Department, Dong-A University, Busan 52121, Korea

Energies 2017, 10(10), 1551; https://doi.org/10.3390/en10101551 - 9 Oct 2017

Cited by 5 | Viewed by 4895

Abstract

This paper presents a novel approach to determine geometric shapes of flux modulation poles (FMPs) by using the analytical equations for flux density distribution due to armature windings. The magnetic field by the windings is modulated by the FMPs. Then, the resulting magnetic [...] Read more.

This paper presents a novel approach to determine geometric shapes of flux modulation poles (FMPs) by using the analytical equations for flux density distribution due to armature windings. The magnetic field by the windings is modulated by the FMPs. Then, the resulting magnetic field produces the torque by interacting with the rotor permanent magnets (PMs). Thus, to improve the output power of the machine, the FMP shape should be optimized in terms of the magnetic flux modulation. To do so, the permeance function which can consider the changes of the geometric parameters for the FMPs is defined using the Fourier series analysis method. Consequently, the working harmonic, which is the spatial harmonic of the air-gap magnetic field due to the windings and creates the torque, is given as the function of the geometric variables. The optimal set of design variables to maximize the working harmonic in the analytical equation is obtained by employing the genetic algorithm. The finite element analysis results show that the proposed method improves the output torque of the surface-mounted permanent magnet vernier (SPMV) machines up to 31%. In addition, the torque ripple can be minimized by regulating the harmonic components of the permeance in the analytical equations. Full article

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

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23 pages, 23920 KiB

Open AccessArticle

Gas-In-Place Estimate for Potential Gas Hydrate Concentrated Zone in the Kumano Basin, Nankai Trough Forearc, Japan

by Katie Taladay^1,2,*, Brian Boston^1,3 and Gregory F. Moore¹

¹ Department of Geology & Geophysics, University of Hawaii at Manoa, Honolulu, HI 96822, USA

² Department of Geography, University of Hawaii at Manoa, Honolulu, HI 96822, USA

³ Research and Development Center for Earthquake and Tsunami, Japan Agency for Marine-Earth Science and Technology, Yokohama, Kanagawa 236-0001, Japan

Energies 2017, 10(10), 1552; https://doi.org/10.3390/en10101552 - 9 Oct 2017

Cited by 18 | Viewed by 7125

Abstract

Methane hydrate concentrated zones (MHCZs) have become targets for energy exploration along continental margins worldwide. In 2013, exploratory drilling in the eastern Nankai Trough at Daini Atsumi Knoll confirmed that MHCZs tens of meters thick occur directly above bottom simulating reflections imaged in [...] Read more.

Methane hydrate concentrated zones (MHCZs) have become targets for energy exploration along continental margins worldwide. In 2013, exploratory drilling in the eastern Nankai Trough at Daini Atsumi Knoll confirmed that MHCZs tens of meters thick occur directly above bottom simulating reflections imaged in seismic data. This study uses 3-dimensional (3D) seismic and borehole data collected from the Kumano Basin offshore Japan to identify analogous MHCZs. Our survey region is located ~100 km southwest of the Daini Atsumi Knoll, site of the first offshore gas hydrate production trial. Here we provide a detailed analysis of the gas hydrate system within our survey area of the Kumano forearc including: (1) the 3D spatial distribution of bottom simulating reflections; (2) a thickness map of potential MHCZs; and (3) a volumetric gas-in-place estimate for these MHCZs using constraints from our seismic interpretations as well as previously collected borehole data. There is evidence for two distinct zones of concentrated gas hydrate 10–90 m thick, and we estimate that the amount of gas-in-place potentially locked up in these MHCZs is 1.9–46.3 trillion cubic feet with a preferred estimate of 15.8 trillion cubic feet. Full article

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

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14 pages, 1211 KiB

Open AccessArticle

Finite Control Set Model Predictive Control for a Three-Phase Shunt Active Power Filter with a Kalman Filter-Based Estimation

by Ramon Guzmán^1,*,†

, Luís García de Vicuña^2,†, Miguel Castilla^2,†

, Jaume Miret^2,†

and Antonio Camacho^2,†

¹ Department of Automatic Control, Universitat Politècnica de Catalunya, 08800 Barcelona, Spain

² Department of Electronic Engineering, Universitat Politècnica de Catalunya, 08800 Barcelona, Spain

^† These authors contributed equally to this work.

Energies 2017, 10(10), 1553; https://doi.org/10.3390/en10101553 - 10 Oct 2017

Cited by 14 | Viewed by 4311

Abstract

In this paper, the finite control set model predictive control is combined with the vector operation technique to be applied in the control of a three-phase active power filter. Typically, in the finite control set technique applied to three-phase power converters, eight different [...] Read more.

In this paper, the finite control set model predictive control is combined with the vector operation technique to be applied in the control of a three-phase active power filter. Typically, in the finite control set technique applied to three-phase power converters, eight different vectors are considered in order to obtain the optimum control signal by minimizing a cost function. On the other hand, the vector operation technique is based on dividing the grid voltage period into six different regions. The main advantage of combining both techniques is that for each region the number of possible voltage vectors to be considered can be reduced to a half, thus reducing the computational load employed by the control algorithm. Besides, in each region, only two phase-legs are switching at high frequency while the remaining phase-leg is maintained to a constant dc-voltage value during this interval. Accordingly, a reduction of the switching losses is obtained. Unlike the typical model predictive control methods which make use of the discrete differential equations of the converter, this method considers a Kalman filter in order to improve the behavior of the closed-loop system in noisy environments. Selected experimental results are exposed in order the demonstrate the validity of the control proposal. Full article

(This article belongs to the Special Issue Control and Communication in Distributed Generation Systems)

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19 pages, 971 KiB

Open AccessArticle

Community Microgrid Scheduling Considering Network Operational Constraints and Building Thermal Dynamics

by Guodong Liu^1,*

, Thomas B. Ollis¹

, Bailu Xiao¹, Xiaohu Zhang² and Kevin Tomsovic²

¹ Power & Energy Systems Group, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA

² Department of Electrical Engineering and Computer Science, The University of Tennessee, Knoxville, TN 37996, USA

Energies 2017, 10(10), 1554; https://doi.org/10.3390/en10101554 - 10 Oct 2017

Cited by 13 | Viewed by 3442

Abstract

This paper proposes a Mixed Integer Conic Programming (MICP) model for community microgrids considering the network operational constraints and building thermal dynamics. The proposed multi-objective optimization model optimizes not only the operating cost, including fuel cost, electricity purchasing/selling, storage degradation, voluntary load shedding [...] Read more.

This paper proposes a Mixed Integer Conic Programming (MICP) model for community microgrids considering the network operational constraints and building thermal dynamics. The proposed multi-objective optimization model optimizes not only the operating cost, including fuel cost, electricity purchasing/selling, storage degradation, voluntary load shedding and the cost associated with customer discomfort as a result of the room temperature deviation from the customer setting point, but also several performance indices, including voltage deviation, network power loss and power factor at the Point of Common Coupling (PCC). In particular, we integrate the detailed thermal dynamic model of buildings into the distribution optimal power flow (D-OPF) model for the optimal operation. Thus, the proposed model can directly schedule the heating, ventilation and air-conditioning (HVAC) systems of buildings intelligently so as to to reduce the electricity cost without compromising the comfort of customers. Results of numerical simulation validate the effectiveness of the proposed model and significant savings in electricity cost with network operational constraints satisfied. Full article

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

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15 pages, 5094 KiB

Open AccessArticle

Chemical Characteristics and NaCl Component Behavior of Biochar Derived from the Salty Food Waste by Water Flushing

by Ye-Eun Lee^1,2, Jun-Ho Jo¹, I-Tae Kim¹ and Yeong-Seok Yoo^1,2,*

¹ Division of Environment and Plant Engineering, Korea Institute of Civil Engineering and Building Technology 283, Goyang-daero, Ilsanseo-gu, Goyang-si, Gyeonggi-do 10223, Korea

² Department of Construction Environment Engineering, University of Science and Technology, 217, Gajeong-ro, Yuseong-gu, Daejeon KS015, Korea

Energies 2017, 10(10), 1555; https://doi.org/10.3390/en10101555 - 10 Oct 2017

Cited by 19 | Viewed by 4943

Abstract

Biochar is the product of the pyrolysis of organic materials in a reduced state. In recent years, biochar has received attention due to its applicability to organic waste management, thereby leading to active research on biochar. However, there have been few studies using [...] Read more.

Biochar is the product of the pyrolysis of organic materials in a reduced state. In recent years, biochar has received attention due to its applicability to organic waste management, thereby leading to active research on biochar. However, there have been few studies using food waste. In particular, the most significant difference between food waste and other organic waste is the high salinity of food waste. Therefore, in this paper, we compare the chemical characteristics of biochar produced using food waste containing low- and high-concentration salt and biochar flushed with water to remove the concentrated salt. In addition, we clarify the salt component behavior of biochar. Peak analysis of XRD confirms that it is difficult to find salt crystals in flushed char since salt remains in the form of crystals when salty food waste is pyrolyzed washed away after water flushing. In addition, the Cl content significantly decreased to 1–2% after flushing, similar to that of Cl content in the standard, non-salted food waste char. On the other hand, a significant amount of Na was found in pyrolyzed char even after flushing resulting from a phenomenon in which salt is dissolved in water while flushing and Na ions are adsorbed. FT-IR analysis showed that salt in waste affects the binding of aromatic carbons to compounds in the pyrolysis process. The NMR spectroscopy demonstrated that the aromatic carbon content, which indicates the stability of biochar, is not influenced by the salt content and increases with increasing pyrolysis temperature. Full article

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

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17 pages, 3778 KiB

Open AccessArticle

Influences of Traction Load Shock on Artificial Partial Discharge Faults within Traction Transformer—Experimental Test for Pattern Recognition

by Shuaibing Li

, Guoqiang Gao, Guangcai Hu, Bo Gao, Haojie Yin, Wenfu Wei^*

and Guangning Wu

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

Energies 2017, 10(10), 1556; https://doi.org/10.3390/en10101556 - 10 Oct 2017

Cited by 10 | Viewed by 4896

Abstract

Partial discharge (PD) measurement and its pattern recognition are vital to fault diagnosis of transformers, especially to those traction substation transformers undergoing repetitive traction load shocks. This paper presents the primary factors induced by traction load shocks including high total harmonics distortion (THD), [...] Read more.

Partial discharge (PD) measurement and its pattern recognition are vital to fault diagnosis of transformers, especially to those traction substation transformers undergoing repetitive traction load shocks. This paper presents the primary factors induced by traction load shocks including high total harmonics distortion (THD), transient voltage impulse and high-temperature rise, and their effects on the feature parameters of PD. Experimental tests are conducted on six artificial PD models with these factors introduced one by one. Results reveal that the maximum PD quantity and the PD repetitive rate are favorable to be enlarged when the oil temperature exceeds 80 °C or the THD is higher than 16% with certain orders of harmonic. The decline in PD inception voltage can mainly be attributed to the transient voltage impulse. The variation in central frequency of the fast Fourier transformation (FFT) spectra transformed from ultra-high frequency signals can mainly be attributed to high THD, especially when it exceeds 20%. The temperature rise has no significant influence on the FFT spectra; the transient voltage impulse, however, can result in a central frequency shift of the floating particle discharge. With the rapid development of high-speed railways, the study presented in this paper will be helpful for field PD detection and recognition of traction substation transformers in the future. Full article

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16 pages, 8696 KiB

Open AccessArticle

Impact of Vitiation on a Swirl-Stabilized and Premixed Methane Flame

by Mao Li^*

, Yiheng Tong, Jens Klingmann and Marcus Thern

Department of Energy Sciences, Lund University, Ole Römers väg 1, SE-221 00 Lund, Sweden

Energies 2017, 10(10), 1557; https://doi.org/10.3390/en10101557 - 10 Oct 2017

Cited by 5 | Viewed by 6166

Abstract

Vitiation refers to the condition where the oxygen concentration in the air is reduced due to the mix of dilution gas. The vitiation effects on a premixed methane flame were investigated on a swirl-stabilized gas turbine model combustor under atmospheric pressure. The main [...] Read more.

Vitiation refers to the condition where the oxygen concentration in the air is reduced due to the mix of dilution gas. The vitiation effects on a premixed methane flame were investigated on a swirl-stabilized gas turbine model combustor under atmospheric pressure. The main purpose is to analyze the combustion stability and CO emission performance in vitiated air and compare the results with the flame without vitiation. The N₂, CO₂, and H₂O (steam) were used as the dilution gas. Measurements were conducted in a combustor inlet temperature of 384 K and 484 K. The equivalence ratio was varied from stoichiometric conditions to the LBO (Lean Blowout) limits where the flame was physically blown out from the combustor. The chemical kinetics calculation was performed with Chemkin software to analyze the vitiation effects on the flame reaction zone. Based on the calculation results, the changes in the temperature gradient, CO concentration, and active radicals across the flame reaction zone were identified. The time-averaged CH chemiluminescence images were recorded and the results indicated the features of the flame shape and location. The CH signal intensity provided the information about the heat-release zone in the combustor. The combustion LBO limits were measured and the vitiation of CO₂ and H₂O were found to have a stronger impact to elevate the LBO limits than N₂. Near the LBO limits, the instability of the flame reaction was revealed by the high-speed chemiluminescence imaging and the results were analyzed by FFT (Fast Fourier Transfer). CO emission was measured with a water-cooled probe which is located at the exit of the combustor. The combustion vitiation has been found to have the compression effect on the operation range for low CO emission. However, this compression effect could be compensated by improving the combustor inlet temperature. Full article

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

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11 pages, 1912 KiB

Open AccessArticle

Verification of the Performance of a Vertical Ground Heat Exchanger Applied to a Test House in Melbourne, Australia

by Koon Beng Ooi^* and Masa Noguchi

Faculty of Architecture, Building and Planning, Melbourne School of Design, The University of Melbourne, Buildings 133, Parkville, VIC 3010, Australia

Energies 2017, 10(10), 1558; https://doi.org/10.3390/en10101558 - 10 Oct 2017

Cited by 5 | Viewed by 4584

Abstract

The ground heat exchanger is traditionally used as a heat source or sink for the heat pump that raises the temperature of water to about 50 °C to heat houses. However, in winter, the heating thermostat (temperature at which heating begins) in the [...] Read more.

The ground heat exchanger is traditionally used as a heat source or sink for the heat pump that raises the temperature of water to about 50 °C to heat houses. However, in winter, the heating thermostat (temperature at which heating begins) in the Australian Nationwide House Energy Rating Scheme (NatHERS) is only 20 °C during daytime and 15 °C at night. In South-East Melbourne, the temperature at the bottom of a 50-meter-deep borehole has been recorded with an Emerson™ recorder at 17 °C. Melbourne has an annual average temperature of 15 °C, so the ground temperature increases by 2 °C per 50-m depth. A linear projection gives 23 °C at 200-m of depth, and as the average undisturbed temperature of the ground for a 400-m-deep vertical ground heat exchanger (VGHE). This study, by simulation and experimentation, aims to verify that the circulation of water in the VGHE’s U-tube to low-temperature radiators (LTRs) could heat a house to thermal comfort. A literature review is included in the introduction. A simulation, using a model of a 60-m² experimental house, shows that the daytime circulation of water in this VGHE/LTR-on-opposite-walls system during the 8-month cold half of the year, heats the indoors to NatHERS settings. Simulation for the cold half shows that this VGHE-LTR system could cool the indoors. Instead, a fan creating a cooling sensation of up to 4 °C is used so that the VGHE is available for the regeneration of heat extracted from the ground during the cold portion. Simulations for this hot portion show that a 3.4-m² flat plate solar collector can collect more than twice the heat extracted from the ground in the cold portion. Thus, it can thus replenish the ground heat extracted for houses double the size of this 60-m² experimental house. Therefore, ground heat is sustainable for family-size homes. Since no heat pump is used, the cost of VGHE-LTR systems could be comparable to systems using the ground source heat pump. Water circulation pumps and fans require low power that can be supplied by photovoltaic thermal (PVT). The EnergyPlus™ v8.7 object modeling the PVT requires user-defined efficiencies, so a PVT will be tested in the experimental house. Full article

(This article belongs to the Special Issue Selected Papers from ZEMCH 2016: Building Energy Performance Evaluation/Simulation)

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15 pages, 4502 KiB

Open AccessArticle

Revising the Static Geological Reservoir Model of the Upper Triassic Stuttgart Formation at the Ketzin Pilot Site for CO₂ Storage by Integrated Inverse Modelling

by Thomas Kempka^1,*

, Ben Norden², Alexandra Ivanova³ and Stefan Lüth³

¹ Fluid Systems Modelling, GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany

² Geothermal Energy Systems, GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany

³ Geological Storage, GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany

Energies 2017, 10(10), 1559; https://doi.org/10.3390/en10101559 - 11 Oct 2017

Cited by 8 | Viewed by 4032

Abstract

The Ketzin pilot site for CO

_{2}

storage in Germany has been operated from 2007 to 2013 with about 67 kt of CO

_{2}

injected into the Upper Triassic Stuttgart Formation. Main objectives of this undertaking were assessing general feasibility of CO [...] Read more.

The Ketzin pilot site for CO

_{2}

storage in Germany has been operated from 2007 to 2013 with about 67 kt of CO

_{2}

injected into the Upper Triassic Stuttgart Formation. Main objectives of this undertaking were assessing general feasibility of CO

_{2}

storage in saline aquifers as well as testing and integrating efficient monitoring and long-term prediction strategies. The present study aims at revising the latest static geological reservoir model of the Stuttgart Formation by applying an integrated inverse modelling approach. Observation data considered for this purpose include bottomhole pressures recorded during hydraulic testing and almost five years of CO

_{2}

injection as well as gaseous CO

_{2}

contours derived from 3D seismic repeat surveys carried out in 2009 and 2012. Inverse modelling results show a remarkably good agreement with the hydraulic testing and CO

_{2}

injection bottomhole pressures (R

^{2}

= 0.972), while spatial distribution and thickness of the gaseous CO

_{2}

derived from 3D seismic interpretation exhibit a generally good agreement with the simulation results (R

^{2}

= 0.699 to 0.729). The present study successfully demonstrates how the integrated inverse modelling approach, applied for effective permeability calibration in a geological model here, can substantially reduce parameter uncertainty. Full article

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14 pages, 3292 KiB

Open AccessArticle

State of Charge Estimation for Lithium-Ion Battery with a Temperature-Compensated Model

by Shichun Yang, Cheng Deng^*

, Yulong Zhang and Yongling He

School of Transportation Science and Engineering, Beihang University, Beijing 100191, China

Energies 2017, 10(10), 1560; https://doi.org/10.3390/en10101560 - 11 Oct 2017

Cited by 51 | Viewed by 7082

Abstract

Accurate estimation of the state of charge (SOC) of batteries is crucial in a battery management system. Many studies on battery SOC estimation have been investigated recently. Temperature is an important factor that affects the SOC estimation accuracy while it is still not [...] Read more.

Accurate estimation of the state of charge (SOC) of batteries is crucial in a battery management system. Many studies on battery SOC estimation have been investigated recently. Temperature is an important factor that affects the SOC estimation accuracy while it is still not adequately addressed at present. This paper proposes a SOC estimator based on a new temperature-compensated model with extended Kalman Filter (EKF). The open circuit voltage (OCV), capacity, and resistance and capacitance (RC) parameters in the estimator are temperature dependent so that the estimator can maintain high accuracy at various temperatures. The estimation accuracy decreases when applied in high current continuous discharge, because the equivalent polarization resistance decreases as the discharge current increases. Therefore, a polarization resistance correction coefficient is proposed to tackle this problem. The estimator also demonstrates a good performance in dynamic operating conditions. However, the equivalent circuit model shows huge uncertainty in the low SOC region, so measurement noise variation is proposed to improve the estimation accuracy there. Full article

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19 pages, 3762 KiB

Open AccessArticle

Optimization of Solar Water Heating System under Time and Spatial Partition Heating in Rural Dwellings

by Yanfeng Liu^*, Tao Li, Yaowen Chen and Dengjia Wang

School of Environment and Municipal Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, China

Energies 2017, 10(10), 1561; https://doi.org/10.3390/en10101561 - 11 Oct 2017

Cited by 16 | Viewed by 5886

Abstract

This paper proposes the application of time and spatial partition heating to a solar water heating system. The heating effect and system performance were analyzed under the continuous and whole space heating and time and spatial partition heating using TRNSYS. The results were [...] Read more.

This paper proposes the application of time and spatial partition heating to a solar water heating system. The heating effect and system performance were analyzed under the continuous and whole space heating and time and spatial partition heating using TRNSYS. The results were validated by comparing with the test results of the demonstration building. Compared to continuous and whole space heating, the use of time and spatial partition heating increases the solar fraction by 16.5%, reduces the auxiliary heating by 7390 MJ, and reduces the annual operation cost by 2010 RMB. Under time and spatial partition heating, optimization analyses were conducted for the two system capacity parameters of the solar collector area and tank volume and the one operation parameter of auxiliary heater setting outlet temperature. The results showed that a reasonable choice of the solar collector area can reduce the dynamic annual cost, the increased tank volume is advantageous to heat storage, and the auxiliary heater setting outlet temperature have greater influence on the indoor heating effect. The advanced opening of solar water heating system and the normal opening of passive air vents are recommended. Based on the comparison of the two modes, the time and spatial partition heating technology is a better choice for rural dwellings. Full article

(This article belongs to the Special Issue Solar Technologies for Buildings)

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22 pages, 5833 KiB

Open AccessArticle

On the Energy Efficiency of Dual Clutch Transmissions and Automated Manual Transmissions

by Fabio Vacca¹, Stefano De Pinto^1,2, Ahu Ece Hartavi Karci¹, Patrick Gruber¹, Fabio Viotto³, Carlo Cavallino³, Jacopo Rossi³ and Aldo Sorniotti^1,*

¹ Department of Mechanical Engineering Sciences, University of Surrey, Guildford GU2 7XH, UK

² McLaren Automotive Ltd, Woking GU21 4YH, UK

³ Oerlikon Graziano S.p.A., 10098 Rivoli, Italy

Energies 2017, 10(10), 1562; https://doi.org/10.3390/en10101562 - 11 Oct 2017

Cited by 26 | Viewed by 9681

Abstract

The main benefits of dual clutch transmissions (DCTs) are: (i) a higher energy efficiency than automatic transmission systems with torque converters; and (ii) the capability to fill the torque gap during gear shifts to allow seamless longitudinal acceleration profiles. Therefore, DCTs are viable [...] Read more.

The main benefits of dual clutch transmissions (DCTs) are: (i) a higher energy efficiency than automatic transmission systems with torque converters; and (ii) the capability to fill the torque gap during gear shifts to allow seamless longitudinal acceleration profiles. Therefore, DCTs are viable alternatives to automated manual transmissions (AMTs). For vehicles equipped with engines that can generate considerable torque, large clutch-slip energy losses occur during power-on gear shifts and, as a result, DCTs need wet clutches for effective heat dissipation. This requirement substantially reduces DCT efficiency because of the churning and ancillary power dissipations associated with the wet clutch pack. To the knowledge of the authors, this study is the first to analyse the detailed power loss contributions of a DCT with wet clutches, and their relative significance along a set of driving cycles. Based on these results, a novel hybridised AMT (HAMT) with a single dry clutch and an electric motor is proposed for the same vehicle. The HAMT architecture combines the high mechanical efficiency typical of AMTs with a single dry clutch, with the torque-fill capability and operational flexibility allowed by the electric motor. The measured efficiency maps of a case study DCT and HAMT are compared. This is then complemented by the analysis of the respective fuel consumption along the driving cycles, which is simulated with an experimentally validated vehicle model. In its internal combustion engine mode, the HAMT reduces fuel consumption by >9% with respect to the DCT. Full article

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

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17 pages, 3791 KiB

Open AccessArticle

Influence of Dynamic Efficiency in the DC Microgrid Power Balance

by Hongwei Wu

, Manuela Sechilariu^*

and Fabrice Locment

Sorbonne University, Université de Technologie de Compiègne, EA7284 Avenues, 60203 Compiègne, France

Energies 2017, 10(10), 1563; https://doi.org/10.3390/en10101563 - 11 Oct 2017

Cited by 9 | Viewed by 3680

Abstract

This work aims to enhance the ability of a direct current (DC) microgrid to guarantee the power supply without interruptions by considering the dynamic efficiency of each power converter in the power balance. Previous works show that the converter efficiency varies according to [...] Read more.

This work aims to enhance the ability of a direct current (DC) microgrid to guarantee the power supply without interruptions by considering the dynamic efficiency of each power converter in the power balance. Previous works show that the converter efficiency varies according to the instant power. If the variable efficiency of the converters in the microgrid is not considered, some extra power must be considered to compensate the losses in the power balance. However, this leads to a waste of available energy and unnecessary load shedding. The work presented here includes the power converters’ dynamic efficiencies in the control of a DC microgrid to improve its performance. MATLAB/Simulink simulations were carried out and the results show that the dynamic efficiency can reduce the load shedding and improve the total DC microgrid efficiency. Full article

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

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21 pages, 4702 KiB

Open AccessArticle

Condition Monitoring for Roller Bearings of Wind Turbines Based on Health Evaluation under Variable Operating States

by Lei Fu^1,2, Yanding Wei^1,2,*

, Sheng Fang², Xiaojun Zhou² and Junqiang Lou³

¹ The State Key Lab of Fluid Power and Mechatronic Systems, College of Mechanical Engineering, Zhejiang University, Hangzhou 310027, China

² Key Laboratory of Advanced Manufacturing Technology of Zhejiang Province, College of Mechanical Engineering, Zhejiang University, Hangzhou 310027, China

³ Faculty of Mechanical Engineering and Mechanics, Ningbo University, Ningbo 315211, China

Energies 2017, 10(10), 1564; https://doi.org/10.3390/en10101564 - 11 Oct 2017

Cited by 16 | Viewed by 4602

Abstract

Condition monitoring (CM) is used to assess the health status of wind turbines (WT) by detecting turbine failure and predicting maintenance needs. However, fluctuating operating conditions cause variations in monitored features, therefore increasing the difficulty of CM, for example, the frequency-domain analysis may [...] Read more.

Condition monitoring (CM) is used to assess the health status of wind turbines (WT) by detecting turbine failure and predicting maintenance needs. However, fluctuating operating conditions cause variations in monitored features, therefore increasing the difficulty of CM, for example, the frequency-domain analysis may lead to an inaccurate or even incorrect prediction when evaluating the health of the WT components. In light of this challenge, this paper proposed a method for the health evaluation of WT components based on vibration signals. The proposed approach aimed to reduce the evaluation error caused by the impact of the variable operating condition. First, the vibration signal was decomposed into a set of sub-signals using variational mode decomposition (VMD). Next, the sub-signal energy and the probability distribution were obtained and normalized. Finally, the concept of entropy was introduced to evaluate the health condition of a monitored object to provide an effective guide for maintenance. In particular, the health evaluation for CM was based on a performance review over a range of operating conditions, rather than at a certain single operating condition. Experimental investigations were performed which verified the efficiency of the evaluation method, as well as a comparison with the previous method. Full article

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26 pages, 9569 KiB

Open AccessArticle

Comparative Analysis and Optimization of Power Loss Based on the Isolated Series/Multi Resonant Three-Port Bidirectional DC-DC Converter

by Bo Chen, Ping Wang

, Yifeng Wang^*

, Wei Li, Fuqiang Han and Shuhuai Zhang

School of Electrical Engineering and Automation, Tianjin University, Tianjin 300072, China

Energies 2017, 10(10), 1565; https://doi.org/10.3390/en10101565 - 11 Oct 2017

Cited by 9 | Viewed by 3895

Abstract

Based on the loss distribution and efficiency analysis, a comparative study between a series resonant three-port bidirectional DC-DC converter (SR-TBC) and a multi-resonant three-port bi-directional DC-DC converter (MR-TBC) is reported here. By using the Fourier equivalent analysis method in hand, the resonant current, [...] Read more.

Based on the loss distribution and efficiency analysis, a comparative study between a series resonant three-port bidirectional DC-DC converter (SR-TBC) and a multi-resonant three-port bi-directional DC-DC converter (MR-TBC) is reported here. By using the Fourier equivalent analysis method in hand, the resonant current, switching current expressions, zero voltage soft switching (ZVS) conditions of MR-TBC and SR-TBC are deduced. Besides, in consideration of efficiency and soft switching aspects, the loss models of main power components and resonant elements are integrated and optimized for both topologies. Their loss distributions are established, and the different effects derived from the adoption of SiC MOSFET and Si MOSFET on the converter efficiency are discussed. Finally, to verify the theoretical analyses, comparative experiments under diverse load states are conducted based on the prototypes of the MR-TBC and SR-TBC. The obtained results demonstrate that the MR-TBC successfully broadens the ZVS range and thus achieves higher efficiency along the entire load range. Full article

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14 pages, 5601 KiB

Open AccessArticle

The Characteristics of Methane Combustion Suppression by Water Mist and Its Engineering Applications

by Rongkun Pan^1,2,3,*

, Zejun Xiao¹ and Minggao Yu^1,4

¹ Department of Safety & Science Engineering, Henan Polytechnic University, Jiaozuo 454003, China

² The Collaborative Innovation Center of Coal Safety Production of Henan Province, Henan Polytechnic University, Jiaozuo 454003, China

³ Henan Key Laboratory of Prevention and Cure of Mine Methane & Fires, Jiaozuo 45403, China

⁴ State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, China

Energies 2017, 10(10), 1566; https://doi.org/10.3390/en10101566 - 11 Oct 2017

Cited by 9 | Viewed by 4578

Abstract

To safely mine coal, engineers must prevent gas combustion and explosions, as well as seek feasible and reasonable techniques to control for these types of incidents. This paper analyzes the causes and characteristics of methane combustion and explosions. Water mist is proposed to [...] Read more.

To safely mine coal, engineers must prevent gas combustion and explosions, as well as seek feasible and reasonable techniques to control for these types of incidents. This paper analyzes the causes and characteristics of methane combustion and explosions. Water mist is proposed to prevent and control methane combustion in an underground confined space. We constructed an experiment platform to investigate the suppression of methane combustion using water mist for different conditions. The experimental results showed that water mist is highly effective for methane flame inhibition. The flame was extinguished with water mist endothermic cooling. However, the annular regions of water vapor around the fire played a vital role in flame extinction. Water from the evaporating mist replaces the oxygen available to the fuel. Additionally, the time required for fuel ignition is prolonged. For these reasons, the water particle action to flame surface is reinforced and the fuel’s reaction with air is delayed. As a result, flame stretching and disturbances occur, which serve to extinguish the flame. Engineering application tests were carried out in the goaf, drill hole and upper-corner to investigate the prevention and control of methane gas combustion, with the results showing a good application effect. Full article

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23 pages, 6099 KiB

Open AccessArticle

A Harmonic Resonance Suppression Strategy for a High-Speed Railway Traction Power Supply System with a SHE-PWM Four-Quadrant Converter Based on Active-Set Secondary Optimization

by Runze Zhang¹, Fei Lin^1,*, Zhongping Yang¹, Hu Cao² and Yuping Liu²

¹ School of Electrical Engineering, Beijing Jiaotong University, Beijing 100089, China

² CCRC Qingdao Sifang Rolling Stock Research Institute Co. Ltd., Qingdao 266000, China

Energies 2017, 10(10), 1567; https://doi.org/10.3390/en10101567 - 11 Oct 2017

Cited by 17 | Viewed by 6452

Abstract

Pulse width modulation (PWM) technology is widely used in traction converters for high-speed railways. The harmonic distribution caused by PWM is quite extensive, and increases the possibility of grid–train coupling resonance in the traction power supply system (TPSS). This paper first analyzes the [...] Read more.

Pulse width modulation (PWM) technology is widely used in traction converters for high-speed railways. The harmonic distribution caused by PWM is quite extensive, and increases the possibility of grid–train coupling resonance in the traction power supply system (TPSS). This paper first analyzes the mechanism of resonance, when the characteristic harmonic frequency of a four-quadrant converter (4QC) current that injects into the traction grid matches the resonant frequency of the traction grid, which may result in resonance in the system. To suppress resonance, this paper adopts specific harmonic elimination–pulse width modulation (SHE-PWM) technology combined with a transient direct current control strategy to eliminate the harmonics in the resonant frequency, which may suppress the grid–train coupling resonance. Due to the fact that the SHE-PWM process with multiple switching angles contains complex transcendental equations, the initial value is difficult to provide, and is difficult to solve using ordinary iterative algorithms. In this paper, an active-set secondary optimization method is used to solve the equation. The algorithm has the benefits of low dependence on initial values, fast convergence and high solution accuracy. Finally, the feasibility of the resonant suppression algorithm is verified by means of Matlab simulation. Full article

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

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19 pages, 6097 KiB

Open AccessArticle

Flexible Compensation of Voltage and Current Unbalance and Harmonics in Microgrids

by Seyyed Yousef Mousazadeh Mousavi¹, Alireza Jalilian^1,2,*, Mehdi Savaghebi³

and Josep M. Guerrero³

¹ Department of Electrical Engineering, Iran University of Science and Technology, Tehran 16846-13114, Iran

² Center of Excellence for Power System Automation and Operation, Iran University of Science and Technology, Tehran 16846-13114, Iran

³ Department of Energy Technology, Aalborg University, Aalborg 9220, Denmark

Energies 2017, 10(10), 1568; https://doi.org/10.3390/en10101568 - 11 Oct 2017

Cited by 18 | Viewed by 4697

Abstract

In recent years, the harmonics and unbalance problems endanger the voltage and current quality of power systems, due to increasing usage of nonlinear and unbalanced loads. Use of Distributed Generation (DG)-interfacing inverters is proposed for voltage or current compensation. In this paper, a [...] Read more.

In recent years, the harmonics and unbalance problems endanger the voltage and current quality of power systems, due to increasing usage of nonlinear and unbalanced loads. Use of Distributed Generation (DG)-interfacing inverters is proposed for voltage or current compensation. In this paper, a flexible control method is proposed to compensate voltage and current unbalance and harmonics using the distributed generation (DG)-interfacing inverters. This method is applicable to both grid-connected and islanded Microgrids (MGs). In the proposed method, not only the proper control of active and reactive powers can be achieved, but also there is flexibility in compensating the voltage or current quality problems at DG terminals or Points of Common Coupling (PCCs). This control strategy consists of active and reactive power controllers and a voltage/current quality-improvement block. The controller is designed in a stationary (αβ) frame. An extensive simulation study has been performed and the results demonstrate the effectiveness of the proposed control scheme. Depending on the compensation modes, the harmonics and unbalance compensation of DG output current, MG-injected current to the grid, as well as PCC and DG voltages, can be achieved in grid-connected operation of MG while in the islanded operation, and the PCC and DG voltages compensation can be obtained through the proposed control scheme. Full article

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19 pages, 9158 KiB

Open AccessArticle

A Stable and Fast-Transient Performance Switched-Mode Power Amplifier for a Power Hardware in the Loop (PHIL) System

by Jianjun Sun¹, Chenxu Yin^2,*, Jinwu Gong¹, Yewei Chen¹, Zhiqiang Liao¹ and Xiaoming Zha¹

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

² State Grid Anhui Economic Research Institute, Hefei 230022, China

Energies 2017, 10(10), 1569; https://doi.org/10.3390/en10101569 - 11 Oct 2017

Cited by 4 | Viewed by 3925

Abstract

Power Hardware in the Loop (PHIL) systems are used to test a power system with the help of combined software and hardware. Generally, to construct a PHIL system, a switched-mode power amplifier that has a stable performance is used, because of their large, [...] Read more.

Power Hardware in the Loop (PHIL) systems are used to test a power system with the help of combined software and hardware. Generally, to construct a PHIL system, a switched-mode power amplifier that has a stable performance is used, because of their large, linear signal control-to-output characteristics. However, the fundamental limitations of a switch-mode power amplifier (PA) are the dynamic performance and output bandwidth. In this paper, a compound controller has been used for the rectifier part of a PA, which can ensure the stability of a PA under transient or fault operating conditions. Moreover, a compound controller, which involves a feed-forward controller, a proportional controller and a repetitive controller, is proposed in the inverter part of a PA, and it can be used for PHIL applications. Experimental results are obtained under various operating conditions, such as transient responses under load step change, and output voltage bandwidth testing for a PHIL system, it is concluded that a proposed switched-mode power amplifier is useful for the PHIL system. Full article

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

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20 pages, 1041 KiB

Open AccessArticle

Multi-Variable Optimization of Building Thermal Design Using Genetic Algorithms

by Joanna Ferdyn-Grygierek^1,* and Krzysztof Grygierek²

¹ Faculty of Energy and Environmental Engineering, The Silesian University of Technology, Konarskiego 18, 44-100 Gliwice, Poland

² Faculty of Civil Engineering, The Silesian University of Technology, Akademicka 5, 44-100 Gliwice, Poland

Energies 2017, 10(10), 1570; https://doi.org/10.3390/en10101570 - 11 Oct 2017

Cited by 60 | Viewed by 5271

Abstract

The building sector is one of the largest energy consumers in the world, comprising about 40% of the total energy consumption in numerous countries. Early design decisions have a significant impact on the energy performance of buildings. The paper presents the multi-variable optimization [...] Read more.

The building sector is one of the largest energy consumers in the world, comprising about 40% of the total energy consumption in numerous countries. Early design decisions have a significant impact on the energy performance of buildings. The paper presents the multi-variable optimization of the selected design parameters in a single-family building in temperate climate conditions. The influence of four types of windows, their size, building orientation, insulation of external wall, roof and ground floor and infiltration on the life cycle costs (LCC) is analyzed. Optimal selection of the design parameters is carried out using genetic algorithms by coupling the building performance simulation program EnergyPlus with optimization environment. The simulations were conducted for seven optimization cases. The analysis is performed for two variants of a building with heating and cooling systems and with a heating system only. Depending on the analyzed case, the life cycle costs decreased from 7% to 34% LCC value of the reference building. In the case of temperate climate, the building optimization (in terms of heat demand only) substantially reduces the heating costs, yet the summer thermal comfort conditions deteriorate significantly. Full article

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17 pages, 12230 KiB

Open AccessArticle

Position and Speed Estimation of Permanent Magnet Machine Sensorless Drive at High Speed Using an Improved Phase-Locked Loop

by Guan-Ren Chen¹, Shih-Chin Yang^1,*, Yu-Liang Hsu²

and Kang Li¹

¹ Department of Mechanical Engineering, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan

² Department of Automatic Control Engineering, Feng Chia University, No. 100 Wenhwa Road, Taichung 40724, Taiwan

Energies 2017, 10(10), 1571; https://doi.org/10.3390/en10101571 - 11 Oct 2017

Cited by 19 | Viewed by 4382

Abstract

In conventional position sensorless permanent magnet (PM) machine drives, the rotor position is obtained from the phase-locked loop (PLL) with the regulation of spatial signal in estimated back electromotive force (EMF) voltages. Due to the sinusoidal distribution of back-EMF voltages, a small-signal approximation [...] Read more.

In conventional position sensorless permanent magnet (PM) machine drives, the rotor position is obtained from the phase-locked loop (PLL) with the regulation of spatial signal in estimated back electromotive force (EMF) voltages. Due to the sinusoidal distribution of back-EMF voltages, a small-signal approximation is assumed in the PLL in order to estimate the position. That is, the estimated position is almost equal to the actual position per sample instant. However, at high speed when the ratio of sampling frequency, f_sample, over the rotor operating frequency, f_e, is low, this approximation might not be valid during the speed and load transient. To overcome this limitation, a position estimation is proposed specifically for the high-speed operation of a PM machine drive. A discrete-time EMF voltage estimator is developed to obtain the machine spatial signal. In addition, an arctangent calculation is cascaded to the PLL in order to remove this small-signal approximation for better sensorless drive performance. By using the discrete-time EMF estimation and modified PLL, the drive is able to maintain the speed closed-loop at 36 krpm with only 4.2 sampling points per electrical cycle on a PM machine, according to experimental results. Full article

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

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23 pages, 3276 KiB

Open AccessReview

Intermittent Smoothing Approaches for Wind Power Output: A Review

by Muhammad Jabir¹, Hazlee Azil Illias¹

, Safdar Raza² and Hazlie Mokhlis^1,*

¹ Department of Electrical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia

² Department of Electrical Engineering, NFC IET, Multan 60000, Pakistan

Energies 2017, 10(10), 1572; https://doi.org/10.3390/en10101572 - 12 Oct 2017

Cited by 61 | Viewed by 6838

Abstract

Wind energy is one of the most common types of renewable energy resource. Due to its sustainability and environmental benefits, it is an emerging source for electric power generation. Rapid and random changes of wind speed makes it an irregular and inconsistent power [...] Read more.

Wind energy is one of the most common types of renewable energy resource. Due to its sustainability and environmental benefits, it is an emerging source for electric power generation. Rapid and random changes of wind speed makes it an irregular and inconsistent power source when connected to the grid, causing different technical problems in protection, power quality and generation dispatch control. Due to these problems, effective intermittent smoothing approaches for wind power output are crucially needed to minimize such problems. This paper reviews various intermittent smoothing approaches used in smoothing the output power fluctuations caused by wind energy. Problems associated with the inclusion of wind energy resources to grid are also briefly reviewed. From this review, it has been found that battery energy storage system is the most suitable and effective smoothing approach, provided that an effective control strategy is available for optimal utilization of battery energy system. This paper further demonstrates different control strategies built for battery energy storage system to obtain the smooth output wind power. Full article

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

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16 pages, 4198 KiB

Open AccessArticle

LCC Resonant Multilevel Converter for X-ray Applications

by A. M. Pernía^*

, Miguel J. Prieto

, Pedro J. Villegas

, Juan Díaz

and Juan A. Martín-Ramos

Department of Electrical Engineering, University of Oviedo, 33203 Gijón, Asturias, Spain

Energies 2017, 10(10), 1573; https://doi.org/10.3390/en10101573 - 12 Oct 2017

Cited by 15 | Viewed by 5834

Abstract

Medical X-ray appliances use high-voltage power supplies that must be able to work with very different energy requirements. Two techniques can be distinguished in X-ray medical imaging: fluoroscopy and radioscopy. The former involves low power radiation with a long exposure time, while radioscopy [...] Read more.

Medical X-ray appliances use high-voltage power supplies that must be able to work with very different energy requirements. Two techniques can be distinguished in X-ray medical imaging: fluoroscopy and radioscopy. The former involves low power radiation with a long exposure time, while radioscopy requires large power during short radiographic exposure times. Since the converter has to be designed by taking into account the maximum power specification, it will exhibit a poor efficiency when operating at low power levels. Such a problem can be solved by using a new multilevel LCC topology. This topology is based on a classical series-parallel resonant topology, but includes an additional low-voltage auxiliary transformer whose function depends on the X-ray technique considered. When radioscopy operation is selected, the transformer will allow the power to be shared between two full-bridges. If fluoroscopy mode is activated, the auxiliary full bridge is disconnected and the magnetizing inductance of the auxiliary transformer is used to increase the resonant inductor in order to reduce the resonant currents, thus improving the efficiency of the converter. Full article

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10 pages, 5388 KiB

Open AccessArticle

Brosimum Alicastrum as a Novel Starch Source for Bioethanol Production

by Edgar Olguin-Maciel¹, Alfonso Larqué-Saavedra², Daisy Pérez-Brito³, Luis F. Barahona-Pérez¹, Liliana Alzate-Gaviria¹, Tanit Toledano-Thompson¹, Patricia E. Lappe-Oliveras⁴, Emy G. Huchin-Poot¹ and Raúl Tapia-Tussell^1,*

¹ Unidad de Energía Renovable, Centro de Investigación Científica de Yucatán AC, Carretera Sierra Papacal-Chuburná Puerto, Km 5, Sierra Papacal, Mérida 97302, Yucatán, Mexico

² Unidad de Recursos Naturales, Centro de Investigación Científica de Yucatán AC, Calle 43 No. 130 x 32 y 34 Col. Chuburná de Hidalgo, Mérida 97205, Yucatán, Mexico

³ Laboratorio GeMBio, Centro de Investigación Científica de Yucatán AC, Calle No. 130 43 x 32 y 34 Col. Chuburná de Hidalgo, Mérida 97205, Yucatán, Mexico

⁴ Laboratorio de Micología, Instituto de Biología, Universidad Nacional Autónoma de México, Ciudad de México 04510, Mexico

Energies 2017, 10(10), 1574; https://doi.org/10.3390/en10101574 - 12 Oct 2017

Cited by 12 | Viewed by 4779

Abstract

Ramon (Brosimum alicastrum) is a forest tree native to the Mesoamerican region and the Caribbean. The flour obtained from Ramon seeds is 75% carbohydrate, of which 63% is starch, indicating its potential as a novel raw material for bioethanol production. The [...] Read more.

Ramon (Brosimum alicastrum) is a forest tree native to the Mesoamerican region and the Caribbean. The flour obtained from Ramon seeds is 75% carbohydrate, of which 63% is starch, indicating its potential as a novel raw material for bioethanol production. The objective of this study was to produce ethanol from Ramon flour using a 90 °C thermic treatment for 30 min and a native yeast strain (Candida tropicalis) for the fermentation process. In addition, the structure of the flour and the effects of pretreatment were observed via scanning electron microscopy. The native yeast strain was superior to the commercial strain, fermenting 98.8% of the reducing sugar (RS) at 48 h and generating 31% more ethanol than commercial yeast. One ton of flour yielded 213 L of ethanol. These results suggest that Ramon flour is an excellent candidate for ethanol production. This is the first report on bioethanol production using the starch from Ramon seed flour and a native yeast strain isolated from this feedstock. This alternative material for bioethanol production minimizes the competition between food and energy production, a priority for Mexico that has led to significant changes in public policies to enhance the development of renewable energies. Full article

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17 pages, 7433 KiB

Open AccessArticle

Determination of Klinkenberg Permeability Conditioned to Pore-Throat Structures in Tight Formations

by Guangfeng Liu^1,*

, Yaoxing Bai²

, Zhaoqi Fan³ and Daihong Gu¹

¹ CMOE Key Laboratory of Petroleum Engineering, China University of Petroleum-Beijing, Beijing 102249, China

² Shanxi Natural Gas Limited Company, Taiyuan, Shanxi 030002, China

³ Petroleum Systems Engineering, Faculty of Engineering and Applied Science, University of Regina, Regina, SK S4S 0A2, Canada

Energies 2017, 10(10), 1575; https://doi.org/10.3390/en10101575 - 12 Oct 2017

Cited by 14 | Viewed by 5432

Abstract

This paper has developed a pragmatic technique to efficiently and accurately determine the Klinkenberg permeability for tight formations with different pore-throat structures. Firstly, the authors use steady-state experiments to measure the Klinkenberg permeability of 56 tight core samples under different mean pore pressures [...] Read more.

This paper has developed a pragmatic technique to efficiently and accurately determine the Klinkenberg permeability for tight formations with different pore-throat structures. Firstly, the authors use steady-state experiments to measure the Klinkenberg permeability of 56 tight core samples under different mean pore pressures and confining pressures. Secondly, pressure-controlled mercury injection (PMI) experiments and thin-section analyses are conducted to differentiate pore-throat structures. After considering capillary pressure curve, pore types, throat size, particle composition, and grain size, the pore-throat structure in the target tight formation was classified into three types: a good sorting and micro-fine throat (GSMFT) type, a moderate sorting and micro-fine throat (MSMFT) type, and a bad sorting and micro throat (BSMT) type. This study found that a linear relationship exists between the Klinkenberg permeability and measured gas permeability for all three types of pore-throat structures. Subsequently, three empirical equations are proposed, based on 50 core samples of data, to estimate the Klinkenberg permeability by using the measured gas permeability and mean pore pressure for each type of pore-throat structure. In addition, the proposed empirical equations can generate accurate estimates of the Klinkenberg permeability with a relative error of less than 5% in comparison to its measured value. The application of the proposed empirical equations to the remaining six core samples has demonstrated that it is necessary to use an appropriate equation to determine the Klinkenberg permeability of a specific type of pore-throat structure. Consequently, the newly developed technique is proven to be qualified for accurately determining the Klinkenberg permeability of tight formations in a timely manner. Full article

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13 pages, 1420 KiB

Open AccessArticle

High Voltage Overhead Power Line Routing under an Objective Observability Criterion

by L. Alfredo Fernandez-Jimenez^*, Montserrat Mendoza-Villena

, Eduardo Garcia-Garrido, Pedro M. Lara-Santillan, Pedro J. Zorzano-Santamaria, Enrique Zorzano-Alba

and Alberto Falces

Department of Electrical Engineering, University of La Rioja, 26004 Logroño, Spain

Energies 2017, 10(10), 1576; https://doi.org/10.3390/en10101576 - 12 Oct 2017

Cited by 4 | Viewed by 3149

Abstract

The construction of new high voltage overhead power lines (HVOPLs) has become a controversial issue for electricity companies due to social opposition. Citizens are concerned about how these power lines may have an impact on their lives, basically caused by their effects on [...] Read more.

The construction of new high voltage overhead power lines (HVOPLs) has become a controversial issue for electricity companies due to social opposition. Citizens are concerned about how these power lines may have an impact on their lives, basically caused by their effects on health and safety. Visual impact is one of the most easily perceived. Although there are several published works that deal with the assessment of the visual impact produced by HVOPLs, no methodology has been proposed to assess this impact from an objective perspective. This work presents an original methodology which helps to identify the optimal routes for a new HVOPL under an objective observability criterion, enabling the selection of those with the lowest visibility in a zone. The application of the proposed methodology achieves a set of routes that links new HVOPL origin and destination points creating a corridor which includes all possible routes with an observability of its towers under a threshold limit. This methodology is illustrated by a real-life use corresponding to the selection of the route with least observability for a new power line in La Rioja (Spain). The results obtained may help to achieve a consensus between key stakeholders since it is focused on the specific issues of the planned HVOPL and its observability from an objective perspective. Full article

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

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16 pages, 2135 KiB

Open AccessArticle

Battery State-Of-Charge Estimation Based on a Dual Unscented Kalman Filter and Fractional Variable-Order Model

by Ming Cai, Weijie Chen and Xiaojun Tan^*

School of Engineering, Sun Yat-sen University, 135 Xingang Xi Road, Haizhu District, Guangzhou 510275, China

Energies 2017, 10(10), 1577; https://doi.org/10.3390/en10101577 - 12 Oct 2017

Cited by 42 | Viewed by 4615

Abstract

State-of-charge (SOC) estimation is essential for the safe and effective utilization of lithium-ion batteries. As the SOC cannot be directly measured by sensors, an accurate battery model and a corresponding estimation method is needed. Compared with electrochemical models, the equivalent circuit models are [...] Read more.

State-of-charge (SOC) estimation is essential for the safe and effective utilization of lithium-ion batteries. As the SOC cannot be directly measured by sensors, an accurate battery model and a corresponding estimation method is needed. Compared with electrochemical models, the equivalent circuit models are widely used due to their simplicity and feasibility. However, such integer order-based models are not sufficient to simulate the key behavior of the battery, and therefore, their accuracy is limited. In this paper, a new model with fractional order elements is presented. The fractional order values are adaptively updated over time. For battery SOC estimation, an unscented fractional Kalman filter (UFKF) is employed based on the proposed model. Furthermore, a dual estimation scheme is designed to estimate the variable orders simultaneously. The accuracy of the proposed model is verified under different dynamic profiles, and the experimental results indicate the stability and accuracy of the estimation method. Full article

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17 pages, 894 KiB

Open AccessArticle

The Impact of Environmental Regulation on Total Factor Energy Efficiency: A Cross-Region Analysis in China

by Jianting Lin^1,2,* and Changxin Xu¹

¹ Business School, Hohai University, Nanjing 211100, China

² Department of Systems Design Engineering, University of Waterloo, Waterloo, ON N2L 3G1, Canada

Energies 2017, 10(10), 1578; https://doi.org/10.3390/en10101578 - 12 Oct 2017

Cited by 29 | Viewed by 5506

Abstract

Environmental regulations are the key measure by which governments achieve sustainable environmental and economic development. This study aimed to determine the direct and indirect impacts of environmental regulations on total factor energy efficiency of regions in China. Since regions have different levels of [...] Read more.

Environmental regulations are the key measure by which governments achieve sustainable environmental and economic development. This study aimed to determine the direct and indirect impacts of environmental regulations on total factor energy efficiency of regions in China. Since regions have different levels of economic development and resource endowment, we used the slacks-based measure (SBM)-undesirable model to calculate total factor energy efficiency considering regional technology heterogeneity and examined the regional impacts of environmental regulation on this efficiency using the Tobit regression model. A positive direct impact was generated in the eastern region of China by the forced mechanism, which forced enterprises to reduce fossil fuel energy demand and increase clean energy consumption; whereas a negative direct impact was generated in the middle and western regions owing to the green paradox, which is the observation that expected stringent environmental regulation prompts energy owners to accelerate resource extraction. Moreover, indirect impacts through technological progress and foreign direct investment were taken into account in the model, and the results show that the indirect impacts vary across regions. A logical response to these findings would be to develop different policies for different regions. Full article

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18 pages, 2148 KiB

Open AccessArticle

Energy Consumption Forecasting for University Sector Buildings

by Khuram Pervez Amber^1,*, Muhammad Waqar Aslam², Anzar Mahmood³, Anila Kousar³, Muhammad Yamin Younis¹, Bilal Akbar¹, Ghulam Qadar Chaudhary¹ and Syed Kashif Hussain¹

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

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

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

Energies 2017, 10(10), 1579; https://doi.org/10.3390/en10101579 - 12 Oct 2017

Cited by 99 | Viewed by 8117

Abstract

Reliable energy forecasting helps managers to prepare future budgets for their buildings. Therefore, a simple, easier, less time consuming and reliable forecasting model which could be used for different types of buildings is desired. In this paper, we have presented a forecasting model [...] Read more.

Reliable energy forecasting helps managers to prepare future budgets for their buildings. Therefore, a simple, easier, less time consuming and reliable forecasting model which could be used for different types of buildings is desired. In this paper, we have presented a forecasting model based on five years of real data sets for one dependent variable (the daily electricity consumption) and six explanatory variables (ambient temperature, solar radiation, relative humidity, wind speed, weekday index and building type). A single mathematical equation for forecasting daily electricity usage of university buildings has been developed using the Multiple Regression (MR) technique. Data of two such buildings, located at the Southwark Campus of London South Bank University in London, have been used for this study. The predicted test results of MR model are examined and judged against real electricity consumption data of both buildings for year 2011. The results demonstrate that out of six explanatory variables, three variables; surrounding temperature, weekday index and building type have significant influence on buildings energy consumption. The results of this model are associated with a Normalized Root Mean Square Error (NRMSE) of 12% for the administrative building and 13% for the academic building. Finally, some limitations of this study have also been discussed. Full article

(This article belongs to the Special Issue Selected Papers from SEEP2017: The 10th International Conference on Sustainable Energy and Environmental Protection)

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18 pages, 6997 KiB

Open AccessArticle

Natural Contamination and Surface Flashover on Silicone Rubber Surface under Haze–Fog Environment

by Ang Ren^1,2

, Hongshun Liu^1,2,*

, Jianchun Wei^1,2 and Qingquan Li^1,2

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

² Shandong Provincial Key laboratory of UHV Transmission Technology and Equipments, #17923 Jingshi Road, Jinan 250061, China

Energies 2017, 10(10), 1580; https://doi.org/10.3390/en10101580 - 12 Oct 2017

Cited by 16 | Viewed by 4711

Abstract

Anti-pollution flashover of insulator is important for power systems. In recent years, haze-fog weather occurs frequently, which makes discharge occurs easily on the insulator surface and accelerates insulation aging of insulator. In order to study the influence of haze-fog on the surface discharge [...] Read more.

Anti-pollution flashover of insulator is important for power systems. In recent years, haze-fog weather occurs frequently, which makes discharge occurs easily on the insulator surface and accelerates insulation aging of insulator. In order to study the influence of haze-fog on the surface discharge of room temperature vulcanized silicone rubber, an artificial haze-fog lab was established. Based on four consecutive years of insulator contamination accumulation and atmospheric sampling in haze-fog environment, the contamination configuration appropriate for RTV-coated surface discharge test under simulation environment of haze-fog was put forward. ANSYS Maxwell was used to analyze the influence of room temperature vulcanized silicone rubber surface attachments on electric field distribution. The changes of droplet on the polluted room temperature vulcanized silicone rubber surface and the corresponding surface flashover voltage under alternating current (AC), direct current (DC) positive polar (+), and DC negative polar (−) power source were recorded by a high speed camera. The results are as follows: The main ion components from haze-fog atmospheric particles are NO₃⁻, SO₄²⁻, NH₄⁺, and Ca²⁺. In haze-fog environment, both the equivalent salt deposit density (ESDD) and non-soluble deposit density (NSDD) of insulators are higher than that under general environment. The amount of large particles on the AC transmission line is greater than that of the DC transmission line. The influence of DC polarity power source on the distribution of contamination particle size is not significant. After the deposition of haze-fog, the local conductivity of the room temperature vulcanized silicone rubber surface increased, which caused the flashover voltage reduce. Discharge is liable to occur at the triple junction point of droplet, air, and room temperature vulcanized silicone rubber surface. After the deformation or movement of droplets, a new triple junction point would be formed, which would seriously reduce the dielectric strength of room temperature vulcanized silicone rubber. Full article

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

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16 pages, 6180 KiB

Open AccessArticle

Assessment of Bearing Capacity and Stiffness in New Steel Sets Used for Roadway Support in Coal Mines

by Renshu Yang¹, Qinghai Li^1,2,*, Qing Li¹ and Xianlei Zhu¹

¹ School of Mechanics and Civil Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China

² State Key Laboratory of Mining Disaster Prevention and Control Co-Founded by Shandong Province and the Ministry of Science and Technology, Shandong University of Science and Technology, Qingdao 266590, China

Energies 2017, 10(10), 1581; https://doi.org/10.3390/en10101581 - 12 Oct 2017

Cited by 12 | Viewed by 3687

Abstract

There is high demand for roadway support in coal mines for the swelling soft rocks. As high strength steel sets can be taken as an effective alternative to control large deformation in this type of rocks, based on an original set, three new [...] Read more.

There is high demand for roadway support in coal mines for the swelling soft rocks. As high strength steel sets can be taken as an effective alternative to control large deformation in this type of rocks, based on an original set, three new sets, including a floor beam set, a roof and floor beams set, and a roof and floor beams and braces set, are proposed in this research. In order to examine the strengths of new sets, four scaled sets of one original set, and three new sets, have been manufactured and tested in loading experiments. Results indicated that three new sets all exhibited higher strength than the original set. In experiments, the roof beam in set plays a significant effect on top arch strengthening, while the floor beam plays significant effect on bottom arch strengthening. The maximum bearing capacity and stiffness of the top arch with roof beam are increased to 1.63 times and 3.06 times of those in the original set, and the maximum bearing capacity and stiffness of the bottom arch with floor beam are increased to 1.44 times and 3.55 times of those in original set. Based on the roof and floor beams, two more braces in the bottom arch also play a significant effect in bottom corners strengthening, but extra braces play little role in top arch strengthening. These new sets provide more choices for roadway support in swelling soft rocks. Full article

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9 pages, 2093 KiB

Open AccessArticle

Self-Powered Electrochemical Lactate Biosensing

by Ankit Baingane and Gymama Slaughter^*

Bioelectronics Laboratory, Department of Computer Science and Electrical Engineering, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA

Energies 2017, 10(10), 1582; https://doi.org/10.3390/en10101582 - 12 Oct 2017

Cited by 32 | Viewed by 5156

Abstract

This work presents the development and characterization of a self-powered electrochemical lactate biosensor for real-time monitoring of lactic acid. The bioanode and biocathode were modified with D-lactate dehydrogenase (D-LDH) and bilirubin oxidase (BOD), respectively, to facilitate the oxidation and reduction of lactic acid [...] Read more.

This work presents the development and characterization of a self-powered electrochemical lactate biosensor for real-time monitoring of lactic acid. The bioanode and biocathode were modified with D-lactate dehydrogenase (D-LDH) and bilirubin oxidase (BOD), respectively, to facilitate the oxidation and reduction of lactic acid and molecular oxygen. The bioelectrodes were arranged in a parallel configuration to construct the biofuel cell. This biofuel cell’s current–voltage characteristic was analyzed in the presence of various lactic acid concentrations over a range of 1–25 mM. An open circuit voltage of 395.3 mV and a short circuit current density of 418.8 µA/cm² were obtained when operating in 25 mM lactic acid. Additionally, a 10 pF capacitor was integrated via a charge pump circuit to the biofuel cell to realize the self-powered lactate biosensor with a footprint of 1.4 cm × 2 cm. The charge pump enabled the boosting of the biofuel cell voltage in bursts of 1.2–1.8 V via the capacitor. By observing the burst frequency of a 10 pF capacitor, the exact concentration of lactic acid was deduced. As a self-powered lactate sensor, a linear dynamic range of 1–100 mM lactic acid was observed under physiologic conditions (37 °C, pH 7.4) and the sensor exhibited an excellent sensitivity of 125.88 Hz/mM-cm². This electrochemical lactate biosensor has the potential to be used for the real-time monitoring of lactic acid level in biological fluids. Full article

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

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19 pages, 4652 KiB

Open AccessArticle

Estimating Health Condition of the Wind Turbine Drivetrain System

by Peng Qian¹, Xiandong Ma¹ and Dahai Zhang^2,*

¹ Engineering Department, Lancaster University, Lancaster LA1 4YW, UK

² Ocean College, Zhejiang University, Hangzhou 310058, China

Energies 2017, 10(10), 1583; https://doi.org/10.3390/en10101583 - 12 Oct 2017

Cited by 20 | Viewed by 12830

Abstract

Condition Monitoring (CM) has been considered as an effective method to enhance the reliability of wind turbines and implement cost-effective maintenance. Thus, adopting an efficient approach for condition monitoring of wind turbines is desirable. This paper presents a data-driven model-based CM approach for [...] Read more.

Condition Monitoring (CM) has been considered as an effective method to enhance the reliability of wind turbines and implement cost-effective maintenance. Thus, adopting an efficient approach for condition monitoring of wind turbines is desirable. This paper presents a data-driven model-based CM approach for wind turbines based on the online sequential extreme learning machine (OS-ELM) algorithm. A physical kinetic energy correction model is employed to normalize the temperature change to the value at the rated power output to eliminate the effect of variable speed operation of the turbines. The residual signal, obtained by comparing the predicted values and practical measurements, is processed by the physical correction model and then assessed with a Bonferroni interval method for fault diagnosis. Models have been validated using supervisory control and data acquisition (SCADA) data acquired from an operational wind farm, which contains various types of temperature data of the gearbox. The results show that the proposed method can detect more efficiently both the long-term aging characteristics and the short-term faults of the gearbox. Full article

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

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15 pages, 5318 KiB

Open AccessArticle

Pre-Arcing Time Prediction in a Making Test for a 420 kV 63 kA High-Speed Earthing Switch

by Min-Cheol Kang¹

, Kyong-Hoe Kim² and Yong Tae Yoon^1,*

¹ Department of Electrical and Computer Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Korea

² Department of Heavy Industry, ILJIN Electric Inc., 905-17, Mannyeon-ro, Hwaseong-si, Gyeonggi-do 18365, Korea

Energies 2017, 10(10), 1584; https://doi.org/10.3390/en10101584 - 12 Oct 2017

Cited by 1 | Viewed by 6005

Abstract

A high-speed earthing switch (HSES) of a gas-insulated switchgear (GIS) performs a secondary role in protecting the power system in the event of an accident. After being interrupted by a circuit breaker (CB), the short-circuit current remaining in the network should be earthed [...] Read more.

A high-speed earthing switch (HSES) of a gas-insulated switchgear (GIS) performs a secondary role in protecting the power system in the event of an accident. After being interrupted by a circuit breaker (CB), the short-circuit current remaining in the network should be earthed by the HSES. However, as the contacts of the HSES may have been damaged by a pre-arc during the closing operation, the HSES may fail to ground the short-circuit current. To successfully ground the short-circuit current, the contacts of the HSES must be protected from damage by the pre-arc. Thus, minimizing the pre-arcing time is required to step up the making performance. This paper analyzes the making performance of the HSES by predicting the pre-arcing time within the short-circuit current making test. To estimate the pre-arcing time, we compared the results of analytical calculations based on streamer discharge theory and the numerical simulations of the electric field strength. By conducting a short-circuit current making test for a 420 kV 63 kA HSES in a high-power laboratory, the pre-arcing time calculation results were verified. A comparison of the results showed that the proposed prediction method was useful for verifying the performance of the HSES. Full article

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12 pages, 1117 KiB

Open AccessArticle

Energy Consumption and Energy-Related CO₂ Emissions from China’s Petrochemical Industry Based on an Environmental Input-Output Life Cycle Assessment

by Lu Meng^1,* and Jalel Sager²

¹ School of Business Administration, China University of Petroleum-Beijing, Beijing 102249, China

² Energy and Resources Group, University of California-Berkeley, Berkeley, CA 94720, USA

Energies 2017, 10(10), 1585; https://doi.org/10.3390/en10101585 - 12 Oct 2017

Cited by 15 | Viewed by 4439

Abstract

The fast-growing petrochemical industry is one of the largest energy consumers and emitters in China, exerting a strong impact on the national economic, energy and environmental systems. We provide a holistic picture of energy consumption and energy-related CO₂ emissions from China’s petrochemical [...] Read more.

The fast-growing petrochemical industry is one of the largest energy consumers and emitters in China, exerting a strong impact on the national economic, energy and environmental systems. We provide a holistic picture of energy consumption and energy-related CO₂ emissions from China’s petrochemical industry in 2012 through an environmental input-output life-cycle assessment (EIO-LCA). We combine two perspectives: (1) direct energy consumption and emissions, and (2) the indirect energy and emissions embodied and reallocated from other sectors in the supply chain to satisfy final demand in the petrochemical industry. Results indicate that the total of its direct and indirect energy consumption and CO₂ emissions accounts for approximately 32% and 18% of China’s industrial total, respectively, exerting high “influence” and “induction” with regards to the rest of the economic sectors. Most of the petrochemical industry’s embodied energy and CO₂ emissions comes from the “Production and Supply of Electric and Heat Power”. We also identified five other sectors key to China’s energy conservation and CO₂ mitigation efforts due to their high influence and induction effects: “Smelting and Pressing of Ferrous Metals”, “Manufacture of Non-metallic Mineral Products”, “Smelting and Pressing of Non-ferrous Metals”, “Transport, Storage and Post”, and “Mining and Washing of Coal”. A systematic view of direct and indirect energy, environmental relationships, and the conveying effects among sectors is crucial for policymaking in China to achieve its energy and mitigation goals. Full article

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14 pages, 6260 KiB

Open AccessArticle

Adsorption Properties of Hydrocarbons (n-Decane, Methyl Cyclohexane and Toluene) on Clay Minerals: An Experimental Study

by Jie Zhang^1,2, Shuangfang Lu¹, Junqian Li^1,*, Pengfei Zhang^1,2, Haitao Xue¹, Xu Zhao^3,4 and Liujuan Xie^1,2

¹ Research Institute of Unconventional Oil & Gas and Renewable Energy, China University of Petroleum (East China), Qingdao 266580, China

² School of Geosciences, China University of Petroleum (East China), Qingdao 266580, China

³ Exploration & Production Research Institute SINOPEC, Beijing 100083, China

⁴ Shandong Provincial Key Laboratory of Depositional Mineralization & Sedimentary Mineral, Shandong University of Science and Technology, Qingdao 266590, China

Energies 2017, 10(10), 1586; https://doi.org/10.3390/en10101586 - 12 Oct 2017

Cited by 18 | Viewed by 5325

Abstract

Adsorption of hydrocarbons may significantly affect hydrocarbon migration in unconventional reservoirs. Clay minerals form the primary adsorbent surfaces for hydrocarbons adsorbed in mudstone/shale. To study the adsorption properties of hydrocarbons (n-decane (C₁₀H₂₂), methyl cyclohexane (C₇H₁₄) [...] Read more.

Adsorption of hydrocarbons may significantly affect hydrocarbon migration in unconventional reservoirs. Clay minerals form the primary adsorbent surfaces for hydrocarbons adsorbed in mudstone/shale. To study the adsorption properties of hydrocarbons (n-decane (C₁₀H₂₂), methyl cyclohexane (C₇H₁₄) and toluene (C₇H₈)) on clay minerals (i.e., cookeite, ripidolite, kaolinite, illite, illite/smectite mixed-layer, Na-montmorillonite and Ca-montmorillonite), hydrocarbon vapor adsorption (HVA) tests were conducted at 298.15 K. The results showed that (i) the adsorption amounts of C₁₀H₂₂, C₇H₁₄ and C₇H₈ ranged from 0.45–1.03 mg/m², 0.28–0.90 mg/m² and 0.16–0.53 mg/m², respectively; (ii) for cookeite, ripidolite and kaolinite, the adsorption capacity of C₁₀H₂₂ was less than C₇H₁₄, which was less than C₇H₈; (iii) for illite, Na-montmorillonite and Ca-montmorillonite, the adsorption capacity of C₁₀H₂₂ was greater than that of C₇H₈, and the adsorption capacity of C₇H₁₄ was the lowest; (iv) for an illite/smectite mixed-layer, C₇H₁₄ had the highest adsorption capacity, followed by C₁₀H₂₂, and C₇H₈ had the lowest capacity. Adsorption properties were correlated with the microscopic parameters of pores in clay minerals and with experimental pressure. Finally, the weighted average method was applied to evaluate the adsorption properties of C₁₀H₂₂, C₇H₁₄ and C₇H₈ on clay minerals in oil-bearing shale from the Shahejie Formation of Dongying Sag in the Bohai Bay Basin, China. For these samples, the adsorbed amounts of C₇H₁₄ ranged from 18.03–28.02 mg/g (mean 23.33 mg/g), which is larger than that of C₁₀H₂₂, which ranges from 15.40–21.72 mg/g (mean 18.82 mg/g). The adsorption capacity of C₇H₈ was slightly low, ranging from 10.51–14.60 mg/g (mean 12.78 mg/g). Full article

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

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19 pages, 656 KiB

Open AccessArticle

Validation of Calibrated Energy Models: Common Errors

by Germán Ramos Ruiz^*

and Carlos Fernández Bandera

School of Architecture, University of Navarra, 31009 Pamplona, Spain

Energies 2017, 10(10), 1587; https://doi.org/10.3390/en10101587 - 12 Oct 2017

Cited by 312 | Viewed by 10982

Abstract

Nowadays, there is growing interest in all the smart technologies that provide us with information and knowledge about the human environment. In the energy field, thanks to the amount of data received from smart meters and devices and the progress made in both [...] Read more.

Nowadays, there is growing interest in all the smart technologies that provide us with information and knowledge about the human environment. In the energy field, thanks to the amount of data received from smart meters and devices and the progress made in both energy software and computers, the quality of energy models is gradually improving and, hence, also the suitability of Energy Conservation Measures (ECMs). For this reason, the measurement of the accuracy of building energy models is an important task, because once the model is validated through a calibration procedure, it can be used, for example, to apply and study different strategies to reduce its energy consumption in maintaining human comfort. There are several agencies that have developed guidelines and methodologies to establish a measure of the accuracy of these models, and the most widely recognized are: ASHRAE Guideline 14-2014, the International Performance Measurement and Verification Protocol (IPMVP) and the Federal Energy Management Program (FEMP). This article intends to shed light on these validation measurements (uncertainty indices) by focusing on the typical mistakes made, as these errors could produce a false belief that the models used are calibrated. Full article

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20 pages, 7971 KiB

Open AccessArticle

Analysis and Design of a Wireless Power Transfer System with Dual Active Bridges

by Xin Liu¹

, Tianfeng Wang¹, Xijun Yang^1,*, Nan Jin² and Houjun Tang¹

¹ Key Laboratory of Control of Power Transmission and Transformation Ministry of Education, Shanghai Jiao Tong University, 800 Dongchuan RD., Shanghai 200240, China

² College of Electric and Information Engineering, Zhengzhou University of Light Industry, Zhengzhou 450002, China

Energies 2017, 10(10), 1588; https://doi.org/10.3390/en10101588 - 12 Oct 2017

Cited by 41 | Viewed by 7314

Abstract

Nowadays, work on Wireless Power Transfer (WPT) systems with dual active bridges is attracting great attention due to their low conduction losses, power regulation, load transformation and reactance compensation. However, in these studies limitations such as overall analysis, design and realization techniques of [...] Read more.

Nowadays, work on Wireless Power Transfer (WPT) systems with dual active bridges is attracting great attention due to their low conduction losses, power regulation, load transformation and reactance compensation. However, in these studies limitations such as overall analysis, design and realization techniques of the system were not considered properly. To address the aforementioned issues, this paper presents a detailed analysis, design and realization of a Series-Series (SS) WPT system with dual active bridges, which will improve the overall performance. Three independent Phase Angles (PAs) have been analyzed and designed in this study, one PA on the primary side and the other two PAs on the secondary side. This Multiple Degrees of Phase Control (MDPC) method can achieve additional reactance compensation, load transformation and output regulation simultaneously. To realize the proposed method in practice, key implementation techniques have been investigated in detail, including additional reactance estimation, mutual inductance estimation, phase detection and synchronization. The feasibility and effectiveness of the proposed system is verified through simulation and experimental results. Full article

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27 pages, 16534 KiB

Open AccessArticle

A Flexible Experimental Laboratory for Distributed Generation Networks Based on Power Inverters

by Jaume Miret^1,*

, José Luís García de Vicuña¹, Ramón Guzmán²

, Antonio Camacho¹

and Mohammad Moradi Ghahderijani¹

¹ Department of Electronic Engineering, Technical University of Catalonia, 08800 Vilanova i la Geltrú, Spain

² Department of Automatic Control, Technical University of Catalonia, 08800 Vilanova i la Geltrú, Spain

Energies 2017, 10(10), 1589; https://doi.org/10.3390/en10101589 - 13 Oct 2017

Cited by 23 | Viewed by 6295

Abstract

In the recently deregulated electricity market, distributed generation based on renewable sources is becoming more and more relevant. In this area, two main distributed scenarios are focusing the attention of recent research: grid-connected mode, where the generation sources are connected to a grid [...] Read more.

In the recently deregulated electricity market, distributed generation based on renewable sources is becoming more and more relevant. In this area, two main distributed scenarios are focusing the attention of recent research: grid-connected mode, where the generation sources are connected to a grid mainly supplied by big power plants, and islanded mode, where the distributed sources, energy storage devices, and loads compose an autonomous entity that in its general form can be named a microgrid. To conduct a successful research in these two scenarios, it is essential to have a flexible experimental setup. This work deals with the description of a real laboratory setup composed of four nodes that can emulate both scenarios of a distributed generation network. A comprehensive description of the hardware and software setup will be done, focusing especially in the dual-core DSP used for control purposes, which is next to the industry standards and able to emulate real complexities. A complete experimental section will show the main features of the system. Full article

(This article belongs to the Special Issue Control and Communication in Distributed Generation Systems)

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18 pages, 7631 KiB

Open AccessArticle

Impact of Different Driving Cycles and Operating Conditions on CO₂ Emissions and Energy Management Strategies of a Euro-6 Hybrid Electric Vehicle

by Claudio Cubito¹

, Federico Millo^1,*, Giulio Boccardo¹, Giuseppe Di Pierro¹

, Biagio Ciuffo², Georgios Fontaras²

, Simone Serra²

, Marcos Otura Garcia² and Germana Trentadue²

¹ Department of Energy, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy

² Joint Research Centre—European Commission, Via Enrico Fermi 2749, 21027 Ispra, Italy

Energies 2017, 10(10), 1590; https://doi.org/10.3390/en10101590 - 13 Oct 2017

Cited by 55 | Viewed by 8230

Abstract

Although Hybrid Electric Vehicles (HEVs) represent one of the key technologies to reduce CO₂ emissions, their effective potential in real world driving conditions strongly depends on the performance of their Energy Management System (EMS) and on its capability to maximize the efficiency [...] Read more.

Although Hybrid Electric Vehicles (HEVs) represent one of the key technologies to reduce CO₂ emissions, their effective potential in real world driving conditions strongly depends on the performance of their Energy Management System (EMS) and on its capability to maximize the efficiency of the powertrain in real life as well as during Type Approval (TA) tests. Attempting to close the gap between TA and real world CO₂ emissions, the European Commission has decided to introduce from September 2017 the Worldwide Harmonized Light duty Test Procedure (WLTP), replacing the previous procedure based on the New European Driving Cycle (NEDC). The aim of this work is the analysis of the impact of different driving cycles and operating conditions on CO₂ emissions and on energy management strategies of a Euro-6 HEV through the limited number of information available from the chassis dyno tests. The vehicle was tested considering different initial battery State of Charge (SOC), ranging from 40% to 65%, and engine coolant temperatures, from −7 °C to 70 °C. The change of test conditions from NEDC to WLTP was shown to lead to a significant reduction of the electric drive and to about a 30% increase of CO₂ emissions. However, since the specific energy demand of WLTP is about 50% higher than that of NEDC, these results demonstrate that the EMS strategies of the tested vehicle can achieve, in test conditions closer to real life, even higher efficiency levels than those that are currently evaluated on the NEDC, and prove the effectiveness of HEV technology to reduce CO₂ emissions. Full article

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

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17 pages, 1163 KiB

Open AccessArticle

Probabilistic Solar Forecasting Using Quantile Regression Models

by Philippe Lauret^1,*, Mathieu David¹

and Hugo T. C. Pedro²

¹ PIMENT Laboratory, Université de La Réunion,15 Avenue René Cassin, 97715 Saint-Denis, France

² Department of Mechanical and Aerospace Engineering, Jacobs School of Engineering, Center for Energy Research University of California, San Diego, La Jolla, CA 92093, USA

Energies 2017, 10(10), 1591; https://doi.org/10.3390/en10101591 - 13 Oct 2017

Cited by 92 | Viewed by 6518

Abstract

In this work, we assess the performance of three probabilistic models for intra-day solar forecasting. More precisely, a linear quantile regression method is used to build three models for generating 1 h–6 h-ahead probabilistic forecasts. Our approach is applied to forecasting solar irradiance [...] Read more.

In this work, we assess the performance of three probabilistic models for intra-day solar forecasting. More precisely, a linear quantile regression method is used to build three models for generating 1 h–6 h-ahead probabilistic forecasts. Our approach is applied to forecasting solar irradiance at a site experiencing highly variable sky conditions using the historical ground observations of solar irradiance as endogenous inputs and day-ahead forecasts as exogenous inputs. Day-ahead irradiance forecasts are obtained from the Integrated Forecast System (IFS), a Numerical Weather Prediction (NWP) model maintained by the European Center for Medium-Range Weather Forecast (ECMWF). Several metrics, mainly originated from the weather forecasting community, are used to evaluate the performance of the probabilistic forecasts. The results demonstrated that the NWP exogenous inputs improve the quality of the intra-day probabilistic forecasts. The analysis considered two locations with very dissimilar solar variability. Comparison between the two locations highlighted that the statistical performance of the probabilistic models depends on the local sky conditions. Full article

(This article belongs to the Special Issue Solar Forecasting)

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15 pages, 7353 KiB

Open AccessArticle

Mechanical Characteristics of Superhigh-Water Content Material Concretion and Its Application in Longwall Backfilling

by Xufeng Wang^1,2,3, Dongdong Qin^1,*, Dongsheng Zhang^1,4, Chundong Sun⁵, Chengguo Zhang⁶, Mengtang Xu⁷ and Bo Li¹

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

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

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

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

⁵ Jizhong Energy Handan Mining Industry Group, Handan 056002, China

⁶ School of Mining Engineering, University of New South Wales, Sydney, NSW 2052, Australia

⁷ School of Mines, Guizhou Institute of Technology, Guiyang 550003, China

Energies 2017, 10(10), 1592; https://doi.org/10.3390/en10101592 - 13 Oct 2017

Cited by 9 | Viewed by 3455

Abstract

Superhigh-water content material (SCM) has been widely utilized for goaf backfilling, grouting, and fire prevention and extinguishing. In this paper, the engineering mechanical characteristics of superhigh-water content material concretion (SCMC) were studied for two types of backfilling technologies in longwall mining—open-type and pocket-type [...] Read more.

Superhigh-water content material (SCM) has been widely utilized for goaf backfilling, grouting, and fire prevention and extinguishing. In this paper, the engineering mechanical characteristics of superhigh-water content material concretion (SCMC) were studied for two types of backfilling technologies in longwall mining—open-type and pocket-type backfilling. The mechanical properties and responses of the SCMC were assessed under different cementation states, varying loading conditions and at different scales. The results indicate that: (1) the compressive and tensile strengths of SCMC specimens in different cementation states increase as the curing time increases—the SCMC formed by a mixture of SCM and gangues has higher strength than that of pure SCM; (2) the SCMC is under different loading and confinement conditions when different backfilling technologies is applied; however the strength of SCMC increases with curing time and decreases with water volume percentage; and (3) large-size specimens of pure SCMC enter into an accelerated creep state at a leveled load of 1.4 MPa. The effects of SCM backfilling on subsidence control has been verified by field applications. The results presented in this paper can provide data support for the optimization of backfill mining technology using SCM, as well as for the design of hydraulic supports parameters at longwall faces. Full article

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

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23 pages, 3107 KiB

Open AccessArticle

Thermo-Economic Performance Analysis of a Regenerative Superheating Organic Rankine Cycle for Waste Heat Recovery

by Zhonghe Han

, Peng Li^*

, Xu Han

, Zhongkai Mei and Zhi Wang

Key Lab of Condition Monitoring and Control for Power Plant Equipment, North China Electric Power University, Ministry of Education, Baoding 071003, China

Energies 2017, 10(10), 1593; https://doi.org/10.3390/en10101593 - 13 Oct 2017

Cited by 32 | Viewed by 5210

Abstract

The Organic Rankine Cycle (ORC) is a promising form of technology for recovering low-grade waste heat. In this study, a regenerative ORC system is established to recover the waste flue gas of 160 °C. Focusing on thermodynamic and economic performance while simultaneously considering [...] Read more.

The Organic Rankine Cycle (ORC) is a promising form of technology for recovering low-grade waste heat. In this study, a regenerative ORC system is established to recover the waste flue gas of 160 °C. Focusing on thermodynamic and economic performance while simultaneously considering the limitations of volume flow ratio (VFR) and the effect of superheat, working fluid selection and parameter optimization have been investigated. The optimization of the evaporation temperature is carried out by analyzing the variation of net power output and specific investment cost (SIC). Then, the net power output, specific net power output, total exergy destruction rate, VFR, total capital cost, and levelized electricity cost (LEC) are selected as criteria, and a fuzzy multi-criteria evaluation method is adopted to select a more suitable working fluid and determine the optimal degree of superheat. In addition, the preheating coefficient, latent heat coefficient, superheating coefficient, and internal heat coefficient were proposed to explore the effect of working fluid critical temperature on thermal efficiency. Research studies demonstrate that there is an optimal evaporation temperature, maximizing net power output and minimizing the SIC. Isohexane and butane have greater specific net power output due to greater latent heat. A suitable degree of superheat is not only conducive to improving the working capacity of working fluids, but also reduces the VFR, total capital cost, SIC, and LEC for different working fluids. Thus, the system’s thermodynamic and economic performance—as well as the operational stability—are improved. Among the six working fluids, butane exhibits the best comprehensive performance, and its optimal evaporation temperature and degree of superheat are 100 °C and 5 °C, respectively. Full article

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

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14 pages, 4194 KiB

Open AccessArticle

A Comparative Study on Damage Mechanism of Sandwich Structures with Different Core Materials under Lightning Strikes

by Jiangyan Yan¹, Guozheng Wang²

, Qingmin Li^1,*, Li Zhang², Joseph D. Yan³, Chun Chen⁴ and Zhiyang Fang⁴

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

² School of Electrical Engineering, Shandong University, Jinan 250061, China

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

⁴ Sinoma Wind Power Blade Co., Ltd., Beijing 102100, China

Energies 2017, 10(10), 1594; https://doi.org/10.3390/en10101594 - 13 Oct 2017

Cited by 20 | Viewed by 3949

Abstract

Wind turbine blades are easily struck by lightning, a phenomenon that has attracted more and more attention in recent years. On this subject a large current experiment was conducted on three typical blade sandwich structures to simulate the natural lightning-induced arc effects. The [...] Read more.

Wind turbine blades are easily struck by lightning, a phenomenon that has attracted more and more attention in recent years. On this subject a large current experiment was conducted on three typical blade sandwich structures to simulate the natural lightning-induced arc effects. The resulting damage to different composite materials has been compared: polyvinyl chloride (PVC) and polyethylene terephthalate (PET) suffered pyrolysis and cracks inside, while the damage to balsa wood was fibers breaking off and large delamination between it and the resin layer, and only a little chemical pyrolysis. To analyze the damage mechanism on sandwich structures of different materials, a finite element method (FEM) model to calculate the temperature and pressure distribution was built, taking into consideration heat transfer and flow expansion due to impulse currents. According to the simulation results, PVC had the most severe temperature and pressure distribution, while PET and balsa wood were in the better condition after the experiments. The temperature distribution results explained clearly why balsa wood suffered much less chemical pyrolysis than PVC. Since balsa wood had better thermal stability than PET, the pyrolysis area of PET was obviously larger than that of balsa wood too. Increasing the volume fraction of solid components of porous materials can efficiently decrease the heat transfer velocity in porous materials. Permeability didn’t influence that much. The findings provide support for optimum material selection and design in blade manufacturing. Full article

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24 pages, 2947 KiB

Open AccessFeature PaperArticle

Engineering Support for Handling Controller Conflicts in Energy Storage Systems Applications

by Claudia Zanabria^*

, Ali Tayyebi, Filip Pröstl Andrén, Johannes Kathan and Thomas Strasser

Center for Energy–Electric Energy Systems, AIT Austrian Institute of Technology, 1210 Vienna, Austria

Energies 2017, 10(10), 1595; https://doi.org/10.3390/en10101595 - 13 Oct 2017

Cited by 8 | Viewed by 5424

Abstract

Energy storage systems will play a major role in the decarbonization of future sustainable electric power systems, allowing a high penetration of distributed renewable energy sources and contributing to the distribution network stability and reliability. To accomplish this, a storage system is required [...] Read more.

Energy storage systems will play a major role in the decarbonization of future sustainable electric power systems, allowing a high penetration of distributed renewable energy sources and contributing to the distribution network stability and reliability. To accomplish this, a storage system is required to provide multiple services such as self-consumption, grid support, peak-shaving, etc. The simultaneous activation of controllers operation may lead to conflicts, as a consequence the execution of committed services is not guaranteed. This paper presents and discusses a solution to the exposed issue by developing an engineering support approach to semi-automatically detect and handle conflicts for multi-usage storage systems applications. To accomplish that an ontology is developed and exploited by model-driven engineering mechanisms. The proposed approach is evaluated by implementing a use case example, where detection of conflicts is automatically done at an early design stage. Besides this, exploitable source code for conflicts resolution is generated and used during the design and prototype stages of controllers development. Thus, the proposed engineering support enhances the design and development of storage system controllers, especially for multi-usage applications. Full article

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

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12 pages, 854 KiB

Open AccessArticle

Location of Faults in Power Transmission Lines Using the ARIMA Method

by Danilo Pinto Moreira de Souza¹, Eliane Da Silva Christo^1,*

and Aryfrance Rocha Almeida²

¹ Computational Modeling in Science and Technology (MCCT), Fluminense Federal University (UFF), Volta Redonda 21941-916, Brazil

² Technology Center, Federal University of Piauí (UFPI), Teresina 60455-760, Brazil

Energies 2017, 10(10), 1596; https://doi.org/10.3390/en10101596 - 13 Oct 2017

Cited by 22 | Viewed by 5519

Abstract

One of the major problems in transmission lines is the occurrence of failures that affect the quality of the electric power supplied, as the exact localization of the fault must be known for correction. In order to streamline the work of maintenance teams [...] Read more.

One of the major problems in transmission lines is the occurrence of failures that affect the quality of the electric power supplied, as the exact localization of the fault must be known for correction. In order to streamline the work of maintenance teams and standardize services, this paper proposes a method of locating faults in power transmission lines by analyzing the voltage oscillographic signals extracted at the line monitoring terminals. The developed method relates time series models obtained specifically for each failure pattern. The parameters of the autoregressive integrated moving average (ARIMA) model are estimated in order to adjust the voltage curves and calculate the distance from the initial fault localization to the terminals. Simulations of the failures are performed through the ATPDraw

^{®}

(5.5) software and the analyses were completed using the RStudio

^{®}

(1.0.143) software. The results obtained with respect to the failures, which did not involve earth return, were satisfactory when compared with widely used techniques in the literature, particularly when the fault distance became larger in relation to the beginning of the transmission line. Full article

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

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16 pages, 1796 KiB

Open AccessArticle

An Integrated Approach for Estimating the Energy Efficiency of Seventeen Countries

by Chia-Nan Wang^1,*

, Hong-Xuyen Thi Ho^1,2,* and Ming-Hsien Hsueh^1,*

¹ Department of Industrial Engineering and Management, National Kaohsiung University of Applied Sciences, Kaohsiung 80778, Taiwan

² Department of Economics, Ho Chi Minh City University of Technology and Education, Ho Chi Minh City 800010, Vietnam

Energies 2017, 10(10), 1597; https://doi.org/10.3390/en10101597 - 13 Oct 2017

Cited by 25 | Viewed by 4699

Abstract

Increased energy efficiency is one of the most effective ways to achieve climate change mitigation. This study aims to evaluate the energy efficiency of seventeen countries. The evaluation is based on an integrated method that combines the super slack-based (super SBM) model and [...] Read more.

Increased energy efficiency is one of the most effective ways to achieve climate change mitigation. This study aims to evaluate the energy efficiency of seventeen countries. The evaluation is based on an integrated method that combines the super slack-based (super SBM) model and the Malmquist productivity index (MPI) to investigate the energy efficiency of seventeen countries during the period of 2010–2015. The results in this study are that the United States, Columbia, Japan, China, and Saudi Arabia perform the best in energy efficiency, whereas Brazil, Russia, Indonesia, and India perform the worst during the entire sample period. The energy efficiency of these countries arrived mainly from technological improvement. The study provides suggestions for the seventeen countries’ government to control the energy consumption and contribute to environmental protection. Full article

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

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18 pages, 5719 KiB

Open AccessArticle

Optimal Energy Management and MPC Strategies for Electrified RTG Cranes with Energy Storage Systems

by Feras Alasali^1,*

, Stephen Haben², Victor Becerra³ and William Holderbaum^1,4,*

¹ School of Systems Engineering, University of Reading, Whiteknights, Reading RG6 6AY, UK

² Mathematical Institute, University of Oxford, Andrew Wiles Building, Oxford OX2 6GG, UK

³ School of Engineering, University of Portsmouth, Anglesea Road, Portsmouth PO1 3DJ, UK

⁴ School of Engineering, Manchester Metropolitan University, Manchester M1 5GD, UK

Energies 2017, 10(10), 1598; https://doi.org/10.3390/en10101598 - 13 Oct 2017

Cited by 27 | Viewed by 6495

Abstract

This article presents a study of optimal control strategies for an energy storage system connected to a network of electrified Rubber Tyre Gantry (RTG) cranes. The study aims to design optimal control strategies for the power flows associated with the energy storage device, [...] Read more.

This article presents a study of optimal control strategies for an energy storage system connected to a network of electrified Rubber Tyre Gantry (RTG) cranes. The study aims to design optimal control strategies for the power flows associated with the energy storage device, considering the highly volatile nature of RTG crane demand and difficulties in prediction. Deterministic optimal energy management controller and a Model Predictive Controller (MPC) are proposed as potentially suitable approaches to minimise the electric energy costs associated with the real-time electricity price and maximise the peak demand reduction, under given energy storage system parameters and network specifications. A specific case study is presented in to test the proposed optimal strategies and compares them to a set-point controller. The proposed models used in the study are validated using data collected from an instrumented RTG crane at the Port of Felixstowe, UK and are compared to a standard set-point controller. The results of the proposed control strategies show a significant reduction in the potential electricity costs and peak power demand from the RTG cranes. Full article

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

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21 pages, 10821 KiB

Open AccessArticle

Sensitivity Analysis to Control the Far-Wake Unsteadiness Behind Turbines

by Esteban Ferrer^1,2,*

, Oliver M.F. Browne³ and Eusebio Valero^1,2

¹ ETSIAE (School of Aeronautics)—Universidad Politécnica de Madrid, Pza Cardenal Cisneros 3, E-28040 Madrid, Spain

² Center for Computational Simulation—Universidad Politécnica de Madrid, Boadilla del Monte, E-28660 Madrid, Spain

³ Department of Aerospace and Mechanical Engineering, University of Arizona, Tucson, AZ 85721, USA

Energies 2017, 10(10), 1599; https://doi.org/10.3390/en10101599 - 13 Oct 2017

Cited by 11 | Viewed by 5166

Abstract

We explore the stability of wakes arising from 2D flow actuators based on linear momentum actuator disc theory. We use stability and sensitivity analysis (using adjoints) to show that the wake stability is controlled by the Reynolds number and the thrust force (or [...] Read more.

We explore the stability of wakes arising from 2D flow actuators based on linear momentum actuator disc theory. We use stability and sensitivity analysis (using adjoints) to show that the wake stability is controlled by the Reynolds number and the thrust force (or flow resistance) applied through the turbine. First, we report that decreasing the thrust force has a comparable stabilising effect to a decrease in Reynolds numbers (based on the turbine diameter). Second, a discrete sensitivity analysis identifies two regions for suitable placement of flow control forcing, one close to the turbines and one far downstream. Third, we show that adding a localised control force, in the regions identified by the sensitivity analysis, stabilises the wake. Particularly, locating the control forcing close to the turbines results in an enhanced stabilisation such that the wake remains steady for significantly higher Reynolds numbers or turbine thrusts. The analysis of the controlled flow fields confirms that modifying the velocity gradient close to the turbine is more efficient to stabilise the wake than controlling the wake far downstream. The analysis is performed for the first flow bifurcation (at low Reynolds numbers) which serves as a foundation of the stabilization technique but the control strategy is tested at higher Reynolds numbers in the final section of the paper, showing enhanced stability for a turbulent flow case. Full article

(This article belongs to the Collection Wind Turbines)

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12 pages, 5865 KiB

Open AccessArticle

Effect of Relative Movement between the Shroud and Blade on Tip Leakage Flow Characteristics

by Xiaochun Wang, Jianhua Wang^*, Fei He^* and Hong Zhang

Department of Thermal Science and Energy Engineering, University of Science and Technology of China, Jinzhai Road 96, Hefei 230027, China

Energies 2017, 10(10), 1600; https://doi.org/10.3390/en10101600 - 13 Oct 2017

Cited by 2 | Viewed by 3422

Abstract

An experimental and numerical investigation into the tip leakage flow of a turbine rotor is carried out using a particle image velocimetry (PIV) system and the commercial software ANSYS CFX 14.0. The specimen used in this work is a typical GE-E³ model [...] Read more.

An experimental and numerical investigation into the tip leakage flow of a turbine rotor is carried out using a particle image velocimetry (PIV) system and the commercial software ANSYS CFX 14.0. The specimen used in this work is a typical GE-E³ model with a new squealer tip design. The experimental data are used to create a turbulence model and numerical strategy. Through the validated turbulence model and numerical strategy, simulations are carried out to compare the characteristics of the tip leakage flow in three cases: (1) the blade is rotating, but the shroud is stationary, which is the real status of turbine rotor operation; (2) the blade is stationary, but the shroud moves, to simulate their relative movement; (3) the blade is stationary, and the shroud is also stationary, this is a simplified case, but has been widely used in the experiments on rotor tip leakage flow. Detailed analysis of the flow phenomena shows that the second case is a reasonable alternative approach to simulate the real state. However, the flow patterns in the third case exhibit some evident differences from the real status. These differences are caused by the inaccurate viscous force arising from the stationary blade and shroud. In this work, a modification method for the experiments conducted in the third case is firstly proposed, which is realized through adding an imaginary roughness at the shroud wall to be close to the real viscous effect, and to thereby reduce the deviation of the experiment from the real case. According to the results calculated by ANSYS CFX, the flow structure in the modification case is very close to the real status. Besides, this modification case is an easy and cheap way to simulate the real tip leakage flow. Full article

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16 pages, 5235 KiB

Open AccessArticle

GECM-Based Voltage Stability Assessment Using Wide-Area Synchrophasors

by Heng-Yi Su^* and Tzu-Yi Liu

Department of Electrical Engineering, Feng Chia University (FCU), No. 100, Wenhwa Road, Seatwen, Taichung 40724, Taiwan

Energies 2017, 10(10), 1601; https://doi.org/10.3390/en10101601 - 13 Oct 2017

Cited by 4 | Viewed by 3352

Abstract

Voltage instability is a crucial issue in the secure operation of power grids. Several methods for voltage stability assessment were presented. Some of them are highly computationally intensive, while others are reported not to work properly under all circumstances. This paper proposes a [...] Read more.

Voltage instability is a crucial issue in the secure operation of power grids. Several methods for voltage stability assessment were presented. Some of them are highly computationally intensive, while others are reported not to work properly under all circumstances. This paper proposes a new methodology based on the generator equivalent circuit model (GECM) and the phasor measurement unit (PMU) technology for online voltage stability monitoring of a power grid. First, the proposed methodology utilizes synchronized phasor (synchrophasor) measurements to determine the impedance parameters of a transmission grid by means of the recursive least squares (RLS) algorithm. Furthermore, it incorporates the dynamic models of generators to handle the cases with generator reactive power limit violations. After that, an enhanced voltage stability index with GECMs incorporated is developed for reliable and accurate voltage stability assessment. The proposed methodology was first demonstrated on several standard IEEE power systems, and then applied to a practical power system, the Taiwan power (Taipower) system. The test results demonstrate the flexibility and effectiveness of the proposed methodology. Full article

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

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24 pages, 4545 KiB

Open AccessArticle

Rate Decline Analysis of Vertically Fractured Wells in Shale Gas Reservoirs

by Xiaoyang Zhang^1,2,3, Xiaodong Wang^1,2,*

, Xiaochun Hou^1,2 and Wenli Xu^1,3

¹ School of Energy Resources, China University of Geosciences (Beijing), Beijing 100083, China

² Beijing Key Laboratory of Unconventional Natural Gas Geological Evaluation and Development Engineering, Beijing 100083, China

³ Key Laboratory of Strategy Evaluation for Shale Gas, Ministry of Land and Resources, Beijing 100083, China

Energies 2017, 10(10), 1602; https://doi.org/10.3390/en10101602 - 13 Oct 2017

Cited by 16 | Viewed by 4258

Abstract

Based on the porous flow theory, an extension of the pseudo-functions approach for the solution of non-linear partial differential equations considering adsorption-desorption effects was used to investigate the transient flow behavior of fractured wells in shale gas reservoirs. The pseudo-time factor was employed [...] Read more.

Based on the porous flow theory, an extension of the pseudo-functions approach for the solution of non-linear partial differential equations considering adsorption-desorption effects was used to investigate the transient flow behavior of fractured wells in shale gas reservoirs. The pseudo-time factor was employed to effectively linearize the partial differential equations of the unsteady flow response. The production performance of vertically fractured wells in shale gas reservoirs under either constant flow rate or constant bottom-hole pressure conditions was analyzed using the composite flow model. The calculation results indicate that the non-linearities that develop in the gas diffusivity equation have significant effects on the unsteady response, leading to a larger pressure depletion and rate decline in the late-time period. In addition, gas desorption from the shale acts as a recharge source, which relieves the gas production rate of decline. Greater values for the Langmuir volumes or Langmuir pressures provide additional pressure support, leading to a lower rate decline while the flowing well bottom-hole pressure is maintained. The reservoir size mainly affects the duration of the pressure depletion and rate decline. In the case of ignoring the non-linearity and adsorption-desorption effect in the differential equation, a greater rate decline under constant bottom-hole pressure production can be obtained during the boundary-dominated depletion. This work provides a better understanding of gas desorption in shale gas reservoirs and new insight into investigating the production performances of fractured gas well. Full article

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

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20 pages, 7511 KiB

Open AccessArticle

Rapid Optimization of Double-Stators Switched Reluctance Motor with Equivalent Magnetic Circuit

by Wu-Sung Yao

Department of Mechanical and Automation Engineering, National Kaohsiung First University of Science and Technology, No.1, University Rd., Yanchao Dist., Kaohsiung City 824, Taiwan

Energies 2017, 10(10), 1603; https://doi.org/10.3390/en10101603 - 13 Oct 2017

Cited by 5 | Viewed by 5210

Abstract

The primary objective for this paper is to create a methodology to rapidly optimize double-stators switched reluctance motor (DSSRM). An analytical model of equivalent magnetic circuits for the air gap reluctances of aligned and unaligned positions is proposed and the optimal operation point [...] Read more.

The primary objective for this paper is to create a methodology to rapidly optimize double-stators switched reluctance motor (DSSRM). An analytical model of equivalent magnetic circuits for the air gap reluctances of aligned and unaligned positions is proposed and the optimal operation point of the magneto-motive force (MMF) can be determined. Genetic algorithm (GA) integrated of the proposed equivalent magnetic circuit is developed for rapid optimization of DSSRM to reach the maximum of the ratio of torque to volume of DSSRM. Compared to conventional switched reluctance motor (SRM), an illustrated example of a 3-KW three-phase 12-Slot-8-Pole DSSRM is used to verify the efficiency of the proposed method. Simplified 2-D electromagnetic models are analyzed and simulated. Finally, results of the analytical calculations and the finite-element analysis (FEA) are validated by the proposed motor to show the accuracy of the designed strategy. Full article

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24 pages, 4208 KiB

Open AccessArticle

Designing a Sustainable University Recharge Area for Electric Vehicles: Technical and Economic Analysis

by Rosario Miceli and Fabio Viola^*

Dipartimento di Energia, Ingegneria dell’Informazione e Modelli Matematici, University of Palermo, 90133 Palermo, Italy

Energies 2017, 10(10), 1604; https://doi.org/10.3390/en10101604 - 13 Oct 2017

Cited by 47 | Viewed by 5819

Abstract

This article addresses the technical and economic challenges regarding the design of a “green” recharge area for electric vehicles at the University of Palermo in order to reduce costs and pollution connected to the charging process. Based on the behaviour of the student [...] Read more.

This article addresses the technical and economic challenges regarding the design of a “green” recharge area for electric vehicles at the University of Palermo in order to reduce costs and pollution connected to the charging process. Based on the behaviour of the student population, the electrical load is identified and two possible solutions are evaluated to manage the peak load: an orientation of the panels increasing the power at defined time and the use of a storage system. The main strength and weakness points of two systems are investigated by taking into account the Levelized Cost of Energy (LCOE), which reaches 75.3 €/MWh for the orientation of panel and 103 €/MWh for the storage system. Furthermore, the cost of the topologies of power plant and the cost of energy are discussed in depth. Full article

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

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19 pages, 3416 KiB

Open AccessArticle

Energy Efficiency and Scalability of Metallic Nanoparticle Production Using Arc/Spark Discharge

by Martin Slotte^1,2 and Ron Zevenhoven^1,*

¹ Thermal and Flow Engineering, Åbo Akademi University, 20500 Turku, Finland

² Paroc Group Oy, 21600 Parainen, Finland

Energies 2017, 10(10), 1605; https://doi.org/10.3390/en10101605 - 13 Oct 2017

Cited by 14 | Viewed by 3455

Abstract

The increased global demand for metallic nanoparticles for an ever growing number of applications has given rise to a need for larger scale and more efficient nanoparticle (NP) production processes. In this paper one such process is evaluated from the viewpoints of scalability [...] Read more.

The increased global demand for metallic nanoparticles for an ever growing number of applications has given rise to a need for larger scale and more efficient nanoparticle (NP) production processes. In this paper one such process is evaluated from the viewpoints of scalability and energy efficiency. Multiple setups of different scale of an arc/spark process were evaluated for energy efficiency and scalability using exergy analysis, heat loss evaluation and life cycle impact assessment, based on data collected from EU FP7 project partners. The energy efficiency of the process is quite low, with e.g., a specific electricity consumption (SEC) of producing ~80 nm copper NP of 180 kWh/kg while the thermodynamic minimum energy need is 0.03 kWh/kg. This is due to thermal energy use characteristics of the system. During scale-up of the process the SEC remained similar to that of smaller setups. Loss of NP mass in the tubing of larger setups gives a lower material yield. The variation in material yield has a significant impact on the life cycle impact for the produced NP in both the Human Health and Ecosystem Quality categories while the impact is smaller in the Global Warming and Resource Depletion categories. Full article

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20 pages, 4885 KiB

Open AccessArticle

Crosstalk Study of Simultaneous Wireless Power/Information Transmission Based on an LCC Compensation Network

by Li Ji^1,2, Lifang Wang^2,3,*, Chenglin Liao^2,3 and Shufan Li^1,2

¹ University of Chinese Academy of Sciences, Beijing 100190, China

² Key Laboratory of Power Electronics and Electric Drive, Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing 100190, China

³ Beijing Co-Innovation Center for Electric Vehicles, Beijing 100081, China

Energies 2017, 10(10), 1606; https://doi.org/10.3390/en10101606 - 13 Oct 2017

Cited by 5 | Viewed by 4075

Abstract

The effective simultaneous wireless transmission of power and information (SWTPI) is an issue of great interest. To reduce the crosstalk between power and information channels while increasing the transmission air gap and power level, we introduce an inductor–capacitor–capacitor (LCC) compensation network for an [...] Read more.

The effective simultaneous wireless transmission of power and information (SWTPI) is an issue of great interest. To reduce the crosstalk between power and information channels while increasing the transmission air gap and power level, we introduce an inductor–capacitor–capacitor (LCC) compensation network for an SWTPI system. First, the crosstalk between the power and information channels is analyzed. An effective parametric design method is then proposed for the LCC compensation network, which is analyzed theoretically to minimize the crosstalk. Finally, experiments are conducted at 1000 W and 115.2 kbps with an air gap of 100 cm to verify whether the proposed structure and design method of the LCC compensation network are suitable for the SWTPI. Full article

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

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13 pages, 3952 KiB

Open AccessArticle

Power Controllable LED System with Increased Energy Efficiency Using Multi-Sensors for Plant Cultivation

by Yong Deok Ahn¹, Sungwoo Bae²

and Suk-Ju Kang^1,*

¹ Department of Electronic Engineering, Sogang University, Seoul 04107, Korea

² Department of Electrical Engineering, Hanyang University, Seoul 04763, Korea

Energies 2017, 10(10), 1607; https://doi.org/10.3390/en10101607 - 14 Oct 2017

Cited by 12 | Viewed by 4673

Abstract

In this paper, a power-controllable light emitting diode (LED) control system is proposed for plant cultivation. The proposed LED system measures environmental data, such as the distance between the plant and LED system using an infrared sensor and the ambient illuminance based on [...] Read more.

In this paper, a power-controllable light emitting diode (LED) control system is proposed for plant cultivation. The proposed LED system measures environmental data, such as the distance between the plant and LED system using an infrared sensor and the ambient illuminance based on an illuminance sensor. Then, it converts the illuminance to the photosynthetic photon flux density (PPFD) for plant cultivation. It analyzes the relationship between the data and LED PPFD, and generates an optimal pulse width modulation (PWM) signal. Therefore, it controls the LED PPFD dynamically. The proposed LED system is also implemented in hardware, which consists of red and blue LED arrays with suitable wavelengths and a micro-controller. In the experimental results, the proposed LED system preserved the target PPFD regardless of the change of the distance and ambient PPFD. Additionally, the proposed LED system maximally reduced the power consumption of a conventional system by up to 68%. Full article

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13 pages, 4711 KiB

Open AccessArticle

Thrust Force Ripple Reduction of Two C-Core Linear Flux-Switching Permanent Magnet Machines of High Thrust Force Capability

by Wenjuan Hao^1,2,* and Yu Wang²

¹ College of Jincheng, Nanjing University of Aeronautics and Astronautics, Nanjing 211156, China

² Department of Electrical Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 211106, China

Energies 2017, 10(10), 1608; https://doi.org/10.3390/en10101608 - 14 Oct 2017

Cited by 12 | Viewed by 5217

Abstract

Linear flux-switching permanent magnetic (LFSPM) machines are good choices for long stroke applications. These machines deliver high thrust force density in addition to the machine structure where permanent magnetics (PMs) and windings are all on the short mover. For LFSPM machines, their performance [...] Read more.

Linear flux-switching permanent magnetic (LFSPM) machines are good choices for long stroke applications. These machines deliver high thrust force density in addition to the machine structure where permanent magnetics (PMs) and windings are all on the short mover. For LFSPM machines, their performance is always affected by big thrust force ripple. In this paper, for two C-core LFSPM machines of high thrust force capability, including a 6/13 C-core LFSPM (6/13LFSPM-C) machine and a sandwiched C-core LFSPM (SLFSPM-C) machine, and a thrust force ripple reduction method is proposed. The proposed method is developed by reducing the slot effect component of the cogging force based on staggered stator tooth, and suppressing the thrust force ripple caused by unbalanced three phase back-electromagnetic forces (EMFs) based on two end PMs. Based on finite element analysis (FEA) results, both C-core LFSPM machines can achieve small thrust force ripples as well as high sinusoidal back-EMFs, and at the same time, maintain high thrust force capability with the proposed method. It was also found that, the improved SLFSPM-C machine exhibited the same thrust force capability as the improved 6/13LFSPM-C machine, but with a much smaller thrust force ripple. Full article

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

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17 pages, 10963 KiB

Open AccessArticle

Research on Control Strategy of Free-Piston Stirling Power Generating System

by Jigui Zheng^1,2,*, Jing Chen², Ping Zheng¹, Hongxing Wu¹ and Chengde Tong¹

¹ School of Electrical Engineering and Automation, Harbin Institute of Technology, Harbin 150080, China

² Beijing Research Institute of Precise Mechatronics and Controls, Beijing 100076, China

Energies 2017, 10(10), 1609; https://doi.org/10.3390/en10101609 - 16 Oct 2017

Cited by 9 | Viewed by 7556

Abstract

As a clean and fuel adaptive alternative power plant, the Stirling power generating system has drawn attention of experts and scholars in the energy field. In practical application, the instability of free-piston Stirling power generating system caused by abrupt load change is an [...] Read more.

As a clean and fuel adaptive alternative power plant, the Stirling power generating system has drawn attention of experts and scholars in the energy field. In practical application, the instability of free-piston Stirling power generating system caused by abrupt load change is an inevitable problem. Thus, methods to improve the output frequency response and stability of the free-piston Stirling power generating system are necessary. The model of free-piston Stirling power generating system is built by isothermal analysis firstly, and the initial control strategy based on given voltage system is put forward. To further improve the performance of power system, a current feedback decoupling control strategy is proposed, and the mathematical model is established. The influence of full decoupled quadrature-direct (d-q) axis currents is analyzed with respect to the output voltage adjusting time and fluctuation amplitude under the variations of piston displacement and output load. The simulation results show that the system performance is significantly improved, but the dynamic regulation lags caused by the decoupled current control still exist. To solve this problem and improve the performance of decoupled-state feedback current control that relies on parameter accuracy, internal model control based on sliding mode (IMC-SM) current decoupling control strategy is proposed, the system model is established, and then the performance of voltage ripple in generating mode is improved. Finally, the test bench is built, and the steady state and transient voltage control performances are tested. The feasibility and priority of the control strategy is verified by experiment and simulation results. Full article

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13 pages, 4340 KiB

Open AccessArticle

A Digital Hysteresis Current Control for Half-Bridge Inverters with Constrained Switching Frequency

by Triet Nguyen-Van^*, Rikiya Abe and Kenji Tanaka

Internet of Energy Laboratory, Department of Technology Management for Innovation, The University of Tokyo, Tokyo 113-8656, Japan

Energies 2017, 10(10), 1610; https://doi.org/10.3390/en10101610 - 14 Oct 2017

Cited by 32 | Viewed by 8497

Abstract

This paper proposes a new robustly adaptive hysteresis current digital control algorithm for half-bridge inverters, which plays an important role in electric power, and in various applications in electronic systems. The proposed control algorithm is assumed to be implemented on a high-speed Field [...] Read more.

This paper proposes a new robustly adaptive hysteresis current digital control algorithm for half-bridge inverters, which plays an important role in electric power, and in various applications in electronic systems. The proposed control algorithm is assumed to be implemented on a high-speed Field Programmable Gate Array (FPGA) circuit, using measured data with high sampling frequency. The hysteresis current band is computed in each switching modulation period based on both the current error and the negative half switching period during the previous modulation period, in addition to the conventionally used voltages measured at computation instants. The proposed control algorithm is derived by solving the optimization problem—where the switching frequency is always constrained at below the desired constant frequency—which is not guaranteed by the conventional method. The optimization problem also keeps the output current stable around the reference, and minimizes power loss. Simulation results show good performances of the proposed algorithm compared with the conventional one. Full article

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

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21 pages, 3353 KiB

Open AccessArticle

Short-Circuit Fault Tolerant Control of a Wind Turbine Driven Induction Generator Based on Sliding Mode Observers

by Takwa Sellami^1,2,*

, Hanen Berriri¹, Sana Jelassi², A Moumen Darcherif² and M Faouzi Mimouni¹

¹ Electrical Department, National Engineering School of Monastir, Monastir 5000, Tunisia

² ECAM-EPMI, Graduate School of Engineering, 95000 Cergy, France

Energies 2017, 10(10), 1611; https://doi.org/10.3390/en10101611 - 14 Oct 2017

Cited by 19 | Viewed by 6590

Abstract

The installed energy production capacity of wind turbines is growing intensely on a global scale, making the reliability of wind turbine subsystems of greater significance. However, many faults like Inter-Turn Short-Circuit (ITSC) may affect the turbine generator and quickly lead to a decline [...] Read more.

The installed energy production capacity of wind turbines is growing intensely on a global scale, making the reliability of wind turbine subsystems of greater significance. However, many faults like Inter-Turn Short-Circuit (ITSC) may affect the turbine generator and quickly lead to a decline in supplied power quality. In this framework, this paper proposes a Sliding Mode Observer (SMO)-based Fault Tolerant Control (FTC) scheme for Induction Generator (IG)-based variable-speed grid-connected wind turbines. First, the dynamic models of the wind turbine subsystems were developed. The control schemes were elaborated based on the Maximum Power Point Tracking (MPPT) method and Indirect Rotor Flux Oriented Control (IRFOC) method. The grid control was also established by regulating the active and reactive powers. The performance of the wind turbine system and the stability of injected power to the grid were hence analyzed under both healthy and faulty conditions. The robust developed SMO-based Fault Detection and Isolation (FDI) scheme was proved to be fast and efficient for ITSC detection and localization.Afterwards, SMO were involved in scheming the FTC technique. Accordingly, simulation results assert the efficacy of the proposed ITSC FTC method for variable-speed wind turbines with faulty IG in protecting the subsystems from damage and ensuring continuous connection of the wind turbine to the grid during ITSC faults, hence maintaining power quality. Full article

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

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15 pages, 3712 KiB

Open AccessArticle

Extended Gersgorin Theorem-Based Parameter Feasible Domain to Prevent Harmonic Resonance in Power Grid

by Tao Lin^1,*, Rusi Chen¹, Guangzheng Yu^1,2, Ruyu Bi¹ and Xialing Xu³

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

² College of Electrical Engineering, Shanghai University of Electric Power, Shanghai 200090, China

³ Central China Branch of State Grid Corporation of China, Wuhan 430063, China

Energies 2017, 10(10), 1612; https://doi.org/10.3390/en10101612 - 15 Oct 2017

Cited by 7 | Viewed by 2947

Abstract

Harmonic resonance may cause abnormal operation and even damage of power facilities, further threatening normal and safe operation of power systems. For renewable energy generations, controlled loads and parallel reactive power compensating equipment, their operating statuses can vary frequently. Therefore, the parameters of [...] Read more.

Harmonic resonance may cause abnormal operation and even damage of power facilities, further threatening normal and safe operation of power systems. For renewable energy generations, controlled loads and parallel reactive power compensating equipment, their operating statuses can vary frequently. Therefore, the parameters of equivalent fundamental and harmonic admittance/impedance of these components exist in uncertainty, which will change the elements and eigenvalues of harmonic network admittance matrix. Consequently, harmonic resonance in power grid is becoming increasingly more complex. Hence, intense research about prevention and suppression of harmonic resonance, particularly the parameter feasible domain (PFD) which can keep away from harmonic resonance, are needed. For rapid online evaluation of PFD, a novel method without time-consuming pointwise precise eigenvalue computations is proposed. By analyzing the singularity of harmonic network admittance matrix, the explicit sufficient condition that the matrix elements should meet to prevent harmonic resonance is derived by the extended Gersgorin theorem. Further, via the non-uniqueness of similar transformation matrix (STM), a strategy to determine the appropriate STM is proposed to minimize the conservation of the obtained PFD. Eventually, the availability and advantages in computation efficiency and conservation of the method, are demonstrated through four different scale benchmarks. Full article

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

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18 pages, 4623 KiB

Open AccessArticle

Short-Term Electricity-Load Forecasting Using a TSK-Based Extreme Learning Machine with Knowledge Representation

by Chan-Uk Yeom and Keun-Chang Kwak^*

Department of Control and Instrumentation Engineering, Chosun University, Gwangju 61452, Korea

Energies 2017, 10(10), 1613; https://doi.org/10.3390/en10101613 - 16 Oct 2017

Cited by 38 | Viewed by 4120

Abstract

This paper discusses short-term electricity-load forecasting using an extreme learning machine (ELM) with automatic knowledge representation from a given input-output data set. For this purpose, we use a Takagi-Sugeno-Kang (TSK)-based ELM to develop a systematic approach to generating if-then rules, while the conventional [...] Read more.

This paper discusses short-term electricity-load forecasting using an extreme learning machine (ELM) with automatic knowledge representation from a given input-output data set. For this purpose, we use a Takagi-Sugeno-Kang (TSK)-based ELM to develop a systematic approach to generating if-then rules, while the conventional ELM operates without knowledge information. The TSK-ELM design includes a two-phase development. First, we generate an initial random-partition matrix and estimate cluster centers for random clustering. The obtained cluster centers are used to determine the premise parameters of fuzzy if-then rules. Next, the linear weights of the TSK fuzzy type are estimated using the least squares estimate (LSE) method. These linear weights are used as the consequent parameters in the TSK-ELM design. The experiments were performed on short-term electricity-load data for forecasting. The electricity-load data were used to forecast hourly day-ahead loads given temperature forecasts; holiday information; and historical loads from the New England ISO. In order to quantify the performance of the forecaster, we use metrics and statistical characteristics such as root mean squared error (RMSE) as well as mean absolute error (MAE), mean absolute percent error (MAPE), and R-squared, respectively. The experimental results revealed that the proposed method showed good performance when compared with a conventional ELM with four activation functions such sigmoid, sine, radial basis function, and rectified linear unit (ReLU). It possessed superior prediction performance and knowledge information and a small number of rules. Full article

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

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18 pages, 1449 KiB

Open AccessArticle

A New Technique for Reducing Size of a WPT System Using Two-Loop Strongly-Resonant Inductors

by Matjaz Rozman

, Michael Fernando, Bamidele Adebisi^*

, Khaled M. Rabie, Tim Collins

, Rupak Kharel

and Augustine Ikpehai

School of Engineering, Manchester Metropolitan University, Manchester M1 5GD, UK

Energies 2017, 10(10), 1614; https://doi.org/10.3390/en10101614 - 16 Oct 2017

Cited by 13 | Viewed by 5556

Abstract

Mid-range resonant coupling-based high efficient wireless power transfer (WPT) techniques have gained substantial research interest due to the number of potential applications in many industries. This paper presents a novel design of a resonant two-loop WPT technique including the design, fabrication and preliminary [...] Read more.

Mid-range resonant coupling-based high efficient wireless power transfer (WPT) techniques have gained substantial research interest due to the number of potential applications in many industries. This paper presents a novel design of a resonant two-loop WPT technique including the design, fabrication and preliminary results of this proposal. This new design employs a compensation inductor which is combined with the transmitter and receiver loops in order to significantly scale down the size of the transmitter and receiver coils. This can improve the portability of the WPT transmitters in practical systems. Moreover, the benefits of the system enhancement are not only limited to the lessened magnitude of the

T_{X}

&

R_{X}

, simultaneously both the weight and the bill of materials are also minimised. The proposed system also demonstrates compatibility with the conventional electronic components such as capacitors hence the development of the

T_{X}

&

R_{X}

is simplified. The proposed system performance has been validated using the similarities between the experimental and simulation results. The power efficiency of the prototype circuit is found to be 93%, which is close to the efficiency reached by the conventional design. However, the weight of the transmitter and receiver inductors is now reduced by 78%, while the length of these inductors is reduced by 80%. Full article

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12 pages, 1677 KiB

Open AccessArticle

Social Impacts of Solar Home Systems in Rural Areas: A Case Study in Bangladesh

by Ehsanul Kabir¹, Ki-Hyun Kim^2,*

and Jan E. Szulejko²

¹ Department of Farm Power and Machinery, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh

² Department of Civil and Environmental Engineering, Hanyang University, 222 Wangsimni-Ro, Seoul 04763, Korea

Energies 2017, 10(10), 1615; https://doi.org/10.3390/en10101615 - 16 Oct 2017

Cited by 59 | Viewed by 16823

Abstract

As an alternative source of off-grid electric power, solar home systems (SHS) stand out above all other options (e.g., wind, hydro, geo-thermal, tidal systems) because of their wide-scale potential at latitudes less than 45° north or south of the Equator where daily solar [...] Read more.

As an alternative source of off-grid electric power, solar home systems (SHS) stand out above all other options (e.g., wind, hydro, geo-thermal, tidal systems) because of their wide-scale potential at latitudes less than 45° north or south of the Equator where daily solar irradiance is more constant throughout the year and where the bulk of the Third World’s population live. A questionnaire-based survey study was carried out in a rural area of Bangladesh to ascertain the impacts of SHSs on the lives of the rural population. The installation of an SHS was found to improve the comfort and living standard of rural dwellers. Easier access to TV, radio, cellphone, and the Internet helped the rural population become part of a more global culture. More attractive down-payment and installment package options will allow poor target groups to adopt this system. The standard of SHS components and after-sales service should be improved to ensure sustainably and popularity among the mass population for at least 10 years at minimal cost to the consumer. Our findings can also help policymakers adopt more SHS-friendly policies to further the interests of inhabitants of rural areas that are not connected to the grid. Full article

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

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15 pages, 2094 KiB

Open AccessArticle

Sensitivity Analysis of Time Length of Photovoltaic Output Power to Capacity Configuration of Energy Storage Systems

by Mingqi Wang^* and Xinqiao Zheng

School of Energy Power and Mechanical Engineering, North China Electric Power University, Baoding 071000, China

Energies 2017, 10(10), 1616; https://doi.org/10.3390/en10101616 - 16 Oct 2017

Cited by 1 | Viewed by 2997

Abstract

Time interval and time length are two important indexes when analyzing the active output data of photovoltaic (PV) power stations. When the time interval is constant, the length of time is too small, and the included information is less, resulting in a lack [...] Read more.

Time interval and time length are two important indexes when analyzing the active output data of photovoltaic (PV) power stations. When the time interval is constant, the length of time is too small, and the included information is less, resulting in a lack and distortion of information; it the length of time is too large, the included information is redundant and complicated, resulting in unnecessary increases of storage capacity and calculation. Therefore, it is important to determine the appropriate length of data for the analysis of PV output data. In this paper, firstly, the output data of a PV power station is analyzed statistically, and the preliminary conclusions for time length selection are obtained by autocorrelation analysis. Based on the weather characteristics, clustering analysis methods and statistical principles are used to analyze the data and optimal sample capacity estimation, respectively, for different types of photovoltaic output data and determine the required data time length at the time of analyzing the PV power plant output data, the relationship between energy storage capacity demand and data length is investigated, the rationality of the length of the selected time is verified. Meanwhile, the energy storage system capacity configuration based on the optimal data time length is given. The results show that the requirement of data volume of energy storage system capacity configuration can be met when the time length of the PV output data is 23 days. Full article

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

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14 pages, 1832 KiB

Open AccessArticle

New Hybrid Static VAR Compensator with Series Active Filter

by Ayumu Tokiwa¹, Hiroaki Yamada¹, Toshihiko Tanaka^1,*, Makoto Watanabe², Masanao Shirai² and Yuji Teranishi²

¹ Department of Electrical and Electronic Engineering, Yamaguchi University, 2-16-1 Tokiwadai, Ube, Yamaguchi 755-8611, Japan

² The Chugoku Electric Manufacturing Company, Incorporated, 4-4-32 Minamiku Osu, Hiroshima 732-8564, Japan

Energies 2017, 10(10), 1617; https://doi.org/10.3390/en10101617 - 16 Oct 2017

Cited by 20 | Viewed by 7325

Abstract

This paper proposes a new hybrid static VAR compensator (SVC) with a series active filter (AF). The proposed hybrid SVC consists of a series AF and SVC. The series AF, which is connected in series to phase-leading capacitors in the SVC, performs for [...] Read more.

This paper proposes a new hybrid static VAR compensator (SVC) with a series active filter (AF). The proposed hybrid SVC consists of a series AF and SVC. The series AF, which is connected in series to phase-leading capacitors in the SVC, performs for a resistor for source-side harmonic currents. A sinusoidal source current with a unity power factor is obtained with the series AF, although the thyristor-controlled reactor generates harmonic currents. A digital computer simulation was implemented to confirm the validity and high practicability of the proposed hybrid SVC using PSIM software. The simulation results demonstrate that sinusoidal source currents with a unity power factor are achieved with the proposed hybrid SVC. Full article

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

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29 pages, 1482 KiB

Open AccessReview

Supply Chain Management for Improved Energy Efficiency: Review and Opportunities

by Beatrice Marchi

and Simone Zanoni^*

Department of Mechanical and Industrial Engineering, Università degli Studi di Brescia, Via Branze, 38, I-25123 Brescia, Italy

Energies 2017, 10(10), 1618; https://doi.org/10.3390/en10101618 - 16 Oct 2017

Cited by 135 | Viewed by 18173

Abstract

Energy efficiency represents a key resource for economic and social development, providing substantial benefits to different stakeholders, ranging from the entities which develop energy efficient measures to everyone in society. In addition to cost savings, multiple benefits can be achieved by supporting a [...] Read more.

Energy efficiency represents a key resource for economic and social development, providing substantial benefits to different stakeholders, ranging from the entities which develop energy efficient measures to everyone in society. In addition to cost savings, multiple benefits can be achieved by supporting a better alignment between energy issues and strategic business priorities: e.g., improved competitiveness, profitability, quality, etc. Thus, energy efficiency can be a strategic advantage, not just a marginal issue, for companies. However, most firms, especially small and medium enterprises (SMEs), face many problems and, in some cases, hostility when trying to effectively implement energy efficiency actions. The most dominant barriers are the access to capital and the lack of awareness (especially in terms of life cycle cost effects). The supply chain viewpoint represents one of the main opportunities for overcoming those barriers and improving energy performance even for weaker companies. Since the current literature on energy efficiency and practical approaches to ensure energy efficiency mainly focus on energy performance on a single-firm basis, this paper aims to provide a systematic review of papers on the integration of energy efficiency in supply chain design and management published in academic journal, thereby defining potential research streams to close the gaps in the literature. A number of literature reviews have been published focusing on specific aspects of sustainable or on green supply chain management; however, to the best of our knowledge, no review has focused on the energy efficiency issue. Firstly, the present paper shows how considering energy consumption in supply chain management can contribute to more energy-efficient processes from a systemic point of view. Then, the review methodology used is defined and the sampled papers are analyzed and categorized based on the different approaches they propose. From these analyses, potential future research streams are outlined. Full article

(This article belongs to the Special Issue Energy Efficiency in the Supply Chains and Logistics)

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26 pages, 27792 KiB

Open AccessArticle

Effect of Injection Site on Fault Activation and Seismicity during Hydraulic Fracturing

by Zhaohui Chong^1,2, Xuehua Li^1,* and Xiangyu Chen¹

¹ Key Laboratory of Deep Coal Resource, Ministry of Education of China, School of Mines, China University of Mining and Technology, Xuzhou 221116, China

² Faculty of Engineering and Information Sciences, University of Wollongong, Wollongong 2522, Australia

Energies 2017, 10(10), 1619; https://doi.org/10.3390/en10101619 - 16 Oct 2017

Cited by 8 | Viewed by 4334

Abstract

Hydraulic fracturing is a key technology to stimulate oil and gas wells to increase production in shale reservoirs with low permeability. Generally, the stimulated reservoir volume is performed based on pre-existing natural fractures (NF). Hydraulic fracturing in shale reservoirs with large natural fractures [...] Read more.

Hydraulic fracturing is a key technology to stimulate oil and gas wells to increase production in shale reservoirs with low permeability. Generally, the stimulated reservoir volume is performed based on pre-existing natural fractures (NF). Hydraulic fracturing in shale reservoirs with large natural fractures (i.e., faults) often results in fault activation and seismicity. In this paper, a coupled hydro-mechanical model was employed to investigate the effects of injection site on fault activation and seismicity. A moment tensor method was used to evaluate the magnitude and affected areas of seismic events. The micro-parameters of the proposed model were calibrated through analytical solutions of the interaction between hydraulic fractures (HF) and the fault. The results indicated that the slip displacement and activation range of the fault first decreased, then remained stable with the increase in the distance between the injection hole and the fault (L_if). In the scenario of the shortest L_if (L_if = 10 m), the b-value—which represents the proportion of frequency of small events in comparison with large events—reached its maximum value, and the magnitude of concentrated seismic events were in the range of −3.5 to −1.5. The frequency of seismic events containing only one crack was the lowest, and that of seismic events containing more than ten cracks was the highest. The interaction between the injection-induced stress disturbance and fault slip was gentle when L_if was longer than the critical distance (L_if = 40–50 m). The results may help optimize the fracturing treatment designs during hydraulic fracturing. Full article

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12 pages, 2942 KiB

Open AccessArticle

Development of a Numerical Approach to Simulate Compressed Air Energy Storage Subjected to Cyclic Internal Pressure

by Song-Hun Chong

High Speed Railroad Systems Research Center, Korea Railroad Research Institute, 176, Cheoldo bangmulgwan-ro, Uiwang-si, Gyeonggi-do 437-757, Korea

Energies 2017, 10(10), 1620; https://doi.org/10.3390/en10101620 - 16 Oct 2017

Cited by 2 | Viewed by 3424

Abstract

This paper analyzes the long-term response of unlined energy storage located at shallow depth to improve the distance between a wind farm and storage. The numerical approach follows the hybrid scheme that combined a mechanical constitutive model to extract stress and strains at [...] Read more.

This paper analyzes the long-term response of unlined energy storage located at shallow depth to improve the distance between a wind farm and storage. The numerical approach follows the hybrid scheme that combined a mechanical constitutive model to extract stress and strains at the first cycle and polynomial-type strain accumulation functions to track the progressive plastic deformation. In particular, the strain function includes the fundamental features that requires simulating the long-term response of geomaterials: volumetric strain (terminal void ratio) and shear strain (shakedown and ratcheting), the strain accumulation rate, and stress obliquity. The model is tested with a triaxial strain boundary condition under different stress obliquities. The unlined storage subjected to cyclic internal stress is simulated with different storage geometries and stress amplitudes that play a crucial role in estimating the long-term mechanical stability of underground storage. The simulations present the evolution of ground surface, yet their incremental rate approaches towards a terminal void ratio. With regular and smooth displacement fields for the large number of cycles, the inflection point is estimated with the previous surface settlement model. Full article

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14 pages, 3920 KiB

Open AccessArticle

Energy and Microclimate Simulation in a Heritage Building: Further Studies on the Malatestiana Library

by Lamberto Tronchin^1,*,†

and Kristian Fabbri^2,†

¹ Department of Industrial Engineering, University of Bologna, Viale del Risorgimento 2, 40129 Bologna, Italy

² Department of Architecture, University of Bologna, Viale Europa 596, 47521 Cesena, Italy

^† These authors contributed equally to this work.

Energies 2017, 10(10), 1621; https://doi.org/10.3390/en10101621 - 16 Oct 2017

Cited by 46 | Viewed by 5089

Abstract

Historical and heritage (especially UNESCO) buildings need a specific, peculiar approach regarding energy performance, energy behavior, and indoor microclimate. Comparing a new building with a historical (UNESCO) building, it is evident that the degrees of freedom for implementing energy efficiency in historical buildings [...] Read more.

Historical and heritage (especially UNESCO) buildings need a specific, peculiar approach regarding energy performance, energy behavior, and indoor microclimate. Comparing a new building with a historical (UNESCO) building, it is evident that the degrees of freedom for implementing energy efficiency in historical buildings are strongly limited. Several constraints about the materials, the geometry, and the structures do not allow a comprehensive enhancement of energy performance or microclimate parameters. In this paper, we describe an energy building performance criterion adopted in order to find out the energy behavior in the Malatestiana Library. The challenge consists of optimizing energy efficiency and microclimate as well as a full preservation of ancient manuscripts. The study adopts Google Sketchup software to model three-dimensional (3D) buildings, and IESVE software to simulate an indoor microclimate. Software building models allow for the evaluation of different types of natural ventilation and section forms, e.g., original, without attic, and without ground floor. The results of the software modeling allow for a comparison of several building use modality effects and the effect of the presence of an attic and ground floor on indoor microclimate parameters in order to conserve and preserve ancient manuscripts. Full article

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17 pages, 2847 KiB

Open AccessArticle

Using Modularity to Reduce Complexity of Industrialized Building Systems for Mass Customization

by Daniela D. Viana^1,*, Iris D. Tommelein² and Carlos T. Formoso³

¹ Interdisciplinary Department, Campus Litoral Norte, Universidade Federal do Rio Grande do Sul, Tramandai 95590-000, Brazil

² Project Production Systems Laboratory, Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720-1712, USA

³ Building Innovation Research Unit (NORIE), School of Engineering, Universidade Federal do Rio Grande do Sul, Porto Alegre 90035-190, Brazil

Energies 2017, 10(10), 1622; https://doi.org/10.3390/en10101622 - 17 Oct 2017

Cited by 44 | Viewed by 9664

Abstract

It is widely known that industrialized building systems can positively impact construction projects in terms of efficiency, duration, safety, and quality. Although the use of industrialized building systems can potentially simplify the production process on-site, the complexity of the overall delivery system tends [...] Read more.

It is widely known that industrialized building systems can positively impact construction projects in terms of efficiency, duration, safety, and quality. Although the use of industrialized building systems can potentially simplify the production process on-site, the complexity of the overall delivery system tends to be high, especially in engineered-to-order (ETO) environments, due to factors such as uncertainty related to goals and methods, conflicts between different trades on-site, and interdependence between supply chain members. This paper explores the concept of modularity, which has proven to be useful in different industries as a way of dealing with complex systems. The aim of this paper is to illustrate how modularity can reduce the complexity of ETO industrialized building systems, in companies that adopt a mass customization strategy. This investigation is based on two descriptive case studies on the development of modular structural steel systems for buildings that have adopted innovative beam-to-column connections. The main contribution of this research is demonstrating the need to adopt an integrated product and process-oriented conceptualization of modularity in industrialized building systems. Moreover, the comparison between the two case studies pointed out that the management of tolerances plays a key role in achieving high productivity and short lead times in structural steel building systems. This investigation also illustrates how the adoption of a limited set of modular components can be used to decouple design decisions, and standardize different types of processes. Full article

(This article belongs to the Special Issue Selected Papers from ZEMCH 2016: Building Energy Performance Evaluation/Simulation)

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21 pages, 2809 KiB

Open AccessArticle

A Novel Probabilistic Optimal Power Flow Method to Handle Large Fluctuations of Stochastic Variables

by Xiaoyang Deng, Jinghan He and Pei Zhang^*

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

Energies 2017, 10(10), 1623; https://doi.org/10.3390/en10101623 - 17 Oct 2017

Cited by 22 | Viewed by 4412

Abstract

The traditional cumulant method (CM) for probabilistic optimal power flow (P-OPF) needs to perform linearization on the Karush–Kuhn–Tucker (KKT) first-order conditions, therefore requiring input variables (wind power or loads) varying within small ranges. To handle large fluctuations resulting from large-scale wind power and [...] Read more.

The traditional cumulant method (CM) for probabilistic optimal power flow (P-OPF) needs to perform linearization on the Karush–Kuhn–Tucker (KKT) first-order conditions, therefore requiring input variables (wind power or loads) varying within small ranges. To handle large fluctuations resulting from large-scale wind power and loads, a novel P-OPF method is proposed, where the correlations among input variables are also taken into account. Firstly, the inverse Nataf transformation and Cholesky decomposition are used to obtain samples of wind speeds and loads with a given correlation matrix. Then, the K-means algorithm is introduced to group the samples of wind power outputs and loads into a number of clusters, so that in each cluster samples of stochastic variables have small variances. In each cluster, the CM for P-OPF is conducted to obtain the cumulants of system variables. According to these cumulants, the moments of system variables corresponding to each cluster are computed. The moments of system variables for the total samples are obtained by combining the moments for all grouped clusters through the total probability formula. Then, the moments for the total samples are used to calculate the corresponding cumulants. Finally, Cornish–Fisher expansion is introduced to obtain the probability density functions (PDFs) of system variables. IEEE 9-bus and 118-bus test systems are modified to examine the proposed method. Study results show that the proposed method can produce more accurate results than traditional CM for P-OPF and is more efficient than Monte Carlo simulation (MCS). Full article

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

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21 pages, 2059 KiB

Open AccessReview

Hydrogen Generation through Solar Photocatalytic Processes: A Review of the Configuration and the Properties of Effective Metal-Based Semiconductor Nanomaterials

by Laura Clarizia¹, Danilo Russo^1,*, Ilaria Di Somma², Roberto Andreozzi¹ and Raffaele Marotta^1,*

¹ Dipartimento di Ingegneria Chimica, dei Materiali e della Produzione Industriale (DICMAPI), ScuolaPolitecnica e delle Scienze di Base, Università di Napoli Federico II, p.le Tecchio, 80, 80125 Napoli, Italy

² Istituto Ricerche sulla Combustione, Centro Nazionale delle Ricerche (IRC-CNR), p.le Tecchio, 80, 80125 Napoli, Italy

Energies 2017, 10(10), 1624; https://doi.org/10.3390/en10101624 - 17 Oct 2017

Cited by 73 | Viewed by 7491

Abstract

Photocatalytic water splitting and organic reforming based on nano-sized composites are gaining increasing interest due to the possibility of generating hydrogen by employing solar energy with low environmental impact. Although great efforts in developing materials ensuring high specific photoactivity have been recently recorded [...] Read more.

Photocatalytic water splitting and organic reforming based on nano-sized composites are gaining increasing interest due to the possibility of generating hydrogen by employing solar energy with low environmental impact. Although great efforts in developing materials ensuring high specific photoactivity have been recently recorded in the literature survey, the solar-to-hydrogen energy conversion efficiencies are currently still far from meeting the minimum requirements for real solar applications. This review aims at reporting the most significant results recently collected in the field of hydrogen generation through photocatalytic water splitting and organic reforming, with specific focus on metal-based semiconductor nanomaterials (e.g., metal oxides, metal (oxy)nitrides and metal (oxy)sulfides) used as photocatalysts under UVA or visible light irradiation. Recent developments for improving the photoefficiency for hydrogen generation of most used metal-based composites are pointed out. The main synthesis and operating variables affecting photocatalytic water splitting and organic reforming over metal-based nanocomposites are critically evaluated. Full article

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22 pages, 11414 KiB

Open AccessArticle

Multi-Objective Analysis of a CHP Plant Integrated Microgrid in Pakistan

by Asad Waqar^*

, Muhammad Shahbaz Tanveer, Jehanzeb Ahmad, Muhammad Aamir, Muneeb Yaqoob and Fareeha Anwar

Department of Electrical Engineering, Bahria University, 44000 Islamabad, Pakistan

Energies 2017, 10(10), 1625; https://doi.org/10.3390/en10101625 - 17 Oct 2017

Cited by 32 | Viewed by 6199

Abstract

In developing countries like Pakistan, the capacity shortage (CS) of electricity is a critical problem. The frequent natural gas (NG) outages compel consumers to use electricity to fulfill the thermal loads, which ends up as an increase in electrical load. In this scenario, [...] Read more.

In developing countries like Pakistan, the capacity shortage (CS) of electricity is a critical problem. The frequent natural gas (NG) outages compel consumers to use electricity to fulfill the thermal loads, which ends up as an increase in electrical load. In this scenario, the authors have proposed the concept of a combined heat & power (CHP) plant to be a better option for supplying both electrical and thermal loads simultaneously. A CHP plant-based microgrid comprising a PV array, diesel generators and batteries (operating in grid-connected as well as islanded modes) has been simulated using the HOMER Pro software. Different configurations of distributed generators (DGs) with/without batteries have been evaluated considering multiple objectives. The multiple objectives include the minimization of the total net present cost (TNPC), cost of generated energy (COE) and the annual greenhouse gas (GHG) emissions, as well as the maximization of annual waste heat recovery (WHR) of thermal units and annual grid sales (GS). These objectives are subject to the constraints of power balance, battery operation within state of charge (SOC) limits, generator operation within capacity limits and zero capacity shortage. The simulations have been performed on six cities including Islamabad, Lahore, Karachi, Peshawar, Quetta and Gilgit. The simulation results have been analyzed to find the most optimal city for the CHP plant integrated microgrid. Full article

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

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21 pages, 3045 KiB

Open AccessArticle

Variable Speed Control of Wind Turbines Based on the Quasi-Continuous High-Order Sliding Mode Method

by Yanwei Jing¹, Hexu Sun¹, Lei Zhang¹ and Tieling Zhang^2,*

¹ School of Control Science and Engineering, Hebei University of Technology, Hongqiao District, Tianjin 300131, China

² School of Mechanical, Materials, Mechatronic and Biomedical Engineering, University of Wollongong, Wollongong, NSW 2522, Australia

Energies 2017, 10(10), 1626; https://doi.org/10.3390/en10101626 - 17 Oct 2017

Cited by 15 | Viewed by 4457

Abstract

The characteristics of wind turbine systems such as nonlinearity, uncertainty and strong coupling, as well as external interference, present great challenges in wind turbine controller design. In this paper, a quasi-continuous high-order sliding mode method is used to design controllers due to its [...] Read more.

The characteristics of wind turbine systems such as nonlinearity, uncertainty and strong coupling, as well as external interference, present great challenges in wind turbine controller design. In this paper, a quasi-continuous high-order sliding mode method is used to design controllers due to its strong robustness to external disturbances, unmodeled dynamics and parameter uncertainties. It can also effectively suppress the chattering toward which the traditional sliding mode control method is ineffective. In this study, the strategy of designing speed controllers based on the quasi-continuous high order sliding mode method is proposed to ensure the wind turbine works well in different wind modes. First, the plant model of the variable speed control system is built as a linearized model; and then a second order speed controller is designed for the model and its stability is proved. Finally, the designed controller is applied to wind turbine pitch control. Based on the simulation results from a simulation of 1200 s which contains almost all wind speed modes, it is shown that the pitch angle can be rapidly adjusted according to wind speed change by the designed controller. Hence, the output power is maintained at the rated value corresponding to the wind speed. In addition, the robustness of the system is verified. Meanwhile, the chattering is found to be effectively suppressed. Full article

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25 pages, 6983 KiB

Open AccessArticle

Experimental Study of a Centralized Control Strategy of a DC Microgrid Working in Grid Connected Mode

by Robert Salas-Puente^*

, Silvia Marzal, Raúl González-Medina

, Emilio Figueres and Gabriel Garcera

Grupo de Sistemas Electrónicos Industriales del Departamento de Ingeniería Electrónica, Universitat Politècnica de València, Camino de Vera s/n, 46022 Valencia, Spain

Energies 2017, 10(10), 1627; https://doi.org/10.3390/en10101627 - 17 Oct 2017

Cited by 19 | Viewed by 5833

Abstract

The results concerning the integration of a set of power management strategies and serial communications for the efficient coordination of the power converters composing an experimental DC microgrid is presented. The DC microgrid operates in grid connected mode by means of an interlinking [...] Read more.

The results concerning the integration of a set of power management strategies and serial communications for the efficient coordination of the power converters composing an experimental DC microgrid is presented. The DC microgrid operates in grid connected mode by means of an interlinking converter. The overall control is carried out by means of a centralized microgrid controller implemented on a Texas Instruments TMS320F28335 DSP. The main objectives of the applied control strategies are to ensure the extract/inject power limits established by the grid operator as well as the renewable generation limits if it is required; to devise a realistic charging procedure of the energy storage batteries as a function of the microgrid status; to manage sudden changes of the available power from the photovoltaic energy sources, of the load power demand and of the power references established by the central controller; and to implement a load shedding functionality. The experimental results demonstrate that the proposed power management methodology allows the control of the power dispatch inside the DC microgrid properly. Full article

(This article belongs to the Special Issue Control and Communication in Distributed Generation Systems)

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14 pages, 2415 KiB

Open AccessArticle

Integrated BMS-MMC Balancing Technique Highlighted by a Novel Space-Vector Based Approach for BEVs Application

by Gianluca Brando¹, Adolfo Dannier¹

, Ivan Spina^1,*

and Pietro Tricoli²

¹ Department of Electrical Eng. and IT, DIETI, University of Naples, Federico II, 80138 Napoli NA, Italy

² Department of Electronic, Electrical and Systems Engineering, University of Birmingham, Birmingham B15 2TT, UK

Energies 2017, 10(10), 1628; https://doi.org/10.3390/en10101628 - 17 Oct 2017

Cited by 18 | Viewed by 3930

Abstract

This paper proposes a new mathematical model of modular multilevel converters for battery electric vehicles with space-vectors enabling a critical analysis of cell balancing for the battery management system. In particular, the requirements for power balancing and the actual number of degrees of [...] Read more.

This paper proposes a new mathematical model of modular multilevel converters for battery electric vehicles with space-vectors enabling a critical analysis of cell balancing for the battery management system. In particular, the requirements for power balancing and the actual number of degrees of freedom of the control are investigated. The paper shows that the traditional approach of cell balancing is a special case of the proposed control methodology. Numerical analyses with Matlab/Simulink™ highlight the reasons of the slow response of the standard balancing technique for specific operating conditions of the battery electric vehicle. The paper suggests potential improvements that could be introduced through the proposed generalised approach. Full article

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

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13 pages, 4121 KiB

Open AccessArticle

Numerical Study of the Gas-Liquid Two-Phase Flow in a Self-Designed Mixer for a Ga-R113 MHD System

by Peng Lu^1,*, Xingwen Zheng¹, Lulu Fang¹, Hulin Huang^2,*

, Shu Xu³

and Yezhen Yu⁴

¹ Jiangsu Province Key Laboratory of Aerospace Power System, Key Laboratory of Thermal Environment and Thermal Structure for Aero Engines of Ministry of Industry and Information Technology, College of Energy and Power Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

² College of Astronautics, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

³ Department of Chemical Engineering, Purdue University, West Lafayette, IN 47907, USA

⁴ School of Energy and Mechanical Engineering, Nanjing Normal University, Nanjing 210042, China

Energies 2017, 10(10), 1629; https://doi.org/10.3390/en10101629 - 17 Oct 2017

Cited by 9 | Viewed by 3722

Abstract

Liquid metal MHD (Magneto-Hydro-Dynamic) systems can be employed to produce electricity from a wide range of heat resources. In such a system, a low-boiling organic fluid and a high-temperature liquid metal fluid mix. The former evaporates, and carries the latter to flow through [...] Read more.

Liquid metal MHD (Magneto-Hydro-Dynamic) systems can be employed to produce electricity from a wide range of heat resources. In such a system, a low-boiling organic fluid and a high-temperature liquid metal fluid mix. The former evaporates, and carries the latter to flow through an MHD channel, where the electricity is generated. The mixing process and the gas-liquid flow characteristics will have a significant effect on the power generating efficiency. In the present work, trifluorotrichloroethane (R113) was chosen as the organic fluid, and gallium (Ga) as the liquid metal, respectively. Numerical study was subsequently carried out on the gas-liquid flow and heat transfer in a self-designed spherical mixer. The effects of the main factors, including the inlet velocities and inlet temperatures of Ga and R113, were separately determined, with suggested values or ranges discussed in detail. Full article

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17 pages, 4130 KiB

Open AccessArticle

Modeling and Control of Air Conditioning Loads for Consuming Distributed Energy Sources

by Dongsheng Yang, Xinyi Zhang^* and Bowen Zhou

College of Information Science and Engineering, Northeastern University, Shenyang 110819, China

Energies 2017, 10(10), 1630; https://doi.org/10.3390/en10101630 - 17 Oct 2017

Cited by 7 | Viewed by 3033

Abstract

This paper aims to tap the potential of air conditioning loads (ACLs) for consuming photovoltaic power (PV) and wind power (WP). By fully considering different thermal comfort of different users, an ACL twice-clustered model based on different ACL parameters and users tolerance values [...] Read more.

This paper aims to tap the potential of air conditioning loads (ACLs) for consuming photovoltaic power (PV) and wind power (WP). By fully considering different thermal comfort of different users, an ACL twice-clustered model based on different ACL parameters and users tolerance values (UTV) is built. Then, a two-stage ACL control method based on both temperature control (TC) and switch control (SC) is proposed, which achieves rapid control of ACLs as well as diminishing users’ discomfort. Widely existent communication time delay in ACL control network causes obvious control error, which leads to ACL consumption deviation from the target. Therefore, on the basis of analyzing errors and impacts of ACLs caused by communication time delay, this paper proposes a time delay compensation method based on a network predictive control system. Applying the ACLs clustered model and the control method into consuming PV and WP, a dual-stage consumption model considering communication time delay is established. Simulations of the PV and WP consumption effects based on ACLs clusters are conducted, and the influence of SC cycle and outdoor temperature on the simulation results are analyzed. The simulation results demonstrate the validity of the model and the methods proposed in this paper, showing a strong adaptability in different circumstances. Full article

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

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17 pages, 2965 KiB

Open AccessFeature PaperArticle

A Model Predictive Control-Based Power Converter System for Oscillating Water Column Wave Energy Converters

by Gimara Rajapakse^1,*

, Shantha Jayasinghe¹, Alan Fleming¹

and Michael Negnevitsky²

¹ Australian Maritime College, University of Tasmania, Newnham, Tasmania 7248, Australia

² Centre for Renewable Energy and Power Systems, University of Tasmania, Hobart, Tasmania 7001, Australia

Energies 2017, 10(10), 1631; https://doi.org/10.3390/en10101631 - 17 Oct 2017

Cited by 19 | Viewed by 5955

Abstract

Despite the predictability and availability at large scale, wave energy conversion (WEC) has still not become a mainstream renewable energy technology. One of the main reasons is the large variations in the extracted power which could lead to instabilities in the power grid. [...] Read more.

Despite the predictability and availability at large scale, wave energy conversion (WEC) has still not become a mainstream renewable energy technology. One of the main reasons is the large variations in the extracted power which could lead to instabilities in the power grid. In addition, maintaining the speed of the turbine within optimal range under changing wave conditions is another control challenge, especially in oscillating water column (OWC) type WEC systems. As a solution to the first issue, this paper proposes the direct connection of a battery bank into the dc-link of the back-to-back power converter system, thereby smoothening the power delivered to the grid. For the second issue, model predictive controllers (MPCs) are developed for the rectifier and the inverter of the back-to-back converter system aiming to maintain the turbine speed within its optimum range. In addition, MPC controllers are designed to control the battery current as well, in both charging and discharging conditions. Operations of the proposed battery direct integration scheme and control solutions are verified through computer simulations. Simulation results show that the proposed integrated energy storage and control solutions are capable of delivering smooth power to the grid while maintaining the turbine speed within its optimum range under varying wave conditions. Full article

(This article belongs to the Special Issue Marine Energy)

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18 pages, 9100 KiB

Open AccessArticle

Experimental Evaluation of the Thermal Performance of Raised Floor Integrated Radiant Heating Panels

by Dong-Woo Kim¹, Goo-Sang Joe¹, Sang-Hoon Park², Myoung-Souk Yeo^3,* and Kwang-Woo Kim³

¹ Department of Architecture and Architectural Engineering, Graduate School of Seoul National University, Seoul 08826, Korea

² Corporate R&D Center, LG Hausys, Anyang 14117, Korea

³ Department of Architecture and Architectural Engineering, College of Engineering, Seoul National University, Seoul 08826, Korea

Energies 2017, 10(10), 1632; https://doi.org/10.3390/en10101632 - 17 Oct 2017

Cited by 9 | Viewed by 5462

Abstract

In this study, we propose a method for the evaluation of the thermal output of radiant heating panels by employing a modification of the currently used method, which is recommended by existing standards, using cooling plates. We aim to overcome the absence in [...] Read more.

In this study, we propose a method for the evaluation of the thermal output of radiant heating panels by employing a modification of the currently used method, which is recommended by existing standards, using cooling plates. We aim to overcome the absence in the measurement method of the downward thermal output as well as to address the challenges in the control of the heat transfer resistance of the heat transfer layer, which arise due to the contact resistance between the layers. Using the modified method, we compare the thermal performance of three types of raised floor integrated radiant heating panels that have different filler materials for the bottom insulation of the panel. We show that the most efficient sample panel is the one that is not filled with a material; with an efficiency of 70.1%. In addition, we show that the value of the gradient of the characteristic curve calculated by the existing method ranged between 7.2% to 14.9% larger than that obtained by modified method. This difference is attributed to the heat transfer resistance of the heat transfer layer that is present in the experiments, and has a value in the interval of 0.1096

m^{2} K / W

to 0.1582

m^{2} K / W

. This is caused by the contact resistance between the heat transfer layer and other layers, even though the heat transfer resistance of the heat transfer layer used in the experiment is 0.0985

m^{2} K / W

. The modified method proposed in this study reveals that the experimental results are not influenced by the heat transfer resistance of the heat transfer layer. We also show that our experimental results are reproducible. Full article

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40 pages, 20349 KiB

Open AccessArticle

New Power Quality Indices for the Assessment of Waveform Distortions from 0 to 150 kHz in Power Systems with Renewable Generation and Modern Non-Linear Loads

by Luisa Alfieri^1,*

, Antonio Bracale²

and Anders Larsson³

¹ Department of Electrical Engineering and Information Technology, University of Naples Federico II, Via Claudio, 21, 80125 Naples, Italy

² Department of Engineering, University of Naples Parthenope, Centro Direzionale of Naples, Is C4, 80143 Naples, Italy

³ Department of Engineering Sciences and Mathematics, Luleå University of Technology, 971 87 Luleå, Sweden

Energies 2017, 10(10), 1633; https://doi.org/10.3390/en10101633 - 17 Oct 2017

Cited by 16 | Viewed by 4013

Abstract

The widespread use of power electronics converters, e.g., to interface renewable generation systems with the grid or to supply some high-efficiency loads, has caused increased levels of waveform distortions in the modern distribution system. Voltage and current waveforms include spectral components from 0 [...] Read more.

The widespread use of power electronics converters, e.g., to interface renewable generation systems with the grid or to supply some high-efficiency loads, has caused increased levels of waveform distortions in the modern distribution system. Voltage and current waveforms include spectral components from 0 kHz to 150 kHz, characterized by a non-uniform time-frequency behavior. This wide interval of frequencies is currently divided into “low-frequency” (from 0 kHz to 2 kHz) and “high-frequency” (from 2 kHz to 150 kHz). While the low-frequencies have been exhaustively investigated in the relevant literature and are covered by adequate standardization, studies for the high-frequencies have been addressed only in the last decade to fill current regulatory gaps. In this paper, new power quality (PQ) indices for the assessment of waveform distortions from 0 kHz to 150 kHz are proposed. Specifically, some currently available indices have been properly modified in order to extend their application also to wide-spectrum waveforms. In the particular case of waveform distortions due to renewable generation, numerical applications prove that the proposed indices are useful tools for the characterization of problems (e.g., overheating, equipment malfunctioning, losses due to skin effects, hysteresis losses or eddy current losses) in cases of both low-frequency and high-frequency distortions. Full article

(This article belongs to the Special Issue Modelling Distribution Systems with Renewable Generation under Abnormal Conditions)

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16 pages, 4061 KiB

Open AccessArticle

Evaluation Model of Specific Indoor Environment Overall Comfort Based on Effective-Function Method

by Tieming Guo^1,2, Songtao Hu^1,* and Guodan Liu¹

¹ School of Environmental and Municipal Engineering, Qingdao University of Technology, Qingdao 266033, China

² School of Architectural Engineering, Qingdao Agricultural University, Qingdao 266109, China

Energies 2017, 10(10), 1634; https://doi.org/10.3390/en10101634 - 17 Oct 2017

Cited by 34 | Viewed by 3539

Abstract

The indoor overall environmental comfort of part limited spaces is studied in this paper. The operative temperature, illumination, and noise intensity are used as objective parameters in order to evaluate the thermal, luminous, and acoustic environment. The thermal, luminous, and acoustic environment are [...] Read more.

The indoor overall environmental comfort of part limited spaces is studied in this paper. The operative temperature, illumination, and noise intensity are used as objective parameters in order to evaluate the thermal, luminous, and acoustic environment. The thermal, luminous, and acoustic environment are investigated by using the subjective questionnaire in this experiment, and the function relation of the single physical parameter is established. Then, using the effective-function comprehensive evaluation carries on non-dimensional, weighting, and penalty substitution synthesis for the evaluation index of thermal, luminous, and acoustic environment, and establishes the evaluation model of the indoor overall environment. According to the experimental results and evaluation analysis, it is considered that the noise intensity and operative temperature have great influence on the indoor environment overall comfort and the illumination has less effect. Referring to the ISO7730 standard and combining it with the situation of our country, the indoor overall environment is divided into the zone of comfort. The predicted overall comfort vote (POCV), which is greater than or equal to −0.5 is the high comfort zone I. The area of −0.5 > POCV ≥ −1.0 is designated as low comfort zone II. It provides a certain basis for the evaluation of indoor overall environmental comfort. Full article

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19 pages, 7626 KiB

Open AccessArticle

An Improved Control and Energy Management Strategy of Three-Level NPC Converter Based DC Distribution Network

by Yuqi Wang¹

, Qingshan Xu^1,*, Zhoujun Ma² and Hong Zhu²

¹ School of Electrical Engineering, Southeast University, Nanjing 210096, China

² State Grid Nanjing Supply Company, Nanjing 210008, China

Energies 2017, 10(10), 1635; https://doi.org/10.3390/en10101635 - 18 Oct 2017

Cited by 10 | Viewed by 4032

Abstract

To meet the challenge of large-scale renewable energy penetration and take full advantage of existing AC infrastructure, the bipolar DC distribution system is of interest. In this article, the system structure and characteristics of the bipolar DC distribution network are proposed. The three-level [...] Read more.

To meet the challenge of large-scale renewable energy penetration and take full advantage of existing AC infrastructure, the bipolar DC distribution system is of interest. In this article, the system structure and characteristics of the bipolar DC distribution network are proposed. The three-level Neural Point Clamped Converter (NPC) is used in the proposed system to construct the bipolar DC system. To optimize the DC system performance, an improved cooperative control and energy management strategy is proposed mainly to mitigate DC voltage fluctuation and balance the positive and negative phase voltage. The improved strategy consists of (1) 2-degree of freedom (2DOF) PID controller in traditional voltage control loop; (2) cooperative controller to take full advantage of storage system; (3) voltage equalization controller to balance two-phase voltages; and (4) the energy management system to dispatch the response job to batteries and supercapacitors. Experiments and simulations are performed to validate the effectiveness of the proposed strategy. Full article

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

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30 pages, 4099 KiB

Open AccessArticle

Advances in Integrated Vehicle Thermal Management and Numerical Simulation

by Yan Wang^1,2, Qing Gao^1,2, Tianshi Zhang^1,2,*, Guohua Wang^1,2, Zhipeng Jiang^1,2 and Yunxia Li³

¹ State Key Laboratory of Automotive Simulation and Control, Jilin University, Changchun 130025, China

² College of Automotive Engineering, Jilin University, Changchun 130025, China

³ China FAW Co., Ltd. R&D Center, Changchun 130025, China

Energies 2017, 10(10), 1636; https://doi.org/10.3390/en10101636 - 18 Oct 2017

Cited by 62 | Viewed by 22735

Abstract

With the increasing demands for vehicle dynamic performance, economy, safety and comfort, and with ever stricter laws concerning energy conservation and emissions, vehicle power systems are becoming much more complex. To pursue high efficiency and light weight in automobile design, the power system [...] Read more.

With the increasing demands for vehicle dynamic performance, economy, safety and comfort, and with ever stricter laws concerning energy conservation and emissions, vehicle power systems are becoming much more complex. To pursue high efficiency and light weight in automobile design, the power system and its vehicle integrated thermal management (VITM) system have attracted widespread attention as the major components of modern vehicle technology. Regarding the internal combustion engine vehicle (ICEV), its integrated thermal management (ITM) mainly contains internal combustion engine (ICE) cooling, turbo-charged cooling, exhaust gas recirculation (EGR) cooling, lubrication cooling and air conditioning (AC) or heat pump (HP). As for electric vehicles (EVs), the ITM mainly includes battery cooling/preheating, electric machines (EM) cooling and AC or HP. With the rational effective and comprehensive control over the mentioned dynamic devices and thermal components, the modern VITM can realize collaborative optimization of multiple thermodynamic processes from the aspect of system integration. Furthermore, the computer-aided calculation and numerical simulation have been the significant design methods, especially for complex VITM. The 1D programming can correlate multi-thermal components and the 3D simulating can develop structuralized and modularized design. Additionally, co-simulations can virtualize simulation of various thermo-hydraulic behaviors under the vehicle transient operational conditions. This article reviews relevant researching work and current advances in the ever broadening field of modern vehicle thermal management (VTM). Based on the systematic summaries of the design methods and applications of ITM, future tasks and proposals are presented. This article aims to promote innovation of ITM, strengthen the precise control and the performance predictable ability, furthermore, to enhance the level of research and development (R&D). Full article

(This article belongs to the Special Issue Advanced Thermal Simulation of Energy Systems)

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15 pages, 2605 KiB

Open AccessArticle

Adaptive Nonsingular Fast Terminal Sliding Mode Control for Braking Systems with Electro-Mechanical Actuators Based on Radial Basis Function

by Bo Liang^1,*, Yuqing Zhu¹, Yuren Li¹, Pengju He² and Weilin Li¹

¹ School of Automation, Northwestern Polytechnical University, Xi’an 710072, China

² Military Representative Office, 95655 Force, Xi’an 710072, China

Energies 2017, 10(10), 1637; https://doi.org/10.3390/en10101637 - 18 Oct 2017

Cited by 24 | Viewed by 4548

Abstract

In this paper an adaptive non-singular fast terminal sliding mode (NFTSM) control scheme is proposed to control the electro-mechanical actuator (EMA) in an electric braking system which is a complex electro-mechanical system. In order to realize high-performance brake pressure servo control, a radial [...] Read more.

In this paper an adaptive non-singular fast terminal sliding mode (NFTSM) control scheme is proposed to control the electro-mechanical actuator (EMA) in an electric braking system which is a complex electro-mechanical system. In order to realize high-performance brake pressure servo control, a radial basis function (RBF) neural network method is adopted to deal with the difficulty of estimating the upper bound of the compound disturbance in the system, to reduce the conservatism of the design of sliding mode switching gain, and effectively eliminate sliding mode chattering. The simulation results show that, compared with a linear controller, the proposed control strategy is able to improve the servo performance and control precision. In addition the response speed of the braking actuator is enhanced significantly, without changing the traditional double-loop control structure. Full article

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

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12 pages, 1256 KiB

Open AccessArticle

Investigation of Permanent Magnet Demagnetization in Synchronous Machines during Multiple Short-Circuit Fault Conditions

by Stefan Sjökvist

and Sandra Eriksson^*

The Division of Electricity, Department of Engineering Sciences, Uppsala University, Box 534, 751 21 Uppsala, Sweden

Energies 2017, 10(10), 1638; https://doi.org/10.3390/en10101638 - 18 Oct 2017

Cited by 22 | Viewed by 6798

Abstract

Faults in electrical machines can vary in severity and affect different parts of the machine. This study focuses on various kinds of short-circuits on the terminal side of a generic 20 kW surface mounted permanent magnet synchronous generator and how successive faults affect [...] Read more.

Faults in electrical machines can vary in severity and affect different parts of the machine. This study focuses on various kinds of short-circuits on the terminal side of a generic 20 kW surface mounted permanent magnet synchronous generator and how successive faults affect the performance of the machine. The study was conducted with the commercially available finite element method software COMSOL Multiphysics

^{®}

, and two time-dependent models for demagnetization of permanent magnets were compared, one using only internal models and the other using a proprietary external function. The study is simulation based and the two models were compared to a previously experimentally verified stationary model. Results showed that the power output decreased by more than 30% after five successive faults. In addition, the no-load voltage had become unsymmetrical, which was explained by the uneven demagnetization of the permanent magnets. The permanent magnet with the lowest reduction in average remanence was decreased by 0.8%, while the highest average reduction was 23.8% in another permanent magnet. The internal simulation model was about four times faster than the external model, but slightly overestimated the demagnetization. Full article

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

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Graphical abstract

12 pages, 6862 KiB

Open AccessArticle

Diesel/CNG Mixture Autoignition Control Using Fuel Composition and Injection Gap

by Firmansyah^*

, A. Rashid A. Aziz^†, Morgan Raymond Heikal^† and Ezrann Z. Zainal A.^†

¹ Centre for Automotive Research and Electric Mobility, Universiti Teknologi Petronas, Bota 32610, Perak, Malaysia

^† These authors contributed equally to this work.

Energies 2017, 10(10), 1639; https://doi.org/10.3390/en10101639 - 18 Oct 2017

Cited by 9 | Viewed by 5749

Abstract

Combustion phasing is the main obstacle to the development of controlled auto-ignition based (CAI) engines to achieve low emissions and low fuel consumption operation. Fuel combinations with substantial differences in reactivity, such as diesel/compressed natural gas (CNG), show desirable combustion outputs and demonstrate [...] Read more.

Combustion phasing is the main obstacle to the development of controlled auto-ignition based (CAI) engines to achieve low emissions and low fuel consumption operation. Fuel combinations with substantial differences in reactivity, such as diesel/compressed natural gas (CNG), show desirable combustion outputs and demonstrate great possibility in controlling the combustion. This paper discusses a control method for diesel/CNG mixture combustion with a variation of fuel composition and fuel stratification levels. The experiments were carried out in a constant volume combustion chamber with both fuels directly injected into the chamber. The mixture composition was varied from 0 to 100% CNG/diesel at lambda 1 while the fuel stratification level was controlled by the injection phasing between the two fuels, with gaps between injections ranging from 0 to 20 ms. The results demonstrated the suppressing effect of CNG on the diesel combustion, especially at the early combustion stages. However, CNG significantly enhanced the combustion performance of the diesel in the later stages. Injection gaps, on the other hand, showed particular behavior depending on mixture composition. Injection gaps show less effect on combustion phasing but a significant effect on the combustion output for higher diesel percentage (≥70%), while it is contradictive for lower diesel percentage (<70%). Full article

(This article belongs to the Collection Bioenergy and Biofuel)

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18 pages, 3962 KiB

Open AccessArticle

Transactive Demand Side Management Programs in Smart Grids with High Penetration of EVs

by Poria Astero^1,2,3,*, Bong Jun Choi^1,2, Hao Liang⁴ and Lennart Söder³

¹ Department of Computer Science, The State University of New York Korea, Incheon 21985, Korea

² Department of Computer Science, Stony Brook University, Stony Brook, NY 11794, USA

³ Department of Electric Power and Energy Systems, KTH Royal Institute of Technology, 114 28 Stockholm, Sweden

⁴ Department of Electrical and Computer Engineering, University of Alberta, Edmonton, AB T6G 2R3, Canada

Energies 2017, 10(10), 1640; https://doi.org/10.3390/en10101640 - 18 Oct 2017

Cited by 15 | Viewed by 4656

Abstract

Due to environmental concerns, economic issues, and emerging new loads, such as electrical vehicles (EVs), the importance of demand side management (DSM) programs has increased in recent years. DSM programs using a dynamic real-time pricing (RTP) method can help to adaptively control the [...] Read more.

Due to environmental concerns, economic issues, and emerging new loads, such as electrical vehicles (EVs), the importance of demand side management (DSM) programs has increased in recent years. DSM programs using a dynamic real-time pricing (RTP) method can help to adaptively control the electricity consumption. However, the existing RTP methods, particularly when they consider the EVs and the power system constraints, have many limitations, such as computational complexity and the need for centralized control. Therefore, a new transactive DSM program is proposed in this paper using an imperfect competition model with high EV penetration levels. In particular, a heuristic two-stage iterative method, considering the influence of decisions made independently by customers to minimize their own costs, is developed to find the market equilibrium quickly in a distributed manner. Simulations in the IEEE 37-bus system with 1141 customers and 670 EVs are performed to demonstrate the effectiveness of the proposed method. The results show that the proposed method can better manage the EVs and elastic appliances than the existing methods in terms of power constraints and cost. Also, the proposed method can solve the optimization problem quick enough to run in real-time. Full article

(This article belongs to the Special Issue Energy Management in Vehicle–Grid–Traffic Nexus)

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16 pages, 3678 KiB

Open AccessArticle

Co-Design Based Lateral Motion Control of All-Wheel-Independent-Drive Electric Vehicles with Network Congestion

by Wanke Cao^1,*

, Helin Liu¹, Cheng Lin¹, Yuhua Chang^2,*, Zhiyin Liu² and Antoni Szumanowski²

¹ National Engineering Laboratory for Electric Vehicles and Collaborative Innovation Center of Electric Vehicles in Beijing, Beijing Institute of Technology (BIT), Beijing 100081, China

² Department of Multisource Propulsion System, Faculty of Automotive and Construction Machinery Engineering, Warsaw University of Technology (WUT), 02-524 Warsaw, Poland

Energies 2017, 10(10), 1641; https://doi.org/10.3390/en10101641 - 18 Oct 2017

Cited by 15 | Viewed by 4592

Abstract

All-wheel-independent-drive electric vehicles (AWID-EVs) have considerable advantages in terms of energy optimization, drivability and driving safety due to the remarkable actuation flexibility of electric motors. However, in their current implementations, various real-time data in the vehicle control system are exchanged via a controller [...] Read more.

All-wheel-independent-drive electric vehicles (AWID-EVs) have considerable advantages in terms of energy optimization, drivability and driving safety due to the remarkable actuation flexibility of electric motors. However, in their current implementations, various real-time data in the vehicle control system are exchanged via a controller area network (CAN), which causes network congestion and network-induced delays. These problems could lead to systemic instability and make the system integration difficult. The goal of this paper is to provide a design methodology that can cope with all these challenges for the lateral motion control of AWID-EVs. Firstly, a continuous-time model of an AWID-EV is derived. Then an expression for determining upper and lower bounds on the delays caused by CAN is presented and with which a discrete-time model of the closed-loop CAN system is derived. An expression on the bandwidth utilization is introduced as well. Thirdly, a co-design based scheme combining a period-dependent linear quadratic regulator (LQR) and a dynamic period scheduler is designed for the resulting model and the stability criterion is also derived. The results of simulations and hard-in-loop (HIL) experiments show that the proposed methodology can effectively guarantee the stability of the vehicle lateral motion control while obviously declining the network congestion. Full article

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19 pages, 10669 KiB

Open AccessArticle

A Method for the Realization of an Interruption Generator Based on Voltage Source Converters

by Junhui Li^1,*, Tianyang Zhang¹, Lei Qi² and Gangui Yan¹

¹ School of Electrical Engineering, Northeast Electric Power University, Jilin 132012, China

² Liaoning Academy of Safety Science, Shenyang 110179, China

Energies 2017, 10(10), 1642; https://doi.org/10.3390/en10101642 - 19 Oct 2017

Cited by 7 | Viewed by 3819

Abstract

In this paper we described the structure and working principle of an interruption generator based on voltage source converters (VSCs). The main circuit parameters of the VSCs are determined according to the target of power transfer capability, harmonic suppression, and dynamic response capability. [...] Read more.

In this paper we described the structure and working principle of an interruption generator based on voltage source converters (VSCs). The main circuit parameters of the VSCs are determined according to the target of power transfer capability, harmonic suppression, and dynamic response capability. A state feedback linearization method in nonlinear differential geometry theory was used for dq axis current decoupling, based on the mathematical model used in the dq coordinate system of VSCs. The direct current control strategy was adopted to achieve the independent regulation of active power and reactive power. The proportional integral (PI) link was used to optimize the dynamic performance of the controller, and PI parameters were adjusted. Disturbance voltage waves were generated by the regular sampling method. PSCAD/EMTDC simulation results and physical prototype experiments showed that the device could generate various disturbance voltage waveforms steadily, and had good dynamic and steady-state performance. Full article

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

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0 pages, 3686 KiB

Open AccessArticle

RETRACTED: Techno-Economic Comparison of Onshore and Offshore Underground Coal Gasification End-Product Competitiveness

by Natalie Christine Nakaten^*

and Thomas Kempka

GFZ German Research Centre for Geosciences, Fluid Systems Modelling, Telegrafenberg, 14473 Potsdam, Germany

Energies 2017, 10(10), 1643; https://doi.org/10.3390/en10101643 - 18 Oct 2017

Cited by 16 | Viewed by 8049 | Retraction

Abstract

Underground Coal Gasification (UCG) enables the utilisation of coal reserves that are currently not economically exploitable due to complex geological boundary conditions. Hereby, UCG produces a high-calorific synthesis gas that can be used for generation of electricity, fuels and chemical feedstock. The present [...] Read more.

Underground Coal Gasification (UCG) enables the utilisation of coal reserves that are currently not economically exploitable due to complex geological boundary conditions. Hereby, UCG produces a high-calorific synthesis gas that can be used for generation of electricity, fuels and chemical feedstock. The present study aims to identify economically competitive, site-specific end-use options for onshore and offshore produced UCG synthesis gas, taking into account the capture and storage (CCS) and/or utilisation (CCU) of resulting CO

_{2}

. Modelling results show that boundary conditions that favour electricity, methanol and ammonia production expose low costs for air separation, high synthesis gas calorific values and H

_{2}

/N

_{2}

shares as well as low CO

_{2}

portions of max. 10%. Hereby, a gasification agent ratio of more than 30% oxygen by volume is not favourable from economic and environmental viewpoints. Compared to the costs of an offshore platform with its technical equipment, offshore drilling costs are negligible. Thus, uncertainties related to parameters influenced by drilling costs are also negligible. In summary, techno-economic process modelling results reveal that scenarios with high CO

_{2}

emissions are the most cost-intensive ones, offshore UCG-CCS/CCU costs are twice as high as the onshore ones, and yet all investigated scenarios except from offshore ammonia production are competitive on the European market. Full article

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

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13 pages, 2128 KiB

Open AccessArticle

Long-Term Stability Evaluation and Pillar Design Criterion for Room-and-Pillar Mines

by Yang Yu¹

, Shen-en Chen²

, Ka-zhong Deng^1,*

and Hong-dong Fan^1,3

¹ School of Environment Science and Spatial Information, China University of Mining and Technology, Xuzhou 221116, China

² Department of Civil and Environmental Engineering, University of North Carolina at Charlotte, 9201 University City Blvd., Charlotte, NC 28223, USA

³ State Key Laboratory of Geohazard Prevention and Geoenvironment Protection, Chengdu University of Technology, Chengdu 610059, China

Energies 2017, 10(10), 1644; https://doi.org/10.3390/en10101644 - 18 Oct 2017

Cited by 33 | Viewed by 7000

Abstract

The collapse of abandoned room-and-pillar mines is often violent and unpredictable. Safety concerns often resulted in mine closures with no post-mining stability evaluations. As a result, large amounts of land resources over room-and-pillar mines are wasted. This paper attempts to establish an understanding [...] Read more.

The collapse of abandoned room-and-pillar mines is often violent and unpredictable. Safety concerns often resulted in mine closures with no post-mining stability evaluations. As a result, large amounts of land resources over room-and-pillar mines are wasted. This paper attempts to establish an understanding of the long-term stability issues of goafs (abandoned mines). Considering progressive pillar failures and the effect of single pillar failure on surrounding pillars, this paper proposes a pillar peeling model to evaluate the long-term stability of coal mines and the associated criteria for evaluating the long-term stability of room-and-pillar mines. The validity of the peeling model was verified by numerical simulation, and field data from 500 pillar cases from China, South Africa, and India. It is found that the damage level of pillar peeling is affected by the peel angle and pillar height and is controlled by the pillar width–height ratio. Full article

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

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30 pages, 3869 KiB

Open AccessReview

Complex Metal Hydrides for Hydrogen, Thermal and Electrochemical Energy Storage

by Kasper T. Møller¹

, Drew Sheppard^1,2, Dorthe B. Ravnsbæk³

, Craig E. Buckley², Etsuo Akiba^4,5,6, Hai-Wen Li^1,4,5,7,*

and Torben R. Jensen^1,*

¹ Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, Aarhus University, DK-8000 Aarhus, Denmark

² Department of Physics and Astronomy, Fuels and Energy Technology Institute, Curtin University, GPO Box U1987, Perth, WA 6845, Australia

³ Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark

⁴ International Research Center for Hydrogen Energy, Kyushu University, Fukuoka 819-0395, Japan

⁵ WPI International Institute for Carbon Neutral Energy Research (WPI-I2CNER), Kyushu University, Fukuoka 819-0395, Japan

⁶ Department of Mechanical Engineering, Faculty of Engineering, Kyushu University, Fukuoka 819-0395, Japan

⁷ Kyushu University Platform of Inter/Transdisciplinary Energy Research, Fukuoka 819-0395, Japan

Energies 2017, 10(10), 1645; https://doi.org/10.3390/en10101645 - 18 Oct 2017

Cited by 191 | Viewed by 14552

Abstract

Hydrogen has a very diverse chemistry and reacts with most other elements to form compounds, which have fascinating structures, compositions and properties. Complex metal hydrides are a rapidly expanding class of materials, approaching multi-functionality, in particular within the energy storage field. This review [...] Read more.

Hydrogen has a very diverse chemistry and reacts with most other elements to form compounds, which have fascinating structures, compositions and properties. Complex metal hydrides are a rapidly expanding class of materials, approaching multi-functionality, in particular within the energy storage field. This review illustrates that complex metal hydrides may store hydrogen in the solid state, act as novel battery materials, both as electrolytes and electrode materials, or store solar heat in a more efficient manner as compared to traditional heat storage materials. Furthermore, it is highlighted how complex metal hydrides may act in an integrated setup with a fuel cell. This review focuses on the unique properties of light element complex metal hydrides mainly based on boron, nitrogen and aluminum, e.g., metal borohydrides and metal alanates. Our hope is that this review can provide new inspiration to solve the great challenge of our time: efficient conversion and large-scale storage of renewable energy. Full article

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19 pages, 1529 KiB

Open AccessArticle

Aggregation Potentials for Buildings—Business Models of Demand Response and Virtual Power Plants

by Zheng Ma^*, Joy Dalmacio Billanes and Bo Nørregaard Jørgensen

Center for Energy Informatics, Mærsk Mc-Kinney Møller Institute, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark

Energies 2017, 10(10), 1646; https://doi.org/10.3390/en10101646 - 20 Oct 2017

Cited by 54 | Viewed by 7925

Abstract

Buildings as prosumers have an important role in the energy aggregation market due to their potential flexible energy consumption and distributed energy resources. However, energy flexibility provided by buildings can be very complex and depend on many factors. The immaturity of the current [...] Read more.

Buildings as prosumers have an important role in the energy aggregation market due to their potential flexible energy consumption and distributed energy resources. However, energy flexibility provided by buildings can be very complex and depend on many factors. The immaturity of the current aggregation market with unclear incentives is still a challenge for buildings to participate in the aggregation market. However, few studies have investigated business models for building participation in the aggregation market. Therefore, this paper develops four business models for buildings to participate in the energy aggregation market: (1) buildings participate in the implicit Demand Response (DR) program via retailers; (2) buildings with small energy consumption participate in the explicit DR via aggregators; (3) buildings directly access the explicit DR program; (4) buildings access energy market via Virtual Power Plant (VPP) aggregators by providing Distributed Energy Resources (DER)s. This paper also determines that it is essential to understand building owners’ needs, comforts, and behaviours to develop feasible market access strategies for different types of buildings. Meanwhile, the incentive programs, national regulations and energy market structures strongly influence buildings’ participation in the aggregation market. Under the current Nordic market regulation, business model one is the most feasible one, and business model two faces more challenges due to regulation barriers and limited monetary incentives. Full article

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

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21 pages, 5363 KiB

Open AccessArticle

Ride Comfort Optimization of In-Wheel-Motor Electric Vehicles with In-Wheel Vibration Absorbers

by Mingchun Liu^1,*

, Feihong Gu² and Yuanzhi Zhang¹

¹ School of Mechatronics Engineering, Nanchang University, Nanchang 330031, China

² School of Automotive Engineering, Jilin University, Jilin 130022, China

Energies 2017, 10(10), 1647; https://doi.org/10.3390/en10101647 - 19 Oct 2017

Cited by 65 | Viewed by 10087

Abstract

This paper presents an in-wheel vibration absorber for in-wheel-motor electric vehicles (IWM EVs), and a corresponding control strategy to improve vehicle ride comfort. The proposed in-wheel vibration absorber, designed for suppressing the motor vibrations, is composed of a spring, an annular rubber bushing, [...] Read more.

This paper presents an in-wheel vibration absorber for in-wheel-motor electric vehicles (IWM EVs), and a corresponding control strategy to improve vehicle ride comfort. The proposed in-wheel vibration absorber, designed for suppressing the motor vibrations, is composed of a spring, an annular rubber bushing, and a controllable damper. The parameters of the in-wheel spring and rubber bushing are determined by an improved particle swarm optimization (IPSO) algorithm, which is executed under the typical driving conditions and can absorb vibration passively. To deal with negative interaction effects between vehicle suspension and in-wheel absorber, a linear quadratic regulator (LQR) algorithm is developed to control suspension damper, and meanwhile a fuzzy proportional-integral-derivative (PID) method is developed to control in-wheel damper as well. Through four evaluation indexes, i.e., vehicle body vertical acceleration, suspension dynamic deflection, wheel dynamic load, and motor wallop, simulation results show that, compared to the conventional electric wheel, the proposed suspension LQR control effectively improves vehicle ride comfort, and the in-wheel absorber exhibits excellent performance in terms of wheel and motor vibration suppression. Full article

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

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16 pages, 4453 KiB

Open AccessArticle

Regenerative Intelligent Brake Control for Electric Motorcycles

by Juan Jesús Castillo Aguilar^*

, Javier Pérez Fernández

, Juan María Velasco García and Juan Antonio Cabrera Carrillo

Department of Mechanical Engineering, University of Málaga, 29071 Málaga, Spain

Energies 2017, 10(10), 1648; https://doi.org/10.3390/en10101648 - 20 Oct 2017

Cited by 10 | Viewed by 7236

Abstract

Vehicle models whose propulsion system is based on electric motors are increasing in number within the automobile industry. They will soon become a reliable alternative to vehicles with conventional propulsion systems. The main advantages of this type of vehicles are the non-emission of [...] Read more.

Vehicle models whose propulsion system is based on electric motors are increasing in number within the automobile industry. They will soon become a reliable alternative to vehicles with conventional propulsion systems. The main advantages of this type of vehicles are the non-emission of polluting gases and noise and the effectiveness of electric motors compared to combustion engines. Some of the disadvantages that electric vehicle manufacturers still have to solve are their low autonomy due to inefficient energy storage systems, vehicle cost, which is still too high, and reducing the recharging time. Current regenerative systems in motorcycles are designed with a low fixed maximum regeneration rate in order not to cause the rear wheel to slip when braking with the regenerative brake no matter what the road condition is. These types of systems do not make use of all the available regeneration power, since more importance is placed on safety when braking. An optimized regenerative braking strategy for two-wheeled vehicles is described is this work. This system is designed to recover the maximum energy in braking processes while maintaining the vehicle’s stability. In order to develop the previously described regenerative control, tyre forces, vehicle speed and road adhesion are obtained by means of an estimation algorithm. A based-on-fuzzy-logic algorithm is programmed to carry out an optimized control with this information. This system recuperates maximum braking power without compromising the rear wheel slip and safety. Simulations show that the system optimizes energy regeneration on every surface compared to a constant regeneration strategy. Full article

(This article belongs to the Special Issue Methods to Improve Energy Use in Road Vehicles)

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15 pages, 2872 KiB

Open AccessArticle

Prospects of Mixtures as Working Fluids in Real-Gas Brayton Cycles

by Costante Mario Invernizzi

Department of Mechanical and Industrial Engineering, University of Brescia, Via Branze 38, 25123 Brescia, Italy

Energies 2017, 10(10), 1649; https://doi.org/10.3390/en10101649 - 19 Oct 2017

Cited by 38 | Viewed by 5309

Abstract

This paper discusses the thermodynamic characteristics of the closed Brayton cycles in which the compression is placed near the critical point of the working fluid. Under these conditions, the specific volumes of the fluid during the compression are a fraction of the corresponding [...] Read more.

This paper discusses the thermodynamic characteristics of the closed Brayton cycles in which the compression is placed near the critical point of the working fluid. Under these conditions, the specific volumes of the fluid during the compression are a fraction of the corresponding values under ideal gas conditions, and the cycle performances improve significantly, mainly at moderate top temperatures. As the heat is discharged at about the critical temperature, the choice of the correct working fluid is strictly correlated with the environmental temperature or with the temperature of potential heat users. To resort to mixtures greatly extend the choice of the right working fluid, allowing a continuous variation of the critical temperature. These cycles have a high power density, and the use of ordinary turbomachinery is accompanied by high capacities (tens of megawatts). In the low power range, microturbines or reciprocating engines are required. One important constraint on the choice of the right working fluid is its thermochemical stability that restricts the operative temperatures. Among the organic compounds, the maximum safe temperatures are limited to about 400 °C and, forecasting high temperature applications, it could be interesting to explore the potentiality of the inorganic compounds as secondary fluids in binary mixtures. Full article

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

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25 pages, 637 KiB

Open AccessFeature PaperArticle

A Survey on PEV Charging Infrastructure: Impact Assessment and Planning

by Ahmed Abdalrahman^*

and Weihua Zhuang

Department of Electrical and Computer Engineering, University of Waterloo, 200 University Avenue West, Waterloo, ON N2L 3G1, Canada

Energies 2017, 10(10), 1650; https://doi.org/10.3390/en10101650 - 20 Oct 2017

Cited by 27 | Viewed by 5983

Abstract

Plug-in electric vehicles (PEVs) represent a huge step forward in a green transportation system, contribute in reduction of greenhouse gas emission, and reduce the dependence on fossil fuel. Integration of PEVs into the electric power system will result in a considerable addition to [...] Read more.

Plug-in electric vehicles (PEVs) represent a huge step forward in a green transportation system, contribute in reduction of greenhouse gas emission, and reduce the dependence on fossil fuel. Integration of PEVs into the electric power system will result in a considerable addition to electricity demand. Due to PEV mobility, this demand has a random distribution in space and time among distribution system nodes. Therefore, short term forecast of PEV charging demand is more challenging than that for conventional loads. Assessment of PEV impacts on the power system is essential to mitigate the impairments from PEV loads. Optimal planning of PEV charging infrastructure will promote the penetration rate of PEVs and minimize the negative impacts of PEVs on the electric power distribution system and transportation road network. Design of charging facilities with integrated distributed energy resources (DER) is considered a solution to alleviate strain on the grid, reduce the integration cost with the distribution network and the charging cost. In this paper, we present a comprehensive literature survey on modelling of PEV charging demand, impact assessment approaches and tools, and charging infrastructure planning. Moreover, an overview on charging facility design with integrated DER is given. Some future research directions are identified. Full article

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16 pages, 5936 KiB

Open AccessArticle

A Novel Supervisory Control Algorithm to Improve the Performance of a Real-Time PV Power-Hardware-In-Loop Simulator with Non-RTDS

by Dae-Jin Kim

, Byungki Kim, Hee-Sang Ko, Moon-Seok Jang and Kyung-Sang Ryu^*

System Convergence Laboratory, Korea Institute of Energy Research, Jeju 63357, Korea

Energies 2017, 10(10), 1651; https://doi.org/10.3390/en10101651 - 19 Oct 2017

Cited by 4 | Viewed by 4296

Abstract

A programmable direct current (DC) power supply with Real-time Digital Simulator (RTDS)-based photovoltaic (PV) Power Hardware-In-the-Loop (PHIL) simulators has been used to improve the control algorithm and reliability of a PV inverter. This paper proposes a supervisory control algorithm for a PV PHIL [...] Read more.

A programmable direct current (DC) power supply with Real-time Digital Simulator (RTDS)-based photovoltaic (PV) Power Hardware-In-the-Loop (PHIL) simulators has been used to improve the control algorithm and reliability of a PV inverter. This paper proposes a supervisory control algorithm for a PV PHIL simulator with a non-RTDS device that is an alternative solution to a high-cost PHIL simulator. However, when such a simulator with the conventional algorithm which is used in an RTDS is connected to a PV inverter, the output is in the transient state and it makes it impossible to evaluate the performance of the PV inverter. Therefore, the proposed algorithm controls the voltage and current target values according to constant voltage (CV) and constant current (CC) modes to overcome the limitation of the Computing Unit and DC power supply, and it also uses a multi-rate system to account for the characteristics of each component of the simulator. A mathematical model of a PV system, programmable DC power supply, isolated DC measurement device, and Computing Unit are integrated to form a real-time processing simulator. Performance tests are carried out with a commercial PV inverter and prove the superiority of this proposed algorithm against the conventional algorithm. Full article

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

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14 pages, 2580 KiB

Open AccessArticle

by Jiejunyi Liang^1,2

, Jian-Hua Zhong^1,*

and Zhi-Xin Yang³

¹ School of Mechanical Engineering and Automation, Fuzhou University, Fuzhou 350108, China

² School of Electrical, Mechanical and Mechatronic Systems, University of Technology Sydney, Sydney, NSW 2007, Australia

³ Department of Electromechanical Engineering, Faculty of Science and Technology, University of Macau, Macau 999078, China

Energies 2017, 10(10), 1652; https://doi.org/10.3390/en10101652 - 19 Oct 2017

Cited by 15 | Viewed by 4058

Abstract

Intelligent fault diagnosis of complex machinery is crucial for industries to reduce the maintenance cost and to improve fault prediction performance. Acoustic signal is an ideal source for diagnosis because of its inherent characteristics in terms of being non-directional and insensitive to structural [...] Read more.

Intelligent fault diagnosis of complex machinery is crucial for industries to reduce the maintenance cost and to improve fault prediction performance. Acoustic signal is an ideal source for diagnosis because of its inherent characteristics in terms of being non-directional and insensitive to structural resonances. However, there are also two main drawbacks of acoustic signal, one of which is the low signal to noise ratio (SNR) caused by its high sensitivity and the other one is the low computational efficiency caused by the huge data size. These would decrease the performance of the fault diagnosis system. Therefore, it is significant to develop a proper feature extraction method to improve computational efficiency and performance in both periodic and irregular fault diagnosis. To enhance SNR of the acquired acoustic signal, the correlation coefficient (CC) method is employed to eliminate the redundant intrinsic mode functions (IMF), which comes from the decomposition procedure of pre-processing known as ensemble empirical mode decomposition (EEMD), because the higher the correlated coefficient of an IMF is, the more significant fault signatures it would contain, and the redundant IMF would compromise both the SNR and the computational cost performance. Singular value decomposition (SVD) and sample Entropy (SampEn) are subsequently used to extract the fault feature, by exploiting their sensitivities to irregular and periodic fault signals, respectively. In addition, the proposed feature extraction method using sparse Bayesian based pairwise coupled extreme learning machine (PC-SBELM) outperforms the existing pairwise-coupling probabilistic neural network (PC-PNN) and pairwise-coupling relevance vector machine (PC-RVM) by 1.8% and 2%, respectively, to achieve an accuracy of 93.9%. The experiments conducted on the periodic and irregular faults in the gears and bearings have demonstrated that the proposed hybrid fault diagnosis system is effective. Full article

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21 pages, 6279 KiB

Open AccessArticle

Lean Maintenance Applied to Improve Maintenance Efficiency in Thermoelectric Power Plants

by Orlando Duran^1,*, Andrea Capaldo² and Paulo Andrés Duran Acevedo³

¹ Mechanical Engineering School, Pontificia Universidad Católica de Valparaíso, Valparaiso 2430000, Chile

² Department of Mechanical Engineering, Politécnico de Milán, Politecnico de Milán, 20133 Milano MI, Italy

³ Inacap Valparaiso, Universidad Tecnológica de Chile INACAP, Valparaiso 2430000, Chile

Energies 2017, 10(10), 1653; https://doi.org/10.3390/en10101653 - 19 Oct 2017

Cited by 24 | Viewed by 8461

Abstract

Thermoelectric power plants consist of a set of critical equipment that require high levels of availability and reliability. Due to this, maintenance of these physical assets is gaining momentum in industry. Maintenance is considered as an activity that contributes to improving the availability, [...] Read more.

Thermoelectric power plants consist of a set of critical equipment that require high levels of availability and reliability. Due to this, maintenance of these physical assets is gaining momentum in industry. Maintenance is considered as an activity that contributes to improving the availability, efficiency and productivity of each piece of equipment. Several techniques have been used to achieve greater efficiencies in maintenance, among which we can find the lean maintenance philosophy. Despite the wide diffusion of lean maintenance, there is no structured method that supports the prescription of lean tools applied to the maintenance function. This paper presents the experience gathered in two lean maintenance projects in thermoelectric power plants. The application of lean techniques was based on using a previously developed multicriterial decision making process that uses the Fuzzy Analytic Hierarchy Process (AHP) methodology to carry out a diagnosis and prescription tasks. That methodology allowed the prescription of the appropriated lean techniques to resolve the main deficiencies in maintenance function. The results of applying such lean tools show that important results can be obtained, making the maintenance function in thermoelectric power plants more efficient and lean. Full article

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

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20 pages, 2335 KiB

Open AccessArticle

Co-Digestion of Napier Grass and Its Silage with Cow Dung for Methane Production

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

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

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

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

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

Energies 2017, 10(10), 1654; https://doi.org/10.3390/en10101654 - 19 Oct 2017

Cited by 35 | Viewed by 9148

Abstract

Methane production from co-digestion of grass with cow dung and silage with cow dung was conducted by a bioaugmentation technique. For self-fermentation, maximum methane yield (MY) of 176.66 and 184.94 mL CH₄/g-VS_added were achieved at a ratio of grass to [...] Read more.

Methane production from co-digestion of grass with cow dung and silage with cow dung was conducted by a bioaugmentation technique. For self-fermentation, maximum methane yield (MY) of 176.66 and 184.94 mL CH₄/g-VS_added were achieved at a ratio of grass to cow dung and silage to cow dung of 1:1, respectively. A higher maximum MY of 179.59 and 208.11 mL CH₄/g-VS_added was obtained from co-digestion of grass with cow dung and silage with cow dung bioaugmented with anaerobic sludge at a ratio of 3:1. The solid residue left over after co-digestion at a ratio of 3:1 was pretreated by alkaline plus enzyme before used to produce methane and a maximum MY of 333.63 and 301.38 mL CH₄/g-VS_added, respectively, was achieved. Overall power generated from co-digestion of grass with cow dung plus pretreated solid residues and co-digestion of silage with cow dung plus pretreated solid residues were 0.0397 and 0.007 watt, respectively. Full article

(This article belongs to the Collection Bioenergy and Biofuel)

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15 pages, 9904 KiB

Open AccessArticle

Noncontact Measurement and Detection of Instantaneous Seismic Attributes Based on Complementary Ensemble Empirical Mode Decomposition

by Yaping Huang^1,2,3

, Haibin Di⁴

, Reza Malekian⁵

, Xuemei Qi^1,* and Zhixiong Li⁶

¹ School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, China

² Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720, USA

³ Key Laboratory of Coal Methane and Fire Control, Ministry of Education, China University of Mining and Technology, Xuzhou 221116, China

⁴ Center for Energy and Geo Processing (CeGP), Georgia Institute of Technology, Atlanta, GA 30308, USA

⁵ Department of Electrical, Electronic & Computer Engineering, University of Pretoria, Pretoria 0002, South Africa

⁶ School of Mechatronics Engineering, China University of Mining and Technology, Xuzhou 221106, China

Energies 2017, 10(10), 1655; https://doi.org/10.3390/en10101655 - 19 Oct 2017

Cited by 8 | Viewed by 5806

Abstract

Hilbert–Huang transform (HHT) is a popular method to analyze nonlinear and non-stationary data. It has been widely used in geophysical prospecting. This paper analyzes the mode mixing problems of empirical mode decomposition (EMD) and introduces the noncontact measurement and detection of instantaneous seismic [...] Read more.

Hilbert–Huang transform (HHT) is a popular method to analyze nonlinear and non-stationary data. It has been widely used in geophysical prospecting. This paper analyzes the mode mixing problems of empirical mode decomposition (EMD) and introduces the noncontact measurement and detection of instantaneous seismic attributes using complementary ensemble empirical mode decomposition (CEEMD). Numerical simulation testing indicates that the CEEMD can effectively solve the mode mixing problems of EMD and can provide stronger anti-noise ability. The decomposed results of the synthetic seismic record show that CEEMD has a better ability to decompose seismic signals. Then, CEEMD is applied to extract instantaneous seismic attributes of 3D seismic data in a real-world coal mine in Inner Mongolia, China. The detection results demonstrate that instantaneous seismic attributes extracted by CEEMD are helpful to effectively identify the undulations of the top interfaces of limestone. Full article

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

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20 pages, 6564 KiB

Open AccessFeature PaperReview

Constant Power Loads (CPL) with Microgrids: Problem Definition, Stability Analysis and Compensation Techniques

by Mohammed Kh. AL-Nussairi^1,2

, Ramazan Bayindir²

, Sanjeevikumar Padmanaban^3,*

, Lucian Mihet-Popa⁴

and Pierluigi Siano⁵

¹ Department of Electrical Engineering, College of Engineering, University of Misan, Al-Amarah, Misan 62001, Iraq

² Department of Electrical and Electronic Engineering, Faculty of Engineering, Gazi University, Besevler, Ankara 06500, Turkey

³ Department of Electrical and Electronics Engineering Science, University of Johannesburg, Auckland Park, Johannesburg 2006, South Africa

⁴ Faculty of Engineering, Østfold University College, Kobberslagerstredet 5, 1671 Kråkeroy, Norway

⁵ Department of Industrial Engineering, University of Salerno, Salerno, 84084 Fisciano (SA), Italy

Energies 2017, 10(10), 1656; https://doi.org/10.3390/en10101656 - 19 Oct 2017

Cited by 132 | Viewed by 17901

Abstract

This paper provides a comprehensive review of the major concepts associated with the μgrid, such as constant power load (CPL), incremental negative resistance or impedance (INR/I) and its dynamic behaviours on the μgrid, and power system distribution (PSD). In general, a μgrid is [...] Read more.

This paper provides a comprehensive review of the major concepts associated with the μgrid, such as constant power load (CPL), incremental negative resistance or impedance (INR/I) and its dynamic behaviours on the μgrid, and power system distribution (PSD). In general, a μgrid is defined as a cluster of different types of electrical loads and renewable energy sources (distributed generations) under a unified controller within a certain local area. It is considered a perfect solution to integrate renewable energy sources with loads as well as with a traditional grid. In addition, it can operate with a conventional grid, for example, by energy sourcing or a controllable load, or it can operate alone as an islanding mode to feed required electric energy to a grid. Hence, one of the important issues regarding the μgrid is the constant power load that results from the tightly designed control when it is applied to power electronic converters. The effect of CPL is incremental negative resistance that impacts the power quality of a power system and makes it at negative damping. Also, in this paper, a comprehensive study on major control and compensation techniques for μgrid has been included to face the instability effects of constant power loads. Finally, the merits and limitations of the compensation techniques are discussed. Full article

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

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14 pages, 3584 KiB

Open AccessArticle

Grid-Connected Control Strategy of Five-level Inverter Based on Passive E-L Model

by Tao Li

, Qiming Cheng^*, Weisha Sun and Lu Chen

College of Automation Engineering, Shanghai University of Electric Power, Shanghai 200090, China

Energies 2017, 10(10), 1657; https://doi.org/10.3390/en10101657 - 19 Oct 2017

Cited by 13 | Viewed by 5056

Abstract

At present, the research on five-level inverters mainly involves the modulation algorithm and topology, and few articles study the five-level inverter from the control strategy. In this paper, the nonlinear passivity-based control (PBC) method is proposed for single-phase uninterruptible power supply inverters. The [...] Read more.

At present, the research on five-level inverters mainly involves the modulation algorithm and topology, and few articles study the five-level inverter from the control strategy. In this paper, the nonlinear passivity-based control (PBC) method is proposed for single-phase uninterruptible power supply inverters. The proposed PBC method is based on an energy shaping and damping injection idea, which is performed to regulate the energy flow of an inverter to a desired level and to assure global asymptotic stability, respectively. Furthermore, this paper presents a control algorithm based on the theory of passivity that gives an inverter in a photovoltaic system additional functions: power factor correction, harmonic currents compensation, and the ability to stabilize the system under varying injection damping. Finally, the effectiveness of the PBC method in terms of both stability and harmonic distortion is verified by the simulation and experiments under resistive and inductive loads. Full article

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

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20 pages, 1117 KiB

Open AccessArticle

Newton Power Flow Methods for Unbalanced Three-Phase Distribution Networks

by Baljinnyam Sereeter^*

, Kees Vuik and Cees Witteveen

Faculty of Electrical Engineering, Mathematics and Computer Science, Delft University of Technology, Mekelweg 4, 2628 CD Delft, The Netherlands

Energies 2017, 10(10), 1658; https://doi.org/10.3390/en10101658 - 20 Oct 2017

Cited by 61 | Viewed by 9655

Abstract

Two mismatch functions (power or current) and three coordinates (polar, Cartesian and complex form) result in six versions of the Newton–Raphson method for the solution of power flow problems. In this paper, five new versions of the Newton power flow method developed for [...] Read more.

Two mismatch functions (power or current) and three coordinates (polar, Cartesian and complex form) result in six versions of the Newton–Raphson method for the solution of power flow problems. In this paper, five new versions of the Newton power flow method developed for single-phase problems in our previous paper are extended to three-phase power flow problems. Mathematical models of the load, load connection, transformer, and distributed generation (DG) are presented. A three-phase power flow formulation is described for both power and current mismatch functions. Extended versions of the Newton power flow method are compared with the backward-forward sweep-based algorithm. Furthermore, the convergence behavior for different loading conditions,

R / X

ratios, and load models, is investigated by numerical experiments on balanced and unbalanced distribution networks. On the basis of these experiments, we conclude that two versions using the current mismatch function in polar and Cartesian coordinates perform the best for both balanced and unbalanced distribution networks. Full article

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

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37 pages, 4603 KiB

Open AccessArticle

Dynamic Modeling and Simulation of Deep Geothermal Electric Submersible Pumping Systems

by Julian Kullick^*

and Christoph M. Hackl

Munich School of Engineering, Research Group “Control of Renewable Energy Systems”, Technical University of Munich, Lichtenbergstraße 4a, 85748 Garching, Germany

Energies 2017, 10(10), 1659; https://doi.org/10.3390/en10101659 - 21 Oct 2017

Cited by 9 | Viewed by 7825

Abstract

Deep geothermal energy systems employ electric submersible pumps (ESPs) in order to lift geothermal fluid from the production well to the surface. However, rough downhole conditions and high flow rates impose heavy strain on the components, leading to frequent failures of the pump [...] Read more.

Deep geothermal energy systems employ electric submersible pumps (ESPs) in order to lift geothermal fluid from the production well to the surface. However, rough downhole conditions and high flow rates impose heavy strain on the components, leading to frequent failures of the pump system. As downhole sensor data is limited and often unrealible, a detailed and dynamical model system will serve as basis for deeper understanding and analysis of the overall system behavior. Furthermore, it allows to design model-based condition monitoring and fault detection systems, and to improve controls leading to a more robust and efficient operation. In this paper, a detailed state-space model of the complete ESP system is derived, covering the electrical, mechanical and hydraulic subsystems. Based on the derived model, the start-up phase of an exemplary yet realistic ESP system in the Megawatt range—located at a setting depth of 950

m

and producing geothermal fluid of 140

^{\circ} C

temperature at a rate of 0.145

m^{3} s^{- 1}

—is simulated in MATLAB/Simulink. The simulation results show that the system reaches a stable operating point with realistic values. Furthermore, the effect of self-excitation between the filter capacitor and the motor inductor can clearly be observed. A full set of parameters is provided, allowing for direct model implementation and reproduction of the presented results. Full article

(This article belongs to the Special Issue Low Enthalpy Geothermal Energy)

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26 pages, 23206 KiB

Open AccessEditor’s ChoiceArticle

Predictions of Surface Solar Radiation on Tilted Solar Panels using Machine Learning Models: A Case Study of Tainan City, Taiwan

by Chih-Chiang Wei

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

Energies 2017, 10(10), 1660; https://doi.org/10.3390/en10101660 - 20 Oct 2017

Cited by 37 | Viewed by 9390

Abstract

In this paper, forecasting models were constructed to estimate surface solar radiation on an hourly basis and the solar irradiance received by solar panels at different tilt angles, to enhance the capability of photovoltaic systems by estimating the amount of electricity they generate, [...] Read more.

In this paper, forecasting models were constructed to estimate surface solar radiation on an hourly basis and the solar irradiance received by solar panels at different tilt angles, to enhance the capability of photovoltaic systems by estimating the amount of electricity they generate, thereby improving the reliability of the power they supply. The study site was Tainan in southern Taiwan, which receives abundant sunlight because of its location at a latitude of approximately 23°. Four forecasting models of surface solar irradiance were constructed, using the multilayer perceptron (MLP), random forests (RF), k-nearest neighbors (kNN), and linear regression (LR), algorithms, respectively. The forecast horizon ranged from 1 to 12 h. The findings are as follows: first, solar irradiance was effectively estimated when a combination of ground weather data and solar position data was applied. Second, the mean absolute error was higher in MLP than in RF and kNN, and LR had the worst predictive performance. Third, the observed total solar irradiance was 1.562 million w/m² per year when the solar-panel tilt angle was 0° (i.e., the non-tilted position) and peaked at 1.655 million w/m² per year when the angle was 20–22°. The level of the irradiance was almost the same when the solar-panel tilt angle was 0° as when the angle was 41°. In summary, the optimal solar-panel tilt angle in Tainan was 20–22°. Full article

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

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13 pages, 3389 KiB

Open AccessArticle

Risk Assessment of Failure of Outdoor High Voltage Polluted Insulators under Combined Stresses Near Shoreline

by Muhammad Majid Hussain^1,*

, Shahab Farokhi¹, Scott G. McMeekin¹ and Masoud Farzaneh²

¹ School of Engineering and Built Environment, Glasgow Caledonian University, Glasgow G4 0BA, UK

² Department of Applied Sciences, University of Quebec at Chicoutimi, Saguenay, QC G7H 2B1, Canada

Energies 2017, 10(10), 1661; https://doi.org/10.3390/en10101661 - 20 Oct 2017

Cited by 23 | Viewed by 4948

Abstract

The aim of this paper is to investigate the various effects of climate conditions on outdoor insulators in coastal areas as a result of saline contamination under acidic and normal cold fog, determining significant electrical and physico-chemical changes on the insulator surface and [...] Read more.

The aim of this paper is to investigate the various effects of climate conditions on outdoor insulators in coastal areas as a result of saline contamination under acidic and normal cold fog, determining significant electrical and physico-chemical changes on the insulator surface and considering the effect of discharge current, electric field distribution and surface roughness. To replicate similar conditions near the shoreline, experimental investigations have been carried out on insulation materials with the combined application of saline contamination and acidic or normal cold fog. The test samples included silicone rubber (SiR), ethylene propylene diene monomer (EPDM) and high-density polyethylene (HDPE), which were used as reference. The materials are of the same composition as those used in real-life outdoor high voltage insulators. All samples were aged separately in an environmental chamber for 150 h for various saline contaminations combined with acidic and normal cold fog, and were generated by means of the adopted experimental setup. This analysis represented conditions similar to those existing near the shoreline exposed to saline and acid spray during winter and early spring. Electric field and discharge current along polymeric samples were examined under acidic and normal cold fog. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopic (SEM) were used to probe the physico-chemical changes on the samples surface and investigate the hydrophobicity recovery property after aging tests. Finally, a comparative study was carried out on polymeric samples before and after being exposed to the acidic and normal cold fog based on the results obtained from the experiment. Research data may provide references for the better prediction of surface degradation as well as for the better material coating and design of external insulation. Full article

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8 pages, 2265 KiB

Open AccessArticle

The Heat Transfer of Microencapsulated Phase Change Material Slurry and Its Thermal Energy Storage Performance of Combined Heat and Power Generating Units

by Yonghong Guo¹, Xinglong Zhang², Lijun Yang¹, Chao Xu¹ and Xiaoze Du^1,*

¹ Key Laboratory of Condition Monitoring and Control for Power Plant Equipment (North China Electric Power University), Ministry of Education, Beijing 102206, China

² Northeast Electric Power Design Institute Co., Ltd of China Power Engineering Consulting Group, Changchun 13002, China

Energies 2017, 10(10), 1662; https://doi.org/10.3390/en10101662 - 20 Oct 2017

Cited by 12 | Viewed by 4539

Abstract

The application of thermal energy storage (TES) is an effective way of improving the power load regulation capability of combined heat and power (CHP) generating units. In this paper, a theoretical investigation on the thermal energy storage system of a CHP unit that [...] Read more.

The application of thermal energy storage (TES) is an effective way of improving the power load regulation capability of combined heat and power (CHP) generating units. In this paper, a theoretical investigation on the thermal energy storage system of a CHP unit that employs the microencapsulated phase change material slurry (MPCMS) as the working fluid is carried out. The results indicate that the microcapsule particle internal melting rate is progressively small; 90% latent heat can be absorbed in 63% total melting time. The melting time of particles in micron is very short, and the diameter is an important factor for microcapsule melting. For the MPCMS flow in a circular tube, the temperature distribution between laminar flows and turbulent flows is different. In a turbulent flow, there is an approximate isothermal section along the tube, which cannot be found in a laminar flow. Additionally, a thermal storage system with MPCMS as heat transfer fluid for a CHP unit is proposed. A case study for a 300 MW CHP unit found that the use of an MPSMS thermal energy storage system increases the power peak shaving capacity by 81.4%. This indicates that the thermal storage system increases the peak shaving capacity of cogeneration units. Full article

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24 pages, 4273 KiB

Open AccessArticle

A Multi-Energy System Expansion Planning Method Using a Linearized Load-Energy Curve: A Case Study in South Korea

by Woong Ko¹, Jong-Keun Park¹, Mun-Kyeom Kim^2,* and Jae-Haeng Heo³

¹ School of Electrical Engineering & Computer Science, Seoul National University, Gwanak-ro 1, Gwanak-gu, Seoul 08826, Korea

² Department of Energy System Engineering, Chung-Ang University, 84 Heukseok-ro, Dongjak-gu, Seoul 06974, Korea

³ Research and Development Laboratory, Raonfreinds, 23, 16 Cheomdanbencheo-ro, Buk-gu, Gwangju 61009, Korea

Energies 2017, 10(10), 1663; https://doi.org/10.3390/en10101663 - 20 Oct 2017

Cited by 15 | Viewed by 5465

Abstract

Multi-energy systems can integrate heat and electrical energy efficiently, using resources such as cogeneration. In order to meet energy demand cost-effectively in a multi-energy system, adopting appropriate energy resources at the right time is of great importance. In this paper, we propose an [...] Read more.

Multi-energy systems can integrate heat and electrical energy efficiently, using resources such as cogeneration. In order to meet energy demand cost-effectively in a multi-energy system, adopting appropriate energy resources at the right time is of great importance. In this paper, we propose an expansion planning method for a multi-energy system that supplies heat and electrical energy. The proposed approach formulates expansion planning as a mixed integer linear programming (MILP) problem. The objective is to minimize the sum of the annualized cost of the multi-energy system. The candidate resources that constitute the cost of the multi-energy system are fuel-based power generators, heat-only boilers, a combined heat and power (CHP) unit, energy storage resources, and a renewable electrical power source. We use a load-energy curve, instead of a load-duration curve, for constructing the optimization model, which is subsequently linearized using a Douglas-Peucker algorithm. The residual load-energy curve, for utilizing the renewable electrical power source, is also linearized. This study demonstrates the effectiveness of the proposed method through a comparison with a conventional linearization method. In addition, we evaluate the cost and planning schedules of different case studies, according to the configuration of resources in the multi-energy system. Full article

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

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17 pages, 2848 KiB

Open AccessArticle

Multi-Objective Optimal Design of Stand-Alone Hybrid Energy System Using Entropy Weight Method Based on HOMER

by Jiaxin Lu^1,*, Weijun Wang^1,*

, Yingchao Zhang² and Song Cheng²

¹ Department of Electrical Engineering, Army Logistics University of PLA, Chongqing 401331, China

² Department of Electrical Engineering, Chongqing Communication Institute, Chongqing 400036, China

Energies 2017, 10(10), 1664; https://doi.org/10.3390/en10101664 - 20 Oct 2017

Cited by 89 | Viewed by 6317

Abstract

Implementation of hybrid energy system (HES) is generally considered as a promising way to satisfy the electrification requirements for remote areas. In the present study, a novel decision making methodology is proposed to identify the best compromise configuration of HES from a set [...] Read more.

Implementation of hybrid energy system (HES) is generally considered as a promising way to satisfy the electrification requirements for remote areas. In the present study, a novel decision making methodology is proposed to identify the best compromise configuration of HES from a set of feasible combinations obtained from HOMER. For this purpose, a multi-objective function, which comprises four crucial and representative indices, is formulated by applying the weighted sum method. The entropy weight method is employed as a quantitative methodology for weighting factors calculation to enhance the objectivity of decision-making. Moreover, the optimal design of a stand-alone PV/wind/battery/diesel HES in Yongxing Island, China, is conducted as a case study to validate the effectiveness of the proposed method. Both the simulation and optimization results indicate that, the optimization method is able to identify the best trade-off configuration among system reliability, economy, practicability and environmental sustainability. Several useful conclusions are given by analyzing the operation of the best configuration. Full article

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

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13 pages, 3031 KiB

Open AccessArticle

A Maximum Power Transfer Tracking Method for WPT Systems with Coupling Coefficient Identification Considering Two-Value Problem

by Xin Dai^*

, Xiaofei Li

, Yanling Li, Pengqi Deng

and Chunsen Tang

College of Automation, Chongqing University, Chongqing 400044, China

Energies 2017, 10(10), 1665; https://doi.org/10.3390/en10101665 - 20 Oct 2017

Cited by 18 | Viewed by 4850

Abstract

Maximum power transfer tracking (MPTT) is meant to track the maximum power point during the system operation of wireless power transfer (WPT) systems. Traditionally, MPTT is achieved by impedance matching at the secondary side when the load resistance is varied. However, due to [...] Read more.

Maximum power transfer tracking (MPTT) is meant to track the maximum power point during the system operation of wireless power transfer (WPT) systems. Traditionally, MPTT is achieved by impedance matching at the secondary side when the load resistance is varied. However, due to a loosely coupling characteristic, the variation of coupling coefficient will certainly affect the performance of impedance matching, therefore MPTT will fail accordingly. This paper presents an identification method of coupling coefficient for MPTT in WPT systems. Especially, the two-value issue during the identification is considered. The identification approach is easy to implement because it does not require additional circuit. Furthermore, MPTT is easy to realize because only two easily measured DC parameters are needed. The detailed identification procedure corresponding to the two-value issue and the maximum power transfer tracking process are presented, and both the simulation analysis and experimental results verified the identification method and MPTT. Full article

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

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13 pages, 9604 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Energy Production by Means of Pumps As Turbines in Water Distribution Networks

by Mauro Venturini^*

, Stefano Alvisi

, Silvio Simani

and Lucrezia Manservigi

Dipartimento di Ingegneria, Università degli Studi di Ferrara, 44122 Ferrara, Italy

Energies 2017, 10(10), 1666; https://doi.org/10.3390/en10101666 - 20 Oct 2017

Cited by 31 | Viewed by 4794

Abstract

This paper deals with the estimation of the energy production by means of pumps used as turbines to exploit residual hydraulic energy, as in the case of available head and flow rate in water distribution networks. To this aim, four pumps with different [...] Read more.

This paper deals with the estimation of the energy production by means of pumps used as turbines to exploit residual hydraulic energy, as in the case of available head and flow rate in water distribution networks. To this aim, four pumps with different characteristics are investigated to estimate the producible yearly electric energy. The performance curves of Pumps As Turbines (PATs), which relate head, power, and efficiency to the volume flow rate over the entire PAT operation range, were derived by using published experimental data. The four considered water distribution networks, for which experimental data taken during one year were available, are characterized by significantly different hydraulic features (average flow rate in the range 10–116 L/s; average pressure reduction in the range 12–53 m). Therefore, energy production accounts for actual flow rate and head variability over the year. The conversion efficiency is also estimated, for both the whole water distribution network and the PAT alone. Full article

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21 pages, 2724 KiB

Open AccessArticle

A Mobile Battery Swapping Service for Electric Vehicles Based on a Battery Swapping Van

by Sujie Shao^*

, Shaoyong Guo and Xuesong Qiu

State Key Laboratory of Networking and Switching Technology, Beijing University of Posts and Telecommunications, Beijing 100876, China

Energies 2017, 10(10), 1667; https://doi.org/10.3390/en10101667 - 20 Oct 2017

Cited by 71 | Viewed by 12571

Abstract

This paper presents a novel approach for providing a mobile battery swapping service for electric vehicles (EVs) that is provided by a mobile battery swapping van. This battery swapping van can carry many fully charged batteries and drive up to an EV to [...] Read more.

This paper presents a novel approach for providing a mobile battery swapping service for electric vehicles (EVs) that is provided by a mobile battery swapping van. This battery swapping van can carry many fully charged batteries and drive up to an EV to swap a battery within a few minutes. First, a reasonable EV battery swapping architecture based on a battery swapping van is established in this paper. The function and role of each participant and the relationships between each participant are determined, especially their changes compared with the battery charging service. Second, the battery swapping service is described, including the service request priority and service request queuing model. To provide the battery swapping service efficiently and effectively, the battery swapping service request scheduling is analyzed well, and a minimum waiting time based on priority and satisfaction scheduling strategy (MWT-PS) is proposed. Finally, the battery swapping service is simulated, and the performance of MWT-PS is evaluated in simulation scenarios. The simulation results show that this novel approach can be used as a reference for a future system that provides reasonable and satisfying battery swapping service for EVs. Full article

(This article belongs to the Special Issue Battery Energy Storage Applications in Smart Grid)

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20 pages, 888 KiB

Open AccessArticle

Learning-Based Adaptive Imputation Methodwith kNN Algorithm for Missing Power Data

by Minkyung Kim¹, Sangdon Park¹, Joohyung Lee^2,*, Yongjae Joo³ and Jun Kyun Choi¹

¹ Department of Electrical Engineering, Korea Advanced Institute of Science and Technology, Daejeon 34141, Korea

² Department of Software, Gachon University, Seongnam 13120, Korea

³ Korea Electric Power Research Institute, Daejeon 305-760, Korea

Energies 2017, 10(10), 1668; https://doi.org/10.3390/en10101668 - 21 Oct 2017

Cited by 62 | Viewed by 6366

Abstract

This paper proposes a learning-based adaptive imputation method (LAI) for imputing missing power data in an energy system. This method estimates the missing power data by using the pattern that appears in the collected data. Here, in order to capture the patterns from [...] Read more.

This paper proposes a learning-based adaptive imputation method (LAI) for imputing missing power data in an energy system. This method estimates the missing power data by using the pattern that appears in the collected data. Here, in order to capture the patterns from past power data, we newly model a feature vector by using past data and its variations. The proposed LAI then learns the optimal length of the feature vector and the optimal historical length, which are significant hyper parameters of the proposed method, by utilizing intentional missing data. Based on a weighted distance between feature vectors representing a missing situation and past situation, missing power data are estimated by referring to the k most similar past situations in the optimal historical length. We further extend the proposed LAI to alleviate the effect of unexpected variation in power data and refer to this new approach as the extended LAI method (eLAI). The eLAI selects a method between linear interpolation (LI) and the proposed LAI to improve accuracy under unexpected variations. Finally, from a simulation under various energy consumption profiles, we verify that the proposed eLAI achieves about a 74% reduction of the average imputation error in an energy system, compared to the existing imputation methods. Full article

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16 pages, 2496 KiB

Open AccessArticle

An Optimized Prediction Intervals Approach for Short Term PV Power Forecasting

by Qiang Ni^1,*, Shengxian Zhuang¹, Hanmin Sheng², Song Wang¹ and Jian Xiao¹

¹ School of Electric Engineering, Southwest Jiangtong University, Chengdu 610031, China

² School of Automation Engineering, University of Electronic Science and Technology of China, Chengdu 610031, China

Energies 2017, 10(10), 1669; https://doi.org/10.3390/en10101669 - 23 Oct 2017

Cited by 25 | Viewed by 4014

Abstract

High quality photovoltaic (PV) power prediction intervals (PIs) are essential to power system operation and planning. To improve the reliability and sharpness of PIs, in this paper, a new method is proposed, which involves the model uncertainties and noise uncertainties, and PIs are [...] Read more.

High quality photovoltaic (PV) power prediction intervals (PIs) are essential to power system operation and planning. To improve the reliability and sharpness of PIs, in this paper, a new method is proposed, which involves the model uncertainties and noise uncertainties, and PIs are constructed with a two-step formulation. In the first step, the variance of model uncertainties is obtained by using extreme learning machine to make deterministic forecasts of PV power. In the second stage, innovative PI-based cost function is developed to optimize the parameters of ELM and noise uncertainties are quantization in terms of variance. The performance of the proposed approach is examined by using the PV power and meteorological data measured from 1kW rooftop DC micro-grid system. The validity of the proposed method is verified by comparing the experimental analysis with other benchmarking methods, and the results exhibit a superior performance. Full article

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

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14 pages, 6263 KiB

Open AccessArticle

An Improved Coordinated Control Strategy for PV System Integration with VSC-MVDC Technology

by Yanbo Che^1,*

, Wenxun Li¹, Xialin Li¹, Jinhuan Zhou¹, Shengnan Li² and Xinze Xi²

¹ Key Laboratory of Smart Grid of Ministry of Education, Tianjin University, Tianjin 300072, China

² Electric Power Research Institute of Yunnan Power Grid Co. Ltd., Kunming 650217, China

Energies 2017, 10(10), 1670; https://doi.org/10.3390/en10101670 - 22 Oct 2017

Cited by 11 | Viewed by 5026

Abstract

The rapid development of renewable energy calls for feasible and reliable technologies to transmit and integrate power into grids. Voltage Source Converter (VSC)- Direct Current (DC) technology is considered as a promising solution for its independent control of active and reactive power. Modeling [...] Read more.

The rapid development of renewable energy calls for feasible and reliable technologies to transmit and integrate power into grids. Voltage Source Converter (VSC)- Direct Current (DC) technology is considered as a promising solution for its independent control of active and reactive power. Modeling and coordinated control of a large-scale concentrating photovoltaic integration system with VSC-MVDC (Voltage Source Converter-Medium Voltage Direct Current) technology have been investigated in this paper. The average controlled-source model of PhotoVoltaic (PV) integration system is firstly established. Then, a novel control strategy without fast communication is proposed to improve the reliability of the coordinated control system. An extra voltage loop is added to the basic control block, which is able to assure stable operation of the PV system in various conditions. Finally, the proposed control strategy is verified with simulation results. Full article

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

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14 pages, 3233 KiB

Open AccessArticle

Laser Radiation Induces Growth and Lipid Accumulation in the Seawater Microalga Chlorella pacifica

by Haonan Zhang^†, Zhengquan Gao^*,†, Zhe Li, Huanmin Du, Bin Lin, Meng Cui, Yonghao Yin, Fengming Lei, Chunyu Yu and Chunxiao Meng^*

¹ School of Life Sciences, Shandong University of Technology, Zibo 255049, China

^† These authors equally contributed to this work.

Energies 2017, 10(10), 1671; https://doi.org/10.3390/en10101671 - 22 Oct 2017

Cited by 11 | Viewed by 4248

Abstract

The impacts of laser radiation (Nd: YAG laser, 1064 nm at 800 mW, He–Ne laser 808 nm at 6 W, semiconductor laser 632.8 nm at 40 mW) on growth and lipid accumulation of Chlorella pacifica were investigated in this study. The results showed [...] Read more.

The impacts of laser radiation (Nd: YAG laser, 1064 nm at 800 mW, He–Ne laser 808 nm at 6 W, semiconductor laser 632.8 nm at 40 mW) on growth and lipid accumulation of Chlorella pacifica were investigated in this study. The results showed growth rates increased 1.23, 1.41, and 1.40-fold over controls by 4 min Nd: YAG, 4 min He–Ne, and 8 min semiconductor laser treatments, respectively, whereas the corresponding nitrate reductase observed increased 1.25, 1.63, and 2.08-fold over controls. Moreover, total chlorophyll concentration was increased to 1.09, 1.29, and 1.33-fold over controls, respectively. After 20 days cultivation, the highest lipid content was 35.99%, 18.46%, and 31.00% after 2 min Nd: YAG, 4 min He–Ne, and 4 min semiconductor laser treatments, corresponding to 2.86, 1.50, and 2.46-fold increase over controls, respectively. Furthermore, the lipid productivity of the above 3 treatments were 15.25 ± 2.56, 16.25 ± 2.45, and 14.75 ± 2.11 mg L⁻¹ d⁻¹. However, the highest lipid productivity was 22.00 ± 3.28, 16.25 ± 2.45, and 19.25 ± 1.78 mg L⁻¹ d⁻¹, in response to treatment for 2 min Nd: YAG, 1 min He–Ne, and 4 min semiconductor laser treatments, with 2.67, 1.97, and 2.33-fold increase over controls, respectively. These results indicated that lipid accumulation efficiency of C. pacifica could be significantly improved by laser irradiation using Nd: YAG, He–Ne, and semiconductor laser treatments. Full article

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

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32 pages, 8785 KiB

Open AccessReview

Building Applications, Opportunities and Challenges of Active Shading Systems: A State-of-the-Art Review

by Joud Al Dakheel and Kheira Tabet Aoul^*

Architectural Engineering Department, United Arab Emirates University, P.O. Box 15551 Al Ain, UAE

Energies 2017, 10(10), 1672; https://doi.org/10.3390/en10101672 - 23 Oct 2017

Cited by 98 | Viewed by 14568

Abstract

Active shading systems in buildings have emerged as a high performing shading solution that selectively and optimally controls daylight and heat gains. Active shading systems are increasingly used in buildings, due to their ability to mainly improve the building environment, reduce energy consumption [...] Read more.

Active shading systems in buildings have emerged as a high performing shading solution that selectively and optimally controls daylight and heat gains. Active shading systems are increasingly used in buildings, due to their ability to mainly improve the building environment, reduce energy consumption and in some cases generate energy. They may be categorized into three classes: smart glazing, kinetic shading and integrated renewable energy shading. This paper reviews the current status of the different types in terms of design principle and working mechanism of the systems, performance, control strategies and building applications. Challenges, limitations and future opportunities of the systems are then discussed. The review highlights that despite its high initial cost, the electrochromic (EC) glazing is the most applied smart glazing due to the extensive use of glass in buildings under all climatic conditions. In terms of external shadings, the rotating shading type is the predominantly used one in buildings due to its low initial cost. Algae façades and folding shading systems are still emerging types, with high initial and maintenance costs and requiring specialist installers. The algae façade systems and PV integrated shading systems are a promising solution due to their dual benefits of providing shading and generating electricity. Active shading systems were found to save 12 to 50% of the building cooling electricity consumption. Full article

(This article belongs to the Special Issue Selected Papers from ZEMCH 2016: Building Energy Performance Evaluation/Simulation)

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19 pages, 1177 KiB

Open AccessArticle

Performance Assessment of Black Box Capacity Forecasting for Multi-Market Trade Application

by Pamela MacDougall^1,3,*

, Bob Ran¹, George B. Huitema^1,2 and Geert Deconinck³

¹ Monitoring and Control Services, TNO, 9701 BK Groningen, The Netherlands

² Faculty of Economics and Business, University of Groningen, 9700 AV Groningen, The Netherlands

³ Department of Electrical Engineering, University of Leuven, 3001 Leuven, Belgium

Energies 2017, 10(10), 1673; https://doi.org/10.3390/en10101673 - 23 Oct 2017

Cited by 9 | Viewed by 4442

Abstract

With the growth of renewable generated electricity in the energy mix, large energy storage and flexible demand, particularly aggregated demand response is becoming a front runner as a new participant in the wholesale energy markets. One of the biggest barriers for the integration [...] Read more.

With the growth of renewable generated electricity in the energy mix, large energy storage and flexible demand, particularly aggregated demand response is becoming a front runner as a new participant in the wholesale energy markets. One of the biggest barriers for the integration of aggregator services into market participation is knowledge of the current and future flexible capacity. To calculate the available flexibility, the current aggregator pilot and simulation implementations use lower level measurements and device specifications. This type of implementation is not scalable due to computational constraints, as well as it could conflict with end user privacy rights. Black box machine learning approaches have been proven to accurately estimate the available capacity of a cluster of heating devices using only aggregated data. This study will investigate the accuracy of this approach when applied to a heterogeneous virtual power plant (VPP). Firstly, a sensitivity analysis of the machine learning model is performed when varying the underlying device makeup of the VPP. Further, the forecasted flexible capacity of a heterogeneous residential VPP was applied to a trade strategy, which maintains a day ahead schedule, as well as offers flexibility to the imbalance market. This performance is then compared when using the same strategy with no capacity forecasting, as well as perfect knowledge. It was shown that at most, the highest average error, regardless of the VPP makeup, was still less than 9%. Further, when applying the forecasted capacity to a trading strategy, 89% of the optimal performance can be met. This resulted in a reduction of monthly costs by approximately 20%. Full article

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

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11 pages, 3504 KiB

Open AccessArticle

A Comparative Study of CFD Models of a Real Wind Turbine in Solar Chimney Power Plants

by Ehsan Gholamalizadeh

and Jae Dong Chung^*

Department of Mechanical Engineering, Sejong University, Seoul 05006, Korea

Energies 2017, 10(10), 1674; https://doi.org/10.3390/en10101674 - 23 Oct 2017

Cited by 13 | Viewed by 6029

Abstract

A solar chimney power plant consists of four main parts, a solar collector, a chimney, an energy storage layer, and a wind turbine. So far, several investigations on the performance of the solar chimney power plant have been conducted. Among them, different approaches [...] Read more.

A solar chimney power plant consists of four main parts, a solar collector, a chimney, an energy storage layer, and a wind turbine. So far, several investigations on the performance of the solar chimney power plant have been conducted. Among them, different approaches have been applied to model the turbine inside the system. In particular, a real wind turbine coupled to the system was simulated using computational fluid dynamics (CFD) in three investigations. Gholamalizadeh et al. simulated a wind turbine with the same blade profile as the Manzanares SCPP’s turbine (FX W-151-A blade profile), while a CLARK Y blade profile was modelled by Guo et al. and Ming et al. In this study, simulations of the Manzanares prototype were carried out using the CFD model developed by Gholamalizadeh et al. Then, results obtained by modelling different turbine blade profiles at different turbine rotational speeds were compared. The results showed that a turbine with the CLARK Y blade profile significantly overestimates the value of the pressure drop across the Manzanares prototype turbine as compared to the FX W-151-A blade profile. In addition, modelling of both blade profiles led to very similar trends in changes in turbine efficiency and power output with respect to rotational speed. Full article

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15 pages, 2951 KiB

Open AccessArticle

A Novel Topology of Hybrid HVDC Circuit Breaker for VSC-HVDC Application

by Van-Vinh Nguyen¹, Ho-Ik Son¹, Thai-Thanh Nguyen¹

, Hak-Man Kim^1,2,*

and Chan-Ki Kim³

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

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

³ Transmission & Distribution Lab., The R&D Center of Korea Electric Power Co., 105 Munji-ro, Yuseong-gu, Daejeon 34056, Korea

Energies 2017, 10(10), 1675; https://doi.org/10.3390/en10101675 - 23 Oct 2017

Cited by 19 | Viewed by 7097

Abstract

The use of high voltage direct current (HVDC) circuit breakers (CBs) with the capabilities of bidirectional fault interruption, reclosing, and rebreaking can improve the reliable and safe operation of HVDC grids. Although several topologies of CBs have been proposed to perform these capabilities, [...] Read more.

The use of high voltage direct current (HVDC) circuit breakers (CBs) with the capabilities of bidirectional fault interruption, reclosing, and rebreaking can improve the reliable and safe operation of HVDC grids. Although several topologies of CBs have been proposed to perform these capabilities, the limitation of these topologies is either high on-state losses or long time interruption in the case bidirectional fault current interruption. Long time interruption results in the large magnitude of the fault current in the voltage source converter based HVDC (VSC-HVDC) system due to the high rate of rise of fault current. This paper proposes a new topology of hybrid CB (HCB) with lower conduction loss and lower interruption time to solve the problems. The proposed topology is based on the inverse current injection method, which uses the capacitor to enforce the fault current to zero. In the case of the bidirectional fault current interruption, the capacitor does not change its polarity after identifying the direction of fault current, which can reduce the interruption time accordingly. A switching control algorithm for the proposed topology is presented in detail. Different operation modes of proposed HCB, such as normal current mode, breaking fault current mode, discharging, and reversing capacitor voltage modes after clearing the fault, are considered in the proposed algorithm. The proposed topology with the switching control algorithm is tested in a simulation-based system. Different simulation scenarios such as temporary and permanent faults are carried out to verify the performance of the proposed topology. The simulation is performed in the Matlab/Simulink environment. Full article

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

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10 pages, 1316 KiB

Open AccessArticle

Solar-Enhanced Air-Cooled Heat Exchangers for Geothermal Power Plants

by Kamel Hooman^1,*

, Xiaoxue Huang² and Fangming Jiang²

¹ School of Mechanical and Mining Engineering, The University of Queensland, Brisbane, QLD 4072, Australia

² Laboratory of Advanced Energy Systems, Guangdong Key Laboratory of New and Renewable Energy Research and Development, CAS Key Laboratory of Renewable Energy, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences (CAS), Guangzhou 510640, China

Energies 2017, 10(10), 1676; https://doi.org/10.3390/en10101676 - 23 Oct 2017

Cited by 10 | Viewed by 4308

Abstract

This paper focuses on the optimization of a Solar-Enhanced Natural-Draft Dry-Cooling Tower (SENDDCT), originally designed by the Queensland Geothermal Energy Centre of Excellence (QGECE), as the air-cooled condenser of a geothermal power plant. The conventional method of heat transfer augmentation through fin-assisted area [...] Read more.

This paper focuses on the optimization of a Solar-Enhanced Natural-Draft Dry-Cooling Tower (SENDDCT), originally designed by the Queensland Geothermal Energy Centre of Excellence (QGECE), as the air-cooled condenser of a geothermal power plant. The conventional method of heat transfer augmentation through fin-assisted area extension is compared with a metal foam-wrapped tube bundle. Both lead to heat-transfer enhancement, albeit at the expense of a higher pressure drop when compared to the bare tube bundle as our reference case. An optimal design is obtained through the use of a simplified analytical model and existing correlations by maximizing the heat transfer rate with a minimum pressure drop goal as the constraint. Sensitivity analysis was conducted to investigate the effect of sunroof diameter, as well as tube bundle layouts and tube spacing, on the overall performance of the system. Aiming to minimize the flow and thermal resistances for a SENDDCT, an optimum design is presented for an existing tower to be equipped with solar panels to afterheat the air leaving the heat exchanger bundles, which are arranged vertically around the tower skirt. Finally, correlations are proposed to predict the total pressure drop and heat transfer of the extended surfaces considered here. Full article

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

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22 pages, 819 KiB

Open AccessArticle

Design of Parallel Air-Cooled Battery Thermal Management System through Numerical Study

by Kai Chen^1,*

, Zeyu Li¹, Yiming Chen¹, Shuming Long¹, Junsheng Hou¹, Mengxuan Song² and Shuangfeng Wang^1,*

¹ Key Laboratory of Enhanced Heat Transfer and Energy Conservation of the Ministry of Education, School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510640, China

² Department of Control Science and Engineering, Tongji University, Shanghai 201804, China

Energies 2017, 10(10), 1677; https://doi.org/10.3390/en10101677 - 23 Oct 2017

Cited by 82 | Viewed by 9558

Abstract

In electric vehicles, the battery pack is one of the most important components that strongly influence the system performance. The battery thermal management system (BTMS) is critical to remove the heat generated by the battery pack, which guarantees the appropriate working temperature for [...] Read more.

In electric vehicles, the battery pack is one of the most important components that strongly influence the system performance. The battery thermal management system (BTMS) is critical to remove the heat generated by the battery pack, which guarantees the appropriate working temperature for the battery pack. Air cooling is one of the most commonly-used solutions among various battery thermal management technologies. In this paper, the cooling performance of the parallel air-cooled BTMS is improved through choosing appropriate system parameters. The flow field and the temperature field of the system are calculated using the computational fluid dynamics method. Typical numerical cases are introduced to study the influences of the operation parameters and the structure parameters on the performance of the BTMS. The operation parameters include the discharge rate of the battery pack, the inlet air temperature and the inlet airflow rate. The structure parameters include the cell spacing and the angles of the divergence plenum and the convergence plenum. The results show that the temperature rise and the temperature difference of the batter pack are not affected by the inlet air flow temperature and are increased as the discharge rate increases. Increasing the inlet airflow rate can reduce the maximum temperature, but meanwhile significantly increase the power consumption for driving the airflow. Adopting smaller cell spacing can reduce the temperature and the temperature difference of the battery pack, but it consumes much more power. Designing the angles of the divergence plenum and the convergence plenum is an effective way to improve the performance of the BTMS without occupying more system volume. An optimization strategy is used to obtain the optimal values of the plenum angles. For the numerical cases with fixed power consumption, the maximum temperature and the maximum temperature difference at the end of the five-current discharge process for the optimized BTMS are respectively reduced by 2.1 K and 4.3 K, compared to the original system. Full article

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

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13 pages, 9405 KiB

Open AccessArticle

Characterization and Prediction of the Gas Hydrate Reservoir at the Second Offshore Gas Production Test Site in the Eastern Nankai Trough, Japan

by Machiko Tamaki^1,*, Tetsuya Fujii² and Kiyofumi Suzuki²

¹ Japan Oil Engineering Co., Ltd. (JOE), Kachidoki Sun-Square 1-7-3, Kachidoki, Chuo-ku, Tokyo 104-0054, Japan

² Japan Oil, Gas and Metals National Corporation (JOGMEC), 1-2-2 Hamada Mihama-ku, Chiba-shi, Chiba 261-0025, Japan

Energies 2017, 10(10), 1678; https://doi.org/10.3390/en10101678 - 23 Oct 2017

Cited by 75 | Viewed by 7894

Abstract

Following the world’s first offshore production test that was conducted from a gas hydrate reservoir by a depressurization technique in 2013, the second offshore production test has been planned in the eastern Nankai Trough. In 2016, the drilling survey was performed ahead of [...] Read more.

Following the world’s first offshore production test that was conducted from a gas hydrate reservoir by a depressurization technique in 2013, the second offshore production test has been planned in the eastern Nankai Trough. In 2016, the drilling survey was performed ahead of the production test, and logging data that covers the reservoir interval were newly obtained from three wells around the test site: one well for geological survey, and two wells for monitoring surveys, during the production test. The formation evaluation using the well log data suggested that our target reservoir has a more significant heterogeneity in the gas hydrate saturation distribution than we expected, although lateral continuity of sand layers is relatively good. To evaluate the spatial distribution of gas hydrate, the integration analysis using well and seismic data was performed. The seismic amplitude analysis supports the lateral reservoir heterogeneity that has a significant positive correlation with the resistivity log data at the well locations. The spatial distribution of the apparent low-resistivity interval within the reservoir observed from log data was investigated by the P-velocity volume derived from seismic inversion. The integrated results were utilized for the pre-drill prediction of the reservoir quality at the producing wells. These approaches will reduce the risk of future commercial production from the gas hydrate reservoir. Full article

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

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13 pages, 4377 KiB

Open AccessFeature PaperArticle

Flat Optical Fiber Daylighting System with Lateral Displacement Sun-Tracking Mechanism for Indoor Lighting

by Ngoc Hai Vu

and Seoyong Shin^*

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

Energies 2017, 10(10), 1679; https://doi.org/10.3390/en10101679 - 23 Oct 2017

Cited by 11 | Viewed by 6792

Abstract

An essential impact which can improve the indoor environment and save on power consumption for artificial lighting is utilization of daylight. Optical fiber daylighting technology offers a way to use direct daylight for remote spaces in a building. However, the existing paradigm based [...] Read more.

An essential impact which can improve the indoor environment and save on power consumption for artificial lighting is utilization of daylight. Optical fiber daylighting technology offers a way to use direct daylight for remote spaces in a building. However, the existing paradigm based on the precise orientation of sunlight concentrator toward the Sun is very costly and difficult to install on the roof of buildings. Here, we explore an alternative approach using mirror-coated lens array and planar waveguide to develop a flat optical fiber daylighting system (optical fiber daylighting panel) with lateral displacement Sun-tracking mechanism. Sunlight collected and reflected by each mirror-coated lens in a rectangular lens array is coupled into a planar waveguide using cone prisms placed at each lens focus. This geometry yields a thin, flat profile for Sunlight concentrator. Our proposed concentrating panel can be achieved with 35 mm thickness while the concentrator’s width and length are 500 mm × 500 mm. The commercial optical simulation tool (LightTools^TM) was used to develop the simulation models and analyze the system performance. Simulation results based on the designed system demonstrated an optical efficiency of 51.4% at a concentration ratio of 125. The system can support utilizing a lateral displacement Sun-tracking system, which allows for replacing bulky and robust conventional rotational Sun-tracking systems. This study shows a feasibility of a compact and inexpensive optical fiber daylighting system to be installed on the roof of buildings. Full article

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

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21 pages, 7121 KiB

Open AccessArticle

Numerical Simulation of Hydraulic Fracture Propagation Guided by Single Radial Boreholes

by Tiankui Guo^*

, Zhanqing Qu, Facheng Gong and Xiaozhi Wang

College of Petroleum Engineering, China University of Petroleum, Huadong, Qingdao 266580, China

Energies 2017, 10(10), 1680; https://doi.org/10.3390/en10101680 - 23 Oct 2017

Cited by 31 | Viewed by 6150

Abstract

Conventional hydraulic fracturing is not effective in target oil development zones with available wellbores located in the azimuth of the non-maximum horizontal in-situ stress. To some extent, we think that the radial hydraulic jet drilling has the function of guiding hydraulic fracture propagation [...] Read more.

Conventional hydraulic fracturing is not effective in target oil development zones with available wellbores located in the azimuth of the non-maximum horizontal in-situ stress. To some extent, we think that the radial hydraulic jet drilling has the function of guiding hydraulic fracture propagation direction and promoting deep penetration, but this notion currently lacks an effective theoretical support for fracture propagation. In order to verify the technology, a 3D extended finite element numerical model of hydraulic fracturing promoted by the single radial borehole was established, and the influences of nine factors on propagation of hydraulic fracture guided by the single radial borehole were comprehensively analyzed. Moreover, the term ‘Guidance factor (G_f)’ was introduced for the first time to effectively quantify the radial borehole guidance. The guidance of nine factors was evaluated through gray correlation analysis. The experimental results were consistent with the numerical simulation results to a certain extent. The study provides theoretical evidence for the artificial control technology of directional propagation of hydraulic fracture promoted by the single radial borehole, and it predicts the guidance effect of a single radial borehole on hydraulic fracture to a certain extent, which is helpful for planning well-completion and fracturing operation parameters in radial borehole-promoted hydraulic fracturing technology. Full article

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