Energies

Editorial

3 pages, 148 KiB

Open AccessEditorial

Advanced Energy Storage Technologies and Their Applications (AESA2017)

by Rui Xiong^1,2,*

, Hailong Li^3,4 and Xuan Zhou⁵

¹ National Engineering Laboratory for Electric Vehicles, Department of Vehicle Engineering, School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081, China

² Faculty of Science, Engineering and Technology, Swinburne University of Technology, John Street, Hawthorn, VIC 3122, Australia

³ Energy Technology, School of Business, Society and Technology Mälardalens University, Box 883, 72123 Västerås, Sweden

⁴ Tianjin Key Laboratory of Refrigeration Technology, School of Mechanical Engineering, Tianjin University of Commerce, Tianjin 300134, China

⁵ Electrical and Computer Engineering Department, Kettering University, 1700 University Avenue, Flint, MI 48504, USA

Energies 2017, 10(9), 1366; https://doi.org/10.3390/en10091366 - 9 Sep 2017

Cited by 4 | Viewed by 4877

Abstract

This editorial summarizes the performance of the special issue entitled Advanced Energy Storage Technologies and Applications (AESA), which is published in MDPI’s Energies journal in 2017. The special issue includes a total of 22 papers from four countries. Lithium-ion battery, electric vehicle, and [...] Read more.

This editorial summarizes the performance of the special issue entitled Advanced Energy Storage Technologies and Applications (AESA), which is published in MDPI’s Energies journal in 2017. The special issue includes a total of 22 papers from four countries. Lithium-ion battery, electric vehicle, and energy storage were the topics attracting the most attentions. New methods have been proposed with very sound results. Full article

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

Research

Jump to: Editorial, Review, Other

20 pages, 3765 KiB

Open AccessArticle

Dynamic Pricing for Demand Response Considering Market Price Uncertainty

by Mohammad Ali Fotouhi Ghazvini^1,*

, João Soares¹

, Hugo Morais²

, Rui Castro³

and Zita Vale¹

¹ GECAD—Research Group on Intelligent Engineering and Computing for Advanced Innovation and Development-Polytechnic of Porto (IPP), R. Dr. António Bernardino de Almeida 431, 4200-072 Porto, Portugal

² Automation and Control Group, Department of Electrical Engineering, Technical University of Denmark (DTU), Elektrovej, Building 326, DK-2800 Kgs. Lyngby, Denmark

³ Instituto de Engenharia de Sistemas e Computadores—Investigação e Desenvolvimento/Instituto Superior Técnico (INESC-ID/IST), University of Lisbon, 1049-001 Lisbon, Portugal

Energies 2017, 10(9), 1245; https://doi.org/10.3390/en10091245 - 23 Aug 2017

Cited by 18 | Viewed by 5841

Abstract

Retail energy providers (REPs) can employ different strategies such as offering demand response (DR) programs, participating in bilateral contracts, and employing self-generation distributed generation (DG) units to avoid financial losses in the volatile electricity markets. In this paper, the problem of setting dynamic [...] Read more.

Retail energy providers (REPs) can employ different strategies such as offering demand response (DR) programs, participating in bilateral contracts, and employing self-generation distributed generation (DG) units to avoid financial losses in the volatile electricity markets. In this paper, the problem of setting dynamic retail sales price by a REP is addressed with a robust optimization technique. In the proposed model, the REP offers price-based DR programs while it faces uncertainties in the wholesale market price. The main contribution of this paper is using a robust optimization approach for setting the short-term dynamic retail rates for an asset-light REP. With this approach, the REP can decide how to participate in forward contracts and call options. They can also determine the optimal operation of the self-generation DG units. Several case studies have been carried out for a REP with 10,679 residential consumers. The deterministic approach and its robust counterpart are used to solve the problem. The results show that, with a slight decrease in the expected payoff, the REP can effectively protect itself against price variations. Offering time-variable retail rates also can increase the expected profit of the REPs. Full article

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

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14 pages, 3292 KiB

Open AccessArticle

Effects of Loading Rate on Gas Seepage and Temperature in Coal and Its Potential for Coal-Gas Disaster Early-Warning

by Chong Zhang^1,2, Xiaofei Liu^1,2,*, Guang Xu^3,*

and Xiaoran Wang²

¹ Key Laboratory of Coal Methane and Fire Control (China University of Mining and Technology), Ministry of Education, Xuzhou 221116, China

² School of Safety Engineering, China University of Mining and Technology, Xuzhou 221116, China

³ Department of Mining Engineering and Metallurgical Engineering, Western Australian School of Mines, Curtin University, Kalgoorlie, WA 6430, Australia

Energies 2017, 10(9), 1246; https://doi.org/10.3390/en10091246 - 23 Aug 2017

Cited by 6 | Viewed by 4365

Abstract

The seepage velocity and temperature externally manifest the changing structure, gas desorption and energy release that occurs in coal containing gas failure under loading. By using the system of coal containing gas failure under loading, this paper studies the law of seepage velocity [...] Read more.

The seepage velocity and temperature externally manifest the changing structure, gas desorption and energy release that occurs in coal containing gas failure under loading. By using the system of coal containing gas failure under loading, this paper studies the law of seepage velocity and temperature under different loading rates and at 1.0 MPa confining pressure and 0.5 MPa gas pressure, and combined the on-site results of gas pressure and temperature. The results show that the stress directly affects the seepage velocity and temperature of coal containing gas, and the pressure and content of gas have the most sensitivity to mining stress. Although the temperature is not sensitive to mining stress, it has great correlation with mining stress. Seepage velocity has the characteristic of critically slowing down under loading. This is demonstrated by the variance increasing before the main failure of the samples. Therefore, the variance of seepage velocity with time and temperature can provide an early warning for coal containing gas failing and gas disasters in a coal mine. Full article

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

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17 pages, 628 KiB

Open AccessArticle

The Importance of Government Effectiveness for Transitions toward Greater Electrification in Developing Countries

by Rohan Best^*

and Paul J. Burke

Crawford School of Public Policy, Australian National University, Acton, ACT 2601, Australia

Energies 2017, 10(9), 1247; https://doi.org/10.3390/en10091247 - 23 Aug 2017

Cited by 25 | Viewed by 5945

Abstract

Electricity is a vital factor underlying modern living standards, but there are many developing countries with low levels of electricity access and use. We seek to systematically identify the crucial elements underlying transitions toward greater electrification in developing countries. We use a cross-sectional [...] Read more.

Electricity is a vital factor underlying modern living standards, but there are many developing countries with low levels of electricity access and use. We seek to systematically identify the crucial elements underlying transitions toward greater electrification in developing countries. We use a cross-sectional regression approach with national-level data up to 2012 for 135 low- and middle-income countries. The paper finds that the effectiveness of governments is the most important governance attribute for encouraging the transition to increased electrification in developing countries, on average. The results add to the growing evidence on the importance of governance for development outcomes. Donors seeking to make more successful contributions to electrification may wish to target countries with more effective governments. Full article

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

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18 pages, 4018 KiB

Open AccessArticle

Multivalued Coefficient Prestorage and Block Parallel Method for Real-Time Simulation of Microgrid on FRTDS

by Bingda Zhang^*, Dan Zhao, Zhao Jin and Yanjie Wu

The Key Laboratory of Smart Grid of Ministry of Education, Tianjin University, Tianjin 300072, China

Energies 2017, 10(9), 1248; https://doi.org/10.3390/en10091248 - 23 Aug 2017

Cited by 7 | Viewed by 3801

Abstract

The microgrid containing a large amount of high frequency power switches and nonlinear components has put forward high requirements for power system real-time simulation technology. Multivalued coefficient prestorage can reduce the calculation steps in real-time simulation. In order to reduce the storage pressure [...] Read more.

The microgrid containing a large amount of high frequency power switches and nonlinear components has put forward high requirements for power system real-time simulation technology. Multivalued coefficient prestorage can reduce the calculation steps in real-time simulation. In order to reduce the storage pressure of the multivalued coefficients, the whole network is divided into multiple subnetworks that can be simulated in parallel, and only the parameters for computing input variables and internal variables are prestored. The multiport hybrid equivalent is performed to reduce the number of simultaneous network equations. The input variables are tied to state variables of the circuit so that the iterative calculation is limited to the local network. The devised methodology is validated through simulation of a low-voltage microgrid on a field programmable gate array (FPGA)-based real-time digital simulation (FRTDS) platform at a 5 μs time step. Comparison with a power systems computer aided design (PSCAD)/electromagnetic transients including DC (EMTDC) model shows that the proposed method is effective. Full article

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

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14 pages, 2877 KiB

Open AccessArticle

Numerical Simulation and Optimization of the Melting Process of Phase Change Material inside Horizontal Annulus

by Saiwei Li, Yu Chen and Zhiqiang Sun^*

School of Energy Science and Engineering, Central South University, Changsha 410083, China

Energies 2017, 10(9), 1249; https://doi.org/10.3390/en10091249 - 23 Aug 2017

Cited by 29 | Viewed by 4533

Abstract

Latent heat storage (LHS) technologies adopting phase change materials (PCMs) are increasingly being used to bridge the spatiotemporal mismatch between energy production and demand, especially in industries like solar power, where strong cyclic fluctuations exist. The shell-and-tube configuration is among the most prevalent [...] Read more.

Latent heat storage (LHS) technologies adopting phase change materials (PCMs) are increasingly being used to bridge the spatiotemporal mismatch between energy production and demand, especially in industries like solar power, where strong cyclic fluctuations exist. The shell-and-tube configuration is among the most prevalent ones in LHS and thus draws special attention from researchers. This paper presents numerical investigations on the melting of PCM, a paraffin blend RT27, inside a horizontal annulus. The volume of fluid model was adopted to permit density changes with the solidification/melting model wherein natural convection was taken into account. The eccentricity and diameter of the inner tube, sub-cooling degree of the PCM, and the heating-surface temperature were considered as variables for study. Through the evaluation of the melting time and exergy efficiency, the optimal parameters of the horizontal annulus were obtained. The results showed that the higher the heating boundary temperature, the earlier the convection appeared and the shorter the melting time. Also, the different eccentricity and diameters of the inner tube influenced the annulus tube interior temperature distribution, which in turn determined the strength and distribution of the resulting natural convection, resulting in varying melting rates. Full article

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

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25 pages, 5935 KiB

Open AccessArticle

A Novel Method for Idle-Stop-Start Control of Micro Hybrid Construction Equipment—Part B: A Real-Time Comparative Study

by Truong Quang Dinh^1,*, James Marco¹, Hui Niu¹, David Greenwood¹

, Lee Harper² and David Corrochano²

¹ Warwick Manufacturing Group (WMG), University of Warwick, Coventry CV4 7AL, UK

² JCB, Rocester, Straffordshire ST14 5JP, UK

Energies 2017, 10(9), 1250; https://doi.org/10.3390/en10091250 - 23 Aug 2017

Cited by 3 | Viewed by 6186

Abstract

Micro hybrid propulsion (MHP) technologies have emerged as promising solutions for minimisation of fuel consumption and pollutant emissions of off-highway construction machines (OHCMs). Their performance and economic feasibility strongly depend on the way they utilize the idle-stop-start control (ISSC) concept. The ISSC design [...] Read more.

Micro hybrid propulsion (MHP) technologies have emerged as promising solutions for minimisation of fuel consumption and pollutant emissions of off-highway construction machines (OHCMs). Their performance and economic feasibility strongly depend on the way they utilize the idle-stop-start control (ISSC) concept. The ISSC design process and performance evaluation are particularly challenging due to the peculiar structures and dynamics of OHCMs compared to other vehicles and, therefore, require significant development time and efforts. This paper is the second of a two-part study focusing on prediction-based idle-start-stop control (PISSC) for micro hybrid OHCMs. In part A, the powertrain model and the procedure to design the PISSC system have been presented. The PISSC-based engine control performance has been investigated through numerical simulations with the designed model. In this Part B, a hardware-in-the-loop (HIL) test platform is established in HIL Control Laboratory for the rapid validation of the proposed technique in terms of the fuel/pollutant emission saving in real-time. First, the powertrain architecture and PISSC algorithm presented in Part A are briefly reviewed. Second, the process to build the HIL test platform is clearly stated. Third, experiments and analysis are carried out for a number of comparative studies to validate the superiority and practical applicability of the PISSC approach. Full article

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

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20 pages, 4281 KiB

Open AccessArticle

Exploring Marine Energy Potential in the UK Using a Whole Systems Modelling Approach

by Anna Stegman^1,2,3,*, Adrian De Andres², Henry Jeffrey², Lars Johanning³

and Stuart Bradley¹

¹ Energy Technologies Institute, Loughborough LE11 3UZ, UK

² Institute of Energy Systems, University of Edinburgh, Edinburgh EH9 3DW, UK

³ College of Engineering, Mathematics and Physical Sciences, University of Exeter, Penryn TR10 9EZ, UK

Energies 2017, 10(9), 1251; https://doi.org/10.3390/en10091251 - 23 Aug 2017

Cited by 14 | Viewed by 6703

Abstract

The key market drivers for marine energy are to reduce carbon emissions, and improve the security and sustainability of supply. There are other technologies that also meet these requirements, and therefore the marine energy market is dependent on the technology being cost effective, [...] Read more.

The key market drivers for marine energy are to reduce carbon emissions, and improve the security and sustainability of supply. There are other technologies that also meet these requirements, and therefore the marine energy market is dependent on the technology being cost effective, and competitive. The potential UK wave and tidal stream energy market is assessed using ETI’s energy systems modelling environment (ESME) which uses a multi-vector approach including energy generation, demand, heat, transport, and infrastructure. This is used to identify scenarios where wave and tidal energy form part of the least-cost energy system for the UK by 2050, and will assess what Levelised Cost of Energy (LCOE) reductions are required to improve the commercialization rate. The results indicate that an installed capacity of 4.9 GW of wave and 2.5 GW of tidal stream could be deployed by 2050 if the LCOE is within 4.5 and 7 p/kWh for each respective technology. If there is a step reduction to the LCOE of wave energy, however, a similar capacity of 5 GW could be deployed by 2050 at a LCOE of 11 p/kWh. Full article

(This article belongs to the Special Issue Marine Energy)

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17 pages, 3739 KiB

Open AccessArticle

Proposal for a Simplified CFD Procedure for Obtaining Patterns of the Age of Air in Outdoor Spaces for the Natural Ventilation of Buildings

by Miguel Ángel Padilla-Marcos^*

, Alberto Meiss

and Jesús Feijó-Muñoz

GIR Architecture & Energy, TS Architecture, University of Valladolid, Av Salamanca, 47014 Valladolid, Spain

Energies 2017, 10(9), 1252; https://doi.org/10.3390/en10091252 - 23 Aug 2017

Cited by 10 | Viewed by 4107

Abstract

Built urban environments modify the air quality of the natural ventilation processes in buildings. The experimental assessment of outdoor air change (OACH) processes is complex due to the air volumes involved. The quality of the OACH can be analysed through the ventilation efficiency [...] Read more.

Built urban environments modify the air quality of the natural ventilation processes in buildings. The experimental assessment of outdoor air change (OACH) processes is complex due to the air volumes involved. The quality of the OACH can be analysed through the ventilation efficiency concept, which has been extensively studied in order to characterize the ventilation of indoor spaces. Ventilation efficiency through the age-of-the-air concept assesses the air-change capacity of a certain space. A procedure formulation for obtaining an adequate control domain (CD) to evaluate outdoor air change efficiency (OACE) is proposed. A methodology in two phases is presented: first, an evaluation stage, in which the outdoor air behaviour patterns are studied; then, a second phase where an ideal control domain (ICD) is obtained in order to comparatively assess several cases in similar urban environments. The outcomes determine a proposed ICD for evaluating the design of efficiently ventilated buildings in open urban built environments. The methodology of validation proposed simplifies the assessment of the building shape and its impact on the quality of the OACH by the OACE. The suggested ICD has dimensions of L = 5H; D = 3H; and T = 2H. ICD enables the representation of the air behaviour and fulfils the imposed requirements to evaluate efficiency with a mean accuracy lower than 0.6%. Full article

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

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17 pages, 11365 KiB

Open AccessFeature PaperArticle

Status Quo of the Air-Conditioning Market in Europe: Assessment of the Building Stock

by Simon Pezzutto^1,*, Matteo De Felice²

, Reza Fazeli³, Lukas Kranzl⁴ and Stefano Zambotti¹

¹ Institute for Renewable Energy, European Academy of Bozen/Bolzano (Eurac Research), Viale Druso 1, 39100 Bolzano, Italy

² Climate Impacts & Modelling laboratory, ENEA, Via Martiri di Monte Sole 4, 40129 Bologna, Italy

³ Faculty of Life and Environmental Sciences, University of Iceland, Sæmundargata 2, 101 Reykjavík, Iceland

⁴ Energy Economics Group, Institute of Energy Systems and Electric Drives, Vienna University of Technology, Gusshausstrasse 25-29/370-3, 1040 Vienna, Austria

Energies 2017, 10(9), 1253; https://doi.org/10.3390/en10091253 - 23 Aug 2017

Cited by 41 | Viewed by 8203

Abstract

This study fills in knowledge gaps for the European air-conditioning (AC) market, which is fundamentally important to raising awareness about primary energy utilization. In contrast to space heating (SH) and domestic hot water (DHW) preparation, the European Union (EU) AC market is barely [...] Read more.

This study fills in knowledge gaps for the European air-conditioning (AC) market, which is fundamentally important to raising awareness about primary energy utilization. In contrast to space heating (SH) and domestic hot water (DHW) preparation, the European Union (EU) AC market is barely explored in scientific literature. While the focus of previous research has been on the residential sector, a shortfall of data for the services (wholesale and retail, offices, education, health, hotels and bars) exists. In this paper, data describing the actual space cooling (SC) market in Europe (quantity of SC units, equivalent full-load hours, installed capacities, seasonal energy efficiency values as well as cooled floor area per AC type and/or sector) is collected and explored using a bottom-up approach. Results indicate that SC is responsible for a significant portion of EU electricity consumption in households (nearly 5%) and even more in the service sector (~13%). Energy consumption for SC in the EU28 appears to be more than 140 TWh/y. The quantification of the European AC consumption shows a significant difference between the service and residential sectors: about 115 versus 25 TWh/y respectively. The SC market in Europe is characterized by a high potential for growth, especially in households. Full article

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12 pages, 2846 KiB

Open AccessArticle

Acquisition System Verification for Energy Efficiency Analysis of Building Materials

by Natalia Cid¹, Ana Ogando¹ and M. A. Gómez^2,*

¹ Department of Mechanical Engineering, Heat Engines and Fluid Mechanics, School of Industrial Engineering, University of Vigo, 36310 Vigo, Spain

² Defense University Center, Spanish Naval Academy, Plaza de España s/n, 36900 Marín, Spain

Energies 2017, 10(9), 1254; https://doi.org/10.3390/en10091254 - 23 Aug 2017

Cited by 2 | Viewed by 4062

Abstract

Climate change and fossil fuel depletion foster interest in improving energy efficiency in buildings. There are different methods to achieve improved efficiency; one of them is the use of additives, such as phase change materials (PCMs). To prove this method’s effectiveness, a building’s [...] Read more.

Climate change and fossil fuel depletion foster interest in improving energy efficiency in buildings. There are different methods to achieve improved efficiency; one of them is the use of additives, such as phase change materials (PCMs). To prove this method’s effectiveness, a building’s behaviour should be monitored and analysed. This paper describes an acquisition system developed for monitoring buildings based on Supervisory Control and Data Acquisition (SCADA) and with a 1-wire bus network as the communication system. The system is empirically tested to prove that it works properly. With this purpose, two experimental cubicles are made of self-compacting concrete panels, one of which has a PCM as an additive to improve its energy storage properties. Both cubicles have the same dimensions and orientation, and they are separated by six feet to avoid shadows. The behaviour of the PCM was observed with the acquisition system, achieving results that illustrate the differences between the cubicles directly related to the PCM’s characteristics. Data collection devices included in the system were temperature sensors, some of which were embedded in the walls, as well as humidity sensors, heat flux density sensors, a weather station and energy counters. The analysis of the results shows agreement with previous studies of PCM addition; therefore, the acquisition system is suitable for this application. Full article

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16 pages, 4833 KiB

Open AccessArticle

Integrated Bioethanol Fermentation/Anaerobic Digestion for Valorization of Sugar Beet Pulp

by Joanna Berlowska^*

, Katarzyna Pielech-Przybylska

, Maria Balcerek

, Weronika Cieciura, Sebastian Borowski and Dorota Kregiel

Institute of Fermentation Technology and Microbiology, Lodz University of Technology, Wolczanska 171/173, 90-924 Lodz, Poland

Energies 2017, 10(9), 1255; https://doi.org/10.3390/en10091255 - 23 Aug 2017

Cited by 37 | Viewed by 7935

Abstract

Large amounts of waste biomass are generated in sugar factories from the processing of sugar beets. After diffusion with hot water to draw the sugar from the beet pieces, a wet material remains called pulp. In this study, waste sugar beet pulp biomass [...] Read more.

Large amounts of waste biomass are generated in sugar factories from the processing of sugar beets. After diffusion with hot water to draw the sugar from the beet pieces, a wet material remains called pulp. In this study, waste sugar beet pulp biomass was enzymatically depolymerized, and the obtained hydrolyzates were subjected to fermentation processes. Bioethanol, biomethane, and biohydrogen were produced directly from the substrate or in combined mode. Stillage, a distillery by-product, was used as a feedstock for anaerobic digestion. During biosynthesis of ethanol, most of the carbohydrates released from the sugar beet pulp were utilized by a co-culture of Saccharomyces cerevisiae Ethanol Red, and Scheffersomyces stipitis LOCK0047 giving 12.6 g/L of ethanol. Stillage containing unfermented sugars (mainly arabinose, galactose and raffinose) was found to be a good substrate for methane production (444 dm³ CH₄/kg volatile solids (VS)). Better results were achieved with this medium than with enzymatic saccharified biomass. Thermal pre-treatment and adjusting the pH of the inoculum resulted in higher hydrogen production. The largest (p < 0.05) hydrogen yield (252 dm³ H₂/kg VS) was achieved with sugar beet stillage (SBS). In contrast, without pre-treatment the same medium yielded 35 dm³ H₂/kg VS. However, dark fermentation of biohydrogen was more efficient when sugar beet pulp hydrolyzate was used. Full article

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21 pages, 3114 KiB

Open AccessArticle

Towards a Residential Air-Conditioner Usage Model for Australia

by Mark Goldsworthy

Commonwealth Scientific and Industrial Research Organisation (CSIRO), Newcastle 2304, Australia

Energies 2017, 10(9), 1256; https://doi.org/10.3390/en10091256 - 24 Aug 2017

Cited by 14 | Viewed by 4279

Abstract

Realistic models of occupant behaviour in relation to air-conditioner (a/c) use are fundamentally important for developing accurate building energy simulation tools. In Australia and elsewhere, such simulation tools are inextricably bound both in legislation and in the design of new technology, electricity infrastructure [...] Read more.

Realistic models of occupant behaviour in relation to air-conditioner (a/c) use are fundamentally important for developing accurate building energy simulation tools. In Australia and elsewhere, such simulation tools are inextricably bound both in legislation and in the design of new technology, electricity infrastructure and regulatory schemes. An increasing number of studies in the literature confirm just how important occupants are in determining overall energy consumption, but obtaining the data on which to build behaviour models is a non-trivial task. Here data is presented on air-conditioner usage derived from three different types of case study analyses. These are: (i) use of aggregate energy consumption data coupled with weather, demographic and building statistics across Australia to estimate key predictors of energy use at the aggregate level; (ii) use of survey data to determine characteristic a/c switch on/off behaviours and usage frequencies; and (iii) use of detailed household level sub-circuit monitoring from 140 households to determine a/c switch on/off probabilities and their dependence on different building and occupant parameters. These case studies are used to assess the difficulties associated with translation of different forms of individual, aggregate and survey based information into a/c behaviour simulation models. Finally a method of linking the data gathering methodologies with the model development is suggested. This method would combine whole-of-house “smart”-meter data measurements with linked targeted occupant surveying. Full article

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

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21 pages, 3176 KiB

Open AccessArticle

A Three-Part Electricity Price Mechanism for Photovoltaic-Battery Energy Storage Power Plants Considering the Power Quality and Ancillary Service

by Yajing Gao^*, Fushen Xue^*, Wenhai Yang, Yanping Sun, Yongjian Sun, Haifeng Liang and Peng Li

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

Energies 2017, 10(9), 1257; https://doi.org/10.3390/en10091257 - 24 Aug 2017

Cited by 8 | Viewed by 5886

Abstract

To solve the problem of solar abandoning, which is accompanied by the rapid development of photovoltaic (PV) power generation, a demonstration of a photovoltaic-battery energy storage system (PV-BESS) power plant has been constructed in Qinghai province in China. However, it is difficult for [...] Read more.

To solve the problem of solar abandoning, which is accompanied by the rapid development of photovoltaic (PV) power generation, a demonstration of a photovoltaic-battery energy storage system (PV-BESS) power plant has been constructed in Qinghai province in China. However, it is difficult for the PV-BESS power plant to survive and develop with the current electricity price mechanism and subsidy policy. In this paper, a three-part electricity price mechanism is proposed based on a deep analysis of the construction and operation costs and economic income. The on-grid electricity price is divided into three parts: the capacity price, graded electricity price, and ancillary service price. First, to ensure that the investment of the PV-BESS power plant would achieve the industry benchmark income, the capacity price and benchmark electricity price are calculated using the discounted cash flow method. Then, the graded electricity price is calculated according to the grade of the quality of grid-connected power. Finally, the ancillary service price is calculated based on the graded electricity price and ancillary service compensation. The case studies verify the validity of the three-part electricity price mechanism. The verification shows that the three-part electricity price mechanism can help PV-BESS power plants to obtain good economic returns, which can promote the development of PV-BESS power plants. Full article

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

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28 pages, 1091 KiB

Open AccessArticle

An Intelligent Hybrid Heuristic Scheme for Smart Metering based Demand Side Management in Smart Homes

by Awais Manzoor¹, Nadeem Javaid^1,*

, Ibrar Ullah²

, Wadood Abdul³

, Ahmad Almogren³

and Atif Alamri³

¹ COMSATS Institute of Information Technology, Islamabad 44000, Pakistan

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

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

Energies 2017, 10(9), 1258; https://doi.org/10.3390/en10091258 - 24 Aug 2017

Cited by 75 | Viewed by 6608

Abstract

Smart grid is an emerging technology which is considered to be an ultimate solution to meet the increasing power demand challenges. Modern communication technologies have enabled the successful implementation of smart grid (SG), which aims at provision of demand side management mechanisms (DSM), [...] Read more.

Smart grid is an emerging technology which is considered to be an ultimate solution to meet the increasing power demand challenges. Modern communication technologies have enabled the successful implementation of smart grid (SG), which aims at provision of demand side management mechanisms (DSM), such as demand response (DR). In this paper, we propose a hybrid technique named as teacher learning genetic optimization (TLGO) by combining genetic algorithm (GA) with teacher learning based optimization (TLBO) algorithm for residential load scheduling, assuming that electric prices are announced on a day-ahead basis. User discomfort is one of the key aspects which must be addressed along with cost minimization. The major focus of this work is to minimize consumer electricity bill at minimum user discomfort. Load scheduling is formulated as an optimization problem and an optimal schedule is achieved by solving the minimization problem. We also investigated the effect of power-flexible appliances on consumers’ bill. Furthermore, a relationship among power consumption, cost and user discomfort is also demonstrated by feasible region. Simulation results validate that our proposed technique performs better in terms of cost reduction and user discomfort minimization, and is able to obtain the desired trade-off between consumer electricity bill and user discomfort. Full article

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

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18 pages, 30745 KiB

Open AccessArticle

Analysis of Vibrations in Interior Permanent Magnet Synchronous Motors Considering Air-Gap Deformation

by Yi Li^1,2

, Feng Chai^1,2,*, Zaixin Song²

and Zongyang Li²

¹ State Key Laboratory of Robotics and System, Harbin Institute of Technology, Harbin 150001, China

² Department of Electrical Engineering, Harbin Institute of Technology, Harbin 150001, China

Energies 2017, 10(9), 1259; https://doi.org/10.3390/en10091259 - 24 Aug 2017

Cited by 30 | Viewed by 6920

Abstract

This paper studies the non-uniform air-gap caused by stator and rotor deformations, together with its effects on the spatial and temporal spectrum of the radial magnetic force density in an interior permanent magnet synchronous motor (IPMSM). According to the mathematical model of the [...] Read more.

This paper studies the non-uniform air-gap caused by stator and rotor deformations, together with its effects on the spatial and temporal spectrum of the radial magnetic force density in an interior permanent magnet synchronous motor (IPMSM). According to the mathematical model of the deformed air-gap length, the superposition method is adopted to derive the air-gap permeance. Then, the formulas of the magnetic flux field and radial force density of the IPMSM considering air-gap deformation are obtained. Considering the stator oval deformation and the rotor centrifugal distortion in the electromagnetic finite element models (FEMs), the finite element analysis (FEA) and experiments of the investigated IPMSM are carried out to verify the results obtained by the theoretical analysis at different operations. Finally, the mathematical correlation between air-gap deformation and electromagnetic vibration is obtained. The result is helpful in solving problems of mutual influence between electromagnetic and mechanical characteristics during the optimization design of IPMSM. Full article

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

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15 pages, 528 KiB

Open AccessArticle

Game-Based Generation Scheduling Optimization for Power Plants Considering Long-Distance Consumption of Wind-Solar-Thermal Hybrid Systems

by Tiejiang Yuan¹, Tingting Ma², Yiqian Sun³, Ning Chen⁴ and Bingtuan Gao^2,*

¹ School of Electrical Engineering, Dalian University of Technology, Dalian 116024, China

² School of Electrical Engineering, Southeast University, Nanjing 210096, China

³ Electric Power Research Institute, State Grid Xinjiang Electric Power Corporation, Urumqi 830002, China

⁴ China Electric Power Research Institute, Nanjing 210003, China

Energies 2017, 10(9), 1260; https://doi.org/10.3390/en10091260 - 24 Aug 2017

Cited by 11 | Viewed by 3695

Abstract

With the increasing penetration of renewable energy in power systems, fluctuation of renewable energy power plants has great influence on stability of the system, and renewable power curtailment is also becoming more and more serious due to the insufficient consumptive ability of local [...] Read more.

With the increasing penetration of renewable energy in power systems, fluctuation of renewable energy power plants has great influence on stability of the system, and renewable power curtailment is also becoming more and more serious due to the insufficient consumptive ability of local power grid. In order to maximize the utilization of renewable energy, this paper focuses on the generation scheduling optimization for a wind-solar-thermal hybrid system considering that the produced energy will be transmitted over a long distance to satisfy the demands of the receiving end system through ultra-high voltage (UHV) transmission lines. Accordingly, a bilevel optimization based on a non-cooperative game method is proposed to maximize the profit of power plants in the hybrid system. Users in the receiving end system are at the lower level of the bilevel programming, and power plants in the transmitting end system are at the upper level. Competitive behavior among power plants is formulated as a non-cooperative game and the profit of power plant is scheduled by adjusting generation and bidding strategies in both day-ahead markets and intraday markets. In addition, generation cost, wheeling cost, and carbon emissions are all considered in the non-cooperative game model. Moreover, a distributed algorithm is presented to obtain the generalized Nash equilibrium solution, which realizes the optimization in terms of maximizing profit. Finally, several simulations are implemented and analyzed to verify the effectiveness of the proposed optimization method. Full article

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17 pages, 1120 KiB

Open AccessArticle

Layout Optimisation of Wave Energy Converter Arrays

by Pau Mercadé Ruiz^1,*

, Vincenzo Nava^2,3

, Mathew B. R. Topper⁴

, Pablo Ruiz Minguela², Francesco Ferri¹

and Jens Peter Kofoed¹

¹ Department of Civil Engineering, Aalborg University, Thomas Manns Vej 23, 9220 Aalborg, Denmark

² Tecnalia Research and Innovation, Energy and Environmental Division, Parque Tecnologico de Bizkaia, 48160 Derio, Spain

³ Basque Centre for Applied Mathematics BCAM, 48009 Bilbao, Spain

⁴ Institute for Energy Systems, The University of Edinburgh, Edinburgh EH9 3DW, Scotland, UK

Energies 2017, 10(9), 1262; https://doi.org/10.3390/en10091262 - 24 Aug 2017

Cited by 60 | Viewed by 5975

Abstract

This paper proposes an optimisation strategy for the layout design of wave energy converter (WEC) arrays. Optimal layouts are sought so as to maximise the absorbed power given a minimum q-factor, the minimum distance between WECs, and an area of deployment. To [...] Read more.

This paper proposes an optimisation strategy for the layout design of wave energy converter (WEC) arrays. Optimal layouts are sought so as to maximise the absorbed power given a minimum q-factor, the minimum distance between WECs, and an area of deployment. To guarantee an efficient optimisation, a four-parameter layout description is proposed. Three different optimisation algorithms are further compared in terms of performance and computational cost. These are the covariance matrix adaptation evolution strategy (CMA), a genetic algorithm (GA) and the glowworm swarm optimisation (GSO) algorithm. The results show slightly higher performances for the latter two algorithms; however, the first turns out to be significantly less computationally demanding. Full article

(This article belongs to the Special Issue Marine Energy)

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16 pages, 7852 KiB

Open AccessArticle

Particulate Matter and Gaseous Emission of Hydrous Ethanol Gasoline Blends Fuel in a Port Injection Gasoline Engine

by Maji Luo^1,2,*, Musaab O. El-Faroug^1,2,3

, Fuwu Yan^1,2 and Yinan Wang^1,2

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

² Hubei Collaborative Innovation Center for Automotive Components Technology, Wuhan University of Technology, Wuhan 430070, China

³ Mechanical Engineering Department, Faculty of Engineering, Elimam Elmahdi University, Kosti 11588, Sudan

Energies 2017, 10(9), 1263; https://doi.org/10.3390/en10091263 - 25 Aug 2017

Cited by 12 | Viewed by 6637

Abstract

The industrialization that increases day by day needs more and more power/fuel sources that are commonly available, abundant, renewable, and environmentally friendly. Recently, nearly all of the cities in China (PRC) have been influenced by haze. However, the pollutants from automobiles have always [...] Read more.

The industrialization that increases day by day needs more and more power/fuel sources that are commonly available, abundant, renewable, and environmentally friendly. Recently, nearly all of the cities in China (PRC) have been influenced by haze. However, the pollutants from automobiles have always been seriously considered to be the main contamination causes of the haze and that influence human health. This study concerns the impact of hydrous ethanol on in-cylinder pressure, particulate matter (PM), and gaseous emissions (oxides of nitrogen (NO_x) and unburned hydrocarbon (HC)) from a port fuel injection (PFI) gasoline engine. Tests were conducted on a four-cylinder port injection gasoline engine at different engine loads at an engine speed of 2000 rev/min for commercial gasoline, hydrous ethanol-gasoline blends (10% and 20% hydrous ethanol by volume), and an anhydrous ethanol-gasoline blend (20% anhydrous ethanol by volume). The results show that the peak in-cylinder pressure with the use of gasoline was the highest compared with the hydrous ethanol and anhydrous ethanol blends. Compared with the anhydrous ethanol blend, the hydrous ethanol blends performed well at a high load condition, equivalent to a low load. In addition, the total particulate number (PN) declines with an increase in engine operating loads for all of the fuels tested. The outcome of this study is an important reduction in PM number, mass emissions, and mean diameters of particles as the use of hydrous ethanol blends increases, while the form of the particulate size distribution remains the same. Furthermore, the NO_x emission is raised with a rise in engine load, and NO_x and HC emissions are reduced with the use of hydrous ethanol and anhydrous ethanol blend as equated with pure gasoline. Moreover, the correlation between the total particle number against NO_x and HC has been found; the number of particles increases when the NO_x emission decreases, and the opposite trend is exhibited for the HC emission. Therefore, it can be concluded that hydrous ethanol blends look to be a good selection for PM, NO_x, and HC reduction for gasoline engines. Full article

(This article belongs to the Special Issue Methods to Improve Energy Use in Road Vehicles)

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11 pages, 908 KiB

Open AccessArticle

Fractionation of Lignocellulosic Residues Coupling Steam Explosion and Organosolv Treatments Using Green Solvent γ-Valerolactone

by Mattia Gelosia^*, David Ingles

, Enrico Pompili, Silvia D’Antonio, Gianluca Cavalaglio

, Alessandro Petrozzi and Valentina Coccia

CIRIAF—Biomass Research Centre Section, University of Perugia, Via G. Duranti 67, 06125 Perugia, Italy

Energies 2017, 10(9), 1264; https://doi.org/10.3390/en10091264 - 25 Aug 2017

Cited by 11 | Viewed by 4545

Abstract

A two-step fractionation of lignocellulosic residues of Phragmites australis in its main components (cellulose-pulp, soluble hemicellulose sugars, and lignin) is described, based on the biomass-derived solvent γ-valerolactone (GVL). The solvent used is an excellent substitute for traditional organic solvents as it is not [...] Read more.

A two-step fractionation of lignocellulosic residues of Phragmites australis in its main components (cellulose-pulp, soluble hemicellulose sugars, and lignin) is described, based on the biomass-derived solvent γ-valerolactone (GVL). The solvent used is an excellent substitute for traditional organic solvents as it is not toxic, it is renewable, and it can be recycled after the extraction process. Prior the GVL-organosolv extraction process, a steam explosion pretreatment was performed in order to break up the tight lignocellulosic structure and partially depolymerise hemicellulose into soluble sugars, making lignin easier to be solubilised. Three common extraction techniques were compared: soxhlet, closed vessel microwave-assisted, and open vessel on a hotplate stirrer. The two-step approach resulted in a cellulose-rich solid, water-soluble hemicellulose sugars and lignin-rich GVL liquor which was further purified for lignin isolation. The two best resulting pulps presented a high cellulose content (75.47% and 78.68%) starting from 38.13% and a content of lignin down to 11.96% and 13.09% starting from 23.02%. Almost all hemicellulose was removed with a final content of 0.72% and 2.20% starting from 20.5%. Full article

(This article belongs to the Special Issue 17th CIRIAF National Congress – Sustainable Development, Environment and Human Health Protection)

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21 pages, 1920 KiB

Open AccessArticle

Spatial Variation in Sediment Organic Carbon Distribution across the Alaskan Beaufort Sea Shelf

by Richard B. Coffin^1,4,*, Joseph P. Smith², Brandon Yoza³, Thomas J. Boyd⁴ and Michael T. Montgomery⁴

¹ Department of Physical and Environmental Sciences, Texas A&M University-Corpus Christi, Corpus Christi, TX 78412, USA

² Department of Oceanography, US Naval Academy, Annapolis, MD 21402, USA

³ Hawaii Natural Energy Institute, University of Hawaii, Honolulu, HI 96822, USA

⁴ Marine Biogeochemistry, Naval Research Laboratory, Washington, DC 20375, USA

Energies 2017, 10(9), 1265; https://doi.org/10.3390/en10091265 - 25 Aug 2017

Cited by 9 | Viewed by 4873

Abstract

In September 2009, a series of sediment cores were collected across the Alaskan Beaufort Sea shelf-slope. Sediment and porewater organic carbon (OC) concentrations and stable carbon isotope ratios (δ¹³C) were measured to investigate spatial variations in sediment organic matter (OM) sources [...] Read more.

In September 2009, a series of sediment cores were collected across the Alaskan Beaufort Sea shelf-slope. Sediment and porewater organic carbon (OC) concentrations and stable carbon isotope ratios (δ¹³C) were measured to investigate spatial variations in sediment organic matter (OM) sources and distribution of these materials across the shelf. Cores were collected along three main nearshore (shelf) to offshore (slope) sampling lines (transects) from east-to-west along the North Slope of Alaska: Hammerhead (near Camden Bay), Thetis Island (near Prudhoe Bay), and Cape Halkett (towards Point Barrow). Measured sediment organic carbon (TOC) and porewater dissolved organic carbon (DOC) concentrations and their respective δ¹³C values were used to investigate the relative contribution of different OM sources to sediment OC pool cycled at each location. Sources of OM considered included: water column-sourced phytodetritus, deep sediment methane (CH₄), and terrestrial, tundra/river-sourced OM. Results of these measurements, when coupled with results from previous research and additional analyses of sediment and porewater composition, show a pattern of spatial variation in sediment OC concentrations, OM source contributions, and OM cycled along the Alaskan Beaufort Sea shelf. In general, measured sediment total organic carbon (TOC) concentrations, δ¹³C_TOC values, porewater DOC concentrations, and δ¹³C_DOC values are consistent with an east-to-west transport of modern Holocene sediments with higher OC concentrations primarily sourced from relatively labile terrestrial, tundra OM sources and phytodetritus along the Alaskan Beaufort shelf. Sediment transport along the shelf results in the medium-to-long term accumulation and burial of sediment OM focused to the west which in turn results in higher biogenic CH₄ production rates and higher upward CH₄ diffusion through the sediments resulting in CH₄⁻AMO-sourced contribution to sediment OC westward along the shelf. Understanding current OM sources and distributions along the Alaskan Beaufort shelf is important for enhancing models of carbon cycling in Arctic coastal shelf systems. This will help support the prediction of the climate response of the Arctic created in the face of future warming scenarios. Full article

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16 pages, 1946 KiB

Open AccessArticle

Electrochemical Model-Based Condition Monitoring via Experimentally Identified Li-Ion Battery Model and HPPC

by Md Ashiqur Rahman¹, Sohel Anwar^1,*

and Afshin Izadian²

¹ Department of Mechanical Engineering, Indiana University–Purdue University Indianapolis, Indianapolis, IN 46202, USA

² Energy Systems and Power Electronics Laboratory, Indiana University–Purdue University Indianapolis, Indianapolis, IN 46202, USA

Energies 2017, 10(9), 1266; https://doi.org/10.3390/en10091266 - 25 Aug 2017

Cited by 15 | Viewed by 4946

Abstract

Electrochemical model-based condition monitoring of a Li-Ion battery using an experimentally identified battery model and Hybrid Pulse Power Characterization (HPPC) cycle is presented in this paper. LiCoO₂ cathode chemistry was chosen in this work due to its higher energy storage capabilities. Battery [...] Read more.

Electrochemical model-based condition monitoring of a Li-Ion battery using an experimentally identified battery model and Hybrid Pulse Power Characterization (HPPC) cycle is presented in this paper. LiCoO₂ cathode chemistry was chosen in this work due to its higher energy storage capabilities. Battery electrochemical model parameters are subject to change under severe or abusive operating conditions resulting in, for example, Navy over-discharged battery, 24 h over-discharged battery, and overcharged battery. Stated battery fault conditions can cause significant variations in a number of electrochemical battery model parameters from nominal values, and can be considered as separate models. Output error injection based partial differential algebraic equation (PDAE) observers have been used to generate the residual voltage signals in order to identify these abusive conditions. These residuals are then used in a Multiple Model Adaptive Estimation (MMAE) algorithm to detect the ongoing fault conditions of the battery. HPPC cycle simulated load profile based analysis shows that the proposed algorithm can detect and identify the stated fault conditions accurately using measured input current and terminal output voltage. The proposed model-based fault diagnosis can potentially improve the condition monitoring performance of a battery management system. Full article

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20 pages, 4323 KiB

Open AccessArticle

Achievement of Fuel Savings in Wheel Loader by Applying Hydrodynamic Mechanical Power Split Transmissions

by Xiaojun Liu, Dongye Sun^*, Datong Qin and Junlong Liu

State Key Laboratory of Mechanical Transmissions & School of Automotive Engineering, Chongqing University, Chongqing 400044, China

Energies 2017, 10(9), 1267; https://doi.org/10.3390/en10091267 - 25 Aug 2017

Cited by 36 | Viewed by 6259

Abstract

The fuel economy of wheel loaders is deeply affected by the efficiency of their propelling transmissions, however, the torque converter (TC) in existing propelling transmissions is a low-efficiency component and leads to excessive energy consumption. Accordingly, this paper replaces the TC with a [...] Read more.

The fuel economy of wheel loaders is deeply affected by the efficiency of their propelling transmissions, however, the torque converter (TC) in existing propelling transmissions is a low-efficiency component and leads to excessive energy consumption. Accordingly, this paper replaces the TC with a hydrodynamic mechanical power split transmission (HMPST) for improving the fuel economy of wheel loader. Based on probability similarity theory, the typical operating mode for the vehicles is constructed, which is used to evaluate the energy consumption performance of the selected solutions. The four reasonable solutions, which can be initially applied to wheel loaders, are selected from among the HMPSTs using the lever diagram. Furthermore, the comparisons on efficiency and loading characteristics between these four solutions and a prototype TC are conducted. The design optimization for all the four solutions is implemented, in order to find the optimal fuel saving solution relative to the prototype TC, and only one solution with pure power split can meet the constraints. Finally, a simulation model of the wheel loader powertrain is established for validating the effectiveness of this optimal solution. The results show that the optimized solution can effectively improve the fuel economy of wheel loaders compared to the prototype TC and provides a novel substitute for current technology. Full article

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

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23 pages, 12690 KiB

Open AccessArticle

Modelling and Simulation of Electric Vehicle Fast Charging Stations Driven by High Speed Railway Systems

by Morris Brenna¹

, Michela Longo^1,*

and Wahiba Yaïci²

¹ Department of Energy, Politecnico di Milano, via La Masa, 34-20156 Milano, Italy

² CanmetENERGY Research Centre, Natural Resources Canada, 1 Haanel Drive, Ottawa, ON K1A 1M1, Canada

Energies 2017, 10(9), 1268; https://doi.org/10.3390/en10091268 - 25 Aug 2017

Cited by 26 | Viewed by 9616

Abstract

The aim of this investigation is the analysis of the opportunity introduced by the use of railway infrastructures for the power supply of fast charging stations located in highways. Actually, long highways are often located far from urban areas and electrical infrastructure, therefore [...] Read more.

The aim of this investigation is the analysis of the opportunity introduced by the use of railway infrastructures for the power supply of fast charging stations located in highways. Actually, long highways are often located far from urban areas and electrical infrastructure, therefore the installations of high power charging areas can be difficult. Specifically, the aim of this investigation is the analysis of the opportunity introduced by the use of railway infrastructures for the power supply of fast charging stations located in highways. Specifically, this work concentrates on fast-charging electric cars in motorway service areas by using high-speed lines for supplying the required power. Economic, security, safety and environmental pressures are motivating and pushing countries around the globe to electrify transportation, which currently accounts for a significant amount, above 70 percent of total oil demand. Electric cars require fast-charging station networks to allowing owners to rapidly charge their batteries when they drive relatively long routes. In other words, this means about the infrastructure towards building charging stations in motorway service areas and addressing the problem of finding solutions for suitable electric power sources. A possible and promising solution is proposed in the study that involves using the high-speed railway line, because it allows not only powering a high load but also it can be located relatively near the motorway itself. This paper presents a detailed investigation on the modelling and simulation of a 2 × 25 kV system to feed the railway. A model has been developed and implemented using the SimPower systems tool in MATLAB/Simulink to simulate the railway itself. Then, the model has been applied to simulate the battery charger and the system as a whole in two successive steps. The results showed that the concept could work in a real situation. Nonetheless if more than twenty 100 kW charging bays are required in each direction or if the line topology is changed for whatever reason, it cannot be guaranteed that the railway system will be able to deliver the additional power that is necessary. 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, 8133 KiB

Open AccessFeature PaperArticle

3-D FEM Analysis, Prototyping and Tests of an Axial Flux Permanent-Magnet Wind Generator

by Joya C. Kappatou^1,*, Georgios D. Zalokostas² and Dimitrios A. Spyratos³

¹ Department of Electrical and Computer Engineering, University of Patras, 26500 Patras, Greece

² Electrical and Computer Engineer, Amazonon 3 Evrytania, 36100 Karpenissi, Greece

³ Electrical and Computer Engineering student, University of Patras, 26500 Patras, Greece

Energies 2017, 10(9), 1269; https://doi.org/10.3390/en10091269 - 26 Aug 2017

Cited by 19 | Viewed by 7132

Abstract

This paper contributes to the research and development of Axial Flux Permanent Magnet Synchronous Machines (AFPMSM); and in particular the design, the construction stages and measurements of a double rotor single internal non-ferromagnetic stator with a trapezoidal-concentrated winding machine for wind power generation [...] Read more.

This paper contributes to the research and development of Axial Flux Permanent Magnet Synchronous Machines (AFPMSM); and in particular the design, the construction stages and measurements of a double rotor single internal non-ferromagnetic stator with a trapezoidal-concentrated winding machine for wind power generation applications. The initial dimensions of the machine were calculated using analytical formulas and a model was created and analyzed using the 3D Finite Element Method (FEM). The shape of the magnets of the machine was optimized and presented in a previous paper and a prototype was constructed and tested in the laboratory. In addition, a temperature test of the stator was performed experimentally. Finally, the effect of the different axial widths of the two air gaps on the electrical magnitudes and the field of the machine were investigated using both FEM analysis and experiments. Full article

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

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25 pages, 3133 KiB

Open AccessArticle

A Decision Framework for Electric Vehicle Charging Station Site Selection for Residential Communities under an Intuitionistic Fuzzy Environment: A Case of Beijing

by Yunna Wu^1,2, Chao Xie^1,2,*, Chuanbo Xu^1,2 and Fang Li^1,2

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

² Beijing Key Laboratory of New Energy and Low-Carbon Development, North China Electric Power University, Beijing 102206, China

Energies 2017, 10(9), 1270; https://doi.org/10.3390/en10091270 - 26 Aug 2017

Cited by 62 | Viewed by 7045

Abstract

Electric vehicle charging station (EVCS) site selection occupies a prominent position in the development of the electric community to solve the hard problem of Electric Vehicle (EV) charging. However, two critical issues have not been solved by the existing research. Firstly, the scope [...] Read more.

Electric vehicle charging station (EVCS) site selection occupies a prominent position in the development of the electric community to solve the hard problem of Electric Vehicle (EV) charging. However, two critical issues have not been solved by the existing research. Firstly, the scope of EVCS site selection only considers the whole city, which deviates from the actual situation. Secondly, the uncertainty and hesitation of decision information is not well expressed. To handle the above problems, this paper builds a comprehensive EVCS site selection decision framework for Residential Communities (EVCSRC) with triangular intuitionistic fuzzy numbers (TIFNs). First of all, the distinctive index system of EVCSRC site selection factors including economy, social, environment, planning and feature portrait of residential communities is established. Then, the TIFNs is utilized for decision makers (DMs) to express the indeterminate information. Furthermore, a fuzzy Vlsekriterijumska Optimizacija I Kompromisno Resenje (Fuzzy-VIKOR) is approach is utilized to rank the alternative EVCSRC sites. Finally, a case of Beijing is studied to demonstrate the validity of the proposed site selection framework. The result shows the EVCSRC site located at Sijiqing community in Haidian district should be selected as the optimal site. This paper presents a feasible and easy-to-use decision-making framework for investors. Full article

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

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18 pages, 7768 KiB

Open AccessArticle

Multi-Objective Optimal Charging Method for Lithium-Ion Batteries

by Xiaogang Wu^1,2,*, Wenwen Shi^1,3

and Jiuyu Du³

¹ College of Electrical and Electronics Engineering, Harbin University of Science and Technology, Harbin 150080, China

² State Key Laboratory of Power Transmission Equipment & System Security and New Technology, Chongqing University, Chongqing 400044, China

³ State Key Laboratory of Automotive Safety and Energy, Tsinghua University, Beijing 100084, China

Energies 2017, 10(9), 1271; https://doi.org/10.3390/en10091271 - 26 Aug 2017

Cited by 29 | Viewed by 6374

Abstract

In order to optimize the charging of lithium-ion batteries, a multi-stage charging method that considers the charging time and energy loss as optimization targets has been proposed in this paper. First, a dynamic model based on a first-order circuit has been established, and [...] Read more.

In order to optimize the charging of lithium-ion batteries, a multi-stage charging method that considers the charging time and energy loss as optimization targets has been proposed in this paper. First, a dynamic model based on a first-order circuit has been established, and the model parameters have been identified. Second, on the basis of the established model, we treat the objective function of the optimization problem as a weighted sum of charging time and energy loss. Finally, a dynamic programming algorithm (DP) has been used to calculate the charging current of the objective function. Simulation and experimental results show that the proposed charging method could effectively reduce the charging time and decrease the energy loss, compared with the constant-current constant-voltage charging method, under the premise of exerting little influence on the attenuation of battery capacity. Full article

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

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13 pages, 4726 KiB

Open AccessArticle

An Electro-Geometric Model for Lightning Shielding of Multiple Wind Turbines

by Li Zhang¹, Guozheng Wang^1,*

, Wenfang Zhang¹, Yufei Ma², Zixin Guo² and Qingmin Li²

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

² School of Electrical & Electronic Engineering, North China Electric Power University, Beijing 102206, China

Energies 2017, 10(9), 1272; https://doi.org/10.3390/en10091272 - 26 Aug 2017

Cited by 9 | Viewed by 6798

Abstract

Wind turbine blades being struck by lightning is one of the most urgent problems facing wind farms. In order to reduce the probability of lightning accidents on wind farms, this paper presents a new electro-geometric model for multiple turbines. In this new model, [...] Read more.

Wind turbine blades being struck by lightning is one of the most urgent problems facing wind farms. In order to reduce the probability of lightning accidents on wind farms, this paper presents a new electro-geometric model for multiple turbines. In this new model, based on the physical model of lightning leader development, the striking distance range of the blade tip receptor is calculated, taking into account the influence of the charged particles around the blade. Lightning shielding amongst multiple turbines is provided in combination with the traditional electro-geometric model, and a criterion formula is obtained for mutual shielding for multiple turbines. The influence of environmental factors, such as temperature, atmospheric pressure, air humidity, and altitude, on lightning shielding on large-scale wind farms is also analyzed by studying the lightning shielding distance between wind turbines. The calculation shows that the larger the relative air density and the absolute humidity, and the lower the altitude, and the larger the lightning shielding distance between wind turbines. The method proposed in this paper provides a theoretical basis for the lightning protection on wind farms under different environmental conditions. Full article

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

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15 pages, 2392 KiB

Open AccessArticle

A Principal Components Rearrangement Method for Feature Representation and Its Application to the Fault Diagnosis of CHMI

by Zhuo Liu¹

, Tianzhen Wang^1,*

, Tianhao Tang¹ and Yide Wang²

¹ Department of Electrical Automation, Shanghai Maritime University, Shanghai 201306, China

² Institut d’Electronique et Télécommunications de Rennes, UMR CNRS 6164, Polytech Nantes, Rue Christian Pauc, BP 50609, 44306 Nantes CEDEX 3, France

Energies 2017, 10(9), 1273; https://doi.org/10.3390/en10091273 - 26 Aug 2017

Cited by 14 | Viewed by 4200

Abstract

Cascaded H-bridge Multilevel Inverter (CHMI) is widely used in industrial applications thanks to its many advantages. However, the reliability of a CHMI is decreased with the increase of its levels. Fault diagnosis techniques play a key role in ensuring the reliability of a [...] Read more.

Cascaded H-bridge Multilevel Inverter (CHMI) is widely used in industrial applications thanks to its many advantages. However, the reliability of a CHMI is decreased with the increase of its levels. Fault diagnosis techniques play a key role in ensuring the reliability of a CHMI. The performance of a fault diagnosis method depends on the characteristics of the extracted features. In practice, some extracted features may be very similar to ensure a good diagnosis performance at some H-bridges of CHMI. The situation becomes even worse in the presence of noise. To fix these problems, in this paper, signal denoising and data preprocessing techniques are firstly developed. Then, a Principal Components Rearrangement method (PCR) is proposed to represent the different features sufficiently distinct from each other. Finally, a PCR-based fault diagnosis strategy is designed. The performance of the proposed strategy is compared with other fault diagnosis strategies, based on a 7-level CHMI hardware platform. Full article

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

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16 pages, 3479 KiB

Open AccessArticle

A Study on the Prediction of the Optimum Performance of a Small-Scale Desalination System Using Solar Heat Energy

by Yong-Joon Jun¹

, Young-Hak Song² and Kyung-Soon Park^3,*

¹ Department of Architectural Engineering, Dong-Eui University, Busan 47340, Korea

² Department of Architectural Engineering, ERI, Gyeongsang National University, Jinju 52828, Korea

³ Architectural Engineering Major, Division of Urban, Architecture and Civil Engineering, Dong-Eui University, Busan 47340, Korea

Energies 2017, 10(9), 1274; https://doi.org/10.3390/en10091274 - 27 Aug 2017

Cited by 9 | Viewed by 3911

Abstract

Although water is an essential element for the survival of all humankind, there are, however, still areas where water is not sufficiently supplied. It is a reality today that supplying energy for producing clean water is also difficult in such areas. This study [...] Read more.

Although water is an essential element for the survival of all humankind, there are, however, still areas where water is not sufficiently supplied. It is a reality today that supplying energy for producing clean water is also difficult in such areas. This study develops a fresh water generator using solar heat, which is a clean energy source, and a small-scale desalination system which can be configured in parallel so that it can cope with various changes in the water supply situation. In addition, this study has developed a simulation program capable of estimating the optimum installation angle of a solar collector in such a way as to be suitable for the period of water demand, as well as the environment of the installation area, by allowing for the fact that it is difficult to change the installation angle or conditions after the installation of a fixed solar collector. In order to carry out these issues, this study has set up the experimental apparatus of a small-scale desalination system and obtained data on the amounts of fresh water generation depending on solar heat storage temperatures through empirical experiments. By applying the data in the simulation program, this study proposed the optimum installation angle for the necessary conditions. Full article

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

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25 pages, 5965 KiB

Open AccessArticle

A Novel Locality Algorithm and Peer-to-Peer Communication Infrastructure for Optimizing Network Performance in Smart Microgrids

by Silvia Marzal^*, Raul González-Medina

, Robert Salas-Puente

, Emilio Figueres and Gabriel Garcerá

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(9), 1275; https://doi.org/10.3390/en10091275 - 27 Aug 2017

Cited by 20 | Viewed by 6386

Abstract

Peer-to-Peer (P2P) overlay communications networks have emerged as a new paradigm for implementing distributed services in microgrids due to their potential benefits: they are robust, scalable, fault-tolerant, and they can route messages even when a large number of nodes are frequently entering or [...] Read more.

Peer-to-Peer (P2P) overlay communications networks have emerged as a new paradigm for implementing distributed services in microgrids due to their potential benefits: they are robust, scalable, fault-tolerant, and they can route messages even when a large number of nodes are frequently entering or leaving the network. However, current P2P systems have been mainly developed for file sharing or cycle sharing applications where the processes of searching and managing resources are not optimized. Locality algorithms have gained a lot of attention due to their potential to provide an optimized path to groups with similar interests for routing messages in order to achieve better network performance. This paper develops a fully functional decentralized communication architecture with a new P2P locality algorithm and a specific protocol for monitoring and control of microgrids. Experimental results show that the proposed locality algorithm reduces the number of lookup messages and the lookup delay time. Moreover, the proposed communication architecture heavily depends of the lookup used algorithm as well as the placement of the communication layers within the architecture. Experimental results will show that the proposed techniques meet the network requirements of smart microgrids, even with a large number of nodes on stream. Full article

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

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29 pages, 2805 KiB

Open AccessArticle

Control Structures Evaluation for a Salt Extractive Distillation Pilot Plant: Application to Bio-Ethanol Dehydration

by Carlos Alberto Torres Cantero, Guadalupe Lopez Lopez^*

, Victor M. Alvarado, Ricardo F. Escobar Jimenez

, Jesse Y. Rumbo Morales and Eduardo M. Sanchez Coronado

Tecnológico Nacional de México, TecNM/CENIDET, Int. Interado Palmira S/N, Col. Palmira, Cuernavaca 62490, Mexico

Energies 2017, 10(9), 1276; https://doi.org/10.3390/en10091276 - 27 Aug 2017

Cited by 24 | Viewed by 7972

Abstract

This paper addresses the challenge of evaluating control structures for a salt extractive distillation column producing absolute ethanol for use as biofuel. A sensitivity analysis aided with designing a pseudo-binary distillation pilot plant and examining the conceived process and the influence of the [...] Read more.

This paper addresses the challenge of evaluating control structures for a salt extractive distillation column producing absolute ethanol for use as biofuel. A sensitivity analysis aided with designing a pseudo-binary distillation pilot plant and examining the conceived process and the influence of the reflux ratio on both product purity and energy consumption. We compare three control structures for inferential tracking of the distillate composition: a dual-temperature control with an RV (reflux/boilup) structure and two single-end temperature control configurations, and their performance is measured using deterministic indicators. The result is the proposal of a pilot plant design for treating 15 kg/h of a diluted mixture with mole fraction of ethanol equal to 0.2 and assuming a column efficiency of 50%. The R/F (reflux to feed ratio) configuration is the best control structure, given that its corresponding performance indicators conduct lowest steady-state errors, less oscillating responses, and reduced settling times. For this configuration, the reflux flow rate is rationed to the feed flow rate, and the temperature is controlled manipulating the distillate flow rate. Even subject to perturbations, the energy consumption of the plant remains close to the nominal value. The three evaluated control structures consistently met international quality standards for fuel ethanol and enhanced the use of salts in ethanol dehydration. Full article

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8 pages, 1031 KiB

Open AccessArticle

The Effect of Imbalanced Carrier Transport on the Efficiency Droop in GaInN-Based Blue and Green Light-Emitting Diodes

by Jun Hyuk Park¹, Jaehee Cho^2,*

, E. Fred Schubert³ and Jong Kyu Kim^1,*

¹ Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang 37673, Korea; junhyuk@postech.ac.kr

² School of Semiconductor and Chemical Engineering, Semiconductor Physics Research Center, Chonbuk National University, Jeonju 54896, Korea

³ Department for Electrical, Computer, and Systems Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180, USA; efschubert@rpi.edu

Energies 2017, 10(9), 1277; https://doi.org/10.3390/en10091277 - 27 Aug 2017

Cited by 15 | Viewed by 4374

Abstract

The effect of strongly-imbalanced carrier concentration and mobility on efficiency droop is studied by comparing the onset voltage of high injection, the onset current density of the droop, and the magnitude of the droop, as well as their temperature dependence, of GaInN-based blue [...] Read more.

The effect of strongly-imbalanced carrier concentration and mobility on efficiency droop is studied by comparing the onset voltage of high injection, the onset current density of the droop, and the magnitude of the droop, as well as their temperature dependence, of GaInN-based blue and green light-emitting diodes (LEDs). An n-to-p asymmetry factor is defined as σn/σp, and was found to be 17.1 for blue LEDs and 50.1 for green LEDs. Green LEDs, when compared to blue LEDs, were shown to enter the high-injection regime at a lower voltage, which is attributed to their less favorable p-type transport characteristics. Green LEDs, with lower hole concentration and mobility, have a lower onset current density of the efficiency droop and a higher magnitude of the efficiency droop when compared to blue LEDs. The experimental results are in quantitative agreement with the imbalanced carrier transport causing the efficiency droop, thus providing guidance for alleviating the phenomenon of efficiency droop. Full article

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

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22 pages, 2176 KiB

Open AccessArticle

Electrochemical-Thermal Modelling and Optimisation of Lithium-Ion Battery Design Parameters Using Analysis of Variance

by Elham Hosseinzadeh^*, James Marco and Paul Jennings

Warwick Manufacturing Group, International Digital Laboratory, University of Warwick, Coventry CV4 7AL, UK

Energies 2017, 10(9), 1278; https://doi.org/10.3390/en10091278 - 28 Aug 2017

Cited by 69 | Viewed by 7408

Abstract

A 1D electrochemical-thermal model of an electrode pair of a lithium ion battery is developed in Comsol Multiphysics. The mathematical model is validated against the literature data for a 10 Ah lithium phosphate (LFP) pouch cell operating under 1 C to 5 C [...] Read more.

A 1D electrochemical-thermal model of an electrode pair of a lithium ion battery is developed in Comsol Multiphysics. The mathematical model is validated against the literature data for a 10 Ah lithium phosphate (LFP) pouch cell operating under 1 C to 5 C electrical load at 25 °C ambient temperature. The validated model is used to conduct statistical analysis of the most influential parameters that dictate cell performance; i.e., particle radius (

r_{p}

); electrode thickness (

L_{p o s}

); volume fraction of the active material (

ε_{s, p o s}

) and C-rate; and their interaction on the two main responses; namely; specific energy and specific power. To achieve an optimised window for energy and power within the defined range of design variables; the range of variation of the variables is determined based on literature data and includes:

r_{p}

: 30–100 nm;

L_{p o s}

: 20–100 μm;

ε_{s, p o s}

: 0.3–0.7; C-rate: 1–5. By investigating the main effect and the interaction effect of the design variables on energy and power; it is observed that the optimum energy can be achieved when (r_p < 40 nm); (75 μm < L_pos < 100 μm); (0.4 < ε_s,pos < 0.6) and while the C-rate is below 4C. Conversely; the optimum power is achieved for a thin electrode (

L_{p o s}

< 30 μm); with high porosity and high C-rate (5 C). Full article

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

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14 pages, 3975 KiB

Open AccessArticle

Recovery of Low Permeability Reservoirs Considering Well Shut-Ins and Surfactant Additivities

by Shuai Li^1,2,*, Jun Tang^3,*, Yunhong Ding¹, Shimin Liu², Guangfeng Liu⁴ and Bo Cai¹

¹ Research Institute of Petroleum Exploration & Development, PetroChina, Beijing 100083, China

² Department of Energy and Mineral Engineering, G3 Center and Energy Institute, Pennsylvania State University, University Park, PA 16802, USA

³ School of Geosciences, Yangtze University, Wuhan 430100, China

⁴ Education Ministry Key Laboratory of Petroleum Engineering, China University of Petroleum, Beijing 102249, China

Energies 2017, 10(9), 1279; https://doi.org/10.3390/en10091279 - 28 Aug 2017

Cited by 22 | Viewed by 3997

Abstract

To investigate the mechanism whereby well shut-ins and surfactant additivities can increase hydrocarbon output after hydraulic fracturing, in this paper, we simulated well shut-ins with one end open (OEO) rock samples and performed a serious of imbibition experiments with different surfactant additivities based [...] Read more.

To investigate the mechanism whereby well shut-ins and surfactant additivities can increase hydrocarbon output after hydraulic fracturing, in this paper, we simulated well shut-ins with one end open (OEO) rock samples and performed a serious of imbibition experiments with different surfactant additivities based on contact angle (CA) and interfacial tension (IFT) measurements. Scanning electron microscope (SEM) and nuclear magnetic resonance (NMR) methods were also been adopted in the detection before and after shut-ins. The results demonstrated that cationic surfactants result in better improving oil recovery (IOR) performance due to their high wettability alteration ability on vertical fracture faces, while different kinds of surfactants have a similar ability in lowering IFT. As for shut-ins duration, the NMR transverse relaxation time (T₂) spectrum move towards the left side, indicating that aqueous phases migrate to smaller pores spaces and deeper distances. Aqueous migration during the shut-ins period can remove near-fracture trapped water, while surfactant additivities can accelerate and enhance this process, and these two points are the most direct reasons for the observed hydrocarbon output increases. Full article

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

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18 pages, 4697 KiB

Open AccessArticle

Experimental Investigation of the Condensation Heat Transfer Coefficient of R134a inside Horizontal Smooth and Micro-Fin Tubes

by Qingpu Li^*, Leren Tao, Lei Li, Yongpan Hu and Shengli Wu

Institute of Refrigeration and Cryogenics, University of Shanghai for Science and Technology, Shanghai 200093, China

Energies 2017, 10(9), 1280; https://doi.org/10.3390/en10091280 - 28 Aug 2017

Cited by 10 | Viewed by 5842

Abstract

The condensation heat transfer coefficient of R134a was experimentally studied inside two smooth and four micro-fin tubes. The working conditions and structural parameters of the test tubes were selected as the influencing factors, and the experiment was conducted under mass velocities of 400–1100 [...] Read more.

The condensation heat transfer coefficient of R134a was experimentally studied inside two smooth and four micro-fin tubes. The working conditions and structural parameters of the test tubes were selected as the influencing factors, and the experiment was conducted under mass velocities of 400–1100 kg·m⁻²·s⁻¹, condensation temperatures of 35–45 °C and water-testing Reynolds numbers of 8000–22,000, with an inlet superheat of 1–2 °C and outlet subcooling of 1–2 °C at the test section for the refrigerant. Experimental results indicate that the heat transfer coefficient increases with increasing mass velocity and decreasing condensation temperature and water-testing Reynolds number. The heat transfer coefficient of the micro-fin tube with a helix angle of 28° is the highest and that of smooth tube is the lowest for test tubes with the same inner diameter. Tube diameter has a small influence on the heat transfer coefficient for the smooth tubes while the heat transfer coefficient increases with decreasing tube diameter for the micro-fin tubes. The heat transfer coefficient inside the test tube was compared with some well-known existing correlations, and results show that correlations by Cavallini et al., Thome et al., Shah and Akers et al. can estimate the experimental data with mean absolute deviation of less than 30%, and correlations of Dobson and Chato et al. and Jung et al. cannot be used to capture the heat transfer coefficient with mean absolute deviations of 140.18% and 146.23%, respectively. While the Miyara et al. correlation overestimates the heat transfer coefficient, correlations of Cavallini et al., Koyama et al. and Oliver et al. all underestimate the experimental data for the micro-fin tube. Their deviations are from 25 to 55% for micro-fin tubes 3 and 4, while their deviations keep to within 30% for micro-fin tubes 5 and 6. Finally, to improve the correlation prediction accuracy, a dimensionless parameter was introduced to the correlations of Dobson and Chato et al. and Jung et al., and correlations of Cavallini et al., Koyama et al. and Oliver et al. were modified by enhancing the turbulence effect. The prediction accuracy of all modified correlations can be controlled to within 30%. Full article

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20 pages, 6890 KiB

Open AccessArticle

Optimization Design Method and Experimental Validation of a Solar PVT Cogeneration System Based on Building Energy Demand

by Chao Zhou

, Ruobing Liang and Jili Zhang^*

Faculty of Infrastructure Engineering, Dalian University of Technology, Dalian 116024, China

Energies 2017, 10(9), 1281; https://doi.org/10.3390/en10091281 - 28 Aug 2017

Cited by 30 | Viewed by 5416

Abstract

Photovoltaic-thermal (PVT) technology refers to the integration of a photovoltaic (PV) and a conventional solar thermal collector, representing the deep exploitation and utilization of solar energy. In this paper, we evaluate the performance of a solar PVT cogeneration system based on specific building [...] Read more.

Photovoltaic-thermal (PVT) technology refers to the integration of a photovoltaic (PV) and a conventional solar thermal collector, representing the deep exploitation and utilization of solar energy. In this paper, we evaluate the performance of a solar PVT cogeneration system based on specific building energy demand using theoretical modeling and experimental study. Through calculation and simulation, the dynamic heating load and electricity load is obtained as the basis of the system design. An analytical expression for the connection of PVT collector array is derived by using basic energy balance equations and thermal models. Based on analytical results, an optimized design method was carried out for the system. In addition, the fuzzy control method of frequency conversion circulating water pumps and pipeline switching by electromagnetic valves is introduced in this paper to maintain the system at an optimal working point. Meanwhile, an experimental setup is established, which includes 36 PVT collectors with every 6 PVT collectors connected in series. The thermal energy generation, thermal efficiency, power generation and photovoltaic efficiency have been given in this paper. The results demonstrate that the demonstration solar PVT cogeneration system can meet the building energy demand in the daytime in the heating season. Full article

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

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15 pages, 5094 KiB

Open AccessArticle

Development of a Transmission and Distribution Integrated Monitoring and Analysis System for High Distributed Generation Penetration

by Jaewan Suh^1,2,†

, Sungchul Hwang¹

and Gilsoo Jang^1,*

¹ School of Electrical Engineering, Korea University, Anam-ro, Sungbuk-gu, Seoul 02841, Korea

² R&D Evaluation Center, Korea Institute of S&T Evaluation and Planning, 68 Mabang-ro, Seocho-gu, Seoul 06775, Korea

^† The research reported in this study was conducted while Jaewan Suh was affiliated with Korea University

Energies 2017, 10(9), 1282; https://doi.org/10.3390/en10091282 - 28 Aug 2017

Cited by 22 | Viewed by 4788

Abstract

To date, power system analysis has been performed separately for transmission and distribution systems. Due to the small influence of distribution systems on transmission systems, separate analyses have had no accuracy problems in existing power systems. However, as the amount of distributed generation [...] Read more.

To date, power system analysis has been performed separately for transmission and distribution systems. Due to the small influence of distribution systems on transmission systems, separate analyses have had no accuracy problems in existing power systems. However, as the amount of distributed generation (DG) in distribution systems increases, neighboring distribution systems and even transmission systems can be affected by the distributed generation. Therefore, a power system operator needs a new system to analyze the power system, one that considers the mutual interactions between the transmission and distribution systems. This paper presents with applications and case studies a transmission and distribution integrated monitoring and analysis system for high DG penetration. The integrated system analyzes the mutual interaction between the transmission and distribution systems due to DG. The preliminary evaluation of the DG connections is automated in this system, using real time online data. Case studies with practical data show the need and effectiveness of transmission and distribution integrated monitoring and analysis for real power systems with high DG penetration. Full article

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

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15 pages, 6165 KiB

Open AccessArticle

Impacts of Power Grid Frequency Deviation on Time Error of Synchronous Electric Clock and Worldwide Power System Practices on Time Error Correction

by Yao Zhang^1,*, Wenxuan Yao¹

, Shutang You¹

, Wenpeng Yu¹, Ling Wu¹, Yi Cui¹ and Yilu Liu^1,2

¹ Department of Electrical Engineering & Computer Science, The University of Tennessee, Knoxville, TN 37996, USA

² Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA

Energies 2017, 10(9), 1283; https://doi.org/10.3390/en10091283 - 29 Aug 2017

Cited by 12 | Viewed by 6228

Abstract

Synchronous electric clocks utilize power grid frequency as their timing reference. Power grid frequency deviation away from its nominal value results in synchronous electric clocks running fast or running slow (also known as the time error). In this article, statistical analysis on time [...] Read more.

Synchronous electric clocks utilize power grid frequency as their timing reference. Power grid frequency deviation away from its nominal value results in synchronous electric clocks running fast or running slow (also known as the time error). In this article, statistical analysis on time error of synchronous electric clocks around the world is firstly presented using the power grid frequency measurements recorded by the wide-area frequency monitoring network FNET/GridEye. Then, the time error correction (TEC) process provided by electric utilities is analyzed and the worldwide TEC practice is investigated. Eventually, regions of the world where electric utilities provide TEC service are differentiated from those without TEC services. Analytical results demonstrate that the average time error of synchronous electric clocks in North America seems to be less than five seconds, and it has not changed very much over the past few years. On the other hand, the identification results present that up to the end of 2016, many electric utilities around the world, especially in North America and Europe, provided the TEC service to periodically remove the accumulative time error of synchronous electric clocks. Full article

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

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11 pages, 4394 KiB

Open AccessArticle

Online Lithium-Ion Battery Internal Resistance Measurement Application in State-of-Charge Estimation Using the Extended Kalman Filter

by Dian Wang, Yun Bao^* and Jianjun Shi

Department of Physics, Donghua University, Shanghai 201620, China

Energies 2017, 10(9), 1284; https://doi.org/10.3390/en10091284 - 29 Aug 2017

Cited by 97 | Viewed by 16613

Abstract

The lithium-ion battery is a viable power source for hybrid electric vehicles (HEVs) and, more recently, electric vehicles (EVs). Its performance, especially in terms of state of charge (SOC), plays a significant role in the energy management of these vehicles. The extended Kalman [...] Read more.

The lithium-ion battery is a viable power source for hybrid electric vehicles (HEVs) and, more recently, electric vehicles (EVs). Its performance, especially in terms of state of charge (SOC), plays a significant role in the energy management of these vehicles. The extended Kalman filter (EKF) is widely used to estimate online SOC as an efficient estimation algorithm. However, conventional EKF algorithms cannot accurately estimate the difference between individual batteries, which should not be ignored. However, the internal resistance of a battery can represent this difference. Therefore, this work proposes using an EKF with internal resistance measurement based on the conventional algorithm. Lithium-ion battery real-time resistances can help the Kalman filter overcome defects from simplistic battery models. In addition, experimental results show that it is useful to introduce online internal resistance to the estimation of SOC. Full article

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

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37 pages, 9746 KiB

Open AccessArticle

A Novel Hybrid Approach for Numerical Modeling of the Nucleating Flow in Laval Nozzle and Transonic Steam Turbine Blades

by Edris Yousefi Rad

and Mohammad Reza Mahpeykar^*

Department of Mechanical Engineering, Ferdowsi University of Mashhad, Mashhad 9177948974, Iran

Energies 2017, 10(9), 1285; https://doi.org/10.3390/en10091285 - 29 Aug 2017

Cited by 14 | Viewed by 5171

Abstract

In the present research, considering the importance of desirable steam turbine design, improvement of numerical modeling of steam two-phase flows in convergent and divergent channels and the blades of transonic steam turbines has been targeted. The first novelty of this research is the [...] Read more.

In the present research, considering the importance of desirable steam turbine design, improvement of numerical modeling of steam two-phase flows in convergent and divergent channels and the blades of transonic steam turbines has been targeted. The first novelty of this research is the innovative use of combined Convective Upstream Pressure Splitting (CUSP) and scalar methods to update the flow properties at each calculation point. In other words, each property (density, temperature, pressure and velocity) at each calculation point can be computed from either the CUSP or scalar method, depending on the least deviation criterion. For this reason this innovative method is named “hybrid method”. The next novelty of this research is the use of an inverse method alongside the proposed hybrid method to find the amount of the important parameter

z

in the CUSP method, which is herein referred to as “CUSP’s convergence parameter”. Using a relatively simple computational grid, firstly, five cases with similar conditions to those of the main cases under study in this research with available experimental data were used to obtain the value of z by the Levenberg-Marquardt inverse method. With this innovation, first, an optimum value of

z = 2.667

was obtained using the inverse method and then directly used for the main cases considered in the research. Given that the aim is to investigate the two-dimensional, steady state, inviscid and adiabatic modeling of steam nucleating flows in three different nozzle and turbine blade geometries, flow simulation was performed using a relatively simple mesh and the innovative proposed hybrid method (scalar + CUSP, with the desired value of

z = 2.667

). A comparison between the results of the hybrid modeling of the three main cases with experimental data showed a very good agreement, even within shock zones, including the condensation shock region, revealing the efficiency of this numerical modeling method innovation. The main factor in improving the aforementioned results was found to be a reduction of the numerical errors by up to 70% in comparison to conventional methods (scalar, Jameson original), so that the mass flow rate is well conserved, thereby proving better satisfaction of the conservation laws. It should be noted that by using this innovative hybrid method, one can take advantages of both central difference scheme and upstream scheme (scalar and CUSP, respectively) at the same time in simulating complex flows in any other finite volume scheme. Full article

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

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18 pages, 1563 KiB

Open AccessArticle

A Real-Time SOSM Super-Twisting Technique for a Compound DC Motor Velocity Controller

by Onofre A. Morfin¹, Carlos E. Castañeda²

, Antonio Valderrabano-Gonzalez^3,*

, Miguel Hernandez-Gonzalez⁴ and Fredy A. Valenzuela⁵

¹ Departamento de Ingeniería Eléctrica y Computación, Instituto de Ingeniería y Tecnología, Universidad Autónoma de Ciudad Juárez, Chihuahua 32310, Mexico

² Centro Universitario de los Lagos, Universidad de Guadalajara, Lagos de Moreno 47460, Mexico

³ Facultad de Ingeniería, Universidad Panamericana, Zapopan 45615, Mexico

⁴ Facultad de Ciencias Físico-Matemáticas, Universidad Autónoma de Nuevo León, San Nicolás de los Garza 66450, Mexico

⁵ División Académica de Ingeniería y Arquitectura, Universidad Juárez Autónoma de Tabasco, Cunduacán 86040, Mexico

Energies 2017, 10(9), 1286; https://doi.org/10.3390/en10091286 - 29 Aug 2017

Cited by 13 | Viewed by 5278

Abstract

In this paper, a real-time robust closed-loop control scheme for controlling the velocity of a Direct Current (DC) motor in a compound connection is proposed. This scheme is based on the state-feedback linearization technique combined with a second-order sliding mode algorithm, named super-twisting, [...] Read more.

In this paper, a real-time robust closed-loop control scheme for controlling the velocity of a Direct Current (DC) motor in a compound connection is proposed. This scheme is based on the state-feedback linearization technique combined with a second-order sliding mode algorithm, named super-twisting, for stabilizing the system and achieving control goals. The control law is designed to track a periodic square reference signal, being one of the most severe tests applied to closed-loop systems. The DC motor drives a squirrel-cage induction generator which represents the load; this generator must work above the synchronous velocity to deliver the generated power towards the grid. A classical proportional-integral (PI) controller is designed for comparison purposes of the time-domain responses with the proposed second-order sliding mode (SOSM) super-twisting controller. This robust controller uses only a velocity sensor, as is the case of the PI controller, as the time derivative of the velocity tracking variable is estimated via a robust differentiator. Therefore, the measurements of field current and stator current, the signal from a load torque observer, and machine parameters are not necessary for the controller design. The validation and robustness test of the proposed controller is carried out experimentally in a laboratory, where the closed-loop system is subject to an external disturbance and a time-varying tracking signal. This test is performed in real time using a workbench consisting of a DC motor—Alternating Current (AC) generator group, a DC/AC electronic drive, and a dSPACE 1103 controller board. Full article

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16 pages, 1369 KiB

Open AccessArticle

Methodology for the Evaluation of Resilience of ICT Systems for Smart Distribution Grids

by Pau Lloret-Gallego¹

, Mònica Aragüés-Peñalba¹, Lien Van Schepdael², Eduard Bullich-Massagué¹

, Pol Olivella-Rosell¹

and Andreas Sumper^1,*

¹ Centre d’Innovació Tecnològica en Convertidors Estàtics i Accionaments (CITCEA-UPC), Departament d’Enginyeria Elèctrica, ETS d’Enginyeria Industrial de Barcelona, Universitat Politècnica de Catalunya, Avinguda Diagonal, 647, Pl. 2, 08028 Barcelona, Spain

² ELECTA, Electrical Engineering Department, KU Leuven, Kasteelpark Arenberg 10, 3001 Leuven, Belgium

Energies 2017, 10(9), 1287; https://doi.org/10.3390/en10091287 - 29 Aug 2017

Cited by 7 | Viewed by 5516

Abstract

Ensuring resilient operation and control of smart grids is fundamental for empowering their deployment, but challenging at the same time. Accordingly, this study proposes a novel methodology for evaluating resilience of Information and Communication Technology (ICT) systems for smart distribution grids. Analysing how [...] Read more.

Ensuring resilient operation and control of smart grids is fundamental for empowering their deployment, but challenging at the same time. Accordingly, this study proposes a novel methodology for evaluating resilience of Information and Communication Technology (ICT) systems for smart distribution grids. Analysing how the system behaves under changing operating conditions a power system perspective allows to understand how resilient the smart distribution grid is, but the resilience of the ICT system in charge of its operation affects the overall performance of the system and does, therefore, condition its resilience. With the aim of systematising the evaluation of ICT systems’ resilience, this study proposes to combine a standardized modelling of Smart Grids, the Smart Grid Architecture Model (SGAM), with a data structured diagram, the Entity Relationship Model (ERM). The architecture of smart distribution grids is analysed through SGAM. Then, their technical characteristics and functionalities are defined and represented in a ERM diagram. Finally, the attributes or properties of the system components are used to formulate resilience indicators against different types of disturbances. This methodology is then applied to analyse the resilience of a ICT platform being developed in EMPOWER H2020 project. Full article

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

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18 pages, 344 KiB

Open AccessArticle

Optimal Energy Management for Microgrids with Combined Heat and Power (CHP) Generation, Energy Storages, and Renewable Energy Sources

by Guanglin Zhang^1,*

, Yu Cao¹, Yongsheng Cao¹, Demin Li¹ and Lin Wang^2,*

¹ College of Information Science and Technology, Engineering Research Center of Digitized Textile and Fashion Technology, Ministry of Education, Donghua University, Shanghai 201620, China

² Department of Automation, Shanghai Jiaotong University, Shanghai 200240, China

Energies 2017, 10(9), 1288; https://doi.org/10.3390/en10091288 - 29 Aug 2017

Cited by 39 | Viewed by 5463

Abstract

This paper studies an energy management problem for a typical grid-connected microgrid system that consists of renewable energy sources, Combined Heat and Power (CHP) co-generation, and energy storages to satisfy electricity and heat demand simultaneously. We formulate this problem into a stochastic non-convex [...] Read more.

This paper studies an energy management problem for a typical grid-connected microgrid system that consists of renewable energy sources, Combined Heat and Power (CHP) co-generation, and energy storages to satisfy electricity and heat demand simultaneously. We formulate this problem into a stochastic non-convex optimization programming to achieve the minimum microgrid’s operating cost, which is difficult to solve due to its non-convexity and coupling feature of constraints. Existing approaches such as dynamic programming (DP) assume that all the system dynamics are known, which results in a high computational complexity and thus are not feasible in practice. The focus of this paper is on the design of a real-time energy management strategy for the optimal operation of microgrids with low computational complexity. Specifically, derived from a modified Lyapunov optimization technique, an online algorithm with random inputs (e.g., the charging/discharging of energy storage devices, power from the CHP system, the electricity from external power grid, and the renewables generation, etc.), which requires no statistic system information, is proposed. We provide an implementation of the proposed energy management algorithm and prove its optimality theoretically. Based on real-world data traces, extensive empirical evaluations are presented to verify the performance of our algorithm. Full article

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

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12 pages, 3878 KiB

Open AccessArticle

Development of a New Battery Management System with an Independent Balance Module for Electrical Motorcycles

by Jeng-Chyan Muti Lin

Electrical Engineering Department, National Chinyi University of Technology, No. 57, Sec. 2, Zhongshan Rd., Taiping Dist., Taichung 41170, Taiwan

Energies 2017, 10(9), 1289; https://doi.org/10.3390/en10091289 - 29 Aug 2017

Cited by 15 | Viewed by 6742

Abstract

Conventional balance modules are integrated with the battery management system (BMS) and occupy a large area of the BMS system. In addition large balance currents generate high heating rates and require heat dissipation mechanisms. This study proposes an independent structure for the balance [...] Read more.

Conventional balance modules are integrated with the battery management system (BMS) and occupy a large area of the BMS system. In addition large balance currents generate high heating rates and require heat dissipation mechanisms. This study proposes an independent structure for the balance module. Specifically the balance module is removed from of the BMS and is integrated with an off board charger. A new BMS structure is therefore created with a simplified BMS inside the battery module and the heat dissipation requirement for the balance module could be easily met on the charger side. The design, fabrication and test of this new type of BMS on a 72 V heavy electric motorcycle application is detailed in the current work. The new BMS reduces the space and weight required for the BMS in the e-motorcycle. Complexity in the battery module or on the EV side is significantly reduced. The heat dissipation problem associated with the large balance current is also resolved by moving the balance module to the charger end. Full article

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

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17 pages, 3499 KiB

Open AccessArticle

Biodiesel Production Potential from Littered Edible Oil Fraction Using Directly Synthesized S-TiO₂/MCM-41 Catalyst in Esterification Process via Non-Catalytic Subcritical Hydrolysis

by Md Sufi Ullah Siddik Bhuyan¹, Abul Hasnat Md Ashraful Alam¹, Younghwan Chu² and Yong Chan Seo^1,*

¹ Department of Environmental Engineering, Sangji University, Usan-dong, 83 Sangjidae-gil, Wonju-si, Gangwon-do 26339, Korea

² CNS Scientific, 2710-1 Bugwonro, Wonju-si, Gangwon-do 26316, Korea

Energies 2017, 10(9), 1290; https://doi.org/10.3390/en10091290 - 29 Aug 2017

Cited by 12 | Viewed by 5278

Abstract

Due to uncontrolled consumption of fossil fuel it is necessary to use alternative resources as renewable energy. Among all the available liquid fuels biodiesel has drawn attention for producing less emissions and having less aromatic contents than diesel and because it can also [...] Read more.

Due to uncontrolled consumption of fossil fuel it is necessary to use alternative resources as renewable energy. Among all the available liquid fuels biodiesel has drawn attention for producing less emissions and having less aromatic contents than diesel and because it can also be obtained from inferior grade feedstocks. Since the various uses of fats and oils have increased, a significant amount of waste animal fat and used edible oil is generated every year. In this work, we produced biodiesel from littered edible oil fraction (LEOF) via hydrolysis followed by catalytic esterification. Nearly 90% free fatty acids (FFA) content was achieved at 275 °C, after 45 min during hydrolysis and linoleic acid (C18:2) was observed to be the highest component. Compared to refined soybean oil (SBO) the reaction rate was accelerated by the auto-catalytic behavior of free fatty acids (FFA) in littered edible oil fraction (LEOF). For catalytic esterification, S-TiO₂/MCM-41 catalyst was directly synthesized and characterized by using XRD, SEM, NH₃-TPD and Brunauer Emmett Teller (B.E.T). The parameters such as; SO₄⁻² content, TiO₂ loading and calcination temperature were varied to get optimum free fatty acids (FFA) conversion. Fatty acid methyl ester (FAME) conversion was 99.29% using 1% S-TiO₂/MCM-41 catalyst at 240 °C whereas 86.18% was observed with 3.5% catalyst at 180 °C with 20 min. Thus, using S-TiO₂/MCM-41 catalyst in esterification via hydrolysis would be a better option for treating low quality feedstocks. Full article

(This article belongs to the Collection Bioenergy and Biofuel)

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20 pages, 5711 KiB

Open AccessArticle

Day-Ahead Active Power Scheduling in Active Distribution Network Considering Renewable Energy Generation Forecast Errors

by Pengwei Cong, Wei Tang^*, Lu Zhang, Bo Zhang and Yongxiang Cai

College of Information and Electrical Engineering, China Agricultural University, Beijing 100083, China

Energies 2017, 10(9), 1291; https://doi.org/10.3390/en10091291 - 29 Aug 2017

Cited by 24 | Viewed by 5003

Abstract

With large-scale integration of distributed energy resources (DERs), distribution networks have turned into active distribution networks (ADNs). However, management risks and obstacles are caused by this in due to renewable energy generation (REG) forecasting errors. In this paper, a day-ahead active power scheduling [...] Read more.

With large-scale integration of distributed energy resources (DERs), distribution networks have turned into active distribution networks (ADNs). However, management risks and obstacles are caused by this in due to renewable energy generation (REG) forecasting errors. In this paper, a day-ahead active power scheduling method considering REG forecast errors is proposed to eliminate the risks, minimize the costs of distribution companies and achieve optimal power flow. A hierarchical coordination optimization model based on chance constrained programming is established to realize day-ahead optimal scheduling of active power in ADNs coordinated with network reconfiguration, achieving an optimal solution of network topologies and DER outputs. The hierarchical method includes three levels: the first level provides initial values, and multiple iterations between the second and third level are used to solve the multi-period mixed integer nonlinear optimization problem. The randomness due to REG forecast errors is tackled with chance constrained programming in the scheduling procedure. The hybrid particle swarm optimization algorithm is employed to solve the proposed model. Simulation results verify the validity of the proposed method with an improved 33 nodes distribution network. Full article

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

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17 pages, 8968 KiB

Open AccessEditor’s ChoiceArticle

Numerical Analysis of the Combustion and Emission Characteristics of Diesel Engines with Multiple Injection Strategies Using a Modified 2-D Flamelet Model

by Gyujin Kim, Sunyoung Moon, Seungha Lee and Kyoungdoug Min^*

Department of Mechanical and Aerospace Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Korea

Energies 2017, 10(9), 1292; https://doi.org/10.3390/en10091292 - 29 Aug 2017

Cited by 14 | Viewed by 6448

Abstract

The multiple injection strategy has been widely used in diesel engines to reduce engine noise, NO_x and soot formation. Fuel injection developments such as the common-rail and piezo-actuator system provide more precise control of the injection quantity and time under higher injection [...] Read more.

The multiple injection strategy has been widely used in diesel engines to reduce engine noise, NO_x and soot formation. Fuel injection developments such as the common-rail and piezo-actuator system provide more precise control of the injection quantity and time under higher injection pressures. As various injection strategies become accessible, it is important to understand the interaction of each fuel stream and following combustion process under the multiple injection strategy. To investigate these complex processes quantitatively, numerical analysis using CFD is a good alternative to overcome the limitation of experiments. A modified 2-D flamelet model is further developed from previous work to model multi-fuel streams with higher accuracy. The model was validated under various engine operating conditions and captures the combustion and emissions characteristics as well as several parametric variations. The model is expected to be used to suggest advanced injection strategies in engine development processes. Full article

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15 pages, 1672 KiB

Open AccessArticle

Effect of Temperature on the Structural and Physicochemical Properties of Biochar with Apple Tree Branches as Feedstock Material

by Shi-Xiang Zhao, Na Ta and Xu-Dong Wang^*

College of Resources & Environment, Northwest A&F University, 3 Taicheng Road, Yangling 712100, China

Energies 2017, 10(9), 1293; https://doi.org/10.3390/en10091293 - 30 Aug 2017

Cited by 494 | Viewed by 15609

Abstract

The objective of this study was to study the structure and physicochemical properties of biochar derived from apple tree branches (ATBs), whose valorization is crucial for the sustainable development of the apple industry. ATBs were collected from apple orchards located on the Weibei [...] Read more.

The objective of this study was to study the structure and physicochemical properties of biochar derived from apple tree branches (ATBs), whose valorization is crucial for the sustainable development of the apple industry. ATBs were collected from apple orchards located on the Weibei upland of the Loess Plateau and pyrolyzed at 300, 400, 500 and 600 °C (BC300, BC400, BC500 and BC600), respectively. Different analytical techniques were used for the characterization of the different biochars. In particular, proximate and element analyses were performed. Furthermore, the morphological, and textural properties were investigated using scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, Boehm titration and nitrogen manometry. In addition, the thermal stability of biochars was also studied by thermogravimetric analysis. The results indicated that the increasing temperature increased the content of fixed carbon (C), the C content and inorganic minerals (K, P, Fe, Zn, Ca, Mg), while the yield, the content of volatile matter (VM), O and H, cation exchange capacity, and the ratios of O/C and H/C decreased. Comparison between the different samples show that highest pH and ash content were observed in BC500. The number of acidic functional groups decreased as a function of pyrolysis temperature, especially for the carboxylic functional groups. In contrast, a reverse trend was found for the basic functional groups. At a higher temperature, the brunauer–emmett–teller (BET) surface area and pore volume are higher mostly due to the increase of the micropore surface area and micropore volume. In addition, the thermal stability of biochars also increased with the increasing temperature. Hence, pyrolysis temperature has a strong effect on biochar properties, and therefore biochars can be produced by changing pyrolysis temperature in order to better meet their applications. Full article

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

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19 pages, 1555 KiB

Open AccessArticle

Identification of Critical Transmission Lines in Complex Power Networks

by Ziqi Wang¹, Jinghan He^1,*, Alexandru Nechifor², Dahai Zhang¹ and Peter Crossley²

¹ Power System Protection and Control Research Laboratory, Beijing Jiaotong University, Shangyuancun No. 3, Haidian District, Beijing 100044, China

² School of Electrical and Electronic Engineering, The University of Manchester, Manchester M13 9PL, UK

Energies 2017, 10(9), 1294; https://doi.org/10.3390/en10091294 - 30 Aug 2017

Cited by 26 | Viewed by 6013

Abstract

Growing load demands, complex operating conditions, and the increased use of intermittent renewable energy pose great challenges to power systems. Serious consequences can occur when the system suffers various disturbances or attacks, especially those that might initiate cascading failures. Accurate and rapid identification [...] Read more.

Growing load demands, complex operating conditions, and the increased use of intermittent renewable energy pose great challenges to power systems. Serious consequences can occur when the system suffers various disturbances or attacks, especially those that might initiate cascading failures. Accurate and rapid identification of critical transmission lines is helpful in assessing the system vulnerability. This can realize rational planning and ensure reliable security pre-warning to avoid large-scale accidents. In this study, an integrated “betweenness” based identification method is introduced, considering the line’s role in power transmission and the impact when it is removed from a power system. At the same time, the sensitive regions of each line are located by a cyclic addition algorithm (CAA), which can reduce the calculation time and improve the engineering value of the betweenness, especially in large-scale power systems. The simulation result verifies the effectiveness and the feasibility of the identification method. Full article

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

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24 pages, 5804 KiB

Open AccessArticle

Analyses of the Extensible Blade in Improving Wind Energy Production at Sites with Low-Class Wind Resource

by Jiale Li¹

and Xiong (Bill) Yu^1,2,*

¹ Department of Civil Engineering, Case Western Reserve University, 10900 Euclid Avenue, Bingham Building, Cleveland, OH 44106-7201, USA

² Department of Electrical Engineering and Computer Science, Case Western Reserve University, Cleveland, OH 44106, USA

Energies 2017, 10(9), 1295; https://doi.org/10.3390/en10091295 - 30 Aug 2017

Cited by 18 | Viewed by 5795

Abstract

This paper describes the feasibility analysis of an innovative, extensible blade technology. The blade aims to significantly improve the energy production of a wind turbine, particularly at locations with unfavorable wind conditions. The innovative ‘smart’ blade will be extended at low wind speed [...] Read more.

This paper describes the feasibility analysis of an innovative, extensible blade technology. The blade aims to significantly improve the energy production of a wind turbine, particularly at locations with unfavorable wind conditions. The innovative ‘smart’ blade will be extended at low wind speed to harvest more wind energy; on the other hand, it will be retracted to its original shape when the wind speed is above the rated wind speed to protect the blade from damages by high wind loads. An established aerodynamic model is implemented in this paper to evaluate and compare the power output of extensible blades versus a baseline conventional blade. The model was first validated with a monitored power production curve based on the wind energy production data of a conventional turbine blade, which is subsequently used to estimate the power production curve of extended blades. The load-on-blade structures are incorporated as the mechanical criteria to design the extension strategies. Wind speed monitoring data at three different onshore and offshore sites around Lake Erie are used to predict the annual wind energy output with different blades. The effects of extension on the dynamic characteristics of blade are analyzed. The results show that the extensive blade significantly increases the annual wind energy production (up to 20% to 30%) with different blade extension strategies. It, therefore, has the potential to significantly boost wind energy production for utility-scale wind turbines located at sites with low-class wind resource. Full article

(This article belongs to the Collection Wind Turbines)

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13 pages, 5242 KiB

Open AccessArticle

One-Step Self-Assembly Synthesis α-Fe₂O₃ with Carbon-Coated Nanoparticles for Stabilized and Enhanced Supercapacitors Electrode

by Yizhi Yan

, Haolin Tang^*

, Fan Wu, Rui Wang

and Mu Pan

State Key Laboratory of Advanced Technology for Material Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, Hubei, China

Energies 2017, 10(9), 1296; https://doi.org/10.3390/en10091296 - 30 Aug 2017

Cited by 43 | Viewed by 6939

Abstract

A cocoon-like α-Fe₂O₃ nanocomposite with a novel carbon-coated structure was synthesized via a simple one-step hydrothermal self-assembly method and employed as supercapacitor electrode material. It was observed from electrochemical measurements that the obtained α-Fe₂O₃@C electrode showed [...] Read more.

A cocoon-like α-Fe₂O₃ nanocomposite with a novel carbon-coated structure was synthesized via a simple one-step hydrothermal self-assembly method and employed as supercapacitor electrode material. It was observed from electrochemical measurements that the obtained α-Fe₂O₃@C electrode showed a good specific capacitance (406.9 Fg⁻¹ at 0.5 Ag⁻¹) and excellent cycling stability, with 90.7% specific capacitance retained after 2000 cycles at high current density of 10 Ag⁻¹. These impressive results, presented here, demonstrated that α-Fe₂O₃@C could be a promising alternative material for application in high energy density storage. Full article

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

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19 pages, 3484 KiB

Open AccessArticle

Interconnecting Microgrids via the Energy Router with Smart Energy Management

by Yingshu Liu^*, Yue Fang and Jun Li

School of Electrical and Information Engineering, Tianjin University, Tianjin 300072, China

Energies 2017, 10(9), 1297; https://doi.org/10.3390/en10091297 - 30 Aug 2017

Cited by 65 | Viewed by 7923

Abstract

A novel and flexible interconnecting framework for microgrids and corresponding energy management strategies are presented, in response to the situation of increasing renewable-energy penetration and the need to alleviate dependency on energy storage equipment. The key idea is to establish complementary energy exchange [...] Read more.

A novel and flexible interconnecting framework for microgrids and corresponding energy management strategies are presented, in response to the situation of increasing renewable-energy penetration and the need to alleviate dependency on energy storage equipment. The key idea is to establish complementary energy exchange between adjacent microgrids through a multiport electrical energy router, according to the consideration that adjacent microgrids may differ substantially in terms of their patterns of energy production and consumption, which can be utilized to compensate for each other’s instant energy deficit. Based on multiport bidirectional voltage source converters (VSCs) and a shared direct current (DC) power line, the energy router serves as an energy hub, and enables flexible energy flow among the adjacent microgrids and the main grid. The analytical model is established for the whole system, including the energy router, the interconnected microgrids and the main grid. Various operational modes of the interconnected microgrids, facilitated by the energy router, are analyzed, and the corresponding control strategies are developed. Simulations are carried out on the Matlab/Simulink platform, and the results have demonstrated the validity and reliability of the idea for microgrid interconnection as well as the corresponding control strategies for flexible energy flow. 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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13 pages, 6760 KiB

Open AccessArticle

New Prototype of Photovoltaic Solar Tracker Based on Arduino

by Carlos Morón^1,*

, Daniel Ferrández¹, Pablo Saiz², Gabriela Vega¹ and Jorge Pablo Díaz³

¹ Departamento de Tecnología de la Edificación, Universidad Politécnica de Madrid, 28040 Madrid, Spain

² Departamento de Construcciones Arquitectónicas y su Control, Universidad Politécnica de Madrid, 28040 Madrid, Spain

³ Ciclo de Eficiencia Energética y Energía Solar Térmica, Institución Profesional Salesiana, Salesianos Carabanchel, 28044 Madrid, Spain

Energies 2017, 10(9), 1298; https://doi.org/10.3390/en10091298 - 30 Aug 2017

Cited by 33 | Viewed by 16724

Abstract

The global increase in energy demand and exponential exhaustion of fossil recourses has favored the development of new systems of electricity production. Photovoltaic solar energy is undoubtedly one that has the highest application in housings, due to its simplicity and easy implementation. In [...] Read more.

The global increase in energy demand and exponential exhaustion of fossil recourses has favored the development of new systems of electricity production. Photovoltaic solar energy is undoubtedly one that has the highest application in housings, due to its simplicity and easy implementation. In this work, a new prototype of photovoltaic solar tracker with Arduino platform was developed. Feedback control system that allows carrying out solar tracking with two axes using a stepper motor and linear actuator was established through an electronic circuit based on photodiodes. Moreover, real construction of the prototype was carried out, where the effectiveness of the design and its capacity to draw a maximum benefit of an incident radiation can be observed, placing the panel perpendicularly to the received energy and improving its performance for its application in future installations in housings. Results obtained from the comparison between the developed prototype and a static panel oriented according to the latitude of the area, show about 18% energy gain. Full article

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17 pages, 6967 KiB

Open AccessArticle

Research on an Integrated Hydrostatic-Driven Electric Generator with Controllable Load for Renewable Energy Applications

by Tao Wang^1,*

and He Wang²

¹ Ocean College, Zhejiang University, Zhoushan 316000, China

² College of Mechanical and Vehicle Engineering, Hunan University, Changsha 410082, China

Energies 2017, 10(9), 1299; https://doi.org/10.3390/en10091299 - 30 Aug 2017

Cited by 6 | Viewed by 4652

Abstract

A hydrostatic transmission is a promising technology in renewable energy harvesting, such as wind energy and wave energy, where the hydrostatic-driven electric generator is a key energy conversion component. By using analytical and experimental methods, this paper investigates the performance of a novel [...] Read more.

A hydrostatic transmission is a promising technology in renewable energy harvesting, such as wind energy and wave energy, where the hydrostatic-driven electric generator is a key energy conversion component. By using analytical and experimental methods, this paper investigates the performance of a novel hydrostatic-driven electric generator which integrates the functions of an axial piston hydrostatic motor and a permanent magnet electric generator together. The experimental platform consists of a prototype, an adjustable hydrostatic power source, a controllable electrical load, and various sensors. Energy conversions between hydrostatic and electrical forms are evaluated under different operating velocities and control signals. Power loss distributions are presented by combining measured data and analytical calculation. Thermal experiments are implemented under both of natural and oil-forced cooling conditions and it is found that the temperature rise is much lower when the machine is cooled by hydraulic oil. The experiments validate the energy conversion efficiency, steady controllability, and cooling capability of the integrated hydrostatic-driven electric generator. The results can provide references for further efficiency optimization, dynamic control, as well as practical application. Full article

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

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16 pages, 2721 KiB

Open AccessArticle

Modeling and Simulating Long-Timescale Cascading Faults in Power Systems Caused by Line-Galloping Events

by Lizheng Chen¹

, Hengxu Zhang^1,*

, Changgang Li¹ and Huadong Sun²

¹ Key Laboratory of Power System Intelligent Dispatch and Control of the Ministry of Education, Shandong University, Jinan 250061, China

² China Electric Power Research Institute, Haidian District, Beijing 100192, China

Energies 2017, 10(9), 1301; https://doi.org/10.3390/en10091301 - 30 Aug 2017

Cited by 100 | Viewed by 3281

Abstract

With the increasing occurrence of extreme weather events, the short circuit and line-breaking faults in transmission lines caused by line galloping have been threatening the security operation of power systems. These faults are also hard to be simulated with current simulation tools. A [...] Read more.

With the increasing occurrence of extreme weather events, the short circuit and line-breaking faults in transmission lines caused by line galloping have been threatening the security operation of power systems. These faults are also hard to be simulated with current simulation tools. A numerical simulation approach of power systems is presented to simulate the clustered, cascading faults of long-timescale caused by line-galloping events. A simulation framework is constructed in which large numbers of fault scenarios are simulated to reflect the randomness of line galloping. The interaction mechanism between power system operation states and line galloping processes is revealed and simulated by the solution of differences of timescales and parameters. Based on Power System Simulator/Engineering (PSS/E), an extended software package for line galloping simulation is developed with Python, which extends the functionalities of the PSS/E in power system simulation. An example is given to demonstrate the feasibility of the proposed simulation method. Full article

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

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14 pages, 2184 KiB

Open AccessArticle

A Simulation-Based Optimization Method for Hybrid Frequency Regulation System Configuration

by Jie Song¹

, Xin Pan¹, Chao Lu^2,* and Hanchen Xu³

¹ Department of Industrial Engineering, College of Engineering, Peking University, Beijing 100871, China

² Department of Electrical Engineering, Tsinghua University, Beijing 100084, China

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

Energies 2017, 10(9), 1302; https://doi.org/10.3390/en10091302 - 30 Aug 2017

Cited by 8 | Viewed by 3944

Abstract

Frequency regulation is essential for the stability of a power grid with high load fluctuation and integration of new energies. Constrained by the large ramping, a generator alone is not capable of conducting load frequency controls effectively and economically. In this paper, an [...] Read more.

Frequency regulation is essential for the stability of a power grid with high load fluctuation and integration of new energies. Constrained by the large ramping, a generator alone is not capable of conducting load frequency controls effectively and economically. In this paper, an energy storage system (ESS) is introduced to coordinate with generators in automatic generation control (AGC), where ESS and the generator respectively deal with high-frequency load fluctuation and low-portion. We develop a system configuration framework for such a hybrid system, including the operation strategy and capacity optimization. Due to the complexity of the hybrid system, the operation process is captured by a simulation model which considers practical constraints as well as remaining energy management of ESS. Taking advantage of the gradient-based approximation algorithm, we are then able to optimize the capacity of a hybrid system. According to the numerical experiments with real historical AGC data, the hybrid system is shown to perform well in cost reduction and to achieve the regulation tasks. Full article

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

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12 pages, 4796 KiB

Open AccessArticle

Safety Analysis of Grounding Resistance with Depth of Water for Floating PVs

by Jae Woo Ko¹, Hae Lim Cha¹, David Kwang-Soon Kim¹, Jong Rok Lim¹, Gyu Gwang Kim¹, Byeong Gwan Bhang¹, Chang Sub Won², Han Sang Jung³, Dong Hyung Kang⁴ and Hyung Keun Ahn^1,*

¹ Department of Electrical Engineering, Konkuk University, 120 Neungdong-ro, Gwangjin-gu, Seoul 05029, Korea

² Power Conversion R&D Center, LS IS Co., Ltd., LS-ro 116 beon-gil 40, Dongan-gu, Anyang-si 14118, Gyeonggi-do, Korea

³ Water Facility Research Center, K-Water Institute (KWI), 125, 1689 beon-gil, Yuseong-daero, Yuseong-gu, Daejeon 34045, Korea

⁴ Operation & Management Team, K-Water Institute (KWI), K-Water Hapcheon Dam Office, 705, Hapcheonhosu-ro, Yongju-myeon, Hapcheon-gun 50215, Gyeongsangnam-do, Korea

Energies 2017, 10(9), 1304; https://doi.org/10.3390/en10091304 - 1 Sep 2017

Cited by 11 | Viewed by 5693

Abstract

Underwater grounding methods could be applied in deep water for grounding a floating PV (photovoltaic) system. However, the depth at which the electrodes should be located is a controversial subject. In this study, grounding resistance was measured for the first time by analyzing [...] Read more.

Underwater grounding methods could be applied in deep water for grounding a floating PV (photovoltaic) system. However, the depth at which the electrodes should be located is a controversial subject. In this study, grounding resistance was measured for the first time by analyzing the water temperature at different water depths in an area where a floating PV system is installed. The theoretical calculation of the grounding resistance has a maximum error range of 8% compared to the experimentally measured data. In order to meet the electrical safety standards of a floating PV system, a number of electrodes were connected in parallel. In addition, the distance between electrodes and number of electrodes were considered in the test to obtain a formula for the grounding resistance. In addition, the coefficient of corrosion was obtained from an electrode installed underwater a year ago, and it was added to the formula. Through this analysis, it is possible to predict the grounding resistance prior to installing the floating PV system. Furthermore, the electrical safety of the floating PV system could be achieved by considering the seasonal changes in water temperature. Full article

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

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32 pages, 3537 KiB

Open AccessArticle

A Hybrid Approach for Power System Security Enhancement via Optimal Installation of Flexible AC Transmission System (FACTS) Devices

by Tong Kang^1,*

, Jiangang Yao¹, ThanhLong Duong², Shengjie Yang³ and Xiangqian Zhu¹

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

² Department of Electrical Engineering, Industrial University of Ho Chi Minh City, Ho Chi Minh City 700000, Vietnam

³ College of Computer and Information Engineering, Hunan University of Commerce, Changsha 410205, China

Energies 2017, 10(9), 1305; https://doi.org/10.3390/en10091305 - 1 Sep 2017

Cited by 43 | Viewed by 7250

Abstract

Increasing demand for electricity has placed heavy stress on power system security. Therefore, this paper focuses on the problem of how to maximize power system static security in terms of branch loading and voltage level under normal operation and even the most critical [...] Read more.

Increasing demand for electricity has placed heavy stress on power system security. Therefore, this paper focuses on the problem of how to maximize power system static security in terms of branch loading and voltage level under normal operation and even the most critical single line contingency conditions. This paper proposes a hybrid approach to find out the optimal locations and settings of two classical types of flexible AC transmission system (FACTS) devices, namely thyristor-controlled series compensators (TCSCs) and static var compensators (SVCs) for solving this problem. Our proposed approach requires a two-step strategy. Firstly, the min cut algorithm (MCA) and tangent vector technique (TVT) are applied to determine the proper candidate locations of TCSC and SVC respectively so as to reduce the search scope for a solution to the problem, and then the cuckoo search algorithm (CSA) is employed to solve this problem by simultaneously optimizing the locations and settings for TCSC and SVC installation. The proposed hybrid approach has been verified on the IEEE 6-bus and modified IEEE 14-bus test systems. The results indicate that CSA outperforms particle swarm optimization (PSO), proving its effectiveness and potential, and they also show that our proposed hybrid approach can find the best locations and settings for TCSC and SVC devices as an effective way for enhancing power system static security by removing or alleviating the overloads and voltage violations under normal operation and even the most critical single line contingency conditions. Using this hybrid approach, the search space for solution to the problem becomes limited hence the computational burden will be decreased. Full article

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

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19 pages, 3068 KiB

Open AccessArticle

Energy Saving Potential of a Thermoelectric Heat Pump-Assisted Liquid Desiccant System in a Dedicated Outdoor Air System

by Min-Hwi Kim¹

, Joon-Young Park² and Jae-Weon Jeong^2,*

¹ New and Renewable Energy Research Division, Korea Institute of Energy Research, 152 Gajeong-Ro, Yuseong-Gu, Daejeon 34129, Korea

² Department of Architectural Engineering, College of Engineering, Hanyang University, 222 Wangsimni-Ro, Seongdong-Gu, Seoul 04763, Korea

Energies 2017, 10(9), 1306; https://doi.org/10.3390/en10091306 - 1 Sep 2017

Cited by 6 | Viewed by 5499

Abstract

The main objective of this study was to develop a thermoelectric heat pump and liquid desiccant system based on a dedicated outdoor air system (THPLD-DOAS). An internally-cooled and -heated liquid desiccant system was used and a thermoelectric heat pump (THP) served as the [...] Read more.

The main objective of this study was to develop a thermoelectric heat pump and liquid desiccant system based on a dedicated outdoor air system (THPLD-DOAS). An internally-cooled and -heated liquid desiccant system was used and a thermoelectric heat pump (THP) served as the desiccant cooling and heating energy source for dehumidification and regeneration of the desiccant solution, respectively. In order to investigate the energy-saving potential of the proposed system, its thermal performance and operating energy consumption during the cooling season were compared to those of a conventional dedicated outdoor air system with a ceiling radiant cooling panel system (DOAS-CRCP). Detailed simulations for each system were conducted under hot and humid climatic conditions. Their thermal performance under various room sensible heat factor (RSHF) conditions was evaluated to observe the energy performance, depending on the dehumidification performance, of the liquid desiccant system integrated with the THP. The results showed that the coefficient of performance (COP) of the THP ranged from 0.8 to 1.2 to maintain a sufficient dehumidification rate. The operating energy of the THPLD of the proposed system was 6.6% to 16.0% less than that of the chiller operating energy of a conventional DOAS. Consequently, the proposed system consumed 0.6–23.5% less operating energy compared to the conventional DOAS. Full article

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9 pages, 1764 KiB

Open AccessCommunication

Properties of Gasoline Stored in Various Containers

by Cheol-Hwan Jeon^1,2, Cheon-Kyu Park¹, Byung-Ki Na^2,* and Jae-Kon Kim^1,*

¹ Research Institute of Petroleum Technology, Korea Petroleum Quality & Distribution Authority, Cheongju 28115, Korea

² Department of Chemical Engineering, Chungbuk National University, Cheongju 28644, Korea

Energies 2017, 10(9), 1307; https://doi.org/10.3390/en10091307 - 1 Sep 2017

Cited by 6 | Viewed by 4017

Abstract

Recently, consumers in rural areas have complained about the reduction of the octane number for gasoline stored in storage containers made of polyethylene (PE) in Korea. In addition, problems have been found in gasoline that has not been used for a long time [...] Read more.

Recently, consumers in rural areas have complained about the reduction of the octane number for gasoline stored in storage containers made of polyethylene (PE) in Korea. In addition, problems have been found in gasoline that has not been used for a long time in dual-fueled cars that use liquefied petroleum gas and gasoline at the same time. The reduction of the octane number has caused problems in the quality of fuels. To understand the fuel quality problems, the fuel properties of gasoline for automobiles were investigated in this study by storing gasoline for a long time in various simplified storage containers (tin-coated steel, PE, and polyethylene terephthalate (PET)) in a laboratory scale. For the four months of the storage period, the storage containers were kept indoors and outdoors to monitor the research octane number (RON), vapor pressure, oxidation stability, and the content of all the components to evaluate the fuel properties. In addition, the surfaces of containers were analyzed by scanning electron microscope (SEM) images of the PE storage containers that were kept outdoors under extremely harsh conditions. Depending on the storage period, some of the PE storage containers kept indoors and outdoors failed to satisfy the specification of quality standards of the gasoline as the samples with high octane numbers and low boiling points evaporated. In addition, the octane number of the gasoline in PE storage container stored indoors decreased as the content of n-paraffin and olefins having low boiling point components decreased during the storage period. The surface analysis of the PE storage containers kept indoors showed that the gasoline permeated into the surface of the containers. In this study, it has been showed that tin-coated steel material storage containers for gasoline storage are less affected by external influences than PE material storage containers and thus are more advantageous for maintaining stable fuel quality. Full article

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18 pages, 1817 KiB

Open AccessArticle

Cost Analysis for a Hybrid Advanced Metering Infrastructure in Korea

by Sung-Won Park

and Sung-Yong Son^*

Department of Electrical Engineering, Gachon University, 1342 Seongnamdaero, Sujeong-Gu, Seongnam-Si, Gyeonggi-Do 13120, Korea

Energies 2017, 10(9), 1308; https://doi.org/10.3390/en10091308 - 1 Sep 2017

Cited by 7 | Viewed by 5678

Abstract

Advanced metering infrastructure (AMI) refers to the electricity service infrastructure between electricity consumers and suppliers and is technically essential for the realization of a smart grid environment. To implement AMI, various communications technologies are being used based on the application environment according to [...] Read more.

Advanced metering infrastructure (AMI) refers to the electricity service infrastructure between electricity consumers and suppliers and is technically essential for the realization of a smart grid environment. To implement AMI, various communications technologies are being used based on the application environment according to the utility. However, using a single communications method can give rise to attenuation in the downtown underground distribution line section or cause higher supply costs due to decreased density in the range from farming to fishing areas. A hybrid AMI is one solution to this problem. According to an economic analysis of previous AMI deployment, the cost to install a communications network accounts on average for 45% of the total cost. Since the installation cost of a communications network is influenced by the density of the installation environment, a hybrid AMI, which allows the configuration of a flexible network using both wired and wireless communications, can be a good alternative, both technically and financially. This study conducted a simulation based on density of the installation environment and configuration of the communications network to analyze the economic effect of installing a hybrid AMI communications network. It assumed that a hybrid AMI was deployed in an overhead distribution line in a low-density area. The simulation outcomes were compared and analyzed against the power line communication (PLC)-only AMI method. The results showed that the hybrid AMI method had a 10% communications network cost reduction effect compared to the PLC-only AMI method. In addition, the analysis indicated that there was a maximum 19% cost reduction effect in communications network installation depending on the method of network installation, suggesting that the hybrid AMI was economically more effective than the PLC-only AMI method. Full article

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

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19 pages, 5636 KiB

Open AccessArticle

Investigation of Hydraulic-Mechanical Properties of Paste Backfill Containing Coal Gangue-Fly Ash and Its Application in an Underground Coal Mine

by Xinguo Zhang¹, Jia Lin^2,*

, Jinxiao Liu^1,3, Fei Li³ and Zhenzhong Pang³

¹ 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

² School of Civil, Mining and Environmental Engineering, University of Wollongong, Wollongong, NSW 2500, Australia

³ College of Mining and Safety Engineering, Shandong University of Science and Technology, Qingdao 266590, China

Energies 2017, 10(9), 1309; https://doi.org/10.3390/en10091309 - 1 Sep 2017

Cited by 106 | Viewed by 6567

Abstract

Backfilling is widely used to control surface subsidence and stope stability to improve pillar recovery. Furthermore, it is also an effective way to process and dispose of mining waste such as coal gangue and tailings. In this study, the hydraulic-mechanical properties of cemented [...] Read more.

Backfilling is widely used to control surface subsidence and stope stability to improve pillar recovery. Furthermore, it is also an effective way to process and dispose of mining waste such as coal gangue and tailings. In this study, the hydraulic-mechanical properties of cemented paste backfill materials (CPB) were investigated. Twenty-eight cemented coal gangue-fly ash backfill mixtures were prepared with different water, cement, fly ash and coal gangue content and the slump, segregation and water bleeding ratio tests were conducted. Increasing fly ash content increased the slump value and decreased the segregation value of the slurry. The uniaxial compressive strength (UCS) of the cemented coal gangue-fly ash backfill samples were tested at different curing times. Based on the test results, an optimized recipe was used for the field trial. Longwall cut and backfilling mining method was used in the 2300 mining district to recycle the coal pillar between longwall 2301 and 2302. Both stress and displacement meters were installed in the goaf and their performance was monitored continuously. An increase in stress and displacement values were observed to occur with the working face advanced (up to 325 m and 375 m, respectively); thereafter, a trend of stabilization was observed. The monitoring results suggest that the backfills can efficiently control the roof movement and surface subsidence as well as improve pillar recovery. Full article

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

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11 pages, 2308 KiB

Open AccessArticle

Investigation on Slot–Pole Combinations of a PM Vernier Motor with Fractional-Slot Concentrated Winding Configurations

by Byungtaek Kim

Department of Electrical Engineering, Kunsan National University, Gunsan-si 54150, Korea

Energies 2017, 10(9), 1310; https://doi.org/10.3390/en10091310 - 1 Sep 2017

Cited by 12 | Viewed by 6194

Abstract

This paper presents a new method to find available slot–pole combination of a permanent magnet (PM) vernier motor with fractional-slot concentrated winding (FSCW) configurations instead of the conventional design rule. To this aim, for a common structure of PM vernier machines with FSCW, [...] Read more.

This paper presents a new method to find available slot–pole combination of a permanent magnet (PM) vernier motor with fractional-slot concentrated winding (FSCW) configurations instead of the conventional design rule. To this aim, for a common structure of PM vernier machines with FSCW, the air gap flux densities including modulation flux due to vernier effects are investigated from the magnetic view points and then a general condition to effectively use the modulation flux is derived. Under the obtained condition, the specific design condition for slot–pole combinations are established for the most popular FSCW configurations with the coil spans of ±2π/3. Using the established condition, all available vernier structures including those which could not be found by the previous rule are obtained, and the back-electromotive force (EMF) of each structure is analytically estimated to check the vernier effects. During these procedures, it is also revealed that some of general FSCW-PM motors possess vernier effects and thus can be classified into vernier motors. To verify the proposed ideas, the characteristics of back EMF are analyzed through finite element (FE)-simulations for various models, and compared with their analytical calculation results. Finally, the characteristics of torque regarding to slot–pole combinations of the vernier motors are discussed. Full article

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

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11 pages, 3204 KiB

Open AccessArticle

A New Approach for Retaining Mercury in Energy Generation Processes: Regenerable Carbonaceous Sorbents

by Nuria Fernández-Miranda, Elena Rodríguez

, Maria Antonia Lopez-Anton^*, Roberto García and Maria Rosa Martínez-Tarazona

Instituto Nacional del Carbón (CSIC), Francisco Pintado Fe, 26, 33011 Oviedo, Spain

Energies 2017, 10(9), 1311; https://doi.org/10.3390/en10091311 - 1 Sep 2017

Cited by 20 | Viewed by 3603

Abstract

The energy production processes from fossil fuels represent the first anthropogenic source of mercury emissions in Europe and the second in the world. Among the different possibilities that can be posed to reduce these emissions, this work focuses on the use of regenerable [...] Read more.

The energy production processes from fossil fuels represent the first anthropogenic source of mercury emissions in Europe and the second in the world. Among the different possibilities that can be posed to reduce these emissions, this work focuses on the use of regenerable sorbents based on gold nanoparticles dispersed on activated carbon foam. The use of regenerable sorbents would not only allow the objective of reducing mercury emissions, but also avoiding the generation of new toxic wastes. The results showed a retention efficiency of 100% and a retention capacity close to 600 µg·g⁻¹ over several cycles of regeneration. Moreover, acid gases did not poison the support. It was observed that mercury capture in this simulated oxy-combustion atmosphere was a consequence of two mechanisms: (1) the amalgamation of elemental mercury and elemental gold and (2) the oxidation of elemental mercury in the presence of HCl, with the subsequent retention of the oxidized mercury on the surface of the activated carbon foam. The nanodispersion of gold on such supports involves a high initial investment. However, this would be counterbalanced by the remarkable regeneration capacity of the sorbent and the possibility of recovering all the materials used. Full article

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

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14 pages, 2861 KiB

Open AccessArticle

Ethyl Methyl Sulfone-Based Electrolytes for Lithium Ion Battery Applications

by Peter Hilbig¹, Lukas Ibing², Ralf Wagner², Martin Winter^1,2 and Isidora Cekic-Laskovic^1,2,*

¹ Helmholtz-Institute Münster, IEK-12, Forschungszentrum Jülich GmbH, Corrensstrasse 46, 48149 Münster, Germany

² MEET Battery Research Center/Institute of Physical Chemistry, University of Münster, Corrensstrasse 46, 48149 Münster, Germany

Energies 2017, 10(9), 1312; https://doi.org/10.3390/en10091312 - 1 Sep 2017

Cited by 27 | Viewed by 8361

Abstract

Sulfone-based electrolytes, known for their higher oxidative stability compared to the typically used organic carbonate-based electrolytes, are considered promising electrolytes for high voltage cathode materials towards the objective of obtaining increased energy density in lithium ion batteries. Nevertheless, sulfones suffer from high viscosity [...] Read more.

Sulfone-based electrolytes, known for their higher oxidative stability compared to the typically used organic carbonate-based electrolytes, are considered promising electrolytes for high voltage cathode materials towards the objective of obtaining increased energy density in lithium ion batteries. Nevertheless, sulfones suffer from high viscosity as well as incompatibility with highly graphitic anode materials, which limit their application. In this paper, the effect of fluoroethylene carbonate (FEC) as an electrolyte additive for the application of ethyl methyl sulfone (EMS) electrolytes containing LiPF₆ as conducting salt, is studied in graphite-based cells by means of selected electrochemical and spectroscopic methods. In addition, influence of ethylene acetate (EA) as co-solvent on the electrolyte viscosity and conductivity of the EMS-based electrolytes is discussed, revealing improved overall nickel cobalt manganese oxide (NMC)/graphite cell performance. X-ray photoelectron spectroscopy (XPS) measurements provide information about the surface chemistry of the graphite electrodes after galvanostatic cycling. The concept of EA as co-solvent is found to be applicable for other sulfones such as isopropyl methyl sulfone (MeiPrSO₂) and ethyl isopropyl sulfone (EtiPrSO₂). Full article

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

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19 pages, 2348 KiB

Open AccessArticle

A New State of Charge Estimation Algorithm for Lithium-Ion Batteries Based on the Fractional Unscented Kalman Filter

by Yixing Chen¹, Deqing Huang^1,*

, Qiao Zhu², Weiqun Liu², Congzhi Liu³ and Neng Xiong²

¹ School of Electrical Engineering, Southwest Jiaotong University, Chengdu 610031, China

² School of Mechanical Engineering, Southwest Jiaotong University, Chengdu 610031, China

³ The State Key Laboratory of Automotive Safety and Energy, Tsinghua University, Beijing 100084, China

Energies 2017, 10(9), 1313; https://doi.org/10.3390/en10091313 - 1 Sep 2017

Cited by 41 | Viewed by 5131

Abstract

An accurate state of charge (SOC) estimation is the basis of the Battery Management System (BMS). In this paper, a new estimation method which considers fractional calculus is proposed to estimate the lithium battery state of charge. Firstly, a modified second-order RC model [...] Read more.

An accurate state of charge (SOC) estimation is the basis of the Battery Management System (BMS). In this paper, a new estimation method which considers fractional calculus is proposed to estimate the lithium battery state of charge. Firstly, a modified second-order RC model based on fractional calculus theory is developed to model the lithium battery characteristics. After that, a pulse characterization test is implemented to obtain the battery terminal voltage and current, in which the parameter identification is completed based on least square method. Furthermore, the proposed method based on Fractional Unscented Kalman Filter (FUKF) algorithm is applied to estimate the battery state of charge value in both static and dynamic battery discharging experiment. The experimental results have demonstrated that the proposed method shows high accuracy and efficiency for state of charge estimation and the fractional calculus contributes to the battery state of charge estimation. Full article

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20 pages, 3144 KiB

Open AccessFeature PaperArticle

Cost Projection of State of the Art Lithium-Ion Batteries for Electric Vehicles Up to 2030

by Gert Berckmans^*

, Maarten Messagie, Jelle Smekens, Noshin Omar, Lieselot Vanhaverbeke and Joeri Van Mierlo

MOBI Research Group, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium

Energies 2017, 10(9), 1314; https://doi.org/10.3390/en10091314 - 1 Sep 2017

Cited by 478 | Viewed by 54156

Abstract

The negative impact of the automotive industry on climate change can be tackled by changing from fossil driven vehicles towards battery electric vehicles with no tailpipe emissions. However their adoption mainly depends on the willingness to pay for the extra cost of the [...] Read more.

The negative impact of the automotive industry on climate change can be tackled by changing from fossil driven vehicles towards battery electric vehicles with no tailpipe emissions. However their adoption mainly depends on the willingness to pay for the extra cost of the traction battery. The goal of this paper is to predict the cost of a battery pack in 2030 when considering two aspects: firstly a decade of research will ensure an improvement in material sciences altering a battery’s chemical composition. Secondly by considering the price erosion due to the production cost optimization, by maturing of the market and by evolving towards to a mass-manufacturing situation. The cost of a lithium Nickel Manganese Cobalt Oxide (NMC) battery (Cathode: NMC 6:2:2 ; Anode: graphite) as well as silicon based lithium-ion battery (Cathode: NMC 6:2:2 ; Anode: silicon alloy), expected to be on the market in 10 years, will be predicted to tackle the first aspect. The second aspect will be considered by combining process-based cost calculations with learning curves, which takes the increasing battery market into account. The 100 dollar/kWh sales barrier will be reached respectively between 2020-2025 for silicon based lithium-ion batteries and 2025–2030 for NMC batteries, which will give a boost to global electric vehicle adoption. Full article

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

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15 pages, 8202 KiB

Open AccessArticle

Thermal Behaviour under Service Loads of a Thermo-Active Precast Pile

by Borja Badenes^1,*,†

, Teresa Magraner^1,†, Cristina De Santiago², Fernando Pardo de Santayana² and Javier F. Urchueguía¹

¹ Instituto de Aplicaciones de las Comunicaciones Avanzadas (ITACA), Universitat Politècnica de València, Camino de Vera S/N, 46022 Valencia, Spain

² Laboratorio de Geotecnia (CEDEX) C/Alfonso XII, 3 y 5, 28014 Madrid, Spain

^† These authors contributed equally to this work.

Energies 2017, 10(9), 1315; https://doi.org/10.3390/en10091315 - 1 Sep 2017

Cited by 5 | Viewed by 4187

Abstract

A research project was developed in Spain to undertake some studies on the geothermal use of pile foundations (PITERM PROJECT). The experiment consists of a specifically designed, constructed and fully monitored geothermal precast pile driven at Polytechnic University of Valencia. An important distinctive [...] Read more.

A research project was developed in Spain to undertake some studies on the geothermal use of pile foundations (PITERM PROJECT). The experiment consists of a specifically designed, constructed and fully monitored geothermal precast pile driven at Polytechnic University of Valencia. An important distinctive feature of the developed pile was the fact that it was assembled from two identical sections connected with a specific joint, developed by Rodio-Kronsa. This allows the installation of much longer precast piles into the ground. The pile is under two types of loads: mechanical and thermal. The mechanical load was applied by means of a mechanical frame anchored to the ground and three additional anchors used to induce an active compressive force. The thermal load was produced by means of a thermal rig able to inject heat or extract heat from the pile at any desired programable heat injection/extraction rate. One of the features of this precast pile is its geometry, similar to a single U borehole heat exchanger (BHE) which is not common in thermoactive piles, usually equipped with probes attached to the armatures. In our study, we have characterized the thermal behaviour of the precast pile experimentally and simulated its temperature response by means of a TRNSYS model. This article describes part of a test series carried out where the mechanical and thermal behaviour of a pile subjected to thermal and mechanical loads simulating a real pile in a building was studied. Therefore, this publication has only focused on the thermal performance of the pile and its thermal modelling by computer. From this model, the thermal parameters of the soil–pile system have been extracted and compared with those of a single standard single U BHE. In essence, our assessment points to a quite similar thermal behaviour of the studied precast pile compared to a conventional single U borehole heat exchanger of the same length and equivalent diameter, while the installation costs of such elements would be substantially lower due to its double, structural and thermal, function. Full article

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

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15 pages, 1593 KiB

Open AccessArticle

Maximum Power Point Tracking of Photovoltaic Panels by Using Improved Pattern Search Methods

by Andrés Tobón¹, Julián Peláez-Restrepo¹

, Juan P. Villegas-Ceballos¹, Sergio Ignacio Serna-Garcés¹

, Jorge Herrera^2,*

and Asier Ibeas^2,3

¹ Departamento de Electrónica y Telecomunicaciones, Facultad de Ingenierías, Instituto Tecnológico Metropolitano, Medellín, Antioquia, Colombia

² Departamento de Ingeniería, Facultad de Ciencias Naturales e Ingeniería, Universidad de Bogotá Jorge Tadeo Lozano, Bogotá, Distrito Capital, Colombia

³ Departament de Telecomunicació i d’Enginyeria de Sistemes, Escola d’Enginyeria Universitat Autònoma de Barcelona (UAB), Bellaterra, Cerdanyola del Vallés, 08193 Barcelona, Spain

Energies 2017, 10(9), 1316; https://doi.org/10.3390/en10091316 - 1 Sep 2017

Cited by 51 | Viewed by 6688

Abstract

This paper deals with the optimization of maximum power point tracking when a photovoltaic panel is modelled as two diodes. The adopted control is implemented using a sliding mode control (SMC) and the optimization is implemented using an improved Pattern Search Method. Thus, [...] Read more.

This paper deals with the optimization of maximum power point tracking when a photovoltaic panel is modelled as two diodes. The adopted control is implemented using a sliding mode control (SMC) and the optimization is implemented using an improved Pattern Search Method. Thus, the problem of maximum power point tracking is reduced to an optimization problem whose solution is implemented by Pattern Search Techniques, inheriting their convergence properties. Simulation examples show the effectiveness of the proposed technique in practice, being able to deal with different radiations. In addition, improved pattern search method (IPSM) is compared with other techniques such as perturb & observe and Particle Swarm optimization, after which IPSM presents lower energy losses in comparison with the other two algorithms, with the advantage of ensuring the location of the optimal power point in all cases. Full article

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

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20 pages, 848 KiB

Open AccessArticle

Economic Valuation of Low-Load Operation with Auxiliary Firing of Coal-Fired Units

by Gang Wang, Daihai You, Suhua Lou^*, Zhe Zhang and Li Dai

State Key Laboratory of Advanced Electromagnetic Engineering and Technology, Huazhong University of Science and Technology, No.1037, Luoyu Road, 430074 Wuhan, China

Energies 2017, 10(9), 1317; https://doi.org/10.3390/en10091317 - 1 Sep 2017

Cited by 15 | Viewed by 3165

Abstract

It is often claimed that coal-fired units are highly inflexible to accommodate variable renewable energy. However, a recently published report illustrates that making existing coal-fired units more flexible is both technically and economically feasible. Auxiliary firing is an effective and promising measure for [...] Read more.

It is often claimed that coal-fired units are highly inflexible to accommodate variable renewable energy. However, a recently published report illustrates that making existing coal-fired units more flexible is both technically and economically feasible. Auxiliary firing is an effective and promising measure for coal-fired units to reduce their minimum loads and thus augment their flexibility. To implement the economic valuation of low-load operation with auxiliary firing (LLOAF) of coal-fired units, we improve the traditional fuel cost model to express the operating costs of LLOAF and present the economic criterion and economic index to assess the economics of LLOAF for a single coal-fired unit. Moreover, we investigate the economic value of LLOAF in the power system operation via day-ahead unit commitment problem and analyze the impacts on the scheduling results from unit commitment policies and from extra auxiliary fuel costs. Numerical simulations show that with the reduction of the extra auxiliary fuel costs LLOAF of coal-fired units can remarkably decrease the total operating costs of the power system. Some further conclusions are finally drawn. Full article

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

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23 pages, 4604 KiB

Open AccessArticle

An Energy-Efficient Coverage Algorithm for Macrocell—Small Cell Network Systems

by Yao-Liang Chung

Department of Communications, Navigation and Control Engineering, National Taiwan Ocean University, Keelung City 20224, Taiwan

Energies 2017, 10(9), 1319; https://doi.org/10.3390/en10091319 - 1 Sep 2017

Cited by 6 | Viewed by 3614

Abstract

The energy efficiency of a macrocell base station (MBS) can be substantially improved via the deployment of small cell base stations (SBSs) within the coverage area of the MBS. Moreover, this approach is expected to remain a key feature of communication network markets [...] Read more.

The energy efficiency of a macrocell base station (MBS) can be substantially improved via the deployment of small cell base stations (SBSs) within the coverage area of the MBS. Moreover, this approach is expected to remain a key feature of communication network markets in the future. However, little research has been conducted to uncover effective solutions to the issue of coverage holes (i.e., specific locations or areas in which a user is not able to get an adequate signal from the wireless network) that may occur in the context of such a network architecture. To address this dearth of relevant research, the present study proposes an energy-efficient coverage algorithm utilizing novel system configurations, for use in such macrocell—small cell network systems. The goal of the proposed algorithm is providing the maximum possible reduction of the combined power consumed by the transceivers of all the BSs (that is, the SBSs and the MBS), while simultaneously guaranteeing the provision of comprehensive wireless signal coverage to users under various scenarios. In order to accomplish this aim in an efficient manner, the algorithm smartly adjusts the power levels of all the SBSs in a given system, including the full deactivation of a previously active SBS, or the activation of a previously inactive SBS, according to the dynamics of the given network traffic, thereby modifying their power consumption as necessary. The results for simulations of various test scenarios indicated that the algorithm exhibits better performance than two conventional methods in terms of its overall effects on coverage, power usage, and average transmission rate. The simulated power savings yielded by the proposed algorithm were particularly notable, as it garnered an improvement as high as 78% under the condition of light traffic volumes. Full article

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25 pages, 5278 KiB

Open AccessArticle

Wave Energy Resource Assessment off the Coast of China around the Zhoushan Islands

by Yong Wan^1,2,3,*, Chenqing Fan², Jie Zhang², Junmin Meng², Yongshou Dai¹, Ligang Li¹, Weifeng Sun¹, Peng Zhou¹, Jing Wang³ and Xudong Zhang³

¹ College of Information and Control Engineering, China University of Petroleum, No. 66, Changjiangxi Road, Huangdao District, Qingdao 266580, China

² The First Institute of Oceanography, State Oceanic Administration, No. 6, Xianxialing Road, Laoshan District, Qingdao 266061, China

³ College of Information Science and Engineering, Ocean University of China, No. 238, Songling Road, Laoshan District, Qingdao 266100, China

Energies 2017, 10(9), 1320; https://doi.org/10.3390/en10091320 - 1 Sep 2017

Cited by 24 | Viewed by 4894

Abstract

Based on ERA-Interim reanalysis wave field data for the 36 years from 1979 to 2014, the temporal and spatial distributions and development potential of wave energy are studied in detail in the offshore and relatively nearshore waters adjacent to the Zhoushan Islands. The [...] Read more.

Based on ERA-Interim reanalysis wave field data for the 36 years from 1979 to 2014, the temporal and spatial distributions and development potential of wave energy are studied in detail in the offshore and relatively nearshore waters adjacent to the Zhoushan Islands. The results show that areas of relatively high wave energy are located in the offshore waters to the east and southeast of the Zhoushan Islands. The potential wave energy in relatively nearshore waters (water depths from 10 m to 65 m) is relatively higher and especially in the nearshore waters to the southeast of the city of Taizhou, Zhejiang Province, which are suitable locations for wave energy development. The conclusions provide scientific guidance for wave energy development in the sea areas adjacent to the Zhoushan Islands. Full article

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

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17 pages, 2802 KiB

Open AccessArticle

Green Carbon Composite-Derived Polymer Resin and Waste Cotton Fibers for the Removal of Alizarin Red S Dye

by Béchir Wanassi^1,2, Ichrak Ben Hariz³, Camélia Matei Ghimbeu^2,*

, Cyril Vaulot² and Mejdi Jeguirim^2,*

¹ Laboratoire du Génie Textile, LGTex, Université de Monastir, Ksar Hellal 5078, Tunisia

² Institut de Science des Matériaux de Mulhouse, UMR 7361 CNRS, UHA, 15, rue Jean-Starcky, 68057 Mulhouse, France

³ Société Tunisienne des Industries de Raffinage, P8, 7021 Zarzouna, Tunisia

Energies 2017, 10(9), 1321; https://doi.org/10.3390/en10091321 - 1 Sep 2017

Cited by 24 | Viewed by 4939

Abstract

Phenolic resin and waste cotton fiber were investigated as green precursors for the successful synthesis using a soft template approach of a composite carbon with carbon nanofibers embedded in a porous carbon network with ordered and periodically pore structure. The optimal composite carbon [...] Read more.

Phenolic resin and waste cotton fiber were investigated as green precursors for the successful synthesis using a soft template approach of a composite carbon with carbon nanofibers embedded in a porous carbon network with ordered and periodically pore structure. The optimal composite carbon (PhR/NC-1), exhibited a specific surface area of 394 m²∙g⁻¹ with the existence of both microporosity and mesoporosity. PhR/NC-1 carbon was evaluated as an adsorbent of Alizarin Red S (ARS) dye in batch solution. Various operating conditions were examined and the maximum adsorption capacity of 104 mg∙g⁻¹ was achieved under the following conditions, i.e., T = 25 °C, pH = 3, contact time = 1440 min. The adsorption and desorption heat was assessed by flow micro-calorimetry (FMC), and the presence of both exothermic and endothermic peaks with different intensity was evidenced, meaning a partially reversible nature of ARS adsorption. A pseudo-second-order model proved to be the most suitable kinetic model to describe the ARS adsorption according to the linear regression factor. In addition, the best isotherm equilibrium has been achieved with a Freundlich model. The results show that the eco-friendly composite carbon derived from green phenolic resin mixed with waste cotton fibers improves the removal of ARS dye from textile effluents. Full article

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

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13 pages, 4023 KiB

Open AccessArticle

Magnetron Sputter Epitaxy of High-Quality GaN Nanorods on Functional and Cost-Effective Templates/Substrates

by Elena Alexandra Serban

, Justinas Palisaitis, Muhammad Junaid, Lina Tengdelius, Hans Högberg, Lars Hultman, Per Ola Åke Persson, Jens Birch

and Ching-Lien Hsiao^*

Thin Film Physics Division, Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping SE-58183, Sweden

Energies 2017, 10(9), 1322; https://doi.org/10.3390/en10091322 - 2 Sep 2017

Cited by 25 | Viewed by 6937

Abstract

We demonstrate the versatility of magnetron sputter epitaxy by achieving high-quality GaN nanorods on different substrate/template combinations, specifically Si, SiC, TiN/Si, ZrB₂/Si, ZrB₂/SiC, Mo, and Ti. Growth temperature was optimized on Si, TiN/Si, and ZrB₂/Si, resulting in [...] Read more.

We demonstrate the versatility of magnetron sputter epitaxy by achieving high-quality GaN nanorods on different substrate/template combinations, specifically Si, SiC, TiN/Si, ZrB₂/Si, ZrB₂/SiC, Mo, and Ti. Growth temperature was optimized on Si, TiN/Si, and ZrB₂/Si, resulting in increased nanorod aspect ratio with temperature. All nanorods exhibit high purity and quality, proved by the strong bandedge emission recorded with cathodoluminescence spectroscopy at room temperature as well as transmission electron microscopy. These substrates/templates are affordable compared to many conventional substrates, and the direct deposition onto them eliminates cumbersome post-processing steps in device fabrication. Thus, magnetron sputter epitaxy offers an attractive alternative for simple and affordable fabrication in optoelectronic device technology. Full article

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

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19 pages, 6863 KiB

Open AccessArticle

Peak Forces on Wave Energy Linear Generators in Tsunami and Extreme Waves

by Linnea Sjökvist^1,2,* and Malin Göteman¹

¹ Department of Engineering Sciences, Uppsala University, SE-752 21 Uppsala, Sweden

² Center for Natural Disaster Science (CNDS), Villavägen 16, SE-752 36 Uppsala, Sweden

Energies 2017, 10(9), 1323; https://doi.org/10.3390/en10091323 - 2 Sep 2017

Cited by 14 | Viewed by 5720

Abstract

The focus of this paper is the survivability of wave energy converters (WECs) in extreme waves and tsunamis, using realistic WEC parameters. The impact of a generator damping factor has been studied, and the peak forces plotted as a function of wave height. [...] Read more.

The focus of this paper is the survivability of wave energy converters (WECs) in extreme waves and tsunamis, using realistic WEC parameters. The impact of a generator damping factor has been studied, and the peak forces plotted as a function of wave height. The paper shows that an increased damping decreases the force in the endstop hit, which is in agreement with earlier studies. However, when analyzing this in more detail, we can show that friction damping and velocity dependent generator damping affect the performance of the device differently, and that friction can have a latching effect on devices in tsunami waves, leading to higher peak forces. In addition, we study the impact of different line lengths, and find that longer line lengths reduce the endstop forces in extreme regular waves, but on the contrary increase the forces in tsunami waves due to the different fluid velocity fields. Full article

(This article belongs to the Special Issue Wave Energy Potential, Behavior and Extraction)

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28 pages, 6024 KiB

Open AccessArticle

Hosting Capacity of the Power Grid for Renewable Electricity Production and New Large Consumption Equipment

by Math H. J. Bollen^*

and Sarah K. Rönnberg^*

Electric Power Engineering, Luleå University of Technology, 931 87 Skellefteå, Sweden

Energies 2017, 10(9), 1325; https://doi.org/10.3390/en10091325 - 2 Sep 2017

Cited by 149 | Viewed by 11461

Abstract

After a brief historical introduction to the hosting-capacity approach, the hosting capacity is presented in this paper as a tool for distribution-system planning under uncertainty. This tool is illustrated by evaluating the readiness of two low-voltage networks for increasing amounts of customers with [...] Read more.

After a brief historical introduction to the hosting-capacity approach, the hosting capacity is presented in this paper as a tool for distribution-system planning under uncertainty. This tool is illustrated by evaluating the readiness of two low-voltage networks for increasing amounts of customers with PV panels or with EV chargers. Both undervoltage and overvoltage are considered in the studies presented here. Probability distribution functions are calculated for the worst-case overvoltage and undervoltage as a function of the number of customers with PV or EV chargers. These distributions are used to obtain 90th percentile values that act as a performance index. This index is compared with an overvoltage or undervoltage limit to get the hosting capacity. General aspects of the hosting-capacity calculations (performance indices, limits, and calculation methods) are discussed for a number of other phenomena: overcurrent; fast voltage magnitude variations; voltage unbalance; harmonics and supraharmonics. The need for gathering data and further development of models for existing demand is emphasised in the discussion and conclusions. Full article

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

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17 pages, 714 KiB

Open AccessArticle

Automated Energy Scheduling Algorithms for Residential Demand Response Systems

by Laihyuk Park, Yongwoon Jang, Hyoungchel Bae, Juho Lee, Chang Yun Park and Sungrae Cho^*

School of Computer Science and Engineering, Chung-Ang University, 221 Heukseok, Dongjak, Seoul 156-756, Korea

Energies 2017, 10(9), 1326; https://doi.org/10.3390/en10091326 - 2 Sep 2017

Cited by 25 | Viewed by 6822

Abstract

Demand response technology is a key technology for distributing electricity tasks in response to electricity prices in a smart grid system. In the current demand response research, there has been much demand for an automated energy scheduling scheme that uses smart devices for [...] Read more.

Demand response technology is a key technology for distributing electricity tasks in response to electricity prices in a smart grid system. In the current demand response research, there has been much demand for an automated energy scheduling scheme that uses smart devices for residential customers in the smart grid. In this paper, two automated energy scheduling schemes are proposed for residential smart grid demand response systems: semi-automated scheduling and fully-automated scheduling. If it is possible to set the appliance preference, semi-automated scheduling will be conducted, and if it is impossible, fully-automated scheduling will be operated. The formulated optimization problems consider the electricity bill along with the user convenience. For the fully-automated scheduling, the appliance preference can automatically be found according to appliance type from the electricity consumption statistics. A performance evaluation validates that the proposed scheme shifts operation to avoid peak load, that the electricity bill is significantly reduced, and that user convenience is satisfied. Full article

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

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14 pages, 6529 KiB

Open AccessArticle

An Improved Modulation Strategy Combining Phase Shifted PWM and Phase Disposition PWM for Cascaded H-Bridge Inverters

by Muxuan Xiao, Qianming Xu^*

and Honglin Ouyang

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

Energies 2017, 10(9), 1327; https://doi.org/10.3390/en10091327 - 2 Sep 2017

Cited by 16 | Viewed by 5674

Abstract

Abstract: Multilevel modulation strategy is an important factor affecting the output performance of multilevel converters. In this paper, the relationship between phase-shifted pulse width modulation (PWM) and phase disposition PWM is analyzed, and then an improved hybrid modulation strategy is proposed for cascaded [...] Read more.

Abstract: Multilevel modulation strategy is an important factor affecting the output performance of multilevel converters. In this paper, the relationship between phase-shifted pulse width modulation (PWM) and phase disposition PWM is analyzed, and then an improved hybrid modulation strategy is proposed for cascaded H-bridge. In addition, the implementation method of multilevel discontinuous modulation for an improved modulation strategy is described. The new modulation strategy is optimized to increase the DC link voltage utilization and further improvement in output harmonics by the injection of a common voltage into the reference. Simulation and experiment verify the effectiveness of the proposed modulation strategy. Full article

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

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15 pages, 2709 KiB

Open AccessFeature PaperArticle

On the Influence of Operational and Control Parameters in Thermal Response Testing of Borehole Heat Exchangers

by Borja Badenes^1,*,†

, Miguel Ángel Mateo Pla^1,†

, Lenin G. Lemus-Zúñiga^1,†

, Begoña Sáiz Mauleón^2,† and Javier F. Urchueguía^1,†

¹ Instituto de Aplicaciones de las Comunicaciones Avanzadas (ITACA), Universitat Politècnica de València, Camino de Vera S/N, 46022 Valencia, Spain

² Escuela Técnica Superior de Ingeniería del Diseño (ETSID), Universitat Politècnica de València, Camino de Vera S/N, 46022 Valencia, Spain

^† These authors contributed equally to this work.

Energies 2017, 10(9), 1328; https://doi.org/10.3390/en10091328 - 3 Sep 2017

Cited by 21 | Viewed by 4333

Abstract

Thermal response test (TRT) is a common procedure for characterization of ground and borehole thermal properties needed for the design of a shallow geothermal heat pump system. In order to investigate and to develop more accurate and robust procedures for TRT control, modelling, [...] Read more.

Thermal response test (TRT) is a common procedure for characterization of ground and borehole thermal properties needed for the design of a shallow geothermal heat pump system. In order to investigate and to develop more accurate and robust procedures for TRT control, modelling, and evaluation in semi-permeable soils with large water content, a pilot borehole heat exchanger was built in the main campus of the Universitat Politècnica de València. The present work shows the results of the experiments performed at the site, analysing the improvements that have been introduced both in the control of the heat injected during TRTs and in the methods to infer the ground thermal parameter. Three models are compared: two based on the infinite-line source theory and one based on the finite-line source scheme. The models were tested under two possible configurations of the equipment, i.e., with and without strict control of injected heat. Our results show the importance of heat injection control for a robust parameter assessment and the existence of additional heat transfer processes that the used models cannot completely characterize and that are related to the presence of significant groundwater flow at the site. In addition, our experience with the current installation and the knowledge about its strengths and weaknesses have allowed us to design a new and more complete test-site to help in the analysis and validation of new ground heat exchanger geometries. Full article

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

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15 pages, 4415 KiB

Open AccessArticle

Enhanced Efficiency of Thermoelectric Generator by Optimizing Mechanical and Electrical Structures

by Jinlong Chen¹, Kewen Li^1,2,*, Changwei Liu¹, Mao Li³, Youchang Lv³, Lin Jia¹ and Shanshan Jiang¹

¹ School of Energy Resources, China University of Geosciences (Beijing), Beijing 100083, China

² Department of Energy Resources Engineering, Stanford University, Stanford, CA 94305, USA

³ State Key Laboratory of Development and Utilization of Coking-coal Resources, China Pingmei Shenma Group, Pingdingshan 467000, China

Energies 2017, 10(9), 1329; https://doi.org/10.3390/en10091329 - 4 Sep 2017

Cited by 84 | Viewed by 13372

Abstract

Much attention has been paid to the application of low temperature thermal resources, especially for power generation in recent years. Most of the current commercialized thermal (including geothermal) power-generation technologies convert thermal energy to electric energy indirectly, that is, making mechanical work before [...] Read more.

Much attention has been paid to the application of low temperature thermal resources, especially for power generation in recent years. Most of the current commercialized thermal (including geothermal) power-generation technologies convert thermal energy to electric energy indirectly, that is, making mechanical work before producing electricity. Technology using a thermoelectric generator (TEG), however, can directly transform thermal energy into electricity through the Seebeck effect. TEG technology has many advantages such as compactness, quietness, and reliability because there are no moving parts. One of the biggest disadvantages of TEGs is the low efficiency from thermal to electric energy. For this reason, we redesigned and modified our previous 1 KW (at a temperature difference of around 120 °C) TEG system. The output power of the system was improved significantly, about 34.6% greater; the instantaneous efficiency of the TEG system could reach about 6.5%. Laboratory experiments have been conducted to measure the output power at different conditions: different connection modes between TEG modules, different mechanical structures, and different temperature differences between hot and cold sides. The TEG apparatus has been tested and the data have been presented. This kind of TEG power system can be applied in many thermal and geothermal sites with low temperature resources, including oil fields where fossil and geothermal energies are coproduced. 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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15 pages, 3950 KiB

Open AccessArticle

Experimental Validation of the Simulation Model of a DOAS Equipped with a Desiccant Wheel and a Vapor Compression Refrigeration System

by Pedro J. Martínez^*

, Carlos Llorca, José A. Pla and Pedro Martínez

Departamento de Ingeniería Mecánica y Energía, Universidad Miguel Hernández, Avda. de la, Universidad, s/n, 03202 Elche, Spain

Energies 2017, 10(9), 1330; https://doi.org/10.3390/en10091330 - 4 Sep 2017

Cited by 15 | Viewed by 3849

Abstract

A dedicated outdoor air system (DOAS) can be designed to supply 100% of the outside air and meet the latent load of the room with dry air. The objectives of this study were to develop a model of a DOAS equipped with a [...] Read more.

A dedicated outdoor air system (DOAS) can be designed to supply 100% of the outside air and meet the latent load of the room with dry air. The objectives of this study were to develop a model of a DOAS equipped with a desiccant wheel and a vapor-compression refrigeration system, build a prototype, validate the model with experimental data, and gain knowledge about the system operation. The test facility was designed with the desiccant wheel downstream of the cooling coil to take advantage of the operating principles of cooling coils and desiccants. A model of the DOAS was developed in the TRNSYS environment. The root mean standard error (RMSE) was used for model validation by comparing the measured air and refrigerant properties with the corresponding calculated values. The results obtained with the developed model showed that the DOAS was able to maintain an indoor humidity ratio depending on outdoor conditions. Laboratory tests were also used to investigate the effect of changes in the regeneration air temperature and the process airflow rate on the process air humidity ratio at the outlet of the wheel. The results are consistent with the technical literature. Full article

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16 pages, 3245 KiB

Open AccessArticle

Adaptive Under-Frequency Load Shedding Scheme in System Integrated with High Wind Power Penetration: Impacts and Improvements

by Shun Li, Fei Tang^*

, Youguo Shao and Qingfen Liao

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

Energies 2017, 10(9), 1331; https://doi.org/10.3390/en10091331 - 4 Sep 2017

Cited by 20 | Viewed by 6301

Abstract

As the requirements of economical operation and reliability on power grid are enhanced gradually nowadays, the existing under frequency load shedding (UFLS) scheme is not quite fit for the modern power system that integrates high wind power. In this paper, the impacts of [...] Read more.

As the requirements of economical operation and reliability on power grid are enhanced gradually nowadays, the existing under frequency load shedding (UFLS) scheme is not quite fit for the modern power system that integrates high wind power. In this paper, the impacts of high wind power penetration on the UFLS are discussed thoroughly. A novel adaptive load shedding (LS) scheme is presented taking the high wind power penetration into account. In the proposed scheme, the equivalent inertia constant (EIC) is calculated accurately to improve the power deficit accuracy so as to reduce the error of LS. The dynamic correction of power deficit is able to solve the negative effects of the wind power output random reduction/the wind generator tripping. Besides, the locking criterion is capable of avoiding the influences of the wind power output random increase on the LS, thus cutting down the LS costs and even preventing the frequency overshoot. Moreover, in terms of the LS parameters setting, the coordination of the low frequency protection of the wind generator and the frequency threshold is addressed. The location and capacity model of LS, which is based on the load characteristics, can ameliorate the frequency recovery process. Finally, the validity and robustness of the proposed scheme are verified in the simulations on the IEEE-39 bus system with high wind power penetration. Full article

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

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24 pages, 291 KiB

Open AccessFeature PaperArticle

Exploring Everyday Energy Usage Practices in Australian Households: A Qualitative Analysis

by Elizabeth V. Hobman^1,*, Karen Stenner^2,3 and Elisha R. Frederiks²

¹ CSIRO Land & Water, Black Mountain Science and Innovation Park, Clunies Ross Street, Black Mountain, Canberra, ACT 2601, Australia

² CSIRO Land & Water, EcoSciences Precinct, 41 Boggo Road, Dutton Park, Brisbane, QLD 4102, Australia

³ Concentric.Energy, P.O. Box 767, Paddington, QLD 4064, Australia

Energies 2017, 10(9), 1332; https://doi.org/10.3390/en10091332 - 4 Sep 2017

Cited by 8 | Viewed by 4716

Abstract

In recent years, energy conservation research has identified a number of household actions that have the potential to drive significant reductions in carbon emissions in the near-term, without requiring substantial changes to householders’ lifestyles or imposing significant financial costs. In this qualitative study, [...] Read more.

In recent years, energy conservation research has identified a number of household actions that have the potential to drive significant reductions in carbon emissions in the near-term, without requiring substantial changes to householders’ lifestyles or imposing significant financial costs. In this qualitative study, we investigate the potential of some of these actions for behavioral modification by asking householders to reveal the reasons why they perform (or fail to perform) such actions. As part of a telephone survey, a sample of customers (n = 1541) from an Australian energy retailer were asked about their reasons for engaging in specific energy usage practices in one of five household domains: laundry, kitchen, bathroom, space heating/cooling or general appliance usage. Qualitative analyses of participants’ open-ended responses revealed that practices in the laundry and kitchen appear to hold the greatest promise for behavioral change, whereas practices in the shower may be more challenging to modify. Integrating our findings with current psychological and sociological knowledge, we present a range of possibilities for future behavior change interventions at the practice-level. Full article

18 pages, 3974 KiB

Open AccessArticle

A Personalized Rolling Optimal Charging Schedule for Plug-In Hybrid Electric Vehicle Based on Statistical Energy Demand Analysis and Heuristic Algorithm

by Fanrong Kong^1,2,3, Jianhui Jiang¹, Zhigang Ding^2,3, Junjie Hu⁴

, Weian Guo^5,*

and Lei Wang⁶

¹ School of Software Engineering, Tongji University, Shanghai 201804, China

² Shanghai Development Center of Computer Software Technology, Shanghai 201112, China

³ Shanghai Industrial Technology Institute, Shanghai 201206, China

⁴ Department of Electrical Engineering, Center for Electric Power and Energy, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark

⁵ Sino-German College of Applied Sciences, Tongji University, Shanghai 201804, China

⁶ School of Electronics and Information Science, Tongji University, Shanghai 201804, China

Energies 2017, 10(9), 1333; https://doi.org/10.3390/en10091333 - 4 Sep 2017

Cited by 6 | Viewed by 4052

Abstract

To alleviate the emission of greenhouse gas and the dependence on fossil fuel, Plug-in Hybrid Electrical Vehicles (PHEVs) have gained an increasing popularity in current decades. Due to the fluctuating electricity prices in the power market, a charging schedule is very influential to [...] Read more.

To alleviate the emission of greenhouse gas and the dependence on fossil fuel, Plug-in Hybrid Electrical Vehicles (PHEVs) have gained an increasing popularity in current decades. Due to the fluctuating electricity prices in the power market, a charging schedule is very influential to driving cost. Although the next-day electricity prices can be obtained in a day-ahead power market, a driving plan is not easily made in advance. Although PHEV owners can input a next-day plan into a charging system, e.g., aggregators, day-ahead, it is a very trivial task to do everyday. Moreover, the driving plan may not be very accurate. To address this problem, in this paper, we analyze energy demands according to a PHEV owner’s historical driving records and build a personalized statistic driving model. Based on the model and the electricity spot prices, a rolling optimization strategy is proposed to help make a charging decision in the current time slot. On one hand, by employing a heuristic algorithm, the schedule is made according to the situations in the following time slots. On the other hand, however, after the current time slot, the schedule will be remade according to the next tens of time slots. Hence, the schedule is made by a dynamic rolling optimization, but it only decides the charging decision in the current time slot. In this way, the fluctuation of electricity prices and driving routine are both involved in the scheduling. Moreover, it is not necessary for PHEV owners to input a day-ahead driving plan. By the optimization simulation, the results demonstrate that the proposed method is feasible to help owners save charging costs and also meet requirements for driving. Full article

(This article belongs to the Special Issue Theory and Application of Computational Intelligence in Electric Vehicles and their Integration within Smart Energy Networks)

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21 pages, 4099 KiB

Open AccessArticle

Multi-Objective Optimization of the Hydrodynamic Performance of the Second Stage of a Multi-Phase Pump

by Jun-Won Suh^1,2, Jin-Woo Kim^1,3, Young-Seok Choi^1,3, Jin-Hyuk Kim^1,3,*

, Won-Gu Joo² and Kyoung-Yong Lee¹

¹ Thermal & Fluid System R&D Group, Korea Institute of Industrial Technology, Cheonan 31056, Korea

² Department of Mechanical Engineering, Yonsei University, Seoul 03722, Korea

³ Advanced Energy and Technology, University of Science and Technology, Daejeon 34141, Korea

Energies 2017, 10(9), 1334; https://doi.org/10.3390/en10091334 - 4 Sep 2017

Cited by 59 | Viewed by 4564

Abstract

Most multi-phase pumps used in crude oil production have been developed to satisfy certain pressure specifications. In the design of these pumps, the flow characteristics of the posterior stage are different from those of the prior stage. For this reason, the design of [...] Read more.

Most multi-phase pumps used in crude oil production have been developed to satisfy certain pressure specifications. In the design of these pumps, the flow characteristics of the posterior stage are different from those of the prior stage. For this reason, the design of the second stage needs to be supplemented. To optimize performance in this stage, multi-objective optimization to simultaneously increase pressure and efficiency is reported in this article. Flow analyses of the single and multiple phases of the multi-phase pump were conducted by solving three-dimensional steady Reynolds-averaged Navier–Stokes equations. For the numerical optimization, two design variables related to the blade inlet angle were selected. The impeller and the diffuser blades were optimized using a systematic optimization technique combined with a central composite method and a hybrid multi-objective evolutionary algorithm coupled with a surrogate model. The selected optimal model yielded better hydrodynamic performance than the base model, and reasons for this are investigated through internal flow field analysis. Full article

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14 pages, 2777 KiB

Open AccessArticle

Performance Study of a Novel Solar Solid Dehumidification/Regeneration Bed for Use in Buildings Air Conditioning Systems

by Wansheng Yang¹, Wenhui Wang¹, Zezhi Ding¹, Zhangyuan Wang^1,*, Xudong Zhao² and Song He¹

¹ School of Civil and Transportation Engineering, Guangdong University of Technology, Guangzhou 510006, China

² School of Engineering, University of Hull, Hull HU6 7RX, UK

Energies 2017, 10(9), 1335; https://doi.org/10.3390/en10091335 - 4 Sep 2017

Cited by 11 | Viewed by 4456

Abstract

In this paper, a novel solar solid dehumidification/regeneration bed has been proposed, and its three regeneration methods, i.e., simulated solar radiation regeneration, microwave regeneration, and combined regeneration of the microwave and simulated solar radiation, were experimentally investigated and compared, as well as the [...] Read more.

In this paper, a novel solar solid dehumidification/regeneration bed has been proposed, and its three regeneration methods, i.e., simulated solar radiation regeneration, microwave regeneration, and combined regeneration of the microwave and simulated solar radiation, were experimentally investigated and compared, as well as the dehumidification performance. The degree of regeneration of the proposed system under the regeneration method combining both microwave irradiation and simulated solar radiation could reach 77.7%, which was 3.77 times higher than that of the system under the simulated solar regeneration method and 1.05 times higher than that of the system under the microwave regeneration. The maximum energy efficiency of the proposed system under the combined regeneration method was 21.7%, while it was only 19.4% for the system under microwave regeneration. All these proved that the combined regeneration method of the simulated solar and microwave radiation not only improved the regeneration efficiency of the system, but also enhanced the energy efficiency. For the dehumidification performance, the maximum transient moisture removal was 14.1 g/kg, the maximum dehumidification efficiency was 68.0% and the maximum speed of dehumidification was 0.294 g/(kg·s) when the inlet air temperature was at 26.09 °C and the air relative humidity was at 89.23%. By comparing the testing results with the semi-empirical results from the Page model, it was indicated that the Page model can predict the regeneration characteristics of the novel solar solid dehumidification/regeneration bed under the combined method of microwave and simulated solar regeneration. The results of this research should prove useful to researchers and engineers to exploit the potential of solar technologies in buildings worldwide. Full article

(This article belongs to the Special Issue Solar Technologies for Buildings)

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18 pages, 3158 KiB

Open AccessArticle

Coordination Strategy for Optimal Scheduling of Multiple Microgrids Based on Hierarchical System

by Won-Poong Lee¹, Jin-Young Choi² and Dong-Jun Won^1,*

¹ Department of Electrical Engineering, Inha University, 100, Inha-ro, Nam-gu, Incheon 22212, Korea

² LG CNS, 28F, FKI Tower, 24, Yeoui-daero, Yeongdeungpo-gu, Seoul 07320, Korea

Energies 2017, 10(9), 1336; https://doi.org/10.3390/en10091336 - 5 Sep 2017

Cited by 20 | Viewed by 4280

Abstract

Research on the operation of the multiple microgrid (MMG) has been increasing as the power system is operated through the microgrid. Some of the studies related to MMG have introduced various operation strategies by introducing concepts such as power sharing and power trading [...] Read more.

Research on the operation of the multiple microgrid (MMG) has been increasing as the power system is operated through the microgrid. Some of the studies related to MMG have introduced various operation strategies by introducing concepts such as power sharing and power trading for power exchange between microgrids. In this paper, a strategy for obtaining optimal scheduling of MMG systems with power sharing through coordination among microgrids that have no cost function of generation units is proposed. There are microgrid-energy management systems (MG-EMSs) in the lower level that determine individual schedules for each microgrid in a hierarchical system. In the upper level, the microgrid of microgrids center (MoMC) implements the coordination among microgrids. In order to achieve the optimal operation of the entire system, MoMC calculates the amount of power sharing based on a predetermined limit value and allocates the command for coordination to each MG-EMS. MG-EMS changes the individual schedule based on the command. These processes are repeatedly performed, and when the change of the total cost becomes smaller than a specified size, the process is terminated and the schedule is determined. The advantages of the proposed algorithm are as follows. (1) It is a power sharing strategy of multiple microgrids considering multiple feeder structures as well as a single feeder structure for minimizing the operation cost of the entire system; (2) it is a power sharing strategy between microgrids that can be applied in a microgrid where only units that do not have a cost function exist; (3) since it is the optimization of the distributed form, the computation time decreases sharply compared with the one performed at the central center. The verification of the proposed algorithm was performed through MATLAB. Full article

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

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23 pages, 8217 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Flame Front Propagation in an Optical GDI Engine under Stoichiometric and Lean Burn Conditions

by Santiago Martinez¹, Adrian Irimescu², Simona Silvia Merola^2,*, Pedro Lacava¹ and Pedro Curto-Riso³

¹ Technological Institute of Aeronautics, São Jose dos Campos 12228-900, Brazil

² Istituto Motori, Consiglio Nazionale delle Ricerche, 80125 Napoli, Italy

³ Department of Applied Thermodynamics, University of La República, Montevideo 11200, Uruguay

Energies 2017, 10(9), 1337; https://doi.org/10.3390/en10091337 - 5 Sep 2017

Cited by 35 | Viewed by 9604

Abstract

Lean fueling of spark ignited (SI) engines is a valid method for increasing efficiency and reducing nitric oxide (NO_x) emissions. Gasoline direct injection (GDI) allows better fuel economy with respect to the port-fuel injection configuration, through greater flexibility to load changes, [...] Read more.

Lean fueling of spark ignited (SI) engines is a valid method for increasing efficiency and reducing nitric oxide (NO_x) emissions. Gasoline direct injection (GDI) allows better fuel economy with respect to the port-fuel injection configuration, through greater flexibility to load changes, reduced tendency to abnormal combustion, and reduction of pumping and heat losses. During homogenous charge operation with lean mixtures, flame development is prolonged and incomplete combustion can even occur, causing a decrease in stability and engine efficiency. On the other hand, charge stratification results in fuel impingement on the combustion chamber walls and high particle emissions. Therefore, lean operation requires a fundamentally new understanding of in-cylinder processes for developing the next generation of direct-injection (DI) SI engines. In this paper, combustion was investigated in an optically accessible DISI single cylinder research engine fueled with gasoline. Stoichiometric and lean operations were studied in detail through a combined thermodynamic and optical approach. The engine was operated at a fixed rotational speed (1000 rpm), with a wide open throttle, and at the start of the injection during the intake stroke. The excess air ratio was raised from 1 to values close to the flammability limit, and spark timing was adopted according to the maximum brake torque setting for each case. Cycle resolved digital imaging and spectroscopy were applied; the optical data were correlated to in-cylinder pressure traces and exhaust gas emission measurements. Flame front propagation speed, flame morphology parameters, and centroid motion were evaluated through image processing. Chemical kinetics were characterized based on spectroscopy data. Lean burn operation demonstrated increased flame distortion and center movement from the location of the spark plug compared to the stoichiometric case; engine stability decreased as the lean flammability limit was approached. Full article

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

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20 pages, 1676 KiB

Open AccessArticle

Numerical Simulations of Sloshing and the Thermodynamic Response Due to Mixing

by Erlend Liavåg Grotle^*

and Vilmar Æsøy

Department of Ocean Operations and Civil Engineering, Faculty of Engineering Science, Norwegian University of Science and Engineering, Larsgårdvegen 2, 6009 Ålesund, Norway

Energies 2017, 10(9), 1338; https://doi.org/10.3390/en10091338 - 5 Sep 2017

Cited by 28 | Viewed by 5379

Abstract

In this paper, we apply computational fluid dynamics (CFD) to study the thermodynamic response enhanced by sloshing inside liquefied natural gas (LNG) fuel tanks. An existing numerical solver provided by OpenFOAM is used to simulate sloshing in a model scaled tank of similar [...] Read more.

In this paper, we apply computational fluid dynamics (CFD) to study the thermodynamic response enhanced by sloshing inside liquefied natural gas (LNG) fuel tanks. An existing numerical solver provided by OpenFOAM is used to simulate sloshing in a model scaled tank of similar form to an LNG fuel tank. The interface area has been estimated for different sloshing regimes on three different numerical grids representing the tank in 3D. Estimating the interface area is done by performing a grid-independence study. In the most severe sloshing conditions, convergence is not achieved. By combining the results from experiments and CFD, it is found that the interface area and the condensation mass flow rate are in phase for the most severe sloshing condition. The existing CFD solver is modified to determine the pressure drop. The simulation results are compared to the experimental data, and the results are acceptable and thereby show a potential in applying CFD to predict the thermodynamic response due to sloshing. By plotting the temperature contours, indications are found that the exchange of cold bulk and saturated liquid due to sloshing has a significant influence on the thermodynamic response. Full article

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

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16 pages, 2083 KiB

Open AccessArticle

Determining the Optimal Configuration of the Multi-Ring Tree for Bluetooth Multi-Hop Networks

by Chih-Min Yu^1,*

and Ting-Wei Hsu²

¹ The Department of Electronics Engineering, Chung Hua University, Hsinchu 30012, Taiwan

² The Department of Electrical Engineering, Chung Hua University, Hsinchu 30012, Taiwan

Energies 2017, 10(9), 1339; https://doi.org/10.3390/en10091339 - 5 Sep 2017

Cited by 4 | Viewed by 3536

Abstract

In this work, a multi-ring tree algorithm is proposed for Bluetooth low-energy networks with non-uniform distribution of devices. In a dense area, a leader root is elected during the leader election phase and a min-path algorithm is introduced to determine the optimal number [...] Read more.

In this work, a multi-ring tree algorithm is proposed for Bluetooth low-energy networks with non-uniform distribution of devices. In a dense area, a leader root is elected during the leader election phase and a min-path algorithm is introduced to determine the optimal number of rings for various numbers of discoverable roots. According to the optimal configuration, the leader root connects to its one-hop neighboring roots to form the first-tier ring; each new root connects with one downstream root, and these roots connect together to form the second-tier ring until the desired outermost ring is reached. In sparse areas, each root constructs its own spanning tree subnet, finally creating a multi-ring tree scatternet. To achieve the least route discovery overhead, a multi-hop self-routing protocol is developed to efficiently deliver packets. Computer simulations show that the optimal multi-ring subnet can be determined; the optimal multi-ring tree outperforms conventional dual ring-tree (DRT) and Bluetooth hybrid ring-tree (BlueHRT) in terms of network performance. Full article

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

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12 pages, 1481 KiB

Open AccessArticle

Performance of Commercially Available Supercapacitors

by Mazen Yassine^* and Drazen Fabris^*

Mechanical Engineering Department, Santa Clara University, Santa Clara, CA 95053, USA

Energies 2017, 10(9), 1340; https://doi.org/10.3390/en10091340 - 5 Sep 2017

Cited by 186 | Viewed by 8818

Abstract

High energy density storage device exhibiting a reliable lifecycle is needed in the 21st century. Hence, energy storage research is critical for reducing energy consumption. Supercapacitors exhibit such characteristics via interfacial ion electrosorption and fast redox reactions. They are a feasible solution for [...] Read more.

High energy density storage device exhibiting a reliable lifecycle is needed in the 21st century. Hence, energy storage research is critical for reducing energy consumption. Supercapacitors exhibit such characteristics via interfacial ion electrosorption and fast redox reactions. They are a feasible solution for transportation applications, among others, due to their superb characteristics. In this paper, we provide a background on supercapacitors, review public data on commercially available supercapacitors for performance characteristics, and finally summarize their performance in terms of energy density, equivalent series resistance, and device time consistency. Full article

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17 pages, 5938 KiB

Open AccessArticle

Wire Structure Heat Exchangers—New Designs for Efficient Heat Transfer

by Hannes Fugmann^*

, Eric Laurenz

and Lena Schnabel

Fraunhofer ISE, Fraunhofer Institute for Solar Energy Systems, Heidenhofstr. 2, 79110 Freiburg, Germany

Energies 2017, 10(9), 1341; https://doi.org/10.3390/en10091341 - 5 Sep 2017

Cited by 19 | Viewed by 6741

Abstract

Enhancing the heat transfer mechanism by increasing the heat exchanger surface area is a standard way to overcome low heat transfer on the gas side of heat exchangers. Different geometrical shapes, for example, plain, wavy, or interrupted fin geometries for plate-fin or tube-fin [...] Read more.

Enhancing the heat transfer mechanism by increasing the heat exchanger surface area is a standard way to overcome low heat transfer on the gas side of heat exchangers. Different geometrical shapes, for example, plain, wavy, or interrupted fin geometries for plate-fin or tube-fin heat exchangers, are used for this task. Wire structures with dimensions in the submillimeter range are already used in regenerators for their heat capacity, but are rarely used in recuperators as heat transfer enhancers. New textile developments enable the fabrication of adapted structures with irregular grid sizes, and purpose-built for heat exchanger application. These wire structures allow for enlarging the heat transfer surface area, decreasing material utilization, and enabling flexibility of different geometrical dimensions. Possibilities for manufacturing and design selection are studied in the project, EffiMet, and thereafter at Fraunhofer ISE for the implementation of highly efficient heat exchanger geometries based on wire structures. Full article

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

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16 pages, 412 KiB

Open AccessArticle

Evaluation of Demand-Side Management over Pricing Competition of Multiple Suppliers Having Heterogeneous Energy Sources

by Kireem Han¹

, Joohyung Lee^2,* and Junkyun Choi¹

¹ School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 34051 Daejeon, Korea

² Department of Software, Gachon University, Seongnam 13120, Korea;

Energies 2017, 10(9), 1342; https://doi.org/10.3390/en10091342 - 5 Sep 2017

Cited by 12 | Viewed by 3884

Abstract

This study investigates a demand-side management problem in which multiple suppliers compete with each other to maximize their own revenue. We consider that suppliers have heterogeneous energy sources and individually set the unit price of each energy source. Then, consumers that share a [...] Read more.

This study investigates a demand-side management problem in which multiple suppliers compete with each other to maximize their own revenue. We consider that suppliers have heterogeneous energy sources and individually set the unit price of each energy source. Then, consumers that share a net utility react to the suppliers’ decisions on prices by deciding the amount of energy to request, or how to split the consumers’ aggregated demand over multiple suppliers. In this case, the consumers need to consider the power loss and the price to pay for procuring electricity. We analyze the economic benefits of such a pricing competition among suppliers (e.g., a demand-side management that considers consumers’ reaction). This is achieved by designing a hierarchical decision-making scheme as a multileader–multifollower Stackelberg game. We show that the behaviors of both consumers and suppliers based on well-designed utility functions converge to a unique equilibrium solution. This allows them to maximize the payoff from all participating consumers and suppliers. Accordingly, closed-form expressions are provided for the corresponding strategies of the consumers and the suppliers. Finally, we provide numerical examples to illustrate the effectiveness of the solutions. This game-theoretic study provides an example of incentives and insight for demand-side management in future power grids. Full article

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

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19 pages, 3521 KiB

Open AccessArticle

The Impact of Climate Change on the Generation of Hydroelectric Power—A Case Study in Southern Spain

by Kepa Solaun^1,2,*

and Emilio Cerdá³

¹ School of Sciences, Universidad de Navarra, Campus Universitario, 31080 Pamplona, Spain

² Factor CO2, Colón de Larreátegui, 26, Planta 1, 48006 Bilbao, Spain

³ Instituto Complutense de Estudios Internacionales (ICEI), Universidad Complutense de Madrid, Campus de Somosaguas, Pozuelo de Alarcón, 28223 Madrid, Spain

Energies 2017, 10(9), 1343; https://doi.org/10.3390/en10091343 - 5 Sep 2017

Cited by 27 | Viewed by 5935

Abstract

Climate change could pose a significant threat to the energy sector in various countries. The objective of this study is to analyze the long-term impact of changes in precipitation and water availability on hydroelectric production. To do so, the study focuses on three [...] Read more.

Climate change could pose a significant threat to the energy sector in various countries. The objective of this study is to analyze the long-term impact of changes in precipitation and water availability on hydroelectric production. To do so, the study focuses on three hydroelectric power plants in Southern Spain combining climatological, technical and economic data and projections. A physical model has been designed that reproduces the plants’ operations and incorporates various scenarios for the evolution of contributions to the basin. The results predict a 10 to 49% drop in production by the end of the century, depending on the plant and scenario. This decrease in production, in accordance with our economic and operational hypotheses, would significantly affect the operating margins of the facilities and, in certain scenarios, could reach an economically unsustainable level by the end of the century. An investment analysis has been carried out as well, showing that climate change may jeopardize future investments in similar facilities. Full article

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14 pages, 7190 KiB

Open AccessArticle

Design Improvisation for Reduced Harmonic Distortion in a Flux Pump-Integrated HTS Generator

by Ravichandra Kulkarni^1,*, Krishnamachar Prasad¹, Tek Tjing Lie¹, Rodney A. Badcock²

, Chris W. Bumby² and Hae-Jin Sung²

¹ Department of Electrical and Electronic Engineering, Auckland University of Technology, Auckland 1010, New Zealand

² Robinson Research Institute, Victoria University of Wellington, Wellington 5010, New Zealand

Energies 2017, 10(9), 1344; https://doi.org/10.3390/en10091344 - 6 Sep 2017

Cited by 9 | Viewed by 4860

Abstract

This paper presents a design improvisation of a flux pump-integrated 10 kW high-temperature superconducting (HTS) proof of concept generator for reduced harmonic distortion. To carry out the design improvisation, a finite element analysis (FEA) model of the 10 kW HTS generator is developed, [...] Read more.

This paper presents a design improvisation of a flux pump-integrated 10 kW high-temperature superconducting (HTS) proof of concept generator for reduced harmonic distortion. To carry out the design improvisation, a finite element analysis (FEA) model of the 10 kW HTS generator is developed, and time-stepped magnetic transient simulations are conducted on the 2D model. The effects of stator yoke material, winding pitch factors, and load configurations on total harmonic distortion (THD) are investigated. The results showed that fibre-reinforced polymer (FRP) epoxy (G10) can be used as the stator yoke material to effectively avoid the hysteresis and eddy current losses. In addition, the study results show that for the non-conventional design of the machine, a winding pitch of 2/3 and the armature-load configuration of Star-Delta gives THD values within the standard limit defined by IEEE Standard 519-2014. The THD values indicate that the machine design configuration is suitable for the development of machines for both stand-alone and grid-connected operations, according to IEEE STD 519-2014. Full article

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

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14 pages, 3093 KiB

Open AccessArticle

An Adaptive Square Root Unscented Kalman Filter Approach for State of Charge Estimation of Lithium-Ion Batteries

by Shulin Liu, Naxin Cui^*

and Chenghui Zhang^*

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

Energies 2017, 10(9), 1345; https://doi.org/10.3390/en10091345 - 6 Sep 2017

Cited by 41 | Viewed by 6588

Abstract

An accurate state of charge (SOC) estimation is of great importance for the battery management systems of electric vehicles. To improve the accuracy and robustness of SOC estimation, lithium-ion battery SOC is estimated using an adaptive square root unscented Kalman filter (ASRUKF) method. [...] Read more.

An accurate state of charge (SOC) estimation is of great importance for the battery management systems of electric vehicles. To improve the accuracy and robustness of SOC estimation, lithium-ion battery SOC is estimated using an adaptive square root unscented Kalman filter (ASRUKF) method. The square roots of the variance matrices of the SOC and noise can be calculated directly by the ASRUKF algorithm, which ensures the symmetry and nonnegative definiteness of the matrices. The process values and measurement noise covariance can be adaptively adjusted, which greatly improves the accuracy, stability, and self-adaptability of the filter. The effectiveness of the proposed method has been verified through experiments under different operating conditions. The obtained results were compared with those of extended Kalman filter (EKF) and unscented Kalman filter (UKF) , which indicates that the ASRUKF method provides better accuracy, robustness and convergence in the estimation of battery SOC for electric vehicles. The proposed method has a mean SOC estimation error of 0.5% and a maximum SOC estimation error of 0.8%. These errors are lower than those of other methods. Full article

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

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29 pages, 6639 KiB

Open AccessArticle

A Design Method for Making an LCC Compensation Two-Coil Wireless Power Transfer System More Energy Efficient Than an SS Counterpart

by Xu Liu¹

, Lindsay Clare², Xibo Yuan², Chonglin Wang¹ and Jianhua Liu^1,*

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

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

Energies 2017, 10(9), 1346; https://doi.org/10.3390/en10091346 - 6 Sep 2017

Cited by 46 | Viewed by 9013

Abstract

A new design approach is presented in this paper to show that under certain conditions, in a two-coil wireless power transfer system, the double-sided inductor-capacitor-capacitor (LCC) compensated wireless power transfer (LCC-WPT) system can be more energy efficient than the series-series (SS) compensated wireless [...] Read more.

A new design approach is presented in this paper to show that under certain conditions, in a two-coil wireless power transfer system, the double-sided inductor-capacitor-capacitor (LCC) compensated wireless power transfer (LCC-WPT) system can be more energy efficient than the series-series (SS) compensated wireless power transfer (SS-WPT) system for the same load power, with special attention being paid to the effect that the parasitic coil and capacitor resistances have on the system efficiency. To make a fair comparison between the SS and LCC WPT systems, the direct current (DC) link voltage was adjusted to set equal load power for the two systems whilst using identical transmit and receive coils, coil-to-coil distance and load resistance. The system performance in terms of the system efficiency, the voltage stresses on the components, and the losses in the power devices were analysed for a practical system, comparing the LCC-WPT system and the SS-WPT system with respect to the load resistance. The effect of coil misalignment on the transferred power and efficiency for the two systems was compared. The theoretical proof and the conditions for meeting the objective are derived and practically verified in a two-coil WPT practical prototype, showing good agreement between analysis and experiments. Full article

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

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18 pages, 2451 KiB

Open AccessArticle

An Improved Droop Control Strategy for Low-Voltage Microgrids Based on Distributed Secondary Power Optimization Control

by Demin Li¹

, Bo Zhao², Zaijun Wu^1,*, Xuesong Zhang² and Leiqi Zhang²

¹ School of Electrical Engineering, Southeast University, Nanjing 210096, China

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

Energies 2017, 10(9), 1347; https://doi.org/10.3390/en10091347 - 7 Sep 2017

Cited by 21 | Viewed by 4746

Abstract

To achieve accurate reactive power sharing and voltage frequency and amplitude restoration in low-voltage microgrids, a control strategy combining an improved droop control with distributed secondary power optimization control is proposed. The active and reactive power that each distributed generator (DG) shares is [...] Read more.

To achieve accurate reactive power sharing and voltage frequency and amplitude restoration in low-voltage microgrids, a control strategy combining an improved droop control with distributed secondary power optimization control is proposed. The active and reactive power that each distributed generator (DG) shares is calculated by extracting load information and utilizing a power sharing ratio, and is reset to be the nominal power to recalculate droop gains. The droop control curves are reconstructed according to the nominal active and reactive power and the recalculated droop gains. The reconstructed active power-frequency droop control can regulate active power adaptively and keep frequency at a nominal value. Meanwhile, the reconstructed reactive power voltage droop control can reduce voltage amplitude deviation to a certain extent. A distributed secondary power optimization control is added to the reconstructed reactive power voltage droop control by using average system voltage. The average system voltage is obtained by using a consensus algorithm in a distributed, sparse communication network which is constituted by all controllers of DGs. As a result, accurate reactive power sharing is realized, average system voltage is kept at a nominal value, and all voltage amplitude deviations are further reduced. Due to the absence of a microgrid central controller, the reliability of the strategy is enhanced. Finally, the simulation results validate the proposed method. Full article

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17 pages, 3355 KiB

Open AccessArticle

A Floating Platform with Embedded Wave Energy Harvesting Arrays in Regular and Irregular Seas

by Hai-Cheng Zhang¹

, Dao-Lin Xu^1,*, Chun-Rong Liu² and You-Sheng Wu³

¹ State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body, Hunan University, Changsha 410082, China

² School of Civil Engineering & Architecture, Xiamen University of Technology, Xiamen 316005, China

³ China Ship Scientific Research Center, Wuxi 214082, China

Energies 2017, 10(9), 1348; https://doi.org/10.3390/en10091348 - 6 Sep 2017

Cited by 18 | Viewed by 5028

Abstract

This paper presents a study on a cost-effective engineering model that integrates an array of floating wave energy converters with a vast platform, a viable option for multi-functional performance in renewable energy capture and ocean space utilization. The wave energy converters are floating [...] Read more.

This paper presents a study on a cost-effective engineering model that integrates an array of floating wave energy converters with a vast platform, a viable option for multi-functional performance in renewable energy capture and ocean space utilization. The wave energy converters are floating buoyance columns flexibly connected with the elastic platform. Hydrodynamic interactions among the columns are analyzed using an exact matrix transform method based on linear wave theory in the frequency domain. A parametric governing equation of compounded wave energy converter referred to as a wave farm is formulated by using Hamilton’s principle which can be discretized using the Galerkin method. The effects of wave conditions and the parameters of hydraulic power take-off (PTO) on the wave energy absorption and dynamic characteristics of the energy harvesting system are investigated. Furthermore, the wave energy capture on irregular waves is also discussed. This research work aims at providing a theoretical guidance for wave energy harvesting system design. Full article

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18 pages, 5466 KiB

Open AccessArticle

Heat Transfer in a Drilling Fluid with Geothermal Applications

by Wei-Tao Wu¹, Nadine Aubry², James F. Antaki¹, Mark L. McKoy³ and Mehrdad Massoudi^4,*

¹ Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA

² Department of Mechanical and Industrial Engineering, Northeastern University, Boston, MA 02115, USA

³ U. S. Department of Energy, National Energy Technology Laboratory (NETL), 3610 Collins Ferry Road, Morgantown, WV 26507-0880, USA

⁴ U. S. Department of Energy, National Energy Technology Laboratory (NETL), 626 Cochrans Mill Road, Pittsburgh, PA 15236-0940, USA

Energies 2017, 10(9), 1349; https://doi.org/10.3390/en10091349 - 6 Sep 2017

Cited by 8 | Viewed by 5602

Abstract

The effects of various conditions on the fluid flow, particle migration and heat transfer in non-linear fluids encountered in drilling and geothermal applications are studied. We assume that the drilling fluid is a suspension composed of various substances, behaving as a non-linear complex [...] Read more.

The effects of various conditions on the fluid flow, particle migration and heat transfer in non-linear fluids encountered in drilling and geothermal applications are studied. We assume that the drilling fluid is a suspension composed of various substances, behaving as a non-linear complex fluid, where the effects of particle volume fraction, shear rate, and temperature on the viscosity and thermal diffusivity are considered. The motion of the particles is described using a concentration flux equation. Two problems are studied: flow in a vertical pipe and flow between two (eccentric) cylinders where the inner cylinder is rotating. We consider effects of earth temperature, the rotational speed of the inner cylinder, and the bulk volume fraction on the flow and heat transfer. Full article

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

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11 pages, 1765 KiB

Open AccessArticle

Permeability Change Caused by Stress Damage of Gas Shale

by Chuanliang Yan^1,2,*, Yuanfang Cheng², Fucheng Deng^3,* and Ji Tian¹

¹ State Key Laboratory of Offshore Oil Exploitation, CNOOC Research Institute, Beijing 100028, China

² School of Petroleum Engineering, China University of Petroleum (East China), Qingdao 266580, China

³ School of Mechanical Engineering, Yangtze University, Wuhan 430100, China

Energies 2017, 10(9), 1350; https://doi.org/10.3390/en10091350 - 6 Sep 2017

Cited by 22 | Viewed by 4245

Abstract

Stress damage of shale during the uniaxial loading process will cause the change of permeability. The study of stress sensitivity of shale has focused on the influence of confining pressure on shale permeability and the change of shale permeability during the loading process [...] Read more.

Stress damage of shale during the uniaxial loading process will cause the change of permeability. The study of stress sensitivity of shale has focused on the influence of confining pressure on shale permeability and the change of shale permeability during the loading process of axial stress is lacking. The permeability of gas shale during loading process was tested. The results show that shale damage macroscopically reflects the process of axial micro-cracks generation and expansion, and the axial micro-cracks will cause permeability change during the loading process. There is a good corresponding relationship between damage development and micro-crack expansion during the process of shale loading. The damage factor will increase in the linear elastic stage and enlarge rapidly after entering the stage of unstable micro-crack expansion, and the permeability of shale increases with the increasing of shale damage. The research results provide a reliable test basis for further analysis of the borehole instability and hydraulic fracture mechanisms in shale gas reservoirs. Full article

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

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18 pages, 397 KiB

Open AccessArticle

Probabilistic Modeling of Electric Vehicle Charging Pattern Associated with Residential Load for Voltage Unbalance Assessment

by Azhar Ul-Haq^1,*, Marium Azhar², Yousef Mahmoud³, Aqib Perwaiz¹ and Essam A. Al-Ammar⁴

¹ College of Electrical and Mechanical Engineering, National University of Sciences and Technology, Islamabad 44000, Pakistan

² Department of Electrical Engineering, Lahore College for Women University, Lahore 54000, Pakistan

³ Worcester Polytechnic Institute, Worcester, MA 01609, USA

⁴ Department of Electrical Engineering, King Saud University, Riyadh 12372, Saudi Arabia

Energies 2017, 10(9), 1351; https://doi.org/10.3390/en10091351 - 7 Sep 2017

Cited by 57 | Viewed by 7081

Abstract

It has been recognized that an increased penetration of electric vehicles (EVs) may potentially alter load profile in a distribution network. As EVs are regarded as a diversely distributed load so a deterministic method, to predict EV charging load, may not account for [...] Read more.

It has been recognized that an increased penetration of electric vehicles (EVs) may potentially alter load profile in a distribution network. As EVs are regarded as a diversely distributed load so a deterministic method, to predict EV charging load, may not account for all possible factors that could affect the power system. Thus, a stochastic approach is applied that takes into account various realistic factors such as EV battery capacity, state of charge (SOC), driving habit/need, i.e., involving type and purpose of trip, plug-in time, mileage, recharging frequency per day, charging power rate and dynamic EV charging price under controlled and uncontrolled charging schemes. A probabilistic model of EVs charging pattern associated with residential load profile is developed. The probabilistic model gives an activity based residential load profile and EV charging pattern over a period of 24 h. Then, the model output is used to assess the power quality index such as voltage unbalance factor under different electric vehicle penetration levels at different nodes of the system. An uneven EV charging scenario is identified that could cause the voltage unbalance to exceed its permissible limit. Full article

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12 pages, 1489 KiB

Open AccessArticle

Factors Contributing to Haze Pollution: Evidence from Macao, China

by Wai-Ming To¹

, Peter K. C. Lee^2,*

and Chi To Ng²

¹ School of Business, Macao Polytechnic Institute, Macao, China

² Department of Logistics and Maritime Studies, The Hong Kong Polytechnic University, Hong Kong, China

Energies 2017, 10(9), 1352; https://doi.org/10.3390/en10091352 - 7 Sep 2017

Cited by 7 | Viewed by 4628

Abstract

Haze is a major environmental concern in many cities because it adversely affects people’s physiological and psychological well-being. This paper examines the extent of haze in Macao during the period 1986–2016. It identifies the relationships between haze, energy use, and meteorological conditions directly. [...] Read more.

Haze is a major environmental concern in many cities because it adversely affects people’s physiological and psychological well-being. This paper examines the extent of haze in Macao during the period 1986–2016. It identifies the relationships between haze, energy use, and meteorological conditions directly. The haze in Macao changed over the period 1986–2016 with air pollution getting worse and then improving after 2007. Specifically, the number of haze hours increased from 3 in 1986 to 766 in 2007, and then dropped to 57 in 2016, while the total energy use increased from 12,246 TJ in 1986 to 37,144 TJ in 2007, and then to 42,405 TJ in 2016. As per primary energy, Macao used 12,096 TJ in 1986, 21,388 TJ in 2007, and 16,647 TJ in 2016 excluding aviation kerosene. Bivariate correlations show that haze was most positively and significantly associated with annual primary energy use. Multiple regression analysis indicates that the number of hours with haze was significantly, positively related to the consumption of gas oil/diesel, fuel oil, and natural gas in Macao and aviation kerosene. Nevertheless, the improvement in Macao could come at a cost to areas in downwind of Zhuhai’s coal power stations supplying Macao’s electricity energy. Full article

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23 pages, 1450 KiB

Open AccessArticle

An Anonymous Authentication and Key Establish Scheme for Smart Grid: FAuth

by Yuwen Chen^*

, José-Fernán Martínez, Pedro Castillejo

and Lourdes López

Departamento de Ingeniería Telemática y Electrónica (DTE), Escuela Técnica Superior de Ingeniería y Sistemas de Telecomunicación (ETSIST), Universidad Politécnica de Madrid (UPM), C/Nikola Tesla, s/n, 28031 Madrid, Spain

Energies 2017, 10(9), 1354; https://doi.org/10.3390/en10091354 - 7 Sep 2017

Cited by 59 | Viewed by 4432

Abstract

The smart meters in electricity grids enable fine-grained consumption monitoring. Thus, suppliers could adjust their tariffs. However, as smart meters are deployed within the smart grid field, authentication and key establishment between smart grid parties (smart meters, aggregators, and servers) become an urgency. [...] Read more.

The smart meters in electricity grids enable fine-grained consumption monitoring. Thus, suppliers could adjust their tariffs. However, as smart meters are deployed within the smart grid field, authentication and key establishment between smart grid parties (smart meters, aggregators, and servers) become an urgency. Besides, as privacy is becoming a big concern for smart meters, smart grid parties are reluctant to leak their real identities during the authentication phase. In this paper, we analyze the recent authentication schemes in smart grids and other applied fields, and propose an anonymous authentication and key establishment scheme between smart grid parties: FAuth. The proposed scheme is based on bilinear maps and the computational Diffie–Hellman problem. We changed the way the smart meter parties registered at Key Generation Center, making the proposed scheme robust against various potential attacks that could be launched by the Key Generation Center, as the scheme could avoid the private key of the smart meter parties from leaking to the Key Generation Center. Besides, the proposed scheme reduced the computational load, both at the smart meter side and at the aggregator side, which make it perfectly suitable for computation-constrained devices. Security proof results show the proposed scheme is secure under the BAN logic and random oracle model. Full article

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17 pages, 1923 KiB

Open AccessArticle

Impedance-Based Stability Analysis in Grid Interconnection Impact Study Owing to the Increased Adoption of Converter-Interfaced Generators

by Youngho Cho¹

, Kyeon Hur^1,*

, Yong Cheol Kang²

and Eduard Muljadi³

¹ School of Electrical and Electronic Engineering, Yonsei University, Seoul 03722, Korea

² Department of Electrical Engineering, Chonbuk National University, Jeonju 54896, Korea

³ National Renewable Energy Laboratory, Golden, CO 80401, USA

Energies 2017, 10(9), 1355; https://doi.org/10.3390/en10091355 - 8 Sep 2017

Cited by 14 | Viewed by 5309

Abstract

This study investigates the emerging harmonic stability concerns to be addressed by grid planners in generation interconnection studies, owing to the increased adoption of renewable energy resources connected to the grid via power electronic converters. The wideband and high-frequency electromagnetic transient (EMT) characteristics [...] Read more.

This study investigates the emerging harmonic stability concerns to be addressed by grid planners in generation interconnection studies, owing to the increased adoption of renewable energy resources connected to the grid via power electronic converters. The wideband and high-frequency electromagnetic transient (EMT) characteristics of these converter-interfaced generators (CIGs) and their interaction with the grid impedance are not accurately captured in the typical dynamic studies conducted by grid planners. This paper thus identifies the desired components to be studied and subsequently develops a practical process for integrating a new CIG into a grid with the existing CIGs. The steps of this process are as follows: the impedance equation of a CIG using its control dynamics and an interface filter to the grid, for example, an LCL filter (inductor-capacitor-inductor type), is developed; an equivalent impedance model including the existing CIGs nearby and the grid observed from the point of common coupling are derived; the system stability for credible operating scenarios is assessed. Detailed EMT simulations validate the accuracy of the impedance models and stability assessment for various connection scenarios. By complementing the conventional EMT simulation studies, the proposed analytical approach enables grid planners to identify critical design parameters for seamlessly integrating a new CIG and ensuring the reliability of the grid. Full article

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18 pages, 7708 KiB

Open AccessArticle

A Combined Approach Effectively Enhancing Traffic Performance for HSR Protocol in Smart Grids

by Nguyen Xuan Tien¹

, Jong Myung Rhee¹ and Sang Yoon Park^2,*

¹ Department of Information and Communications Engineering, Myongji University, 116 Myongji-ro, Yongin, Gyeonggi 17058, Korea

² Department of Electronic Engineering, Myongji University, 116 Myongji-ro, Yongin, Gyeonggi 17058, Korea

Energies 2017, 10(9), 1356; https://doi.org/10.3390/en10091356 - 8 Sep 2017

Cited by 2 | Viewed by 3883

Abstract

In this paper, we propose a very effectively filtering approach (EFA) to enhance network traffic performance for high-availability seamless redundancy (HSR) protocol in smart grids. The EFA combines a novel filtering technique for QuadBox rings (FQR) with two existing filtering techniques, including quick [...] Read more.

In this paper, we propose a very effectively filtering approach (EFA) to enhance network traffic performance for high-availability seamless redundancy (HSR) protocol in smart grids. The EFA combines a novel filtering technique for QuadBox rings (FQR) with two existing filtering techniques, including quick removing (QR) and port locking (PL), to effectively reduce redundant unicast traffic within HSR networks. The EFA filters unicast traffic for both unused terminal rings by using the PL technique and unused QuadBox rings based on the newly-proposed FQR technique. In addition, by using the QR technique, the EFA prevents the unicast frames from being duplicated and circulated in rings; the EFA thus significantly reduces redundant unicast traffic in HSR networks compared with the standard HSR protocol and existing traffic filtering techniques. The EFA also reduces control overhead compared with the filtering HSR traffic (FHT) technique. In this study, the performance of EFA was analyzed, evaluated, and compared to that of the standard HSR protocol and existing techniques, and various simulations were conducted to validate the performance analysis. The analytical and simulation results showed that for the sample networks, the proposed EFA reduced network unicast traffic by 80% compared with the standard HSR protocol and by 26–62% compared with existing techniques. The proposed EFA also reduced control overhead by up to 90% compared with the FHT, thus decreasing control overhead, freeing up network bandwidth, and improving network traffic performance. Full article

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

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16 pages, 3115 KiB

Open AccessArticle

Modeling and Analysis of the Common Mode Voltage in a Cascaded H-Bridge Electronic Power Transformer

by Yun Yang, Chengxiong Mao, Dan Wang

, Jie Tian^* and Ming Yang

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

Energies 2017, 10(9), 1357; https://doi.org/10.3390/en10091357 - 8 Sep 2017

Cited by 5 | Viewed by 5945

Abstract

Electronic power transformers (EPTs) have been identified as emerging intelligent electronic devices in the future smart grid, e.g., the Energy Internet, especially in the application of renewable energy conversion and management. Considering that the EPT is directly connected to the medium-voltage grid, e.g., [...] Read more.

Electronic power transformers (EPTs) have been identified as emerging intelligent electronic devices in the future smart grid, e.g., the Energy Internet, especially in the application of renewable energy conversion and management. Considering that the EPT is directly connected to the medium-voltage grid, e.g., a10 kV distribution system, and its cascaded H-bridges structure, the common mode voltage (CMV) issue will be more complex and severe. The CMV will threaten the insulation of the entire EPT device and even produce common mode current. This paper investigates the generated mechanism and characteristics of the CMV in a cascaded H-bridge EPT (CHB-EPT) under both balanced and fault grid conditions. First, the CHB-EPT system is introduced. Then, a three-phase simplified circuit model of the high-voltage side of the EPT system is presented. Combined with a unipolar modulation strategy and carrier phase shifting technology by rigorous mathematical analysis and derivation, the EPT internal CMV and its characteristics are obtained. Moreover, the influence of the sinusoidal pulse width modulation dead time is considered and discussed based on analytical calculation. Finally, the simulation results are provided to verify the validity of the aforementioned model and the analysis results. The proposed theoretical analysis method is also suitable for other similar cascaded converters and can provide a useful theoretical guide for structural design and power density optimization. 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, 1001 KiB

Open AccessArticle

A Data Analysis Technique to Estimate the Thermal Characteristics of a House

by Seyed Amin Tabatabaei^1,*, Wim Van der Ham², Michel C. A. Klein¹ and Jan Treur¹

¹ Behavioural Informatics Group, Deptartment of Computer Science, VU University Amsterdam, 1081 HV Amsterdam, The Netherlands

² Quby, Joan Muyskenweg 22, 1096 CJ Amsterdam, The Netherlands

Energies 2017, 10(9), 1358; https://doi.org/10.3390/en10091358 - 8 Sep 2017

Cited by 9 | Viewed by 5461

Abstract

Almost one third of the energy is used in the residential sector, and space heating is the largest part of energy consumption in our houses. Knowledge about the thermal characteristics of a house can increase the awareness of homeowners about the options to [...] Read more.

Almost one third of the energy is used in the residential sector, and space heating is the largest part of energy consumption in our houses. Knowledge about the thermal characteristics of a house can increase the awareness of homeowners about the options to save energy, for example by showing that there is room for improvement of the insulation level. However, calculating the exact value of these characteristics is not possible without precise thermal experiments. In this paper, we propose a method to automatically estimate two of the most important thermal characteristics of a house, i.e., the loss rate and the heat capacity, based on collected data about the temperature and gas usage. The method is evaluated with a data set that has been collected in a real-life case study. Although a ground truth is lacking, the analyses show that there is evidence that this method could provide a feasible way to estimate those values from the thermostat data. More detailed data about the houses in which the data was collected is required to draw stronger conclusions. We conclude that the proposed method is a promising way to add energy saving advice to smart thermostats. Full article

(This article belongs to the Collection Smart Grid)

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15 pages, 2295 KiB

Open AccessArticle

Numerical Simulation of Density-Driven Flow and Heat Transport Processes in Porous Media Using the Network Method

by Manuel Cánovas^1,*

, Iván Alhama², Gonzalo García²

, Emilio Trigueros³ and Francisco Alhama⁴

¹ Metallurgical and Mining Engineering Department, Universidad Católica del Norte, Avda. Angamos, Antofagasta 0610, Chile

² Civil Engineering Department, Universidad Politécnica de Cartagena, Paseo Alfonso XIII, 52 30203 Cartagena, Spain

³ Mining, Geologic and Cartographic Engineering Department, Universidad Politécnica de Cartagena, Paseo Alfonso XIII, 52 30203 Cartagena, Spain

⁴ Applied Physics Department, Universidad Politécnica de Cartagena, Paseo Alfonso XIII, 52 30203 Cartagena, Spain

Energies 2017, 10(9), 1359; https://doi.org/10.3390/en10091359 - 8 Sep 2017

Cited by 12 | Viewed by 4167

Abstract

Density-driven flow and heat transport processes in 2-D porous media scenarios are governed by coupled, non-linear, partial differential equations that normally have to be solved numerically. In the present work, a model based on the network method simulation is designed and applied to [...] Read more.

Density-driven flow and heat transport processes in 2-D porous media scenarios are governed by coupled, non-linear, partial differential equations that normally have to be solved numerically. In the present work, a model based on the network method simulation is designed and applied to simulate these processes, providing steady state patterns that demonstrate its computational power and reliability. The design is relatively simple and needs very few rules. Two applications in which heat is transported by natural convection in confined and saturated media are studied: slender boxes heated from below (a kind of Bénard problem) and partially heated horizontal plates in rectangular domains (the Elder problem). The streamfunction and temperature patterns show that the results are coherent with those of other authors: steady state patterns and heat transfer depend both on the Rayleigh number and on the characteristic Darcy velocity derived from the values of the hydrological, thermal and geometrical parameters of the problems. Full article

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

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14 pages, 2443 KiB

Open AccessArticle

Biodiesel Production from Bombacopsis glabra Oil by Methyl Transesterification Method

by Francisca Diana Da Silva Araújo¹, Antonio Do Nascimento Cavalcante², Maria das Dores B. Sousa¹, Carla Verônica Rodarte De Moura¹, Mariana Helena Chaves^1,*, Sabria Aued-Pimentel³, Miriam Solange Fernandes Caruso³, Luimar José Tozetto⁴ and Soane Kaline Morais Chaves⁵

¹ Department of Chemistry, Federal University of Piauí, 64049-550 Teresina, PI, Brazil

² Institute of Education, Science and Technology of Maranhão, 65760-000 Presidente Dutra, MA, Brazil

³ Instituto Adolfo Lutz. Division of Food Science and Chemistry, CP 1783, 01059-970 São Paulo, SP, Brazil

⁴ Development Company of the Valleys of the São Francisco and Parnaíba, Codevasf, 70830-901 Brasília, DF, Brazil

⁵ Department of Pharmacy, Federal University of Piauí, 64049-550 Teresina, PI, Brazil

Energies 2017, 10(9), 1360; https://doi.org/10.3390/en10091360 - 8 Sep 2017

Cited by 5 | Viewed by 4365

Abstract

The objective of this work was to produce methyl biodiesel from Bombacopis glabra (B. glabra) oil degummed with H₃PO₄. The methyl biodiesel was prepared in an alkaline medium, and characterized by physico-chemical parameters, thin-layer chrmatograghy (TLC), gas [...] Read more.

The objective of this work was to produce methyl biodiesel from Bombacopis glabra (B. glabra) oil degummed with H₃PO₄. The methyl biodiesel was prepared in an alkaline medium, and characterized by physico-chemical parameters, thin-layer chrmatograghy (TLC), gas chromatograph (GC), (Nuclear magnetic resonance of hydrogen (H-NMR), thermogravimetry and infrared analysis. The physico-chemical parameters of biodiesel were in accordance with the limits established by National Agency of Petroleum, Natural Gas and Biofuels (ANP) Resolution 45/2014, except oxidation stability, where it was corrected with the addition of antioxidants such as TBHQ and BHT. Full article

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17 pages, 6707 KiB

Open AccessArticle

Development of an Integrated Thermal Energy Storage and Free-Piston Stirling Generator for a Concentrating Solar Power System

by Songgang Qiu^*

, Laura Solomon

and Garrett Rinker

Department of Mechanical and Aerospace Engineering, Benjamin M. Statler College of Engineering and Mineral Resources, West Virginia University, Morgantown, WV 26506, USA

Energies 2017, 10(9), 1361; https://doi.org/10.3390/en10091361 - 8 Sep 2017

Cited by 26 | Viewed by 6477

Abstract

Incorporating thermal energy storage (TES) into a concentrating solar power (CSP) system extends the power production hours, eliminating intermittency and reducing the Levelized Cost of the Energy (LCOE). The designed TES system was integrated with a 3 kW free-piston Stirling convertor. A NaF–NaCl [...] Read more.

Incorporating thermal energy storage (TES) into a concentrating solar power (CSP) system extends the power production hours, eliminating intermittency and reducing the Levelized Cost of the Energy (LCOE). The designed TES system was integrated with a 3 kW free-piston Stirling convertor. A NaF–NaCl eutectic salt was chosen as the phase change material (PCM) with a melting temperature of 680 °C. This eutectic salt has an energy density that is 5 to 10 times that of a typical molten salt PCM. In order to overcome the drawbacks of the material having a low thermal conductivity, heat pipes were embedded into the PCM to enhance the heat transfer rate within the system. Since the dish collector tracks the sun over the course of the day, two operational extremes were tested on the system; horizontal (zero solar elevation at sunrise/sunset) and vertical (solar noon). Although the system’s performance was below the expectations due to improperly sized wicks in the secondary heat pipes, the results indicated that the Stirling engine was able to produce 1.3 kWh of electricity by extracting latent heat energy from the PCM; thus, the concept of the design was validated. Full article

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

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24 pages, 2682 KiB

Open AccessArticle

Enumerative Optimization Procedure for the Gear Train Optimization Problem of a Two-Speed Dedicated Electric Transmission

by Xiangyang Xu^1,2,3, Zhifeng Chen^1,2,3, Yanjing Liu^1,2,3, Peng Dong^1,2,3,* and Yanfang Liu^1,2,3

¹ School of Transportation Science and Engineering, Beihang University, 37 Xueyuan Road, Haidian District, Beijing 100191, China

² Beijing Key Laboratory for High-Efficient Power Transmission and System Control of New Energy Resource Vehicle, Beihang University, 37 Xueyuan Road, Haidian District, Beijing 100191, China

³ DYNAVOLT TECH. and Beihang University Joint Lab for New Energy Resource Vehicle Transmission Technology, Beihang University, 37 Xueyuan Road, Haidian District, Beijing 100191, China

Energies 2017, 10(9), 1362; https://doi.org/10.3390/en10091362 - 8 Sep 2017

Cited by 10 | Viewed by 4457

Abstract

Gear train optimization problems (GTOPs) can be very difficult. This paper proposes an enumerative optimization procedure (EOP) for the GTOP of a two-speed dedicated electric transmission (2DET) for electric vehicles (EVs). The EOP combines enumeration with the Min-Max Principle of Optimality (MMPO). First, [...] Read more.

Gear train optimization problems (GTOPs) can be very difficult. This paper proposes an enumerative optimization procedure (EOP) for the GTOP of a two-speed dedicated electric transmission (2DET) for electric vehicles (EVs). The EOP combines enumeration with the Min-Max Principle of Optimality (MMPO). First, the requirements of the EV and the requirements of manufacture and operation were checked in a dedicated order to obtain the feasible region of the GTOP. Then, the MMPO was implemented within the feasible region to reveal the global optimum in terms of the performance of the EV, the load capacity of the gears and the size of the gear train (GT). Results demonstrated that the EOP was effective in determining the feasible region and simultaneously and globally optimizing multiple criteria for the GTOP. The idea of combining enumeration with optimization, as the EOP presents, may be helpful to solve other GTOPs and provide global optima that are immediately practical and applicable. Full article

(This article belongs to the Special Issue Methods to Improve Energy Use in Road Vehicles)

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17 pages, 2380 KiB

Open AccessArticle

Gas Turbine Engine Identification Based on a Bank of Self-Tuning Wiener Models Using Fast Kernel Extreme Learning Machine

by Feng Lu^*

, Yu Ye and Jinquan Huang^*

Jiangsu Province Key Laboratory of Aerospace Power Systems, College of Energy & Power Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, Jiangsu, China

Energies 2017, 10(9), 1363; https://doi.org/10.3390/en10091363 - 8 Sep 2017

Cited by 7 | Viewed by 4126

Abstract

In order to simultaneously obtain global optimal model structure and coefficients, this paper proposes a novel Wiener model to identify the dynamic and static behavior of a gas turbine engine. An improved kernel extreme learning machine is presented to build up a bank [...] Read more.

In order to simultaneously obtain global optimal model structure and coefficients, this paper proposes a novel Wiener model to identify the dynamic and static behavior of a gas turbine engine. An improved kernel extreme learning machine is presented to build up a bank of self-tuning block-oriented Wiener models; the time constant values of linear dynamic element in Wiener model are designed to tune engine operating conditions. Reduced-dimension matrix inversion incorporated with the fast leave one out cross validation strategy is utilized to decrease computational time for the selection of engine model feature parameters. An optimization algorithm is no longer needed compared to the former method. The contribution of this study is that a more convenient and appropriate methodology is developed to describe aircraft engine thermodynamic behavior during its static and dynamic operations. The methodology is evaluated in terms of computational efforts, dynamic and static estimation accuracy through a case study involving data that are generated by general aircraft engine simulation. The results confirm our viewpoints in this paper. Full article

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

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15 pages, 2856 KiB

Open AccessArticle

Experimental and Numerical Investigation of Forced Convection in a Double Skin Façade

by Tuğba İnan¹, Tahsin Başaran^2,* and Aytunç Erek³

¹ Department of Architecture, Niğde Ömer Halisdemir University, Niğde 51240, Turkey

² Department of Architecture, İzmir Institute of Technology, İzmir 35430, Turkey

³ Department of Mechanical Engineering, Dokuz Eylül University, İzmir 35397, Turkey

Energies 2017, 10(9), 1364; https://doi.org/10.3390/en10091364 - 8 Sep 2017

Cited by 21 | Viewed by 4226

Abstract

Flow and heat transfer of the air cavity between two glass façades designed in the box window type of double skin façade (DSF) was evaluated in a test room which was set up for measurements in the laboratory environment and analyzed under different [...] Read more.

Flow and heat transfer of the air cavity between two glass façades designed in the box window type of double skin façade (DSF) was evaluated in a test room which was set up for measurements in the laboratory environment and analyzed under different working conditions by using a computational fluid dynamics tool. Using data from the experimental studies, the verification of the numerical studies was conducted and the air flow and heat transfer in the cavity between the two glass façades were examined numerically in detail. The depth to height of the cavity, the aspect ratio, was changed between 0.10 and 0.16, and was studied for three different flow velocities. Reynolds and average Nusselt numbers ranging from 28,000 to 56,500 and 134 to 272, respectively, were calculated and a non-dimensional correlation between Reynolds and Nusselt numbers was constructed to evaluate the heat transfer from the cavity (except inlet and outlet sections) air to the inside environment and it could be used the box window type of DSF applications having relatively short cavities. Full article

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

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15 pages, 21305 KiB

Open AccessArticle

A Torque Error Compensation Algorithm for Surface Mounted Permanent Magnet Synchronous Machines with Respect to Magnet Temperature Variations

by Chang-Seok Park¹

and Jae Suk Lee^2,*

¹ Department of Electrical Engineering, Kyungnam University, Changwon-si 51767, Korea

² Department of Electrical Engineering, Chonbuk National University, Jeonju-si 54896, Korea

Energies 2017, 10(9), 1365; https://doi.org/10.3390/en10091365 - 24 Aug 2018

Cited by 13 | Viewed by 6503

Abstract

This paper presents a torque error compensation algorithm for a surface mounted permanent magnet synchronous machine (SPMSM) through real time permanent magnet (PM) flux linkage estimation at various temperature conditions from medium to rated speed. As known, the PM flux linkage in SPMSMs [...] Read more.

This paper presents a torque error compensation algorithm for a surface mounted permanent magnet synchronous machine (SPMSM) through real time permanent magnet (PM) flux linkage estimation at various temperature conditions from medium to rated speed. As known, the PM flux linkage in SPMSMs varies with the thermal conditions. Since a maximum torque per ampere look up table, a control method used for copper loss minimization, is developed based on estimated PM flux linkage, variation of PM flux linkage results in undesired torque development of SPMSM drives. In this paper, PM flux linkage is estimated through a stator flux linkage observer and the torque error is compensated in real time using the estimated PM flux linkage. In this paper, the proposed torque error compensation algorithm is verified in simulation and experiment. Full article

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

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15 pages, 5919 KiB

Open AccessArticle

Thermal Performance Analysis of Multi-Phase Change Material Layer-Integrated Building Roofs for Energy Efficiency in Built-Environment

by K. S. Reddy¹, Vijay Mudgal¹

and Tapas K. Mallick^2,*

¹ Heat Transfer and Thermal Power Laboratory, Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600036, India

² Environment and Sustainability Institute, University of Exeter, Penryn Campus, Penryn Cornwall TR10 9FE, UK

Energies 2017, 10(9), 1367; https://doi.org/10.3390/en10091367 - 9 Sep 2017

Cited by 46 | Viewed by 7060

Abstract

Thermal energy storage using phase change materials (PCMs) plays a significant role in maintaining thermal comfort and reducing energy consumption in a building because of its ability to absorb/release heat within small temperature variations. In this paper, the thermal performance of roofs has [...] Read more.

Thermal energy storage using phase change materials (PCMs) plays a significant role in maintaining thermal comfort and reducing energy consumption in a building because of its ability to absorb/release heat within small temperature variations. In this paper, the thermal performance of roofs has been investigated based on various factors like the integration of a single PCM layer, integration of a double PCM layer, the thickness of the PCM, phase transition temperature and heat of fusion of the PCM. The analysis shows that integration of a single PCM layer of different thickness and phase transition temperature and heat of fusion in roof structures is unable to maintain a comfortable constant temperature inside the building due to incomplete solidification and melting of the PCM. However, the analysis shows that with multi-PCM layers of appropriate thickness it is possible to maintain a constant comfortable temperature of about 28 °C in the building throughout the day in Chennai, India. The analysis also shows that there is reduction in heat gain by 17 to 26% for a single PCM layered roof and 25 to 36% for a double PCM layered roof compared to the roof without PCM layer for the different months of the year. Full article

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

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22 pages, 1553 KiB

Open AccessArticle

Using Thermostats for Indoor Climate Control in Office Buildings: The Effect on Thermal Comfort

by Georgios D. Kontes^1,2,*

, Georgios I. Giannakis³, Philip Horn⁴, Simone Steiger² and Dimitrios V. Rovas⁵

¹ Department of Mechanical Engineering and Building Services Engineering, Technische Hochschule Nürnberg Georg Simon Ohm, 90489 Nuremberg, Germany

² Technical Building Systems Group, Nuremberg Branch, Department of Energy Efficiency and Indoor Climate, Fraunhofer Institute for Building Physics, 90429 Nuremberg, Germany

³ School of Production Engineering and Management, Technical University of Crete, Chania 73100, Greece

⁴ Energy Department, Austrian Institute of Technology, 1220 Vienna, Austria

⁵ The Bartlett School of Environment, Energy and Resources, Faculty of the Built Environment, University College London, London WC1E 6BT, UK

Energies 2017, 10(9), 1368; https://doi.org/10.3390/en10091368 - 10 Sep 2017

Cited by 40 | Viewed by 8538

Abstract

Thermostats are widely used in temperature regulation of indoor spaces and have a direct impact on energy use and occupant thermal comfort. Existing guidelines make recommendations for properly selecting set points to reduce energy use, but there is little or no information regarding [...] Read more.

Thermostats are widely used in temperature regulation of indoor spaces and have a direct impact on energy use and occupant thermal comfort. Existing guidelines make recommendations for properly selecting set points to reduce energy use, but there is little or no information regarding the actual achieved thermal comfort of the occupants. While dry-bulb air temperature measured at the thermostat location is sometimes a good proxy, there is less understanding of whether thermal comfort targets are actually met. In this direction, we have defined an experimental simulation protocol involving two office buildings; the buildings have contrasting geometrical and construction characteristics, as well as different building services systems for meeting heating and cooling demands. A parametric analysis is performed for combinations of controlled variables and boundary conditions. In all cases, occupant thermal comfort is estimated using the Fanger index, as defined in ISO 7730. The results of the parametric study suggest that simple bounds on the dry-bulb air temperature are not sufficient to ensure comfort, and in many cases, more detailed considerations taking into account building characteristics, as well as the types of building heating and cooling services are required. The implication is that the calculation or estimation of detailed comfort indices, or even the use of personalised comfort models, is key towards a more human-centric approach to building design and operation. Full article

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17 pages, 8300 KiB

Open AccessArticle

Performance Investigation of the Novel Solar-Powered Dehumidification Window for Residential Buildings

by Wansheng Yang¹, Hao Deng¹, Zhangyuan Wang^1,*, Xudong Zhao² and Song He¹

¹ School of Civil and Transportation Engineering, Guangdong University of Technology, Guangzhou 510006, China

² School of Engineering, University of Hull, Hull HU6 7RX, UK

Energies 2017, 10(9), 1369; https://doi.org/10.3390/en10091369 - 10 Sep 2017

Cited by 12 | Viewed by 4804

Abstract

In this paper, a solar-powered dehumidification window (SPDW), combining a conventional double-glazed building window with a solid desiccant packed bed and a photovoltaic panel, has been proposed to dehumidify the air supplied to a residential building in an energy-saving way. The solid desiccant [...] Read more.

In this paper, a solar-powered dehumidification window (SPDW), combining a conventional double-glazed building window with a solid desiccant packed bed and a photovoltaic panel, has been proposed to dehumidify the air supplied to a residential building in an energy-saving way. The solid desiccant packed bed was installed between the double layers of the residential window to achieve the compact building-integrated window-dehumidifying system that could be regenerated by solar energy, and the photovoltaic panel was used to compensate the electricity for the operation of the fans to supply the air to the building. To investigate the dehumidification and regeneration performance of the SPDW, the transient moisture removal, dehumidification efficiency, temperature difference between the building inlet and outlet air, heat transfer characteristics, desiccant temperature, regeneration rate, and the power of the fans and the photovoltaic panel were analysed for different inlet air conditions and simulated solar radiation. It was found that, for the system operated under an inlet air temperature of 19.2 °C and a relative humidity of 86.1% during the dehumidification process, the system performed with a maximum transient moisture removal of 7.1 g/kg, a maximum dehumidification efficiency of 58.60%, a maximum temperature difference between the inlet and outlet air of 10.7 °C, and a maximum released adsorption heat absorbed by the dehumidified air of 89.66%. In the regeneration process, the system performed with a maximum desiccant temperature of 35.3 °C, a maximum regeneration rate of 153 g/h, and a maximum power of the photovoltaic panels of 39.83 W under the simulated solar radiation of 900 W/m². The results from the established semi-empirical model agreed well with the testing results, and the model could be used to predict the water content ratio of the desiccant modules during the dehumidification process under different conditions, which will be helpful in the analysis and application of the SPDW in the future. Full article

(This article belongs to the Special Issue Solar Technologies for Buildings)

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14 pages, 3078 KiB

Open AccessArticle

Biomass Production of Three Biofuel Energy Plants’ Use of a New Carbon Resource by Carbonic Anhydrase in Simulated Karst Soils: Mechanism and Capacity

by Rui Wang^1,2,*, Yanyou Wu^2,*

, Deke Xing³, Hongtao Hang², Xiaolin Xie¹, Xiuqun Yang¹, Kaiyan Zhang² and Sen Rao^1,2

¹ Food and Pharmaceutical Engineering Institute, Guiyang University, Guiyang 550005, China

² State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China

³ Key Laboratory of Modern Agricultural Equipment and Technology, Ministry of Education & Jiangsu Province, Institute of Agricultural Engineering, Jiangsu University, Zhenjiang 212013, China

Energies 2017, 10(9), 1370; https://doi.org/10.3390/en10091370 - 10 Sep 2017

Cited by 14 | Viewed by 4404

Abstract

To determine whether the bicarbonate in karst limestone soil could be used as a new carbon resource for biomass production by the catalysis of carbonic anhydrase (CA), a simulative karst drought stress experiment was designed and performed. Three plants used for biofuel energy, [...] Read more.

To determine whether the bicarbonate in karst limestone soil could be used as a new carbon resource for biomass production by the catalysis of carbonic anhydrase (CA), a simulative karst drought stress experiment was designed and performed. Three plants used for biofuel energy, Orychophragmus violaceus L. (Ov), Brassica juncea L. (Bj), and Euphorbia lathyris L. (El), were grown under simulated karst drought stress. In response to drought stress, the photosynthesis of the three energy plants was inhibited, but their CA activity increased. The hypothesis was confirmed by plant physiological and stable isotope techniques. The obtained results showed that plant biomass was produced with atmospheric CO₂ as well as bicarbonate under drought stress. Bicarbonate use was proportional to the CA activity of the plants. With high CA activity over a long period, El had the highest proportional bicarbonate use compared to Ov and Bj, reaching 26.95%. Additionally, a new method is proposed for the screening of plants grown for energy in karst habitats. Full article

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

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20 pages, 6904 KiB

Open AccessArticle

Hanging Wall Pressure Relief Mechanism of Horizontal Section Top-Coal Caving Face and Its Application—A Case Study of the Urumqi Coalfield, China

by Jinshuai Guo¹, Liqiang Ma^2,3,*

, Ye Wang⁴ and Fangtian Wang²

¹ State Key Laboratory for Geomechanics & Deep Underground Engineering, School of Mechanics and Civil Engineering, China University of Mining and Technology, Xuzhou 221116, China

² State Key Laboratory of Coal Resources and Safe Mining, School of Mines, China University of Mining and Technology, Xuzhou 221116, China

³ College of Earth and Mineral Sciences, the Pennsylvania State University, University Park, PA 16802, USA

⁴ Jiangou Coal Mine, Shenxin Energy Company, Urumqi 830001, China

Energies 2017, 10(9), 1371; https://doi.org/10.3390/en10091371 - 10 Sep 2017

Cited by 29 | Viewed by 4651

Abstract

Abundant steeply-dipping thick coal seams (SDTCS) have been found in Xinjiang, China, and they are mined largely by the horizontal section top-coal caving (HSTCC) method. The hanging wall of the HSTCC face is nearly vertical and does not fracture easily after the underlying [...] Read more.

Abundant steeply-dipping thick coal seams (SDTCS) have been found in Xinjiang, China, and they are mined largely by the horizontal section top-coal caving (HSTCC) method. The hanging wall of the HSTCC face is nearly vertical and does not fracture easily after the underlying coal is extracted. As a result, stress tends to concentrate in the hanging wall of the lower-section working face (LSWF) and then induce dynamic disasters. In this study, a mechanical model of a HSTCC face’s hanging wall in steeply-dipping seams was constructed to study the characteristics of hanging wall deformation. The mechanism of hanging wall pressure relief by deep-hole blasting (DHB) was analyzed and the effectiveness of DHB was investigated by simulation using the LS-DYNA software. Based on these studies, parameters relevant to pressure relief by DHB were determined and then DHB was applied to the 4301 working face in the Jiangou coal mine. The results show that the average pressure of measured at the 4301 working face decreased about 34% from those at the 4501 face where the hanging wall was not blasted. Accidents related to dynamic rock pressure, such as support crushing and large-scale rib fall, did not occur at the 4301 working face throughout the mining process. Additionally, in order to constrain the surface “V”-shaped collapsed grooves induced by repeated mining of HSTCC faces and prevent the subsequent failure of the surrounding rock on the sides of the collapsed grooves, loess was used to fill in the grooves to provide constraint and dynamic control on the surrounding rock. The two complementary technologies proposed in this study provide a guide on how to control hanging wall of SDTCS in similar conditions. Full article

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18 pages, 967 KiB

Open AccessArticle

Simplified 1D Incompressible Two-Fluid Model with Artificial Diffusion for Slug Flow Capturing in Horizontal and Nearly Horizontal Pipes

by Arianna Bonzanini¹, Davide Picchi²

and Pietro Poesio^1,*

¹ Dipartimento di Ingegneria Meccanica ed Industriale, Università degli Studi di Brescia, Via Branze, 38, 25123 Brescia, Italy

² Energy Resources Engineering, Stanford University, Stanford, CA 94305, USA

Energies 2017, 10(9), 1372; https://doi.org/10.3390/en10091372 - 10 Sep 2017

Cited by 15 | Viewed by 4352

Abstract

This article proposes a numerical resolution of a one-dimensional (1D), transient, simplified two-fluid model regularized with an artificial diffusion term for modeling stratified, wavy and slug flow in horizontal and nearly horizontal pipes. Artificial diffusion is introduced to prevent the unbounded growth of [...] Read more.

This article proposes a numerical resolution of a one-dimensional (1D), transient, simplified two-fluid model regularized with an artificial diffusion term for modeling stratified, wavy and slug flow in horizontal and nearly horizontal pipes. Artificial diffusion is introduced to prevent the unbounded growth of instabilities where the 1D two-fluid model is ill-posed. We propose a method to set the artificial diffusion case by case to obtain the desired cut-off at short wavelengths by combining the choice of the spatial discretisation and the amplification factors obtained by the linear stability analysis of the model. A proper criterion to simulate two-phase to single-phase flow transition, which occurs during slug formation, is also developed. Flow pattern transitions have been numerically computed and compared against theoretical transition boundaries and experimental observations. Moreover, we showed that the developed code computes slug initiation and slug characteristics, in a reasonably accurate way considering the simplicity of the model, comparing numerical results with well-known empirical correlations and experimental data. Furthermore, the model simplicity leads to a computationally-inexpensive numerical resolution; this can be useful in engineering applications where obtaining fast numerical results is fundamental, such as applications involving automated control for two-phase flows. Full article

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27 pages, 9979 KiB

Open AccessArticle

New Design of a CNG-H₂-AIR Mixer for Internal Combustion Engines: An Experimental and Numerical Study

by Hussein A. Mahmood^1,2,*, Nor Mariah. Adam¹

, B. B. Sahari¹ and S. U. Masuri¹

¹ Department of Mechanical and Manufacturing Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia

² The Engineering Affairs Department, Presidency of the University of Baghdad, 999048 Baghdad, Iraq

Energies 2017, 10(9), 1373; https://doi.org/10.3390/en10091373 - 10 Sep 2017

Cited by 14 | Viewed by 6690

Abstract

Several studies have aimed to convert diesel engines to dual- or tri-fuel engines to improve their fuel economy and reduce the emissions from diesel engine, however, most of these studies do not consider enhancing the homogeneity of fuel mixtures inside the engine and [...] Read more.

Several studies have aimed to convert diesel engines to dual- or tri-fuel engines to improve their fuel economy and reduce the emissions from diesel engine, however, most of these studies do not consider enhancing the homogeneity of fuel mixtures inside the engine and accurately controlling the air fuel ratio. In this study, a new air-fuel mixer was designed, manufactured and tested. The proposed air-gaseous fuel mixer design was conceived to be suitable for mixing air with compressed natural gas (CNG) and a blend of hydrogen and compressed natural gas (HCNG) that gives homogenous mixtures with high uniformity index and also to be easily connected with an Electronic Control Unit (ECU) for controlling accurately the air-gaseous fuel ratio for different engine speeds. For optimizing the homogeneity inside the new mixer, fourteen different mixer models were created to investigate the effects of diameter, location, and the number of holes inside the mixer on the homogeneity and distribution of the mixtures. Computational fluid dynamics analysis software was used to check the flow behavior, distribution and homogeneity of mixtures inside the new mixer models. The simulation results revealed that the best uniformity index (UI) values are obtained in model 7 where the UI values are 0.939 and 0.937, respectively, for an air fuel ratio for a blend of hydrogen and compressed natural gas (AFRHCNG) = 51.31 and the air fuel ratio for compressed natural gas (AFRCNG) = 34.15. According to the numerical and experimental results for the new mixer (model 7) under different engine speeds (1000–4000) and air-CNG ratio of 34.15, a meaningful agreement is reached between the experimental and numerical values for AFRCNG (coefficient of determination (R²) = 0.96 and coefficient of variation (CoV) = 0.001494). Full article

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11 pages, 3917 KiB

Open AccessArticle

Improved Reactive Current Detection Method of SVG

by Xueliang Wei¹, Guorong Zhu^2,*, Jianghua Lu², Wenjing Li² and And Erjie Qi²

¹ College of Geophysics and Information Engineering, China University of Petroleum-Beijing, Beijing 100000, China

² School of Automation, Wuhan University of Technology, Wuhan 430000, China

Energies 2017, 10(9), 1374; https://doi.org/10.3390/en10091374 - 10 Sep 2017

Cited by 3 | Viewed by 4381

Abstract

The static VAR generator (SVG) is an important device in flexible AC transmission systems (FACTS) for the development of smart grids. Based on the basis principle of SVG and instantaneous reactive power theory, the conventional i_p–i_q and dq methods have [...] Read more.

The static VAR generator (SVG) is an important device in flexible AC transmission systems (FACTS) for the development of smart grids. Based on the basis principle of SVG and instantaneous reactive power theory, the conventional i_p–i_q and dq methods have a certain error when the three phase voltages are unbalanced. In this paper, the current detection algorithm is improved in cases of three-phase power asymmetry by using the fundamental positive-sequence reactive current instead of the voltage as the input of phase locked loop (PLL). So the problems caused by unbalanced three-phase voltages could be avoided. In addition, a moving average filter is designed to improve the performance of the detection accuracy and dynamic response. Experiments verify the correctness and effectiveness of the proposed scheme. 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, 6339 KiB

Open AccessArticle

Spectrometer-Based Line-of-Sight Temperature Measurements during Alkali-Pulverized Coal Combustion in a Power Station Boiler

by Weijie Yan¹, Yunqi Ya¹, Feng Du², Hao Shao³ and Peitao Zhao^1,*

¹ School of Electrical and Power Engineering, China University of Mining and Technology, No.1, Daxue Road, Xuzhou 221116, China

² Huadian Power International Corporation Limited Zouxian power plant, Tangcun town, Zhoucheng 273500, China

³ School of Safety Engineering, China University of Mining and Technology, No.1, Daxue Road, Xuzhou 221116, China

Energies 2017, 10(9), 1375; https://doi.org/10.3390/en10091375 - 10 Sep 2017

Cited by 19 | Viewed by 4921

Abstract

A portable spectrometer system that simultaneously measures the temperature, emissivity, and radiation intensity of an alkali metal was used in a 1000 MW coal-fired power plant boiler furnace. A calibrated fiber-optic spectrometer system was applied to obtain the radiation intensity of the flame. [...] Read more.

A portable spectrometer system that simultaneously measures the temperature, emissivity, and radiation intensity of an alkali metal was used in a 1000 MW coal-fired power plant boiler furnace. A calibrated fiber-optic spectrometer system was applied to obtain the radiation intensity of the flame. A simple method based on polynomial fitting was used to separate the continuous baseline from the measured flame spectra that contained both continuous and discontinuous bands. Nine synthetic spectra that included the baseline, noise, and three simulated discontinuous bands based on a Gaussian function were created to test the accuracy of the separation method. The accuracy of the estimated continuous baseline was evaluated by the goodness-of-fit coefficient quality metric. The results indicated good spectral matching for the selected profiles. The soot emissivity model by Hottel and Broughton was employed to calculate temperature and emissivity. The influence of discontinuous emission spectra on the temperature and emissivity calculations was evaluated. The results showed that the maximum difference of the measurement points of the calculated temperature was only 6 K and that the relative difference in emissivity among the measurement points was less than 5%. In addition, a comparison between the actual intensity of the alkali metal and the calculated temperature indicated that the change in the radiation intensity of the alkali metal followed the trend of the calculated temperature. This study serves as a preliminary investigation for measuring gas-phase alkali metal concentrations in a furnace. Full article

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15 pages, 1750 KiB

Open AccessArticle

Transmission Expansion Planning Using TLBO Algorithm in the Presence of Demand Response Resources

by Amir Sadegh Zakeri and Hossein Askarian Abyaneh^*

Tehran Polytechnic, Amirkabir University of Technology, 424 Hafez Ave, 159163-4311 Tehran, Iran

Energies 2017, 10(9), 1376; https://doi.org/10.3390/en10091376 - 11 Sep 2017

Cited by 22 | Viewed by 3622

Abstract

Transmission Expansion Planning (TEP) involves determining if and how transmission lines should be added to the power grid so that the operational and investment costs are minimized. TEP is a major issue in smart grid development, where demand response resources affect short- and [...] Read more.

Transmission Expansion Planning (TEP) involves determining if and how transmission lines should be added to the power grid so that the operational and investment costs are minimized. TEP is a major issue in smart grid development, where demand response resources affect short- and long-term power system decisions, and these in turn, affect TEP. First, this paper discusses the effects of demand response programs on reducing the final costs of a system in TEP. Then, the TEP problem is solved using a Teaching Learning Based Optimization (TLBO) algorithm taking into consideration power generation costs, power loss, and line construction costs. Simulation results show the optimal effect of demand response programs on postponing the additional cost of investments for supplying peak load. Full article

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

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11 pages, 2384 KiB

Open AccessArticle

Selection of Optimal Polymerization Degree and Force Field in the Molecular Dynamics Simulation of Insulating Paper Cellulose

by Xiaobo Wang¹, Chao Tang^1,*, Qian Wang², Xiaoping Li² and Jian Hao³

¹ College of Engineering and Technology, Southwest University, Chongqing 400715, China

² State Grid Chongqing Electric Power Co. Chongqing Electric Power Research Institute, Chongqing 401123, China

³ Laboratory of Power Transmission Equipment & System Security and New Technology, Chongqing University, Chongqing 400044, China

Energies 2017, 10(9), 1377; https://doi.org/10.3390/en10091377 - 11 Sep 2017

Cited by 70 | Viewed by 7128

Abstract

To study the microscopic thermal aging mechanism of insulating paper cellulose through molecular dynamics simulation, it is important to select suitable DP (Degree of Polymerization) and force field for the cellulose model to shorten the simulation time and obtain correct and objective simulation [...] Read more.

To study the microscopic thermal aging mechanism of insulating paper cellulose through molecular dynamics simulation, it is important to select suitable DP (Degree of Polymerization) and force field for the cellulose model to shorten the simulation time and obtain correct and objective simulation results. Here, the variation of the mechanical properties and solubility parameters of models with different polymerization degrees and force fields were analyzed. Numerous cellulose models with different polymerization degrees were constructed to determine the relative optimal force field from the perspectives of the similarity of the density of cellulose models in equilibrium to the actual cellulose density, and the volatility and repeatability of the mechanical properties of the models through the selection of a stable polymerization degree using the two force fields. The results showed that when the polymerization degree was more than or equal to 10, the mechanical properties and solubility of cellulose models with the COMPASS (Condensed-phase Optimized Molecular Potential for Atomistic Simulation Studies) and PCFF (Polymer Consistent Force Field) force fields were in steady states. The steady-state density of the cellulose model using the COMPASS force field was closer to the actual density of cellulose. Thus, the COMPASS force field is favorable for molecular dynamics simulation of amorphous cellulose. Full article

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23 pages, 2227 KiB

Open AccessArticle

User-Aware Electricity Price Optimization for the Competitive Market

by Allegra De Filippo^*, Michele Lombardi and Michela Milano

Department of Computer Science and Engineering, University of Bologna, Viale Risorgimento 2, 40126 Bologna, Italy

Energies 2017, 10(9), 1378; https://doi.org/10.3390/en10091378 - 11 Sep 2017

Cited by 17 | Viewed by 4449

Abstract

Demand response mechanisms and load control in the electricity market represent an important area of research at the international level: the trend towards competition and market liberalization has led to the development of methodologies and tools to support energy providers. Demand side management [...] Read more.

Demand response mechanisms and load control in the electricity market represent an important area of research at the international level: the trend towards competition and market liberalization has led to the development of methodologies and tools to support energy providers. Demand side management helps energy suppliers to reduce the peak demand and remodel load profiles. This work is intended to support energy suppliers and policy makers in developing strategies to act on the behavior of energy consumers, with the aim to make a more efficient use of energy. We develop a non-linear optimization model for the dynamics of the electricity market, which can be used to obtain tariff recommendations or for setting the goals of a sensibilization campaign. The model comes in two variants: a stochastic version, designed for residential electricity consumption, and a deterministic version, suitable for large electricity users (e.g., public buildings, industrial users). We have tested our model on data from the Italian energy market and performed an extensive analysis of different scenarios. We also tested the optimization model in a real setting in the context of the FP7 DAREED project (http://www.dareed.eu/), where the model has been employed to provide tariff recommendations or to help the identification of goals for local policies. Full article

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

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22 pages, 6224 KiB

Open AccessArticle

A Pontryagin Minimum Principle-Based Adaptive Equivalent Consumption Minimum Strategy for a Plug-in Hybrid Electric Bus on a Fixed Route

by Shaobo Xie^1,2,*, Huiling Li¹, Zongke Xin¹, Tong Liu¹ and Lang Wei¹

¹ School of Automotive Engineering, Chang’an University, Southern 2nd Road, Xi’an 710064, China

² National Engineering Laboratory for Electric Vehicles, Beijing Institute of Technology, No. 5 South Zhongguancun Street, Haidian District, Beijing 100081, China

Energies 2017, 10(9), 1379; https://doi.org/10.3390/en10091379 - 11 Sep 2017

Cited by 74 | Viewed by 7805

Abstract

When developing a real-time energy management strategy for a plug-in hybrid electric vehicle, it is still a challenge for the Equivalent Consumption Minimum Strategy to achieve near-optimal energy consumption, because the optimal equivalence factor is not readily available without the trip information. With [...] Read more.

When developing a real-time energy management strategy for a plug-in hybrid electric vehicle, it is still a challenge for the Equivalent Consumption Minimum Strategy to achieve near-optimal energy consumption, because the optimal equivalence factor is not readily available without the trip information. With the help of realistic speeding profiles sampled from a plug-in hybrid electric bus running on a fixed commuting line, this paper proposes a convenient and effective approach of determining the equivalence factor for an adaptive Equivalent Consumption Minimum Strategy. Firstly, with the adaptive law based on the feedback of battery SOC, the equivalence factor is described as a combination of the major component and tuning component. In particular, the major part defined as a constant is applied to the inherent consistency of regular speeding profiles, while the second part including a proportional and integral term can slightly tune the equivalence factor to satisfy the disparity of daily running cycles. Moreover, Pontryagin’s Minimum Principle is employed and solved by using the shooting method to capture the co-state dynamics, in which the Secant method is introduced to adjust the initial co-state value. And then the initial co-state value in last shooting is taken as the optimal stable constant of equivalence factor. Finally, altogether ten successive driving profiles are selected with different initial SOC levels to evaluate the proposed method, and the results demonstrate the excellent fuel economy compared with the dynamic programming and PMP method. Full article

(This article belongs to the Special Issue Energy Management in Vehicle–Grid–Traffic Nexus)

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17 pages, 2410 KiB

Open AccessArticle

Acceleration of Gas Flow Simulations in Dual-Continuum Porous Media Based on the Mass-Conservation POD Method

by Yi Wang^1,2,3,4, Shuyu Sun^5,* and Bo Yu⁶

¹ National Engineering Laboratory for Pipeline Safety, China University of Petroleum, Beijing 102249, China

² MOE Key Laboratory of Petroleum Engineering, China University of Petroleum, Beijing 102249, China

³ Beijing Key Laboratory of Urban Oil and Gas Distribution Technology, China University of Petroleum, Beijing 102249, China

⁴ Key Laboratory of Thermo-Fluid Science and Engineering, Xi’an Jiaotong University, Ministry of Education, Xi’an 710049, China

⁵ Computational Transport Phenomena Laboratory, Division of Physical Science and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia

⁶ School of Mechanical Engineering, Beijing Institute of Petrochemical Technology, Beijing 102617, China

Energies 2017, 10(9), 1380; https://doi.org/10.3390/en10091380 - 12 Sep 2017

Cited by 27 | Viewed by 4029

Abstract

Reduced-order modeling approaches for gas flow in dual-porosity dual-permeability porous media are studied based on the proper orthogonal decomposition (POD) method combined with Galerkin projection. The typical modeling approach for non-porous-medium liquid flow problems is not appropriate for this compressible gas flow in [...] Read more.

Reduced-order modeling approaches for gas flow in dual-porosity dual-permeability porous media are studied based on the proper orthogonal decomposition (POD) method combined with Galerkin projection. The typical modeling approach for non-porous-medium liquid flow problems is not appropriate for this compressible gas flow in a dual-continuum porous media. The reason is that non-zero mass transfer for the dual-continuum system can be generated artificially via the typical POD projection, violating the mass-conservation nature and causing the failure of the POD modeling. A new POD modeling approach is proposed considering the mass conservation of the whole matrix fracture system. Computation can be accelerated as much as 720 times with high precision (reconstruction errors as slow as 7.69 × 10⁻⁴%~3.87% for the matrix and 8.27 × 10⁻⁴%~2.84% for the fracture). Full article

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

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19 pages, 7096 KiB

Open AccessArticle

Use of Rod Compactors for High Voltage Overhead Power Lines Magnetic Field Mitigation

by Fabio Bignucolo^*

, Massimiliano Coppo

, Andrea Savio and Roberto Turri

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

Energies 2017, 10(9), 1381; https://doi.org/10.3390/en10091381 - 12 Sep 2017

Cited by 9 | Viewed by 4704

Abstract

In the last decades, strengthening the high voltage transmission system through the installation of new overhead power lines has become critical, especially in highly developed areas. Present laws concerning the human exposure to electric and magnetic fields introduce constraints to be considered in [...] Read more.

In the last decades, strengthening the high voltage transmission system through the installation of new overhead power lines has become critical, especially in highly developed areas. Present laws concerning the human exposure to electric and magnetic fields introduce constraints to be considered in both new line construction and existing systems. In the paper, a technique for passive magnetic field mitigation in areas close to overhead power lines is introduced, fully modelled and discussed through a parametric analysis. The investigated solution, which basically consists in approaching line conductors along the span making use of rod insulators, is applicable on both existing and under-design overhead lines as an alternative to other mitigating actions. Making use of a 3-dimensional representation, the procedure computes both positions of phase conductors and forces acting on insulators, towers, conductors and compactors, with the aim of evaluating the additional mechanical stress introduced by the compactors. Finally, a real case study is reported to demonstrate and quantify the benefits in terms of ground magnetic field reduction achievable by applying the proposed solution, in comparison to a traditional configuration. Furthermore, using compactors to passively reduce the magnetic field is simple to be applied, minimally invasive and quite inexpensive as regards to alternative mitigating actions. Full article

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

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18 pages, 6432 KiB

Open AccessArticle

Gas Permeability Evolution Mechanism and Comprehensive Gas Drainage Technology for Thin Coal Seam Mining

by Fangtian Wang¹, Cun Zhang^2,3,* and Ningning Liang¹

¹ State Key Laboratory of Coal Resources and Mine Safety, School of Mines, Key Laboratory of Deep Coal Resource Mining, Ministry of Education of China, China University of Mining and Technology, Xuzhou 221116, China

² State Key Laboratory of Coal Resources and Mine Safety, College of Resources & Safety Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China

³ Beijing Key Laboratory for Precise Mining of Intergrown Energy and Resources, China University of Mining and Technology (Beijing), Beijing 100083, China

Energies 2017, 10(9), 1382; https://doi.org/10.3390/en10091382 - 12 Sep 2017

Cited by 38 | Viewed by 5199

Abstract

A thin coal seam mined as a protective coal seam above a gas outburst coal seam plays a central role in decreasing the degree of stress placed on a protected seam, thus increasing gas permeability levels and desorption capacities to dramatically eliminate gas [...] Read more.

A thin coal seam mined as a protective coal seam above a gas outburst coal seam plays a central role in decreasing the degree of stress placed on a protected seam, thus increasing gas permeability levels and desorption capacities to dramatically eliminate gas outburst risk for the protected seam. However, when multiple layers of coal seams are present, stress-relieved gas from adjacent coal seams can cause a gas explosion. Thus, the post-drainage of gas from fractured and de-stressed strata should be applied. Comprehensive studies of gas permeability evolution mechanisms and gas seepage rules of protected seams close to protective seams that occur during protective seam mining must be carried out. Based on the case of the LongWall (LW) 23209 working face in the Hancheng coal mine, Shaanxi Province, this paper presents a seepage model developed through the FLAC3D software program (version 5.0, Itasca Consulting Group, Inc., Minneapolis, MI, USA) from which gas flow characteristics can be reflected by changes in rock mass permeability. A method involving theoretical analysis and numerical simulation was used to analyze stress relief and gas permeability evolution mechanisms present during broken rock mass compaction in a goaf. This process occurs over a reasonable amount of extraction time and in appropriate locations for comprehensive gas extraction technologies. In using this comprehensive gas drainage technological tool, the safe and efficient co-extraction of thin coal seams and gas resources can be realized, thus creating a favorable environment for the safe mining of coal and gas outburst seams. Full article

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14 pages, 1853 KiB

Open AccessArticle

The Impact of Spectral Composition of White LEDs on Spinach (Spinacia oleracea) Growth and Development

by Chiara Burattini^*, Benedetta Mattoni

and Fabio Bisegna

Department of Astronautic, Electric and Energy Engineering (DIAEE), Sapienza University, 00184 Rome, Italy

Energies 2017, 10(9), 1383; https://doi.org/10.3390/en10091383 - 12 Sep 2017

Cited by 23 | Viewed by 6756

Abstract

Light-emitting diodes (LED) are a promising light source for the cultivation of edible vegetables in greenhouses. The spectral radiation of the light sources has an impact on plants physiological parameters, as well as on morphological features. In this study the growth of spinach [...] Read more.

Light-emitting diodes (LED) are a promising light source for the cultivation of edible vegetables in greenhouses. The spectral radiation of the light sources has an impact on plants physiological parameters, as well as on morphological features. In this study the growth of spinach plants has been carried out in experimental boxes under two white LED treatments having different correlate color temperature (CCT): the cold lighting (CL) corresponded to 6500 K, while the warm lighting (WL) to 3000 K. The work was aimed to investigate the influence of the two light spectra on plant development and comparing the results. Results showed that the different lighting treatments impact differently on plant development and on growth parameters. Full article

(This article belongs to the Special Issue 17th CIRIAF National Congress – Sustainable Development, Environment and Human Health Protection)

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20 pages, 8537 KiB

Open AccessArticle

A Novel Sensorless Control Strategy for Brushless Direct Current Motor Based on the Estimation of Line Back Electro-Motive Force

by Chengde Tong^1,2

, Mingqiao Wang¹

, Baige Zhao³, Zuosheng Yin¹ and Ping Zheng^1,4,*

¹ School of Electrical Engineering and Automation, Harbin Institute of Technology, Harbin 150080, China

² School of Astronautics, Harbin Institute of Technology, Harbin 150080, China

³ 704 Institute, China Shipbuilding Industry Corporation, Xuhui District, Shanghai 200030, China

⁴ State Key Laboratory of Robotics and System, Harbin Institute of Technology, Harbin 150080, China

Energies 2017, 10(9), 1384; https://doi.org/10.3390/en10091384 - 12 Sep 2017

Cited by 12 | Viewed by 4622

Abstract

In this paper, a novel sensorless control strategy based on the estimation of line back electro-motive force (BEMF) is proposed. According to the phase relationship between the ideal commutation points of the brushless direct current motor (BLDCM) and the zero-crossing points (ZCPs) of [...] Read more.

In this paper, a novel sensorless control strategy based on the estimation of line back electro-motive force (BEMF) is proposed. According to the phase relationship between the ideal commutation points of the brushless direct current motor (BLDCM) and the zero-crossing points (ZCPs) of the line BEMF, the calculation formula of line BEMF is simplified properly and the commutation rule for different positions of the rotor is presented. The estimation error of line BEMF caused by the freewheeling current of silent phase is analyzed, and the solution is given. With the phase shift of the low-pass filter considered, a compensation method using “60°-α” and “120°-α” is studied in this paper to eliminate the error. Finally, the simulation and experimental results show that the rotor-position-detection error is reduced effectively and the motor driven by the accurate commutation signal can work well at low and high speed. Full article

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

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19 pages, 14744 KiB

Open AccessArticle

Thermal Impact Assessment of Groundwater Heat Pumps (GWHPs): Rigorous vs. Simplified Models

by Bruno Piga, Alessandro Casasso

, Francesca Pace

, Alberto Godio and Rajandrea Sethi^*

Department of Environment, Land and Infrastructure Engineering (DIATI), Politecnico di Torino, corso Duca degli Abruzzi 24, 10129 Torino, Italy

Energies 2017, 10(9), 1385; https://doi.org/10.3390/en10091385 - 12 Sep 2017

Cited by 46 | Viewed by 5669

Abstract

Groundwater Heat Pumps (GWHPs) are increasingly adopted for air conditioning in urban areas, thus reducing CO₂ emissions, and this growth needs to be managed to ensure the sustainability of the thermal alteration of aquifers. However, few studies have addressed the propagation of [...] Read more.

Groundwater Heat Pumps (GWHPs) are increasingly adopted for air conditioning in urban areas, thus reducing CO₂ emissions, and this growth needs to be managed to ensure the sustainability of the thermal alteration of aquifers. However, few studies have addressed the propagation of thermal plumes from open-loop geothermal systems from a long-term perspective. We provide a comprehensive sensitivity analysis, performed with numerical finite-element simulations, to assess how the size of the thermally affected zone is driven by hydrodynamic and thermal subsurface properties, the vadose zone and aquifer thickness, and plant setup. In particular, we focus the analysis on the length and width of thermal plumes, and on their time evolution. Numerical simulations are compared with two simplified methods, namely (i) replacing the time-varying thermal load with its yearly average and (ii) analytical formulae for advective heat transport in the aquifer. The former proves acceptable for the assessment of plume length, while the latter can be used to estimate the width of the thermally affected zone. The results highlight the strong influence of groundwater velocity on the plume size and, especially for its long-term evolution, of ground thermal properties and of subsurface geometrical parameters. Full article

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

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23 pages, 9283 KiB

Open AccessArticle

A Modular AC-DC Power Converter with Zero Voltage Transition for Electric Vehicles

by Jazmin Ramirez-Hernandez¹, Ismael Araujo-Vargas^1,*

and Marco Rivera²

¹ Escuela Superior de Ingenieria Mecanica y Electrica, Unidad Culhuacan, Instituto Politecnico Nacional of Mexico, ESIME Cul. Av. Santa Ana No. 1000, Col. San Francisco Culhuacan, C.P. 04430 Mexico City, Mexico

² Electrical Engineering Department, Universidad de Talca, Merced 437, C.P. 3341717 Curicó, Chile

Energies 2017, 10(9), 1386; https://doi.org/10.3390/en10091386 - 12 Sep 2017

Cited by 8 | Viewed by 7139

Abstract

A study of the fundamental of operation of a three-phase AC-DC power converter that uses Zero-Voltage Transition (ZVT) together with Space Vector Pulse Width Modulation (SVPWM) is presented. The converter is basically an active rectifier divided into two converters: a matrix converter and [...] Read more.

A study of the fundamental of operation of a three-phase AC-DC power converter that uses Zero-Voltage Transition (ZVT) together with Space Vector Pulse Width Modulation (SVPWM) is presented. The converter is basically an active rectifier divided into two converters: a matrix converter and an H bridge, which transfer energy through a high-frequency transformer, resulting in a modular AC-DC wireless converter appropriate for Plug-in Electric Vehicles (PEVs). The principle of operation of this converter considers high power quality, output regulation and low semiconductor power loss. The circuit operation, idealized waveforms and modulation strategy are explained together with simulation results of a 5 kW design. 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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17 pages, 541 KiB

Open AccessArticle

Proportional-Type Performance Recovery DC-Link Voltage Tracking Algorithm for Permanent Magnet Synchronous Generators

by Seok-Kyoon Kim

Department of Creative Convergence Engineering, Hanbat National University, 125, Dongseo-daero, Yuseong-gu, Daejeon 34158, Korea

Energies 2017, 10(9), 1387; https://doi.org/10.3390/en10091387 - 12 Sep 2017

Cited by 2 | Viewed by 4744

Abstract

This study proposes a disturbance observer-based proportional-type DC-link voltage tracking algorithm for permanent magnet synchronous generators (PMSGs). The proposed technique feedbacks the only proportional term of the tracking errors, and it contains the nominal static and dynamic feed-forward compensators coming from the first-order [...] Read more.

This study proposes a disturbance observer-based proportional-type DC-link voltage tracking algorithm for permanent magnet synchronous generators (PMSGs). The proposed technique feedbacks the only proportional term of the tracking errors, and it contains the nominal static and dynamic feed-forward compensators coming from the first-order disturbance observers. It is rigorously proved that the proposed method ensures the performance recovery and offset-free properties without the use of the integrators of the tracking errors. A wind power generation system has been simulated to verify the efficacy of the proposed method using the PSIM (PowerSIM) software with the DLL (Dynamic Link Library) block. 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, 7858 KiB

Open AccessArticle

A New Tree-Type Fracturing Method for Stimulating Coal Seam Gas Reservoirs

by Qian Li^1,2, Yiyu Lu^1,2,*, Zhaolong Ge^1,2, Zhe Zhou^1,2,*

, Jingwei Zheng^1,2 and Songqiang Xiao^1,2

¹ State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, China

² National & Local Joint Engineering Laboratory of Gas Drainage in Complex Coal Seam, Chongqing University, Chongqing 400044, China

Energies 2017, 10(9), 1388; https://doi.org/10.3390/en10091388 - 13 Sep 2017

Cited by 26 | Viewed by 4631

Abstract

Hydraulic fracturing is used widely to stimulate coalbed methane production in coal mines. However, some factors associated with conventional hydraulic fracturing, such as the simple morphology of the fractures it generates and inhomogeneous stress relief, limit its scope of application in coal mines. [...] Read more.

Hydraulic fracturing is used widely to stimulate coalbed methane production in coal mines. However, some factors associated with conventional hydraulic fracturing, such as the simple morphology of the fractures it generates and inhomogeneous stress relief, limit its scope of application in coal mines. These problems mean that gas extraction efficiency is low. Conventional fracturing may leave hidden pockets of gas, which will be safety hazards for subsequent coal mining operations. Based on a new drilling technique applicable to drilling boreholes in coal seams, this paper proposes a tree-type fracturing technique for stimulating reservoir volumes. Tree-type fracturing simulation experiments using a large-scale triaxial testing apparatus were conducted in the laboratory. In contrast to the single hole drilled for conventional hydraulic fracturing, the tree-type sub-boreholes induce radial and tangential fractures that form complex fracture networks. These fracture networks can eliminate the “blank area” that may host dangerous gas pockets. Gas seepage in tree-type fractures was analyzed, and gas seepage tests after tree-type fracturing showed that permeability was greatly enhanced. The equipment developed for tree-type fracturing was tested in the Fengchun underground coal mine in China. After implementing tree-type fracturing, the gas extraction rate was around 2.3 times greater than that for traditional fracturing, and the extraction rate remained high for a long time during a 30-day test. This shortened the gas drainage time and improved gas extraction efficiency. Full article

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14 pages, 3508 KiB

Open AccessArticle

Elimination of Chattering by Control Strategy Based on the Multiphase Sliding Model Control for Efficient Power Conversion in a DC-DC Circuit

by Woonki Na¹, Pengyuan Chen¹ and Jonghoon Kim^2,*

¹ Electrical and Computer Engineering, California State University, Fresno 93740, CA, USA

² Electrical Engineering, Chungnam National University, Daejeon 34134, Korea

Energies 2017, 10(9), 1389; https://doi.org/10.3390/en10091389 - 13 Sep 2017

Viewed by 4030

Abstract

In this paper, a multiphase sliding mode (MPSM) control method with a master–slave structure is proposed and analyzed in order to suppress ripples at input terminals or output terminals in DC/DC converter applications. With the proposed MPSM, the switching frequency of a multiphase [...] Read more.

In this paper, a multiphase sliding mode (MPSM) control method with a master–slave structure is proposed and analyzed in order to suppress ripples at input terminals or output terminals in DC/DC converter applications. With the proposed MPSM, the switching frequency of a multiphase DC/DC converter does not need to be operating such a high switching frequency as adopted in a conventional sliding mode control-based DC/DC converter. As a result, switching power losses could be reduced in this converter. Another advantage of this proposed method is that the master–slave multiphase slide control loop could figure out a proper phase shift between each switching phase of a DC/DC converter instead of precalculated phase shift. The proposed concepts are proven by the PSIM computer simulations and the feasibility of the proposed concepts is validated through the test experiments. Full article

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20 pages, 5239 KiB

Open AccessArticle

Charge Equalization Controller Algorithm for Series-Connected Lithium-Ion Battery Storage Systems: Modeling and Applications

by Mahammad A. Hannan^1,*, Mohammad M. Hoque², Pin J. Ker¹, Rawshan A. Begum³ and Azah Mohamed⁴

¹ Department of Electrical Power Engineering, Universiti Tenaga Nasional, Kajang 43000, Malaysia

² Department of Electrical & Electronic Engineering, University of Chittagong, Chittagong 4331, Bangladesh

³ Institute of Climate Change, Universiti Kebangsaan Malaysia, Bangi 43600, Selangor, Malaysia

⁴ Department of Electrical, Electronic and Systems Engineering, Universiti Kebangsaan Malaysia, Bangi 43600, Selangor, Malaysia

Energies 2017, 10(9), 1390; https://doi.org/10.3390/en10091390 - 13 Sep 2017

Cited by 37 | Viewed by 7732

Abstract

This study aims to develop an accurate model of a charge equalization controller (CEC) that manages individual cell monitoring and equalizing by charging and discharging series-connected lithium-ion (Li-ion) battery cells. In this concept, an intelligent control algorithm is developed to activate bidirectional cell [...] Read more.

This study aims to develop an accurate model of a charge equalization controller (CEC) that manages individual cell monitoring and equalizing by charging and discharging series-connected lithium-ion (Li-ion) battery cells. In this concept, an intelligent control algorithm is developed to activate bidirectional cell switches and control direct current (DC)–DC converter switches along with pulse width modulation (PWM) generation. Individual models of an electric vehicle (EV)-sustainable Li-ion battery, optimal power rating, a bidirectional flyback DC–DC converter, and charging and discharging controllers are integrated to develop a small-scale CEC model that can be implemented for 10 series-connected Li-ion battery cells. Results show that the charge equalization controller operates at 91% efficiency and performs well in equalizing both overdischarged and overcharged cells on time. Moreover, the outputs of the CEC model show that the desired balancing level occurs at 2% of state of charge difference and that all cells are operated within a normal range. The configuration, execution, control, power loss, cost, size, and efficiency of the developed CEC model are compared with those of existing controllers. The proposed model is proven suitable for high-tech storage systems toward the advancement of sustainable EV technologies and renewable source of applications. Full article

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

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19 pages, 2351 KiB

Open AccessArticle

Analysis of the Brazilian Energy Efficiency Program for Electricity Distribution Systems

by Rogério Diogne de Souza e Silva^1,*, Rosana Cavalcante de Oliveira² and Maria Emília de Lima Tostes¹

¹ Graduate Program in Electrical Engineering, Federal University of Para, Belem 66075-110, Brazil

² Laboratory of Artificial Intelligence and Decision Support, Institute for Systems and Computer Engineering, Technology and Science, 4200 Porto, Portugal

Energies 2017, 10(9), 1391; https://doi.org/10.3390/en10091391 - 13 Sep 2017

Cited by 13 | Viewed by 4464

Abstract

In this paper, a methodology was developed to analyze the results of energy efficiency programs used in the electricity distribution sector in Brazil. Analyzing the gains obtained through the investments made, and classifying which actions resulted in the best performance, contributed to decision [...] Read more.

In this paper, a methodology was developed to analyze the results of energy efficiency programs used in the electricity distribution sector in Brazil. Analyzing the gains obtained through the investments made, and classifying which actions resulted in the best performance, contributed to decision making on the best allocation of investments to obtain the greatest energy savings. The Brazilian Energy Efficiency program was analyzed with a developed non-parametric model, using the data envelopment analysis method, and the categories of projects with better performance were determined. A database of the results from 1704 projects, from 2008 to 2016 in the Energy Efficiency program in Brazil´s electricity distribution sector, was used. The results obtained show that the best performance was achieved by projects in the industrial and cogeneration categories; however, in Brazil these constitute only 4.24% of the projects presented and 5.28% of the total investments in the last eight years, indicating a need to review the regulatory strategies for energy efficiency in this country. Full article

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

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26 pages, 3032 KiB

Open AccessArticle

Techno-Economic Analysis of Solar Tower Aided Coal-Fired Power Generation System

by Yong Zhu^1,*

, Rongrong Zhai¹, Yongping Yang¹ and Miguel Angel Reyes-Belmonte²

¹ School of Energy, Power and Mechanical Engineering, North China Electric Power University, Beijing 102206, China

² IMDEA Energy Institute, Ramon de la Sagra 3, 28935 Móstoles, Spain

Energies 2017, 10(9), 1392; https://doi.org/10.3390/en10091392 - 14 Sep 2017

Cited by 29 | Viewed by 5762

Abstract

In this paper, we conduct a techno-economic analysis of a 1000 MWe solar tower aided coal-fired power generation system for the whole life cycle. Firstly, the power output (from coal and solar thermal energy) under variable direct normal irradiance and grid demand are [...] Read more.

In this paper, we conduct a techno-economic analysis of a 1000 MWe solar tower aided coal-fired power generation system for the whole life cycle. Firstly, the power output (from coal and solar thermal energy) under variable direct normal irradiance and grid demand are studied. Secondly, a financial assessment is performed, including profits and losses of the plant project. Thirdly, sensitivity analysis is taken on some external factors that can affect the cost or profits and losses of the plant project. The results indicate that the project has high profits with an internal rate of return (IRR) of 8.7%. In addition, the effects of solar tower field cost, power purchase agreement (PPA) price of solar thermal electricity, coal price, and the interest rate of debt on the main criteria decrease gradually. Therefore, it is better to improve solar tower technology first, and then look for low-interest debts from banks to cope with the reduction of PPA price of solar thermal electricity and the increase of coal price. Despite the introduction of solar tower field increasing levelized cost of electricity (LCOE), it contributes to the reduction of CO₂ capture cost compared to the case of standard coal-fired power plants. 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, 7078 KiB

Open AccessArticle

Sensitivity Analysis of Seismic Velocity and Attenuation Variations for Longmaxi Shale during Hydraulic Fracturing Testing in Laboratory

by Hongyu Zhai¹, Xu Chang^1,*, Yibo Wang¹, Ziqiu Xue²

, Xinglin Lei³ and Yi Zhang²

¹ Key Laboratory of Shale Gas and Geoengineering, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China

² Research Institute of Innovative Technology for the Earth (RITE), 9-2 Kizugawadai, Kizu-cho, Soraku-gun, Kyoto 619-0292, Japan

³ Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST), Central 7, Higashi 1-1, Tsukuba City, Ibaraki 305-8567, Japan

Energies 2017, 10(9), 1393; https://doi.org/10.3390/en10091393 - 13 Sep 2017

Cited by 15 | Viewed by 5704

Abstract

During the hydraulic fracturing procedure in shale-gas exploitation, the poroelastic properties of shale formation can be altered significantly. However, it is difficult to evaluate these variations using microseismic field data. In this study, we conduct a hydro-fracturing experiment using Longmaxi shale, which is [...] Read more.

During the hydraulic fracturing procedure in shale-gas exploitation, the poroelastic properties of shale formation can be altered significantly. However, it is difficult to evaluate these variations using microseismic field data. In this study, we conduct a hydro-fracturing experiment using Longmaxi shale, which is a major formation for shale-gas production in China, to simulate the water injection and rock fracturing procedure. The variation of the velocity and attenuation for primary/secondary (P/S) ultrasonic waves was investigated throughout the entire experimental procedure. The results show that the attenuation is more sensitive to sample rupture than the velocity. However, P-wave attenuation loses sensitivity to the water injection after the fractures are saturated with water. In that case, it is preferable to use S-wave attenuation to identify the opening/closing of the fractures. Based on the experimental results, we can conclude that the variation of the attenuation must be considered during microseismic data processing and interpretation. Full article

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

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14 pages, 1742 KiB

Open AccessFeature PaperArticle

Liquid vs. Gas Phase CO₂ Photoreduction Process: Which Is the Effect of the Reaction Medium?

by Alberto Olivo¹

, Elena Ghedini¹, Michela Signoretto^1,*

, Matteo Compagnoni² and Ilenia Rossetti²

¹ CatMat Lab, Department of Molecular Sciences and Nanosystems, Ca’ Foscari University Venice and Consortium INSTM, RU of Venice, Via Torino 155, 30172 Venezia, Italy

² Chemical Plants and Industrial Chemistry Group, Department of Chemistry, Università Degli Studi di Milano, Consortium INSTM, RU of Milano Università and CNR-ISTM, via C. Golgi 19, 20133 Milan, Italy

Energies 2017, 10(9), 1394; https://doi.org/10.3390/en10091394 - 13 Sep 2017

Cited by 61 | Viewed by 9333

Abstract

The use of carbon dioxide, the most concerning environmental issue of the 21st century, as a feedstock for fuels productions still represents an innovative, yet challenging, task for the scientific community. CO₂ photoreduction processes have the potential to transform this hazardous pollutant [...] Read more.

The use of carbon dioxide, the most concerning environmental issue of the 21st century, as a feedstock for fuels productions still represents an innovative, yet challenging, task for the scientific community. CO₂ photoreduction processes have the potential to transform this hazardous pollutant into important products for the energy industry (e.g., methane and methanol) employing a photocatalyst and light as the only energy input. In order to design an effective process, the high sustainability of this reaction should be matched with the perfect reaction conditions to allow the reactant, photocatalyst, and light source to come together: therefore, the choice of reaction conditions, and in particular its medium, is a crucial issue that needs to be investigated. Throughout this paper, a careful study of carbon dioxide photoreduction in liquid and vapour phases are reported, focusing on their effect on catalyst performances in terms of light harvesting, productivity, and selectivity. Different from most papers in the literature, catalytic tests were performed under extremely low light irradiance, in order to minimise the primary energy input, highlighting that this experimental variable has a great effect on the reaction pathway and, thus, product distribution. Full article

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

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19 pages, 5414 KiB

Open AccessArticle

Exergo-Economic Evaluation of the Cost for Solar Thermal Depuration of Water

by Nicola Dainelli¹

, Giampaolo Manfrida¹

, Karolina Petela^2,*

and Federico Rossi¹

¹ School of Engineering, Department of Industrial Engineering, Università degli studi di Firenze, 50121 Firenze, Italy

² Department of Energy and Environmental Engineering, Institute of Thermal Technology, Silesian University of Technology, Gliwice 44-100, Poland

Energies 2017, 10(9), 1395; https://doi.org/10.3390/en10091395 - 13 Sep 2017

Cited by 8 | Viewed by 4913

Abstract

A detailed assessment of the cumulative cost of clean water production by a natural circulation solar thermal system is presented. The system is designed and sized for sufficient residence time for pasteurisation, in a buoyancy-driven self-compensating circuit. Since it does not consume electricity, [...] Read more.

A detailed assessment of the cumulative cost of clean water production by a natural circulation solar thermal system is presented. The system is designed and sized for sufficient residence time for pasteurisation, in a buoyancy-driven self-compensating circuit. Since it does not consume electricity, it is suitable for developing countries or emergency locations with safe drinking water issues. The principles for design and off-design simulations are explained and discussed. The simulations were performed for seven different locations, representing variable climate conditions in selected regions where there is an evident need for safe water. The results include an exergy and exergo-economic analysis. The production capacity reaches typically from 0.04 to 0.1 m³/day per m² of solar collector depending on the location. The annual cost of water production ranges between 2.2 and 6.8 €/m³ making the proposed system fairly competitive; the energy- and price-performance of the system is compared to a reverse osmosis/photovoltaic system, representing a high-tech alternative for the purpose of water purification. Full article

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16 pages, 1682 KiB

Open AccessArticle

Potential for Energy Production from Farm Wastes Using Anaerobic Digestion in the UK: An Economic Comparison of Different Size Plants

by Gabriel D. Oreggioni^1,*, Baboo Lesh Gowreesunker¹, Savvas A. Tassou¹, Giuseppe Bianchi¹

, Matthew Reilly², Marie E. Kirby²

, Trisha A. Toop² and Mike K. Theodorou²

¹ RCUK National Centre for Sustainable Energy Use in Food Chains, Institute of Energy Futures, Brunel University London, Uxbridge, Middlesex UB8 3PH, UK

² Agricultural Centre for Sustainable Energy Systems, Department of Animal Production, Welfare and Veterinarian Sciences, Harper Adams University, New Port TF10 8NB, UK

Energies 2017, 10(9), 1396; https://doi.org/10.3390/en10091396 - 13 Sep 2017

Cited by 39 | Viewed by 6958

Abstract

Anaerobic digestion (AD) plants enable renewable fuel, heat, and electricity production, with their efficiency and capital cost strongly dependent on their installed capacity. In this work, the technical and economic feasibility of different scale AD combined heat and power (CHP) plants was analyzed. [...] Read more.

Anaerobic digestion (AD) plants enable renewable fuel, heat, and electricity production, with their efficiency and capital cost strongly dependent on their installed capacity. In this work, the technical and economic feasibility of different scale AD combined heat and power (CHP) plants was analyzed. Process configurations involving the use of waste produced in different farms as feedstock for a centralized AD plant were assessed too. The results show that the levelized cost of electricity are lower for large-scale plants due to the use of more efficient conversion devices and their lower capital cost per unit of electricity produced. The levelized cost of electricity was estimated to be 4.3 p/kWh_e for AD plants processing the waste of 125 dairy cow sized herds compared to 1.9 p/kWh_e for AD plants processing waste of 1000 dairy cow sized herds. The techno-economic feasibility of the installation of CO₂ capture units in centralized AD-CHP plants was also undertaken. The conducted research demonstrated that negative CO₂ emission AD power generation plants could be economically viable with currently paid feed-in tariffs in the UK. Full article

(This article belongs to the Special Issue Economics of Bioenergy 2016)

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16 pages, 1288 KiB

Open AccessArticle

Energy Flexibility Management Based on Predictive Dispatch Model of Domestic Energy Management System

by Amin Shokri Gazafroudi^1,*

, Francisco Prieto-Castrillo^1,2,3, Tiago Pinto¹, Javier Prieto^1,4

, Juan Manuel Corchado^1,5

and Javier Bajo¹

¹ BISITE Research Group, University of Salamanca, Edificio I+D+i, 37008 Salamanca, Spain

² MediaLab, Massachusetts Institute of Technology, Cambridge, MA 02139-4307, USA

³ Harvard T.H. Chan School of Public Health, Harvard University, Boston, MA 02115, USA

⁴ StageMotion, R&D Department, C/Orfebres 10, 34005 Palencia, Spain

⁵ Osaka Institute of Technology, Asahi-ku Ohmiya, Osaka 535-8585, Japan

Energies 2017, 10(9), 1397; https://doi.org/10.3390/en10091397 - 13 Sep 2017

Cited by 17 | Viewed by 5137

Abstract

This paper proposes a predictive dispatch model to manage energy flexibility in the domestic energy system. Electric Vehicles (EV), batteries and shiftable loads are devices that provide energy flexibility in the proposed system. The proposed energy management problem consists of two stages: day-ahead [...] Read more.

This paper proposes a predictive dispatch model to manage energy flexibility in the domestic energy system. Electric Vehicles (EV), batteries and shiftable loads are devices that provide energy flexibility in the proposed system. The proposed energy management problem consists of two stages: day-ahead and real time. A hybrid method is defined for the first time in this paper to model the uncertainty of the PV power generation based on its power prediction. In the day-ahead stage, the uncertainty is modeled by interval bands. On the other hand, the uncertainty of PV power generation is modeled through a stochastic scenario-based method in the real-time stage. The performance of the proposed hybrid Interval-Stochastic (InterStoch) method is compared with the Modified Stochastic Predicted Band (MSPB) method. Moreover, the impacts of energy flexibility and the demand response program on the expected profit and transacted electrical energy of the system are assessed in the case study presented in this paper. Full article

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

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16 pages, 3832 KiB

Open AccessArticle

A Grey-Box Dynamic Model of Plate Heat Exchangers Used in an Urban Heating System

by Qingwei Miao¹, Shijun You¹, Wandong Zheng^1,2,*,†, Xuejing Zheng^1,*,†, Huan Zhang¹ and Yaran Wang¹

¹ School of Environment Science and Technology, Tianjin University, Tianjin 300072, China

² State Key Laboratory of Building Safety and Built Environment, China Academy of Building Research, Beijing 100013, China

^† These authors contributed equally to this work.

Energies 2017, 10(9), 1398; https://doi.org/10.3390/en10091398 - 13 Sep 2017

Cited by 19 | Viewed by 8590

Abstract

This paper deals with the establishment of a grey-box model of plate heat exchangers. First, a second-order state space model of plate heat exchangers is developed. Then, the model is solved by the white-box method and grey-box method, respectively. In the white-box method, [...] Read more.

This paper deals with the establishment of a grey-box model of plate heat exchangers. First, a second-order state space model of plate heat exchangers is developed. Then, the model is solved by the white-box method and grey-box method, respectively. In the white-box method, the linearization of the state space model is carried out by implicit difference scheme and the overall heat transfer coefficient was calculated with empirical correlation of the Nusselt number. In the grey-box method, a newly developed parameter identification method was established. The simulation results of two outlet temperatures by the grey-box and white-box method, respectively, are compared with the test data. It is shown that the grey-box method is more suitable and accurate for the simulations of outlet temperatures than the white-box method. Thus, it can provide practitioners and heating engineers with tools to design controllers for district heating systems. Full article

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

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26 pages, 4126 KiB

Open AccessArticle

Dynamic Modeling of the Two-Phase Leakage Process of Natural Gas Liquid Storage Tanks

by Xia Wu^1,*, Changjun Li¹, Yufa He² and Wenlong Jia¹

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

² China National Offshore Oil Corporation (CNOOC) Research Institute, Beijing 100028, China

Energies 2017, 10(9), 1399; https://doi.org/10.3390/en10091399 - 13 Sep 2017

Cited by 18 | Viewed by 6473

Abstract

The leakage process simulation of a Natural Gas Liquid (NGL) storage tank requires the simultaneous solution of the NGL’s pressure, temperature and phase state in the tank and across the leak hole. The methods available in the literature rarely consider the liquid/vapor phase [...] Read more.

The leakage process simulation of a Natural Gas Liquid (NGL) storage tank requires the simultaneous solution of the NGL’s pressure, temperature and phase state in the tank and across the leak hole. The methods available in the literature rarely consider the liquid/vapor phase transition of the NGL during such a process. This paper provides a comprehensive pressure-temperature-phase state method to solve this problem. With this method, the phase state of the NGL is predicted by a thermodynamic model based on the volume translated Peng-Robinson equation of state (VTPR EOS). The tank’s pressure and temperature are simulated according to the pressure-volume-temperature and isenthalpic expansion principles of the NGL. The pressure, temperature, leakage mass flow rate across the leak hole are calculated from an improved Homogeneous Non-Equilibrium Diener-Schmidt (HNE-DS) model and the isentropic expansion principle. In particular, the improved HNE-DS model removes the ideal gas assumption used in the original HNE-DS model by using a new compressibility factor developed from the VTPR EOS to replace the original one derived from the Clausius-Clayperon equation. Finally, a robust procedure of simultaneously solving the tank model and the leak hole model is proposed and the method is validated by experimental data. A variety of leakage cases demonstrates that this method is effective in simulating the dynamic leakage process of NGL tanks under critical and subcritical releasing conditions associated with vapor/liquid phase change. Full article

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

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18 pages, 7537 KiB

Open AccessArticle

A Study of Two Multi-Element Resonant DC-DC Topologies with Loss Distribution Analyses

by Yifeng Wang^1,†

, Liang Yang^1,*,†

, Fuqiang Han^1,†, Shijie Tu² and Weiya Zhang³

¹ School of Electrical Engineering and Automation, Tianjin University, Tianjin 300072, China

² State Grid Jiangxi Electric Power Company Repair Branch, Nanchang 330000, China

³ State Grid Nanjing Power Supply Company, Nanjing 210000, China

^† These authors contributed equally to this work.

Energies 2017, 10(9), 1400; https://doi.org/10.3390/en10091400 - 13 Sep 2017

Cited by 5 | Viewed by 3932

Abstract

In this paper, two multi-element resonant DC-DC converters are analyzed in detail. Since their resonant tanks have multiple resonant components, the converters display different resonant characteristics within different operating frequency ranges. Through appropriate design, both of the two proposed converters successfully lower the [...] Read more.

In this paper, two multi-element resonant DC-DC converters are analyzed in detail. Since their resonant tanks have multiple resonant components, the converters display different resonant characteristics within different operating frequency ranges. Through appropriate design, both of the two proposed converters successfully lower the conversion losses and, meanwhile, broaden the voltage gain ranges as well: one converter is able to take full usage of the third order harmonic to deliver the active power, and thus the effective utilization rate of the resonant current is elevated; while the another minimizes the entire switching losses for power switching devices by restricting the input impedance angle of the resonant tank. Besides, the loss distribution is analyzed for the purpose of guiding the component design. In the end, two 500 W prototypes are fabricated to test the theoretical analyses. The results demonstrate that the two proposed converters can achieve wide voltage gain with the small frequency deviation, which noticeably contributes to highly efficient conversion. Their peak efficiencies are measured as 95.4% and 95.3%, respectively. Full article

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21 pages, 3813 KiB

Open AccessArticle

Experimental Investigation of Flow Domain Division in Beds Packed with Different Sized Particles

by Xin Yang^1,2

, Tianhong Yang^1,2,*, Zenghe Xu¹ and Bin Yang^1,2

¹ Center of Rock Instability and Seismicity Research, School of Resources and Civil Engineering, Northeastern University, Shenyang 110819, China

² Key Laboratory of Ministry of Education on Safe Mining of Deep Metal Mines, Northeastern University, Shenyang 110819, China

Energies 2017, 10(9), 1401; https://doi.org/10.3390/en10091401 - 14 Sep 2017

Cited by 25 | Viewed by 4728

Abstract

Seepage in a medium packed with particles of variable granular size can be seen in many fields of engineering applications. Due to the relative complex spatial aspect of pore geometry, there are notable differences in the critical parameters of flow transition (Reynolds number [...] Read more.

Seepage in a medium packed with particles of variable granular size can be seen in many fields of engineering applications. Due to the relative complex spatial aspect of pore geometry, there are notable differences in the critical parameters of flow transition (Reynolds number and Forchheimer number) between different structures. It is difficult to distinguish the available range of seepage equations and predict the water flux accurately. This work aims to establish the relationship between particle size and flow transition. This is conducted according to the results of flow region division, which obtains the application range for seepage equations. Experiments were carried out in sand columns with nine different particle sizes of sand with mean diameters of 0.0375, 0.1125, 0.225, 0.45, 0.8, 1.5, 2.18, 3.555 and 7.125 mm. Four flow regimes were identified (pre-Darcy regime, Darcy regime, Forchheimer regime and turbulent regime). The experimental data indicate that the permeability increases exponentially and the inertia factor reduces exponentially with an increase in particle diameter. The inertial effect becomes more significant in the medium with larger particles than with finer particles when the flow transition occurs. Full article

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27 pages, 14396 KiB

Open AccessArticle

Backflow Power Optimization Control for Dual Active Bridge DC-DC Converters

by Fei Xiong^*

, Junyong Wu, Liangliang Hao and Zicheng Liu

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

Energies 2017, 10(9), 1403; https://doi.org/10.3390/en10091403 - 14 Sep 2017

Cited by 16 | Viewed by 6533

Abstract

This paper proposes optimized control methods for global minimum backflow power based on a triple-phase-shift (TPS) control strategy. Three global optimized methods are derived to minimize the backflow power on the primary side, on the secondary side and on both sides, respectively. Backflow [...] Read more.

This paper proposes optimized control methods for global minimum backflow power based on a triple-phase-shift (TPS) control strategy. Three global optimized methods are derived to minimize the backflow power on the primary side, on the secondary side and on both sides, respectively. Backflow power transmission is just a portion of non-active power transmission in a dual active bridge (DAB) converter. Non-active power transmission time is proposed in this paper, which unifies zero power transmission and backflow power transmission. Based on the proposed index, an optimized control method is derived to achieve both the maximum effective power transmission time and minimum current stress of DAB at the same time. A comparative analysis is performed to show the limitations of the minimum backflow power optimization method. Finally, a prototype is built to verify the effectiveness of our theoretical analysis and the proposed control methods by experimental results. Full article

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

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24 pages, 4676 KiB

Open AccessArticle

Determining Division Location for Sectional Wind Turbine Blades

by Zhiwen Qin^1,2,*

, Lei Zhang²

, Ke Yang^2,*, Jihui Wang^1,*, Caicai Liao² and Jianzhong Xu²

¹ School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070, China

² National Energy Wind Turbine Blade R&D Center, Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing 100190, China

Energies 2017, 10(9), 1404; https://doi.org/10.3390/en10091404 - 14 Sep 2017

Cited by 7 | Viewed by 6228

Abstract

Sectional wind turbine blades, by dividing an intact blade into multiple segments, have the advantage of being easy to handle and transport. To determine a suitable blade division location, this study was performed to clarify some crucial aspects and challenges for sectional blades. [...] Read more.

Sectional wind turbine blades, by dividing an intact blade into multiple segments, have the advantage of being easy to handle and transport. To determine a suitable blade division location, this study was performed to clarify some crucial aspects and challenges for sectional blades. This paper proposes a method to estimate the effects of the location of the blade division on structural, manufacturing, and assembling performance of sectional blades. The advantage of this method is the ease of the assessment process, since it can be performed at an early stage of blade design, where only the aerodynamic profile, mass density and stiffness distribution, and service fatigue loads of original blades are essential. A case study with the proposed method was carried out based on a 38-meter commercial blade. Results show that the best position for the division of sectional blades is located 20% from the blade root by balancing the three aspects listed above. The key approaches to reduce additional increases in stiffness and weight of sectional blades are related to improving the fatigue strength and the choice of low-modulus materials for connecting bolts. The effects of the division location on assembling accessibility and natural frequencies of scaled sectional blades are consistent with the basic sectional blade. Unfavorable effects occur when up-scaling the diameter of the bolts; and, harsh external loads on the connections have negative effects on the application of sectional blades with larger wind turbines. In this regard, lightweight design is indispensable to reduce bolt stress. Full article

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

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19 pages, 2033 KiB

Open AccessArticle

Optimization Model of an Efficient Collaborative Power Dispatching System for Carbon Emissions Trading in China

by Qinliang Tan^1,2,*, Yihong Ding¹ and Yimei Zhang³

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

² Research Center for Beijing Energy Development, Beijing 102206, China

³ Environmental Research Institute, Suzhou Research Institute, North China Electric Power University, Beijing 102206, China

Energies 2017, 10(9), 1405; https://doi.org/10.3390/en10091405 - 14 Sep 2017

Cited by 18 | Viewed by 3820

Abstract

In this paper, a collaborative power dispatching system (CPDS) was developed to maximize the profit of a regional biomass power system consisting of an independent power grid. A power generating, dispatching and carbon emissions trading system (CETS) could be engaged in joint strategic [...] Read more.

In this paper, a collaborative power dispatching system (CPDS) was developed to maximize the profit of a regional biomass power system consisting of an independent power grid. A power generating, dispatching and carbon emissions trading system (CETS) could be engaged in joint strategic planning and operational execution. The principal of CPDS is interactive planning of generating units in power generation and carbon emissions trading. An efficient carbon emissions trading plan for a CPDS would lead to optimized power generation levels under available power production capacities and carbon emissions. In a case study, four generator policies are proposed by considering basic CETSs to comparatively analyze the function of each generator in the CPDS. Results of four scenarios are compared, showing that biomass energy could replace thermal units to a certain extent, the carbon emissions and coal consumption of the CPDS would lie at a lower level, and a pumped storage unit could adjust the load fluctuations. The results of a carbon trading analysis show that the CETS has no significant impact on the CPDS, but along with the increase in trading price or the decrease in the free quota, the economic interests of power plants will be reduced accordingly. This may lead to carrying out low-carbon projects and reducing carbon emissions. Therefore, it is imperative to reduce carbon emissions by replacing power units with high energy consumption, and improve the consumption capacity of renewable energy. Full article

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12 pages, 3068 KiB

Open AccessArticle

Optimization and Practice of Support Working Resistance in Fully-Mechanized Top Coal Caving in Shallow Thick Seam

by Peng Huang¹, Feng Ju^1,*, Kashi Vishwanath Jessu², Meng Xiao¹ and Shuai Guo¹

¹ State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining and Technology, Xuzhou 221116, China

² Western Australia School of Mines, Curtin University, Kalgoorlie, WA 6430, Australia

Energies 2017, 10(9), 1406; https://doi.org/10.3390/en10091406 - 14 Sep 2017

Cited by 22 | Viewed by 4239

Abstract

Based on the overburdened structure of shallow coal seams in the West of China, the traditional support resistance method may not apply in such regions due to many roof shear and support crushing accidents. Four support working resistance indexes—rated working resistance, average working [...] Read more.

Based on the overburdened structure of shallow coal seams in the West of China, the traditional support resistance method may not apply in such regions due to many roof shear and support crushing accidents. Four support working resistance indexes—rated working resistance, average working resistance, average-partial working resistance, and average-upper working resistance are counted as the candidate working resistance. The method of optimizing and inverting working resistance was put forward based on the roof control effect and working resistance overrun percentage. The simulation of a fully-mechanized top coal caving working face was built by using the UDEC software to analyze the top coal cavability and roof subsidence under different supporting strengths to determine the final working resistance. The project practice of 1322 working face in Jindi coal mine shows that the working resistance is 80–90% of calculated rated working resistance. The hydraulic support is worked under good condition. There is no pillar shrinkage and support crushing during coal mining. Full article

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42 pages, 4350 KiB

Open AccessArticle

An Improved Fuzzy C-Means Algorithm for the Implementation of Demand Side Management Measures

by Ioannis Panapakidis^1,2,*, Nikolaos Asimopoulos¹, Athanasios Dagoumas³ and Georgios C. Christoforidis^1,*

¹ Department of Electrical Engineering, Western Macedonia University of Applied Sciences, Kozani 50100, Greece

² Department of Electrical Engineering, Technological Educational Institute of Thessaly, Larisa 41110, Greece

³ Energy and Environmental Policy Laboratory, School of Economics, Business and International Studies, University of Piraeus, Piraeus 18532, Greece

Energies 2017, 10(9), 1407; https://doi.org/10.3390/en10091407 - 14 Sep 2017

Cited by 13 | Viewed by 4902

Abstract

Load profiling refers to a procedure that leads to the formulation of daily load curves and consumer classes regarding the similarity of the curve shapes. This procedure incorporates a set of unsupervised machine learning algorithms. While many crisp clustering algorithms have been proposed [...] Read more.

Load profiling refers to a procedure that leads to the formulation of daily load curves and consumer classes regarding the similarity of the curve shapes. This procedure incorporates a set of unsupervised machine learning algorithms. While many crisp clustering algorithms have been proposed for grouping load curves into clusters, only one soft clustering algorithm is utilized for the aforementioned purpose, namely the Fuzzy C-Means (FCM) algorithm. Since the benefits of soft clustering are demonstrated in a variety of applications, the potential of introducing a novel modification of the FCM in the electricity consumer clustering process is examined. Additionally, this paper proposes a novel Demand Side Management (DSM) strategy for load management of consumers that are eligible for the implementation of Real-Time Pricing (RTP) schemes. The DSM strategy is formulated as a constrained optimization problem that can be easily solved and therefore, making it a useful tool for retailers’ decision-making framework in competitive electricity markets. Full article

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

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27 pages, 5672 KiB

Open AccessFeature PaperArticle

A Combined Experimental and Computational Fluid Dynamics Investigation of Particulate Matter Emissions from a Wall-Guided Gasoline Direct Injection Engine

by Davide D. Sciortino, Fabrizio Bonatesta^*, Edward Hopkins, Changho Yang

and Denise Morrey

Department of Mechanical Engineering and Mathematical Sciences, Oxford Brookes University, Wheatley Campus, Oxford OX33 1HX, UK

Energies 2017, 10(9), 1408; https://doi.org/10.3390/en10091408 - 14 Sep 2017

Cited by 14 | Viewed by 5494

Abstract

The latest generation of high-efficiency gasoline direct injection (GDI) engines continues to be a significant source of dangerous ultra-fine particulate matter (PM) emissions. The forthcoming advent in the 2017–2020 timeframe of the real driving emission (RDE) standards affords little time for the identification [...] Read more.

The latest generation of high-efficiency gasoline direct injection (GDI) engines continues to be a significant source of dangerous ultra-fine particulate matter (PM) emissions. The forthcoming advent in the 2017–2020 timeframe of the real driving emission (RDE) standards affords little time for the identification of viable solutions. The present research work aims to contribute towards a much-needed improved understanding of the process of PM formation in theoretically-homogeneous stoichiometric spark-ignition combustion. Experimental measurements of engine-out PM have been taken from a wall-guided GDI engine operated at part-load; through parallel computational fluid dynamics (CFD) simulations of the test-engine, the process of mixture preparation was investigated. About 80% of the total particle number is emitted on average in the 5–50 nm range, with the vast majority being below the regulated lower limit of 23 nm. The results suggest that both improved charge homogeneity and lower peak combustion temperature contribute to lower particle number density (PN_Den) and larger particle size, as engine speed and load increase. The effect of engine load is stronger and results from greater injection pressure through better fuel droplet atomisation. Increases in pre-combustion homogeneity of 6% are associated with one order of magnitude reductions of PN_Den. A simplified two-equation functional model was developed, which returns satisfactory qualitative predictions of PN_Den as a function of basic engine control variables. Full article

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20 pages, 9325 KiB

Open AccessArticle

Class E Power Amplifier Design and Optimization for the Capacitive Coupled Wireless Power Transfer System in Biomedical Implants

by Narayanamoorthi R.¹

, Vimala Juliet A.², Bharatiraja Chokkalingam¹

, Sanjeevikumar Padmanaban^3,*

and Zbigniew M. Leonowicz⁴

¹ Department of Electrical and Electronics Engineering, SRM University, Chennai 603 203, India

² Department of Electronics and Instrumentation Engineering, SRM University, Chennai 603 203, India

³ Department of Electrical and Electronics Engineering, University of Johannesburg, Auckland Park 2006, South Africa

⁴ Department of Electrical Engineering, Wroclaw University of Science and Technology, Politechnika Wroclawska | Wyb. Wyspianskiego 27, 50-370 Wroclaw, Poland

Energies 2017, 10(9), 1409; https://doi.org/10.3390/en10091409 - 15 Sep 2017

Cited by 36 | Viewed by 9509

Abstract

The capacitive coupled wireless power transfer (CCWPT) operating at megahertz (MHz) frequency is broadly considered as the promising solution for low power biomedical implants. The class E power amplifier is attractive in MHz range wireless power transfer (WPT) applications due to zero voltage [...] Read more.

The capacitive coupled wireless power transfer (CCWPT) operating at megahertz (MHz) frequency is broadly considered as the promising solution for low power biomedical implants. The class E power amplifier is attractive in MHz range wireless power transfer (WPT) applications due to zero voltage switching (ZVS) and zero voltage derivative switching (ZVDS) properties. The existing design of class E amplifier is investigated only for inductive resonant coupled (IRC) WPT systems; the modelling and optimization of the class E amplifier for CCWPT systems are not deliberated with load variation. Meanwhile, the variations in the coupling distance and load are common in real time applications, which could reduce the power amplifier (PA) efficiency. The purpose of this paper is to model and optimize the class E amplifier for CCWPT systems used in MHz range applications. The analytical model of PA parameters and efficiency are derived to determine the optimal operating conditions. Also, an inductive-capacitive-inductive (LCL) impedance matching network is designed for the robust operation of the PA, which improves the efficiency and maintains required impedance compression. The maximum efficiency of the proposed design reached up to 96.34% at 13.56 MHz and the experimental results are closely matched with the simulation. Full article

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18 pages, 5080 KiB

Open AccessArticle

Design, Fabrication and Performance Analysis of a Two Input—Single Output DC-DC Converter

by Sivaprasad Athikkal, Kumaravel Sundaramoorthy^* and Ashok Sankar

Department of Electrical Engineering, National Institute of Technology Calicut, Calicut 673601, Kerala, India

Energies 2017, 10(9), 1410; https://doi.org/10.3390/en10091410 - 15 Sep 2017

Cited by 19 | Viewed by 7508

Abstract

A novel modified bridge-type dual input DC-DC converter, which is proficient for integrating distinct V-I characteristic sources such as solar-PV, wind, etc., and storages including battery, ultracapacitor, fuel cell, etc., is proposed in this paper. Three modes of operations such as boost, buck, [...] Read more.

A novel modified bridge-type dual input DC-DC converter, which is proficient for integrating distinct V-I characteristic sources such as solar-PV, wind, etc., and storages including battery, ultracapacitor, fuel cell, etc., is proposed in this paper. Three modes of operations such as boost, buck, and buck-boost are possible using the same structure of the converter, and the converter can operate even with the failure of any one of the input energy sources to deliver power to the load. A software simulation and experimental realization of the converter have been carried out for the buck, boost, and buck-boost operations. The voltage and current stress analysis of the power switches available in the converter have been carried out for the better selection of power switches. A simple power control strategy is proposed for the steady state, and dynamic performance analysis of the converter and performance comparison with existing converter topologies have been carried out based on the different parameters like duty ratio, efficiency, etc. The performance comparison shows that the proposed converter has high voltage gain, low voltage stress, reduced part counts and high efficiency. Full article

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

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16 pages, 4972 KiB

Open AccessArticle

Breakdown Voltage and Its Influencing Factors of Thermally Aged Oil-Impregnated Paper at Pulsating DC Voltage

by Jing Zhang¹, Feipeng Wang^1,*, Jian Li^1,*, Hehuan Ran¹, Xudong Li¹ and Qiang Fu²

¹ State Key Laboratory of Power Transmission Equipment & System Security and New Technology, School of Electrical Engineering, Chongqing University, Chongqing 400044, China

² Electric Power Research Institute of Guangdong Power Grid Co., Ltd., Guangzhou 510080, China

Energies 2017, 10(9), 1411; https://doi.org/10.3390/en10091411 - 15 Sep 2017

Cited by 13 | Viewed by 4707

Abstract

Breakdown strength is an important electrical property of insulating paper. Oil-impregnated paper of various aging states was prepared. Its breakdown voltage was then measured at pulsating direct current (DC) voltage with various ripple factors, and alternating current (AC) and DC voltage for comparison, [...] Read more.

Breakdown strength is an important electrical property of insulating paper. Oil-impregnated paper of various aging states was prepared. Its breakdown voltage was then measured at pulsating direct current (DC) voltage with various ripple factors, and alternating current (AC) and DC voltage for comparison, respectively. The AC breakdown voltage is the smallest, and pulsating DC (r = 1/5) breakdown voltage is the greatest before the paper reaches its end of life. A dielectric model was adopted to investigate the difference in magnitude of breakdown voltage at different voltage waveforms. Meanwhile, it was found that breakdown voltage fluctuated and even increased occasionally during the thermal aging process, and a somewhat opposite changing tendency versus aging time was observed for breakdown voltage at DC voltage and pulsating DC voltage with small ripple factors (r = 1/5 and 1/3), compared with AC voltage. The degree of polymerization (DP) and moisture content of the paper were measured, and the characteristics of the pores and cracks of the paper were obtained to investigate the possible influencing factors of breakdown voltage at different aging states. The results showed that the moisture content, oil absorption ability associated with pores and cracks of paper, and the damage to paper structure all contributed to the variation of the breakdown voltage versus aging time, while the importance of their influence differed as the aging state of paper varied. Full article

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

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17 pages, 1098 KiB

Open AccessFeature PaperArticle

Stability of DC Distribution Systems: An Algebraic Derivation

by Nils H. Van der Blij^1,*

, Laura M. Ramirez-Elizondo¹, Matthijs T. J. Spaan² and Pavol Bauer¹

¹ Department of Electrical Sustainable Energy, Delft University of Technology, Mekelweg 4, 2628 CD Delft, The Netherlands

² Department of Software Technology, Delft University of Technology, Mekelweg 4, 2628 CD Delft, The Netherlands

Energies 2017, 10(9), 1412; https://doi.org/10.3390/en10091412 - 15 Sep 2017

Cited by 14 | Viewed by 3865

Abstract

Instability caused by low inertia and constant power loads is a major challenge of DC distribution grids. Previous research uses oversimplified models or does not provide general rules for stability. Therefore, a comprehensive approach to analyze the stability of DC distribution systems is [...] Read more.

Instability caused by low inertia and constant power loads is a major challenge of DC distribution grids. Previous research uses oversimplified models or does not provide general rules for stability. Therefore, a comprehensive approach to analyze the stability of DC distribution systems is desired. This paper presents a method to algebraically analyze the stability of any DC distribution system through the eigenvalues of its state-space matrices. Furthermore, using this method, requirements are found for the stability of three example systems. Additionally, a sensitivity analysis is performed, which considers the effect of several system parameters on the stability and disputes some overgeneralized conclusions of previous research. Moreover, various simulations are performed to illustrate the dynamic behavior of a stable and an unstable DC distribution system. Full article

(This article belongs to the Special Issue DC Systems)

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7 pages, 6964 KiB

Open AccessArticle

Wave Equation Datuming Applied to Seismic Data in Shallow Water Environment and Post-Critical Water Bottom Reflection

by Umberta Tinivella^1,*

, Michela Giustiniani¹

and Ivan Vargas-Cordero²

¹ Istituto Nazionale di Oceanografia e di Geofisica Sperimentale—OGS, 34010 Sgonico, Italy

² Facultad de Ingeniería, Universidad Andres Bello, Quillota, Viña del Mar 980, Chile

Energies 2017, 10(9), 1414; https://doi.org/10.3390/en10091414 - 15 Sep 2017

Cited by 4 | Viewed by 3585

Abstract

Coastal areas are generally characterized by human manufacturing; thus, seismic data analysis is necessary to characterize the properties of the subsoil, the main purpose of which is to clarify risk situations. In the case of very shallow water environments, seismic multiple attenuation becomes [...] Read more.

Coastal areas are generally characterized by human manufacturing; thus, seismic data analysis is necessary to characterize the properties of the subsoil, the main purpose of which is to clarify risk situations. In the case of very shallow water environments, seismic multiple attenuation becomes a challenge when the reflection of the seafloor is post-critical, so it is not recorded because of the acquisition parameters. We propose an approach to attenuate the multiples by using wave equation datuming that does not require the detection of seafloor reflection and avoids the seafloor reflection prediction and related approximations in the post-critical conditions. Moreover, this approach allows for the enhancement of higher frequencies, and, consequently, an increase in resolution, demonstrating that it is a powerful tool to attenuate multiples and reverberations, especially where other approaches are found to be inefficient. An example of the application of seismic data acquired in the continental shelf of South Chile is reported. Full article

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16 pages, 3850 KiB

Open AccessArticle

Electromagnetic Burst Measurement System Based on Low Cost UHF Dipole Antenna

by Ismael Escalona¹, Gonzalo Avaria^2,4,*, Marcos Díaz¹, Jorge Ardila-Rey³

, José Moreno^2,4, Cristian Pavez^2,4 and Leopoldo Soto^2,4

¹ Electrical Engineering Department, Faculty of Physical and Mathematical Sciences, University of Chile, Av. Tupper 2007, Santiago 8370451, Chile

² Comisión Chilena de Energía Nuclear, Av. Nueva Bilbao 12.501, Las Condes, Santiago 7600713, Chile

³ Department of Electrical Engineering, Federico Santa Maria Technical University, Santiago 8940000, Chile

⁴ Departamento de Ciencias Físicas, Facultad de Ciencias Exactas, Universidad Andres Bello, República 220, Santiago 8370035, Chile

Energies 2017, 10(9), 1415; https://doi.org/10.3390/en10091415 - 15 Sep 2017

Cited by 7 | Viewed by 5451

Abstract

Non-linear high-power devices produce electromagnetic noise (EMN) sources of great intensity that can disrupt and damage the surrounding electrical equipment and devices. This radiative phenomenon is very common at facilities where pulsed power generators are required, particularly those that are needed to produce [...] Read more.

Non-linear high-power devices produce electromagnetic noise (EMN) sources of great intensity that can disrupt and damage the surrounding electrical equipment and devices. This radiative phenomenon is very common at facilities where pulsed power generators are required, particularly those that are needed to produce dense transient plasma experiments. These conditions are found at the Chilean Nuclear Energy Commission (CCHEN), due to the presence of pulsed power generators that switch large currents (kA-MA) in short times (10–100 ns). In order to characterize and establish conditions to mitigate the effects of the EMN on nearby devices, a measurement system based on an ultra-high frequency (UHF) dipole antenna was developed. We evaluated the system measuring the EMN emanated from a plasma focus device, the PF-400J. Measurements at the place indicated broadband and intense electric fields that can couple to nearby cables and equipment (10–300 MHz bandwidth, up to 350 V/MHz spectral intensity, 100 V coupled voltage). Based on these measurements a compact and simple protection system was designed, built and tested, capable of effectively mitigating the high levels of EMN. The proper EMN impact mitigation indicates the correct operation of the suggested system. The developed system can be of interest to the energy community by facilitating EMN measurement produced by arc discharges. Full article

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21 pages, 1098 KiB

Open AccessArticle

Anaerobic Digestion of Feedstock Grown on Marginal Land: Break-Even Electricity Prices

by Yakubu Abdul-Salam^1,*

, Melf-Hinrich Ehlers² and Jelte Harnmeijer^1,3

¹ The James Hutton Institute, Craigiebuckler, Aberdeen AB15 8QH, UK

² Section of International Agricultural Policy and Environmental Governance, Faculty of Organic Agricultural Sciences, University of Kassel, 37213 Witzenhausen, Germany

³ Scene Connect Ltd., Edinburgh Centre for Carbon Innovation, Edinburgh EH1 1LZ, UK

Energies 2017, 10(9), 1416; https://doi.org/10.3390/en10091416 - 15 Sep 2017

Cited by 5 | Viewed by 5140

Abstract

Marginal farm land is land characterised by low food, feed and fodder crop productivity due to soil and environmental limitations. Such land may however be utilised for bio-energy crop production. We investigate the economic viability of small scale combined heat and power anaerobic [...] Read more.

Marginal farm land is land characterised by low food, feed and fodder crop productivity due to soil and environmental limitations. Such land may however be utilised for bio-energy crop production. We investigate the economic viability of small scale combined heat and power anaerobic digestion (CHP AD) projects based on feedstock from farm waste and bio-energy crops grown on a representative temperate latitude marginal farm land in the UK. Using a realistic set of five project feedstock-mix scenarios, and considering standard technology and current market and policy regimes, we deploy a stochastic framework to assess prices of electricity required for these projects to break-even and conduct sensitivity analyses of key project parameters. Accounting for the current market prices and policy tariffs for heat, we find that critical electricity sale prices of about 17.46 p/kWh to 27.12 p/kWh are needed for the projects to break even. These prices are well above the current combined feed-in-tariff support and market prices for electricity over the past years in the UK. We conclude that the use of marginal land to generate power for export using small-scale CHP AD in the UK and the wider temperate latitude countries is unviable, if energy and farming policy regimes do not provide substantial support. Full article

(This article belongs to the Special Issue Economics of Bioenergy 2016)

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28 pages, 7869 KiB

Open AccessArticle

An Efficient Energy Saving Scheme for Base Stations in 5G Networks with Separated Data and Control Planes Using Particle Swarm Optimization

by Min Wook Kang¹ and Yun Won Chung^2,*

¹ Department of Information and Telecommunication Engineering, Graduate School, Soongsil University, Seoul 06978, Korea

² School of Electronic Engineering, Soongsil University, Seoul 06978, Korea

Energies 2017, 10(9), 1417; https://doi.org/10.3390/en10091417 - 15 Sep 2017

Cited by 36 | Viewed by 6671

Abstract

Reducing energy consumption of mobile communication networks has gained significant attentions since it takes a major part of the total energy consumption of information and communication technology (ICT). In this paper, we consider 5G networks with heterogeneous macro cells and small cells, where [...] Read more.

Reducing energy consumption of mobile communication networks has gained significant attentions since it takes a major part of the total energy consumption of information and communication technology (ICT). In this paper, we consider 5G networks with heterogeneous macro cells and small cells, where data and control planes are separated. We consider two types of data traffic, i.e., low rate data traffic and high rate data traffic. In basic separation architecture, a macro cell base station (MBS) manages control signals, while a small cell base station (SBS) manages both low rate data traffic and high rate data traffic. In the considered modified separation architecture, an MBS manages control signals and low rate data traffic, while an SBS manages high rate data traffic. Then, an efficient energy saving scheme for base stations (BSs) is proposed, where the state of a BS is determined depending on the number of user equipments (UEs) that request high rate data traffic and the number of UEs that exist under the overlapping areas commonly covered by the considered BS and the neighbor BSs. We formulate an optimization problem for the proposed energy saving scheme and obtain the solution using particle swarm optimization (PSO). Numerical results show that the proposed energy saving scheme in the modified separated network architecture has better energy efficiency compared to the conventional energy saving schemes in both basic and modified separated network architectures. Also, the proposed energy saving scheme has lower aggregate delay. Full article

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

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19 pages, 298 KiB

Open AccessArticle

Economic and Technical Efficiency of the Biomass Industry in China: A Network Data Envelopment Analysis Model Involving Externalities

by Qingyou Yan¹, Youwei Wan¹, Jingye Yuan², Jieting Yin¹, Tomas Baležentis^3,*

and Dalia Streimikiene³

¹ School of Economics and Management, North China Electric Power University, 2 Beinong Road, Beijing 102206, China

² Department of Technological Economics and Management, Guangxi University, 100 University Road, Nanning 530004, Guangxi, China

³ Lithuanian Institute of Agrarian Economics, Kudirkos Str. 18-2, LT-03105 Vilnius, Lithuania

Energies 2017, 10(9), 1418; https://doi.org/10.3390/en10091418 - 15 Sep 2017

Cited by 16 | Viewed by 4199

Abstract

This paper proposes the network data envelopment analysis (DEA) model accounting for negative externalities and applies it for decomposition of profit inefficiency in the biomass-agriculture circular system (Bio-AG system). A circular structure of the Bio-AG system which is different from the previously applied [...] Read more.

This paper proposes the network data envelopment analysis (DEA) model accounting for negative externalities and applies it for decomposition of profit inefficiency in the biomass-agriculture circular system (Bio-AG system). A circular structure of the Bio-AG system which is different from the previously applied network structures is assumed. Since the negative externalities (i.e., pollutant emissions from the biomass industry) occur in the Bio-AG system, the property rights are taken into consideration to model the externalities-adjusted profits. Therefore, the changes in profits due to changes in the property rights (assuming no property rights, allocating property rights to agricultural sector, and allocating property rights to biomass power generation sector) are quantified. Further, the decomposition shows that the biomass power generation sector is less affected by technical inefficiency if contrasted to allocative inefficiency in terms of the profit loss. The findings suggest that the biomass power generation technology influences the profits of the biomass industry. What is more, the inefficient allocation of resources is now the key factor undermining performance of the biomass industry. Therefore, the government should adopt measures to improve the allocation of resources and prevent excessive investments or development of less efficient technologies. Full article

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21 pages, 8381 KiB

Open AccessArticle

Study and Analysis of an Intelligent Microgrid Energy Management Solution with Distributed Energy Sources

by Swaminathan Ganesan¹

, Sanjeevikumar Padmanaban^2,*

, Ramesh Varadarajan¹

, Umashankar Subramaniam¹ and Lucian Mihet-Popa³

¹ School of Electrical Engineering, Vellore Institute of Technology (VIT) University, Vellore, Tamilnadu 632014, India

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

³ Faculty of Engineering, Østfold University College, Kobberslagerstredet 5, 1671 Kråkeroy-Fredrikstad, Norway

Energies 2017, 10(9), 1419; https://doi.org/10.3390/en10091419 - 16 Sep 2017

Cited by 46 | Viewed by 7975

Abstract

In this paper, a robust energy management solution which will facilitate the optimum and economic control of energy flows throughout a microgrid network is proposed. The increased penetration of renewable energy sources is highly intermittent in nature; the proposed solution demonstrates highly efficient [...] Read more.

In this paper, a robust energy management solution which will facilitate the optimum and economic control of energy flows throughout a microgrid network is proposed. The increased penetration of renewable energy sources is highly intermittent in nature; the proposed solution demonstrates highly efficient energy management. This study enables precise management of power flows by forecasting of renewable energy generation, estimating the availability of energy at storage batteries, and invoking the appropriate mode of operation, based on the load demand to achieve efficient and economic operation. The predefined mode of operation is derived out of an expert rule set and schedules the load and distributed energy sources along with utility grid. 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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15 pages, 1965 KiB

Open AccessArticle

The Influence of Eroded Blades on Wind Turbine Performance Using Numerical Simulations

by Matthias Schramm^1,2,*, Hamid Rahimi^1,2

, Bernhard Stoevesandt¹

and Kim Tangager³

¹ Fraunhofer Institute for Wind Energy and Energy System Technology, Küpkersweg 70, Oldenburg 26129, Germany

² ForWind, University of Oldenburg, Ammerländer Heerstr. 114-118, Oldenburg 26129, Germany

³ Blade Repair Solutions, Hedevej 25, Hadsund 9560, Denmark

Energies 2017, 10(9), 1420; https://doi.org/10.3390/en10091420 - 16 Sep 2017

Cited by 71 | Viewed by 9143

Abstract

During their operation, wind turbine blades are eroded due to rain and hail, or they are contaminated with insects. Since the relative inflow velocity is higher at the outer than at the inner part of the blades, erosion occurs mostly at the outer [...] Read more.

During their operation, wind turbine blades are eroded due to rain and hail, or they are contaminated with insects. Since the relative inflow velocity is higher at the outer than at the inner part of the blades, erosion occurs mostly at the outer blade region. In order to prevent strong erosion, it is possible to install a leading edge protection, which can be applied to the blades after the initial installation, but changes the shape of the initial airfoil sections. It is unclear how this modification influences the aerodynamic performance of the turbine. Hence, it is investigated in this work. The NREL 5 MW turbine is simulated with clean and eroded blades, which are compared to coated blades equipped with leading edge protection. Aerodynamic polars are generated by means of Computational Fluid Dynamics, and load calculations are conducted using the blade element momentum theory. The analysis in this work shows that, compared to clean rotor blades, the worse aerodynamic behaviour of strongly eroded blades can lead to power losses of

9 %

. In contrast, coated blades only have a small impact on the turbine power of less than

1 %

. Full article

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

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30 pages, 2633 KiB

Open AccessArticle

A Hybrid Wind Speed Forecasting System Based on a ‘Decomposition and Ensemble’ Strategy and Fuzzy Time Series

by Hufang Yang¹, Zaiping Jiang^1,* and Haiyan Lu²

¹ School of Statistics, Dongbei University of Finance and Economics, Dalian, 116025, China

² Faculty of Engineering and Information Technology, University of Technology, Sydney, 20000, Australia

Energies 2017, 10(9), 1422; https://doi.org/10.3390/en10091422 - 16 Sep 2017

Cited by 50 | Viewed by 5800

Abstract

Accurate and stable wind speed forecasting is of critical importance in the wind power industry and has measurable influence on power-system management and the stability of market economics. However, most traditional wind speed forecasting models require a large amount of historical data and [...] Read more.

Accurate and stable wind speed forecasting is of critical importance in the wind power industry and has measurable influence on power-system management and the stability of market economics. However, most traditional wind speed forecasting models require a large amount of historical data and face restrictions due to assumptions, such as normality postulates. Additionally, any data volatility leads to increased forecasting instability. Therefore, in this paper, a hybrid forecasting system, which combines the ‘decomposition and ensemble’ strategy and fuzzy time series forecasting algorithm, is proposed that comprises two modules—data pre-processing and forecasting. Moreover, the statistical model, artificial neural network, and Support Vector Regression model are employed to compare with the proposed hybrid system, which is proven to be very effective in forecasting wind speed data affected by noise and instability. The results of these comparisons demonstrate that the hybrid forecasting system can improve the forecasting accuracy and stability significantly, and supervised discretization methods outperform the unsupervised methods for fuzzy time series in most cases. Full article

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

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16 pages, 3171 KiB

Open AccessArticle

Olive Mill Wastewater: From a Pollutant to Green Fuels, Agricultural Water Source and Bio-Fertilizer—Part 1. The Drying Kinetics

by Mejdi Jeguirim^1,*

, Patrick Dutournié¹, Antonis A. Zorpas²

and Lionel Limousy¹

¹ Institut de Sciences des Matériaux de Mulhouse, UMR 7661 CNRS, 15 rue Jean Starcky, 68057 Mulhouse, France

² Faculty of Pure and Applied Sciences, Environmental Conservation and Management, Lab of Chemical Engineering and Engineering Sustainability, Cyprus Open University, Giannou Kranidioti 33, 2252 Latsia, Nicosia, Cyprus

Energies 2017, 10(9), 1423; https://doi.org/10.3390/en10091423 - 16 Sep 2017

Cited by 28 | Viewed by 4702

Abstract

Olive Mill Wastewater (OMWW) treatment is considered to be one of the main challenges that Mediterranean countries face. Although several procedures and technologies are mentioned in the literature, these techniques have several disadvantages or have been limited to laboratory pilot validation without posterior [...] Read more.

Olive Mill Wastewater (OMWW) treatment is considered to be one of the main challenges that Mediterranean countries face. Although several procedures and technologies are mentioned in the literature, these techniques have several disadvantages or have been limited to laboratory pilot validation without posterior industrial projection. Recently, an advanced environmental friendly strategy for the recovery of OMWW was established involving the impregnation of OMWW on dry biomasses, drying of these impregnated samples, and finally green fuels and biochar production. This established strategy revealed that the drying step is crucial for the success of the entire recovery process. Hence, two impregnated samples were prepared through OMWW impregnation on sawdust (IS) and olive mill solid waste (ISW). The drying kinetics of OMWW and impregnated samples (IS and ISW) were examined in a convective dryer (air velocity range from 0.7–1.3 m/s and the temperature from 40–60 °C). The experimental results indicated that the drying of the impregnated samples occurred twice as fast as for the OMWW sample. Such behavior was attributed to the remaining thin layer of oil on the OMWW surface Furthermore, the Henderson and Pabis model showed the suitable fit of the drying curves with a determination coefficient R² above 0.97. The drying rates were extracted from the mathematical models and the drying process was analyzed. The coefficient of effective diffusivity varied between 2.8 and 11.7 × 10⁻¹⁰ m²/s. In addition, the activation energy values ranged between 28.7 and 44.9 kJ/mol. These values were in the same range as those obtained during the drying of other agrifood byproducts. The final results could be very helpful to engineers aiming to improve and optimize the OMWW drying process. Full article

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11 pages, 4817 KiB

Open AccessArticle

Electric Arc Furnace Modeling with Artificial Neural Networks and Arc Length with Variable Voltage Gradient

by Raul Garcia-Segura¹, Javier Vázquez Castillo^1,*, Fernando Martell-Chavez², Omar Longoria-Gandara³ and Jaime Ortegón Aguilar¹

¹ Deparment of Engineering, University of Quintana Roo, Chetumal 77019, Mexico

² Research Center in Optics, Aguascalientes 20200, Mexico

³ Department of Electronics, Systems and IT, ITESO, Tlaquepaque 45604, Mexico

Energies 2017, 10(9), 1424; https://doi.org/10.3390/en10091424 - 16 Sep 2017

Cited by 29 | Viewed by 9844

Abstract

Electric arc furnaces (EAFs) contribute to almost one third of the global steel production. Arc furnaces use a large amount of electrical energy to process scrap or reduced iron and are relevant to study because small improvements in their efficiency account for significant [...] Read more.

Electric arc furnaces (EAFs) contribute to almost one third of the global steel production. Arc furnaces use a large amount of electrical energy to process scrap or reduced iron and are relevant to study because small improvements in their efficiency account for significant energy savings. Optimal controllers need to be designed and proposed to enhance both process performance and energy consumption. Due to the random and chaotic nature of the electric arcs, neural networks and other soft computing techniques have been used for modeling EAFs. This study proposes a methodology for modeling EAFs that considers the time varying arc length as a relevant input parameter to the arc furnace model. Based on actual voltages and current measurements taken from an arc furnace, it was possible to estimate an arc length suitable for modeling the arc furnace using neural networks. The obtained results show that the model reproduces not only the stable arc conditions but also the unstable arc conditions, which are difficult to identify in a real heat process. The presented model can be applied for the development and testing of control systems to improve furnace energy efficiency and productivity. Full article

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

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15 pages, 5241 KiB

Open AccessArticle

Optimal Scheduling Strategy for Domestic Electric Water Heaters Based on the Temperature State Priority List

by Zhaojing Yin¹

, Yanbo Che¹, Dezhi Li², Huanan Liu³

and Dongmin Yu^3,*

¹ Key Laboratory of Smart Grid of Ministry of Education, Tianjin University, Tianjin 300072, China

² China Electric Power Research Institute, Beijing 100192, China

³ Department of Electrical Engineering, Northeast Electric Power University, Jilin 132012, China

Energies 2017, 10(9), 1425; https://doi.org/10.3390/en10091425 - 18 Sep 2017

Cited by 18 | Viewed by 6014

Abstract

With the rapid growth of thermostatically controlled loads, active power fluctuation and peak demand growth within an autonomous micro-grid become serious problems. This paper tries to suppress power fluctuation and shave peak demand for a micro-grid through optimizing domestic electric water heaters (controllable [...] Read more.

With the rapid growth of thermostatically controlled loads, active power fluctuation and peak demand growth within an autonomous micro-grid become serious problems. This paper tries to suppress power fluctuation and shave peak demand for a micro-grid through optimizing domestic electric water heaters (controllable load). In this paper, domestic electric water heater models are first built to optimize power flow within a single water heater. Subsequently, the Monte Carlo method is proposed to simulate power consumption of a cluster of domestic electric water heaters. After that, the temperature state priority list method is presented to suppress power flow and shave peak demand for a given micro-grid. Optimization results show that the proposed temperature state priority list method can reduce peak demand by 12.5%. However, it has a wider active power fluctuation range and needs a longer reaction time compared with the simplified temperature state priority list method. In addition, the optimization results show that by increasing the number of controllable loads participating in load scheduling, active power fluctuation can be reduced and the maximum active power of the given micro-grid can be cut. However, to achieve this, about 1.2% of extra electrical energy needs to be generated by the external grid. Full article

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

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15 pages, 2202 KiB

Open AccessArticle

Hierarchical Distributed Motion Control for Multiple Linear Switched Reluctance Machines

by Bo Zhang^1,2

, Jianping Yuan², Jianjun Luo², Xiaoyu Wu¹, Li Qiu¹ and J.F. Pan^1,*

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

² Laboratory of Advanced Unmanned Systems Technology, Research Institute of Northwestern PolytechnicalUniversity in Shenzhen, Shenzhen 518060, China

Energies 2017, 10(9), 1426; https://doi.org/10.3390/en10091426 - 16 Sep 2017

Cited by 4 | Viewed by 4275

Abstract

This paper investigates a distributed, coordinated motion control network based on multiple direct-drive, linear switched reluctance machines (LSRMs). A hierarchical, two-level synchronization control strategy is proposed for the four LSRMs based motion control network. The high-level, reference signals agreement algorithm is first employed [...] Read more.

This paper investigates a distributed, coordinated motion control network based on multiple direct-drive, linear switched reluctance machines (LSRMs). A hierarchical, two-level synchronization control strategy is proposed for the four LSRMs based motion control network. The high-level, reference signals agreement algorithm is first employed to correct the asynchronous behaviors of the position commands. Then, the low-level tracking synchronization method is applied for the collaborative position control of the four LSRMs. The proposed two-level, fault-tolerant control strategy eliminates the asynchrony of the reference signals and it also guarantees the coordinated tracking control performance of the four LSRMs. Experimental results demonstrate that effective coordinated tracking control can be ensured, based on the successful agreement of reference signals and an absolute tracking error falling within 2 mm can be achieved. Full article

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

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20 pages, 6935 KiB

Open AccessArticle

Design and Numerical Simulations of a Flow Induced Vibration Energy Converter for Underwater Mooring Platforms

by Wenlong Tian^1,*, Zhaoyong Mao^1,2 and Fuliang Zhao¹

¹ School of Marine Science and Technology, Northwestern Polytechnical University, Xi’an 710072, China

² Key Laboratory for Unmanned Underwater Vehicle, Northwestern Polytechnical University, Xi’an 710072, China

Energies 2017, 10(9), 1427; https://doi.org/10.3390/en10091427 - 16 Sep 2017

Cited by 6 | Viewed by 4834

Abstract

Limited battery energy restricts the duration of the underwater operation of underwater mooring platforms (UMPs). In this paper, a flow-induced vibration energy converter (FIVEC) is designed to produce power for the UMPs and extend their operational time. The FIVEC is equipped with a [...] Read more.

Limited battery energy restricts the duration of the underwater operation of underwater mooring platforms (UMPs). In this paper, a flow-induced vibration energy converter (FIVEC) is designed to produce power for the UMPs and extend their operational time. The FIVEC is equipped with a thin plate to capture the kinetic energy in the vortices shed from the surface of the UMP. A magnetic coupling (MC) is applied for the non-contacting transmission of the plate torque to the generators so that the friction loss can be minimized. In order to quantify and evaluate the performance of the FIVEC, two-dimensional computational fluid dynamics (CFD) simulations are performed. Simulations are based on the Reynolds Averaged Navier-Stokes (RANS) equations and the shear stress transport (SST) k-ω turbulent model is utilized. The CFD method is firstly validated using existing experimental data. Then the influences of plate length and system damping on the performance of the FIVEC are evaluated. The results show that the device has a maximum averaged power coefficient of 0.0520 (13.86 W) in the considered situations. The results also demonstrate the feasibility of this energy converter plan. Full article

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

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11 pages, 1910 KiB

Open AccessArticle

Super Capacitor Energy Storage Based MMC for Energy Harvesting in Mine Hoist Application

by Xiaofeng Yang^1,*

, Piao Wen¹, Yao Xue¹, Trillion Q. Zheng¹ and Youyun Wang²

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

² Tianshui Electric Drive Research Institute Co. LTD, Tianshui 741020, China

Energies 2017, 10(9), 1428; https://doi.org/10.3390/en10091428 - 17 Sep 2017

Cited by 10 | Viewed by 6322

Abstract

This paper proposes a super capacitor energy storage-based modular multilevel converter (SCES-MMC) for mine hoist application. Different from the conventional MMCs, the sub-modules employ distributed super capacitor banks, which are designed to absorb the regenerative energy of mine hoist and released in the [...] Read more.

This paper proposes a super capacitor energy storage-based modular multilevel converter (SCES-MMC) for mine hoist application. Different from the conventional MMCs, the sub-modules employ distributed super capacitor banks, which are designed to absorb the regenerative energy of mine hoist and released in the traction condition, so as to improve energy utilization efficiency. The key control technologies are introduced in detail, followed by analysis of the configuration and operation principles. The feasibility of the proposed SCES-MMC topology and the control theory are also verified. Simulation results show that SCES-MMC can adapt to the variable frequency speed regulation of the motor drive, which shows good application prospects in the future for medium- and high-voltage mine hoist systems. Full article

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

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27 pages, 11269 KiB

Open AccessArticle

Investigating the Plasma-Assisted and Thermal Catalytic Dry Methane Reforming for Syngas Production: Process Design, Simulation and Evaluation

by Evangelos Delikonstantis, Marco Scapinello and Georgios D. Stefanidis^*

Process Engineering for Sustainable Systems (ProcESS), Department of Chemical Engineering KU Leuven, Celestijnenlaan 200F, 3001 Leuven, Belgium

Energies 2017, 10(9), 1429; https://doi.org/10.3390/en10091429 - 18 Sep 2017

Cited by 32 | Viewed by 11831

Abstract

The growing surplus of green electricity generated by renewable energy technologies has fueled research towards chemical industry electrification. By adapting power-to-chemical concepts, such as plasma-assisted processes, cheap resources could be converted into fuels and base chemicals. However, the feasibility of those electrified processes [...] Read more.

The growing surplus of green electricity generated by renewable energy technologies has fueled research towards chemical industry electrification. By adapting power-to-chemical concepts, such as plasma-assisted processes, cheap resources could be converted into fuels and base chemicals. However, the feasibility of those electrified processes at large scale has not been investigated yet. Thus, the current work strives to compare, for first time in the literature, plasma-assisted production of syngas, from CH₄ and CO₂ (dry methane reforming), with thermal catalytic dry methane reforming. Specifically, both processes are conceptually designed to deliver syngas suitable for methanol synthesis (H₂/CO ≥ 2 in mole). The processes are simulated in the Aspen Plus process simulator where different process steps are investigated. Heat integration and equipment cost estimation are performed for the most promising process flow diagrams. Collectively, plasma-assisted dry methane reforming integrated with combined steam/CO₂ methane reforming is an effective way to deliver syngas for methanol production. It is more sustainable than combined thermal catalytic dry methane reforming with steam methane reforming, which has also been proposed for syngas production of H₂/CO ≥ 2; in the former process, 40% more CO₂ is captured, while 38% less H₂O is consumed per mol of syngas. Furthermore, the plasma-assisted process is less complex than the thermal catalytic one; it requires higher amount of utilities, but comparable capital investment. Full article

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17 pages, 1514 KiB

Open AccessArticle

Modeling a Hybrid Microgrid Using Probabilistic Reconfiguration under System Uncertainties

by Hadis Moradi^1,*

, Mahdi Esfahanian¹

, Amir Abtahi² and Ali Zilouchian¹

¹ Computer and Electrical Engineering Department, Florida Atlantic University, Boca Raton, FL 33431, USA

² Ocean and Mechanical Engineering Department, Florida Atlantic University, Boca Raton, FL 33431, USA

Energies 2017, 10(9), 1430; https://doi.org/10.3390/en10091430 - 18 Sep 2017

Cited by 22 | Viewed by 6267

Abstract

A novel method for a day-ahead optimal operation of a hybrid microgrid system including fuel cells, photovoltaic arrays, a microturbine, and battery energy storage in order to fulfill the required load demand is presented in this paper. In the proposed system, the microgrid [...] Read more.

A novel method for a day-ahead optimal operation of a hybrid microgrid system including fuel cells, photovoltaic arrays, a microturbine, and battery energy storage in order to fulfill the required load demand is presented in this paper. In the proposed system, the microgrid has access to the main utility grid in order to exchange power when required. Available municipal waste is utilized to produce the hydrogen required for running the fuel cells, and natural gas will be used as the backup source. In the proposed method, an energy scheduling is introduced to optimize the generating unit power outputs for the next day, as well as the power flow with the main grid, in order to minimize the operational costs and produced greenhouse gases emissions. The nature of renewable energies and electric power consumption is both intermittent and unpredictable, and the uncertainty related to the PV array power generation and power consumption has been considered in the next-day energy scheduling. In order to model uncertainties, some scenarios are produced according to Monte Carlo (MC) simulations, and microgrid optimal energy scheduling is analyzed under the generated scenarios. In addition, various scenarios created by MC simulations are applied in order to solve unit commitment (UC) problems. The microgrid’s day-ahead operation and emission costs are considered as the objective functions, and the particle swarm optimization algorithm is employed to solve the optimization problem. Overall, the proposed model is capable of minimizing the system costs, as well as the unfavorable influence of uncertainties on the microgrid’s profit, by generating different scenarios. Full article

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

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19 pages, 7859 KiB

Open AccessArticle

A Blended SPS-ESPS Control DAB-IBDC Converter for a Standalone Solar Power System

by P. Sathishkumar¹, Himanshu¹, Shengxu Piao¹, Muhammad Adil Khan¹, Do-Hyun Kim¹, Min-Soo Kim¹, Dong-Keun Jeong², Cheewoo Lee³ and Hee-Je Kim^1,*

¹ School of Electrical Engineering, Pusan National University, Busandaehak-ro 63 beon-gil 2, Busan 46241, Korea

² Power Conversion and Control Research Centre, HVDC Research Division, KERI, Changwon 51435, Korea

³ School of Electrical Engineering, Pusan National University, Busan 46241, Korea

Energies 2017, 10(9), 1431; https://doi.org/10.3390/en10091431 - 18 Sep 2017

Cited by 21 | Viewed by 7187

Abstract

In sustainable energy applications, standalone solar power systems are mostly preferred for self-powered energy zones. In all standalone renewable power systems, batteries are still preferred as the common energy storage device. On the other hand, batteries are not applicable for high peak power [...] Read more.

In sustainable energy applications, standalone solar power systems are mostly preferred for self-powered energy zones. In all standalone renewable power systems, batteries are still preferred as the common energy storage device. On the other hand, batteries are not applicable for high peak power demand applications because of their low power density. A supercapacitor is a preferable high-power density energy storage device for high peak power applications. A 2 kW, 50 kHz digital control dual active bridge isolated bi-directional dc-dc converter (DAB-IBDC) was developed for interfacing the supercapacitor bank in standalone solar power system. This paper proposes a blended SPS-ESPS digital control algorithm for a DAB-IBDC converter instead of using a traditional single-phase shift (SPS) control algorithm, which is commonly used for large input to output voltage varying applications. This proposed blended SPS-ESPS control algorithm achieved high power conversion efficiency during a large input to output voltage variation, over a traditional phase shift control algorithm by reducing the back-power flow and current stress in a circuit. This system also achieved maximum power point for solar modules and enhanced rapid charging-discharging for a supercapacitor bank. Both SPS and the blended SPS-ESPS control algorithms were verified experimentally using 2 kW DAB-IBDC topology implemented with standalone power system that combination of 2000 W input solar module and 158 Wh supercapacitor bank. Full article

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

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12 pages, 1936 KiB

Open AccessArticle

Modeling and Simulation of Complex Fluid Networks in the Flue Gas System of a Boiler

by Yue Zhang^*, Yuhan Men and Pu Han

Department of Automation, North China Electric Power University, Yonghua North Street, No. 619, Baoding 071003, China

Energies 2017, 10(9), 1432; https://doi.org/10.3390/en10091432 - 18 Sep 2017

Cited by 5 | Viewed by 4107

Abstract

Under the conditions of high demand for energy saving and environmental protection, the thermal power unit is required to phase out the traditional extensive operation mode—a method of oxygen-enriched combustion in a furnace, considering safety first. Achieving efficient and economic operation with an [...] Read more.

Under the conditions of high demand for energy saving and environmental protection, the thermal power unit is required to phase out the traditional extensive operation mode—a method of oxygen-enriched combustion in a furnace, considering safety first. Achieving efficient and economic operation with an optimal proportion of air distribution in these thermal power units is crucial. The high-precision simulation equipment could provide an experimental basis for optimal operation of field units. This paper starts by improving the accuracy of simulation equipment. In this work, the method of dividing nodes and branches in the boiler was based on signal flow graph theory. According to the flow characteristics of the working substance, the method for calculating the node and branch pressure drop was analyzed and set up. Subsequently, a fluid network model of the multi-dimensional flue gas system was constructed. With the help of our self-developed simulation model and data-driven platform, a modular simulation algorithm was designed. The simulation analysis of the boiler showed the accuracy of the model. Full article

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

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13 pages, 1818 KiB

Open AccessEditor’s ChoiceArticle

Development of a Decision-Making Algorithm for the Optimum Size and Placement of Distributed Generation Units in Distribution Networks

by Vasiliki Vita

Department of Electrical and Electronic Engineering Educators, ASPETE—School of Pedagogical and Technological Education, Ν. Ηeraklion, 141 21 Athens, Greece

Energies 2017, 10(9), 1433; https://doi.org/10.3390/en10091433 - 18 Sep 2017

Cited by 162 | Viewed by 9822

Abstract

The paper presents a decision-making algorithm that has been developed for the optimum size and placement of distributed generation (DG) units in distribution networks. The algorithm that is very flexible to changes and modifications can define the optimal location for a DG unit [...] Read more.

The paper presents a decision-making algorithm that has been developed for the optimum size and placement of distributed generation (DG) units in distribution networks. The algorithm that is very flexible to changes and modifications can define the optimal location for a DG unit (of any type) and can estimate the optimum DG size to be installed, based on the improvement of voltage profiles and the reduction of the network’s total real and reactive power losses. The proposed algorithm has been tested on the IEEE 33-bus radial distribution system. The obtained results are compared with those of earlier studies, proving that the decision-making algorithm is working well with an acceptable accuracy. The algorithm can assist engineers, electric utilities, and distribution network operators with more efficient integration of new DG units in the current distribution networks. Full article

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

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18 pages, 1343 KiB

Open AccessArticle

The Economic Feasibility of Residential Energy Storage Combined with PV Panels: The Role of Subsidies in Italy

by Federica Cucchiella^*

, Idiano D’Adamo

and Massimo Gastaldi

Department of Industrial and Information Engineering and Economics, University of L’Aquila, Via G. Gronchi 18, 67100 L’Aquila, Italy

Energies 2017, 10(9), 1434; https://doi.org/10.3390/en10091434 - 18 Sep 2017

Cited by 39 | Viewed by 5740

Abstract

A solar photovoltaic system produces electricity by converting energy from the sun. By the end of 2016, the global installed solar photovoltaic capacity reached 305 GW. Its growth is impressive in the last years; in fact, it was only equal to 41 GW [...] Read more.

A solar photovoltaic system produces electricity by converting energy from the sun. By the end of 2016, the global installed solar photovoltaic capacity reached 305 GW. Its growth is impressive in the last years; in fact, it was only equal to 41 GW in 2010. However, Europe has installed only 6.9 GW in 2016 (−1.7 GW in comparison to previous year) and this annual power installed is equal to 9% of global one in according to data released by Solar Power Europe. The profitability of PV systems in mature markets depends on the harmonization between demanded energy and produced one residential energy storage when combined with photovoltaic panels is able to increase the share of self-consumption. This work proposes a mathematical model, in which a Discounted Cash Flow analysis is conducted to evaluate the financial feasibility of photovoltaic-integrated lead acid battery systems in Italy. The indicator used is Net Present Value. Furthermore, a break-even point analysis, in terms of an increase of self-consumption, is conducted. The residential sector is investigated and energy storage system investment is incentivized by fiscal deduction and regional subsidies. The analysis provides several case studies, determined by combinations of the following variables: photovoltaic plant size, battery capacity, the increase of the share of self-consumption, and the useful lifetime of energy storage system. The same case studies are proposed also in four alternative scenarios, where is the modified the structure of subsidies. Results confirm that the profitability can be reached in presence of subsidies. Full article

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

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18 pages, 3536 KiB

Open AccessArticle

Subsynchronous Torsional Interaction of Wind Farms with FSIG Wind Turbines Connected to LCC-HVDC Lines

by Benfeng Gao¹, Ruixue Zhang^1,*, Ren Li¹, Hongyang Yu² and Guoliang Zhao²

¹ Department of Electrical Engineering, North China Electric Power University, Baoding 071003, China

² State Key Laboratory of Advanced Power Transmission Technology (Global Energy Interconnection Research Institute), Beijing 102209, China

Energies 2017, 10(9), 1435; https://doi.org/10.3390/en10091435 - 18 Sep 2017

Cited by 10 | Viewed by 3978

Abstract

High-voltage direct current (HVDC) lines with line-commutated converter (LCC) are being increasingly employed to transmit bulk wind power over long distance. However, this may cause the sub-synchronous torsional interaction (SSTI) between the wind farms and the LCC-HVDC system. The SSTI characteristics of wind [...] Read more.

High-voltage direct current (HVDC) lines with line-commutated converter (LCC) are being increasingly employed to transmit bulk wind power over long distance. However, this may cause the sub-synchronous torsional interaction (SSTI) between the wind farms and the LCC-HVDC system. The SSTI characteristics of wind farms with fixed-speed induction generator (FSIG) wind turbines connected to LCC-HVDC are investigated in this paper. To simplify the calculations, a modular modeling method is proposed for building the small-signal mathematical model of the investigated system. Small-signal analysis, participation factor analysis, and impact of dominant factors analysis are then applied to investigate the SSTI characteristics under different operating conditions. Three oscillation modes associated with the SSTI are identified in the entire system through small-signal and participation factor analysis, comprising two torsional modes and an electromechanical mode. Impact of dominant factors analysis shows that the system becomes less stable as the wind farm capacity grows and the distance between FSIG wind farm and the rectifier station increases. Moreover, the above analysis suggests that wind farms with FSIG connected to LCC-HVDC lines may not cause unstable SSTI. The electromagnetic transient simulations based on PSCAD/EMTDC (Power Systems Computer-Aided Design/Electromagnetic Transients including DC) verify these results. Full article

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

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14 pages, 2438 KiB

Open AccessFeature PaperArticle

Experimental Model Development of Oxygen-Enriched Combustion Kinetics on Porous Coal Char and Non-Porous Graphite

by Gyeong-Min Kim^1,†

, Jong-Pil Kim^1,†, Kevin Yohanes Lisandy¹ and Chung-Hwan Jeon^1,2,*

¹ School of Mechanical Engineering, Pusan National University, Busan 46241, Korea

² Pusan Clean Coal Center, Pusan National University, Busan 46241, Korea

^† These authors contributed equally to the work.

Energies 2017, 10(9), 1436; https://doi.org/10.3390/en10091436 - 18 Sep 2017

Cited by 8 | Viewed by 5269

Abstract

The effect of oxygen-enriched air on low-rank coal char combustion was experimentally investigated. In this work, a coal-heating reactor equipped with a platinum wire mesh in the reaction chamber was used to analyze the combustion temperature, reaction time, and reaction kinetics. Increasing the [...] Read more.

The effect of oxygen-enriched air on low-rank coal char combustion was experimentally investigated. In this work, a coal-heating reactor equipped with a platinum wire mesh in the reaction chamber was used to analyze the combustion temperature, reaction time, and reaction kinetics. Increasing the oxygen content of the primary combustion air increased the combustion temperature and decreased the reaction time. As the oxygen content increased from 21% to 30%, the average temperature increased by 47.72 K at a setup temperature of 1673 K, and the reaction time decreased by 30.22% at the same temperature. The graphite sample exhibited similar trends in temperature and reaction time, although the degree of change was smaller because the pores produced during char devolatilization expanded the active surface available for oxidation of the char sample. A mathematical model was used to define the intrinsic kinetics of the reaction. As the oxygen content increased from 21% to 30%, the reaction rate of the low-rank coal char increased. These results were also compared with those of the graphite sample. Full article

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

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14 pages, 1829 KiB

Open AccessArticle

A High-Efficient Low-Cost Converter for Capacitive Wireless Power Transfer Systems

by Il-Oun Lee¹

, Joongheon Kim² and Woojoo Lee^3,*

¹ Department of Electrical Engineering, Myongji University, Yongin 17058, Korea

² School of Computer Science and Engineering, Chung-Ang University, Seoul 06974, Korea

³ Department of Electronic Engineering, Myongji University, Yongin 17058, Korea

Energies 2017, 10(9), 1437; https://doi.org/10.3390/en10091437 - 18 Sep 2017

Cited by 7 | Viewed by 4620

Abstract

Growth of the Internet of Things (IoT) spurs need for new ways of delivering power. Wireless power transfer (WPT) has come into the spotlight from both academia and industry as a promising way to power the IoT devices. As one of the well-known [...] Read more.

Growth of the Internet of Things (IoT) spurs need for new ways of delivering power. Wireless power transfer (WPT) has come into the spotlight from both academia and industry as a promising way to power the IoT devices. As one of the well-known WPT techniques, the capacitive power transfer (CPT) has the merit of low electromagnetic radiation and amenability of combined power and data transfer over a capacitive interface. However, applying the CPT to the IoT devices is still challenging in reality. One of the major issues is due to the small capacitance of the capacitive interface, which results in low efficiency of the power transfer. To tackle this problem, we present a new step-up single-switch quasi-resonant (SSQR) converter for the CPT system. To enhance the CPT efficiency, the proposed converter is designed to operate at low frequency and drive small current into the capacitive interfaces. In addition, by eliminating resistor-capacitor-diode (RCD) snubber in the converter, we reduce the implementation cost of the CPT system. Based on intensive experimental work with a CPT system prototype that supports maximum 50 W (100 V/0.5 A) power transfer, we demonstrate the functional correctness of the converter that achieves up to 93% efficiency. Full article

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

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17 pages, 888 KiB

Open AccessArticle

Electricity Interconnection in Chile: Prices versus Costs

by Javier Bustos-Salvagno^* and Fernando Fuentes H.

Faculty of Economics and Business, Universidad Alberto Hurtado, Santiago 8340575, Chile

Energies 2017, 10(9), 1438; https://doi.org/10.3390/en10091438 - 18 Sep 2017

Cited by 11 | Viewed by 5575

Abstract

Having a well-adapted transmission network is key for reaching a sustainable energy system, where generators and consumers participate in an efficient market. The purpose of the present research is to estimate the impact on the final prices of the interconnection of the two [...] Read more.

Having a well-adapted transmission network is key for reaching a sustainable energy system, where generators and consumers participate in an efficient market. The purpose of the present research is to estimate the impact on the final prices of the interconnection of the two largest electrical systems in Chile. To this end, an econometric model is used in which prices, among other variables, are explained by the level of marginal costs in the system (opportunity cost), the degree of concentration in the market (market power), and the variability of marginal costs projected by the agents (risk). The data corresponds to bilateral contracts between generators and major clients, from 2006 to 2014. The basic results indicate that the interconnection would benefit final customers by reducing equilibrium contract prices, as a result of the decreased variability of expected marginal costs and a lower concentration of existing generating companies. This study’s main contribution is to focus on the benefits of electricity interconnection under conditions of competition and risk, instead of using the simple estimation of direct costs, as has traditionally been done. Full article

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16 pages, 13391 KiB

Open AccessArticle

Geostatistical Three-Dimensional Modeling of a Tight Gas Reservoir: A Case Study of Block S6 of the Sulige Gas Field, Ordos Basin, China

by Jinliang Zhang^*, Longlong Liu^* and Ruoshan Wang

College of Resources Science and Technology, Faculty of Geographical Science, Beijing Normal University, Beijing 100875, China

Energies 2017, 10(9), 1439; https://doi.org/10.3390/en10091439 - 18 Sep 2017

Cited by 6 | Viewed by 4503

Abstract

In this study, three-dimensional (3-D) geostatistical models were constructed to quantify distributions of sandstone and mudstone. We propose a new method that employs weight coefficients to balance the sandstone and mudstone data from irregular well patterns during stochastic modeling. This new method begins [...] Read more.

In this study, three-dimensional (3-D) geostatistical models were constructed to quantify distributions of sandstone and mudstone. We propose a new method that employs weight coefficients to balance the sandstone and mudstone data from irregular well patterns during stochastic modeling. This new method begins with classifying well groups according to well distribution patterns; areas with similar well distribution patterns are classified within the same zone. Then, the distributions of sandstone and mudstone for each zone are simulated separately using the sequential indicator simulation (SIS) method, and the relevant variogram parameters for each zone are computed. In this paper, we used block S6 of the Sulige Gas Field in Ordos Basin in China as a case study. We evaluated the quality of each set of parameters through the vacuation checking method; certain wells were removed to generate equiprobable realizations using different seed numbers. Subsequently, the variogram parameters for the entire S6 area were obtained by assigning different weight coefficients to the parameters of each zone. Finally, a quality assessment of the sandstone and mudstone models of the S6 area was conducted using the horizontal wells, which were not involved in the stochastic modeling process. The results show that these variogram parameters, which were calculated using weight coefficients, are reliable. Full article

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17 pages, 852 KiB

Open AccessFeature PaperArticle

Application of Dynamic Non-Linear Programming Technique to Non-Convex Short-Term Hydrothermal Scheduling Problem

by Omid Hoseynpour¹, Behnam Mohammadi-ivatloo¹, Morteza Nazari-Heris¹ and Somayeh Asadi^2,*

¹ Smart Energy Systems Laboratory, Faculty of Electrical and Computer Engineering, University of Tabriz, Tabriz 51666-15813, Iran

² Department of Architectural Engineering, Pennsylvania State University, 104 Engineering Unit A, University Park, PA 16802, USA

Energies 2017, 10(9), 1440; https://doi.org/10.3390/en10091440 - 19 Sep 2017

Cited by 33 | Viewed by 5702

Abstract

Short-term hydro-thermal scheduling aims to obtain optimal generation scheduling of hydro and thermal units for a one-day or a one-week scheduling time horizon. The main goal of the problem is to minimize total operational cost considering a series of equality and inequality constraints. [...] Read more.

Short-term hydro-thermal scheduling aims to obtain optimal generation scheduling of hydro and thermal units for a one-day or a one-week scheduling time horizon. The main goal of the problem is to minimize total operational cost considering a series of equality and inequality constraints. The problem is considered as a non-linear and complex problem involving the valve-point loading effect of conventional thermal units, the water transport delay between connected reservoirs, and transmission loss with a set of equality and inequality constraints such as power balance, water dynamic balance, water discharge, initial and end reservoir storage volume, reservoir volume limits and the operation limits of hydro and thermal plants. A solution methodology to the short-term hydro-thermal scheduling problem with continuous and non-smooth/non-convex cost function is introduced in this research applying dynamic non-linear programming. In this study, the proposed approach is applied to two test systems with different characteristics. The simulation results obtained in this paper are compared with those reported in recent research studies, which show the effectiveness of the presented technique in terms of total operational cost. In addition, the obtained results ensure the capability of the proposed optimization procedure for solving short-term hydro-thermal scheduling problem with transmission losses and valve-point effects. Full article

(This article belongs to the Special Issue Hydropower 2017)

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23 pages, 5225 KiB

Open AccessArticle

Generic Type 3 Wind Turbine Model Based on IEC 61400-27-1: Parameter Analysis and Transient Response under Voltage Dips

by Alberto Lorenzo-Bonache^1,*, Andrés Honrubia-Escribano¹

, Francisco Jiménez-Buendía², Ángel Molina-García³

and Emilio Gómez-Lázaro¹

¹ Renewable Energy Research Institute and DIEEAC-EDII-AB, Universidad de Castilla-La Mancha, 02071 Albacete, Spain

² Siemens Gamesa Renewable Energy, S.A., 31621 Pamplona, Spain

³ Department of Electrical Engineering, Universidad Politécnica de Cartagena, 30202 Cartagena, Spain

Energies 2017, 10(9), 1441; https://doi.org/10.3390/en10091441 - 19 Sep 2017

Cited by 21 | Viewed by 8591

Abstract

This paper analyzes the response under voltage dips of a Type 3 wind turbine topology based on IEC 61400-27-1. The evolution of both active power and rotational speed is discussed in detail when some of the most relevant control parameters, included in the [...] Read more.

This paper analyzes the response under voltage dips of a Type 3 wind turbine topology based on IEC 61400-27-1. The evolution of both active power and rotational speed is discussed in detail when some of the most relevant control parameters, included in the mechanical, active power and pitch control models, are modified. Extensive results are also included to explore the influence of these parameters on the model dynamic response. This work thus provides an extensive analysis of the generic Type 3 wind turbine model and provides an estimation of parameters not previously discussed in the specific literature. Indeed, the International Standard IEC 61400-27-1, recently published in February 2015, defines these generic dynamic simulation models for wind turbines, but does not provide values for the parameters to simulate the response of these models. Thus, there is a pressing need to establish correlations between IEC generic models and specific wind turbine manufacturer models to estimate suitable parameters for simulation purposes. Extensive results and simulations are also included in the paper. Full article

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

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24 pages, 8029 KiB

Open AccessArticle

Techno-Economic Assessment of Wind Energy Potential at Three Locations in South Korea Using Long-Term Measured Wind Data

by Sajid Ali^1,2, Sang-Moon Lee² and Choon-Man Jang^1,2,*

¹ Smart City Construction Engineering, University of Science & Technology (UST), 217, Gajeong-ro, Yuseong-gu, Daejeon 34113, Korea

² Environmental & Plant Engineering Research Division, Korea Institute of Civil Engineering and Building Technology (KICT), Daehwa-dong 283, Goyangdae-Ro, Ilsanseo-Gu, Goyang-Si, Gyeonggi-do 10223, Korea

Energies 2017, 10(9), 1442; https://doi.org/10.3390/en10091442 - 19 Sep 2017

Cited by 46 | Viewed by 8771

Abstract

The present study deals with wind energy analysis and the selection of an optimum type of wind turbine in terms of the feasibility of installing wind power system at three locations in South Korea: Deokjeok-do, Baengnyeong-do and Seo-San. The wind data measurements were [...] Read more.

The present study deals with wind energy analysis and the selection of an optimum type of wind turbine in terms of the feasibility of installing wind power system at three locations in South Korea: Deokjeok-do, Baengnyeong-do and Seo-San. The wind data measurements were conducted during 2005–2015 at Deokjeok-do, 2001–2016 at Baengnyeong-do and 1997–2016 at Seo-San. In the first part of this paper wind conditions, like mean wind speed, wind rose diagrams and Weibull shape and scale parameters are presented, so that the wind potential of all the locations could be assessed. It was found that the prevailing wind directions at all locations was either southeast or southwest in which the latter one being more dominant. After analyzing the wind conditions, 50-year and 1-year extreme wind speeds (EWS) were estimated using the graphical method of Gumbel distribution. Finally, according to the wind conditions at each site and international electro-technical commission (IEC) guidelines, a set of five different wind turbines best suited for each location were shortlisted. Each wind turbine was evaluated on the basis of technical parameters like monthly energy production, annual energy production (AEP) and capacity factors (CF). Similarly, economical parameters including net present value (NPV), internal rate of return (IRR), payback period (PBP) and levelized cost of electricity (LCOE) were considered. The analysis shows that a Doosan model WinDS134/3000 wind turbine is the most suitable for Deokjeok-do and Baengnyeong-do, whereas a Hanjin model HJWT 87/2000 is the most suitable wind turbine for Seo-San. Economic sensitivity analysis is also included and discussed in detail to analyze the impact on economics of wind power by varying turbine’s hub height. Full article

(This article belongs to the Collection Wind Turbines)

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16 pages, 465 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Control Strategies for Improving Energy Efficiency and Reliability in Autonomous Microgrids with Communication Constraints

by Francisco Martins Portelinha Júnior^1,2,*, Antonio Carlos Zambroni de Souza²

, Miguel Castilla³

, Denisson Queiroz Oliveira⁴ and Paulo Fernando Ribeiro²

¹ Radiocommunications Reference Center (CRR) - National Institute of Telecomunications (INATEL), Av. João de Camargo, 510, Santa Rita do Sapucaí 37540-000, Brazil

² Federal University of Itajubá, Av. BPS, 1903, Pinheirinho, Itajubá 37540-000, Brazil

³ Technical University of Catalunya, 08800 Vilanova i la Geltrù, Spain

⁴ Federal University of Maranhão, Av. Portugueses 1966, São Luis 65080-805, Brazil

Energies 2017, 10(9), 1443; https://doi.org/10.3390/en10091443 - 19 Sep 2017

Cited by 14 | Viewed by 5388

Abstract

Microgrids are a feasible path to deploy smart grids, an intelligent and highly automated power system. Their operation demands a dedicated communication infrastructure to manage, control and monitor the intermittent sources of energy and loads. Therefore, smart devices will be connected to support [...] Read more.

Microgrids are a feasible path to deploy smart grids, an intelligent and highly automated power system. Their operation demands a dedicated communication infrastructure to manage, control and monitor the intermittent sources of energy and loads. Therefore, smart devices will be connected to support the growth of grid smartness increasing the dependency on communication networks, which consumes a high amount of power. In an energy-limited scenario, one of the main issues is to enhance the power supply time. Therefore, this paper proposes a hybrid methodology for microgrid energy management, integrated with a communication infrastructure to improve and to optimize islanded microgrid operation at maximum energy efficiency. The hybrid methodology applies some control management rules, such as intentional load shedding, priority load management, and communication energy saving. These energy saving rules establish a trade-off between increasing microgrid energy availability and communication system reliability. To achieve a compromised solution, a continuous time Markov chain model describes the impact of energy saving policies into system reliability. The proposed methodology is simulated and tested with the help of the modified IEEE 34 node test-system. Full article

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

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16 pages, 957 KiB

Open AccessArticle

Optimal Analytical Solution for a Capacitive Wireless Power Transfer System with One Transmitter and Two Receivers

by Ben Minnaert^*

and Nobby Stevens

Research Group DraMCo, ESAT, Technology Campus Ghent, KU Leuven, 9000 Gent, Belgium

Energies 2017, 10(9), 1444; https://doi.org/10.3390/en10091444 - 19 Sep 2017

Cited by 17 | Viewed by 5092

Abstract

Wireless power transfer from one transmitter to multiple receivers through inductive coupling is slowly entering the market. However, for certain applications, capacitive wireless power transfer (CWPT) using electric coupling might be preferable. In this work, we determine closed-form expressions for a CWPT system [...] Read more.

Wireless power transfer from one transmitter to multiple receivers through inductive coupling is slowly entering the market. However, for certain applications, capacitive wireless power transfer (CWPT) using electric coupling might be preferable. In this work, we determine closed-form expressions for a CWPT system with one transmitter and two receivers. We determine the optimal solution for two design requirements: (i) maximum power transfer, and (ii) maximum system efficiency. We derive the optimal loads and provide the analytical expressions for the efficiency and power. We show that the optimal load conductances for the maximum power configuration are always larger than for the maximum efficiency configuration. Furthermore, it is demonstrated that if the receivers are coupled, this can be compensated for by introducing susceptances that have the same value for both configurations. Finally, we numerically verify our results. We illustrate the similarities to the inductive wireless power transfer (IWPT) solution and find that the same, but dual, expressions apply. Full article

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

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19 pages, 5115 KiB

Open AccessArticle

Assessment of the Anticipated Environmental Footprint of Future Nuclear Energy Systems. Evidence of the Beneficial Effect of Extensive Recycling

by Jérôme Serp, Christophe Poinssot and Stéphane Bourg^*

French Nuclear and Alternative Energies Commission, Nuclear Energy Division, Research Department on Mining and Fuel Recycling Processes, CEA Marcoule, F-30207 Bagnols sur Ceze, France

Energies 2017, 10(9), 1445; https://doi.org/10.3390/en10091445 - 19 Sep 2017

Cited by 46 | Viewed by 8559

Abstract

In this early 21st century, our societies have to face a tremendous and increasing energy need while mitigating the global climate change and preserving the environment. Addressing this challenge requires an energy transition from the current fossil energy-based system to a carbon-free energy [...] Read more.

In this early 21st century, our societies have to face a tremendous and increasing energy need while mitigating the global climate change and preserving the environment. Addressing this challenge requires an energy transition from the current fossil energy-based system to a carbon-free energy production system, based on a relevant energy mix combining renewables and nuclear energy. However, such an energy transition will only occur if it is accepted by the population. Powerful and reliable tools, such as life cycle assessments (LCA), aiming at assessing the respective merits of the different energy mix for most of the environmental impact indicators are therefore mandatory for supporting a risk-informed decision-process at the societal level. Before studying the deployment of a given energy mix, a prerequisite is to perform LCAs on each of the components of the mix. This paper addresses two potential nuclear energy components: a nuclear fuel cycle based on the Generation III European Pressurized Reactors (EPR) and a nuclear fuel cycle based on the Generation IV Sodium Fast Reactors (SFR). The basis of this study relies on the previous work done on the current French nuclear fuel cycle using the bespoke NELCAS tool specifically developed for studying nuclear fuel cycle environmental impacts. Our study highlights that the EPR already brings a limited improvement to the current fuel cycle thanks to a higher efficiency of the energy transformation and a higher burn-up of the nuclear fuel (−20% on most of the chosen indicators) whereas the introduction of the GEN IV fast reactors will bring a significant breakthrough by suppressing the current front-end of the fuel cycle thanks to the use of depleted uranium instead of natural enriched uranium (this leads to a decrease of the impact from 17% on water consumption and withdrawal and up to 96% on SO_x emissions). The specific case of the radioactive waste is also studied, showing that only the partitioning and transmutation of the americium in the blanket fuel of the SFR can reduce the footprint of the geological disposal (saving up to a factor of 7 on the total repository volume). Having now at disposition five models (open fuel cycle, current French twice through fuel cycle, EPR twice through fuel cycle, multi-recycling SFR fuel cycle and at a longer term, multi-recycling SFR fuel cycle including americium transmutation), it is possible to model the environmental impact of any fuel cycle combining these technologies. In the next step, these models will be combined with those of other carbon-free energies (wind, solar, biomass…) in order to estimate the environmental impact of future energy mixes and also to analyze the impact on the way these scenarios are deployed (transition pathways). Full article

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Review

Jump to: Editorial, Research, Other

29 pages, 6130 KiB

Open AccessReview

Frequency Regulation Strategies in Grid Integrated Offshore Wind Turbines via VSC-HVDC Technology: A Review

by Jafar Jallad^1,2, Saad Mekhilef¹

and Hazlie Mokhlis^2,*

¹ Power Electronics and Renewable Energy Research Laboratory (PEARL), Department of Electrical Engineering, University of Malaya, Kuala Lumpur 50603, Malaysia

² Department of Electrical Engineering, University of Malaya, Kuala Lumpur 50603, Malaysia

Energies 2017, 10(9), 1244; https://doi.org/10.3390/en10091244 - 23 Aug 2017

Cited by 22 | Viewed by 8220

Abstract

The inclusion of wind energy in a power system network is currently seeing a significant increase. However, this inclusion has resulted in degradation of the inertia response, which in turn seriously affects the stability of the power system’s frequency. This problem can be [...] Read more.

The inclusion of wind energy in a power system network is currently seeing a significant increase. However, this inclusion has resulted in degradation of the inertia response, which in turn seriously affects the stability of the power system’s frequency. This problem can be solved by using an active power reserve to stabilize the frequency within an allowable limit in the event of a sudden load increment or the loss of generators. Active power reserves can be utilized via three approaches: (1) de-loading method (pitching or over-speeding) by a variable speed wind turbine (VSWT); (2) stored energy in the capacitors of voltage source converter-high voltage direct current (VSC-HVDC) transmission; and (3) coordination of frequency regulation between the offshore wind farms and the VSC-HVDC transmission. This paper reviews the solutions that can be used to overcome problems related to the frequency stability of grid- integrated offshore wind turbines. It also details the permanent magnet synchronous generator (PMSG) with full-scale back to back (B2B) converters, its corresponding control strategies, and a typical VSC-HVDC system with an associated control system. The control methods, both on the levels of a wind turbine and the VSC-HVDC system that participate in a system’s primary frequency control and emulation inertia, are discussed. Full article

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

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32 pages, 7508 KiB

Open AccessEditor’s ChoiceReview

Models for Flow Rate Simulation in Gear Pumps: A Review

by Massimo Rundo

Department of Energy, Politecnico di Torino, 10129 Turin, Italy

Energies 2017, 10(9), 1261; https://doi.org/10.3390/en10091261 - 24 Aug 2017

Cited by 108 | Viewed by 18606

Abstract

Gear pumps represent the majority of the fixed displacement machines used for flow generation in fluid power systems. In this context, the paper presents a review of the different methodologies used in the last years for the simulation of the flow rates generated [...] Read more.

Gear pumps represent the majority of the fixed displacement machines used for flow generation in fluid power systems. In this context, the paper presents a review of the different methodologies used in the last years for the simulation of the flow rates generated by gerotor, external gear and crescent pumps. As far as the lumped parameter models are concerned, different ways of selecting the control volumes into which the pump is split are analyzed and the main governing equations are presented. The principles and the applications of distributed models from 1D to 3D are reported. A specific section is dedicated to the methods for the evaluation of the necessary geometric quantities: analytic, numerical and Computer-Aided Design (CAD)-based. The more recent studies taking into account the influence on leakages of the interactions between the fluid and the mechanical parts are explained. Finally the models for the simulation of the fluid aeration are described. The review brings to evidence the increasing effort for improving the simulation models used for the design and the optimization of the gear machines. Full article

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

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27 pages, 1790 KiB

Open AccessReview

Overview of AC Microgrid Controls with Inverter-Interfaced Generations

by Md Alamgir Hossain^1,*

, Hemanshu Roy Pota¹, Walid Issa²

and Md Jahangir Hossain³

¹ School of Engineering & Information Technology, The University of New South Wales, Canberra, ACT 2610, Australia

² Department of Engineering and Mathematics, Sheffield Hallam University, Sheffield S1 1WB, UK

³ Department of Engineering, Macquarie University, Sydney, NSW 2109, Australia

Energies 2017, 10(9), 1300; https://doi.org/10.3390/en10091300 - 30 Aug 2017

Cited by 186 | Viewed by 15768

Abstract

Distributed generation (DG) is one of the key components of the emerging microgrid concept that enables renewable energy integration in a distribution network. In DG unit operation, inverters play a vital role in interfacing energy sources with the grid utility. An effective interfacing [...] Read more.

Distributed generation (DG) is one of the key components of the emerging microgrid concept that enables renewable energy integration in a distribution network. In DG unit operation, inverters play a vital role in interfacing energy sources with the grid utility. An effective interfacing can successfully be accomplished by operating inverters with effective control techniques. This paper reviews and categorises different control methods (voltage and primary) for improving microgrid power quality, stability and power sharing approaches. In addition, the specific characteristics of microgrids are summarised to distinguish from distribution network control. Moreover, various control approaches including inner-loop controls and primary controls are compared according to their relative advantages and disadvantages. Finally, future research trends for microgrid control are discussed pointing out the research opportunities. This review paper will be a good basis for researchers working in microgrids and for industry to implement the ongoing research improvement in real systems. 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, 1834 KiB

Open AccessReview

Recent Trends in Load Forecasting Technology for the Operation Optimization of Distributed Energy System

by Pengwei Su, Xue Tian, Yan Wang, Shuai Deng^*, Jun Zhao, Qingsong An and Yongzhen Wang

Key Laboratory of Efficient Utilization of Low and Medium Grade Energy, Ministry of Education, Tianjin University, Tianjin 300350, China

Energies 2017, 10(9), 1303; https://doi.org/10.3390/en10091303 - 31 Aug 2017

Cited by 40 | Viewed by 5323

Abstract

The introduction of renewable resources into the distributed energy system has challenged the operation optimization of the distributed energy system. Integration of new technologies and diversified characteristics on the demand side has exerted a great influence on the distributed energy system. In this [...] Read more.

The introduction of renewable resources into the distributed energy system has challenged the operation optimization of the distributed energy system. Integration of new technologies and diversified characteristics on the demand side has exerted a great influence on the distributed energy system. In this paper, by way of literature review, first, the topological structure and the mathematical expression of the distributed energy system were summarized, and the trend of enrichment and diversification and the new characteristics of the system were evaluated. Then, the load forecasting technology was reviewed and analyzed from two aspects, fundamental research and application research. Research methods of the distributed energy system under the new trend of energies were discussed, and the boundaries of the broadened distributed energy technology were explored. Full article

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21 pages, 2468 KiB

Open AccessReview

Encapsulated Nitrates Phase Change Material Selection for Use as Thermal Storage and Heat Transfer Materials at High Temperature in Concentrated Solar Power Plants

by Gustavo Cáceres¹, Karina Fullenkamp^1,*, Macarena Montané¹, Krzysztof Naplocha² and Anna Dmitruk²

¹ Facultad de Ingeniería y Ciencias, Universidad Adolfo Ibáñez, Avenida Diagonal Las Torres 2640, Peñalolén, Santiago 7941169, Chile

² Faculty of Mechanical Engineering, Wroclaw University of Science and Technology, Lukasiewicza 5, 50-370 Wroclaw, Poland

Energies 2017, 10(9), 1318; https://doi.org/10.3390/en10091318 - 1 Sep 2017

Cited by 28 | Viewed by 5945

Abstract

In the present paper, the finite element method is used to perform an exhaustive analysis of the thermal behavior of encapsulated phase change materials (EPCMs), which includes an assessment of several materials in order to identify the best combination of PCM and shell [...] Read more.

In the present paper, the finite element method is used to perform an exhaustive analysis of the thermal behavior of encapsulated phase change materials (EPCMs), which includes an assessment of several materials in order to identify the best combination of PCM and shell material in terms of thermal energy storage, heat transfer rate, cost of materials, limit of pressure that they can support and other criteria. It is possible to enhance the heat transfer rate without a considerable decrease of the thermal energy storage density, by increasing the thickness of the shell. In the first examination of thermomechanical coupling effects, the technical feasibility can be determined if the EPCM dimensions are designed considering the thermal expansion and the tensile strength limit of the materials. Moreover, when a proper EPCM shell material and PCM composition is used, and compared with the current storage methods of concentrated solar power (CSP) plants, the use of EPCM allows one to enhance significantly the thermal storage, reaching more than 1.25 GJ/m³ of energy density. Full article

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

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18 pages, 1977 KiB

Open AccessFeature PaperReview

The Mutual Impact of Demand Response Programs and Renewable Energies: A Survey

by Neda Hajibandeh^1,2, Mehdi Ehsan^1,3,*, Soodabeh Soleymani¹, Miadreza Shafie-khah²

and João P. S. Catalão^2,4,5,*

¹ Department Electrical & Computer Engineering, Science and Research Branch, Islamic Azad University, Tehran 14778-93855, Iran

² Center for Mechanical and Aerospace Science and Technologies (C-MAST), University of Beira Interior, 6201-001 Covilhã, Portugal

³ Department Electrical Engineering, Sharif University of Technology, Tehran 11155-8639, Iran

⁴ Instituto de Engenharia de Sistemas e Computadores, Tecnologia e Ciência (INESC TEC), Faculty of Engineering, University of Porto, 4200-465 Porto, Portugal

⁵ Instituto de Engenharia de Sistemas e Computadores, Investigação e Desenvolvimento (INESC-ID), Instituto Superior Técnico, University of Lisbon, 1049-001 Lisbon, Portugal

Energies 2017, 10(9), 1353; https://doi.org/10.3390/en10091353 - 7 Sep 2017

Cited by 15 | Viewed by 5725

Abstract

Renewable energies as a solution for environmental issues have always been a key research area due to Demand Response Programs (DRPs). However, the intermittent nature of such energies may cause economic and technological challenges for Independent System Operators (ISOs) besides DRPs, since the [...] Read more.

Renewable energies as a solution for environmental issues have always been a key research area due to Demand Response Programs (DRPs). However, the intermittent nature of such energies may cause economic and technological challenges for Independent System Operators (ISOs) besides DRPs, since the acceptable effective solution may exceed the requirement of further investigations. Although, previous studies emphasized employing Demand Response and Renewable Energies in power systems, each problem was investigated independently, and there have been few studies which have investigated these problems simultaneously. In these recent studies, authors neither analyzed these problems simultaneously nor discussed which scientific and practical aspects of demand response and renewable energy injection were employed. Motivated by this requirement, this research has focused on a comprehensive review of recent research of these cases to provide a comprehensive reference for future works. Full article

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48 pages, 575 KiB

Open AccessReview

Towards Improved Understanding of the Applicability of Uncertainty Forecasts in the Electric Power Industry

by Ricardo J. Bessa^1,*

, Corinna Möhrlen²

, Vanessa Fundel³, Malte Siefert⁴, Jethro Browell⁵

, Sebastian Haglund El Gaidi⁶, Bri-Mathias Hodge⁷, Umit Cali⁸ and George Kariniotakis⁹

¹ INESC Technology and Science (INESC TEC), 4200-465 Porto, Portugal

² WEPROG, 5610 Assens, Denmark

³ Deutscher Wetterdienst, 63067 Offenbach, Germany

⁴ Fraunhofer Institute for Wind Energy and Energy System Technology (IWES), 34119 Kassel, Germany

⁵ University of Strathclyde, Department of Electronic and Electrical Engineering, Glasgow G1 1XQ, UK

⁶ Royal Institute of Technology, Department of Mechanics, SE-100 44 Stockholm, Sweden

⁷ National Renewable Energy Laboratory, Golden, CO 80401, USA

⁸ University of North Carolina Charlotte, Dept. of Engineering Technology and Construction Management, Charlotte, NC 28223, USA

⁹ MINES ParisTech, PSL Research University, Centre for Processes, Renewable Energies and Energy Systems (PERSEE), 06904 Sophia Antipolis Cedex, France

Energies 2017, 10(9), 1402; https://doi.org/10.3390/en10091402 - 14 Sep 2017

Cited by 95 | Viewed by 12737

Abstract

Around the world wind energy is starting to become a major energy provider in electricity markets, as well as participating in ancillary services markets to help maintain grid stability. The reliability of system operations and smooth integration of wind energy into electricity markets [...] Read more.

Around the world wind energy is starting to become a major energy provider in electricity markets, as well as participating in ancillary services markets to help maintain grid stability. The reliability of system operations and smooth integration of wind energy into electricity markets has been strongly supported by years of improvement in weather and wind power forecasting systems. Deterministic forecasts are still predominant in utility practice although truly optimal decisions and risk hedging are only possible with the adoption of uncertainty forecasts. One of the main barriers for the industrial adoption of uncertainty forecasts is the lack of understanding of its information content (e.g., its physical and statistical modeling) and standardization of uncertainty forecast products, which frequently leads to mistrust towards uncertainty forecasts and their applicability in practice. This paper aims at improving this understanding by establishing a common terminology and reviewing the methods to determine, estimate, and communicate the uncertainty in weather and wind power forecasts. This conceptual analysis of the state of the art highlights that: (i) end-users should start to look at the forecast’s properties in order to map different uncertainty representations to specific wind energy-related user requirements; (ii) a multidisciplinary team is required to foster the integration of stochastic methods in the industry sector. A set of recommendations for standardization and improved training of operators are provided along with examples of best practices. Full article

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

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14 pages, 3495 KiB

Open AccessReview

Life Cycle Analysis of Endosymbiotic Algae in an Endosymbiotic Situation with Paramecium bursaria Using Capillary Flow Cytometry

by Toshiyuki Takahashi

Department of Chemical Science and Engineering, National Institute of Technology, Miyakonojo College, Miyazaki 885-8567, Japan

Energies 2017, 10(9), 1413; https://doi.org/10.3390/en10091413 - 15 Sep 2017

Cited by 7 | Viewed by 7810

Abstract

Along with algae as producers in ecosystems and industrial applications, some microalgae existing in special ecological niches through endosymbiosis with other organisms represent fascinating examples of biological evolution. Although reproducing endosymbiosis experimentally is difficult in many situations, endosymbiosis of several ongoing types is [...] Read more.

Along with algae as producers in ecosystems and industrial applications, some microalgae existing in special ecological niches through endosymbiosis with other organisms represent fascinating examples of biological evolution. Although reproducing endosymbiosis experimentally is difficult in many situations, endosymbiosis of several ongoing types is possible. Endosymbiosis in Paramecium bursaria is a particularly excellent model. Although many studies of P. bursaria have specifically examined infection processes such as the host recognition of symbionts, coordination of host-symbiont division, which has been explored for eukaryotic organelles, is worth pursuing. Evaluating the cell (life) cycle of algae is crucially important for algal applications. Flow cytometry (FCM) has been used to study cell cycles of several eukaryotic cells including microalgae. Microscopy, however, has been used mainly to study endosymbiosis, as with P. bursaria, because of their larger size than suitable cells for FCM with hydrodynamic focusing. Vast amounts of time have been expended for microscopic analysis. This review presents an approach using capillary FCM to elucidate the endosymbiosis of P. bursaria. Results reveal that endosymbiotic algae of P. bursaria finely adjust their cell cycle schedule with their comfortable host and show that a coincident endosymbiont–host life cycle is virtually assured in their endosymbiosis. Full article

(This article belongs to the Special Issue Algae Fuel 2017)

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14 pages, 1981 KiB

Open AccessReview

State-Of-The-Art in Microgrid-Integrated Distributed Energy Storage Sizing

by Ibrahim Alsaidan¹, Abdulaziz Alanazi¹, Wenzhong Gao¹, Hongyu Wu²

and Amin Khodaei^1,*

¹ Department of Electrical and Computer Engineering, University of Denver, Denver, CO 80210, USA

² Department of Electrical and Computer Engineering, Kansas State University, Manhattan, KS 66506, USA

Energies 2017, 10(9), 1421; https://doi.org/10.3390/en10091421 - 16 Sep 2017

Cited by 42 | Viewed by 6588

Abstract

Distributed energy storage (DES) plays an important role in microgrid operation and control, as it can potentially improve local reliability and resilience, reduce operation cost, and mitigate challenges caused by high penetration renewable generation. However, to ensure an acceptable economic and technical performance, [...] Read more.

Distributed energy storage (DES) plays an important role in microgrid operation and control, as it can potentially improve local reliability and resilience, reduce operation cost, and mitigate challenges caused by high penetration renewable generation. However, to ensure an acceptable economic and technical performance, DES must be optimally sized and placed. This paper reviews the existing DES sizing methods for microgrid applications and presents a generic sizing method that enables microgrid planners to efficiently determine the optimal DES size, technology, and location. The proposed method takes into consideration the impact of DES operation on its lifetime to enhance the obtained results accuracy and practicality. The presented model can be used for both grid-tied (considering both grid-connected and islanded modes) and isolated microgrids. Full article

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

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Other

Jump to: Editorial, Research, Review

11 pages, 5546 KiB

Open AccessTechnical Note

Brazilian Test for Tensile Failure of Anisotropic Shale under Different Strain Rates at Quasi-static Loading

by Yu Wang¹, Changhong Li^1,*, Yanzhi Hu² and Tianqiao Mao²

¹ Beijing Key Laboratory of Urban Underground Space Engineering, Department of Civil Engineering, School of Civil & Resource Engineering, University of Science & Technology Beijing, Beijing 100083, China

² Key Laboratory of Shale Gas and Geoengineering, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029,China

Energies 2017, 10(9), 1324; https://doi.org/10.3390/en10091324 - 2 Sep 2017

Cited by 24 | Viewed by 7968

Abstract

Shale formations show obvious anisotropic characteristics in their mechanical properties due to pronounced bedding planes and natural fractures. This anisotropic behavior generally creates complex fracturing networks and is crucial to gas shale stimulation. Although much research has been done to study the anisotropic [...] Read more.

Shale formations show obvious anisotropic characteristics in their mechanical properties due to pronounced bedding planes and natural fractures. This anisotropic behavior generally creates complex fracturing networks and is crucial to gas shale stimulation. Although much research has been done to study the anisotropic compression behaviors of shale with static and quasi-static strain rates, there are limited investigations addressing the anisotropic tensile behaviors of shale at quasi-static strain rate. In this work, the anisotropic tensile behaviors of Longmaxi shales were studied systematically at different strain rates from 10⁻⁵ to 10⁻² s⁻¹ by performing Brazilian splitting tests. Testing results reveal the tensile strength anisotropy, rate dependency, and the stimulated fracture pattern morphology. The results show that the orientation between the applied force and bedding direction has an obvious effect on the tensile strength and fracture pattern. The rate dependency of shale under different loading rates is different for shale samples with various orientations. It was suggested that a complex tensile fracture pattern can be easily formed when using a high loading rate. The result sheds light on how to stimulate a complex fracturing network during field hydraulic fracturing treatment. Full article

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

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