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Energies, Volume 10, Issue 9 (September 2017)

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Cover Story To date the main issues related to energy consumption in buildings has led to energy efficiency [...] Read more.
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Editorial

Jump to: Research, Review, Other

Open AccessEditorial Advanced Energy Storage Technologies and Their Applications (AESA2017)
Energies 2017, 10(9), 1366; doi:10.3390/en10091366
Received: 24 August 2017 / Revised: 7 September 2017 / Accepted: 7 September 2017 / Published: 9 September 2017
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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

Open AccessArticle Dynamic Pricing for Demand Response Considering Market Price Uncertainty
Energies 2017, 10(9), 1245; doi:10.3390/en10091245
Received: 22 May 2017 / Revised: 14 July 2017 / Accepted: 8 August 2017 / Published: 23 August 2017
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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 Electrical Power and Energy System)
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Open AccessArticle Effects of Loading Rate on Gas Seepage and Temperature in Coal and Its Potential for Coal-Gas Disaster Early-Warning
Energies 2017, 10(9), 1246; doi:10.3390/en10091246
Received: 28 July 2017 / Revised: 11 August 2017 / Accepted: 15 August 2017 / Published: 23 August 2017
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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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Open AccessArticle The Importance of Government Effectiveness for Transitions toward Greater Electrification in Developing Countries
Energies 2017, 10(9), 1247; doi:10.3390/en10091247
Received: 15 June 2017 / Revised: 19 August 2017 / Accepted: 20 August 2017 / Published: 23 August 2017
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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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Open AccessArticle Multivalued Coefficient Prestorage and Block Parallel Method for Real-Time Simulation of Microgrid on FRTDS
Energies 2017, 10(9), 1248; doi:10.3390/en10091248
Received: 16 July 2017 / Revised: 15 August 2017 / Accepted: 17 August 2017 / Published: 23 August 2017
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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 Electrical Power and Energy System)
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Open AccessArticle Numerical Simulation and Optimization of the Melting Process of Phase Change Material inside Horizontal Annulus
Energies 2017, 10(9), 1249; doi:10.3390/en10091249
Received: 16 July 2017 / Revised: 18 August 2017 / Accepted: 20 August 2017 / Published: 23 August 2017
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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 Energy Storage and Application)
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Open AccessArticle A Novel Method for Idle-Stop-Start Control of Micro Hybrid Construction Equipment—Part B: A Real-Time Comparative Study
Energies 2017, 10(9), 1250; doi:10.3390/en10091250
Received: 29 July 2017 / Revised: 16 August 2017 / Accepted: 18 August 2017 / Published: 23 August 2017
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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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Open AccessArticle Exploring Marine Energy Potential in the UK Using a Whole Systems Modelling Approach
Energies 2017, 10(9), 1251; doi:10.3390/en10091251
Received: 5 July 2017 / Revised: 11 August 2017 / Accepted: 16 August 2017 / Published: 23 August 2017
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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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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
Energies 2017, 10(9), 1252; doi:10.3390/en10091252
Received: 29 June 2017 / Revised: 29 July 2017 / Accepted: 18 August 2017 / Published: 23 August 2017
Cited by 1 | PDF Full-text (3739 KB) | HTML Full-text | XML Full-text
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 Energy Sources)
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Open AccessFeature PaperArticle Status Quo of the Air-Conditioning Market in Europe: Assessment of the Building Stock
Energies 2017, 10(9), 1253; doi:10.3390/en10091253
Received: 29 June 2017 / Revised: 11 August 2017 / Accepted: 21 August 2017 / Published: 23 August 2017
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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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Open AccessArticle Acquisition System Verification for Energy Efficiency Analysis of Building Materials
Energies 2017, 10(9), 1254; doi:10.3390/en10091254
Received: 4 July 2017 / Revised: 15 August 2017 / Accepted: 21 August 2017 / Published: 23 August 2017
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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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Open AccessArticle Integrated Bioethanol Fermentation/Anaerobic Digestion for Valorization of Sugar Beet Pulp
Energies 2017, 10(9), 1255; doi:10.3390/en10091255
Received: 3 August 2017 / Revised: 16 August 2017 / Accepted: 18 August 2017 / Published: 23 August 2017
Cited by 1 | PDF Full-text (4833 KB) | HTML Full-text | XML Full-text
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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Open AccessArticle Towards a Residential Air-Conditioner Usage Model for Australia
Energies 2017, 10(9), 1256; doi:10.3390/en10091256
Received: 22 June 2017 / Revised: 18 August 2017 / Accepted: 18 August 2017 / Published: 24 August 2017
Cited by 1 | PDF Full-text (3114 KB) | HTML Full-text | XML Full-text
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 Energy Storage and Application)
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Open AccessArticle A Three-Part Electricity Price Mechanism for Photovoltaic-Battery Energy Storage Power Plants Considering the Power Quality and Ancillary Service
Energies 2017, 10(9), 1257; doi:10.3390/en10091257
Received: 8 July 2017 / Revised: 3 August 2017 / Accepted: 16 August 2017 / Published: 24 August 2017
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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 Energy Storage and Application)
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Open AccessArticle An Intelligent Hybrid Heuristic Scheme for Smart Metering based Demand Side Management in Smart Homes
Energies 2017, 10(9), 1258; doi:10.3390/en10091258
Received: 29 June 2017 / Revised: 11 August 2017 / Accepted: 16 August 2017 / Published: 24 August 2017
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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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Open AccessArticle Analysis of Vibrations in Interior Permanent Magnet Synchronous Motors Considering Air-Gap Deformation
Energies 2017, 10(9), 1259; doi:10.3390/en10091259
Received: 13 July 2017 / Revised: 21 August 2017 / Accepted: 21 August 2017 / Published: 24 August 2017
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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
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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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Open AccessArticle Game-Based Generation Scheduling Optimization for Power Plants Considering Long-Distance Consumption of Wind-Solar-Thermal Hybrid Systems
Energies 2017, 10(9), 1260; doi:10.3390/en10091260
Received: 24 July 2017 / Revised: 13 August 2017 / Accepted: 14 August 2017 / Published: 24 August 2017
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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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Open AccessArticle Layout Optimisation of Wave Energy Converter Arrays
Energies 2017, 10(9), 1262; doi:10.3390/en10091262
Received: 19 July 2017 / Revised: 3 August 2017 / Accepted: 22 August 2017 / Published: 24 August 2017
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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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Open AccessArticle Particulate Matter and Gaseous Emission of Hydrous Ethanol Gasoline Blends Fuel in a Port Injection Gasoline Engine
Energies 2017, 10(9), 1263; doi:10.3390/en10091263
Received: 19 July 2017 / Revised: 13 August 2017 / Accepted: 21 August 2017 / Published: 25 August 2017
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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
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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 (NOx) 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 NOx emission is raised with a rise in engine load, and NOx 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 NOx and HC has been found; the number of particles increases when the NOx 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, NOx, 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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Open AccessArticle Fractionation of Lignocellulosic Residues Coupling Steam Explosion and Organosolv Treatments Using Green Solvent γ-Valerolactone
Energies 2017, 10(9), 1264; doi:10.3390/en10091264
Received: 4 July 2017 / Revised: 11 August 2017 / Accepted: 23 August 2017 / Published: 25 August 2017
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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
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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
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Open AccessArticle Spatial Variation in Sediment Organic Carbon Distribution across the Alaskan Beaufort Sea Shelf
Energies 2017, 10(9), 1265; doi:10.3390/en10091265
Received: 17 June 2017 / Revised: 22 August 2017 / Accepted: 23 August 2017 / Published: 25 August 2017
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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
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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, δ13CTOC values, porewater DOC concentrations, and δ13CDOC 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 CH4AMO-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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Open AccessArticle Electrochemical Model-Based Condition Monitoring via Experimentally Identified Li-Ion Battery Model and HPPC
Energies 2017, 10(9), 1266; doi:10.3390/en10091266
Received: 27 June 2017 / Revised: 17 August 2017 / Accepted: 18 August 2017 / Published: 25 August 2017
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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
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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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Open AccessArticle Achievement of Fuel Savings in Wheel Loader by Applying Hydrodynamic Mechanical Power Split Transmissions
Energies 2017, 10(9), 1267; doi:10.3390/en10091267
Received: 5 July 2017 / Revised: 16 August 2017 / Accepted: 21 August 2017 / Published: 25 August 2017
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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
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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 Energy Storage and Application)
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Open AccessArticle Modelling and Simulation of Electric Vehicle Fast Charging Stations Driven by High Speed Railway Systems
Energies 2017, 10(9), 1268; doi:10.3390/en10091268
Received: 26 June 2017 / Revised: 2 August 2017 / Accepted: 10 August 2017 / Published: 25 August 2017
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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
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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
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Open AccessArticle 3-D FEM Analysis, Prototyping and Tests of an Axial Flux Permanent-Magnet Wind Generator
Energies 2017, 10(9), 1269; doi:10.3390/en10091269
Received: 20 June 2017 / Revised: 22 August 2017 / Accepted: 23 August 2017 / Published: 26 August 2017
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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
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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 Electrical Power and Energy System)
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Open AccessArticle A Decision Framework for Electric Vehicle Charging Station Site Selection for Residential Communities under an Intuitionistic Fuzzy Environment: A Case of Beijing
Energies 2017, 10(9), 1270; doi:10.3390/en10091270
Received: 19 July 2017 / Revised: 21 August 2017 / Accepted: 22 August 2017 / Published: 26 August 2017
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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
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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 Energy Storage and Application)
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Open AccessArticle Multi-Objective Optimal Charging Method for Lithium-Ion Batteries
Energies 2017, 10(9), 1271; doi:10.3390/en10091271
Received: 1 August 2017 / Revised: 18 August 2017 / Accepted: 23 August 2017 / Published: 26 August 2017
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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
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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
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Open AccessArticle An Electro-Geometric Model for Lightning Shielding of Multiple Wind Turbines
Energies 2017, 10(9), 1272; doi:10.3390/en10091272
Received: 20 July 2017 / Revised: 18 August 2017 / Accepted: 24 August 2017 / Published: 26 August 2017
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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,
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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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Open AccessArticle A Principal Components Rearrangement Method for Feature Representation and Its Application to the Fault Diagnosis of CHMI
Energies 2017, 10(9), 1273; doi:10.3390/en10091273
Received: 26 July 2017 / Revised: 20 August 2017 / Accepted: 24 August 2017 / Published: 26 August 2017
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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
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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 Energy Fundamentals and Conversion)
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Open AccessArticle A Study on the Prediction of the Optimum Performance of a Small-Scale Desalination System Using Solar Heat Energy
Energies 2017, 10(9), 1274; doi:10.3390/en10091274
Received: 17 July 2017 / Revised: 22 August 2017 / Accepted: 22 August 2017 / Published: 27 August 2017
PDF Full-text (3479 KB) | HTML Full-text | XML Full-text
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
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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 Energy Storage and Application)
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Open AccessArticle A Novel Locality Algorithm and Peer-to-Peer Communication Infrastructure for Optimizing Network Performance in Smart Microgrids
Energies 2017, 10(9), 1275; doi:10.3390/en10091275
Received: 27 June 2017 / Revised: 19 August 2017 / Accepted: 24 August 2017 / Published: 27 August 2017
PDF Full-text (5965 KB) | HTML Full-text | XML Full-text | Supplementary Files
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
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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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Open AccessArticle Control Structures Evaluation for a Salt Extractive Distillation Pilot Plant: Application to Bio-Ethanol Dehydration
Energies 2017, 10(9), 1276; doi:10.3390/en10091276
Received: 21 July 2017 / Revised: 24 August 2017 / Accepted: 25 August 2017 / Published: 27 August 2017
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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
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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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Open AccessArticle The Effect of Imbalanced Carrier Transport on the Efficiency Droop in GaInN-Based Blue and Green Light-Emitting Diodes
Energies 2017, 10(9), 1277; doi:10.3390/en10091277
Received: 21 July 2017 / Revised: 18 August 2017 / Accepted: 24 August 2017 / Published: 27 August 2017
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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
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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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Open AccessArticle Electrochemical-Thermal Modelling and Optimisation of Lithium-Ion Battery Design Parameters Using Analysis of Variance
Energies 2017, 10(9), 1278; doi:10.3390/en10091278
Received: 4 July 2017 / Revised: 24 August 2017 / Accepted: 25 August 2017 / Published: 28 August 2017
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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
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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 (rp < 40 nm); (75 μm < Lpos < 100 μm); (0.4 < εs,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 Energy Storage and Application)
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Open AccessArticle Recovery of Low Permeability Reservoirs Considering Well Shut-Ins and Surfactant Additivities
Energies 2017, 10(9), 1279; doi:10.3390/en10091279
Received: 14 July 2017 / Revised: 17 August 2017 / Accepted: 22 August 2017 / Published: 28 August 2017
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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
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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 Energy Sources)
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Open AccessArticle Experimental Investigation of the Condensation Heat Transfer Coefficient of R134a inside Horizontal Smooth and Micro-Fin Tubes
Energies 2017, 10(9), 1280; doi:10.3390/en10091280
Received: 3 August 2017 / Revised: 22 August 2017 / Accepted: 23 August 2017 / Published: 28 August 2017
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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
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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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Open AccessArticle Optimization Design Method and Experimental Validation of a Solar PVT Cogeneration System Based on Building Energy Demand
Energies 2017, 10(9), 1281; doi:10.3390/en10091281
Received: 7 July 2017 / Revised: 16 August 2017 / Accepted: 24 August 2017 / Published: 28 August 2017
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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
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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 Electrical Power and Energy System)
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Open AccessArticle Development of a Transmission and Distribution Integrated Monitoring and Analysis System for High Distributed Generation Penetration
Energies 2017, 10(9), 1282; doi:10.3390/en10091282
Received: 9 August 2017 / Revised: 22 August 2017 / Accepted: 26 August 2017 / Published: 28 August 2017
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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
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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 Electrical Power and Energy System)
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Open AccessArticle Impacts of Power Grid Frequency Deviation on Time Error of Synchronous Electric Clock and Worldwide Power System Practices on Time Error Correction
Energies 2017, 10(9), 1283; doi:10.3390/en10091283
Received: 7 July 2017 / Revised: 12 August 2017 / Accepted: 25 August 2017 / Published: 29 August 2017
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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
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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 Electrical Power and Energy System)
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Open AccessArticle Online Lithium-Ion Battery Internal Resistance Measurement Application in State-of-Charge Estimation Using the Extended Kalman Filter
Energies 2017, 10(9), 1284; doi:10.3390/en10091284
Received: 2 August 2017 / Revised: 23 August 2017 / Accepted: 24 August 2017 / Published: 29 August 2017
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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
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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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Open AccessArticle A Novel Hybrid Approach for Numerical Modeling of the Nucleating Flow in Laval Nozzle and Transonic Steam Turbine Blades
Energies 2017, 10(9), 1285; doi:10.3390/en10091285
Received: 13 May 2017 / Revised: 16 August 2017 / Accepted: 21 August 2017 / Published: 29 August 2017
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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
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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 Energy Fundamentals and Conversion)
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Open AccessArticle A Real-Time SOSM Super-Twisting Technique for a Compound DC Motor Velocity Controller
Energies 2017, 10(9), 1286; doi:10.3390/en10091286
Received: 20 July 2017 / Revised: 17 August 2017 / Accepted: 24 August 2017 / Published: 29 August 2017
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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,
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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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Open AccessArticle Methodology for the Evaluation of Resilience of ICT Systems for Smart Distribution Grids
Energies 2017, 10(9), 1287; doi:10.3390/en10091287
Received: 6 July 2017 / Revised: 16 August 2017 / Accepted: 23 August 2017 / Published: 29 August 2017
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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
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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 Electrical Power and Energy System)
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Open AccessArticle Optimal Energy Management for Microgrids with Combined Heat and Power (CHP) Generation, Energy Storages, and Renewable Energy Sources
Energies 2017, 10(9), 1288; doi:10.3390/en10091288
Received: 26 July 2017 / Revised: 20 August 2017 / Accepted: 25 August 2017 / Published: 29 August 2017
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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
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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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Open AccessArticle Development of a New Battery Management System with an Independent Balance Module for Electrical Motorcycles
Energies 2017, 10(9), 1289; doi:10.3390/en10091289
Received: 3 July 2017 / Revised: 14 August 2017 / Accepted: 26 August 2017 / Published: 29 August 2017
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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
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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
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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
Energies 2017, 10(9), 1290; doi:10.3390/en10091290
Received: 22 June 2017 / Revised: 12 August 2017 / Accepted: 23 August 2017 / Published: 29 August 2017
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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
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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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Open AccessArticle Day-Ahead Active Power Scheduling in Active Distribution Network Considering Renewable Energy Generation Forecast Errors
Energies 2017, 10(9), 1291; doi:10.3390/en10091291
Received: 25 July 2017 / Revised: 21 August 2017 / Accepted: 25 August 2017 / Published: 29 August 2017
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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
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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 Electrical Power and Energy System)
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Open AccessArticle Numerical Analysis of the Combustion and Emission Characteristics of Diesel Engines with Multiple Injection Strategies Using a Modified 2-D Flamelet Model
Energies 2017, 10(9), 1292; doi:10.3390/en10091292
Received: 2 August 2017 / Revised: 18 August 2017 / Accepted: 27 August 2017 / Published: 29 August 2017
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Abstract
The multiple injection strategy has been widely used in diesel engines to reduce engine noise, NOx 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
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The multiple injection strategy has been widely used in diesel engines to reduce engine noise, NOx 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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Open AccessArticle Effect of Temperature on the Structural and Physicochemical Properties of Biochar with Apple Tree Branches as Feedstock Material
Energies 2017, 10(9), 1293; doi:10.3390/en10091293
Received: 18 April 2017 / Revised: 7 August 2017 / Accepted: 21 August 2017 / Published: 30 August 2017
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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
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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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Open AccessArticle Identification of Critical Transmission Lines in Complex Power Networks
Energies 2017, 10(9), 1294; doi:10.3390/en10091294
Received: 3 August 2017 / Revised: 25 August 2017 / Accepted: 25 August 2017 / Published: 30 August 2017
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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
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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 Electrical Power and Energy System)
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Open AccessArticle Analyses of the Extensible Blade in Improving Wind Energy Production at Sites with Low-Class Wind Resource
Energies 2017, 10(9), 1295; doi:10.3390/en10091295
Received: 24 July 2017 / Revised: 24 August 2017 / Accepted: 27 August 2017 / Published: 30 August 2017
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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
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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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Open AccessArticle One-Step Self-Assembly Synthesis α-Fe2O3 with Carbon-Coated Nanoparticles for Stabilized and Enhanced Supercapacitors Electrode
Energies 2017, 10(9), 1296; doi:10.3390/en10091296
Received: 16 June 2017 / Revised: 26 August 2017 / Accepted: 28 August 2017 / Published: 30 August 2017
PDF Full-text (5242 KB) | HTML Full-text | XML Full-text | Supplementary Files
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
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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 Energy Storage and Application)
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Open AccessArticle Interconnecting Microgrids via the Energy Router with Smart Energy Management
Energies 2017, 10(9), 1297; doi:10.3390/en10091297
Received: 14 July 2017 / Revised: 26 August 2017 / Accepted: 28 August 2017 / Published: 30 August 2017
PDF Full-text (3484 KB) | HTML Full-text | XML Full-text
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
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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
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Open AccessArticle New Prototype of Photovoltaic Solar Tracker Based on Arduino
Energies 2017, 10(9), 1298; doi:10.3390/en10091298
Received: 28 July 2017 / Revised: 19 August 2017 / Accepted: 25 August 2017 / Published: 30 August 2017
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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
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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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Open AccessArticle Research on an Integrated Hydrostatic-Driven Electric Generator with Controllable Load for Renewable Energy Applications
Energies 2017, 10(9), 1299; doi:10.3390/en10091299
Received: 11 August 2017 / Revised: 26 August 2017 / Accepted: 28 August 2017 / Published: 30 August 2017
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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
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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 Energy Fundamentals and Conversion)
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Open AccessArticle Modeling and Simulating Long-Timescale Cascading Faults in Power Systems Caused by Line-Galloping Events
Energies 2017, 10(9), 1301; doi:10.3390/en10091301
Received: 3 July 2017 / Revised: 8 August 2017 / Accepted: 23 August 2017 / Published: 30 August 2017
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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
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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 Electrical Power and Energy System)
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Open AccessArticle A Simulation-Based Optimization Method for Hybrid Frequency Regulation System Configuration
Energies 2017, 10(9), 1302; doi:10.3390/en10091302
Received: 21 July 2017 / Revised: 9 August 2017 / Accepted: 29 August 2017 / Published: 30 August 2017
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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
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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 Energy Storage and Application)
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Open AccessArticle Safety Analysis of Grounding Resistance with Depth of Water for Floating PVs
Energies 2017, 10(9), 1304; doi:10.3390/en10091304
Received: 28 July 2017 / Revised: 27 August 2017 / Accepted: 28 August 2017 / Published: 1 September 2017
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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
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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
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Open AccessArticle A Hybrid Approach for Power System Security Enhancement via Optimal Installation of Flexible AC Transmission System (FACTS) Devices
Energies 2017, 10(9), 1305; doi:10.3390/en10091305
Received: 18 July 2017 / Revised: 16 August 2017 / Accepted: 27 August 2017 / Published: 1 September 2017
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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
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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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Open AccessArticle Energy Saving Potential of a Thermoelectric Heat Pump-Assisted Liquid Desiccant System in a Dedicated Outdoor Air System
Energies 2017, 10(9), 1306; doi:10.3390/en10091306
Received: 2 July 2017 / Revised: 22 August 2017 / Accepted: 29 August 2017 / Published: 1 September 2017
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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
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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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Open AccessCommunication Properties of Gasoline Stored in Various Containers
Energies 2017, 10(9), 1307; doi:10.3390/en10091307
Received: 15 July 2017 / Revised: 28 August 2017 / Accepted: 29 August 2017 / Published: 1 September 2017
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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
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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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Open AccessArticle Cost Analysis for a Hybrid Advanced Metering Infrastructure in Korea
Energies 2017, 10(9), 1308; doi:10.3390/en10091308
Received: 11 July 2017 / Revised: 15 August 2017 / Accepted: 28 August 2017 / Published: 1 September 2017
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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
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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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Open AccessArticle Investigation of Hydraulic-Mechanical Properties of Paste Backfill Containing Coal Gangue-Fly Ash and Its Application in an Underground Coal Mine
Energies 2017, 10(9), 1309; doi:10.3390/en10091309
Received: 6 July 2017 / Revised: 14 August 2017 / Accepted: 28 August 2017 / Published: 1 September 2017
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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
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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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Open AccessArticle Investigation on Slot–Pole Combinations of a PM Vernier Motor with Fractional-Slot Concentrated Winding Configurations
Energies 2017, 10(9), 1310; doi:10.3390/en10091310
Received: 10 August 2017 / Revised: 29 August 2017 / Accepted: 30 August 2017 / Published: 1 September 2017
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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,
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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 Electrical Power and Energy System)
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Open AccessArticle A New Approach for Retaining Mercury in Energy Generation Processes: Regenerable Carbonaceous Sorbents
Energies 2017, 10(9), 1311; doi:10.3390/en10091311
Received: 19 July 2017 / Revised: 22 August 2017 / Accepted: 25 August 2017 / Published: 1 September 2017
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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
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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 Energy Sources)
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Open AccessArticle Ethyl Methyl Sulfone-Based Electrolytes for Lithium Ion Battery Applications
Energies 2017, 10(9), 1312; doi:10.3390/en10091312
Received: 20 July 2017 / Revised: 25 August 2017 / Accepted: 28 August 2017 / Published: 1 September 2017
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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
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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 Energy Storage and Application)
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Open AccessArticle A New State of Charge Estimation Algorithm for Lithium-Ion Batteries Based on the Fractional Unscented Kalman Filter
Energies 2017, 10(9), 1313; doi:10.3390/en10091313
Received: 18 July 2017 / Revised: 19 August 2017 / Accepted: 26 August 2017 / Published: 1 September 2017
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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
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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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Open AccessArticle Cost Projection of State of the Art Lithium-Ion Batteries for Electric Vehicles Up to 2030
Energies 2017, 10(9), 1314; doi:10.3390/en10091314
Received: 20 July 2017 / Revised: 22 August 2017 / Accepted: 24 August 2017 / Published: 1 September 2017
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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
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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 Energy Storage and Application)
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Open AccessArticle Thermal Behaviour under Service Loads of a Thermo-Active Precast Pile
Energies 2017, 10(9), 1315; doi:10.3390/en10091315
Received: 28 July 2017 / Revised: 25 August 2017 / Accepted: 29 August 2017 / Published: 1 September 2017
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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
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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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Open AccessArticle Maximum Power Point Tracking of Photovoltaic Panels by Using Improved Pattern Search Methods
Energies 2017, 10(9), 1316; doi:10.3390/en10091316
Received: 12 June 2017 / Revised: 25 July 2017 / Accepted: 21 August 2017 / Published: 1 September 2017
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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,
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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 Energy Fundamentals and Conversion)
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Open AccessArticle Economic Valuation of Low-Load Operation with Auxiliary Firing of Coal-Fired Units
Energies 2017, 10(9), 1317; doi:10.3390/en10091317
Received: 6 August 2017 / Revised: 28 August 2017 / Accepted: 29 August 2017 / Published: 1 September 2017
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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
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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 Electrical Power and Energy System)
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Open AccessArticle An Energy-Efficient Coverage Algorithm for Macrocell—Small Cell Network Systems
Energies 2017, 10(9), 1319; doi:10.3390/en10091319
Received: 22 July 2017 / Revised: 5 August 2017 / Accepted: 30 August 2017 / Published: 1 September 2017
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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