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Energies, Volume 8, Issue 4 (April 2015) , Pages 2295-3291

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Open AccessArticle
Nearshore Tests of the Tidal Compensation System for Point-Absorbing Wave Energy Converters
Energies 2015, 8(4), 3272-3291; https://doi.org/10.3390/en8043272
Received: 16 February 2015 / Revised: 1 April 2015 / Accepted: 3 April 2015 / Published: 22 April 2015
Cited by 6 | Viewed by 2723 | PDF Full-text (19114 KB) | HTML Full-text | XML Full-text
Abstract
The power production of the linear generator wave energy converter developed at Uppsala University is affected by variations of mean sea level. The reason is that these variations change the distance between the point absorber located on the surface and the linear generator [...] Read more.
The power production of the linear generator wave energy converter developed at Uppsala University is affected by variations of mean sea level. The reason is that these variations change the distance between the point absorber located on the surface and the linear generator located on the seabed. This shifts the average position of the translator with respect to the center of the stator, thereby reducing the generator output power. A device mounted on the point absorber that compensates for tides of small range by regulating the length of the connection line between the buoy at the surface and the linear generator has been constructed and tested. This paper describes the electro-mechanical, measurement, communication and control systems installed on the buoy and shows the results obtained before its connection to the generator. The adjustment of the line was achieved through a linear actuator, which shortens the line during low tides and vice versa. The motor that drives the mechanical device was activated remotely via SMS. The measurement system that was mounted on the buoy consisted of current and voltage sensors, accelerometers, strain gauges and inductive and laser sensors. The data collected were transferred via Internet to a Dropbox server. As described within the paper, after the calibration of the sensors, the buoy was assembled and tested in the waters of Lysekil harbor, a few kilometers from the Uppsala University research site. Moreover, the performance of the sensors, the motion of the mechanical device, the power consumption, the current control strategy and the communication system are discussed. Full article
(This article belongs to the Special Issue Tools and Techniques for Economic Delivery of Ocean Energy)
Open AccessArticle
Life-Cycle Energy and GHG Emissions of Forest Biomass Harvest and Transport for Biofuel Production in Michigan
Energies 2015, 8(4), 3258-3271; https://doi.org/10.3390/en8043258
Received: 1 December 2014 / Revised: 16 March 2015 / Accepted: 15 April 2015 / Published: 22 April 2015
Cited by 19 | Viewed by 3080 | PDF Full-text (679 KB) | HTML Full-text | XML Full-text
Abstract
High dependence on imported oil has increased U.S. strategic vulnerability and prompted more research in the area of renewable energy production. Ethanol production from renewable woody biomass, which could be a substitute for gasoline, has seen increased interest. This study analysed energy use [...] Read more.
High dependence on imported oil has increased U.S. strategic vulnerability and prompted more research in the area of renewable energy production. Ethanol production from renewable woody biomass, which could be a substitute for gasoline, has seen increased interest. This study analysed energy use and greenhouse gas emission impacts on the forest biomass supply chain activities within the State of Michigan. A life-cycle assessment of harvesting and transportation stages was completed utilizing peer-reviewed literature. Results for forest-delivered ethanol were compared with those for petroleum gasoline using data specific to the U.S. The analysis from a woody biomass feedstock supply perspective uncovered that ethanol production is more environmentally friendly (about 62% less greenhouse gas emissions) compared with petroleum based fossil fuel production. Sensitivity analysis was conducted with key inputs associated with harvesting and transportation operations. The results showed that research focused on improving biomass recovery efficiency and truck fuel economy further reduced GHG emissions and energy consumption. Full article
(This article belongs to the Special Issue Bioenergy and Biorefining)
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Open AccessArticle
Development of a Compensation Scheme for a Measurement Voltage Transformer Using the Hysteresis Characteristics of a Core
Energies 2015, 8(4), 3245-3257; https://doi.org/10.3390/en8043245
Received: 3 March 2015 / Revised: 16 April 2015 / Accepted: 17 April 2015 / Published: 22 April 2015
Viewed by 1876 | PDF Full-text (924 KB) | HTML Full-text | XML Full-text
Abstract
This paper describes the design, evaluation, and implementation of a compensation scheme for a measurement voltage transformer (VT) using the hysteresis characteristics of the core. The error of a VT is caused by the primary winding voltage and secondary winding voltage. The latter [...] Read more.
This paper describes the design, evaluation, and implementation of a compensation scheme for a measurement voltage transformer (VT) using the hysteresis characteristics of the core. The error of a VT is caused by the primary winding voltage and secondary winding voltage. The latter depends on the secondary current, whereas the former depends on the primary current, which is an aggregate of the exciting and secondary currents. The secondary current is obtained directly from the secondary voltage and is used to obtain the voltage across the secondary winding. For the primary current, the exciting current is decomposed into two components: core-loss and magnetizing currents. The magnetizing current is obtained by the flux-magnetizing current curve instead of the hysteresis loop to minimize the required loops for compensation. The core-loss current is obtained by dividing the primary induced voltage by the core-loss resistance. Finally, the estimated voltages across the primary and secondary windings are added to the measured secondary voltage for compensation. The scheme can significantly improve the accuracy of a VT. The results of the performance of compensator are shown in the experimental test. The accuracy of the measurement VT improves from 1.0C class to 0.1C class. The scheme can help to significantly reduce the required core cross section of a measurement VT in an electrical energy system. Full article
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Open AccessArticle
Application Study on the Dynamic Programming Algorithm for Energy Management of Plug-in Hybrid Electric Vehicles
Energies 2015, 8(4), 3225-3244; https://doi.org/10.3390/en8043225
Received: 6 February 2015 / Revised: 13 April 2015 / Accepted: 14 April 2015 / Published: 22 April 2015
Cited by 42 | Viewed by 3578 | PDF Full-text (670 KB) | HTML Full-text | XML Full-text
Abstract
To explore the problems associated with applying dynamic programming (DP) in the energy management strategies of plug-in hybrid electric vehicles (PHEVs), a plug-in hybrid bus powertrain is introduced and its dynamic control model is constructed. The numerical issues, including the discretization resolution of [...] Read more.
To explore the problems associated with applying dynamic programming (DP) in the energy management strategies of plug-in hybrid electric vehicles (PHEVs), a plug-in hybrid bus powertrain is introduced and its dynamic control model is constructed. The numerical issues, including the discretization resolution of the relevant variables and the boundary issue of their feasible regions, were considered when implementing DP to solve the optimal control problem of PHEVs. The tradeoff between the optimization accuracy when using the DP algorithm and the computational burden was systematically investigated. As a result of overcoming the numerical issues, the DP-based approach has the potential to improve the fuel-savings potential of PHEVs. The results from comparing the DP-based strategy and the traditional control strategy indicate that there is an approximately 20% improvement in fuel economy. Full article
(This article belongs to the Special Issue Advances in Plug-in Hybrid Vehicles and Hybrid Vehicles)
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Open AccessArticle
Influence of Model Simplifications Excitation Force in Surge for a Floating Foundation for Offshore Wind Turbines
Energies 2015, 8(4), 3212-3224; https://doi.org/10.3390/en8043212
Received: 10 December 2014 / Revised: 10 April 2015 / Accepted: 14 April 2015 / Published: 22 April 2015
Cited by 4 | Viewed by 2945 | PDF Full-text (986 KB) | HTML Full-text | XML Full-text
Abstract
As offshore wind turbines move towards deeper and more distant sites, the concept of floating foundations is a potential technically and economically attractive alternative to the traditional fixed foundations. Unlike the well-studied monopile, the geometry of a floating foundation is complex and, thereby, [...] Read more.
As offshore wind turbines move towards deeper and more distant sites, the concept of floating foundations is a potential technically and economically attractive alternative to the traditional fixed foundations. Unlike the well-studied monopile, the geometry of a floating foundation is complex and, thereby, increases the difficulty in wave force determination due to limitations of the commonly used simplified methods. This paper deals with a physical model test of the hydrodynamic excitation force in surge on a fixed three-columned structure intended as a floating foundation for offshore wind turbines. The experiments were conducted in a wave basin at Aalborg University. The test results are compared with a Boundary Element Method code based on linear diffraction theory for different wave force regimes defined by the column diameter, wave heights and lengths. Furthermore, the study investigates the influence of incident wave direction and stabilizing heave-plates. The structure can be divided into primary, secondary and tertiary parts, defined by the columns, heave-plates and braces to determine the excitation force in surge. The test results are in good agreement with the numerical computation for the primary parts only, which leads to simplified determination of peak frequencies and corresponding dominant force regime. Full article
(This article belongs to the Special Issue Tools and Techniques for Economic Delivery of Ocean Energy)
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Open AccessArticle
LaNi5-Assisted Hydrogenation of MgNi2 in the Hybrid Structures of La1.09Mg1.91Ni9D9.5 and La0.91Mg2.09Ni9D9.4
Energies 2015, 8(4), 3198-3211; https://doi.org/10.3390/en8043198
Received: 26 February 2015 / Revised: 6 April 2015 / Accepted: 13 April 2015 / Published: 21 April 2015
Cited by 8 | Viewed by 2384 | PDF Full-text (1270 KB) | HTML Full-text | XML Full-text
Abstract
This work focused on the high pressure PCT and in situ neutron powder diffraction studies of the LaMg2Ni9-H2 (D2) system at pressures up to 1,000 bar. LaMg2Ni9 alloy was prepared by a powder [...] Read more.
This work focused on the high pressure PCT and in situ neutron powder diffraction studies of the LaMg2Ni9-H2 (D2) system at pressures up to 1,000 bar. LaMg2Ni9 alloy was prepared by a powder metallurgy route from the LaNi9 alloy precursor and Mg powder. Two La3−xMgxNi9 samples with slightly different La/Mg ratios were studied, La1.1Mg1.9Ni9 (sample 1) and La0.9Mg2.1Ni9 (sample 2). In situ neutron powder diffraction studies of the La1.09Mg1.91Ni9D9.5 (1) and La0.91Mg2.09Ni9D9.4 (2) deuterides were performed at 25 bar D2 (1) and 918 bar D2 (2). The hydrogenation properties of the (1) and (2) are dramatically different from those for LaNi3. The Mg-containing intermetallics reversibly form hydrides with DHdes = 24.0 kJ/molH2 and an equilibrium pressure of H2 desorption of 18 bar at 20 °C (La1.09Mg1.91Ni9). A pronounced hysteresis of H2 absorption and desorption, ~100 bar, is observed. The studies showed that LaNi5-assisted hydrogenation of MgNi2 in the LaMg2Ni9 hybrid structure takes place. In the La1.09Mg1.91Ni9D9.5 (1) and La0.91Mg2.09Ni9D9.4 (2) (a = 5.263/5.212; c = 25.803/25.71 Å) D atoms are accommodated in both Laves and CaCu5-type slabs. In the LaNi5 CaCu5-type layer, D atoms fill three types of interstices; a deformed octahedron [La2Ni4], and [La(Mg)2Ni2] and [Ni4] tetrahedra. The overall chemical compositions can be presented as LaNi5H5.6/5.0 + 2*MgNi2H1.95/2.2 showing that the hydrogenation of the MgNi2 slab proceeds at mild H2/D2 pressure of just 20 bar. A partial filling by D of the four types of the tetrahedral interstices in the MgNi2 slab takes place, including [MgNi3] and [Mg2Ni2] tetrahedra. Full article
(This article belongs to the Special Issue Hydrides: Fundamentals and Applications) Printed Edition available
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Open AccessReview
Recent Advances in the Characterization of Gaseous and Liquid Fuels by Vibrational Spectroscopy
Energies 2015, 8(4), 3165-3197; https://doi.org/10.3390/en8043165
Received: 9 February 2015 / Revised: 27 March 2015 / Accepted: 10 April 2015 / Published: 20 April 2015
Cited by 33 | Viewed by 4219 | PDF Full-text (604 KB) | HTML Full-text | XML Full-text
Abstract
Most commercial gaseous and liquid fuels are mixtures of multiple chemical compounds. In recent years, these mixtures became even more complicated when the suppliers started to admix biofuels into the petrochemical basic fuels. As the properties of such mixtures can vary with composition, [...] Read more.
Most commercial gaseous and liquid fuels are mixtures of multiple chemical compounds. In recent years, these mixtures became even more complicated when the suppliers started to admix biofuels into the petrochemical basic fuels. As the properties of such mixtures can vary with composition, there is a need for reliable analytical technologies in order to ensure stable operation of devices such as internal combustion engines and gas turbines. Vibrational spectroscopic methods have proved their suitability for fuel characterization. Moreover, they have the potential to overcome existing limitations of established technologies, because they are fast and accurate, and they do not require sampling; hence they can be deployed as inline sensors. This article reviews the recent advances of vibrational spectroscopy in terms of infrared absorption (IR) and Raman spectroscopy in the context of fuel characterization. The focus of the paper lies on gaseous and liquid fuels, which are dominant in the transportation sector and in the distributed generation of power. On top of an introduction to the physical principles and review of the literature, the techniques are critically discussed and compared with each other. Full article
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Open AccessArticle
Risk Assessment for Natural Gas Hydrate Carriers: A Hazard Identification (HAZID) Study
Energies 2015, 8(4), 3142-3164; https://doi.org/10.3390/en8043142
Received: 8 November 2014 / Accepted: 4 March 2015 / Published: 20 April 2015
Cited by 5 | Viewed by 3177 | PDF Full-text (1640 KB) | HTML Full-text | XML Full-text
Abstract
Sea transport of natural gas in the form of hydrate pellets is a new technological approach. Introducing new technologies bears raises the possibility of introducing unknown risks or—in case of alternatives for already existing technical solutions—higher risk, either human-, environmental-, or property-related. The [...] Read more.
Sea transport of natural gas in the form of hydrate pellets is a new technological approach. Introducing new technologies bears raises the possibility of introducing unknown risks or—in case of alternatives for already existing technical solutions—higher risk, either human-, environmental-, or property-related. The option of gas transport by natural gas hydrate pellets has been introduced within the Korean joint research project. One key task was the safety evaluation of the novel natural gas hydrate carrier (NGH carrier) developed in the project. The aim of this work was to support and assess the risk aspects of the development to ensure that the risk level for the newly developed concept is as low as for existing competing concepts, especially LNG carriers. The NGH carrier is based on the concept of the self-preservation effect and thereby preserves NGH in the form of pellets at atmospheric pressure and temperatures lower than −20 °C. In order to identify all the possible hazards in the system and then enhance the system safety, a Hazard Identification (HAZID) study was conducted. As a result of the HAZID, 80 identified hazards in total were explored and ranked in terms of risk index for the semi-quantitative risk evaluation. Among the hazards identified, three hazards were found to have unacceptable risk level and twenty eight to have acceptable but ALARP risk level. Regarding the hazards with unacceptable risk or ALARP risk, additional safety actions and recommendations for risk control were discussed and proposed in a SAFETY ACTION REGISTER, which would be considered and utilized by designers when developing the detailed system design in the future. In conclusion, the overall safety level of the NGH carrier is considered acceptable. However, it was found that a few external hazards associated with extremely harsh weather could be critical threats to the system. Relevant safety actions against them, therefore, must be provided in the system design. Full article
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Open AccessReview
Hydrazine Borane and Hydrazinidoboranes as Chemical Hydrogen Storage Materials
Energies 2015, 8(4), 3118-3141; https://doi.org/10.3390/en8043118
Received: 27 January 2015 / Revised: 20 February 2015 / Accepted: 7 April 2015 / Published: 20 April 2015
Cited by 30 | Viewed by 2641 | PDF Full-text (1651 KB) | HTML Full-text | XML Full-text
Abstract
Hydrazine borane N2H4BH3 and alkali derivatives (i.e., lithium, sodium and potassium hydrazinidoboranes MN2H3BH3 with M = Li, Na and K) have been considered as potential chemical hydrogen storage materials. They belong [...] Read more.
Hydrazine borane N2H4BH3 and alkali derivatives (i.e., lithium, sodium and potassium hydrazinidoboranes MN2H3BH3 with M = Li, Na and K) have been considered as potential chemical hydrogen storage materials. They belong to the family of boron- and nitrogen-based materials and the present article aims at providing a timely review while focusing on fundamentals so that their effective potential in the field could be appreciated. It stands out that, on the one hand, hydrazine borane, in aqueous solution, would be suitable for full dehydrogenation in hydrolytic conditions; the most attractive feature is the possibility to dehydrogenate, in addition to the BH3 group, the N2H4 moiety in the presence of an active and selective metal-based catalyst but for which further improvements are still necessary. However, the thermolytic dehydrogenation of hydrazine borane should be avoided because of the evolution of significant amounts of hydrazine and the formation of a shock-sensitive solid residue upon heating at >300 °C. On the other hand, the alkali hydrazinidoboranes, obtained by reaction of hydrazine borane with alkali hydrides, would be more suitable to thermolytic dehydrogenation, with improved properties in comparison to the parent borane. All of these aspects are surveyed herein and put into perspective. Full article
(This article belongs to the Special Issue Hydrides: Fundamentals and Applications) Printed Edition available
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Open AccessArticle
Empirical Research on China’s Carbon Productivity Decomposition Model Based on Multi-Dimensional Factors
Energies 2015, 8(4), 3093-3117; https://doi.org/10.3390/en8043093
Received: 1 March 2015 / Revised: 8 April 2015 / Accepted: 10 April 2015 / Published: 20 April 2015
Cited by 14 | Viewed by 2158 | PDF Full-text (1320 KB) | HTML Full-text | XML Full-text
Abstract
Based on the international community’s analysis of the present CO2 emissions situation, a Log Mean Divisia Index (LMDI) decomposition model is proposed in this paper, aiming to reflect the decomposition of carbon productivity. The model is designed by analyzing the factors that [...] Read more.
Based on the international community’s analysis of the present CO2 emissions situation, a Log Mean Divisia Index (LMDI) decomposition model is proposed in this paper, aiming to reflect the decomposition of carbon productivity. The model is designed by analyzing the factors that affect carbon productivity. China’s contribution to carbon productivity is analyzed from the dimensions of influencing factors, regional structure and industrial structure. It comes to the conclusions that: (a) economic output, the provincial carbon productivity and energy structure are the most influential factors, which are consistent with China’s current actual policy; (b) the distribution patterns of economic output, carbon productivity and energy structure in different regions have nothing to do with the Chinese traditional sense of the regional economic development patterns; (c) considering the regional protectionism, regional actual situation need to be considered at the same time; (d) in the study of the industrial structure, the contribution value of industry is the most prominent factor for China’s carbon productivity, while the industrial restructuring has not been done well enough. Full article
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Open AccessArticle
Modelling Wind for Wind Farm Layout Optimization Using Joint Distribution of Wind Speed and Wind Direction
Energies 2015, 8(4), 3075-3092; https://doi.org/10.3390/en8043075
Received: 10 March 2015 / Revised: 7 April 2015 / Accepted: 9 April 2015 / Published: 20 April 2015
Cited by 19 | Viewed by 3291 | PDF Full-text (3076 KB) | HTML Full-text | XML Full-text
Abstract
Reliable wind modelling is of crucial importance for wind farm development. The common practice of using sector-wise Weibull distributions has been found inappropriate for wind farm layout optimization. In this study, we propose a simple and easily implementable method to construct joint distributions [...] Read more.
Reliable wind modelling is of crucial importance for wind farm development. The common practice of using sector-wise Weibull distributions has been found inappropriate for wind farm layout optimization. In this study, we propose a simple and easily implementable method to construct joint distributions of wind speed and wind direction, which is based on the parameters of sector-wise Weibull distributions and interpolations between direction sectors. It is applied to the wind measurement data at Horns Rev and three different joint distributions are obtained, which all fit the measurement data quite well in terms of the coefficient of determination . Then, the best of these joint distributions is used in the layout optimization of the Horns Rev 1 wind farm and the choice of bin sizes for wind speed and wind direction is also investigated. It is found that the choice of bin size for wind direction is especially critical for layout optimization and the recommended choice of bin sizes for wind speed and wind direction is finally presented. Full article
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Open AccessArticle
News Media Analysis of Carbon Capture and Storage and Biomass: Perceptions and Possibilities
Energies 2015, 8(4), 3058-3074; https://doi.org/10.3390/en8043058
Received: 16 December 2014 / Revised: 24 February 2015 / Accepted: 27 March 2015 / Published: 20 April 2015
Cited by 12 | Viewed by 2346 | PDF Full-text (219 KB) | HTML Full-text | XML Full-text
Abstract
In the US, carbon capture and storage (CCS) has received most of its attention when coupled with the fossil fuel industry as a mitigation strategy for climate change. CCS, which is constituted as a broad suite of capture and sequestration technologies and techniques, [...] Read more.
In the US, carbon capture and storage (CCS) has received most of its attention when coupled with the fossil fuel industry as a mitigation strategy for climate change. CCS, which is constituted as a broad suite of capture and sequestration technologies and techniques, does not preclude coupling with other energy industries such as bioenergy (bioenergy and CCS or BECCS). In this paper, we examined news media coverage of CCS and biomass individually in locations throughout the US where these technologies are being explored to determine how they are perceived and what possibilities lay in their coupling for climate change mitigation. From our analyses, we found that individually, both CCS and biomass are perceived generally as beneficial for energy development by the news media, though they are not often mentioned in combination. Combined references do, however, speak to their value for climate change mitigation and as an alternative to fossil fuels. Full article
(This article belongs to the Special Issue Carbon Capture and Storage (CCS): Bio-Energy vs Fossil Fuels)
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Open AccessArticle
Combustion Analysis of a Diesel Engine Running on Different Biodiesel Blends
Energies 2015, 8(4), 3047-3057; https://doi.org/10.3390/en8043047
Received: 13 February 2015 / Revised: 20 March 2015 / Accepted: 27 March 2015 / Published: 20 April 2015
Cited by 15 | Viewed by 2152 | PDF Full-text (773 KB) | HTML Full-text | XML Full-text
Abstract
Rape-seed biodiesel is an interesting option to address the problem of decreasing availability of conventional fossil fuels, as well as to reduce the CO2 emissions of internal combustion engines. The present paper describes an experimental campaign carried out on a current production [...] Read more.
Rape-seed biodiesel is an interesting option to address the problem of decreasing availability of conventional fossil fuels, as well as to reduce the CO2 emissions of internal combustion engines. The present paper describes an experimental campaign carried out on a current production 4-cylinder, 4-stroke naturally aspirated diesel engine, running on standard diesel fuel and on three different blends of rape-seed biodiesel (20%-50%-100%). Performance, emissions and in-cylinder pressure traces were measured at full load. It was found that the influence of rape-seed biodiesel in the fuel blend is not constant at each operating condition. However, as the biodiesel content increases, full load performance tends to drop, in particular brake specific fuel consumption (maximum worsening: +18%), while soot emission goes down. The maximum improvement observed in terms of soot concentration is 37.5%, at 1200 rpm. The combustion analysis revealed that the main differences among the fuels occur in the first phase of combustion: the burn rate is slower for biodiesel blends at low speeds, and faster at high. Full article
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Open AccessArticle
The Three-Phase Power Router and Its Operation with Matrix Converter toward Smart-Grid Applications
Energies 2015, 8(4), 3034-3046; https://doi.org/10.3390/en8043034
Received: 17 December 2014 / Revised: 22 March 2015 / Accepted: 2 April 2015 / Published: 17 April 2015
Cited by 3 | Viewed by 2886 | PDF Full-text (2983 KB) | HTML Full-text | XML Full-text
Abstract
A power router has been recently developed for both AC and DC applications that has the potential for smart-grid applications. This study focuses on three-phase power switching through the development of an experimental setup which consists of a three-phase direct AC/AC matrix converter [...] Read more.
A power router has been recently developed for both AC and DC applications that has the potential for smart-grid applications. This study focuses on three-phase power switching through the development of an experimental setup which consists of a three-phase direct AC/AC matrix converter with a power router attached to its output. Various experimental switching scenarios with the loads connected to different input sources were investigated. The crescent introduction of decentralized power generators throughout the power-grid obligates us to take measurements for a better distribution and management of the power. Power routers and matrix converters have great potential to succeed this goal with the help of power electronics devices. In this paper, a novel experimental three-phase power switching was achieved and the advantages of this operation are presented, such as on-demand and constant power supply at the desired loads. Full article
Open AccessArticle
3D CFD Analysis of a Vertical Axis Wind Turbine
Energies 2015, 8(4), 3013-3033; https://doi.org/10.3390/en8043013
Received: 16 January 2015 / Revised: 1 April 2015 / Accepted: 2 April 2015 / Published: 17 April 2015
Cited by 41 | Viewed by 5749 | PDF Full-text (18638 KB) | HTML Full-text | XML Full-text
Abstract
To analyze the complex and unsteady aerodynamic flow associated with wind turbine functioning, computational fluid dynamics (CFD) is an attractive and powerful method. In this work, the influence of different numerical aspects on the accuracy of simulating a rotating wind turbine is studied. [...] Read more.
To analyze the complex and unsteady aerodynamic flow associated with wind turbine functioning, computational fluid dynamics (CFD) is an attractive and powerful method. In this work, the influence of different numerical aspects on the accuracy of simulating a rotating wind turbine is studied. In particular, the effects of mesh size and structure, time step and rotational velocity have been taken into account for simulation of different wind turbine geometries. The applicative goal of this study is the comparison of the performance between a straight blade vertical axis wind turbine and a helical blade one. Analyses are carried out through the use of computational fluid dynamic ANSYS® Fluent® software, solving the Reynolds averaged Navier–Stokes (RANS) equations. At first, two-dimensional simulations are used in a preliminary setup of the numerical procedure and to compute approximated performance parameters, namely the torque, power, lift and drag coefficients. Then, three-dimensional simulations are carried out with the aim of an accurate determination of the differences in the complex aerodynamic flow associated with the straight and the helical blade turbines. Static and dynamic results are then reported for different values of rotational speed. Full article
Open AccessArticle
Toward Isolation of Salient Features in Stable Boundary Layer Wind Fields that Influence Loads on Wind Turbines
Energies 2015, 8(4), 2977-3012; https://doi.org/10.3390/en8042977
Received: 8 November 2014 / Revised: 3 March 2015 / Accepted: 30 March 2015 / Published: 17 April 2015
Cited by 7 | Viewed by 2445 | PDF Full-text (2310 KB) | HTML Full-text | XML Full-text
Abstract
Neutral boundary layer (NBL) flow fields, commonly used in turbine load studies and design, are generated using spectral procedures in stochastic simulation. For large utility-scale turbines, stable boundary layer (SBL) flow fields are of great interest because they are often accompanied by enhanced [...] Read more.
Neutral boundary layer (NBL) flow fields, commonly used in turbine load studies and design, are generated using spectral procedures in stochastic simulation. For large utility-scale turbines, stable boundary layer (SBL) flow fields are of great interest because they are often accompanied by enhanced wind shear, wind veer, and even low-level jets (LLJs). The generation of SBL flow fields, in contrast to simpler stochastic simulation for NBL, requires computational fluid dynamics (CFD) procedures to capture the physics and noted characteristics—such as shear and veer—that are distinct from those seen in NBL flows. At present, large-eddy simulation (LES) is the most efficient CFD procedure for SBL flow field generation and related wind turbine loads studies. Design standards, such as from the International Electrotechnical Commission (IEC), provide guidance albeit with simplifying assumptions (one such deals with assuming constant variance of turbulence over the rotor) and recommend standard target turbulence power spectra and coherence functions to allow NBL flow field simulation. In contrast, a systematic SBL flow field simulation procedure has not been offered for design or for site assessment. It is instructive to compare LES-generated SBL flow fields with stochastic NBL flow fields and associated loads which we evaluate for a 5-MW turbine; in doing so, we seek to isolate distinguishing characteristics of wind shear, wind veer, and turbulence variation over the rotor plane in the alternative flow fields and in the turbine loads. Because of known differences in NBL-stochastic and SBL-LES wind fields but an industry preference for simpler stochastic simulation in design practice, this study investigates if one can reproduce stable atmospheric conditions using stochastic approaches with appropriate corrections for shear, veer, turbulence, etc. We find that such simple tuning cannot consistently match turbine target SBL load statistics, even though this is possible in some cases. As such, when there is a need to consider different stability regimes encountered by a wind turbine, easy solutions do not exist and large-eddy simulation at least for the stable boundary layer is needed. Full article
(This article belongs to the collection Wind Turbines) Printed Edition available
Open AccessArticle
Online Estimation of Model Parameters and State of Charge of LiFePO4 Batteries Using a Novel Open-Circuit Voltage at Various Ambient Temperatures
Energies 2015, 8(4), 2950-2976; https://doi.org/10.3390/en8042950
Received: 14 January 2015 / Revised: 5 March 2015 / Accepted: 27 March 2015 / Published: 16 April 2015
Cited by 21 | Viewed by 2774 | PDF Full-text (8234 KB) | HTML Full-text | XML Full-text
Abstract
This study describes an online estimation of the model parameters and state of charge (SOC) of lithium iron phosphate batteries in electric vehicles. A widely used SOC estimator is based on the dynamic battery model with predeterminate parameters. However, model parameter variances that [...] Read more.
This study describes an online estimation of the model parameters and state of charge (SOC) of lithium iron phosphate batteries in electric vehicles. A widely used SOC estimator is based on the dynamic battery model with predeterminate parameters. However, model parameter variances that follow with their varied operation temperatures can result in errors in estimating battery SOC. To address this problem, a battery online parameter estimator is presented based on an equivalent circuit model using an adaptive joint extended Kalman filter algorithm. Simulations based on actual data are established to verify accuracy and stability in the regression of model parameters. Experiments are also performed to prove that the proposed estimator exhibits good reliability and adaptability under different loading profiles with various temperatures. In addition, open-circuit voltage (OCV) is used to estimate SOC in the proposed algorithm. However, the OCV based on the proposed online identification includes a part of concentration polarization and hysteresis, which is defined as parametric identification-based OCV (OCVPI). Considering the temperature factor, a novel OCV–SOC relationship map is established by using OCVPI under various temperatures. Finally, a validating experiment is conducted based on the consecutive loading profiles. Results indicate that our method is effective and adaptable when a battery operates at different ambient temperatures. Full article
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Open AccessArticle
Multi-Objective Optimization Design for a Hybrid Energy System Using the Genetic Algorithm
Energies 2015, 8(4), 2924-2949; https://doi.org/10.3390/en8042924
Received: 3 February 2015 / Revised: 20 March 2015 / Accepted: 3 April 2015 / Published: 16 April 2015
Cited by 23 | Viewed by 3016 | PDF Full-text (4526 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
To secure a stable energy supply and bring renewable energy to buildings within a reasonable cost range, a hybrid energy system (HES) that integrates both fossil fuel energy systems (FFESs) and new and renewable energy systems (NRESs) needs to be designed and applied. [...] Read more.
To secure a stable energy supply and bring renewable energy to buildings within a reasonable cost range, a hybrid energy system (HES) that integrates both fossil fuel energy systems (FFESs) and new and renewable energy systems (NRESs) needs to be designed and applied. This paper presents a methodology to optimize a HES consisting of three types of NRESs and six types of FFESs while simultaneously minimizing life cycle cost (LCC), maximizing penetration of renewable energy and minimizing annual greenhouse gas (GHG) emissions. An elitist non-dominated sorting genetic algorithm is utilized for multi-objective optimization. As an example, we have designed the optimal configuration and sizing for a HES in an elementary school. The evolution of Pareto-optimal solutions according to the variation in the economic, technical and environmental objective functions through generations is discussed. The pair wise trade-offs among the three objectives are also examined. Full article
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Open AccessArticle
Reliability Analysis of Fatigue Failure of Cast Components for Wind Turbines
Energies 2015, 8(4), 2908-2923; https://doi.org/10.3390/en8042908
Received: 23 December 2014 / Revised: 20 March 2015 / Accepted: 7 April 2015 / Published: 15 April 2015
Cited by 7 | Viewed by 3240 | PDF Full-text (388 KB) | HTML Full-text | XML Full-text
Abstract
Fatigue failure is one of the main failure modes for wind turbine drivetrain components made of cast iron. The wind turbine drivetrain consists of a variety of heavily loaded components, like the main shaft, the main bearings, the gearbox and the generator. The [...] Read more.
Fatigue failure is one of the main failure modes for wind turbine drivetrain components made of cast iron. The wind turbine drivetrain consists of a variety of heavily loaded components, like the main shaft, the main bearings, the gearbox and the generator. The failure of each component will lead to substantial economic losses such as cost of lost energy production and cost of repairs. During the design lifetime, the drivetrain components are exposed to variable loads from winds and waves and other sources of loads that are uncertain and have to be modeled as stochastic variables. The types of loads are different for offshore and onshore wind turbines. Moreover, uncertainties about the fatigue strength play an important role in modeling and assessment of the reliability of the components. In this paper, a generic stochastic model for fatigue failure of cast iron components based on fatigue test data and a limit state equation for fatigue failure based on the SN-curve approach and Miner’s rule is presented. The statistical analysis of the fatigue data is performed using the Maximum Likelihood Method which also gives an estimate of the statistical uncertainties. Finally, illustrative examples are presented with reliability analyses depending on various stochastic models and partial safety factors. Full article
(This article belongs to the collection Wind Turbines) Printed Edition available
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Open AccessArticle
Regression Models Using Fully Discharged Voltage and Internal Resistance for State of Health Estimation of Lithium-Ion Batteries
Energies 2015, 8(4), 2889-2907; https://doi.org/10.3390/en8042889
Received: 31 December 2014 / Revised: 13 March 2015 / Accepted: 7 April 2015 / Published: 15 April 2015
Cited by 8 | Viewed by 2470 | PDF Full-text (1486 KB) | HTML Full-text | XML Full-text
Abstract
Accurate estimation of lithium-ion battery life is essential to assure the reliable operation of the energy supply system. This study develops regression models for battery prognostics using statistical methods. The resultant regression models can not only monitor a battery’s degradation trend but also [...] Read more.
Accurate estimation of lithium-ion battery life is essential to assure the reliable operation of the energy supply system. This study develops regression models for battery prognostics using statistical methods. The resultant regression models can not only monitor a battery’s degradation trend but also accurately predict its remaining useful life (RUL) at an early stage. Three sets of test data are employed in the training stage for regression models. Another set of data is then applied to the regression models for validation. The fully discharged voltage (Vdis) and internal resistance (R) are adopted as aging parameters in two different mathematical models, with polynomial and exponential functions. A particle swarm optimization (PSO) process is applied to search for optimal coefficients of the regression models. Simulations indicate that the regression models using Vdis and R as aging parameters can build a real state of health profile more accurately than those using cycle number, N. The Monte Carlo method is further employed to make the models adaptive. The subsequent results, however, show that this results in an insignificant improvement of the battery life prediction. A reasonable speculation is that the PSO process already yields the major model coefficients. Full article
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Open AccessArticle
Research on the Torque and Back EMF Performance of a High Speed PMSM Used for Flywheel Energy Storage
Energies 2015, 8(4), 2867-2888; https://doi.org/10.3390/en8042867
Received: 3 December 2014 / Revised: 7 April 2015 / Accepted: 7 April 2015 / Published: 15 April 2015
Cited by 6 | Viewed by 2927 | PDF Full-text (831 KB) | HTML Full-text | XML Full-text
Abstract
Due to advantages such as high energy density, high power density, rapid charge and discharge, high cyclic-life, and environmentally friendly, flywheel energy storage systems (FESs) are widely used in various fields. However, the performance of FES systems depends on the performance of a [...] Read more.
Due to advantages such as high energy density, high power density, rapid charge and discharge, high cyclic-life, and environmentally friendly, flywheel energy storage systems (FESs) are widely used in various fields. However, the performance of FES systems depends on the performance of a high speed machine, therefore, the design and optimization of a high efficiency and high power density machine are very crucial to improve the performance of the whole FES system. In this paper, a high speed permanent-magnet synchronous machine (PMSM) is researched. Considering the requirement of low torque ripple in low speed and loss caused by back electromotive force (EMF) harmonics, the electromagnetic performance is improved from points of view of slot/pole matching, magnetic-pole embrace with the finite element method (FEM). Furthermore, the magnetic-pole eccentricity, the slot opening, the thickness of PM and air-gap length are also optimized with Taguchi method. The electromagnetic performance, such as torque ripple, cogging torque, average torque and back EMF wave are much improved after optimization. Finally, experiments are carried out to verify the calculated results. Full article
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Open AccessArticle
The Use of Energy in Malaysia: Tracing Energy Flows from Primary Source to End Use
Energies 2015, 8(4), 2828-2866; https://doi.org/10.3390/en8042828
Received: 9 December 2014 / Revised: 1 March 2015 / Accepted: 23 March 2015 / Published: 15 April 2015
Cited by 21 | Viewed by 3908 | PDF Full-text (2169 KB) | HTML Full-text | XML Full-text
Abstract
Malaysia is a rapidly developing country in Southeast Asia that aims to achieve high-income country status by 2020; its economic growth is highly dependent on its abundant energy resources, especially natural gas and crude oil. In this paper, a complete picture of Malaysia’s [...] Read more.
Malaysia is a rapidly developing country in Southeast Asia that aims to achieve high-income country status by 2020; its economic growth is highly dependent on its abundant energy resources, especially natural gas and crude oil. In this paper, a complete picture of Malaysia’s energy use from primary source to end use is presented by mapping a Sankey diagram of Malaysia’s energy flows, together with ongoing trends analysis of the main factors influencing the energy flows. The results indicate that Malaysia’s energy use depends heavily on fossil fuels, including oil, gas and coal. In the past 30 years, Malaysia has successfully diversified its energy structure by introducing more natural gas and coal into its power generation. To sustainably feed the rapidly growing energy demand in end-use sectors with the challenge of global climate change, Malaysia must pay more attention to the development of renewable energy, green technology and energy conservation in the future. Full article
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Open AccessArticle
A Combined Optical, Thermal and Electrical Performance Study of a V-Trough PV System—Experimental and Analytical Investigations
Energies 2015, 8(4), 2803-2827; https://doi.org/10.3390/en8042803
Received: 12 February 2015 / Revised: 19 March 2015 / Accepted: 20 March 2015 / Published: 14 April 2015
Cited by 21 | Viewed by 2462 | PDF Full-text (3247 KB) | HTML Full-text | XML Full-text
Abstract
The objective of this study was to achieve higher efficiency of a PV system while reducing of the cost of energy generation. Concentration photovoltaics was employed in the present case as it uses low cost reflectors to enhance the efficiency of the PV [...] Read more.
The objective of this study was to achieve higher efficiency of a PV system while reducing of the cost of energy generation. Concentration photovoltaics was employed in the present case as it uses low cost reflectors to enhance the efficiency of the PV system and simultaneously reduces the cost of electricity generation. For this purpose a V-trough integrated with the PV system was employed for low concentration photovoltaic (LCPV). Since the electrical output of the concentrating PV system is significantly affected by the temperature of the PV cells, the motivation of the research also included studying the ability to actively cool PV cells to achieve the maximum benefit. The optical, thermal and electrical performance of the V-trough PV system was theoretically modeled and validated with experimental results. Optical modeling of V-trough was carried out to estimate the amount of enhanced absorbed radiation. Due to increase in the absorbed radiation the module temperature was also increased which was predicted by thermal model. Active cooling techniques were studied and the effect of cooling was analyzed on the performance of V-trough PV system. With absorbed radiation and module temperature as input parameters, electrical modeling was carried out and the maximum power was estimated. For the V-trough PV system, experiments were performed for validating the numerical models and very good agreement was found between the two. Full article
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Open AccessArticle
The Effects of Envelope Design Alternatives on the Energy Consumption of Residential Houses in Indonesia
Energies 2015, 8(4), 2788-2802; https://doi.org/10.3390/en8042788
Received: 1 November 2014 / Revised: 4 March 2015 / Accepted: 3 April 2015 / Published: 13 April 2015
Cited by 5 | Viewed by 2402 | PDF Full-text (514 KB) | HTML Full-text | XML Full-text
Abstract
As an emerging country and one of the most populous countries in the world, Indonesia requires a sufficient energy supply to ensure the nation’s continued development. In response to this increasing energy demand, various studies have proposed energy-saving measures; building envelope design is [...] Read more.
As an emerging country and one of the most populous countries in the world, Indonesia requires a sufficient energy supply to ensure the nation’s continued development. In response to this increasing energy demand, various studies have proposed energy-saving measures; building envelope design is considered to be a typical energy-saving technique. A significant goal in achieving greener buildings is learning how to reduce a building’s energy consumption by applying an efficient energy-saving design. This study used the eQUEST software to investigate how different types of roof construction, glazing and sun-shading techniques affect the energy consumption of residential structures in Indonesia in common scenarios. The results indicate that window shading has the most significant impact on a building’s overall energy consumption, followed by the use of an appropriate glazing, whereas the roof type produced smaller energy efficiency benefits. Full article
(This article belongs to the Special Issue Energy Conservation in Infrastructures)
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Open AccessArticle
A Robust WLS Power System State Estimation Method Integrating a Wide-Area Measurement System and SCADA Technology
Energies 2015, 8(4), 2769-2787; https://doi.org/10.3390/en8042769
Received: 7 February 2015 / Revised: 20 March 2015 / Accepted: 23 March 2015 / Published: 10 April 2015
Cited by 5 | Viewed by 2779 | PDF Full-text (519 KB) | HTML Full-text | XML Full-textRetraction
Abstract
With the development of modern society, the scale of the power system is rapidly increased accordingly, and the framework and mode of running of power systems are trending towards more complexity. It is nowadays much more important for the dispatchers to know exactly [...] Read more.
With the development of modern society, the scale of the power system is rapidly increased accordingly, and the framework and mode of running of power systems are trending towards more complexity. It is nowadays much more important for the dispatchers to know exactly the state parameters of the power network through state estimation. This paper proposes a robust power system WLS state estimation method integrating a wide-area measurement system (WAMS) and SCADA technology, incorporating phasor measurements and the results of the traditional state estimator in a post-processing estimator, which greatly reduces the scale of the non-linear estimation problem as well as the number of iterations and the processing time per iteration. This paper firstly analyzes the wide-area state estimation model in detail, then according to the issue that least squares does not account for bad data and outliers, the paper proposes a robust weighted least squares (WLS) method that combines a robust estimation principle with least squares by equivalent weight. The performance assessment is discussed through setting up mathematical models of the distribution network. The effectiveness of the proposed method was proved to be accurate and reliable by simulations and experiments. Full article
(This article belongs to the collection Smart Grid)
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Open AccessArticle
High Step-Up 3-Phase Rectifier with Fly-Back Cells and Switched Capacitors for Small-Scaled Wind Generation Systems
Energies 2015, 8(4), 2742-2768; https://doi.org/10.3390/en8042742
Received: 26 November 2014 / Revised: 7 March 2015 / Accepted: 1 April 2015 / Published: 10 April 2015
Cited by 7 | Viewed by 2951 | PDF Full-text (4324 KB) | HTML Full-text | XML Full-text
Abstract
This paper proposes and discusses a novel AC/DC converter suitable for small-scaled wind power generation system applications. By introducing flyback cells into the three-phase single-switch Boost circuit, the proposed converter is designed as single-stage and has both rectification and high step-up power conversion [...] Read more.
This paper proposes and discusses a novel AC/DC converter suitable for small-scaled wind power generation system applications. By introducing flyback cells into the three-phase single-switch Boost circuit, the proposed converter is designed as single-stage and has both rectification and high step-up power conversion functions. It is able to obtain high voltage gain at low input voltage level, and high efficiency, low total harmonic distortion (THD) at rated power. The inherent power factor correction (PFC) is also determined, and can reach 0.99. Besides, since no electrolytic capacitor is employed and high voltage gain is achieved, the converter can also collect weak power at low input voltage in combination with energy storage devices, and contribute to a better low-wind-speed/low-power performance. Finally, a 400 W prototype is built to verify the theoretical analysis, and its efficiency is 87.6%, while THD is 7.4% at rated power. Full article
(This article belongs to the collection Wind Turbines) Printed Edition available
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Open AccessArticle
Multi-Objective Thermo-Economic Optimization Strategy for ORCs Applied to Subcritical and Transcritical Cycles for Waste Heat Recovery
Energies 2015, 8(4), 2714-2741; https://doi.org/10.3390/en8042714
Received: 30 January 2015 / Revised: 13 March 2015 / Accepted: 30 March 2015 / Published: 9 April 2015
Cited by 24 | Viewed by 2506 | PDF Full-text (423 KB) | HTML Full-text | XML Full-text
Abstract
Organic Rankine cycles (ORCs) are an established technology to convert waste heat to electricity. Although several commercial implementations exist, there is still considerable potential for thermo-economic optimization. As such, a novel framework for designing optimized ORC systems is proposed based on a multi-objective [...] Read more.
Organic Rankine cycles (ORCs) are an established technology to convert waste heat to electricity. Although several commercial implementations exist, there is still considerable potential for thermo-economic optimization. As such, a novel framework for designing optimized ORC systems is proposed based on a multi-objective optimization scheme in combination with financial appraisal in a post-processing step. The suggested methodology provides the flexibility to quickly assess several economic scenarios and this without the need of knowing the complex design procedure. This novel way of optimizing and interpreting results is applied to a waste heat recovery case. Both the transcritical ORC and subcritical ORC are investigated and compared using the suggested optimization strategy. Full article
(This article belongs to the Special Issue Organic Rankine Cycle (ORC))
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Open AccessArticle
Melting Behavior and Thermolysis of NaBH4−Mg(BH4)2 and NaBH4−Ca(BH4)2 Composites
Energies 2015, 8(4), 2701-2713; https://doi.org/10.3390/en8042701
Received: 12 March 2015 / Revised: 31 March 2015 / Accepted: 1 April 2015 / Published: 8 April 2015
Cited by 11 | Viewed by 2395 | PDF Full-text (1518 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The physical properties and the hydrogen release of NaBH4–Mg(BH4)2 and NaBH4−Ca(BH4)2 composites are investigated using in situ synchrotron radiation powder X-ray diffraction, thermal analysis and temperature programmed photographic analysis. The composite, xNaBH [...] Read more.
The physical properties and the hydrogen release of NaBH4–Mg(BH4)2 and NaBH4−Ca(BH4)2 composites are investigated using in situ synchrotron radiation powder X-ray diffraction, thermal analysis and temperature programmed photographic analysis. The composite, xNaBH4–(1 − x)Mg(BH4)2, x = 0.4 to 0.5, shows melting/frothing between 205 and 220 °C. However, the sample does not become a transparent molten phase. This behavior is similar to other alkali-alkaline earth metal borohydride composites. In the xNaBH4–(1 − x)Ca(BH4)2 system, eutectic melting is not observed. Interestingly, eutectic melting in metal borohydrides systems leads to partial thermolysis and hydrogen release at lower temperatures and the control of sample melting may open new routes for obtaining high-capacity hydrogen storage materials. Full article
(This article belongs to the Special Issue Hydrides: Fundamentals and Applications) Printed Edition available
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Open AccessArticle
The Impact of a Carbon Tax on the Chilean Electricity Generation Sector
Energies 2015, 8(4), 2674-2700; https://doi.org/10.3390/en8042674
Received: 23 January 2015 / Revised: 22 March 2015 / Accepted: 26 March 2015 / Published: 3 April 2015
Cited by 21 | Viewed by 3892 | PDF Full-text (2669 KB) | HTML Full-text | XML Full-text | Correction
Abstract
This paper aims to analyse the economy-wide implications of a carbon tax applied on the Chilean electricity generation sector. In order to analyse the macroeconomic impacts, both an energy sectorial model and a Dynamic Stochastic General Equilibrium model have been used. During the [...] Read more.
This paper aims to analyse the economy-wide implications of a carbon tax applied on the Chilean electricity generation sector. In order to analyse the macroeconomic impacts, both an energy sectorial model and a Dynamic Stochastic General Equilibrium model have been used. During the year 2014 a carbon tax of 5 US$/tCO2e was approved in Chile. This tax and its increases (10, 20, 30, 40 and 50 US$/tCO2e) are evaluated in this article. The results show that the effectiveness of this policy depends on some variables which are not controlled by policy makers, for example, non-conventional renewable energy investment cost projections, natural gas prices, and the feasibility of exploiting hydroelectric resources. For a carbon tax of 20 US$/tCO2e, the average annual emission reduction would be between 1.1 and 9.1 million tCO2e. However, the price of the electricity would increase between 8.3 and 9.6 US$/MWh. This price shock would decrease the annual GDP growth rate by a maximum amount of 0.13%. This article compares this energy policy with others such as the introduction of non-conventional renewable energy sources and a sectorial cap. The results show that the same global greenhouse gas (GHG) emission reduction can be obtained with these policies, but the impact on the electricity price and GDP are lower than that of the carbon tax. Full article
(This article belongs to the Special Issue Energy Policy and Climate Change) Printed Edition available
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Open AccessArticle
High Efficiency Variable-Frequency Full-Bridge Converter with a Load Adaptive Control Method Based on the Loss Model
Energies 2015, 8(4), 2647-2673; https://doi.org/10.3390/en8042647
Received: 15 December 2014 / Revised: 3 March 2015 / Accepted: 6 March 2015 / Published: 1 April 2015
Cited by 7 | Viewed by 2509 | PDF Full-text (4473 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, a load adaptive control method to improve the efficiency and dynamic performance of the Phase-Shifted Full-Bridge (PSFB) converter which works under a wide range of load conditions is presented. The proposed control method can be used as a battery charger [...] Read more.
In this paper, a load adaptive control method to improve the efficiency and dynamic performance of the Phase-Shifted Full-Bridge (PSFB) converter which works under a wide range of load conditions is presented. The proposed control method can be used as a battery charger since this application demands a wide range of load conditions. The composition of the PSFB converter’s losses and the loss analysis model are both discussed. According to this model, the optimum switching frequency which results in minimum power loss is adopted to improve the efficiency. The relationship between switching frequency and power loss is formulated over a wide load range. Indicated by this kind of relationship, the proposed controller adjusts the switching frequency at different load currents. Moreover, an adaptive gain adjustment controller is applied to replace the traditional controller, with the aim to improve the dynamic performance which is influenced by the changes of the switching frequency and load current. In addition, the experimental results show that the maximum improvement of efficiency is up to 20%. These results confirm the effectiveness of the proposed load adaptive control method. Full article
(This article belongs to the collection Smart Grid)
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