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Energies, Volume 6, Issue 7 (July 2013), Pages 3097-3636

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Open AccessArticle Model-Based Fault Location with Frequency Domain for Power Traction System
Energies 2013, 6(7), 3097-3114; doi:10.3390/en6073097
Received: 21 December 2012 / Revised: 30 May 2013 / Accepted: 4 June 2013 / Published: 25 June 2013
Cited by 1 | PDF Full-text (350 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, precise fault location in electrical traction network systems is discussed in the high-frequency domain. Based on the analysis of the equivalent impedance at the measurement terminal, the relationship between the fault distance and the frequency spectrum extreme points of [...] Read more.
In this paper, precise fault location in electrical traction network systems is discussed in the high-frequency domain. Based on the analysis of the equivalent impedance at the measurement terminal, the relationship between the fault distance and the frequency spectrum extreme points of the system impedance are derived. The exact fault location can be obtained from the relationship curves accordingly. MATLAB simulation experiments have been performed to verify the effectiveness of the proposed algorithm. Full article
Open AccessArticle Development of a Transient Model of a Stirling-Based CHP System
Energies 2013, 6(7), 3115-3133; doi:10.3390/en6073115
Received: 27 March 2013 / Revised: 24 May 2013 / Accepted: 17 June 2013 / Published: 25 June 2013
Cited by 4 | PDF Full-text (530 KB) | HTML Full-text | XML Full-text
Abstract
Although the Stirling engine was invented in 1816, this heat engine still continues to be investigated due to the variety of energy sources that can be used to power it (e.g., solar energy, fossil fuels, biomass, and geothermal energy). To study the [...] Read more.
Although the Stirling engine was invented in 1816, this heat engine still continues to be investigated due to the variety of energy sources that can be used to power it (e.g., solar energy, fossil fuels, biomass, and geothermal energy). To study the performance of these machines, it is necessary to develop and simulate models under different operating conditions. In this paper, we present a one-dimensional dynamic model based on components from Trnsys: principally, a lumped mass and a heat exchanger. The resulting model is calibrated using GenOpt. Furthermore, the obtained model can be used to simulate the machine both under steady-state operation and during a transient response. The results provided by the simulations are compared with data measured in a Stirling engine that has been subjected to different operating conditions. This comparison shows good agreement, indicating that the model is an appropriate method for transient thermal simulations. This new proposed model requires few configuration parameters and is therefore easily adaptable to a wide range of commercial models of Stirling engines. A detailed analysis of the system results reveals that the power is directly related to the difference of temperatures between the hot and cold sources during the transient and steady-state processes. Full article
Open AccessArticle The Analysis of the Aerodynamic Character and Structural Response of Large-Scale Wind Turbine Blades
Energies 2013, 6(7), 3134-3148; doi:10.3390/en6073134
Received: 22 April 2013 / Revised: 20 June 2013 / Accepted: 20 June 2013 / Published: 27 June 2013
Cited by 3 | PDF Full-text (2245 KB) | HTML Full-text | XML Full-text
Abstract
A process of detailed CFD and structural numerical simulations of the 1.5 MW horizontal axis wind turbine (HAWT) blade is present. The main goal is to help advance the use of computer-aided simulation methods in the field of design and development of [...] Read more.
A process of detailed CFD and structural numerical simulations of the 1.5 MW horizontal axis wind turbine (HAWT) blade is present. The main goal is to help advance the use of computer-aided simulation methods in the field of design and development of HAWT-blades. After an in-depth study of the aerodynamic configuration and materials of the blade, 3-D mapping software is utilized to reconstruct the high fidelity geometry, and then the geometry is imported into CFD and structure finite element analysis (FEA) software for completely simulation calculation. This research process shows that the CFD results compare well with the professional wind turbine design and certification software, GH-Bladed. Also, the modal analysis with finite element method (FEM) predicts well compared with experiment tests on a stationary blade. For extreme wind loads case that by considering a 50-year extreme gust simulated in CFD are unidirectional coupled to the FE-model, the results indicate that the maximum deflection of the blade tip is less than the distance between the blade tip (the point of maximum deflection) and the tower, the material of the blade provides enough resistance to the peak stresses the occur at the conjunction of shear webs and center spar cap. Buckling analysis is also included in the study. Full article
(This article belongs to the Special Issue Wind Turbines 2013)
Open AccessArticle Design of a Hydraulic Motor System Driven by Compressed Air
Energies 2013, 6(7), 3149-3166; doi:10.3390/en6073149
Received: 25 February 2013 / Revised: 18 June 2013 / Accepted: 18 June 2013 / Published: 27 June 2013
Cited by 6 | PDF Full-text (577 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents the design of a highly efficient pneumatic motor system. The air engine is currently the most generally used device to convert potential energy of compressed air into mechanical energy. However, the efficiency of the air engines is too low [...] Read more.
This paper presents the design of a highly efficient pneumatic motor system. The air engine is currently the most generally used device to convert potential energy of compressed air into mechanical energy. However, the efficiency of the air engines is too low to provide sufficient operating range for the vehicle. In this study, the energy contained in compressed air/pressurized hydraulic oil is transformed by a hydraulic motor to mechanical energy to enhance the efficiency of using air power. To evaluate the theoretical efficiency, the principle of balance of energy is applied. The theoretical efficiency of converting air into hydraulic energy is found to be a function of pressure; thus, the maximum converting efficiency can be determined. To confirm the theoretical evaluation, a prototype of the pneumatic hydraulic system is built. The experiment verifies that the theoretical evaluation of the system efficiency is reasonable, and that the layout of the system is determined by the results of theoretical evaluation. Full article
Open AccessArticle Hydrogen-Rich Gas Production by Sorption Enhanced Steam Reforming of Woodgas Containing TAR over a Commercial Ni Catalyst and Calcined Dolomite as CO2 Sorbent
Energies 2013, 6(7), 3167-3181; doi:10.3390/en6073167
Received: 15 May 2013 / Revised: 24 June 2013 / Accepted: 26 June 2013 / Published: 1 July 2013
Cited by 10 | PDF Full-text (371 KB) | HTML Full-text | XML Full-text
Abstract
The aim of this work was the evaluation of the catalytic steam reforming of a gaseous fuel obtained by steam biomass gasification to convert topping atmosphere residue (TAR) and CH4 and to produce pure H2 by means of a CO [...] Read more.
The aim of this work was the evaluation of the catalytic steam reforming of a gaseous fuel obtained by steam biomass gasification to convert topping atmosphere residue (TAR) and CH4 and to produce pure H2 by means of a CO2 sorbent. This experimental work deals with the demonstration of the practical feasibility of such concepts, using a real woodgas obtained from fluidized bed steam gasification of hazelnut shells. This study evaluates the use of a commercial Ni catalyst and calcined dolomite (CaO/MgO). The bed material simultaneously acts as reforming catalyst and CO2 sorbent. The experimental investigations have been carried out in a fixed bed micro-reactor rig using a slipstream from the gasifier to evaluate gas cleaning and upgrading options. The reforming/sorption tests were carried out at 650 °C while regeneration of the sorbent was carried out at 850 °C in a nitrogen environment. Both combinations of catalyst and sorbent are very effective in TAR and CH4 removal, with conversions near 100%, while the simultaneous CO2 sorption effectively enhances the water gas shift reaction producing a gas with a hydrogen volume fraction of over 90%. Multicycle tests of reforming/CO2 capture and regeneration were performed to verify the stability of the catalysts and sorbents to remove TAR and capture CO2 during the duty cycle. Full article
(This article belongs to the Special Issue Biomass and Biofuels 2013)
Open AccessArticle Modeling Future Life-Cycle Greenhouse Gas Emissions and Environmental Impacts of Electricity Supplies in Brazil
Energies 2013, 6(7), 3182-3208; doi:10.3390/en6073182
Received: 16 April 2013 / Revised: 13 June 2013 / Accepted: 25 June 2013 / Published: 2 July 2013
Cited by 7 | PDF Full-text (1528 KB) | HTML Full-text | XML Full-text
Abstract
Brazil’s status as a rapidly developing country is visible in its need for more energy, including electricity. While the current electricity generation mix is primarily hydropower based, high-quality dam sites are diminishing and diversification to other sources is likely. We combined life-cycle [...] Read more.
Brazil’s status as a rapidly developing country is visible in its need for more energy, including electricity. While the current electricity generation mix is primarily hydropower based, high-quality dam sites are diminishing and diversification to other sources is likely. We combined life-cycle data for electricity production with scenarios developed using the IAEA’s MESSAGE model to examine environmental impacts of future electricity generation under a baseline case and four side cases, using a Monte-Carlo approach to incorporate uncertainty in power plant performance and LCA impacts. Our results show that, under the cost-optimal base case scenario, Brazil’s GHGs from electricity (excluding hydroelectric reservoir emissions) rise 370% by 2040 relative to 2010, with the carbon intensity per MWh rising 100%. This rise would make Brazil’s carbon emissions targets difficult to meet without demand-side programs. Our results show a future electricity mix dominated by environmental tradeoffs in the use of large-scale renewables, questioning the use tropical hydropower and highlighting the need for additional work to assess and include ecosystem and social impacts, where information is currently sparse. Full article
Open AccessArticle Analysis and Experiment of a Novel Brushless Double Rotor Machine for Power-Split Hybrid Electrical Vehicle Applications
Energies 2013, 6(7), 3209-3223; doi:10.3390/en6073209
Received: 27 March 2013 / Revised: 20 June 2013 / Accepted: 21 June 2013 / Published: 2 July 2013
Cited by 3 | PDF Full-text (1055 KB) | HTML Full-text | XML Full-text
Abstract
A novel brushless double rotor machine (BDRM) is proposed in this paper. The BDRM is an important component in the brushless compound-structure permanent-magnet synchronous machine (CS-PMSM) system, which is a promising technology for power-split hybrid electric vehicle (HEV) applications. Compared with common [...] Read more.
A novel brushless double rotor machine (BDRM) is proposed in this paper. The BDRM is an important component in the brushless compound-structure permanent-magnet synchronous machine (CS-PMSM) system, which is a promising technology for power-split hybrid electric vehicle (HEV) applications. Compared with common double rotor machines, the brushes and slip rings required by rotating winding have been omitted in the BDRM, thus there are no such problems as maintenance, friction losses and so forth. Firstly, the torque characteristics of the BDRM are analyzed. As the stator has ring-shaped centralized windings, the size characteristics of the BDRM are different from those of conventional machines. The new sizing and torque equations are analyzed and the theoretical results are applied to determine the main dimensions. Additionally, studies of the analytical magnetic circuit and finite element method (FEM) model show that the BDRM tends to have high leakage flux and low power factor. Although the scope for improving the serious flux leakage of the BDRM is limited by the special magnetic topology, a method to obtain higher power factor is provided. Finally, a 10 kW prototype machine was manufactured, assembly of the prototype is discussed in detail and experimental tests are performed to validate the analytical and simulation results. Full article
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Open AccessArticle Experimental Research and Control Strategy of Pumped Storage Units Dispatching in the Taiwan Power System Considering Transmission Line Limits
Energies 2013, 6(7), 3224-3244; doi:10.3390/en6073224
Received: 25 February 2013 / Revised: 21 May 2013 / Accepted: 25 June 2013 / Published: 3 July 2013
Cited by 1 | PDF Full-text (403 KB) | HTML Full-text | XML Full-text
Abstract
Taiwan’s power system is isolated and not supported by other interconnected systems. Consequently, the system frequency immediately reflects changes in the system loads. Pumped storage units are crucial for controlling power frequency. These units provide main or auxiliary capacities, reducing the allocation [...] Read more.
Taiwan’s power system is isolated and not supported by other interconnected systems. Consequently, the system frequency immediately reflects changes in the system loads. Pumped storage units are crucial for controlling power frequency. These units provide main or auxiliary capacities, reducing the allocation of frequency-regulating reserve (FRR) and further reducing generation costs in system operations. Taiwan’s Longmen Nuclear Power Plant is set to be converted for commercial operations, which will significantly alter the spinning reserves in the power system. Thus, this study proposes a safe and economic pumped storage unit dispatch strategy. This strategy is used to determine the optimal FRR capacity and 1-min recovery frequency in a generator failure occurrence at the Longmen Power Plant. In addition, this study considered transmission capacity constraints and conducted power flow analysis of the power systems in Northern, Central, and Southern Taiwan. The results indicated that, in the event of a failure at Longmen Power Plant, the proposed strategy can not only recover the system frequency to an acceptable range to prevent underfrequency load-shedding, but can also mitigate transmission line overloading. Full article
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Open AccessArticle Experimental Studies on the Normal Impact of Fly Ash Particles with Planar Surfaces
Energies 2013, 6(7), 3245-3262; doi:10.3390/en6073245
Received: 23 April 2013 / Revised: 25 June 2013 / Accepted: 27 June 2013 / Published: 3 July 2013
Cited by 6 | PDF Full-text (1527 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents the results of a comprehensive program of experiments in which fly ash particles were impacted under controlled conditions against a flat steel surface. The overall aim of these experiments was to gain an understanding of the ash deposition process [...] Read more.
This paper presents the results of a comprehensive program of experiments in which fly ash particles were impacted under controlled conditions against a flat steel surface. The overall aim of these experiments was to gain an understanding of the ash deposition process in a pulverized coal boiler system. A continuous nitrogen flow carrying fly ash particles was used to examine the effect of particle incident velocity and particle diameter (dp) on the normal restitution coefficient, and of the particle diameter on the critical velocity. The effect of the incident normal velocity and particle diameter on the normal restitution coefficient was also examined. The results show that the normal restitution coefficient increases rapidly with increasing incident velocity when this incident velocity is less than the yield velocity, and rapidly decreases with increasing incident velocity when the incident velocity is greater than the yield velocity. The critical velocity, determined solely by the first-contact energy loss, is proportional to dp−5/6 and therefore becomes larger for smaller particles. For instance, in the present work, the velocity vc of a particle with diameter of 85 μm is 0.19 m/s, which increases to 0.42 m/s for particles with a diameter of 65 μm. Full article
(This article belongs to the Special Issue Coal Combustion and Gasification)
Open AccessArticle Hardware-in-the-Loop Simulation of Distributed Intelligent Energy Management System for Microgrids
Energies 2013, 6(7), 3263-3283; doi:10.3390/en6073263
Received: 6 May 2013 / Revised: 19 June 2013 / Accepted: 21 June 2013 / Published: 3 July 2013
Cited by 4 | PDF Full-text (2493 KB) | HTML Full-text | XML Full-text
Abstract
Microgrids are autonomous low-voltage power distribution systems that contain multiple distributed energy resources (DERs) and smart loads that can provide power system operation flexibility. To effectively control and coordinate multiple DERs and loads of microgrids, this paper proposes a distributed intelligent management [...] Read more.
Microgrids are autonomous low-voltage power distribution systems that contain multiple distributed energy resources (DERs) and smart loads that can provide power system operation flexibility. To effectively control and coordinate multiple DERs and loads of microgrids, this paper proposes a distributed intelligent management system that employs a multi-agent-based control system so that delicate decision-making functions can be distributed to local intelligent agents. This paper presents the development of a hardware-in-the-loop simulation (HILS) system for distributed intelligent management system for microgrids and its promising application to an emergency demand response program. In the developed HILS system, intelligent agents are developed using microcontrollers and ZigBee wireless communication technology. Power system dynamic models are implemented in real-time simulation environments using the Opal-RT system. This paper presents key features of the data communication and management schemes based on multi-agent concepts. The performance of the developed system is tested for emergency demand response program applications. Full article
Open AccessArticle Catalytic Steam Reforming of Toluene as a Model Compound of Biomass Gasification Tar Using Ni-CeO2/SBA-15 Catalysts
Energies 2013, 6(7), 3284-3296; doi:10.3390/en6073284
Received: 6 May 2013 / Revised: 16 June 2013 / Accepted: 27 June 2013 / Published: 4 July 2013
Cited by 14 | PDF Full-text (655 KB) | HTML Full-text | XML Full-text
Abstract
Nickel supported on SBA-15 doped with CeO2 catalysts (Ni-CeO2/SBA-15) was prepared, and used for steam reforming of toluene which was selected as a model compound of biomass gasification tar. A fixed-bed lab-scale set was designed and employed to evaluate [...] Read more.
Nickel supported on SBA-15 doped with CeO2 catalysts (Ni-CeO2/SBA-15) was prepared, and used for steam reforming of toluene which was selected as a model compound of biomass gasification tar. A fixed-bed lab-scale set was designed and employed to evaluate the catalytic performances of the Ni-CeO2/SBA-15 catalysts. Experiments were performed to reveal the effects of several factors on the toluene conversion and product gas composition, including the reaction temperature, steam/carbon (S/C) ratio, and CeO2 loading content. Moreover, the catalysts were subjected to analysis of their carbon contents after the steam reforming experiments, as well as to test the catalytic stability over a long experimental period. The results indicated that the Ni-CeO2/SBA-15 catalysts exhibited promising capabilities on the toluene conversion, anti-coke deposition and catalytic stability. The toluene conversion reached as high as 98.9% at steam reforming temperature of 850 °C and S/C ratio of 3 using the Ni-CeO2(3wt%)/SBA-15 catalyst. Negligible coke formation was detected on the used catalyst. The gaseous products mainly consisted of H2 and CO, together with a little CO2 and CH4. Full article
(This article belongs to the Special Issue Biomass and Biofuels 2013)
Open AccessArticle Harmonic Propagation and Interaction Evaluation between Small-Scale Wind Farms and Nonlinear Loads
Energies 2013, 6(7), 3297-3322; doi:10.3390/en6073297
Received: 25 April 2013 / Revised: 26 June 2013 / Accepted: 2 July 2013 / Published: 5 July 2013
Cited by 4 | PDF Full-text (1094 KB) | HTML Full-text | XML Full-text
Abstract
Distributed generation is a flexible and effective way to utilize renewable energy. The dispersed generators are quite close to the load, and pose some power quality problems such as harmonic current emissions. This paper focuses on the harmonic propagation and interaction between [...] Read more.
Distributed generation is a flexible and effective way to utilize renewable energy. The dispersed generators are quite close to the load, and pose some power quality problems such as harmonic current emissions. This paper focuses on the harmonic propagation and interaction between a small-scale wind farm and nonlinear loads in the distribution grid. Firstly, by setting the wind turbines as P Q(V) nodes, the paper discusses the expanding Newton-Raphson power flow method for the wind farm. Then the generalized gamma mixture models are proposed to study the non-characteristic harmonic propagation of the wind farm, which are based on Gaussian mixture models, improved phasor clustering and generalized Gamma models. After the integration of the small-scale wind farm, harmonic emissions of nonlinear loads will become random and fluctuating due to the non-stationary wind power. Furthermore, in this paper the harmonic coupled admittance matrix model of nonlinear loads combined with a wind farm is deduced by rigorous formulas. Then the harmonic propagation and interaction between a real wind farm and nonlinear loads are analyzed by the harmonic coupled admittance matrix and generalized gamma mixture models. Finally, the proposed models and methods are verified through the corresponding simulation models in MATLAB/SIMULINK and PSCAD/EMTDC. Full article
(This article belongs to the Special Issue Wind Turbines 2013)
Open AccessArticle An Analysis of Variable-Speed Wind Turbine Power-Control Methods with Fluctuating Wind Speed
Energies 2013, 6(7), 3323-3338; doi:10.3390/en6073323
Received: 2 May 2013 / Revised: 13 June 2013 / Accepted: 29 June 2013 / Published: 5 July 2013
Cited by 6 | PDF Full-text (680 KB) | HTML Full-text | XML Full-text
Abstract
Variable-speed wind turbines (VSWTs) typically use a maximum power-point tracking (MPPT) method to optimize wind-energy acquisition. MPPT can be implemented by regulating the rotor speed or by adjusting the active power. The former, termed speed-control mode (SCM), employs a speed controller to [...] Read more.
Variable-speed wind turbines (VSWTs) typically use a maximum power-point tracking (MPPT) method to optimize wind-energy acquisition. MPPT can be implemented by regulating the rotor speed or by adjusting the active power. The former, termed speed-control mode (SCM), employs a speed controller to regulate the rotor, while the latter, termed power-control mode (PCM), uses an active power controller to optimize the power. They are fundamentally equivalent; however, since they use a different controller at the outer control loop of the machine-side converter (MSC) controller, the time dependence of the control system differs depending on whether SCM or PCM is used. We have compared and analyzed the power quality and the power coefficient when these two different control modes were used in fluctuating wind speeds through computer simulations. The contrast between the two methods was larger when the wind-speed fluctuations were greater. Furthermore, we found that SCM was preferable to PCM in terms of the power coefficient, but PCM was superior in terms of power quality and system stability. Full article
(This article belongs to the Special Issue Wind Turbines 2013)
Open AccessArticle Yield and Characteristics of Pyrolysis Products Obtained from Schizochytrium limacinum under Different Temperature Regimes
Energies 2013, 6(7), 3339-3352; doi:10.3390/en6073339
Received: 27 March 2013 / Revised: 14 June 2013 / Accepted: 20 June 2013 / Published: 5 July 2013
Cited by 8 | PDF Full-text (418 KB) | HTML Full-text | XML Full-text
Abstract
Pyrolysis-gas chromatographic mass spectrometry (Py-GC/MS) was used to determine the yield and chemical composition of the pyrolysis products of Schizochytrium limacinum. The pyrolysis was carried out by varying the temperature from 300 °C to 800 °C. It was found that the [...] Read more.
Pyrolysis-gas chromatographic mass spectrometry (Py-GC/MS) was used to determine the yield and chemical composition of the pyrolysis products of Schizochytrium limacinum. The pyrolysis was carried out by varying the temperature from 300 °C to 800 °C. It was found that the main decomposition temperature of Schizochytrium limacinum was 428.16 °C, at which up to 66.5% of the mass was lost. A further 18.7% mass loss then occurred in a relatively slow pace until 760.2 °C due to complete decomposition of the ash content of Schizochytrium limacinum. The pyrolysis of Schizochytrium limacinum at 700 °C produced the maximum yield (67.7%) of pyrolysis products compared to 61.2% at 400 °C. While pollutants released at 700 °C (12.3%) was much higher than that of 400 °C (2.1%). Higher temperature will lead to more pollutant (nitrogen compounds and PAHs) release, which is harmful to the environment. Considering the reasonably high yield and minimum release of pollutants, a lower pyrolysis temperature (400 °C) was found to be optimum for producing biofuel from Schizochytrium limacinum. Full article
Open AccessArticle A Long Gravity-Piston Corer Developed for Seafloor Gas Hydrate Coring Utilizing an In Situ Pressure-Retained Method
Energies 2013, 6(7), 3353-3372; doi:10.3390/en6073353
Received: 27 March 2013 / Revised: 29 May 2013 / Accepted: 24 June 2013 / Published: 9 July 2013
Cited by 3 | PDF Full-text (1770 KB) | HTML Full-text | XML Full-text
Abstract
A corer, which can obtain long in situ pressure-retained sediments of up to 30 m core containing gas hydrates, has been applied in the South China Sea (SCS) dozens of times. The corer presented in this paper is a convenient, efficient and [...] Read more.
A corer, which can obtain long in situ pressure-retained sediments of up to 30 m core containing gas hydrates, has been applied in the South China Sea (SCS) dozens of times. The corer presented in this paper is a convenient, efficient and economical long in situ pressure-retained coring and research tool for submarine sediments, that can applied to completely cope with all sediments close to the seafloor ranging from shallow waters to the deep sea depths of 6000 m. This article mainly presents the overall structure, working principles, key pressure-retained components, coring mechanism, sea trials and outlook of the corer. The analyses found that the coring ability was affected by formation characteristics, the outer diameter of the core barrels and inner diameter of the core liners, the shapes of the cutter and the dead weight of the corer. This study can provide the practical basis for the structural optimization of this type of corer and designs for corers with greater penetrability. Sea trials showed that the developed corer presented in this paper can support the in situ pressure of the seafloor sediment core, which is an improvement over the conventional piston corer. Full article
(This article belongs to the Special Issue Natural Gas Hydrate)
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Open AccessArticle Feasibility of a Simple Small Wind Turbine with Variable-Speed Regulation Made of Commercial Components
Energies 2013, 6(7), 3373-3391; doi:10.3390/en6073373
Received: 28 May 2013 / Revised: 28 June 2013 / Accepted: 8 July 2013 / Published: 10 July 2013
Cited by 2 | PDF Full-text (2019 KB) | HTML Full-text | XML Full-text
Abstract
The aim of this study was to propose and evaluate a very small wind turbine (VSWT) that competes with commercial grid-connected VSWTs in terms of simplicity, robustness and price. Its main components are a squirrel-cage induction generator (SCIG) driven by a frequency [...] Read more.
The aim of this study was to propose and evaluate a very small wind turbine (VSWT) that competes with commercial grid-connected VSWTs in terms of simplicity, robustness and price. Its main components are a squirrel-cage induction generator (SCIG) driven by a frequency converter. The system has a direct-drive shaft, and may be constructed with commercial equipment. Simulation of the wind turbine effect is done with a motor. A control program regulates the variable-speed of rotation through three operational modes: (i) to drive the turbine to its optimum operation point; (ii) to limit its maximum rotational speed; and (iii) to limit the maximum power it generates. Two tests were performed, in order to evaluate the dynamic response of this system under variable wind speeds. The tests demonstrate that the system operates at the optimum operational point of the turbine, and within the set limits of maximum rotational speed and maximum generated power. The drop in performance in relation to its nominal value is about 75%, when operating at 50% of the nominal power. In summary, this VSWT with its proposed control program is feasible and reliable for operating direct-shaft grid-connected VSWTs. Full article
(This article belongs to the Special Issue Wind Turbines 2013)
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Open AccessArticle An Energy Storage System Sizing Method for Wind Power Integration
Energies 2013, 6(7), 3392-3404; doi:10.3390/en6073392
Received: 25 April 2013 / Revised: 7 June 2013 / Accepted: 25 June 2013 / Published: 11 July 2013
PDF Full-text (381 KB) | HTML Full-text | XML Full-text
Abstract
Combining an energy storage system (ESS) with a wind farm is an effective way to increase the penetration rate of wind power. ESS sizing is an important part in wind farm planning nowadays. In this paper, a basic method for determining the [...] Read more.
Combining an energy storage system (ESS) with a wind farm is an effective way to increase the penetration rate of wind power. ESS sizing is an important part in wind farm planning nowadays. In this paper, a basic method for determining the optimal capacity of an ESS integrated with a wind power generator to meet the requirements of grid integration is presented. With the proposed method, the necessary ESS capacity which can provide the best benefits between the regulation effects and energy storage size was calculated. The segmentation method and automatic segmentation method are proposed to improve the performance of the basic method. Further work on expanding the method to determine the necessary capacity of ESS for real-time control is studied. The time window method is used to enable the proposed method available under all working conditions. The simulation results verify the effectiveness of the proposed method. Full article
Open AccessArticle Operation and Control of a Direct-Driven PMSG-Based Wind Turbine System with an Auxiliary Parallel Grid-Side Converter
Energies 2013, 6(7), 3405-3421; doi:10.3390/en6073405
Received: 28 March 2013 / Revised: 27 June 2013 / Accepted: 1 July 2013 / Published: 12 July 2013
Cited by 7 | PDF Full-text (544 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, based on the similarity, in structure and principle, between a grid-connected converter for a direct-driven permanent magnet synchronous generator (D-PMSG) and an active power filter (APF), a new D-PMSG-based wind turbine (WT) system configuration that includes not only an [...] Read more.
In this paper, based on the similarity, in structure and principle, between a grid-connected converter for a direct-driven permanent magnet synchronous generator (D-PMSG) and an active power filter (APF), a new D-PMSG-based wind turbine (WT) system configuration that includes not only an auxiliary converter in parallel with the grid-side converter, but also a coordinated control strategy, is proposed to enhance the low voltage ride through (LVRT) capability and improve power quality. During normal operation, the main grid-side converter maintains the DC-link voltage constant, whereas the auxiliary grid-side converter functions as an APF with harmonic suppression and reactive power compensation to improve the power quality. During grid faults, a hierarchical coordinated control scheme for the generator-side converter, main grid-side converter and auxiliary grid-side converter, depending on the grid voltage sags, is presented to enhance the LVRT capability of the direct-driven PMSG WT. The feasibility and the effectiveness of the proposed system’s topology and hierarchical coordinated control strategy were verified using MATLAB/Simulink simulations. Full article
(This article belongs to the Special Issue Wind Turbines 2013)
Open AccessArticle A Power Load Distribution Algorithm to Optimize Data Center Electrical Flow
Energies 2013, 6(7), 3422-3443; doi:10.3390/en6073422
Received: 13 March 2013 / Revised: 15 June 2013 / Accepted: 4 July 2013 / Published: 15 July 2013
Cited by 4 | PDF Full-text (1051 KB) | HTML Full-text | XML Full-text
Abstract
Energy consumption is a matter of common concern in the world today. Research demonstrates that as a consequence of the constantly evolving and expanding field of information technology, data centers are now major consumers of electrical energy. Such high electrical energy consumption [...] Read more.
Energy consumption is a matter of common concern in the world today. Research demonstrates that as a consequence of the constantly evolving and expanding field of information technology, data centers are now major consumers of electrical energy. Such high electrical energy consumption emphasizes the issues of sustainability and cost. Against this background, the present paper proposes a power load distribution algorithm (PLDA) to optimize energy distribution of data center power infrastructures. The PLDA, which is based on the Ford-Fulkerson algorithm, is supported by an environment called ASTRO, capable of performing the integrated evaluation of dependability, cost and sustainability. More specifically, the PLDA optimizes the flow distribution of the energy flow model (EFM). EFMs are responsible for estimating sustainability and cost issues of data center infrastructures without crossing the restrictions of the power capacity that each device can provide (power system) or extract (cooling system). Additionally, a case study is presented that analyzed seven data center power architectures. Significant results were observed, achieving a reduction in power consumption of up to 15.5%. Full article
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Open AccessArticle Comparison and Analysis of Macro Energy Scenarios in China and a Decomposition-Based Approach to Quantifying the Impacts of Economic and Social Development
Energies 2013, 6(7), 3444-3465; doi:10.3390/en6073444
Received: 21 May 2013 / Revised: 8 July 2013 / Accepted: 8 July 2013 / Published: 15 July 2013
Cited by 4 | PDF Full-text (913 KB) | HTML Full-text | XML Full-text
Abstract
China has been experiencing a rapid urbanization and industrialization progress with continuous increase in primary energy consumption. Meanwhile, China’s changing economic and society structure also introduces huge uncertainty to its future energy demand. Many energy research institutes periodically publish projections of macro [...] Read more.
China has been experiencing a rapid urbanization and industrialization progress with continuous increase in primary energy consumption. Meanwhile, China’s changing economic and society structure also introduces huge uncertainty to its future energy demand. Many energy research institutes periodically publish projections of macro energy scenarios of China up to 2030 and 2050, but these projections differ from one another in terms of total amount of energy consumption and energy flows amongst sectors. In this work, we firstly illustrate major differences between existing scenarios based on a literature survey. We then compare and analyze the different projection methods, key policy assumptions, and other boundary conditions adopted in obtaining these scenarios. Then an index decomposition method is introduced with the purpose of decoupling the impacts of economic growth and population growth on the projection to energy consumption and greenhouse gas emissions. Our results illustrate that projections from domestic research institutes tend to be more optimistic regarding clean and sustainable utilization of coal in the future. Also, projections on energy consumption in China are exclusively linearly dependent on projections of economic and population growth in most scenarios, whilst in some other scenarios the impacts of oil price, international trade, and other drivers are also rather significant. Full article
Open AccessArticle Acetylene Black/Sulfur Composites Synthesized by a Solution Evaporation Concentration Crystallization Method and Their Electrochemical Properties for Li/S Batteries
Energies 2013, 6(7), 3466-3480; doi:10.3390/en6073466
Received: 8 May 2013 / Revised: 20 June 2013 / Accepted: 9 July 2013 / Published: 15 July 2013
Cited by 5 | PDF Full-text (44841 KB) | HTML Full-text | XML Full-text
Abstract
A novel technique to prepare carbon/sulfur composites as cathode materials for Li/S batteries is proposed, which we call the ‘solution evaporation concentration crystallization’ method. Three composites with different S loadings were prepared, subject to two different solvent evaporation rates from acetylene black [...] Read more.
A novel technique to prepare carbon/sulfur composites as cathode materials for Li/S batteries is proposed, which we call the ‘solution evaporation concentration crystallization’ method. Three composites with different S loadings were prepared, subject to two different solvent evaporation rates from acetylene black (AB)/sulfur in carbon disulfide solutions. X-ray diffraction, environmental scanning electron microscopy, transmission electron microscopy, and Brunauer-Emmett-Teller measurements all show that the porous AB structure is well-filled with S. Composites prepared at a lower solvent evaporation rate with 50 wt % S content, had good electrochemical properties, with 1609.67 mAh g−1 after 100 cycles. Composites with better dispersibility at a low solvent evaporation rate can effectively prevent polysulfide from dissolving in the electrolyte, and serve to stabilize the structure of the S cathode during the charge-discharge process. Full article
(This article belongs to the Special Issue Li-ion Batteries and Energy Storage Devices)
Open AccessArticle Results from a Novel Method for Corrosion Studies of Electroplated Lithium Metal Based on Measurements with an Impedance Scanning Electrochemical Quartz Crystal Microbalance
Energies 2013, 6(7), 3481-3505; doi:10.3390/en6073481
Received: 3 May 2013 / Revised: 14 June 2013 / Accepted: 3 July 2013 / Published: 15 July 2013
Cited by 4 | PDF Full-text (2752 KB) | HTML Full-text | XML Full-text
Abstract
A new approach to study the chemical stability of electrodeposited lithium on a copper metal substrate via measurements with a fast impedance scanning electrochemical quartz crystal microbalance is presented. The corrosion of electrochemically deposited lithium was compared in two different electrolytes, based [...] Read more.
A new approach to study the chemical stability of electrodeposited lithium on a copper metal substrate via measurements with a fast impedance scanning electrochemical quartz crystal microbalance is presented. The corrosion of electrochemically deposited lithium was compared in two different electrolytes, based on lithium difluoro(oxalato) borate (LiDFOB) and lithium hexafluorophosphate, both salts being dissolved in solvent blends of ethylene carbonate and diethyl carbonate. For a better understanding of the corrosion mechanisms, scanning electron microscopy images of electrodeposited lithium were also consulted. The results of the EQCM experiments were supported by AC impedance measurements and clearly showed two different corrosion mechanisms caused by the different salts and the formed SEIs. The observed mass decrease of the quartz sensor of the LiDFOB-based electrolyte is not smooth, but rather composed of a series of abrupt mass fluctuations in contrast to that of the lithium hexafluorophosphate-based electrolyte. After each slow decrease of mass a rather fast increase of mass is observed several times. The slow mass decrease can be attributed to a consolidation process of the SEI or to the partial dissolution of the SEI leaving finally lithium metal unprotected so that a fast film formation sets in entailing the observed fast mass increases. Full article
(This article belongs to the Special Issue Li-ion Batteries and Energy Storage Devices)
Open AccessArticle Nearly Zero-Energy Buildings of the Lombardy Region (Italy), a Case Study of High-Energy Performance Buildings
Energies 2013, 6(7), 3506-3527; doi:10.3390/en6073506
Received: 28 May 2013 / Revised: 10 July 2013 / Accepted: 11 July 2013 / Published: 16 July 2013
Cited by 9 | PDF Full-text (1007 KB) | HTML Full-text | XML Full-text
Abstract
The topic of nearly zero-energy buildings (n-ZEB), introduced by the Directive 2010/31/EU will direct the building market toward ever greater energy efficiency of new buildings. In some contexts, however, the building market for high-efficiency buildings has evolved, in recent years, on the [...] Read more.
The topic of nearly zero-energy buildings (n-ZEB), introduced by the Directive 2010/31/EU will direct the building market toward ever greater energy efficiency of new buildings. In some contexts, however, the building market for high-efficiency buildings has evolved, in recent years, on the basis of national and regional laws that have contributed to the acceleration of the process. This paper analyses the case study of the Lombardy Region (Italy), which transposed and assimilated the Directive 91/2002 (Energy Performance Building Directive), as of 2006, with regional legislation for energy efficiency of buildings. Within a few years the market for high energy-performance of buildings in the Lombardy Region had grown substantially: to date nearly 7500 energy performance certificates for buildings of Class A and Class A+ have been issued. The paper therefore analyses a success story in what is a field of great current interest, namely n-ZEB buildings. In the first part of the work, the evolution in terms of energy efficiency of the housing market in the Lombardy Region has been analyzed, with particular reference to the high energy-performance of buildings. The second part focuses on a sample of 20 n-ZEB buildings in order to highlight the design choices applied to them. Full article
(This article belongs to the Special Issue Energy Efficient Building Design 2013)
Open AccessArticle Optimization of a Fuzzy-Logic-Control-Based Five-Stage Battery Charger Using a Fuzzy-Based Taguchi Method
Energies 2013, 6(7), 3528-3547; doi:10.3390/en6073528
Received: 6 June 2013 / Revised: 9 July 2013 / Accepted: 9 July 2013 / Published: 17 July 2013
Cited by 3 | PDF Full-text (1581 KB) | HTML Full-text | XML Full-text
Abstract
Lithium ion (Li-ion) batteries have been widely used in various kinds of applications, including consumer electronics, green energy systems and electrical vehicles. Since the charging method has a significant influence on the performance and lifetime of Li-ion batteries, an intelligent charging algorithm [...] Read more.
Lithium ion (Li-ion) batteries have been widely used in various kinds of applications, including consumer electronics, green energy systems and electrical vehicles. Since the charging method has a significant influence on the performance and lifetime of Li-ion batteries, an intelligent charging algorithm which can properly determine the charging current is essential. In this study, a fuzzy-logic-control-based (FLC-based) five-stage Li-ion battery charger is proposed. The proposed charger takes the temperature rise and the gradient of temperature rise of battery into account, and adjusts the charging current accordingly. To further improve the performance of the proposed FLC, the fuzzy-based Taguchi method is utilized to determine the optimal output membership functions (MFs). Comparing with the conventional constant current-constant voltage (CC-CV) method, the charging time, charging efficiency, average temperature rise and the obtained cycle life of the Li-ion battery are improved by about 58.3%, 1.65%, 26.7% and 59.3%, respectively. Full article
Open AccessArticle Determining Adaptability Performance of Artificial Neural Network-Based Thermal Control Logics for Envelope Conditions in Residential Buildings
Energies 2013, 6(7), 3548-3570; doi:10.3390/en6073548
Received: 17 June 2013 / Revised: 4 July 2013 / Accepted: 4 July 2013 / Published: 18 July 2013
Cited by 5 | PDF Full-text (970 KB) | HTML Full-text | XML Full-text
Abstract
This study examines the performance and adaptability of Artificial Neural Network (ANN)-based thermal control strategies for diverse thermal properties of building envelope conditions applied to residential buildings. The thermal performance using two non-ANN-based control logics and two predictive ANN-based control logics was [...] Read more.
This study examines the performance and adaptability of Artificial Neural Network (ANN)-based thermal control strategies for diverse thermal properties of building envelope conditions applied to residential buildings. The thermal performance using two non-ANN-based control logics and two predictive ANN-based control logics was numerically tested using simulation software after validation. The performance tests were conducted for a two-story single-family house for various envelope insulation levels and window-to-wall ratios on the envelopes. The percentages of the period within the targeted ranges for air temperature, humidity and PMV, and the magnitudes of the overshoots and undershoots outside of the targeted comfort range were analyzed for each control logic scheme. The results revealed that the two predictive control logics that employed thermal predictions of the ANN models achieved longer periods of thermal comfort than the non-ANN-based models in terms of the comfort periods and the reductions of the magnitudes of the overshoots and undershoots. The ANN-based models proved their adaptability through accurate control of the thermal conditions in buildings with various architectural variables. The ANN-based predictive control methods demonstrated their potential to create more comfortable thermal conditions in single-family homes compared to non-ANN based control logics. Full article
(This article belongs to the Special Issue Energy Efficient Building Design 2013)
Open AccessArticle Hybrid-Electric Vehicle with Natural Gas-Diesel Engine
Energies 2013, 6(7), 3571-3592; doi:10.3390/en6073571
Received: 19 June 2013 / Revised: 5 July 2013 / Accepted: 11 July 2013 / Published: 18 July 2013
Cited by 9 | PDF Full-text (6538 KB) | HTML Full-text | XML Full-text
Abstract
In this paper we demonstrate the potential of combining electric hybridization with a dual-fuel natural gas-Diesel engine. We show that carbon dioxide emissions can be reduced to 43 gram per kilometer with a subcompact car on the New European Driving Cycle (NEDC). [...] Read more.
In this paper we demonstrate the potential of combining electric hybridization with a dual-fuel natural gas-Diesel engine. We show that carbon dioxide emissions can be reduced to 43 gram per kilometer with a subcompact car on the New European Driving Cycle (NEDC). The vehicle is operated in charge-sustaining mode, which means that all energy is provided by the fuel. The result is obtained by hardware-in-the-loop experiments where the engine is operated on a test bench while the rest of the powertrain as well as the vehicle are simulated. By static engine measurements we demonstrate that the natural gas-Diesel engine reaches efficiencies of up to 39.5%. The engine is operated lean at low loads with low engine out nitrogen oxide emissions such that no nitrogen oxide aftertreatment is necessary. At medium to high loads the engine is operated stoichiometrically, which enables the use of a cost-efficient three-way catalytic converter. By vehicle emulation of a non-hybrid vehicle on the Worldwide harmonized Light vehicles Test Procedure (WLTP), we demonstrate that transient operation of the natural gas-Diesel engine is also possible, thus enabling a non-hybridized powertrain as well. Full article
Open AccessArticle Measurements of Water Permeability in Unconsolidated Porous Media with Methane Hydrate Formation
Energies 2013, 6(7), 3622-3636; doi:10.3390/en6073622
Received: 6 May 2013 / Revised: 17 June 2013 / Accepted: 15 July 2013 / Published: 23 July 2013
Cited by 12 | PDF Full-text (651 KB) | HTML Full-text | XML Full-text
Abstract
Permeability is one of the key factors that determine the fluids flow capacity and production potential of hydrate deposits. In this study, an experimental setup is developed to investigate the flow properties of the porous media, and the permeabilities to water are [...] Read more.
Permeability is one of the key factors that determine the fluids flow capacity and production potential of hydrate deposits. In this study, an experimental setup is developed to investigate the flow properties of the porous media, and the permeabilities to water are measured in the unconsolidated porous media with or without hydrate deposition in the pores. A specialized method of precisely controlling the amount of injected methane gas is employed to form methane hydrate in the core sample, and the hydrate formation process is described by the change characteristics of the gas and hydrate saturations. It is found that the residual gas plays an obstructive role in the water flow and it tends to slightly reduce the water permeability in the porous media, especially under high pressure conditions. After hydrate formation in the core sample, relatively steady flow state can be obtained under suitable water injection rate Q at which hydrate dissociation rate is very slow. The absolute permeability of the porous sample is reduced from 49.2 to 1.2 Darcies when the hydrate saturation increases from 0 to 9.3% in this study, indicating a strong dependence of k on the hydrate saturation. Full article
(This article belongs to the Special Issue Natural Gas Hydrate)

Review

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Open AccessReview Middleware Architectures for the Smart Grid: Survey and Challenges in the Foreseeable Future
Energies 2013, 6(7), 3593-3621; doi:10.3390/en6073593
Received: 7 June 2013 / Revised: 12 July 2013 / Accepted: 15 July 2013 / Published: 22 July 2013
Cited by 9 | PDF Full-text (1149 KB) | HTML Full-text | XML Full-text
Abstract
The traditional power grid is just a one-way supplier that gets no feedback data about the energy delivered, what tariffs could be the most suitable ones for customers, the shifting daily needs of electricity in a facility, etc. Therefore, it is only [...] Read more.
The traditional power grid is just a one-way supplier that gets no feedback data about the energy delivered, what tariffs could be the most suitable ones for customers, the shifting daily needs of electricity in a facility, etc. Therefore, it is only natural that efforts are being invested in improving power grid behavior and turning it into a Smart Grid. However, to this end, several components have to be either upgraded or created from scratch. Among the new components required, middleware appears as a critical one, for it will abstract all the diversity of the used devices for power transmission (smart meters, embedded systems, etc.) and will provide the application layer with a homogeneous interface involving power production and consumption management data that were not able to be provided before. Additionally, middleware is expected to guarantee that updates to the current metering infrastructure (changes in service or hardware availability) or any added legacy measuring appliance will get acknowledged for any future request. Finally, semantic features are of major importance to tackle scalability and interoperability issues. A survey on the most prominent middleware architectures for Smart Grids is presented in this paper, along with an evaluation of their features and their strong points and weaknesses. Full article
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