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Energies, Volume 10, Issue 7 (July 2017)

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Cover Story Alternative fuels are an important aspect of transportation and energy production. The study of [...] Read more.
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Editorial

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Open AccessEditorial Control of Energy Storage
Energies 2017, 10(7), 1010; doi:10.3390/en10071010
Received: 30 May 2017 / Revised: 30 May 2017 / Accepted: 10 July 2017 / Published: 16 July 2017
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Abstract
In the attempt to tackle the issue of climate change, governments across the world have agreed to set global carbon reduction targets. [...] Full article
(This article belongs to the Special Issue Control of Energy Storage)
Open AccessEditorial Energy and Waste Management
Energies 2017, 10(7), 1072; doi:10.3390/en10071072
Received: 22 June 2017 / Revised: 19 July 2017 / Accepted: 19 July 2017 / Published: 24 July 2017
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Abstract
Waste management and energy systems are often interlinked, either directly by waste-to-energy technologies, or indirectly as processes for recovery of resources—such as materials, oils, manure, or sludge—use energy in their processes or substitute conventional production of the commodities for which the recycling processes
[...] Read more.
Waste management and energy systems are often interlinked, either directly by waste-to-energy technologies, or indirectly as processes for recovery of resources—such as materials, oils, manure, or sludge—use energy in their processes or substitute conventional production of the commodities for which the recycling processes provide raw materials. A special issue in Energies on the topic of “Energy and Waste Management” attained a lot of attention from the scientific community. In particular, papers contributing to improved understanding of the combined management of waste and energy were invited. In all, 9 papers were published out of 24 unique submissions. The papers cover technical topics such as leaching of heavy metals, pyrolysis, and production of synthetic natural gas in addition to different systems assessments of horse manure, incineration, and complex future scenarios at a national level. All papers except one focused on energy recovery from waste. That particular paper focused on waste management of infrastructure in an energy system (wind turbines). Published papers illustrate research in the field of energy and waste management on both a current detailed process level as well as on a future system level. Knowledge gained on both types is necessary to be able to make progress towards a circular economy. Full article
(This article belongs to the Special Issue Energy and Waste Management)

Research

Jump to: Editorial, Review, Other

Open AccessArticle A Phase-Shifted Control for Wireless Power Transfer System by Using Dual Excitation Units
Energies 2017, 10(7), 1000; doi:10.3390/en10071000
Received: 14 June 2017 / Revised: 12 July 2017 / Accepted: 12 July 2017 / Published: 14 July 2017
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Abstract
Wireless power transfer (WPT) technology can provide intelligent robots with a flexible, robust, and safe power supply, especially in very harsh environments including high humidity and high temperature. To meet increasing power requirement for robotic applications, this paper proposes a novel method to
[...] Read more.
Wireless power transfer (WPT) technology can provide intelligent robots with a flexible, robust, and safe power supply, especially in very harsh environments including high humidity and high temperature. To meet increasing power requirement for robotic applications, this paper proposes a novel method to increase system power transfer capability without increasing voltage and current stress, realized by using dual excitation units at the primary side. On this basis, this paper proposes a phase-shifted control method for output power regulation which can keep efficiency high. At the same time, the system is proved to have a better output robust characteristic by analysis under the condition of parameter variation. Finally, experimental results show the proposed dual excitation units (DEU)-WPT system can increase output power by at least three times compared to classical WPT system, and the efficiency is improved by 9%. Full article
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Open AccessArticle An Investigation of Fuel Mixing and Reaction in a CH4/Syngas/Air Premixed Impinging Flame with Varied H2/CO Proportion
Energies 2017, 10(7), 900; doi:10.3390/en10070900
Received: 26 April 2017 / Revised: 12 June 2017 / Accepted: 27 June 2017 / Published: 1 July 2017
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Abstract
For industrial applications, we propose a concept of clean and efficient combustion through burning syngas on an impinging burner. We performed experimental measurements of particle image velocimetry, OH radical (OH*) chemiluminescence, flame temperature, and CO emission to examine the fuel mixing and reaction
[...] Read more.
For industrial applications, we propose a concept of clean and efficient combustion through burning syngas on an impinging burner. We performed experimental measurements of particle image velocimetry, OH radical (OH*) chemiluminescence, flame temperature, and CO emission to examine the fuel mixing and reaction of premixed impinging flames of CH4/syngas/air with H2/CO in varied proportions. The velocity distribution of the combustion flow field showed that a deceleration area in the main flow formed through the mutual impingement of two jet flows, which enhanced the mixing of fuel and air because of an increased momentum transfer. The deceleration area expanded with an increased CO proportion, which indicated that the mixing of fuel and air also increased with the increased CO proportion. Our examination of the OH* chemiluminescence demonstrated that its intensity increased with increased CO proportion, which showed that the reaction between fuel and air accordingly increased. CO provided in the syngas hence participated readily in the reaction of the CH4/syngas/air premixed impinging flames when the syngas contained CO in a large proportion. Although the volume flow rate of the provided CO quadrupled, the CO emission increased by only 12% to 15%. The results of this work are useful to improve the feasibility of fuel-injection systems using syngas as an alternative fuel. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
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Open AccessArticle Investigation of Processes of Interaction between Hydraulic and Natural Fractures by PFC Modeling Comparing against Laboratory Experiments and Analytical Models
Energies 2017, 10(7), 1001; doi:10.3390/en10071001
Received: 17 May 2017 / Revised: 23 June 2017 / Accepted: 13 July 2017 / Published: 14 July 2017
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Abstract
Hydraulic fracturing technology is usually used to stimulate tight gas reservoirs for increasing gas production. The stimulated volume depends in part on the pre-existing natural fractures in a reservoir. The mechanisms influencing the interaction between hydraulic fractures and natural fractures have to be
[...] Read more.
Hydraulic fracturing technology is usually used to stimulate tight gas reservoirs for increasing gas production. The stimulated volume depends in part on the pre-existing natural fractures in a reservoir. The mechanisms influencing the interaction between hydraulic fractures and natural fractures have to be well understood in order to achieve a successful application of hydraulic fracturing. In this paper, hydraulic fracturing simulations were performed based on a two-dimensional Particle Flow Code with an embedded Smooth Joint Model to investigate the interactions between hydraulic fractures and natural fractures and compare these against laboratory experimental results and analytical models. Firstly, the ability of the Smooth Joint Model to mimic the natural rock joints was validated. Secondly, the interactions between generated hydraulic fractures and natural fractures were simulated. Lastly, the influence of angle of approach, in situ differential stress, and the permeability of natural fractures was studied. It is found that the model is capable of simulating the variety of interactions between hydraulic fractures and natural fractures such as Crossed type, Arrested type and Dilated type, and the modeling examples agree well with the experimental results. Under high approach angles and high differential stresses, the hydraulic fractures tend to cross pre-existing natural fractures. Under contrary conditions, a hydraulic fracture is more likely to propagate along the natural fracture and re-initiate at a weak point or the tip of the natural fracture. Moreover, these numerical results are in good agreement compared with Blanton’s criterion. The variety of permeability of natural fractures has a great effect on their interactions, which should not be overlooked in hydraulic fracturing studies. Full article
(This article belongs to the Special Issue Oil and Gas Engineering)
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Open AccessArticle Study on the Gas-Insulated Line Equivalent Model and Simplified Model
Energies 2017, 10(7), 901; doi:10.3390/en10070901
Received: 24 April 2017 / Revised: 28 May 2017 / Accepted: 27 June 2017 / Published: 1 July 2017
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Abstract
The gas-insulated line (GIL) is one technical solution to allow the transmission of electricity underground at a high voltage level, yet its equivalent model is quite complicated. Based on an examination of the geometrical structure of the GIL and the way the metallic
[...] Read more.
The gas-insulated line (GIL) is one technical solution to allow the transmission of electricity underground at a high voltage level, yet its equivalent model is quite complicated. Based on an examination of the geometrical structure of the GIL and the way the metallic enclosure is grounded, this paper analyzed the electromagnetic and electrostatic coupling among the inner conductors and the metallic enclosures of the three phases. Then, the paper proposes a modeling method for the widely-used short-distance GIL based on the PI-model (the model consisting of two lumped admittance at each terminal and a lumped impedance in between). The GIL parameters were later simplified with the coupling effect of the metallic enclosure considered, and a simplified PI-model was produced. Finally, the proposed PI-model and its simplified version were built on the Power Systems Computer Aided Design (PSCAD) platform, and their effectiveness verified by simulation results. Full article
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Open AccessArticle Validating a Wave-to-Wire Model for a Wave Energy Converter—Part II: The Electrical System
Energies 2017, 10(7), 1002; doi:10.3390/en10071002
Received: 24 May 2017 / Revised: 3 July 2017 / Accepted: 3 July 2017 / Published: 14 July 2017
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Abstract
The incorporation of the full dynamics of the different conversion stages of wave energy converters (WECs), from ocean waves to the electricity grid, is essential for a realistic evaluation of the power flow in the drive train. WECs with different power take-off (PTO)
[...] Read more.
The incorporation of the full dynamics of the different conversion stages of wave energy converters (WECs), from ocean waves to the electricity grid, is essential for a realistic evaluation of the power flow in the drive train. WECs with different power take-off (PTO) systems, including diverse transmission mechanisms, have been developed in recent decades. However, all the different PTO systems for electricity-producing WECs, regardless of any intermediate transmission mechanism, include an electric generator, linear or rotational. Therefore, accurately modelling the dynamics of electric generators is crucial for all wave-to-wire (W2W) models. This paper presents the models for three popular rotational electric generators (squirrel cage induction machine, permanent magnet synchronous generator and doubly-fed induction generator) and a back-to-back (B2B) power converter and validates such models against experimental data generated using three real electric machines. The input signals for the validation of the mathematical models are designed so that the whole operation range of the electrical generators is covered, including input signals generated using the W2W model that mimic the behaviour of different hydraulic PTO systems. Results demonstrate the effectiveness of the models in accurately reproducing the characteristics of the three electrical machines, including power losses in the different machines and the B2B converter. Full article
(This article belongs to the Special Issue Marine Energy)
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Open AccessArticle Numerical and Experimental Studies on the Heat Transfer Performance of Copper Foam Filled with Paraffin
Energies 2017, 10(7), 902; doi:10.3390/en10070902
Received: 21 March 2017 / Revised: 12 June 2017 / Accepted: 26 June 2017 / Published: 2 July 2017
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Abstract
Abstract: The pore-scale numerical works on the effective thermal conductivity and melting process of copper foam filled with paraffin, and a phase-change material (PCM) with low thermal conductivity, were conducted by utilizing the two-dimensional (2D) hexahedron Calmidi-Mahajan (C-M) model and the three-dimensional
[...] Read more.
Abstract: The pore-scale numerical works on the effective thermal conductivity and melting process of copper foam filled with paraffin, and a phase-change material (PCM) with low thermal conductivity, were conducted by utilizing the two-dimensional (2D) hexahedron Calmidi-Mahajan (C-M) model and the three-dimensional (3D) dodecahedron Boomsma-Poulikakos (B-P) model. The unidirectional heat transfer experiment was established to investigate the effective thermal conductivity of the composite. The simulation results of the effective thermal conductivity of the composite in 2D C-M model were 6.93, 5.41, 4.22 and 2.75 W/(m·K), for porosity of 93%, 95%, 96% and 98% respectively, while the effective thermal conductivity of the composite in 3D B-P model were 7.07, 5.24, 3.07 and 1.22 W/(m·K). The simulated results were in agreement with the experimental data obtained for the composite. It was found that the copper foam can effectively enhance the thermal conductivity of the paraffin, i.e., the smaller the porosity of copper foam, the higher the effective thermal conductivity of the composite. In addition, the Fluent Solidification/Melting model was applied to numerically investigate the melting process of the paraffin in the pore. Lastly, the solid–liquid interface development, completely melted time and temperature field distribution of paraffin in the pore of copper foam were also discussed. Full article
(This article belongs to the Section Energy Storage and Application)
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Open AccessArticle Prediction in Photovoltaic Power by Neural Networks
Energies 2017, 10(7), 1003; doi:10.3390/en10071003
Received: 11 April 2017 / Revised: 11 July 2017 / Accepted: 12 July 2017 / Published: 15 July 2017
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Abstract
The ability to forecast the power produced by renewable energy plants in the short and middle term is a key issue to allow a high-level penetration of the distributed generation into the grid infrastructure. Forecasting energy production is mandatory for dispatching and distribution
[...] Read more.
The ability to forecast the power produced by renewable energy plants in the short and middle term is a key issue to allow a high-level penetration of the distributed generation into the grid infrastructure. Forecasting energy production is mandatory for dispatching and distribution issues, at the transmission system operator level, as well as the electrical distributor and power system operator levels. In this paper, we present three techniques based on neural and fuzzy neural networks, namely the radial basis function, the adaptive neuro-fuzzy inference system and the higher-order neuro-fuzzy inference system, which are well suited to predict data sequences stemming from real-world applications. The preliminary results concerning the prediction of the power generated by a large-scale photovoltaic plant in Italy confirm the reliability and accuracy of the proposed approaches. Full article
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Open AccessArticle Diffusion Strategy-Based Distributed Operation of Microgrids Using Multiagent System
Energies 2017, 10(7), 903; doi:10.3390/en10070903
Received: 19 May 2017 / Revised: 27 June 2017 / Accepted: 28 June 2017 / Published: 2 July 2017
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Abstract
In distributed operation, each unit is operated by its local controller instead of using a centralized controller, which allows the action to be based on local information rather than global information. Most of the distributed solutions have implemented the consensus method, however, convergence
[...] Read more.
In distributed operation, each unit is operated by its local controller instead of using a centralized controller, which allows the action to be based on local information rather than global information. Most of the distributed solutions have implemented the consensus method, however, convergence time of the consensus method is quite long, while diffusion strategy includes a stochastic gradient term and can reach convergence much faster compared with consensus method. Therefore, in this paper, a diffusion strategy-based distributed operation of microgrids (MGs) is proposed using multiagent system for both normal and emergency operation modes. In normal operation, the MG system is operated by a central controller instead of the distributed controller to minimize the operation cost. If any event (fault) occurs in the system, MG system can be divided into two parts to isolate the faulty region. In this case, the MG system is changed to emergency operation mode. The normal part is rescheduled by the central controller while the isolated part schedules its resources in a distributed manner. The isolated part carries out distributed communication using diffusion between neighboring agents for optimal operation of this part. The proposed method enables peer-to-peer communication among the agents without the necessity of a centralized controller, and simultaneously performs resource optimization. Simulation results show that the system can be operated in an economic way in both normal operation and emergency operation modes. Full article
(This article belongs to the Special Issue Distributed Energy Resources Management)
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Open AccessArticle New Adaptive Reclosing Technique in Unbalanced Distribution System
Energies 2017, 10(7), 1004; doi:10.3390/en10071004
Received: 9 June 2017 / Revised: 12 July 2017 / Accepted: 13 July 2017 / Published: 15 July 2017
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Abstract
The conventional reclosing of a distribution system is performed after a fixed dead time. However, it may lead to the increased outage time due to delayed reclosing. To solve this problem, this paper proposes a new adaptive reclosing scheme. The electrostatic induction is
[...] Read more.
The conventional reclosing of a distribution system is performed after a fixed dead time. However, it may lead to the increased outage time due to delayed reclosing. To solve this problem, this paper proposes a new adaptive reclosing scheme. The electrostatic induction is analyzed under at during-fault and post-fault conditions. Based on this analysis, the method to judge the fault clearance using the load current is proposed. The reclosing is adaptively performed after fault clearance. The distribution system and reclosing scheme are modelled by the electromagnetic transient program (EMTP). The various simulations according to the unbalanced ratio and various fault conditions are performed and analyzed. The superiority of the proposed scheme is verified by comparing with the conventional reclosing method. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle Output Impedance Control Method of Inverter-Based Distributed Generators for Autonomous Microgrid
Energies 2017, 10(7), 904; doi:10.3390/en10070904
Received: 25 May 2017 / Revised: 26 June 2017 / Accepted: 28 June 2017 / Published: 2 July 2017
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Abstract
The droop method is the most favorable alternative in microgrid implementations for autonomous control of grid-forming inverter-based distributed generators (DGs) connected in parallel. However, the dynamic characteristic of the conventional droop method is poor because the inertias of inverter-based DG units are extremely
[...] Read more.
The droop method is the most favorable alternative in microgrid implementations for autonomous control of grid-forming inverter-based distributed generators (DGs) connected in parallel. However, the dynamic characteristic of the conventional droop method is poor because the inertias of inverter-based DG units are extremely low and the transmission line is normally very short. An output impedance control method to enhance the dynamic performance and minimize the circulating current between grid-forming DGs is devised in this study. It is shown that it also enhances the power and harmonic sharing accuracy. The proposed method utilizes the virtual output impedance as a control signal for reactive power flow management. The effectiveness of the proposed scheme is validated using the high-speed field programmable gate array (FPGA)-based real-time hardware-in-the-loop test results. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle Numerical Modelling of Mechanical Behavior of Coal Mining Hard Roofs in Different Backfill Ratios: A Case Study
Energies 2017, 10(7), 1005; doi:10.3390/en10071005
Received: 21 June 2017 / Revised: 12 July 2017 / Accepted: 13 July 2017 / Published: 15 July 2017
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Abstract
In coal mining hard roofs are one of the main factors causing the occurrence of rock bursts in working panels. To solve this problem, the solid backfill coal mining (SBCM) technique is proposed and used as an effective measure to prevent the rock
[...] Read more.
In coal mining hard roofs are one of the main factors causing the occurrence of rock bursts in working panels. To solve this problem, the solid backfill coal mining (SBCM) technique is proposed and used as an effective measure to prevent the rock bursts induced by hard roofs. However, due to the different backfill ratios of working planes, the control effects on hard roofs are quite unique. By using a numerical simulation, this study simulates the deformation of hard roofs and distributions of stress and strain energies in different roof-control backfill ratios, so as to reveal the control mechanisms of SBCM on hard roofs. The results show that, when the roof-controlled backfill ratio are 0, 40% and 60%, the ratio exerts no influence on the distributions of advanced abutment stress and strain energies. While for roof-control backfill ratios of 82.5%, 91% and 93%, the advanced abutment stress and strain energies decrease significantly, but the increment of the ratio exerts little influence on the decrease. When the roof-control backfill ratio reaches 97%, the advanced abutment stress and strain energies again decrease. In this context, the stress concentration factor is only 1.5 and the peak strain energy is 544 kJ/m3, the stress concentration factor and peak strain energy decrease by 45.7% and 63.9%, respectively, compared with the caving method. As the roof-controlled backfill ratio rises, backfill materials tend to support hard roofs, thus significantly preventing dynamic hazards. Full article
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Open AccessArticle Multi-Party Energy Management for Networks of PV-Assisted Charging Stations: A Game Theoretical Approach
Energies 2017, 10(7), 905; doi:10.3390/en10070905
Received: 9 May 2017 / Revised: 13 June 2017 / Accepted: 26 June 2017 / Published: 2 July 2017
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Abstract
Motivated by the development of electric vehicles (EVs), this paper addresses the energy management problem for the PV-assisted charging station (PVCS) network. An hour-ahead optimization model for the operation of PVCS is proposed, considering the profit of the PVCS, the local consumption of
[...] Read more.
Motivated by the development of electric vehicles (EVs), this paper addresses the energy management problem for the PV-assisted charging station (PVCS) network. An hour-ahead optimization model for the operation of PVCS is proposed, considering the profit of the PVCS, the local consumption of the photovoltaic (PV) energy and the impacts on the grid. Moreover, a two-level feasible charging region (FCR) model is built to guarantee the service quality for EVs and learning-based decision-making is designed to assist the optimization of the PVCS in various scenarios. The multi-party energy management problem, including several kinds of energy flows of the PVCS network, is formulated as a non-cooperative game. Then, the strategies of the PVCSs are modeled as the demand response (DR) activities to achieve their own optimization goals and a two-level distributed heuristic algorithm is introduced to solve the problem. The simulation results show that the economic profit of the network is increased by 6.34% compared with the common time of use (TOU) prices approach. Besides, the percentage of the PV energy in total charging load (PPTCL) and load rate are promoted by 28.93% and 0.3125, respectively, which demonstrates the validity and practicability of the proposed method. Full article
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Open AccessArticle Transverse Thermoelectricity in Fibrous Composite Materials
Energies 2017, 10(7), 1006; doi:10.3390/en10071006
Received: 21 June 2017 / Revised: 12 July 2017 / Accepted: 12 July 2017 / Published: 16 July 2017
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Abstract
Transverse thermoelectric elements have the potential to decouple the electric current and the heat flow, which could lead to new designs of thermoelectric devices. While many theoretical and experimental studies of transverse thermoelectricity have focused on layered structures, this work examines composite materials
[...] Read more.
Transverse thermoelectric elements have the potential to decouple the electric current and the heat flow, which could lead to new designs of thermoelectric devices. While many theoretical and experimental studies of transverse thermoelectricity have focused on layered structures, this work examines composite materials with aligned fibrous inclusions. A simplified mathematical model was derived based on the Kirchhoff Circuit Laws (KCL), which were used to calculate the equivalent transport properties of the composite structures. These equivalent properties, including Seebeck coefficient, electrical conductivity, and thermal conductivity, compared well with finite element analysis (FEA) results. Peltier cooling performance was also examined using FEA, which exhibited good agreement to KCL model predictions. In addition, a survey was conducted on selected combinations of thermoelectric materials and metals to rank their transverse thermoelectricity with respect to the dimensionless figure of merit. Full article
(This article belongs to the Special Issue Thermoelectric Materials for Energy Conversion)
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Open AccessArticle Thermo-Fluidic Comparison between Sandwich Panels with Tetrahedral Lattice Cores Fabricated by Casting and Metal Sheet Folding
Energies 2017, 10(7), 906; doi:10.3390/en10070906
Received: 15 May 2017 / Revised: 5 June 2017 / Accepted: 26 June 2017 / Published: 2 July 2017
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Abstract
This numerical study compares single-phase forced convective heat transfer between two sandwich panels with tetrahedral metallic lattice cores separately fabricated by investment casting and the more cost-effective metal sheet folding method. The numerical model is validated against available experimental data. For a given
[...] Read more.
This numerical study compares single-phase forced convective heat transfer between two sandwich panels with tetrahedral metallic lattice cores separately fabricated by investment casting and the more cost-effective metal sheet folding method. The numerical model is validated against available experimental data. For a given Reynolds number and core porosity, the results reveal that the brazed sandwich outperforms the casted sandwich, exhibiting a 13% to 16% higher Nusselt number. Bigger vertexes and more evident blockage of mainstream by the ligaments are found to intensify the horseshoe vortex and the counter-rotating vortex pair upstream and downstream of each vertex. Relative to the casted sandwich panel, therefore, endwall heat transfer is enhanced by 22% to 27%, while similar heat transfer is achieved on the ligaments. It is also found that, for a given Reynolds number, the brazed sandwich induces a 1.6 to 1.7 times higher pressure drop relative to the casted sandwich due to more severe flow separation caused by the sharp edges of the rectangular ligaments. Finally, for a given pumping power, both sandwiches provide a similar heat transfer performance. Given that the brazed sandwich is more cost-effective and easier to fabricate than the casted one, the former may be superior from an engineering application point of view. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
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Open AccessArticle An Open-Access Web-Based Tool to Access Global, Hourly Wind and Solar PV Generation Time-Series Derived from the MERRA Reanalysis Dataset
Energies 2017, 10(7), 1007; doi:10.3390/en10071007
Received: 27 June 2017 / Revised: 6 July 2017 / Accepted: 13 July 2017 / Published: 16 July 2017
Cited by 1 | PDF Full-text (1442 KB) | HTML Full-text | XML Full-text
Abstract
Wind and solar energy resources are an increasingly large fraction of generation in global electricity systems. However, the variability of these resources necessitates new datasets and tools for understanding their economics and integration in electricity systems. To enable such analyses and more, we
[...] Read more.
Wind and solar energy resources are an increasingly large fraction of generation in global electricity systems. However, the variability of these resources necessitates new datasets and tools for understanding their economics and integration in electricity systems. To enable such analyses and more, we have developed a free web-based tool (Global Renewable Energy Atlas & Time-series, or GRETA) that produces hourly wind and solar photovoltaic (PV) generation time series for any location on the globe. To do so, this tool applies the Boland–Ridley–Laurent and Perez models to NASA’s (National Aeronautics and Space Administration) Modern-Era Retrospective Analysis for Research and Applications (MERRA) solar irradiance reanalysis dataset, and the Archer and Jacobson model to the MERRA wind reanalysis dataset to produce resource and power data, for a given technology’s power curve. This paper reviews solar and wind resource datasets and models, describes the employed algorithms, and introduces the web-based tool. Full article
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Open AccessArticle Finite Control Set–Model Predictive Control with Modulation to Mitigate Harmonic Component in Output Current for a Grid-Connected Inverter under Distorted Grid Conditions
Energies 2017, 10(7), 907; doi:10.3390/en10070907
Received: 14 June 2017 / Revised: 28 June 2017 / Accepted: 29 June 2017 / Published: 2 July 2017
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Abstract
This paper presents an improved current control strategy for a three-phase grid-connected inverter under distorted grid conditions. In terms of performance, it is important for a grid-connected inverter to maintain the harmonic contents of inverter output currents below the specified limit even when
[...] Read more.
This paper presents an improved current control strategy for a three-phase grid-connected inverter under distorted grid conditions. In terms of performance, it is important for a grid-connected inverter to maintain the harmonic contents of inverter output currents below the specified limit even when the grid is subject to harmonic distortion. To address this problem, this paper proposes a modulated finite control set–model predictive control (FCS-MPC) scheme, which effectively mitigates the harmonic components in output current of a grid-connected inverter. In the proposed scheme, the system behavior in the future is predicted from the system model in the discrete-time domain. Then, the cost function is selected based on the control objective of system. This cost function is minimized during the optimization process to determine the control signals that minimize the cost function. In addition, since the proposed scheme requires pure sinusoidal reference currents in the stationary frame to work successfully, the moving average filter (MAF) is employed to enhance the performance of the traditional phase lock loop (PLL). Due to the control performance of the FCS-MPC scheme as well as the harmonic disturbance rejection capability of the MAF-PLL, the proposed scheme is able to suppress the harmonic distortion even in the presence of distorted grid condition, while retaining fast transient response. Comparative simulation results of different controllers verify the effectiveness of the proposed control scheme in compensating the harmonic disturbance. To validate the practical feasibility of the proposed scheme, the whole control algorithm is implemented on a 32-bit floating-point digital signal processor (DSP) TMS320F28335 to control a 2 kW three-phase grid-connected inverter. As a result, the proposed scheme is a promising approach toward improving the current quality of a grid-connected inverter under distorted grid conditions. Full article
(This article belongs to the Special Issue Control and Communication in Distributed Generation Systems)
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Open AccessArticle A New Miniature Wind Turbine for Wind Tunnel Experiments. Part I: Design and Performance
Energies 2017, 10(7), 908; doi:10.3390/en10070908
Received: 10 May 2017 / Revised: 24 June 2017 / Accepted: 28 June 2017 / Published: 3 July 2017
Cited by 1 | PDF Full-text (1423 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Miniature wind turbines, employed in wind tunnel experiments to study the interaction of turbines with turbulent boundary layers, usually suffer from poor performance with respect to their large-scale counterparts in the field. Moreover, although wakes of wind turbines have been extensively examined in
[...] Read more.
Miniature wind turbines, employed in wind tunnel experiments to study the interaction of turbines with turbulent boundary layers, usually suffer from poor performance with respect to their large-scale counterparts in the field. Moreover, although wakes of wind turbines have been extensively examined in wind tunnel studies, the proper characterization of the performance of wind turbines has received relatively less attention. In this regard, the present study concerns the design and the performance analysis of a new three-bladed horizontal-axis miniature wind turbine with a rotor diameter of 15 cm. Due to its small size, this turbine, called WiRE-01, is particularly suitable for studies of wind farm flows and the interaction of the turbine with an incoming boundary-layer flow. Especial emphasis was placed on the accurate measurement of the mechanical power extracted by the miniature turbine from the incoming wind. In order to do so, a new setup was developed to directly measure the torque of the rotor shaft. Moreover, to provide a better understanding on the connection between the mechanical and electrical aspects of miniature wind turbines, the performance of three different direct-current (DC) generators was studied. It is found that electrical outputs of the tested generators can be used to provide a rather acceptable estimation of the mechanical input power. Force and power measurements showed that the thrust and power coefficients of the miniature turbine can reach 0.8 and 0.4 , respectively, which are close to the ones of large-scale turbines in the field. In Part II of this study, the wake structure and dynamic flow characteristics are studied for the new miniature turbine immersed in a turbulent boundary-layer flow. Full article
(This article belongs to the collection Wind Turbines)
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Open AccessArticle Efficient Model Predictive Control Strategies for Resource Management in an Islanded Microgrid
Energies 2017, 10(7), 1008; doi:10.3390/en10071008
Received: 21 February 2017 / Revised: 6 July 2017 / Accepted: 11 July 2017 / Published: 16 July 2017
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Abstract
The energy research community is continuously pursuing improvements in power system resiliency and reliability. Microgrids offer a unique opportunity for enhanced reliability and resiliency by utilizing localized generation and energy storage when grid power is unavailable or too expensive. Energy management is a
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The energy research community is continuously pursuing improvements in power system resiliency and reliability. Microgrids offer a unique opportunity for enhanced reliability and resiliency by utilizing localized generation and energy storage when grid power is unavailable or too expensive. Energy management is a critical aspect of these systems to ensure proper balancing of sources and ensuring power supply to critical loads with minimum cost, especially in an islanded microgrid. This paper presents a hierarchical real-time optimization with mathematical formulations to achieve optimal operation for an islanded microgrid. The optimization is implemented using simple numerically tractable model predictive control strategies and enables appropriate decisions in response to constantly changing conditions. The optimization method is extended for experimentation within the real-time simulation. Simulation results show that the proposed resource management algorithm shows near-optimal performance while effectively dealing with uncertainties in forecasting. Full article
(This article belongs to the Special Issue Advanced Operation and Control of Smart Microgrids)
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Open AccessArticle Optimal Power Allocation for a Relaying-Based Cognitive Radio Network in a Smart Grid
Energies 2017, 10(7), 909; doi:10.3390/en10070909
Received: 28 April 2017 / Revised: 7 June 2017 / Accepted: 28 June 2017 / Published: 3 July 2017
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Abstract
This paper obtains optimal power allocation to the data aggregator units (DAUs) and relays for cognitive wireless networks in a smart grid (SG). Firstly, the mutual interference between the primary user and the DAU are considered, and the expressions of the DAU transmission
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This paper obtains optimal power allocation to the data aggregator units (DAUs) and relays for cognitive wireless networks in a smart grid (SG). Firstly, the mutual interference between the primary user and the DAU are considered, and the expressions of the DAU transmission signal are derived based on the sensing information. Secondly, we use the particle swarm optimization (PSO) algorithm to search for the optimal power allocation to minimize the costs to the utility company. Finally, the impact of the sensing information on the network performance is studied. Then two special cases (namely, that only one relay is selected, and that the channel is not occupied by the primary user) are discussed. Simulation results demonstrate that the optimal power allocation and the sensing information of the relays can reduce the costs to the utility company for cognitive wireless networks in a smart grid. Full article
(This article belongs to the Special Issue From Smart Metering to Demand Side Management)
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Open AccessArticle Geothermal Resource Exploration by Stream pH Mapping in Mutsu Hiuchi Dake Volcano, Japan
Energies 2017, 10(7), 1009; doi:10.3390/en10071009
Received: 25 May 2017 / Revised: 6 July 2017 / Accepted: 7 July 2017 / Published: 16 July 2017
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Abstract
Although pH measurements of hot spring water are taken in conventional geothermal resource research, previous studies have seldom created pH distribution maps of stream and spring waters for an entire geothermal field as a technique for geothermal exploration. In this study, a pH
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Although pH measurements of hot spring water are taken in conventional geothermal resource research, previous studies have seldom created pH distribution maps of stream and spring waters for an entire geothermal field as a technique for geothermal exploration. In this study, a pH distribution map was created by measuring stream and spring water pH at 75 sites in the Mutsu Hiuchi Dake geothermal field, Japan. Areas of abnormally high pH were detected in midstream sections of the Ohaka and Koaka rivers; these matched the location of the Mutsu Hiuchi Dake East Slope Fault, which is believed to have formed a geothermal reservoir. The abnormally high pH zone is attributed to the trapping of rising volcanic gases in a mature geothermal reservoir with neutral geothermal water. This causes the gas to dissolve and prevents it from reaching the surface. Thus, the mapping of stream water pH distribution in a geothermal field could provide a new and effective method for estimating the locations of geothermal reservoirs. As the proposed method does not require laboratory analysis, and is more temporally and economically efficient than conventional methods, it might help to promote geothermal development in inaccessible and remote regions. Full article
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Open AccessArticle Production of Torrefied Solid Bio-Fuel from Pulp Industry Waste
Energies 2017, 10(7), 910; doi:10.3390/en10070910
Received: 6 January 2017 / Revised: 15 May 2017 / Accepted: 26 June 2017 / Published: 3 July 2017
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Abstract
The pulp industry in Taiwan discharges tons of wood waste and pulp sludge (i.e., wastewater-derived secondary sludge) per year. The mixture of these two bio-wastes, denoted as wood waste with pulp sludge (WPS), has been commonly converted to organic fertilizers for agriculture application
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The pulp industry in Taiwan discharges tons of wood waste and pulp sludge (i.e., wastewater-derived secondary sludge) per year. The mixture of these two bio-wastes, denoted as wood waste with pulp sludge (WPS), has been commonly converted to organic fertilizers for agriculture application or to soil conditioners. However, due to energy demand, the WPS can be utilized in a beneficial way to mitigate an energy shortage. This study elucidated the performance of applying torrefaction, a bio-waste to energy method, to transform the WPS into solid bio-fuel. Two batches of the tested WPS (i.e., WPS1 and WPS2) were generated from a virgin pulp factory in eastern Taiwan. The WPS1 and WPS2 samples contained a large amount of organics and had high heating values (HHV) on a dry-basis (HHD) of 18.30 and 15.72 MJ/kg, respectively, exhibiting a potential for their use as a solid bio-fuel. However, the wet WPS as received bears high water and volatile matter content and required de-watering, drying, and upgrading. After a 20 min torrefaction time (tT), the HHD of torrefied WPS1 (WPST1) can be enhanced to 27.49 MJ/kg at a torrefaction temperature (TT) of 573 K, while that of torrefied WPS2 (WPST2) increased to 19.74 MJ/kg at a TT of 593 K. The corresponding values of the energy densification ratio of torrefied solid bio-fuels of WPST1 and WPST2 can respectively rise to 1.50 and 1.25 times that of the raw bio-waste. The HHD of WPST1 of 27.49 MJ/kg is within the range of 24–35 MJ/kg for bituminous coal. In addition, the wet-basis HHV of WPST1 with an equilibrium moisture content of 5.91 wt % is 25.87 MJ/kg, which satisfies the Quality D coal specification of the Taiwan Power Co. requiring a value of above 20.92 MJ/kg. Full article
(This article belongs to the collection Bioenergy and Biofuel)
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Open AccessArticle Optimization of Guide Vane Closing Schemes of Pumped Storage Hydro Unit Using an Enhanced Multi-Objective Gravitational Search Algorithm
Energies 2017, 10(7), 911; doi:10.3390/en10070911
Received: 13 March 2017 / Revised: 8 June 2017 / Accepted: 28 June 2017 / Published: 3 July 2017
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Abstract
The optimization of guide vane closing schemes (OGVCS) of pumped storage hydro units (PSHUs) is a cooperative control and optimal operation research field in renewable energy power generation technology. This paper presents an OGVCS model of PSHUs considering the rise rate of the
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The optimization of guide vane closing schemes (OGVCS) of pumped storage hydro units (PSHUs) is a cooperative control and optimal operation research field in renewable energy power generation technology. This paper presents an OGVCS model of PSHUs considering the rise rate of the unit rotational speed, the specific node pressure of each hydraulic unit, as well as various complicated hydraulic and mechanical constraints. The OGVCS model is formulated as a multi-objective optimization problem to optimize conflicting objectives, i.e., unit rotational speed and water hammer pressure criteria. In order to realize an efficient solution of the OGVCS model, an enhanced multi-objective bacterial-foraging chemotaxis gravitational search algorithm (EMOBCGSA) is proposed to solve this problem, which adopts population reconstruction, adaptive selection chemotaxis operator of local searching strategy and elite archive set to efficiently solve the multi-objective problem. In particular a novel constraints-handling strategy with elimination and local search based on violation ranking is used to balance the various hydraulic and mechanical constraints. Finally, simulation cases of complex extreme operating conditions (i.e., load rejection and pump outage) of a ‘single tube-double units’ type PSHU system are conducted to verify the feasibility and effectiveness of the proposed EMOBCGSA in solving OGVCS problems. The simulation results indicate that the proposed EMOBCGSA can provide a lower rise rate of the unit rotational speed and smaller water hammer pressure than other methods established recently while considering various complex constraints in OGVCS problems. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
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Open AccessArticle A Novel Layered Bidirectional Equalizer Based on a Buck-Boost Converter for Series-Connected Battery Strings
Energies 2017, 10(7), 1011; doi:10.3390/en10071011
Received: 13 June 2017 / Revised: 9 July 2017 / Accepted: 11 July 2017 / Published: 17 July 2017
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Abstract
To eliminate the influence of the inconsistency on the cycle life and the available capacity of battery packs, and improve the balancing speed, a novel inductor-based layered bidirectional equalizer (IBLBE) is proposed. The equalizer is composed of two layers of balancing circuits connected
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To eliminate the influence of the inconsistency on the cycle life and the available capacity of battery packs, and improve the balancing speed, a novel inductor-based layered bidirectional equalizer (IBLBE) is proposed. The equalizer is composed of two layers of balancing circuits connected in parallel. Each layer contains multiple balancing sub-circuits based on buck-boost converters. These balancing sub-circuits can equalize the corresponding cells simultaneously, and allow the dynamic adjustment of equalization path and equalization threshold. Analysis and simulation results demonstrate the IBLBE has a higher level balancing speed than other equalizers based on switched-capacitor or switched-inductor converters, and reduces the balancing time by 30% compared to existing inductor-based parallel architecture equalizers (PAEs). Experimental results are presented to validate the analysis and effectiveness of the proposed equalizer. Full article
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Open AccessArticle Research on Inverter Integrated Reactive Power Control Strategy in the Grid-Connected PV Systems
Energies 2017, 10(7), 912; doi:10.3390/en10070912
Received: 6 April 2017 / Revised: 7 June 2017 / Accepted: 26 June 2017 / Published: 3 July 2017
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Abstract
In order to solve the problems caused by the susceptibility to changing weather conditions and the complex load conditions of photovoltaic (PV) systems, and the fact a single target inverter control strategy cannot effectively mitigate large voltage fluctuations at point of common coupling
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In order to solve the problems caused by the susceptibility to changing weather conditions and the complex load conditions of photovoltaic (PV) systems, and the fact a single target inverter control strategy cannot effectively mitigate large voltage fluctuations at point of common coupling (PCC), an integrated reactive power control strategy for PV inverters is proposed. According to the weather and load conditions, this strategy is divided into four control modes: normal operation control mode, reverse power control mode, cloudy control mode and night control mode. The four control modes switch between each other under the specific switching rules to ensure an appropriate quantity of reactive power injection or consumption in the PV inverter. The effects of the four control modes in isolated operation were significant. The deviation rate of PCC voltage from its standard value was mitigated at about 2% under the integrated control strategy. Therefore, the proposed control strategy has a high application value in improving power quality and maximizing utilization of PV inverters. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle Performance Predictions of Dry and Wet Vapors Ejectors Over Entire Operational Range
Energies 2017, 10(7), 1012; doi:10.3390/en10071012
Received: 12 April 2017 / Revised: 6 July 2017 / Accepted: 7 July 2017 / Published: 17 July 2017
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Abstract
If a traditional ideal-gas ejector model is used to evaluate the performance of a wet vapor ejector, large deviations from the experimental results will be unavoidable. Moreover, the model usually fails to assess the ejector performance at subcritical mode. In this paper, we
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If a traditional ideal-gas ejector model is used to evaluate the performance of a wet vapor ejector, large deviations from the experimental results will be unavoidable. Moreover, the model usually fails to assess the ejector performance at subcritical mode. In this paper, we proposed a novel model to evaluate the performance of both dry and wet vapors ejectors over the entire operational range at critical or subcritical modes. The model was obtained by integrating the linear characteristic equations of ejector with critical and breakdown points models, which were developed based on the assumptions of constant-pressure mixing and constant-pressure disturbing. In the models, the equations of the two-phase speed of sound and the property of real gas were introduced and ejector component efficiencies were optimized to improve the accuracy of evaluation. It was validated that the proposed model for the entire operational range can achieve a better performance than those existing for R134a, R141b and R245fa. The critical and breakdown points models were further used to investigate the effect of operational parameters on the performance of an ejector refrigeration system (ERS). The theoretical results indicated that decreasing the saturated generating temperature when the actual condensing temperature decreases, and/or increasing the saturated evaporating temperature can improve the performance of ERS significantly. Moreover, superheating the primary flow before it enters the ejector can further improve the performance of an ERS using R134a as a working fluid. Full article
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Open AccessArticle Gelation Behavior Study of a Resorcinol–Hexamethyleneteramine Crosslinked Polymer Gel for Water Shut-Off Treatment in Low Temperature and High Salinity Reservoirs
Energies 2017, 10(7), 913; doi:10.3390/en10070913
Received: 24 April 2017 / Revised: 22 June 2017 / Accepted: 30 June 2017 / Published: 3 July 2017
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Abstract
Mature oilfields usually encounter the problem of high watercut. It is practical to use chemical methods for water-shutoff in production wells, however conventional water-shutoff agents have problems of long gelation time, low gel strength, and poor stability under low temperature and high salinity
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Mature oilfields usually encounter the problem of high watercut. It is practical to use chemical methods for water-shutoff in production wells, however conventional water-shutoff agents have problems of long gelation time, low gel strength, and poor stability under low temperature and high salinity conditions. In this work a novel polymer gel for low temperature and high salinity reservoirs was developed. This water-shutoff agent had controllable gelation time, adjustable gel strength and good stability performance. The crosslinking process of this polymer gel was studied by rheological experiments. The process could be divided into an induction period, a fast crosslinking period, and a stable period. Its gelation behaviors were investigated in detail. According to the Gel Strength Code (GSC) and vacuum breakthrough method, the gel strength was displayed in contour maps. The composition of the polymer gel was optimized to 0.25~0.3% YG100 + 0.6~0.9% resorcinol + 0.2~0.4% hexamethylenetetramine (HMTA) + 0.08~0.27% conditioner (oxalic acid). With the concentration increase of the polymer gel and temperature, the decrease of pH, the induction period became shorter and the crosslinking was more efficient, resulting in better stability performance. Various factors of the gelation behavior which have an impact on the crosslinking reaction process were examined. The relationships between each impact factor and the initial crosslinking time were described with mathematical equations. Full article
(This article belongs to the Section Energy Sources)
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Open AccessArticle Optimal Power Flow Using Particle Swarm Optimization of Renewable Hybrid Distributed Generation
Energies 2017, 10(7), 1013; doi:10.3390/en10071013
Received: 16 May 2017 / Revised: 7 July 2017 / Accepted: 10 July 2017 / Published: 17 July 2017
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Abstract
The problem of voltage collapse in power systems due to increased loads can be solved by adding renewable energy sources like wind and photovoltaic (PV) to some bus-bars. This option can reduce the cost of the generated energy and increase the system efficiency
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The problem of voltage collapse in power systems due to increased loads can be solved by adding renewable energy sources like wind and photovoltaic (PV) to some bus-bars. This option can reduce the cost of the generated energy and increase the system efficiency and reliability. In this paper, a modified smart technique using particle swarm optimization (PSO) has been introduced to select the hourly optimal load flow with renewable distributed generation (DG) integration under different operating conditions in the 30-bus IEEE system. Solar PV and wind power plants have been introduced to selected buses to evaluate theirs benefits as DG. Different solar radiation and wind speeds for the Dammam site in Saudi Arabia have been used as an example to study the feasibility of renewable energy integration and its effect on power system operation. Sensitivity analysis to the load and the other input data has been carried out to predict the sensitivity of the results to any deviation in the input data of the system. The obtained results from the proposed system prove that using of renewable energy sources as a DG reduces the generation and operation cost of the overall power system. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle Numerical Investigation into the Effect of Natural Fracture Density on Hydraulic Fracture Network Propagation
Energies 2017, 10(7), 914; doi:10.3390/en10070914
Received: 3 April 2017 / Revised: 5 June 2017 / Accepted: 26 June 2017 / Published: 3 July 2017
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Abstract
Hydraulic fracturing is an important method to enhance permeability in oil and gas exploitation projects and weaken hard roofs of coal seams to reduce dynamic disasters, for example, rock burst. It is necessary to fully understand the mechanism of the initiation, propagation, and
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Hydraulic fracturing is an important method to enhance permeability in oil and gas exploitation projects and weaken hard roofs of coal seams to reduce dynamic disasters, for example, rock burst. It is necessary to fully understand the mechanism of the initiation, propagation, and coalescence of hydraulic fracture network (HFN) caused by fluid flow in rock formations. In this study, a coupled hydro-mechanical model was built based on synthetic rock mass (SRM) method to investigate the effects of natural fracture (NF) density on HFN propagation. Firstly, the geometrical structures of NF obtained from borehole images at the field scale were applied to the model. Secondly, the micro-parameters of the proposed model were validated against the interaction between NF and hydraulic fracture (HF) in physical experiments. Finally, a series of numerical simulations were performed to study the mechanism of HFN propagation. In addition, confining pressure ratio (CPR) and injection rate were also taken into consideration. The results suggested that the increase of NF density drives the growth of stimulated reservoir volume (SRV), concentration area of injection pressure (CAIP), and the number of cracks caused by NF. The number of tensile cracks caused by rock matrix decrease gradually with the increase of NF density, and the number of shear cracks caused by rock matrix are almost immune to the change of NF density. The propagation orientation of HFN and the breakdown pressure in rock formations are mainly controlled by CPR. Different injection rates would result in a relatively big difference in the gradient of injection pressure, but this difference would be gradually narrowed with the increase of NF density. Natural fracture density is the key factor that influences the percentages of different crack types in HFN, regardless of the value of CPR and injection rate. The proposed model may help predict HFN propagation and optimize fracturing treatment designs in fractured rock formations. Full article
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Open AccessCommunication Proposal for an Experimental Methodology for Evaluation of Natural Lighting Systems Applied in Buildings
Energies 2017, 10(7), 1014; doi:10.3390/en10071014
Received: 11 May 2017 / Revised: 26 June 2017 / Accepted: 27 June 2017 / Published: 17 July 2017
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Abstract
This work has the objective of developing a methodology for the evaluation of indoor natural lighting systems, which, with speed and practicality, provides from real conditions of use a reliable result about the quality and performance of the proposed system. The methodology is
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This work has the objective of developing a methodology for the evaluation of indoor natural lighting systems, which, with speed and practicality, provides from real conditions of use a reliable result about the quality and performance of the proposed system. The methodology is based on the construction of two real-size test environments, which will be subjected to a natural light system through reflexive tubes made from recycled material, and to a commercial system already certified and consolidated, creating the possibility of comparison. Furthermore, the data acquired in the test environments will be examined in light of the values of solar radiation obtained from a digital meteorological station, such that it is possible to stipulate the lighting capacity of the systems at different times of the year. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
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Open AccessArticle Finite Element Computation of Transient Parameters of a Salient-Pole Synchronous Machine
Energies 2017, 10(7), 1015; doi:10.3390/en10071015
Received: 26 June 2017 / Revised: 15 July 2017 / Accepted: 16 July 2017 / Published: 17 July 2017
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Abstract
This paper presents a novel method for calculating the transient parameters of a saturated salient-pole synchronous machine (SPSM) with damper cage using finite element analysis. All detailed leakage inductances in a modified d-q model are discussed and separately extracted. In addition; the frozen
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This paper presents a novel method for calculating the transient parameters of a saturated salient-pole synchronous machine (SPSM) with damper cage using finite element analysis. All detailed leakage inductances in a modified d-q model are discussed and separately extracted. In addition; the frozen permeability method is used in a 2-D finite element analysis to consider saturation and skin effects for determining the inductances. The terminal reactance parameters are obtained from all elements of the d- and q-axis equivalent circuits in all the chosen time constants during the transient process. The variation of leakage inductances of the SPSM in transient processes is also investigated and discussed. To determine transient time constant parameters; the Prony algorithm is applied in the presented method. A program developed to automatically solve the simulation and computation with the proposed method is described. This method is applied to a prototype and validated by experimental results. Some discussion about the relationship between rotor geometric design and the transient parameters of SPSMs is provided. The variation of leakage magnetic field of SPSMs in transient processes is also investigated. This method can be applied in transient parameter estimation and optimization of SPSMs in the design stage. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
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Open AccessArticle Explosion Behaviour of 30% Hydrogen/70% Methane-Blended Fuels in a Weak Turbulent Environment
Energies 2017, 10(7), 915; doi:10.3390/en10070915
Received: 6 June 2017 / Revised: 28 June 2017 / Accepted: 29 June 2017 / Published: 3 July 2017
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Abstract
In the present investigation the explosion characteristics of 30% H2/70% CH4-blended fuels have been experimentally studied in different turbulent environments. Some important indicators about the explosion characteristics, including maximum explosion pressure (pmax), explosion duration (t
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In the present investigation the explosion characteristics of 30% H2/70% CH4-blended fuels have been experimentally studied in different turbulent environments. Some important indicators about the explosion characteristics, including maximum explosion pressure (pmax), explosion duration (tc), maximum rate of pressure rise ((dp/dt)max), deflagration index (KG), and fast burn period (tb) have been studied. Furthermore, the influences of turbulent intensity associated with the equivalence ratio on explosion characteristics have been compressively analysed. The results indicated that, with the increase of turbulent intensity (u’rms), the value of pmax will be correspondingly raised while the equivalent ratio (φ) corresponding to the peak value of pmax gradually changes from stoichiometric to 1.2. Based upon the value of pmax in laminar condition, the growth extent of pmax monotonically rises to u’rms, but under a same u’rms the growth extent of pmax first declines and then rises with the increase of φ in the rage of 0.6 to 1.2. Under a laminar environment, the peak value of (dp/dt)max is attained at φ = 1.0; although such a conclusion is maintained in the studied range of turbulent intensity, the difference on the value of (dp/dt)max between φ = 1.0 and φ = 1.2 is obviously reduced with the increase of u’rms. Meanwhile, from the variation of KG, it could be found that turbulence can raise the hazardous potential of disaster. With the increase of u’rms, both the values of tc and tb reduce, the quota of tb in the explosion performs a similar regulation, but the detailed variation extent is also controlled by u’rms. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
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Open AccessArticle Economic Power Schedule and Transactive Energy through an Intelligent Centralized Energy Management System for a DC Residential Distribution System
Energies 2017, 10(7), 916; doi:10.3390/en10070916
Received: 20 May 2017 / Revised: 19 June 2017 / Accepted: 27 June 2017 / Published: 3 July 2017
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Abstract
Direct current (DC) residential distribution systems (RDS) consisting of DC living homes will be a significant integral part of future green transmission. Meanwhile, the increasing number of distributed resources and intelligent devices will change the power flow between the main grid and the
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Direct current (DC) residential distribution systems (RDS) consisting of DC living homes will be a significant integral part of future green transmission. Meanwhile, the increasing number of distributed resources and intelligent devices will change the power flow between the main grid and the demand side. The utilization of distributed generation (DG) requires an economic operation, stability, and an environmentally friendly approach in the whole DC system. This paper not only presents an optimization schedule and transactive energy (TE) approach through a centralized energy management system (CEMS), but also a control approach to implement and ensure DG output voltages to various DC buses in a DC RDS. Based on data collection, prediction and a certain objectives, the expert system in a CEMS can work out the optimization schedule, after this, the voltage droop control for steady voltage is aligned with the command of the unit power schedule. In this work, a DC RDS is used as a case study to demonstrate the process, the RDS is associated with unit economic models, and a cost minimization objective is proposed that is to be achieved based on the real-time electrical price. The results show that the proposed framework and methods will help the targeted DC residential system to reduce the total cost and reach stability and efficiency. Full article
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Open AccessArticle Multi-Objective Optimization of Building Energy Design to Reconcile Collective and Private Perspectives: CO2-eq vs. Discounted Payback Time
Energies 2017, 10(7), 1016; doi:10.3390/en10071016
Received: 22 May 2017 / Revised: 26 June 2017 / Accepted: 6 July 2017 / Published: 18 July 2017
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Abstract
Building energy design is a multi-objective optimization problem where collective and private perspectives conflict each other. For instance, whereas the collectivity pursues the minimization of environmental impact, the private pursues the maximization of financial viability. Solving such trade-off design problems usually involves a
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Building energy design is a multi-objective optimization problem where collective and private perspectives conflict each other. For instance, whereas the collectivity pursues the minimization of environmental impact, the private pursues the maximization of financial viability. Solving such trade-off design problems usually involves a big computational cost for exploring a huge solution domain including a large number of design options. To reduce that computational cost, a bi-objective simulation-based optimization algorithm, developed in a previous study, is applied in the present investigation. The algorithm is implemented for minimizing the CO2-eq emissions and the discounted payback time (DPB) of a single-family house in cold climate, where 13,456 design solutions including building envelope and heating system options are explored and compared to a predefined reference case. The whole building life is considered by assuming a calculation period of 30 years. The results show that the type of heating system significantly affects energy performance; notably, the ground source heat pump leads to the highest reduction in CO2-eq emissions, around 1300 kgCO2-eq/m2, with 17 year DPB; the oil fire boiler can provide the lowest DPB, equal to 8.5 years, with 850 kgCO2-eq/m2 reduction. In addition, it is shown that using too high levels of thermal insulation is not an effective solution as it causes unacceptable levels of summertime overheating. Finally a multi-objective decision making approach is proposed in order to enable the stakeholders to choice among the optimal solutions according to the weight given to each objective, and thus to each perspective. Full article
(This article belongs to the Special Issue Zero-Carbon Buildings)
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Open AccessArticle Coordinated Operation and Control of Combined Electricity and Natural Gas Systems with Thermal Storage
Energies 2017, 10(7), 917; doi:10.3390/en10070917
Received: 5 April 2017 / Revised: 13 May 2017 / Accepted: 29 June 2017 / Published: 3 July 2017
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Abstract
As one of the most effective approaches in dealing with the energy crisis, combined electricity and natural gas systems have become more and more popular worldwide. To take full advantages of such hybrid energy networks, a proper operation and control method is required.
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As one of the most effective approaches in dealing with the energy crisis, combined electricity and natural gas systems have become more and more popular worldwide. To take full advantages of such hybrid energy networks, a proper operation and control method is required. In this paper, a novel approach coordinating combined heating and power generation is proposed. First, state excursion rate, a criterion describing the deviation of system operation, is defined for system state evaluation. Then, thermal energy storage is allocated to provide more and better operation modes for combined generation. By investigating the state excursion rate of hybrid energy systems, the optimal operation mode is chosen through an analytical strategy. Case studies on hybrid energy networks show that all state variables, including voltages in electric systems and pressures in gas networks, are adjusted to follow proper operation constraints by the implementations of the proposed strategy. In addition to providing sufficient auxiliary services for hybrid systems, it is also possible to maintain the economic and energy-efficient benefits of energy supply. This study provides an effective method to utilize the regulation capability of combined heating and power generations, which is a technical basis of energy internet. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle Distributed Coordination Control Strategy for a Multi-Microgrid Based on a Consensus Algorithm
Energies 2017, 10(7), 1017; doi:10.3390/en10071017
Received: 28 March 2017 / Revised: 11 June 2017 / Accepted: 11 July 2017 / Published: 18 July 2017
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Abstract
Microgrids (MGs) in which power generation and consumption occur locally have gained prominence, and MG demonstration tests have been widely carried out. In accordance with the increase in the number of MG installations, studies regarding the cooperative control of multiple MGs are proceeding
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Microgrids (MGs) in which power generation and consumption occur locally have gained prominence, and MG demonstration tests have been widely carried out. In accordance with the increase in the number of MG installations, studies regarding the cooperative control of multiple MGs are proceeding in various forms. In this paper, the distributed control strategy of a multi-microgrid (MMG) is proposed. Distributed control is the method in which agents of the electric power facility autonomously control their facility through communication with the neighboring agents only. In this process, a consensus algorithm is utilized to obtain the global information required to control the overall system. In this distributed control strategy, a single MG is operated at an optimal economic point using the equality incremental cost constraints while maintaining the balance between the generation and demand. The control strategy of a MMG is that the flow of the point of common coupling (PCC) is maintained at a particular value needed by the utility and the internal change in power is distributed to the MGs according to their reserves. The proposed algorithm is verified in the MG level and the MMG level through a simulation model using PSCAD/EMTDC software in the C language. Full article
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Open AccessFeature PaperArticle Energy-Based Design of Powertrain for a Re-Engineered Post-Transmission Hybrid Electric Vehicle
Energies 2017, 10(7), 918; doi:10.3390/en10070918
Received: 15 May 2017 / Revised: 22 June 2017 / Accepted: 24 June 2017 / Published: 3 July 2017
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Abstract
This paper presents a systematic approach for the design of post-transmission hybrid electric vehicle powertrains, as an instrument aiding the designer in making the right decision. In particular, a post-transmission series/parallel hybrid electric powertrain is considered, and all of the possible energy paths
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This paper presents a systematic approach for the design of post-transmission hybrid electric vehicle powertrains, as an instrument aiding the designer in making the right decision. In particular, a post-transmission series/parallel hybrid electric powertrain is considered, and all of the possible energy paths are taken into account, in order to automatically select the configuration that gives the lowest fuel consumption, thus better fitting to the considered mission. The optimization problem is solved with the Dijkstra algorithm, which is more computationally efficient than other optimization algorithms in the case of massive design spaces. In this way, it is possible to design a vehicle in terms of architecture and component sizes, without making any a priori choices, which are usually based on common sense, likely compromising the overall system efficiency. In order to demonstrate the effectiveness of the methodology, different driving cycles have been simulated, and some results are presented. The methodology is particularly applied to re-engineered vehicles, aimed at maximizing the benefits of the vehicle hybridization process. Results show how the introduction, in the optimization algorithm, of the engine load factor and sharing factor, for the engine torque split between the generator and the wheels, is crucial. For example, a 10% reduction of the original engine size, suggested by a low load factor, is able to allow for a 24% reduction in the fuel consumption. On the other hand, the sharing factor is of particular importance in suggesting if the vehicle architecture should be series, parallel or rather combined. Full article
(This article belongs to the Special Issue Advances in Electric Vehicles and Plug-in Hybrid Vehicles 2017)
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Open AccessArticle Matching Relationship and Alternating Injection for Polymer Flooding in Heterogeneous Formations: A Laboratory Case Study of Daqing Oilfield
Energies 2017, 10(7), 1018; doi:10.3390/en10071018
Received: 13 April 2017 / Revised: 10 July 2017 / Accepted: 11 July 2017 / Published: 18 July 2017
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Abstract
A series of experiments were carried out to study the relationship between polymer and reservoir permeability, as well as the alternating injection pattern for heterogeneous formations. The polymer molecular size (MS) was studied using dynamic light scattering. The parameters such as hydraulic radius,
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A series of experiments were carried out to study the relationship between polymer and reservoir permeability, as well as the alternating injection pattern for heterogeneous formations. The polymer molecular size (MS) was studied using dynamic light scattering. The parameters such as hydraulic radius, molecular weight (MW), concentrations and salinity were studied. The injection capacity and the relationship between polymer and formation were obtained using injection experiments with natural cores, which represent different regions in the Daqing oilfield. Moreover, an improved injection pattern, alternating injection in heterogeneous formation was studied based on the injection experiments of parallel and in-layer heterogeneous artificial cores. The alternate cycle and slug size were investigated. It was proven that the alternating injection can improve the efficiency of low permeability layers up to 7.3% and a mean value of 4.27%. It was also found that the mechanism of alternating injection is blocking the high permeability layers and improving the water injection profile. We suggest that other fields with high heterogeneity could try the alternating injection to optimize the polymer flooding. Meanwhile, further pilot tests or numerical simulation of polymer alternating injection in heterogeneous formation (formation type II) should be conducted. Full article
(This article belongs to the Section Energy Sources)
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Open AccessArticle Comparison of Various Analysis Methods Based on Heat Flowmeters and Infrared Thermography Measurements for the Evaluation of the In Situ Thermal Transmittance of Opaque Exterior Walls
Energies 2017, 10(7), 1019; doi:10.3390/en10071019
Received: 11 June 2017 / Revised: 6 July 2017 / Accepted: 12 July 2017 / Published: 18 July 2017
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Abstract
There are several methods to obtain the in situ thermal transmittance value (U-value) of building envelopes from on-site data, including the three approaches of the progressive average method, average method considering the thermal storage effect, and dynamic method for deriving the U-value from
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There are several methods to obtain the in situ thermal transmittance value (U-value) of building envelopes from on-site data, including the three approaches of the progressive average method, average method considering the thermal storage effect, and dynamic method for deriving the U-value from heat flowmeter (HFM) measurements and the four methods with different formulas to analyze infrared thermography (IRT) measurement data. Since each of these methods considers different parameters and the non-steady characteristics of the heat transfer in building walls in their own way, discrepancies may occur among the obtained results. This study evaluates and compares the in situ U-values by using various methods of analyzing HFM and IRT measurement data. Further, by investigating buildings with similar materials and identical stratigraphies, but with different construction years, we analyze the discrepancy between the designed and measured values caused by material deterioration and evaluate the errors according to the analysis method. The percentage deviation between the U-values obtained by the three methods from the HFM data is found to be satisfactory, being within 10%. When compared with the results of the progressive average method, the deviations for the four different IRT-measurement-based methods vary greatly, being in the range of 6–43%. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
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Open AccessArticle Big-Data-Based Thermal Runaway Prognosis of Battery Systems for Electric Vehicles
Energies 2017, 10(7), 919; doi:10.3390/en10070919
Received: 15 May 2017 / Revised: 25 June 2017 / Accepted: 26 June 2017 / Published: 4 July 2017
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Abstract
A thermal runaway prognosis scheme for battery systems in electric vehicles is proposed based on the big data platform and entropy method. It realizes the diagnosis and prognosis of thermal runaway simultaneously, which is caused by the temperature fault through monitoring battery temperature
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A thermal runaway prognosis scheme for battery systems in electric vehicles is proposed based on the big data platform and entropy method. It realizes the diagnosis and prognosis of thermal runaway simultaneously, which is caused by the temperature fault through monitoring battery temperature during vehicular operations. A vast quantity of real-time voltage monitoring data is derived from the National Service and Management Center for Electric Vehicles (NSMC-EV) in Beijing. Furthermore, a thermal security management strategy for thermal runaway is presented under the Z-score approach. The abnormity coefficient is introduced to present real-time precautions of temperature abnormity. The results illustrated that the proposed method can accurately forecast both the time and location of the temperature fault within battery packs. The presented method is flexible in all disorder systems and possesses widespread application potential in not only electric vehicles, but also other areas with complex abnormal fluctuating environments. Full article
(This article belongs to the Special Issue Advanced Energy Storage Technologies and Their Applications (AESA))
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Open AccessArticle Thermodynamic Analysis of Three Compressed Air Energy Storage Systems: Conventional, Adiabatic, and Hydrogen-Fueled
Energies 2017, 10(7), 1020; doi:10.3390/en10071020
Received: 10 May 2017 / Revised: 15 June 2017 / Accepted: 27 June 2017 / Published: 18 July 2017
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Abstract
We present analyses of three families of compressed air energy storage (CAES) systems: conventional CAES, in which the heat released during air compression is not stored and natural gas is combusted to provide heat during discharge; adiabatic CAES, in which the compression heat
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We present analyses of three families of compressed air energy storage (CAES) systems: conventional CAES, in which the heat released during air compression is not stored and natural gas is combusted to provide heat during discharge; adiabatic CAES, in which the compression heat is stored; and CAES in which the compression heat is used to assist water electrolysis for hydrogen storage. The latter two methods involve no fossil fuel combustion. We modeled both a low-temperature and a high-temperature electrolysis process for hydrogen production. Adiabatic CAES (A-CAES) with physical storage of heat is the most efficient option with an exergy efficiency of 69.5% for energy storage. The exergy efficiency of the conventional CAES system is estimated to be 54.3%. Both high-temperature and low-temperature electrolysis CAES systems result in similar exergy efficiencies (35.6% and 34.2%), partly due to low efficiency of the electrolyzer cell. CAES with high-temperature electrolysis has the highest energy storage density (7.9 kWh per m3 of air storage volume), followed by A-CAES (5.2 kWh/m3). Conventional CAES and CAES with low-temperature electrolysis have similar energy densities of 3.1 kWh/m3. Full article
(This article belongs to the Special Issue Advanced Energy Storage Technologies and Their Applications (AESA))
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Open AccessArticle Advantages of Using Supercapacitors and Silicon Carbide on Hybrid Vehicle Series Architecture
Energies 2017, 10(7), 920; doi:10.3390/en10070920
Received: 9 June 2017 / Revised: 29 June 2017 / Accepted: 30 June 2017 / Published: 4 July 2017
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Abstract
In recent years enormous growth has taken place in the hybrid vehicle sector; parallel architecture is the most widespread configuration regarding medium size cars. At the same time, storage systems and power electronics have experienced some important innovations. The development of supercapacitors has
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In recent years enormous growth has taken place in the hybrid vehicle sector; parallel architecture is the most widespread configuration regarding medium size cars. At the same time, storage systems and power electronics have experienced some important innovations. The development of supercapacitors has permitted management of high power with elevated efficiency. Moreover, the availability on the market of silicon carbide components has allowed a significant reduction of power electronic losses. These improvements may challenge the hybrid architecture used in medium size cars nowadays. On one hand, series architecture would relevantly benefit from an electric powertrain efficiency increase, on the other hand, these innovations would generate low benefits in parallel architectures. The aim of this paper is to evaluate electric component average efficiency over different road missions, in order to estimate fuel economy over various working conditions and finally to establish which hybrid configuration is most efficient in vehicle applications. Full article
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Open AccessArticle Controlled Operation of the Islanded Portion of the International Council on Large Electric Systems (CIGRE) Low Voltage Distribution Network
Energies 2017, 10(7), 1021; doi:10.3390/en10071021
Received: 27 February 2017 / Revised: 24 June 2017 / Accepted: 5 July 2017 / Published: 18 July 2017
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Abstract
In islanding, a portion of the power network, comprised of the loads and distributed generation (DG) units, is isolated from the rest of the power grid and forms a micro grid (MG). In this condition, it becomes essential for the islanded MG to
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In islanding, a portion of the power network, comprised of the loads and distributed generation (DG) units, is isolated from the rest of the power grid and forms a micro grid (MG). In this condition, it becomes essential for the islanded MG to operate in a stable and controlled manner by providing ancillary services. When the MG is cut off from the main grid, the islanding must be detected by the DG units. In this condition it is essential that one of the controllers should be switched to the voltage-frequency (VF) control mode. In islanding, the network loses it slack reference and this reference is established by a VF controller. The voltage and the frequency of the islanded MG deviate when disconnected from the transmission grid and these deviations are caused by the load-generation imbalance. The voltage and the frequency of the islanded MG can be restored to the permissible limits if the desired/exceeded amount of active and reactive power is injected/absorbed by the locally available sources in islanded MG. This paper proposes a control strategy which can compensate the voltage and the frequency deviations in the islanded portion of the International Council on Large Electric Systems (CIGRE) low voltage distribution network by using advanced power electronics devices such as STATCOMs) for Photovoltaic (PV) Units and Battery Energy Storage Systems (BESS) STATCOMs (for battery units). The selection of the VF controller for the most suitable DG unit of this test network is also presented in this paper, and the effectiveness of the controllers is verified by presenting simulation results using DIgSILENT (DIgSILENT GmbH, Gomaringen, Germany) power factory software version 15.0. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle Design and Implementation of a STATCOM Based on a Multilevel FHB Converter with Delta-Connected Configuration for Unbalanced Load Compensation
Energies 2017, 10(7), 921; doi:10.3390/en10070921
Received: 9 January 2017 / Revised: 5 June 2017 / Accepted: 28 June 2017 / Published: 4 July 2017
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Abstract
A delta-connected STATCOM with cascade multilevel full H-bridge (FHB) converter has been applied for phase balancing and power factor correction of unbalanced load in a three-phase, three-wire power distribution system. In this paper, a feedforward compensation formula is presented for the STATCOM by
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A delta-connected STATCOM with cascade multilevel full H-bridge (FHB) converter has been applied for phase balancing and power factor correction of unbalanced load in a three-phase, three-wire power distribution system. In this paper, a feedforward compensation formula is presented for the STATCOM by using the symmetrical components method to compensate unbalanced load. Computer simulation is performed for preliminary verification. Accordingly, a hardware prototype employing a TMS320F2812 DSP-based system is built for final verification test. Experimental results show that the proposed STATCOM is very effective for real-time unbalanced load compensation. Full article
(This article belongs to the Special Issue Power Electronics in Power Quality)
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Open AccessArticle A New Hybrid Wind Power Forecaster Using the Beveridge-Nelson Decomposition Method and a Relevance Vector Machine Optimized by the Ant Lion Optimizer
Energies 2017, 10(7), 922; doi:10.3390/en10070922
Received: 15 May 2017 / Revised: 11 June 2017 / Accepted: 28 June 2017 / Published: 4 July 2017
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Abstract
As one of the most promising kinds of the renewable energy power, wind power has developed rapidly in recent years. However, wind power has the characteristics of intermittency and volatility, so its penetration into electric power systems brings challenges for their safe and
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As one of the most promising kinds of the renewable energy power, wind power has developed rapidly in recent years. However, wind power has the characteristics of intermittency and volatility, so its penetration into electric power systems brings challenges for their safe and stable operation, therefore making accurate wind power forecasting increasingly important, which is also a challenging task. In this paper, a new hybrid wind power forecasting method, named the BND-ALO-RVM forecaster, is proposed. It combines the Beveridge-Nelson decomposition method (BND), relevance vector machine (RVM) and ant lion optimizer (ALO). Considering the nonlinear and non-stationary characteristics of wind power data, the wind power time series were firstly decomposed into deterministic, cyclical and stochastic components using BND. Then, these three decomposed components were respectively forecasted using RVM. Meanwhile, to improve the forecasting performance, the kernel width parameter of RVM was optimally determined by ALO, a new Nature-inspired meta-heuristic algorithm. Finally, the wind power forecasting result was obtained by multiplying the forecasting results of those three components. The proposed BND-ALO-RVM wind power forecaster was tested with real-world hourly wind power data from the Xinjiang Uygur autonomous region in China. To verify the effectiveness and feasibility of the proposed forecaster, it was compared with single RVM without time series decomposition and parameter optimization, RVM with time series decomposition based on BND (BND-RVM), RVM with parameter optimization (ALO-RVM), and Generalized Regression Neural Network with data decomposition based on Wavelet Transform (WT-GRNN) using three forecasting performance criteria, namely MAE (Mean Absolute Error), MAPE (Mean Absolute Percentage Error) and RMSE (Root Mean Square Error). The results indicate the proposed BND-ALO-RVM wind power forecaster has the best forecasting performance of all the tested options, which confirms its validity. Full article
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Open AccessArticle A New Miniature Wind Turbine for Wind Tunnel Experiments. Part II: Wake Structure and Flow Dynamics
Energies 2017, 10(7), 923; doi:10.3390/en10070923
Received: 10 May 2017 / Revised: 24 June 2017 / Accepted: 29 June 2017 / Published: 4 July 2017
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Abstract
An optimized three-bladed horizontal-axis miniature wind turbine, called WiRE-01, with the rotor diameter of 15 cm is designed and fully characterized in Part I of this study. In the current part of the study, we investigate the interaction of the turbine with a
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An optimized three-bladed horizontal-axis miniature wind turbine, called WiRE-01, with the rotor diameter of 15 cm is designed and fully characterized in Part I of this study. In the current part of the study, we investigate the interaction of the turbine with a turbulent boundary layer. The comparison of the spectral density of the thrust force and the one of the incoming velocity revealed new insights on the use of turbine characteristics to estimate incoming flow conditions. High-resolution stereoscopic particle image-velocimetry (S-PIV) measurements were also performed in the wake of the turbine operating at optimal conditions. Detailed information on the velocity and turbulence structure of the turbine wake is presented and discussed, which can serve as a complete dataset for the validation of numerical models. The PIV data are also used to better understand the underlying mechanisms leading to unsteady loads on a downstream turbine at different streamwise and spanwise positions. To achieve this goal, a new method is developed to quantify and compare the effect of both turbulence and mean shear on the moment of the incoming momentum flux for a hypothetical turbine placed downstream. The results show that moment fluctuations caused by turbulence are bigger under full-wake conditions, whereas those caused by mean shear are clearly dominant under partial-wake conditions. Especial emphasis is also placed on how the mean wake flow distribution is affected by wake meandering. Conditional averaging based on the instantaneous position of the wake center revealed that when the wake meanders laterally to one side, a high-speed region exists on the opposite side. The results show that, due to this high-speed region, large lateral meandering motions do not lead to the expansion of the mean wake cross-section in the lateral direction. Full article
(This article belongs to the collection Wind Turbines)
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Open AccessArticle Combustion, Performance, and Emission Evaluation of a Diesel Engine with Biodiesel Like Fuel Blends Derived From a Mixture of Pakistani Waste Canola and Waste Transformer Oils
Energies 2017, 10(7), 1023; doi:10.3390/en10071023
Received: 12 June 2017 / Revised: 1 July 2017 / Accepted: 12 July 2017 / Published: 18 July 2017
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Abstract
The aim of this work was to study the combustion, performance, and emission characteristics of a 5.5 kW four-stroke single-cylinder water-cooled direct-injection diesel engine operated with blends of biodiesel-like fuel (BLF15, BLF20 & BLF25) obtained from a 50:50 mixture of transesterified waste transformer
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The aim of this work was to study the combustion, performance, and emission characteristics of a 5.5 kW four-stroke single-cylinder water-cooled direct-injection diesel engine operated with blends of biodiesel-like fuel (BLF15, BLF20 & BLF25) obtained from a 50:50 mixture of transesterified waste transformer oil (TWTO) and waste canola oil methyl esters (WCOME) with petroleum diesel. The mixture of the waste oils was named as biodiesel-like fuel (BLF).The engine fuelled with BLF blends was evaluated in terms of combustion, performance, and emission characteristics. FTIR analysis was carried out to know the functional groups in the BLF fuel. The experimental results revealed the shorter ignition delay and marginally higher brake specific fuel consumption (BSFC), brake thermal efficiency (BTE) and exhaust gas temperature (EGT) values for BLF blends as compared to diesel. The hydrocarbon (HC) and carbon monoxide (CO) emissions were decreased by 10.92–31.17% and 3.80–6.32%, respectively, as compared to those of diesel fuel. Smoke opacity was significantly reduced. FTIR analysis has confirmed the presence of saturated alkanes and halide groups in BLF fuel. In comparison to BLF20 and BLF25, the blend BLF15 has shown higher brake thermal efficiency and lower fuel consumption values. The HC, CO, and smoke emissions of BLF15 were found lower than those of petroleum diesel. The fuel blend BLF15 is suggested to be used as an alternative fuel for diesel engines without any engine modification. Full article
(This article belongs to the Section Energy Sources)
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Open AccessArticle Day-Ahead Market Modeling for Strategic Wind Power Producers under Robust Market Clearing
Energies 2017, 10(7), 924; doi:10.3390/en10070924
Received: 21 March 2017 / Revised: 10 June 2017 / Accepted: 28 June 2017 / Published: 4 July 2017
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Abstract
In this paper, considering real time wind power uncertainties, the strategic behaviors of wind power producers adopting two different bidding modes in day-ahead electricity market is modeled and experimentally compared. These two different bidding modes only provide a wind power output plan and
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In this paper, considering real time wind power uncertainties, the strategic behaviors of wind power producers adopting two different bidding modes in day-ahead electricity market is modeled and experimentally compared. These two different bidding modes only provide a wind power output plan and a bidding curve consisting of bidding price and power output, respectively. On the one hand, to significantly improve wind power accommodation, a robust market clearing model is employed for day-ahead market clearing implemented by an independent system operator. On the other hand, since the Least Squares Continuous Actor-Critic algorithm is demonstrated as an effective method in dealing with Markov decision-making problems with continuous state and action sets, we propose the Least Squares Continuous Actor-Critic-based approaches to model and simulate the dynamic bidding interaction processes of many wind power producers adopting two different bidding modes in the day-head electricity market under robust market clearing conditions, respectively. Simulations are implemented on the IEEE 30-bus test system with five strategic wind power producers, which verify the rationality of our proposed approaches. Moreover, the quantitative analysis and comparisons conducted in our simulations put forward some suggestions about leading wind power producers to reasonably bid in market and bidding mode selections. Full article
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Open AccessArticle Secure Plug-in Electric Vehicle PEV Charging in a Smart Grid Network
Energies 2017, 10(7), 1024; doi:10.3390/en10071024
Received: 26 June 2017 / Revised: 12 July 2017 / Accepted: 13 July 2017 / Published: 19 July 2017
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Abstract
Charging of plug-in electric vehicles (PEVs) exposes smart grid systems and their users to different kinds of security and privacy attacks. Hence, a secure charging protocol is required for PEV charging. Existing PEV charging protocols are usually based on insufficiently represented and simplified
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Charging of plug-in electric vehicles (PEVs) exposes smart grid systems and their users to different kinds of security and privacy attacks. Hence, a secure charging protocol is required for PEV charging. Existing PEV charging protocols are usually based on insufficiently represented and simplified charging models that do not consider the user’s charging modes (charging at a private location, charging as a guest user, roaming within one’s own supplier network or roaming within other suppliers’ networks). However, the requirement for charging protocols depends greatly on the user’s charging mode. Consequently, available solutions do not provide complete protocol specifications. Moreover, existing protocols do not support anonymous user authentication and payment simultaneously. In this paper, we propose a comprehensive end-to-end charging protocol that addresses the security and privacy issues in PEV charging. The proposed protocol uses nested signatures to protect users’ privacy from external suppliers, their own suppliers and third parties. Our approach supports anonymous user authentication, anonymous payment, as well as anonymous message exchange between suppliers within a hierarchical smart grid architecture. We have verified our protocol using the AVISPA software verification tool and the results showed that our protocol is secure and works as desired. Full article
(This article belongs to the Special Issue Innovative Methods for Smart Grids Planning and Management)
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Open AccessArticle Study of Dielectric Breakdown Performance of Transformer Oil Based Magnetic Nanofluids
Energies 2017, 10(7), 1025; doi:10.3390/en10071025
Received: 21 March 2017 / Revised: 4 July 2017 / Accepted: 10 July 2017 / Published: 19 July 2017
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Abstract
Research on the transformer oil-based nanofluids (NFs) has been raised expeditiously over the past decade. Although, there is discrepancy in the stated results and inadequate understanding of the mechanisms of improvement of dielectric nanofluids, these nanofluids have emerged as a potential substitute of
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Research on the transformer oil-based nanofluids (NFs) has been raised expeditiously over the past decade. Although, there is discrepancy in the stated results and inadequate understanding of the mechanisms of improvement of dielectric nanofluids, these nanofluids have emerged as a potential substitute of mineral oils as insulating and heat removal fluids for high voltage equipment. The transformer oil (TO) based magnetic fluids (ferrofluids) may be regarded as the posterity insulation fluids as they propose inspiring unique prospectus to improve dielectric breakdown strength, as well as heat transfer efficiency, as compared to pure transformer oils. In this work, transformer oil-based magnetic nanofluids (MNFs) are prepared by dispersal of Fe3O4 nanoparticles (MNPs) into mineral oil as base oil, with various NPs loading from 5 to 80% w/v. The lightning impulse breakdown voltages (BDV) measurement was conducted in accordance with IEC 60897 by using needle to sphere electrodes geometry. The test results showed that dispersion of magnetic NPs may improve the insulation strength of MO. With the increment of NPs concentrations, the positive lightning impulse (LI) breakdown strength of TO is first raised, up to the highest value at 40% loading, and then tends to decrease at higher concentrations. The outcomes of negative LI breakdown showed that BDV of MNFs, with numerous loadings, were inferior to the breakdown strength of pure MO. The 40% concentration of nanoparticles (optimum concentration) was selected, and positive and negative LI breakdown strength was also further studied at different sizes (10 nm, 20 nm, 30 nm and 40 nm) of NPs and different electrode gap distances. Augmentation in the BDV of the ferrofluids (FFs) is primarily because of dielectric and magnetic features of Fe3O4 nanoaprticles, which act as electron scavengers and decrease the rate of free electrons produced in the ionization process. Research challenges and technical difficulties associated with ferrofluids for practical applications are mentioned. The advantages and disadvantages linked with magnetic fluids are also presented. Full article
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Open AccessArticle Integration of Degradation Processes in a Strategic Offshore Wind Farm O&M Simulation Model
Energies 2017, 10(7), 925; doi:10.3390/en10070925
Received: 28 April 2017 / Revised: 25 June 2017 / Accepted: 29 June 2017 / Published: 4 July 2017
PDF Full-text (2332 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Decision support models for offshore wind farm operation and maintenance (O&M) are required to represent the failure behavior of wind turbine components. Detailed degradation modelling is already incorporated in models for specific components and applications. However, component degradation is only one of many
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Decision support models for offshore wind farm operation and maintenance (O&M) are required to represent the failure behavior of wind turbine components. Detailed degradation modelling is already incorporated in models for specific components and applications. However, component degradation is only one of many effects that must be captured in high-level strategic decision support models that simulate entire wind farms. Thus, for practical applications, a trade-off is needed between detailed degradation modelling and the level of simplicity of input data representation. To this end, this paper discusses two alternative approaches for taking into account component degradation processes in strategic offshore wind farm O&M simulation models: (1) full integration of the degradation process in the O&M simulation model; and (2) loose integration where the degradation process is translated into simplified input to the O&M model. As a proof-of-concept, a Markov process for blade degradation has been considered. Simulations using the NOWIcob O&M model show that the difference between full and loose integration is small in terms of aggregated output parameters such as average wind turbine availability and O&M costs. Although loose integration models some effects less accurately than full integration, the former is more flexible and convenient, and the accuracy is for most purposes sufficient for such O&M models. Full article
(This article belongs to the Special Issue Wind Turbine 2017)
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Open AccessFeature PaperArticle Grid Synchronization of a Seven-Phase Wind Electric Generator Using d-q PLL
Energies 2017, 10(7), 926; doi:10.3390/en10070926
Received: 10 May 2017 / Revised: 22 June 2017 / Accepted: 26 June 2017 / Published: 4 July 2017
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Abstract
The evolving multiphase induction generators (MPIGs) with more than three phases are receiving prominence in high power generation systems. This paper aims at the development of a comprehensive model of the wind turbine driven seven-phase induction generator (7PIG) along with the necessary power
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The evolving multiphase induction generators (MPIGs) with more than three phases are receiving prominence in high power generation systems. This paper aims at the development of a comprehensive model of the wind turbine driven seven-phase induction generator (7PIG) along with the necessary power electronic converters and the controller for grid interface. The dynamic model of the system is developed in MATLAB/Simulink (R2015b, The MathWorks, Inc., Natick, MA, USA). A synchronous reference frame phase-locked loop (SRFPLL) system is incorporated for grid synchronization. The modeling aspects are detailed and the system response is observed for various wind velocities. The effectiveness of the seven phase induction generator is demonstrated with the fault tolerant capability and high output power with reduced phase current when compared to the conventional 3-phase wind generation scheme. The response of the PLL is analysed and the results are presented. Full article
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Open AccessArticle Design of a H Robust Controller with μ-Analysis for Steam Turbine Power Generation Applications
Energies 2017, 10(7), 1026; doi:10.3390/en10071026
Received: 10 March 2017 / Revised: 23 June 2017 / Accepted: 13 July 2017 / Published: 19 July 2017
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Abstract
Concentrated Solar Power plants are complex systems subjected to quite sensitive variations of the steam production profile and external disturbances, thus advanced control techniques that ensure system stability and suitable performance criteria are required. In this work, a multi-objective H robust controller
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Concentrated Solar Power plants are complex systems subjected to quite sensitive variations of the steam production profile and external disturbances, thus advanced control techniques that ensure system stability and suitable performance criteria are required. In this work, a multi-objective H robust controller is designed and applied to the power control of a Concentered Solar Power plant composed by two turbines, a gear and a generator. In order to provide robust performance and stability in presence of disturbances, not modeled plant dynamics and plant-parameter variations, the advanced features of the μ-analysis are exploited. A high order controller is obtained from the process of synthesis that makes the implementation of the controller difficult and computational more demanding for a Programmable Logic Controller. Therefore, the controller order is reduced through the Balanced Truncation method and then discretized. The obtained robust control is compared to the current Proportional Integral Derivative-based governing system in order to evaluate its performance, considering unperturbed as well as perturbed scenarios, taking into account variations of steam conditions, sensor measurement delays and power losses. The simulations results show that the proposed controller achieves better robustness and performance compared to the existing Proportional Integral Derivative controller. Full article
(This article belongs to the Special Issue Energy Production Systems)
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Open AccessArticle Analysis of GHG Emission Reduction in South Korea Using a CO2 Transportation Network Optimization Model
Energies 2017, 10(7), 1027; doi:10.3390/en10071027
Received: 26 January 2017 / Revised: 5 July 2017 / Accepted: 13 July 2017 / Published: 19 July 2017
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Abstract
Korea’s national carbon capture and storage (CCS) master plan aims to commercialize CCS projects by 2030. Furthermore, the Korean government is forced to reduce emissions from various sectors, including industries and power generation, by 219 million tons by 2030. This study analyzes a
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Korea’s national carbon capture and storage (CCS) master plan aims to commercialize CCS projects by 2030. Furthermore, the Korean government is forced to reduce emissions from various sectors, including industries and power generation, by 219 million tons by 2030. This study analyzes a few scenarios of Korean CCS projects with a CO2 pipeline transportation network optimization model for minimizing the total facility cost and pipeline cost. Our scenarios are based on the “2030 basic roadmap for reducing greenhouse gases” established by the government. The results for each scenario demonstrate that the effective design and implementation of CO2 pipeline network enables the lowering of CO2 units cost. These suggest that CO2 transportation networks, which connect the capture and sequestration parts, will be more important in the future and can be used to substitute and supplement the emission reduction target in case the execution of other reduction options faces uncertainty. Our mathematical model and scenario designs will be helpful for various countries which plan to introduce CCS technology. Full article
(This article belongs to the Special Issue Energy Production Systems)
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Open AccessArticle Design of Ecological CO2 Enrichment System for Greenhouse Production using TBAB + CO2 Semi-Clathrate Hydrate
Energies 2017, 10(7), 927; doi:10.3390/en10070927
Received: 15 April 2017 / Revised: 1 June 2017 / Accepted: 29 June 2017 / Published: 4 July 2017
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Abstract
This paper proposes an innovative CO2 enrichment system for crop production under a controlled greenhouse environment by means of tetra-n-butylammonium bromide (TBAB) + CO2 semi-clathrate hydrate (SC). In this system, CO2 is captured directly from exhaust gas from
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This paper proposes an innovative CO2 enrichment system for crop production under a controlled greenhouse environment by means of tetra-n-butylammonium bromide (TBAB) + CO2 semi-clathrate hydrate (SC). In this system, CO2 is captured directly from exhaust gas from a combustion heater at night, which can be used for stimulating photosynthesis of crops in greenhouses during daytime. Although the gas capacity of TBAB + CO2 SC is less than that of CO2 gas hydrate, it is shown that TBAB + CO2 SC can store CO2 for CO2 enrichment in crop production even under moderate pressure conditions (<1.0 MPa) at 283 K. Full article
(This article belongs to the Special Issue Methane Hydrate Research and Development)
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Open AccessArticle Parameter Design and Energy Control of the Power Train in a Hybrid Electric Boat
Energies 2017, 10(7), 1028; doi:10.3390/en10071028
Received: 26 April 2017 / Revised: 7 July 2017 / Accepted: 11 July 2017 / Published: 19 July 2017
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Abstract
With the continuous development worldwide of the inland shipping industry, emissions to the atmosphere have become a serious threat in terms of pollution. Hybrid power technology is an important means for reducing pollution due to emissions from ships. This paper considers a power
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With the continuous development worldwide of the inland shipping industry, emissions to the atmosphere have become a serious threat in terms of pollution. Hybrid power technology is an important means for reducing pollution due to emissions from ships. This paper considers a power train series in a hybrid electric inland waterway boat. From the analysis of the structure and principle of the power train, the parameter design for its key devices is presented, and a novel energy control strategy is proposed. Navigation experience shows that the proposed design method and control strategy are useful and satisfactory. Full article
(This article belongs to the Section Energy Storage and Application)
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Open AccessArticle Power Balancing Control for Grid Energy Storage System in Photovoltaic Applications—Real Time Digital Simulation Implementation
Energies 2017, 10(7), 928; doi:10.3390/en10070928
Received: 19 May 2017 / Revised: 29 June 2017 / Accepted: 30 June 2017 / Published: 5 July 2017
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Abstract
A grid energy storage system for photo voltaic (PV) applications contains three different power sources i.e., PV array, battery storage system and the grid. It is advisable to isolate these three different sources to ensure the equipment safety. The configuration proposed in this
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A grid energy storage system for photo voltaic (PV) applications contains three different power sources i.e., PV array, battery storage system and the grid. It is advisable to isolate these three different sources to ensure the equipment safety. The configuration proposed in this paper provides complete isolation between the three sources. A Power Balancing Control (PBC) method for this configuration is proposed to operate the system in three different modes of operation. Control of a dual active bridge (DAB)-based battery charger which provides a galvanic isolation between batteries and other sources is explained briefly. Various modes of operation of a grid energy storage system are also presented in this paper. Hardware-In-the-Loop (HIL) simulation is carried out to check the performance of the system and the PBC algorithm. A power circuit (comprised of the inverter, dual active bridge based battery charger, grid, PV cell, batteries, contactors, and switches) is simulated and the controller hardware and user interface panel are connected as HIL with the simulated power circuit through Real Time Digital Simulator (RTDS). HIL simulation results are presented to explain the control operation, steady-state performance in different modes of operation and the dynamic response of the system. Full article
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Open AccessArticle Stochastic Navigation in Smart Cities
Energies 2017, 10(7), 929; doi:10.3390/en10070929
Received: 18 April 2017 / Revised: 9 June 2017 / Accepted: 30 June 2017 / Published: 5 July 2017
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Abstract
In this work we show how a simple model based on chemical signaling can reduce the exploration times in urban environments. The problem is relevant for smart city navigation where electric vehicles try to find recharging stations with unknown locations. To this end
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In this work we show how a simple model based on chemical signaling can reduce the exploration times in urban environments. The problem is relevant for smart city navigation where electric vehicles try to find recharging stations with unknown locations. To this end we have adapted the classical ant foraging swarm algorithm to urban morphologies. A perturbed Markov chain model is shown to qualitatively reproduce the observed behaviour. This consists of perturbing the lattice random walk with a set of perturbing sources. As the number of sources increases the exploration times decrease consistently with the swarm algorithm. This model provides a better understanding of underlying process dynamics. An experimental campaign with real prototypes provided experimental validation of our models. This enables us to extrapolate conclusions to optimize electric vehicle routing in real city topologies. Full article
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Open AccessArticle Economic Impact of the Use of Inertia in an Urban Bus Company
Energies 2017, 10(7), 1029; doi:10.3390/en10071029
Received: 24 April 2017 / Revised: 7 July 2017 / Accepted: 11 July 2017 / Published: 19 July 2017
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Abstract
Public transport companies face great expenses. In order to be profitable companies, they need to reduce costs in all aspects. In addition, many countries have increased taxes to force transport companies to reduce their fuel consumption and, thus, greenhouse effect emissions. Efficient driving
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Public transport companies face great expenses. In order to be profitable companies, they need to reduce costs in all aspects. In addition, many countries have increased taxes to force transport companies to reduce their fuel consumption and, thus, greenhouse effect emissions. Efficient driving is the cheapest way to achieve this goal. In this paper, we analyze the economic impact of one of the most influential efficient driving techniques in an urban bus company. We calculate the difference of consumption between a well-performed deceleration using the inertia of the vehicle and a loss of speed obtained by using the brakes. For this purpose, we compare a real track performed by any driver in a precise vehicle with a simulated ideal track. To obtain the deceleration of the simulation, we develop a linear regression model on over 170,000 samples captured from the same vehicle over a period of one month. The results show that the costs of the vehicle under test in one month may be reduced by more than 2500 Full article
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Open AccessArticle Development of a Diesel Engine Thermal Overload Monitoring System with Applications and Test Results
Energies 2017, 10(7), 830; doi:10.3390/en10070830
Received: 19 April 2017 / Revised: 5 June 2017 / Accepted: 14 June 2017 / Published: 22 June 2017
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Abstract
In this research, the development of a diesel engine thermal overload monitoring system is presented with applications and test results. The designed diesel engine thermal overload monitoring system consists of two set of sensors, i.e., a lambda sensor to measure the oxygen concentration
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In this research, the development of a diesel engine thermal overload monitoring system is presented with applications and test results. The designed diesel engine thermal overload monitoring system consists of two set of sensors, i.e., a lambda sensor to measure the oxygen concentration and a fast response thermocouple to measure the temperature of the gas leaving the cylinder. A medium speed Ruston diesel engine is instrumented to measure the required engine process parameters, measurements are taken at constant load and variable fuel delivery i.e., normal and excessive injection. It is indicated that with excessive injection, the test engine is of high risk to be operated at thermal overload condition. Further tests were carried out on a Sulzer 7RTA84T engine to explore the influence of engine operating at thermal overload condition on exhaust gas temperature and oxygen concentration in the blow down gas. It is established that a lower oxygen concentration in the blow down gas corresponds to a higher exhaust gas temperature. The piston crown wear rate will then be much higher due to the high rate of heat transfer from a voluminous flame. Full article
(This article belongs to the Special Issue Internal Combustion Engines)
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Open AccessArticle Influence of Catalytic Formulation and Operative Conditions on Coke Deposition over CeO2-SiO2 Based Catalysts for Ethanol Reforming
Energies 2017, 10(7), 1030; doi:10.3390/en10071030
Received: 8 June 2017 / Revised: 2 July 2017 / Accepted: 14 July 2017 / Published: 19 July 2017
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Abstract
In this work, a series of CeO2-SiO2 (30 wt % of ceria)-based catalysts was prepared by the wetness impregnation method and tested for ESR (ethanol steam reforming) at 450–500 °C, atmospheric pressure and a water/ethanol ratio increasing from 4 to
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In this work, a series of CeO2-SiO2 (30 wt % of ceria)-based catalysts was prepared by the wetness impregnation method and tested for ESR (ethanol steam reforming) at 450–500 °C, atmospheric pressure and a water/ethanol ratio increasing from 4 to 6 (the ethanol concentration being fixed to 10 vol %); after every test, coke gasification measurements were performed at the same water partial pressure, and the temperature of the test and the gasified carbon was measured from the areas under the CO and CO2 profiles. Finally, oxidation measurements under a 5% O2/N2 stream made it possible to calculate the total carbon deposited. In an attempt to improve the coke resistance of a Pt-Ni/CeO2-SiO2 catalyst, the effect of support basification by alkali addition (K and Cs), as well as Pt substitution by Rh was investigated. The novel catalysts, especially those containing Rh, displayed a lowering in the carbon formation rate; however, a faster reduction of ethanol conversion with time-on-stream and lessened hydrogen selectivities were recorded. In addition, no significant gain in terms of coke gasification rates was observed. The most active catalyst (Pt-Ni/CeO2-SiO2) was also tested under different operative conditions, in order to study the effect of temperature and water/ethanol ratio on carbon formation and gasification. The increase in the water content resulted in an enhanced reactor-plugging time due to reduced carbonaceous deposits formation; however, no effect of steam concentration on the carbon gasification rate were recorded. On the other hand, the increase in temperature from 450–500 °C lowered the coke selectivity by almost one order of magnitude improving, at the same time, the contribution of the gasification reactions. Full article
(This article belongs to the collection Bioenergy and Biofuel)
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Open AccessArticle Capacitive Emulation for LCL-Filtered Grid-Connected Converters
Energies 2017, 10(7), 930; doi:10.3390/en10070930
Received: 1 June 2017 / Revised: 30 June 2017 / Accepted: 3 July 2017 / Published: 5 July 2017
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Abstract
This paper proposes an effective capacitive emulation (CE) technique to reduce the grid current distortion when the converter currents are controlled (converter current feedback (CCF)) in grid-connected converters with an LCL filter. Although the CCF scheme is preferable to the grid current feedback
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This paper proposes an effective capacitive emulation (CE) technique to reduce the grid current distortion when the converter currents are controlled (converter current feedback (CCF)) in grid-connected converters with an LCL filter. Although the CCF scheme is preferable to the grid current feedback (GCF) scheme in terms of stability and inherent current limitation of the power semiconductors, the former presents a problem of additional grid-current harmonic distortion due to the LCL capacitor, which generates a distorted current by line voltage differentiation. To solve this problem, the distorting capacitive current is reproduced on the converter output, so that both cancel out each other on the grid. That is, the converter emulates a negative capacitance while delivering the active and reactive power at the fundamental frequency. This is achieved by adding an estimation of the distorting capacitive current to the converter current reference. Moreover, an effective CE technique requires a current control capable of tracking all harmonics added to the current reference and compensating for any control delay. To compensate this delay, the paper proposes a buffer-based method to advance and filter the current reference. The effectiveness of the CE method has been tested on a 10-kVA transformerless inverter with CCF and a simple proportional-integral (PI) control with grid-voltage feedforward cancellation. Experimental results prove that the proposed solution reduces the line current THD (total harmonic distortion) compared with the GCF strategy with proportional-resonant (PR) control. Full article
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Open AccessArticle A Computational Tool for Comparative Energy Cost Analysis of Multiple-Crop Production Systems
Energies 2017, 10(7), 831; doi:10.3390/en10070831
Received: 5 April 2017 / Revised: 29 May 2017 / Accepted: 13 June 2017 / Published: 22 June 2017
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Abstract
Various crops can be considered as potential bioenergy and biofuel production feedstocks. The selection of the crops to be cultivated for that purpose is based on several factors. For an objective comparison between different crops, a common framework is required to assess their
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Various crops can be considered as potential bioenergy and biofuel production feedstocks. The selection of the crops to be cultivated for that purpose is based on several factors. For an objective comparison between different crops, a common framework is required to assess their economic or energetic performance. In this paper, a computational tool for the energy cost evaluation of multiple-crop production systems is presented. All the in-field and transport operations are considered, providing a detailed analysis of the energy requirements of the components that contribute to the overall energy consumption. A demonstration scenario is also described. The scenario is based on three selected energy crops, namely Miscanthus, Arundo donax and Switchgrass. The tool can be used as a decision support system for the evaluation of different agronomical practices (such as fertilization and agrochemicals application), machinery systems, and management practices that can be applied in each one of the individual crops within the production system. Full article
(This article belongs to the collection Bioenergy and Biofuel)
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Open AccessArticle High Breakdown Field CaCu3Ti4O12 Ceramics: Roles of the Secondary Phase and of Sr Doping
Energies 2017, 10(7), 1031; doi:10.3390/en10071031
Received: 30 March 2017 / Revised: 11 May 2017 / Accepted: 16 May 2017 / Published: 19 July 2017
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Abstract
In this work, two methods of CaCu3Ti4O12-CuAl2O4 composite and SrCu3Ti4O12-CaCu3Ti4O12 composite were prepared to improve the breakdown field in CaCu3Ti4
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In this work, two methods of CaCu3Ti4O12-CuAl2O4 composite and SrCu3Ti4O12-CaCu3Ti4O12 composite were prepared to improve the breakdown field in CaCu3Ti4O12 ceramics. CaCu3Ti4O12-0.5CuAl2O4 and 0.4SrCu3Ti4O12-0.6CaCu3Ti4O12 samples with proper sintering conditions were found to have greatly enhanced breakdown fields of more than 20 kV·cm1 compared to the ordinary value of 1–2 kV·cm1 in CaCu3Ti4O12 ceramics. In addition, reduced dielectric loss tangent of these samples remained about 0.1 at a low frequency of 0.1 Hz, indicating superior dielectric properties. No abnormal grain growth was found in either composite with a high breakdown field, which was attributed to the pining effect and consumption of Cu-rich phase at grain boundaries. Under analysis of the relaxation process by electric modulus, compared to conventional CaCu3Ti4O12 ceramics, interstitial Ali··· and increasing interfaces were responsible for variation in activation energy in CaCu3Ti4O12-0.5CuAl2O4 composites, while the integrated action of a strong solid solution effect and weak Sr-stretching effect contributed to the elevated potential barrier height and enhanced breakdown field in 0.4SrCu3Ti4O12-0.6CaCu3Ti4O12 composites. Full article
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Open AccessArticle Optimizing the Weather Research and Forecasting (WRF) Model for Mapping the Near-Surface Wind Resources over the Southernmost Caribbean Islands of Trinidad and Tobago
Energies 2017, 10(7), 931; doi:10.3390/en10070931
Received: 17 May 2017 / Revised: 30 June 2017 / Accepted: 1 July 2017 / Published: 5 July 2017
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Abstract
Numerical wind mapping is currently the wind power industry’s standard for preliminary assessments for sites of good wind resources. Of the various available numerical models, numerical weather prediction (NWP) models are best suited for modeling mesoscale wind flows across small islands. In this
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Numerical wind mapping is currently the wind power industry’s standard for preliminary assessments for sites of good wind resources. Of the various available numerical models, numerical weather prediction (NWP) models are best suited for modeling mesoscale wind flows across small islands. In this study, the Weather Research and Forecast (WRF) NWP model was optimized for simulating the wind resources of the Caribbean islands of Trinidad and Tobago in terms of spin-up period for developing mesoscale features, the input initial and boundary conditions, and the planetary boundary layer (PBL) parameterizations. Hourly model simulations of wind speed and wind direction for a one-month period were compared with corresponding 10 m level wind observations. The National Center for Environmental Prediction (NCEP)-Department of Energy (DOE) reanalysis of 1.875° horizontal resolution was found to be better suited to provide initial and boundary conditions (ICBCs) over the 1° resolution NCEP final analysis (FNL); 86% of modeled wind speeds were within ±2 m/s of measured values at two locations when the coarse resolution NCEP reanalysis was used as compared with 55–64% of modeled wind speeds derived from FNL. Among seven PBL schemes tested, the Yonsei University PBL scheme with topographic drag enabled minimizes the spatial error in wind speed (mean bias error +0.16 m/s, root-mean-square error 1.53 m/s and mean absolute error 1.21 m/s) and is capable of modeling the bimodal wind speed histogram. These sensitivity tests provide a suitable configuration for the WRF model for mapping the wind resources over Trinidad and Tobago, which is a factor in developing a wind energy sector in these islands. Full article
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Open AccessFeature PaperArticle Effect of Fuel Injection Strategy on the Carbonaceous Structure Formation and Nanoparticle Emission in a DISI Engine Fuelled with Butanol
Energies 2017, 10(7), 832; doi:10.3390/en10070832
Received: 8 May 2017 / Revised: 16 June 2017 / Accepted: 16 June 2017 / Published: 22 June 2017
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Abstract
Within the context of ever wider expansion of direct injection in spark ignition engines, this investigation was aimed at improved understanding of the correlation between fuel injection strategy and emission of nanoparticles. Measurements performed on a wall guided engine allowed identifying the mechanisms
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Within the context of ever wider expansion of direct injection in spark ignition engines, this investigation was aimed at improved understanding of the correlation between fuel injection strategy and emission of nanoparticles. Measurements performed on a wall guided engine allowed identifying the mechanisms involved in the formation of carbonaceous structures during combustion and their evolution in the exhaust line. In-cylinder pressure was recorded in combination with cycle-resolved flame imaging, gaseous emissions and particle size distribution. This complete characterization was performed at three injection phasing settings, with butanol and commercial gasoline. Optical accessibility from below the combustion chamber allowed visualization of diffusive flames induced by fuel deposits; these localized phenomena were correlated to observed changes in engine performance and pollutant species. With gasoline fueling, minor modifications were observed with respect to combustion parameters, when varying the start of injection. The alcohol, on the other hand, featured marked sensitivity to the fuel delivery strategy. Even though the start of injection was varied in a relatively narrow crank angle range during the intake stroke, significant differences were recorded, especially in the values of particle emissions. This was correlated to the fuel jet-wall interactions; the analysis of diffusive flames, their location and size confirmed the importance of liquid film formation in direct injection engines, especially at medium and high load. Full article
(This article belongs to the Special Issue Automotive Engines Emissions and Control)
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Open AccessArticle Harmonic Distortion Minimization in Power Grids with Wind and Electric Vehicles
Energies 2017, 10(7), 932; doi:10.3390/en10070932
Received: 1 March 2017 / Revised: 12 May 2017 / Accepted: 25 June 2017 / Published: 5 July 2017
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Abstract
Power-electronic interfacing based devices such as wind generators (WGs) and electrical vehicles (EVs) cause harmonic distortions on the power grid. Higher penetration and uncoordinated operation of WGs and EVs can lead to voltage and current harmonic distortions, which may exceed IEEE limits. It
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Power-electronic interfacing based devices such as wind generators (WGs) and electrical vehicles (EVs) cause harmonic distortions on the power grid. Higher penetration and uncoordinated operation of WGs and EVs can lead to voltage and current harmonic distortions, which may exceed IEEE limits. It is interesting to note that WGs and EVs have some common harmonic profiles. Therefore, when EVs are connected to the grid, the harmonic pollution EVs impart onto the grid can be reduced to some extent by the amount of wind power injecting into the grid and vice versa. In this context, this work studies the impact of EVs on harmonic distortions and careful utilization of wind power to minimize the distortions in distribution feeders. For this, a harmonic unbalanced distribution feeder model is developed in OpenDSS and interfaced with Genetic Algorithm (GA) based optimization algorithm in MATLAB to solve optimal harmonic power flow (OHPF) problems. The developed OHPF model is first used to study impact of EV penetration on current/voltage total harmonic distortions (THDs) in distribution grids. Next, dispatch of WGs are found at different locations on the distribution grid to demonstrate reduction in the current/voltage THDs when EVs are charging. Full article
(This article belongs to the Special Issue Smart Microgrids: Developing the Intelligent Power Grid of Tomorrow)
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Open AccessArticle Multidisciplinary Energy Assessment of Tertiary Buildings: Automated Geomatic Inspection, Building Information Modeling Reconstruction and Building Performance Simulation
Energies 2017, 10(7), 1032; doi:10.3390/en10071032
Received: 27 March 2017 / Revised: 10 June 2017 / Accepted: 13 July 2017 / Published: 19 July 2017
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Abstract
There is an urgent need for energy efficiency in buildings within the European framework, considering its environmental implications, and Europe’s energy dependence. Furthermore, the need for enhancing and increasing productivity in the building industry turns new technologies and building energy performance simulation environments
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There is an urgent need for energy efficiency in buildings within the European framework, considering its environmental implications, and Europe’s energy dependence. Furthermore, the need for enhancing and increasing productivity in the building industry turns new technologies and building energy performance simulation environments into extremely interesting solutions towards rigorous analysis and decision making in renovation within acceptable risk levels. The present work describes a multidisciplinary approach for the estimation of the energy performance of an educational building. The research involved data acquisition with advanced geomatic tools, the development of an optimized building information model, and energy assessment in Building Performance Simulation (BPS) software. Interoperability issues were observed in the different steps of the process. The inspection and diagnostic phases were conducted in a timely, accurate manner thanks to automated data acquisition and subsequent analysis using Building Information Modeling based tools (BIM-based tools). Energy simulation was performed using Design Builder, and the results obtained were compared with those yielded by the official software tool established by Spanish regulations for energy certification. The discrepancies between the results of both programs have proven that the official software program is conservative in this sense. This may cause the depreciation of the assessed buildings. Full article
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Open AccessArticle Grid-Forming-Mode Operation of Boost-Power-Stage Converter in PV-Generator-Interfacing Applications
Energies 2017, 10(7), 1033; doi:10.3390/en10071033
Received: 8 June 2017 / Revised: 5 July 2017 / Accepted: 13 July 2017 / Published: 19 July 2017
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Abstract
The application of constant power control and inclusion of energy storage in grid-connected photovoltaic (PV) energy systems may increase the use of two-stage system structures composed of DC–DC-converter-interfaced PV generator and grid-connected inverter connected in cascade. A typical PV-generator-interfacing DC–DC converter is a
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The application of constant power control and inclusion of energy storage in grid-connected photovoltaic (PV) energy systems may increase the use of two-stage system structures composed of DC–DC-converter-interfaced PV generator and grid-connected inverter connected in cascade. A typical PV-generator-interfacing DC–DC converter is a boost-power-stage converter. The renewable energy system may operate in three different operation modes—grid-forming, grid-feeding, and grid-supporting modes. In the last two operation modes, the outmost feedback loops are taken from the input terminal of the associated power electronic converters, which usually does not pose stability problems in terms of their input sources. In the grid-forming operation mode, the outmost feedback loops have to be connected to the output terminal of the associated power electronic converters, and hence the input terminal will behave as a negative incremental resistor at low frequencies. This property will limit the operation of the PV interfacing converter in either the constant voltage or constant current region of the PV generator for ensuring stable operation. The boost-power-stage converter can be applied as a voltage or current-fed converter limiting the stable operation region accordingly. The investigations of this paper show explicitly that only the voltage-fed mode would provide feasible dynamic and stability properties as a viable interfacing converter. Full article
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Open AccessArticle Break-Even Points of Battery Energy Storage Systems for Peak Shaving Applications
Energies 2017, 10(7), 833; doi:10.3390/en10070833
Received: 24 April 2017 / Revised: 13 June 2017 / Accepted: 15 June 2017 / Published: 22 June 2017
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Abstract
In the last few years, several investigations have been carried out in the field of optimal sizing of energy storage systems (ESSs) at both the transmission and distribution levels. Nevertheless, most of these works make important assumptions about key factors affecting ESS profitability
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In the last few years, several investigations have been carried out in the field of optimal sizing of energy storage systems (ESSs) at both the transmission and distribution levels. Nevertheless, most of these works make important assumptions about key factors affecting ESS profitability such as efficiency and life cycles and especially about the specific costs of the ESS, without considering the uncertainty involved. In this context, this work aims to answer the question: what should be the costs of different ESS technologies in order to make a profit when considering peak shaving applications? The paper presents a comprehensive sensitivity analysis of the interaction between the profitability of an ESS project and some key parameters influencing the project performance. The proposed approach determines the break-even points for different ESSs considering a wide range of life cycles, efficiencies, energy prices, and power prices. To do this, an optimization algorithm for the sizing of ESSs is proposed from a distribution company perspective. From the results, it is possible to conclude that, depending on the values of round trip efficiency, life cycles, and power price, there are four battery energy storage systems (BESS) technologies that are already profitable when only peak shaving applications are considered: lead acid, NaS, ZnBr, and vanadium redox. Full article
(This article belongs to the Section Energy Storage and Application)
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