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Energies, Volume 11, Issue 5 (May 2018)

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Cover Story (view full-size image) Lithium-ion battery manufacturing is a multi-step process involving synthesis, mixing, casting, [...] Read more.
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Editorial

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Open AccessEditorial Energy Efficiency and Controllability of Fluid Power Systems
Energies 2018, 11(5), 1169; https://doi.org/10.3390/en11051169
Received: 24 April 2018 / Revised: 2 May 2018 / Accepted: 3 May 2018 / Published: 7 May 2018
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Abstract
Fluid power refers to the discipline that involves the use of fluids to perform mechanical actuations, it is a well-established and independent discipline that has a defined research area and scholarly activities since at least seven decades.[...] Full article
(This article belongs to the Special Issue Energy Efficiency and Controllability of Fluid Power Systems)

Research

Jump to: Editorial, Review, Other

Open AccessArticle An Experiment on Heat Recovery Performance Improvements in Well-Water Heat-Pump Systems for a Traditional Japanese House
Energies 2018, 11(5), 1023; https://doi.org/10.3390/en11051023
Received: 3 March 2018 / Revised: 12 April 2018 / Accepted: 19 April 2018 / Published: 24 April 2018
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Abstract
Concerns about resource depletion have prompted several countries to promote the usage of renewable energy, such as underground heat. In Japan, underground heat-pump technology has begun to be utilized in large-scale office buildings; however, several economic problems are observed to still exist, such
[...] Read more.
Concerns about resource depletion have prompted several countries to promote the usage of renewable energy, such as underground heat. In Japan, underground heat-pump technology has begun to be utilized in large-scale office buildings; however, several economic problems are observed to still exist, such as high initial costs that include drilling requirements. Further, most of the traditional dwellings “Kyo-machiya” in Kyoto, Japan have a shallow well. This study intends to propose an effective ground-source heat-pump system using the well water from a “Kyo-machiya” home that does not contain any drilling works. In previous research, it was depicted that the well-water temperature decreases as the heat pump (HP) is operated and that the heat extraction efficiency steadily becomes lower. In this study, an experiment is conducted to improve efficiency using a drainage pump. Based on the experimental results, the effect of efficiency improvement and the increase in the electric power consumption of the drainage pump are examined. It is indicated that short-time drainage could help to improve efficiency without consuming excessive energy. Thus, continuous use of the heat pump becomes possible. Full article
(This article belongs to the Special Issue Geothermal Energy: Utilization and Technology)
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Open AccessArticle A Proportional Resonant Controller for Suppressing Resonance in Grid Tied Multilevel Inverter
Energies 2018, 11(5), 1024; https://doi.org/10.3390/en11051024
Received: 28 February 2018 / Revised: 29 March 2018 / Accepted: 13 April 2018 / Published: 24 April 2018
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Abstract
Photovoltaic (PV) resources are connected to power grid through voltage source inverters. The quality of power output from PV inverter should be in grid compliance of IEEE standard. In this regard, the deployment of appropriate low pass filters such as inductor (L), capacitor
[...] Read more.
Photovoltaic (PV) resources are connected to power grid through voltage source inverters. The quality of power output from PV inverter should be in grid compliance of IEEE standard. In this regard, the deployment of appropriate low pass filters such as inductor (L), capacitor (C) or inductor capacitor inductor (LCL) is critical as they aid in minimizing the harmonics being injected into the grid. LCL filters are well entrenched but they bring in stability issue due to resonance and therefore a damping controller with suitable control logic is needed. In this work, to suppress resonance, a Proportional Resonant-Derivative (PR-D) controller has been designed, proposed, and compared with existing counterparts, i.e., two-degree of freedom controller (2DOF) and feedback current controller. The results exhibits that PR-D controller admits meliorate resonance damping and constancy when compared with the two other schemes. The whole system has been simulated in MATLAB/Simulink environment and a prototype has also been made to ensure the performance. Full article
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Open AccessArticle An Enhanced Hybrid Switching-Frequency Modulation Strategy for Fuel Cell Vehicle Three-Level DC-DC Converters with Quasi-Z Source
Energies 2018, 11(5), 1026; https://doi.org/10.3390/en11051026
Received: 28 March 2018 / Revised: 18 April 2018 / Accepted: 19 April 2018 / Published: 24 April 2018
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Abstract
For fuel cell vehicles, the fuel cell stack has a soft output characteristic whereby the output voltage drops quickly with the increasing output current. In order to interface the dynamic low voltage of the fuel cell stack with the required constant high voltage
[...] Read more.
For fuel cell vehicles, the fuel cell stack has a soft output characteristic whereby the output voltage drops quickly with the increasing output current. In order to interface the dynamic low voltage of the fuel cell stack with the required constant high voltage (400 V) of the inverter DC link bus for fuel cell vehicles, an enhanced hybrid switching-frequency modulation strategy that can improve the voltage-gain range is proposed in this paper for the boost three-level DC-DC converter with a quasi-Z source (BTL-qZ) employed in fuel-cell vehicles. The proposed modulation strategy retains the same advantages of the original modulation strategy with more suitable duty cycles [1/3, 2/3) which avoids extreme duty cycles. Finally, the experimental results validate the feasibility of the proposed modulation strategy and the correctness of its operating principles. Therefore, the BTL-qZ converter is beneficial to interface the fuel cell stack and the DC bus for fuel cell vehicles by using the proposed modulation strategy. Full article
(This article belongs to the collection Electric and Hybrid Vehicles Collection)
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Open AccessArticle Conducted EMI Prediction and Mitigation Strategy Based on Transfer Function for a High-Low Voltage DC-DC Converter in Electric Vehicle
Energies 2018, 11(5), 1028; https://doi.org/10.3390/en11051028
Received: 29 March 2018 / Revised: 14 April 2018 / Accepted: 18 April 2018 / Published: 24 April 2018
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Abstract
The high dv/dt and di/dt outputs from power devices in a high-low voltage DC-DC converter on electric vehicles (EVs) can always introduce the unwanted conducted electromagnetic interference (EMI) emissions. A conducted EMI prediction and mitigation strategy that
[...] Read more.
The high dv/dt and di/dt outputs from power devices in a high-low voltage DC-DC converter on electric vehicles (EVs) can always introduce the unwanted conducted electromagnetic interference (EMI) emissions. A conducted EMI prediction and mitigation strategy that is based on transfer function for the high-low voltage DC-DC converter in EVs are proposed. A complete test for the DC-DC converter is conducted to obtain the conducted EMI from DC power cables in the frequency band of 150 kHz-108 MHz. The equivalent circuit with high-frequency parasitic parameters of the DC-DC converter is built`1 based on the measurement results to acquire the characteristics of the conducted EMI of the DC power cables. The common mode (CM) and differential mode (DM) propagation coupling paths are determined, and the corresponding transfer functions of the DM interference and CM interference are established. The simulation results of the conducted EMI can be obtained by software Matlab and Computer Simulation Technology (CST). By analyzing the transfer functions and the simulation results, the dominated interference is the CM interference, which is the main factor of the conducted EMI. A mitigation strategy for the design of the CM interference filter based on the dominated CM interference is proposed. Finally, the mitigation strategy of the conducted EMI is verified by performing the conducted voltage experiment. From the experiment results, the conducted voltage of the DC power cables is decreased, respectively, by 58 dBμV, 55 dBμV, 65 dBμV, 53 dBμV, and 54 dBμV at frequency 200 kHz, 400 kHz, 600 kHz, 1.4 MHz, and 50 MHz. The conduced voltage in the frequency band of 150 kHz–108 MHz can be mitigated by adding the CM interference filters, and the values are lower than the limit level-3 of CISPR25 standard (GB/T 18655-2010). Full article
(This article belongs to the Special Issue Power Electronics for Energy Storage)
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Open AccessArticle Fostering Renewables into the Cold Chain: How Photovoltaics Affect Design and Performance of Refrigerated Automated Warehouses
Energies 2018, 11(5), 1029; https://doi.org/10.3390/en11051029
Received: 20 February 2018 / Revised: 6 April 2018 / Accepted: 19 April 2018 / Published: 24 April 2018
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Abstract
In the industrial food supply chain, cold storage is one of the most important processes where there is a huge but still unused potential for employing renewable energy technologies. This paper analyses how the integration of rooftop photovoltaics affects the design and performance
[...] Read more.
In the industrial food supply chain, cold storage is one of the most important processes where there is a huge but still unused potential for employing renewable energy technologies. This paper analyses how the integration of rooftop photovoltaics affects the design and performance of refrigerated automated warehouses, which are becoming the preferred choice for frozen food storage facilities. The problem is modelled and solved by means of Constraint Programming. Results for the reference case in north-eastern Italy show that photovoltaic installation can lead to both yearly total cost and energy savings. Simulations highlight how design and performance of the refrigerated automated warehouse strictly depend on supply chain decision variables. PV integration offers supply chain managers more opportunities to act on the storage temperature and the incoming product temperatures strictly related to upstream and downstream stages of the whole cold chain. Attention should be paid to system throughput, which presents an intermediate range for which the design optimization of volume and surfaces reduces the convenience of PV integration. Simulations on facility locations reveal how different climate conditions affect the economic and environmental performance of the refrigerated warehouse, as well as country specific carbon intensity and energy price. Full article
(This article belongs to the Special Issue Energy Efficiency in the Supply Chains and Logistics)
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Open AccessArticle Vacuum Exhaust Process in Pilot-Scale Vacuum Pressure Swing Adsorption for Coal Mine Ventilation Air Methane Enrichment
Energies 2018, 11(5), 1030; https://doi.org/10.3390/en11051030
Received: 1 March 2018 / Revised: 28 March 2018 / Accepted: 23 April 2018 / Published: 24 April 2018
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Abstract
Recovery and treatment of methane from coal mine ventilation air methane (VAM) with cost-effective technologies have been an ongoing challenge due to low methane concentrations. In this study, a type of coconut shell-based active carbon was employed to enrich VAM with a three-bed
[...] Read more.
Recovery and treatment of methane from coal mine ventilation air methane (VAM) with cost-effective technologies have been an ongoing challenge due to low methane concentrations. In this study, a type of coconut shell-based active carbon was employed to enrich VAM with a three-bed vacuum pressure swing adsorption unit. A new vacuum exhaust step for the VPSA process was introduced. The results show that the vacuum exhaust step can increase the methane concentration of the product without changing adsorption and desorption pressure. Under laboratory conditions, the concentration of product increased from 0.4% to 0.69% as the vacuum exhaust ratio increased from 0 to 3.1 when the feed gas concentration was 0.2%. A 500 m³/h pilot-scale test system for VAM enrichment was built rendering good correlation with the laboratory results in terms of the vacuum exhaust step. By using a two-stage three-bed separation unit, the VAM was enriched from 0.2% to over 1.2%. Full article
(This article belongs to the Special Issue Unconventional Natural Gas (UNG) Recoveries 2018)
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Open AccessArticle Intrinsic Variability in the Degradation of a Batch of Commercial 18650 Lithium-Ion Cells
Energies 2018, 11(5), 1031; https://doi.org/10.3390/en11051031
Received: 31 March 2018 / Revised: 20 April 2018 / Accepted: 20 April 2018 / Published: 24 April 2018
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Abstract
The use of lithium batteries for power and energy-hungry applications has risen drastically in recent years. For such applications, it is necessary to connect the batteries in large assemblies of cells in series and parallel. With a large number of cells operating together,
[...] Read more.
The use of lithium batteries for power and energy-hungry applications has risen drastically in recent years. For such applications, it is necessary to connect the batteries in large assemblies of cells in series and parallel. With a large number of cells operating together, it is necessary to understand their intrinsic variabilities, not only at the initial stage but also upon aging. In this study, we studied a batch of commercial cells to address their initial cell-to-cell variations and also the variations induced by cycling. To do so, we not only tracked several metrics associated with cell performance, the maximum capacity, the resistance, and the rate capability but also the degradation mechanism via a non-invasive quantification of the loss of lithium inventory (LLI), the loss of active material (LAM) and the kinetic degradation on both electrodes. We found that, even with small initial cell-to-cell variations, significant variations will be observed upon aging because the cells degrade at a different pace. We also observed that these variations were not correlated with the initial variations. Full article
(This article belongs to the Section Energy Storage and Application)
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Open AccessArticle Effect of N2 Replacement by CO2 in Coaxial-Flow on the Combustion and Emission of a Diffusion Flame
Energies 2018, 11(5), 1032; https://doi.org/10.3390/en11051032
Received: 25 March 2018 / Revised: 19 April 2018 / Accepted: 19 April 2018 / Published: 24 April 2018
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Abstract
In this study, a double concentric burner burning methane with an annular coaxially-flowing oxidizer was adopted to operate the diffusion flame in lifted flame regime. The effects of coaxial-flow velocity, coaxial-flow composition variation through total and partial replacement of N2, and
[...] Read more.
In this study, a double concentric burner burning methane with an annular coaxially-flowing oxidizer was adopted to operate the diffusion flame in lifted flame regime. The effects of coaxial-flow velocity, coaxial-flow composition variation through total and partial replacement of N2, and coaxial-flow oxygen enrichment were experimentally investigated in terms of the resultant changes in the flame stability, and thermal and emission characteristics. Consistent with the triple flame theory, the current stability tests show a linear increase in flame lift height with increasing coaxial-flow velocity and the blowout of lifted flames occurred at constant flame tip height. Replacement of N2 by CO2 in the coaxial-flow deteriorated the flame stability by significantly reducing the threshold coaxial-flow velocity. Due to combustion enhancement that is caused by oxygen enrichment, the threshold coaxial-flow velocity increased and this increase is more significant for the N2-diluted flame than CO2-diluted. Two of the most important NOx formation mechanisms, Zeldovich and Fenimore, were analyzed under the relatively low temperature flame conditions, generally below 1300 °C in this study. Results show that NOx is principally produced via the Fenimore mechanism for both N2- and CO2-diluted flames. NOx productions can be significantly affected by coaxial-flow composition and coaxial-flow velocity. An increase in the velocity of N2-diluted coaxial-flow increases NOx emissions, while a reverse trend occurred, as N2 in the coaxial-flow was replaced or partially replaced by CO2, which is ascribed to the strong combustion-resisting behavior of CO2. For all cases, CO emissions vary in the opposite direction of NOx emissions. Due to the strong thermal and chemical effects of CO2 on combustion in comparison to N2, total or partial replacement of N2 by CO2 results in a steep increase in CO emissions. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
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Open AccessArticle Experimental Data-Driven Parameter Identification and State of Charge Estimation for a Li-Ion Battery Equivalent Circuit Model
Energies 2018, 11(5), 1033; https://doi.org/10.3390/en11051033
Received: 9 March 2018 / Revised: 12 April 2018 / Accepted: 17 April 2018 / Published: 24 April 2018
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Abstract
It is well known that accurate identification of the key state parameters and State of Charge (SOC) estimation method for a Li-ion battery cell is of great significance for advanced battery management system (BMS) of electric vehicles (EVs), which further facilitates the commercialization
[...] Read more.
It is well known that accurate identification of the key state parameters and State of Charge (SOC) estimation method for a Li-ion battery cell is of great significance for advanced battery management system (BMS) of electric vehicles (EVs), which further facilitates the commercialization of EVs. This study proposed a systematic experimental data-driven parameter identification scheme and an adaptive extended Kalman Filter (AEKF)-based SOC estimation algorithm for a Li-Ion battery equivalent circuit model in EV applications. The key state parameters of Li-ion battery cell were identified based on the second-order resistor capacitor (RC) equivalent circuit model and the experimental battery test data using genetic algorithm (GA). Meanwhile, the proposed parameter identification procedure was validated by carrying out a comparative study of the simulated and experimental output voltage under the same input current profile. Then, SOC estimation was performed based on the AEKF algorithm. Finally, the effectiveness and feasibility of the proposed SOC estimator was verified by loading different operating profiles. Full article
(This article belongs to the collection Electric and Hybrid Vehicles Collection)
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Open AccessArticle An Enhanced Control Scheme Based on New Adaptive Filters for Cascaded NPC/H-Bridge System
Energies 2018, 11(5), 1034; https://doi.org/10.3390/en11051034
Received: 31 March 2018 / Revised: 18 April 2018 / Accepted: 20 April 2018 / Published: 24 April 2018
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Abstract
This paper studies the voltage fluctuation of dc-link generated in a 13-level cascaded neutral point clamped (NPC)/h-bridge (CNHB) with single-phase active front end (AFE) at the input side of each cell. The voltage fluctuation may deteriorate the power factor (PF) and current harmonics
[...] Read more.
This paper studies the voltage fluctuation of dc-link generated in a 13-level cascaded neutral point clamped (NPC)/h-bridge (CNHB) with single-phase active front end (AFE) at the input side of each cell. The voltage fluctuation may deteriorate the power factor (PF) and current harmonics in the system. In this paper, new adaptive filters are proposed to overcome the problem. The center frequency of the proposed filters can be automatically varied, which allows to eliminate the specific harmonics in the dc-link well rather than the conventional one. Therefore, it can reduce the fluctuation of dc-link and maintain high PF and low current harmonic distortion without additional circuits externally or the current harmonics injection technique. As a result, capacitance for the dc-link can be optimally designed, and even cost and volume of the system can be reduced. This paper analyzes reasons of increasing voltage fluctuation theoretically and the conventional filter and proposed two types of adaptive filters are compared. In addition, the optimal design method of the dc-link capacitor necessarily used in NPC/h-bridge is presented. To verify the principle and feasibility of the proposed control method, a simulation and experiment are implemented with the CNHB system. Full article
(This article belongs to the Special Issue Power Electronics 2018)
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Open AccessArticle A Novel Approach for Searching the Upper/Lower Bounds of Uncertainty Parameters in Microgrids
Energies 2018, 11(5), 1035; https://doi.org/10.3390/en11051035
Received: 31 March 2018 / Revised: 19 April 2018 / Accepted: 20 April 2018 / Published: 24 April 2018
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Abstract
In this study, a novel method based on μ analysis is presented to search for the upper/lower bounds of uncertainty parameters in microgrids (MGs). It is well known that uncertainty parameters have important effects in a MG, and they may cause instability. Previous
[...] Read more.
In this study, a novel method based on μ analysis is presented to search for the upper/lower bounds of uncertainty parameters in microgrids (MGs). It is well known that uncertainty parameters have important effects in a MG, and they may cause instability. Previous studies have mainly focused on identifying the stability of a MG with its uncertainty parameters, but they did not address the problem of the upper/lower bounds of uncertainty parameters, i.e., how far the uncertainty parameters can be extended while the system remains stable in the small-signal sense. Thus, we developed an approach for identifying the bounds of uncertainty in MGs. In the current paper, first, a method is proposed for linear fractional transformation (LFT) configuration to express the uncertainty parameters, which makes the stability of the nominal MG system independent of any extension of the bounds. An algorithm based on this configuration is then designed to find the upper/lower bounds for both single parameter and multiple uncertainty parameters in a MG. Finally, the two cases are discussed, and the accuracy of the proposed method is confirmed using the conventional eigenvalue method. Full article
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Open AccessFeature PaperArticle Microbial Biodiesel Production by Direct Transesterification of Rhodotorula glutinis Biomass
Energies 2018, 11(5), 1036; https://doi.org/10.3390/en11051036
Received: 8 March 2018 / Revised: 11 April 2018 / Accepted: 19 April 2018 / Published: 24 April 2018
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Abstract
(1) Background: Lipids derived from oleaginous microbes have become promising alternative feedstocks for biodiesel. This is mainly because the lipid production rate from microbes is one to two orders of magnitude higher than those of energy crops. However, the conventional process for converting
[...] Read more.
(1) Background: Lipids derived from oleaginous microbes have become promising alternative feedstocks for biodiesel. This is mainly because the lipid production rate from microbes is one to two orders of magnitude higher than those of energy crops. However, the conventional process for converting these lipids to biodiesel still requires a large amount of energy and organic solvents; (2) Methods: In this study, an oleaginous yeast, Rhodotorula glutinis, was used for direct transesterification without lipid pre-extraction to produce biodiesel, using sulfuric acid or sodium hydroxide as a catalyst. Such processes decreased the amount of energy and organic solvents required simultaneously; (3) Results: When 1 g of dry R. glutinis biomass was subject to direct transesterification in 20 mL of methanol catalyzed by 0.6 M H2SO4 at 70 °C for 20 h, the fatty acid methyl ester (FAME) yield reached 111%. Using the same amount of biomass and methanol loading but catalyzed by 1 g/L NaOH at 70 °C for 10 h, the FAME yield reached 102%. The acid-catalyzed process showed a superior moisture tolerance; when the biomass contained 70% moisture, the FAME yield was 43% as opposed to 34% of the base-catalyzed counterpart; (4) Conclusions: Compared to conventional transesterification, which requires lipid pre-extraction, direct transesterification not only simplifies the process and shortens the reaction time, but also improves the FAME yield. Full article
(This article belongs to the Special Issue Biofuel and Bioenergy Technology)
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Open AccessArticle Non-Equal Voltage Cell Balancing for Battery and Super-Capacitor Source Package Management System Using Tapped Inductor Techniques
Energies 2018, 11(5), 1037; https://doi.org/10.3390/en11051037
Received: 16 February 2018 / Revised: 16 March 2018 / Accepted: 20 March 2018 / Published: 24 April 2018
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Abstract
The battery management system (BMS) is the key development for energy storage systems, and battery balancing is an important subsystem of the BMS. However, with rapid development of supercapacitors, future energy storage cells are not constrained by one type, while different types of
[...] Read more.
The battery management system (BMS) is the key development for energy storage systems, and battery balancing is an important subsystem of the BMS. However, with rapid development of supercapacitors, future energy storage cells are not constrained by one type, while different types of cells may form a source package (SP). Furthermore, the introduction of second-life batteries from retired electric vehicles promotes the demand of effective balancing systems for SPs with hybrid cells, as well as the requirement that balancing should be extended to any preset ratio rather than 1:1. This paper proposes a novel tapped inductor balancing circuit that allows any ratio of voltage balancing for hybrid energy storage cells. The analysis of the circuit, simulation and experiment results are presented to demonstrate its effectiveness in handling hybrid source balancing. Full article
(This article belongs to the Special Issue Power Electronics for Energy Storage)
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Open AccessArticle A Smart Grid Framework for Optimally Integrating Supply-Side, Demand-Side and Transmission Line Management Systems
Energies 2018, 11(5), 1038; https://doi.org/10.3390/en11051038
Received: 7 March 2018 / Revised: 4 April 2018 / Accepted: 6 April 2018 / Published: 24 April 2018
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Abstract
A coordinated centralized energy management system (ConCEMS) is presented in this paper that seeks to integrate for optimal grid operation—the supply side energy management system (SSEMS), home energy management system (HEMS) and transmission line management system (TLMS). ConCEMS in ensuring the optimal operation
[...] Read more.
A coordinated centralized energy management system (ConCEMS) is presented in this paper that seeks to integrate for optimal grid operation—the supply side energy management system (SSEMS), home energy management system (HEMS) and transmission line management system (TLMS). ConCEMS in ensuring the optimal operation of an IEEE 30-bus electricity network harmonizes the individual objective function of SSEMS, HEMS and TLMS to evolve an optimal dispatch of participating demand response (DR) loads that does not violate transmission line ampacity limits (TLMS constraint) while minimizing consumer cost (HEMS constraint) and supply side operations cost (SSEMS constraint). An externally constrained genetic algorithm (ExC-GA) that is influenced by feedback from TLMS is also presented that intelligently varies the dispatch time of participating DR loads to meet the individual objective functions. Hypothetical day ahead dynamic pricing schemes (Price1, Price2 and Price3) have also been adopted alongside an existing time of use (Price0) pricing scheme for comparison and discussion while a dynamic thermal line rating (DTLR) algorithm has also been incorporated to dynamically compute power limits based on real time associated data. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle Analysis of Particulate Matter (PM) Emissions in Diesel Engines Using Palm Oil Biodiesel Blended with Diesel Fuel
Energies 2018, 11(5), 1039; https://doi.org/10.3390/en11051039
Received: 1 February 2018 / Revised: 13 April 2018 / Accepted: 17 April 2018 / Published: 24 April 2018
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Abstract
This study has focused on the PM emissions of diesel engines. Diesel engines are attractive power units that are used widely in many fields and have become one of the larger contributors of total petroleum consumption. However, diesel engines are among the main
[...] Read more.
This study has focused on the PM emissions of diesel engines. Diesel engines are attractive power units that are used widely in many fields and have become one of the larger contributors of total petroleum consumption. However, diesel engines are among the main contributors of emissions into the air, especially particulate matter (PM) and nitrogen oxides (NOx). PM is one of the major pollutants emitted by diesel engines and has adverse effects on human health. Accordingly, many studies have been conducted to find alternative fuels that are clean and efficient. Biodiesel, which produces less PM than diesel fuel, is preferred as an alternative source for diesel engines. Therefore, using palm oil methyl ester (POME) for diesel engines would be a more economical and sustainable solution. This study has focused on the PM emissions of diesel engines fuelled by a diesel and POME blend (B5, B10, B20, and B100). A comparison between diesel and the POME blend has been made which involves PM mass concentration and its components (soluble organic fraction (SOF) and dry soot (DS)). Combustion characteristics, such as in-cylinder pressure and rate of heat release of the engine, as well as gaseous emissions, have also been observed at different operating engine loads (0.05 MPa 20%, 0.4 MPa 40%, and 0.7 MPa 60%). The results show that PM emissions of B100 are lower than those of diesel fuel owing to the oxygen content of POME. With regard to the SOF concentration, B100 has a higher SOF value than diesel fuel at all engine loads. Meanwhile, the DS for B100 is lower than that of diesel fuel. Moreover, as the engine load increased, PM and SOF concentrations increased, while DS concentration decreased. The observation of in-cylinder pressure showed that the increment of pressure with the increasing POME blend, as well as the increasing engine load due to the high cetane number for B100, led to a short ignition delay. The engine brake thermal efficiency between the POME blend and mineral diesel was comparable. Furthermore, B100 fuels showed lower engine power at higher brake-specific fuel consumption compared to other tested fuels. In terms of gaseous emissions, increasing POME blends led to an increase in NOx emissions. Meanwhile, as the engine load increased, NOx also continued to increase. The effect of the POME blend on the PM-NOx trade-off observation showed that B100 simultaneously increased the NOx and decreased the PM emissions. It can be concluded that POME creates a lower PM concentration while giving some negative feedback to NOx. Full article
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Open AccessArticle Predicting Charging Time of Battery Electric Vehicles Based on Regression and Time-Series Methods: A Case Study of Beijing
Energies 2018, 11(5), 1040; https://doi.org/10.3390/en11051040
Received: 19 March 2018 / Revised: 31 March 2018 / Accepted: 12 April 2018 / Published: 24 April 2018
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Abstract
Battery electric vehicles (BEVs) reduce energy consumption and air pollution as compared with conventional vehicles. However, the limited driving range and potential long charging time of BEVs create new problems. Accurate charging time prediction of BEVs helps drivers determine travel plans and alleviate
[...] Read more.
Battery electric vehicles (BEVs) reduce energy consumption and air pollution as compared with conventional vehicles. However, the limited driving range and potential long charging time of BEVs create new problems. Accurate charging time prediction of BEVs helps drivers determine travel plans and alleviate their range anxiety during trips. This study proposed a combined model for charging time prediction based on regression and time-series methods according to the actual data from BEVs operating in Beijing, China. After data analysis, a regression model was established by considering the charged amount for charging time prediction. Furthermore, a time-series method was adopted to calibrate the regression model, which significantly improved the fitting accuracy of the model. The parameters of the model were determined by using the actual data. Verification results confirmed the accuracy of the model and showed that the model errors were small. The proposed model can accurately depict the charging time characteristics of BEVs in Beijing. Full article
(This article belongs to the Special Issue Energy Efficient and Smart Cities)
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Open AccessArticle Roof Strata Behavior and Support Resistance Determination for Ultra-Thick Longwall Top Coal Caving Panel: A Case Study of the Tashan Coal Mine
Energies 2018, 11(5), 1041; https://doi.org/10.3390/en11051041
Received: 22 March 2018 / Revised: 13 April 2018 / Accepted: 16 April 2018 / Published: 24 April 2018
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Abstract
The Longwall Top Coal Caving (LTCC) method has greatly improved the production of ultra-thick underground coal resources. However, face fall and support closure have been becoming highly frequent accidents at the working face, and seriously threaten the safety of miners. The key to
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The Longwall Top Coal Caving (LTCC) method has greatly improved the production of ultra-thick underground coal resources. However, face fall and support closure have been becoming highly frequent accidents at the working face, and seriously threaten the safety of miners. The key to avoiding these problems is to reveal the structural evolution of the roof strata and then choose a reasonable working resistance for the hydraulic supports. According to physical modeling, theoretical analysis and field observation of the LTCC panel, four kinds of structural models can be found and defined, in consideration of the coincident movement of key strata (KS) and the mining activities of upper face in overburden strata. The KS are performed as cantilever structures, hinged structures and voussoir beam structures at three different positions in roof strata. The structural characteristics of the KS and its movement laws are shown in the four structural modes. The loads acting on the support in the four typical structural models are also analyzed. The structural instability of the broken roof strata on the upper caving panel caused by the lower ultra-thick coal seam mining is considered to be the main reason for its face’s falls and support failures. Consequently, a method is proposed for calculating the working resistance of the support in the LTCC face, which is verified by the mining pressure monitoring in practice. Full article
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Open AccessFeature PaperArticle Theoretical and Computational Analysis on Double-End Submerged Hollow Fibre Membrane Modules
Energies 2018, 11(5), 1042; https://doi.org/10.3390/en11051042
Received: 23 February 2018 / Revised: 15 April 2018 / Accepted: 16 April 2018 / Published: 24 April 2018
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Abstract
This paper studies the potential increase in permeate output flow rate that submerged hollow fibres can achieve when operating in double-end suction. The flow dynamics of submerged hollow fibre membranes with different combinations of fibre inner diameter, membrane thickness, and membrane permeability were
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This paper studies the potential increase in permeate output flow rate that submerged hollow fibres can achieve when operating in double-end suction. The flow dynamics of submerged hollow fibre membranes with different combinations of fibre inner diameter, membrane thickness, and membrane permeability were numerically simulated. Fibre features (fibre inner diameter, membrane thickness, and membrane permeability) are then characterised for their effects on the increment in permeate flow rate due to change in configuration. Concurrently, an analytical model of a fibre in double-end suction is modelled. Analysis on the double-end fibre model has indicated that the fibre characteristic ratio, λ, has a direct influence on the relative increase in output flow rate when both ends are open. Parametric investigations on the three fibre features have shown that their effects on relative output increase agree with the co-relations indicated by λ. For fibres with λ less than 4, a proportional relationship between a fibre’s λ value and the percentage increment in permeate flow rate is observed when adopting double-end suction. The fibre characteristic ratio, λ, in addition to characterising flux uniformity, can further be used to consider the effectiveness of applying double-end suction in Submerged Hollow Fibre Membrane Module (SHFMM) systems at the design stage. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
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Open AccessArticle NO Removal from Simulated Flue Gas with a NaClO2 Mist Generated Using the Ultrasonic Atomization Method
Energies 2018, 11(5), 1043; https://doi.org/10.3390/en11051043
Received: 20 March 2018 / Revised: 15 April 2018 / Accepted: 15 April 2018 / Published: 24 April 2018
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Abstract
In order to enhance the mass transfer efficiency between gas–liquid interfaces, NaClO2 mist generated by an ultrasonic humidifier was used to remove NO from simulated flue gas. The effects of some key parameters (the gas flow rate, the NaClO2 concentration in
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In order to enhance the mass transfer efficiency between gas–liquid interfaces, NaClO2 mist generated by an ultrasonic humidifier was used to remove NO from simulated flue gas. The effects of some key parameters (the gas flow rate, the NaClO2 concentration in the solution, the inlet NO concentration, the NaClO2 solution pH) on NO removal efficiency were investigated preliminarily. The results showed that NaClO2 mist could oxidize NO with a much higher efficiency compared with other mists containing either NaClO or H2O2 as oxidants. With an increase in the gas flow rate from 1.5 to 3.0 L·min−1, the atomizing rate of the NaClO2 solution increased almost linearly from 0.38 to 0.85 mL·min−1. When the gas flow rate was 2.0 L·min−1, a complete removal of NO had been reached. NO removal efficiency increased obviously with an increase in the NaClO2 concentration in the solution. With an increase in the inlet NO concentration, the ratio of NO in the flue gas and NaClO2 in the mist increased almost linearly. Furthermore, the NaClO2 mist exhibited a relatively stable and high NOx removal efficiency in a wide pH range (4–11) of NaClO2 solutions. The reason for the high NO removal efficiency was mainly ascribed to both the strong oxidative ability of NaClO2 and the improved mass transfer at the gas-liquid interface. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle Geological Factors and Reservoir Properties Affecting the Gas Content of Coal Seams in the Gujiao Area, Northwest Qinshui Basin, China
Energies 2018, 11(5), 1044; https://doi.org/10.3390/en11051044
Received: 28 March 2018 / Revised: 20 April 2018 / Accepted: 23 April 2018 / Published: 24 April 2018
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Abstract
Coalbed methane (CBM) well drilling and logging data together with geological data were adopted to provide insights into controlling mechanism of gas content in major coal seams and establish gas accumulation models in the Gujiao area, Northwest Qinshui Basin, China. Gas content of
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Coalbed methane (CBM) well drilling and logging data together with geological data were adopted to provide insights into controlling mechanism of gas content in major coal seams and establish gas accumulation models in the Gujiao area, Northwest Qinshui Basin, China. Gas content of targeted coals is various in the Gujiao area with their burial depth ranging from 295 to 859 m. Highly variable gas content of coals should be derived from the differences among tectonism, magmatism, hydrodynamism, and sedimentation. Gas content preserved in the Gujiao area is divided into two parts by the geological structure. Gas tends to accumulate in the groundwater stagnant zone with a total dissolved solids (TDS) value of 1300–1700 ppm due to water pressure in the Gujiao area. Reservoir properties including moisture content, minerals, and pore structure also significantly result in gas content variability. Subsequently, the gray correlation statistic method was adopted to determine the most important factors controlling gas content. Coal metamorphism and geological structure had marked control on gas content for the targeted coals. Finally, the favorable CBM exploitation areas were comprehensively evaluated in the Gujiao area. The results showed that the most favorable CBM exploitation areas were in the mid-south part of the Gujiao area (Block I). Full article
(This article belongs to the Section Energy Sources)
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Open AccessArticle Energy Efficient Design of Massive MIMO by Considering the Effects of Nonlinear Amplifiers
Energies 2018, 11(5), 1045; https://doi.org/10.3390/en11051045
Received: 23 March 2018 / Revised: 19 April 2018 / Accepted: 20 April 2018 / Published: 24 April 2018
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Abstract
Massive Multiple-Input Multiple-Output (MIMO) alludes to the theory of having a large number of transmitter chains at the base station, which in turn provides the higher spectral and energy efficiency with reduced radiated power and greater simplicity in the signal processing. In this
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Massive Multiple-Input Multiple-Output (MIMO) alludes to the theory of having a large number of transmitter chains at the base station, which in turn provides the higher spectral and energy efficiency with reduced radiated power and greater simplicity in the signal processing. In this paper, we have improved the energy efficiency of Massive MIMO by considering the effects of nonlinear amplifiers in each transmitter branch. We have designed the system by calculating the optimal number of transmitters and receivers with the optimal transmitted power and their corresponding spectral efficiency in terms of energy efficient prospective of Massive MIMO under both the perfect and imperfect channel conditions at different power consumption and area of coverage. We have evaluated the impacts of nonlinear amplifiers by calculating the energy efficiency at different efficiencies and distortion losses of nonlinear power amplifiers. In order to solve the optimization problem of energy efficiency, we have proposed an alternative optimization method which converges quickly and provides the optimal parameters under both the perfect and imperfect channel conditions. Full article
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Open AccessArticle Impact of Cyber Attacks on High Voltage DC Transmission Damping Control
Energies 2018, 11(5), 1046; https://doi.org/10.3390/en11051046
Received: 5 April 2018 / Revised: 16 April 2018 / Accepted: 18 April 2018 / Published: 24 April 2018
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Abstract
Hybrid AC/HVDC (AC-HVDC) grids have evolved to become huge cyber-physical systems that are vulnerable to cyber attacks because of the wide attack surface and increasing dependence on intelligent electronic devices, computing resources and communication networks. This paper, for the first time, studies the
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Hybrid AC/HVDC (AC-HVDC) grids have evolved to become huge cyber-physical systems that are vulnerable to cyber attacks because of the wide attack surface and increasing dependence on intelligent electronic devices, computing resources and communication networks. This paper, for the first time, studies the impact of cyber attacks on HVDC transmission oscillation damping control.Three kinds of cyber attack models are considered: timing attack, replay attack and false data injection attack. Followed by a brief introduction of the HVDC model and conventional oscillation damping control method, the design of three attack models is described in the paper. These attacks are tested on a modified IEEE New England 39-Bus AC-HVDC system. Simulation results have shown that all three kinds of attacks are capable of driving the AC-HVDC system into large oscillations or even unstable conditions. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessFeature PaperArticle Corona Onset Characteristics of Bundle Conductors in UHV AC Power Lines at 2200 m Altitude
Energies 2018, 11(5), 1047; https://doi.org/10.3390/en11051047
Received: 7 April 2018 / Revised: 19 April 2018 / Accepted: 19 April 2018 / Published: 25 April 2018
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Abstract
The corona onset characteristic of bundle conductors is an important limiting factor for the design of UHV AC power lines in high-altitude areas. An experimental study on the corona characteristics of 8 × LGJ630, 6 × LGJ720, 8 × LGJ720 and 10 ×
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The corona onset characteristic of bundle conductors is an important limiting factor for the design of UHV AC power lines in high-altitude areas. An experimental study on the corona characteristics of 8 × LGJ630, 6 × LGJ720, 8 × LGJ720 and 10 × LGJ720 bundle conductors commonly used in UHV power lines under dry and wet conductor conditions, as well as artificial moderate and heavy rain conditions, was conducted in Ping’an County, Xining City (elevation 2200 m). By using the tangent line method, the corona onset voltages and onset electric field of four types of conductors at high altitudes are obtained for the first time. In addition, the calculation model of corona onset voltage considering the outer strands’ effect on the electric field and the geometric factor in the corona cage in high altitude areas is established. The comparison of the calculation results and experimental results under dry conditions verifies the model’s correctness. Based on the results, an optimal selection scheme for high altitudes is proposed. The roughness coefficient was also calculated and analysed: the roughness coefficient of bundled conductors was between 0.59 and 0.77, and the roughness coefficient of the wet conductor was between the dry and rainy conditions. Both the experimental data and the calculation model can provide a reference for conductor selection for UHV AC power lines for use in high-altitude areas. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessFeature PaperArticle Design Method of Controllable Blade Angle and Orthogonal Optimization of Pressure Rise for a Multiphase Pump
Energies 2018, 11(5), 1048; https://doi.org/10.3390/en11051048
Received: 29 March 2018 / Revised: 13 April 2018 / Accepted: 14 April 2018 / Published: 25 April 2018
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Abstract
The hydraulic design method of controllable blade angle for rotodynamic multiphase pump with impeller and diffuser is proposed. The distribution of blade angle along the meridional streamline is governed by the normalized fourth-order and first-order polynomial function for impeller and diffuser, respectively. The
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The hydraulic design method of controllable blade angle for rotodynamic multiphase pump with impeller and diffuser is proposed. The distribution of blade angle along the meridional streamline is governed by the normalized fourth-order and first-order polynomial function for impeller and diffuser, respectively. The orthogonal optimization method with five factors and four levels is employed by numerical simulation to optimize the geometry parameters, including the shroud angle at the leading and trailing edge βIs0, βIs1, the blade difference at inlet ∆βI0, and the coefficients at hub and shroud kh, ks. According to orthogonal analysis, the influence of each factor on pressure rise is estimated, and the optimization values of for those parameters are determined. The pressure rise of optimization multiphase pump is increased by 12.8 kPa in comparison of the base pump. Results show that the distributions of gas volume fraction (GVF) and the pressure become more uniform after optimization, which improves the transporting performance of the multiphase pump. Full article
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Open AccessArticle Investigation of Stratified Thermal Storage Tank Performance for Heating and Cooling Applications
Energies 2018, 11(5), 1049; https://doi.org/10.3390/en11051049
Received: 28 March 2018 / Revised: 16 April 2018 / Accepted: 18 April 2018 / Published: 25 April 2018
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Abstract
A large amount of energy is consumed by heating and cooling systems to provide comfort conditions for commercial building occupants, which generally contribute to peak electricity demands. Thermal storage tanks in HVAC systems, which store heating/cooling energy in the off-peak period for use
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A large amount of energy is consumed by heating and cooling systems to provide comfort conditions for commercial building occupants, which generally contribute to peak electricity demands. Thermal storage tanks in HVAC systems, which store heating/cooling energy in the off-peak period for use in the peak period, can be used to offset peak time energy demand. In this study, a theoretical investigation on stratified thermal storage systems is performed to determine the factors that significantly influence the thermal performance of these systems for both heating and cooling applications. Five fully-insulated storage tank geometries, using water as the storage medium, were simulated to determine the effects of water inlet velocity, tank aspect ratio and temperature difference between charging (inlet) and the tank water on mixing and thermocline formation. Results indicate that thermal stratification enhances with increased temperature difference, lower inlet velocities and higher aspect ratios. It was also found that mixing increased by 303% when the temperature difference between the tank and inlet water was reduced from 80 °C to 10 °C, while decreasing the aspect ratio from 3.8 to 1.0 increased mixing by 143%. On the other hand, increasing the inlet water velocity significantly increased the storage mixing. A new theoretical relationship between the inlet water velocity and thermocline formation has been developed. It was also found that inlet flow rates can be increased, without increasing the mixing, after the formation of the thermocline. Full article
(This article belongs to the Section Energy Storage and Application)
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Open AccessArticle Optimization of Synthetic Inertial Response from Wind Power Plants
Energies 2018, 11(5), 1051; https://doi.org/10.3390/en11051051
Received: 30 March 2018 / Revised: 16 April 2018 / Accepted: 20 April 2018 / Published: 25 April 2018
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Abstract
In this paper the emphasis is on the optimization of synthetic inertial response of wind power plants (WPPs) for power systems with high wind power penetration levels, considering different wind speed operating conditions. The synthetic inertial response of wind power plants can play
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In this paper the emphasis is on the optimization of synthetic inertial response of wind power plants (WPPs) for power systems with high wind power penetration levels, considering different wind speed operating conditions. The synthetic inertial response of wind power plants can play an important role in the resilience of future power systems with low inertia during large frequency disturbances. In order to investigate this role, a generic optimization methodology employing the genetic algorithm is proposed, taking into consideration the frequency nadir, second frequency dip, and time to reach the quasi–steady-state frequency. This optimization methodology comprehends the inertial response capability of WPPs and the frequency control dynamics of the power system. Accordingly, offline parameter tuning of synthetic inertial response is performed at the power system level with the proposed methodology. Based on the optimization results, the relevant aspects to be considered by transmission system operators and wind power plant developers in the process of designing and planning synthetic inertia are identified and analyzed. Additionally, sensitivity analyses are carried out to assess the impact of synthetic inertial response parameters on power system frequency control performance under different contingencies and wind power penetration levels. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle A Fast Equalizer with Adaptive Balancing Current Control
Energies 2018, 11(5), 1052; https://doi.org/10.3390/en11051052
Received: 16 March 2018 / Revised: 12 April 2018 / Accepted: 12 April 2018 / Published: 25 April 2018
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Abstract
In this paper, a fast equalizer for series-connected battery packs with adaptive balancing current control is proposed. As the duty cycle of the power switch in conventional equalizers is kept constant during the equalization process, smaller voltage difference between cells will decrease balancing
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In this paper, a fast equalizer for series-connected battery packs with adaptive balancing current control is proposed. As the duty cycle of the power switch in conventional equalizers is kept constant during the equalization process, smaller voltage difference between cells will decrease balancing current and consequently result in extended balancing time, especially in the later phase of equalization. To deal with this problem and take the battery nonlinearity and circuit parameter non-ideality into consideration, an adaptive balancing current control based on a fuzzy logic inference is proposed. The presented approach can adjust the duty ratio adaptively, according to voltages of individual cells and pack, to keep the balancing current nearly constant: Therefore, the balancing time can be shortened and the balancing efficiency can be improved. Finally, experimental results of three compared methods will be given and discussed to validate the feasibility, effectiveness, and performance improvement of the studied method. Full article
(This article belongs to the Special Issue Battery Storage Technology for a Sustainable Future)
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Open AccessArticle Non-Destructive Failure Detection and Visualization of Artificially and Naturally Aged PV Modules
Energies 2018, 11(5), 1053; https://doi.org/10.3390/en11051053
Received: 28 March 2018 / Revised: 19 April 2018 / Accepted: 23 April 2018 / Published: 25 April 2018
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Abstract
Several series of six-cell photovoltaic test-modules—intact and with deliberately generated failures (micro-cracks, cell cracks, glass breakage and connection defects)—were artificially and naturally aged. They were exposed to various stress conditions (temperature, humidity and irradiation) in different climate chambers in order to identify (i)
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Several series of six-cell photovoltaic test-modules—intact and with deliberately generated failures (micro-cracks, cell cracks, glass breakage and connection defects)—were artificially and naturally aged. They were exposed to various stress conditions (temperature, humidity and irradiation) in different climate chambers in order to identify (i) the stress-induced effects; (ii) the potential propagation of the failures and (iii) their influence on the performance. For comparison, one set of test-modules was also aged in an outdoor test site. All photovoltaic (PV) modules were thoroughly electrically characterized by electroluminescence and performance measurements before and after the accelerated ageing and the outdoor test. In addition, the formation of fluorescence effects in the encapsulation of the test modules in the course of the accelerated ageing tests was followed over time using UV-fluorescence imaging measurements. It was found that the performance of PV test modules with mechanical module failures was rather unaffected upon storage under various stress conditions. However, numerous micro-cracks led to a higher rate of degradation. The polymeric encapsulate of the PV modules showed the build-up of distinctive fluorescence effects with increasing lifetime as the encapsulant material degraded under the influence of climatic stress factors (mainly irradiation by sunlight and elevated temperature) by forming fluorophores. The induction period for the fluorescence effects of the polymeric encapsulant to be detectable was ~1 year of outdoor weathering (in middle Europe) and 300 h of artificial irradiation (with 1000 W/m2 artificial sunlight 300–2500 nm). In the presence of irradiation, oxygen—which permeated into the module through the polymeric backsheet—bleached the fluorescence of the encapsulant top layer between the cells, above cell cracks and micro-cracks. Thus, UV-F imaging is a perfect tool for on-site detection of module failures connected with a mechanical rupture of solar cells. Full article
(This article belongs to the Special Issue PV System Design and Performance)
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Open AccessArticle A Semi-Analytical Methodology for Multiwell Productivity Index of Well-Industry-Production-Scheme in Tight Oil Reservoirs
Energies 2018, 11(5), 1054; https://doi.org/10.3390/en11051054
Received: 22 March 2018 / Revised: 15 April 2018 / Accepted: 19 April 2018 / Published: 25 April 2018
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Abstract
Recently, the well-industry-production-scheme (WIPS) has attracted more and more attention to improve tight oil recovery. However, multi-well pressure interference (MWPI) induced by well-industry-production-scheme (WIPS) strongly challenges the traditional transient pressure analysis methods, which focus on single multi-fractured horizontal wells (SMFHWs) without MWPI. Therefore,
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Recently, the well-industry-production-scheme (WIPS) has attracted more and more attention to improve tight oil recovery. However, multi-well pressure interference (MWPI) induced by well-industry-production-scheme (WIPS) strongly challenges the traditional transient pressure analysis methods, which focus on single multi-fractured horizontal wells (SMFHWs) without MWPI. Therefore, a semi-analytical methodology for multiwell productivity index (MPI) was proposed to study well performance of WIPS scheme in tight reservoir. To facilitate methodology development, the conceptual models of tight formation and WIPS scheme were firstly described. Secondly, seepage models of tight reservoir and hydraulic fractures (HFs) were sequentially established and then dynamically coupled. Numerical simulation was utilized to validate our model. Finally, identification of flow regimes and sensitivity analysis were conducted. Our results showed that there was good agreement between our proposed model and numerical simulation; moreover, our approach also gave promising calculation speed over numerical simulation. Some expected flow regimes were significantly distorted due to WIPS. The slope of type curves which characterize the linear or bi-linear flow regime is bigger than 0.5 or 0.25. The horizontal line which characterize radial flow regime is also bigger 0.5. The smaller the oil rate, the more severely flow regimes were distorted. Well rate mainly determines the distortion of MPI curves, while fracture length, well spacing, fracture spacing mainly determine when the distortion of the MPI curves occurs. The bigger the well rate, the more severely the MPI curves are distorted. While as the well spacing decreases, fracture length increases, fracture spacing increases, occurrence of MWPI become earlier. Stress sensitivity coefficient mainly affects the MPI at the formation pseudo-radial flow stage, almost has no influence on the occurrence of MWPI. This work gains some addictive insights on multi-well performance for WIPS scheme in tight reservoir, which can provide considerable guidance on fracture properties estimation as well as well adjustment of production operation for WIPS scheme. Full article
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Open AccessArticle Thermal Behavior of Coal Used in Rotary Kiln and Its Combustion Intensification
Energies 2018, 11(5), 1055; https://doi.org/10.3390/en11051055
Received: 7 April 2018 / Revised: 16 April 2018 / Accepted: 20 April 2018 / Published: 25 April 2018
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Abstract
Pyrolysis and combustion behaviors of three coals (A, B, and C coals) were investigated and their combustion kinetics were calculated by the Freeman–Carroll method to obtain quantitative insight into their combustion behaviors. Moreover, the effects of coal size, air flow, oxygen content, and
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Pyrolysis and combustion behaviors of three coals (A, B, and C coals) were investigated and their combustion kinetics were calculated by the Freeman–Carroll method to obtain quantitative insight into their combustion behaviors. Moreover, the effects of coal size, air flow, oxygen content, and heating rate on coal combustion behaviors were analyzed. Results showed that the three coals have a similar trend of pyrolysis that occurs at about 670 K and this process continuously proceeds along with their combustion. Combustion characteristics and kinetic parameters can be applied to analyze coal combustion behaviors. Three coals having combustion characteristics of suitable ignition temperature (745–761 K), DTGmax (14.20–15.72%/min), and burnout time (7.45–8.10 min) were analyzed in a rotary kiln. Combustion kinetic parameters provide quantitative insights into coal combustion behavior. The suitable particle size for coal combustion in a kiln is that the content of less than 74 μm is 60% to 80%. Low activation energy and reaction order make coal, especially C coal, have a simple combustion mechanism, great reactivity, be easily ignited, and a low peak temperature in the combustion state. Oxygen-enrichment and high heating rates enhance coal combustion, increasing combustion intensity and peak value, thus shortening burnout time. Full article
(This article belongs to the Section Energy Sources)
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Open AccessArticle Distribution-Level Flexibility Market for Congestion Management
Energies 2018, 11(5), 1056; https://doi.org/10.3390/en11051056
Received: 21 March 2018 / Revised: 17 April 2018 / Accepted: 23 April 2018 / Published: 25 April 2018
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Abstract
Nowadays, problems facing Distribution System Operators (DSOs) due to demand increase and the wide penetration of renewable energy are usually solved by means of grid reinforcement. However, the smart grid paradigm enables the deployment of demand flexibility for congestion management in distribution grids.
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Nowadays, problems facing Distribution System Operators (DSOs) due to demand increase and the wide penetration of renewable energy are usually solved by means of grid reinforcement. However, the smart grid paradigm enables the deployment of demand flexibility for congestion management in distribution grids. This could substitute, or at least postpone, these needed investments. A key role in this scheme is the aggregator, who can act as a “flexibility provider” collecting the available flexibility from the consumers. Under this paradigm, this paper proposes a flexibility market led by the DSO and aimed at solving distribution grid congestions. The proposal also includes a flexibility market clearing algorithm, which is easy to implement, has low computational requirements and considers the energy rebound effect. The proposed design has the advantage of excluding the DSO’s need for trading in energy markets. Also, the solution algorithm proposed is fully compatible with already existing grid analysis tools. The proposed electricity market is tested with two case studies from a real Spanish distribution network, where the proposed clearing algorithm is used, and finally, results are presented and discussed. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle The Effect of Temperature on the Methanogenic Activity in Relation to Micronutrient Availability
Energies 2018, 11(5), 1057; https://doi.org/10.3390/en11051057
Received: 6 April 2018 / Revised: 23 April 2018 / Accepted: 23 April 2018 / Published: 25 April 2018
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Abstract
In the view of microbial community, thermophilic microorganisms were reported to have faster biochemical reaction rates, which are reflected by a higher methane production rate. However, there has no research to discuss the effect of temperature on methanogenic activity in relation to micronutrient
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In the view of microbial community, thermophilic microorganisms were reported to have faster biochemical reaction rates, which are reflected by a higher methane production rate. However, there has no research to discuss the effect of temperature on methanogenic activity in relation to micronutrient transport and availability. The objective of this study was to investigate the effect of temperature on methanogenic activity in relation to nutrient uptakes, micronutrient transports, and mass balance using anaerobic sequencing batch reactors (ASBR) with recycled biogas for treating ethanol wastewater at mesophilic (37 °C) and thermophilic (55 °C) temperatures. The increase in temperature from 37 to 55 °C increased in both of the optimum chemical oxygen demand (COD) loading rate and methanogenic activity, corresponding to the results of N and P uptakes, energy balance, and mass balance. The higher temperature of the thermophilic operation as compared to the mesophilic one caused a lower water solubility of the produced H2S, leading to lowering the reduction of divalent cation micronutrients. The thermophilic operation could prevent the deficit of micronutrients, thus causing a higher methanogenic activity, while the mesophilic operation still had the deficit of most micronutrients, leading to the lower activity. Full article
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Open AccessArticle Gas Supply, Pricing Mechanism and the Economics of Power Generation in China
Energies 2018, 11(5), 1058; https://doi.org/10.3390/en11051058
Received: 28 March 2018 / Revised: 20 April 2018 / Accepted: 24 April 2018 / Published: 25 April 2018
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Abstract
During the “13th Five-Year Plan” period, green energy is the top priority for China. China has realized that natural gas, as a low-carbon energy source, fits with the nation’s energy demand and will play a critical role in the energy transition, but the
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During the “13th Five-Year Plan” period, green energy is the top priority for China. China has realized that natural gas, as a low-carbon energy source, fits with the nation’s energy demand and will play a critical role in the energy transition, but the actual industry development is slower than expected. By analyzing the major gas corporations around the world, the paper finds that the key factors of the sector are supply and price of the energy resource. A comprehensive analysis on domestic and foreign imported gas reveals a trend of oversupply in China in the future. Given the critical import dependence, China has introduced a series of gas price reforms since 2013, which have led to negative impacts on important gas consumption sectors including power generation. With the levelized cost of electricity (LCOE) model, we find that under the prevailing gas supply structure and price level, the economy of utility gas power generation will remain unprofitable, while combined cooling heating and power (CCHP) is only commercially feasible in coastal developed regions. If continuing, such a trend will not only bring forth disastrous consequences to gas power industry, but also damage the upstream gas industry, more importantly, impede the energy transition. We conclude the paper with policy implications on pricing mechanism reform, developing domestic unconventional gas and the R&D of gas turbine. Full article
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Open AccessArticle Model for Estimation of Fuel Consumption of Cruise Ships
Energies 2018, 11(5), 1059; https://doi.org/10.3390/en11051059
Received: 22 March 2018 / Revised: 18 April 2018 / Accepted: 19 April 2018 / Published: 25 April 2018
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Abstract
This article presents a model to estimate the energy use and fuel consumption of cruise ships that sail Norwegian waters. Automatic identification system (AIS) data and technical information about cruise ships provided input to the model, including service speed, total power, and number
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This article presents a model to estimate the energy use and fuel consumption of cruise ships that sail Norwegian waters. Automatic identification system (AIS) data and technical information about cruise ships provided input to the model, including service speed, total power, and number of engines. The model was tested against real-world data obtained from a small cruise vessel and both a medium and large cruise ship. It is sensitive to speed and the corresponding engine load profile of the ship. A crucial determinate for total fuel consumption is also associated with hotel functions, which can make a large contribution to the overall energy use of cruise ships. Real-world data fits the model best when ship speed is 70–75% of service speed. With decreased or increased speed, the model tends to diverge from real-world observations. The model gives a proxy for calculation of fuel consumption associated with cruise ships that sail to Norwegian waters and can be used to estimate greenhouse gas emissions and to evaluate energy reduction strategies for cruise ships. Full article
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Open AccessArticle A Novel Improved Cuckoo Search Algorithm for Parameter Estimation of Photovoltaic (PV) Models
Energies 2018, 11(5), 1060; https://doi.org/10.3390/en11051060
Received: 30 March 2018 / Revised: 23 April 2018 / Accepted: 23 April 2018 / Published: 25 April 2018
PDF Full-text (4754 KB) | HTML Full-text | XML Full-text
Abstract
Parameter estimation of photovoltaic (PV) models from experimental current versus voltage (I-V) characteristic curves acts a pivotal part in the modeling a PV system and optimizing its performance. Although many methods have been proposed for solving this PV model parameter estimation problem, it
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Parameter estimation of photovoltaic (PV) models from experimental current versus voltage (I-V) characteristic curves acts a pivotal part in the modeling a PV system and optimizing its performance. Although many methods have been proposed for solving this PV model parameter estimation problem, it is still challenging to determine highly accurate and reliable solutions. In this paper, this problem is firstly transformed into an optimization problem, and an objective function (OF) is formulated to quantify the overall difference between the experimental and simulated current data. And then, to enhance the performance of original cuckoo search algorithm (CSA), a novel improved cuckoo search algorithm (ImCSA) is proposed, by combining three strategies with CSA. In ImCSA, a quasi-opposition based learning (QOBL) scheme is employed in the population initialization step of CSA. Moreover, a dynamic adaptation strategy is developed and introduced for the step size without Lévy flight step in original CSA. A dynamic adjustment mechanism for the fraction probability (Pa) is proposed to achieve better tradeoff between the exploration and exploitation to increase searching ability. Afterwards, the proposed ImCSA is used for solving the problem of estimating parameters of PV models based on experimental I-V data. Finally, the proposed ImCSA has been demonstrated on the parameter identification of various PV models, i.e., single diode model (SDM), double diode model (DDM) and PV module model (PMM). Experimental results indicate that the proposed ImCSA outperforms the original CSA and its superior performance in comparison with other state-of-the-art algorithms, and they also show that our proposed ImCSA is capable of finding the best values of parameters for the PV models in such effective way for giving the best possible approximation to the experimental I-V data of real PV cells and modules. Therefore, the proposed ImCSA can be considered as a promising alternative to accurately and reliably estimate parameters of PV models. Full article
(This article belongs to the Special Issue PV System Design and Performance)
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Open AccessArticle Value-Added Performance and Thermal Decomposition Characteristics of Dumped Food Waste Compost by Pyrolysis
Energies 2018, 11(5), 1061; https://doi.org/10.3390/en11051061
Received: 6 March 2018 / Revised: 20 April 2018 / Accepted: 20 April 2018 / Published: 25 April 2018
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Abstract
Food waste compost has a high Na content, which interferes with plant growth when used as a soil enhancer and therefore makes it difficult to use. And, compared to the amount of compost produced every day, the amount of consumption required in farms
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Food waste compost has a high Na content, which interferes with plant growth when used as a soil enhancer and therefore makes it difficult to use. And, compared to the amount of compost produced every day, the amount of consumption required in farms is smaller, and the rest is buried underground, which releases greenhouse gases and pollutes underground water. This research compared and analyzed thermal degradation behavior, calorific value, and gas spectrometry during the pyrolysis between food waste compost and sawdust to suggest producing food waste compost biochar by pyrolysis as a new alternative solution to utilize the massive amount of food waste compost. Biochar from pyrolysis of food waste compost had a high carbon content of 51% at 300 °C, and the carbon content decreased as the pyrolysis temperature increased. According to the thermogravimetric analysis (TGA) and derivative thermo-gravimetric (DTG) analysis results, compost showed the largest weight reduction from 240 °C to 365 °C. The weight reduction temperature ranges for compost and sawdust were quite similar. This occurred because food waste of the compost was degraded, but sawdust of compost remained nearly during the composting process. A gas chromatography and mass spectrometry (GC-MS) analysis found that the gases were fragments of fatty acids, protein, and hemi-cellulose. These results could also have been caused by degradation of microorganisms involved in the composting process, sawdust, and small fragments of food waste. In the calorific value of biochar, the highest value (24.33 kJ/g) was obtained 300 °C. At a low pyrolysis temperature, carbon fixation occurred easily since the food waste in compost was degraded by microorganism, and the volatilization of sawdust, which plays an important role in determining the calorific value, was also small. That is why the highest calorific value was shown at 300 °C, not 400 °C or 500 °C. Hence, it seems that food waste compost can be used as a promising alternative fuel at a low pyrolysis temperature, as other lignocellulosic refuse-derived fuels (RDF). Full article
(This article belongs to the Special Issue Biomass Chars: Elaboration, Characterization and Applications Ⅱ)
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Open AccessArticle Autonomous Vehicles for Smart and Sustainable Cities: An In-Depth Exploration of Privacy and Cybersecurity Implications
Energies 2018, 11(5), 1062; https://doi.org/10.3390/en11051062
Received: 1 April 2018 / Revised: 20 April 2018 / Accepted: 22 April 2018 / Published: 25 April 2018
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Abstract
Amidst rapid urban development, sustainable transportation solutions are required to meet the increasing demands for mobility whilst mitigating the potentially negative social, economic, and environmental impacts. This study analyses autonomous vehicles (AVs) as a potential transportation solution for smart and sustainable development. We
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Amidst rapid urban development, sustainable transportation solutions are required to meet the increasing demands for mobility whilst mitigating the potentially negative social, economic, and environmental impacts. This study analyses autonomous vehicles (AVs) as a potential transportation solution for smart and sustainable development. We identified privacy and cybersecurity risks of AVs as crucial to the development of smart and sustainable cities and examined the steps taken by governments around the world to address these risks. We highlight the literature that supports why AVs are essential for smart and sustainable development. We then identify the aspects of privacy and cybersecurity in AVs that are important for smart and sustainable development. Lastly, we review the efforts taken by federal governments in the US, the UK, China, Australia, Japan, Singapore, South Korea, Germany, France, and the EU, and by US state governments to address AV-related privacy and cybersecurity risks in-depth. Overall, the actions taken by governments to address privacy risks are mainly in the form of regulations or voluntary guidelines. To address cybersecurity risks, governments have mostly resorted to regulations that are not specific to AVs and are conducting research and fostering research collaborations with the private sector. Full article
(This article belongs to the Special Issue The Governance of Sustainable Cities and Innovative Transport)
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Open AccessArticle Electricity Purchase Optimization Decision Based on Data Mining and Bayesian Game
Energies 2018, 11(5), 1063; https://doi.org/10.3390/en11051063
Received: 29 March 2018 / Revised: 16 April 2018 / Accepted: 20 April 2018 / Published: 26 April 2018
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Abstract
The openness of the electricity retail market results in the power retailers facing fierce competition in the market. This article aims to analyze the electricity purchase optimization decision-making of each power retailer with the background of the big data era. First, in order
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The openness of the electricity retail market results in the power retailers facing fierce competition in the market. This article aims to analyze the electricity purchase optimization decision-making of each power retailer with the background of the big data era. First, in order to guide the power retailer to make a purchase of electricity, this paper considers the users’ historical electricity consumption data and a comprehensive consideration of multiple factors, then uses the wavelet neural network (WNN) model based on “meteorological similarity day (MSD)” to forecast the user load demand. Second, in order to guide the quotation of the power retailer, this paper considers the multiple factors affecting the electricity price to cluster the sample set, and establishes a Genetic algorithm- back propagation (GA-BP) neural network model based on fuzzy clustering (FC) to predict the short-term market clearing price (MCP). Thirdly, based on Sealed-bid Auction (SA) in game theory, a Bayesian Game Model (BGM) of the power retailer’s bidding strategy is constructed, and the optimal bidding strategy is obtained by obtaining the Bayesian Nash Equilibrium (BNE) under different probability distributions. Finally, a practical example is proposed to prove that the model and method can provide an effective reference for the decision-making optimization of the sales company. Full article
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Open AccessArticle Comparison of Different Technologies for Integrated Solar Combined Cycles: Analysis of Concentrating Technology and Solar Integration
Energies 2018, 11(5), 1064; https://doi.org/10.3390/en11051064
Received: 16 March 2018 / Revised: 20 April 2018 / Accepted: 23 April 2018 / Published: 25 April 2018
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Abstract
This paper compares the annual performance of Integrated Solar Combined Cycles (ISCCs) using different solar concentration technologies: parabolic trough collectors (PTC), linear Fresnel reflectors (LFR) and central tower receiver (CT). Each solar technology (i.e. PTC, LFR and CT) is proposed to integrate solar
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This paper compares the annual performance of Integrated Solar Combined Cycles (ISCCs) using different solar concentration technologies: parabolic trough collectors (PTC), linear Fresnel reflectors (LFR) and central tower receiver (CT). Each solar technology (i.e. PTC, LFR and CT) is proposed to integrate solar energy into the combined cycle in two different ways. The first one is based on the use of solar energy to evaporate water of the steam cycle by means of direct steam generation (DSG), increasing the steam production of the high pressure level of the steam generator. The other one is based on the use of solar energy to preheat the pressurized air at the exit of the gas turbine compressor before it is introduced in the combustion chamber, reducing the fuel consumption. Results show that ISCC with DSG increases the yearly production while solar air heating reduces it due to the incremental pressure drop. However, air heating allows significantly higher solar-to-electricity efficiencies and lower heat rates. Regarding the solar technologies, PTC provides the best thermal results. Full article
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Open AccessArticle Assessment of Energy Production Potential from Tidal Stream Currents in Morocco
Energies 2018, 11(5), 1065; https://doi.org/10.3390/en11051065
Received: 29 January 2018 / Revised: 18 February 2018 / Accepted: 8 March 2018 / Published: 26 April 2018
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Abstract
Energy extracted from the ocean can provide a source of regular and foreseeable electrical production at higher energy densities than any other renewable energy resource. The marine current resource is potentially great and is focused in several sites around the world. The knowledge
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Energy extracted from the ocean can provide a source of regular and foreseeable electrical production at higher energy densities than any other renewable energy resource. The marine current resource is potentially great and is focused in several sites around the world. The knowledge of the energy potential, its constraints and availability are all prerequisites to determine the possibilities for the implementation of infrastructure to produce energy. They are also required to anticipate the structuring of energy routes and to respond to increasing technological needs. Several Moroccan regions want to take advantage by their coastal domain and play a role in the development of the tidal energy sector. They also want to benefit from the associated economic advantages knowing that the Mediterranean coast length is 550 km and the Atlantic length is 3000 km, respectively. The Copernicus Marine Service ocean products provide key input for such technologies, as they can be employed to help evaluate the accessible ocean energy devices and choose the most attractive sites to exploit the tidal energy projects in Morocco. The goal of this research was to evaluate and analyze the tidal marine current resource at the sites which are potentially suitable for the installation of Horizontal Axis Marine Current Turbines in Morocco. Distributions of available power of tidal energy in the Moroccan region are provided, and three possible areas are suggested for installing tidal energy conversion systems. Full article
(This article belongs to the Section Energy Sources)
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Open AccessArticle Energy Management for Community Energy Network with CHP Based on Cooperative Game
Energies 2018, 11(5), 1066; https://doi.org/10.3390/en11051066
Received: 2 April 2018 / Revised: 17 April 2018 / Accepted: 24 April 2018 / Published: 26 April 2018
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Abstract
Integrated energy system (IES) has received increasing attention in micro grid due to the high energy efficiency and low emission of carbon dioxide. Based on the technology of combined heat and power (CHP), this paper develops a novel operation mechanism with community micro
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Integrated energy system (IES) has received increasing attention in micro grid due to the high energy efficiency and low emission of carbon dioxide. Based on the technology of combined heat and power (CHP), this paper develops a novel operation mechanism with community micro turbine and shared energy storage system (ESS) for energy management of prosumers. In the proposed framework, micro-grid operator (MGO) equipped with micro turbine and ESS provides energy selling business and ESS leasing business for prosumers. Prosumers can make energy trading with public grid and MGO, and ESS will be shared among prosumers when they pay for the rent to MGO. Based on such framework, we adopt a cooperative game for prosumers to determine optimal energy trading strategies from MGO and public grid for the next day. Concretely, a cooperative game model is formulated to search the optimal strategies aiming at minimizing the daily cost of coalition, and then a bilateral Shapley value (BSV) is proposed to solve the allocation problem of coalition’s cost among prosumers. To verify the effectiveness of proposed energy management framework, a practical example is conducted with a community energy network containing MGO and 10 residential buildings. Simulation results show that the proposed scheme is able to provide financial benefits to all prosumers, while providing peak load leveling for the grid. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle Maximum Power Point Tracking for Brushless DC Motor-Driven Photovoltaic Pumping Systems Using a Hybrid ANFIS-FLOWER Pollination Optimization Algorithm
Energies 2018, 11(5), 1067; https://doi.org/10.3390/en11051067
Received: 18 March 2018 / Revised: 21 April 2018 / Accepted: 24 April 2018 / Published: 26 April 2018
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Abstract
In this research paper, a hybrid Artificial Neural Network (ANN)-Fuzzy Logic Control (FLC) tuned Flower Pollination Algorithm (FPA) as a Maximum Power Point Tracker (MPPT) is employed to amend root mean square error (RMSE) of photovoltaic (PV) modeling. Moreover, Gaussian membership functions have
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In this research paper, a hybrid Artificial Neural Network (ANN)-Fuzzy Logic Control (FLC) tuned Flower Pollination Algorithm (FPA) as a Maximum Power Point Tracker (MPPT) is employed to amend root mean square error (RMSE) of photovoltaic (PV) modeling. Moreover, Gaussian membership functions have been considered for fuzzy controller design. This paper interprets the Luo converter occupied brushless DC motor (BLDC)-directed PV water pump application. Experimental responses certify the effectiveness of the suggested motor-pump system supporting diverse operating states. The Luo converter, a newly developed DC-DC converter, has high power density, better voltage gain transfer and superior output waveform and can track optimal power from PV modules. For BLDC speed control there is no extra circuitry, and phase current sensors are enforced for this scheme. The most recent attempt using adaptive neuro-fuzzy inference system (ANFIS)-FPA-operated BLDC directed PV pump with advanced Luo converter, has not been formerly conferred. Full article
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Open AccessFeature PaperArticle A Novel Dual-Scale Deep Belief Network Method for Daily Urban Water Demand Forecasting
Energies 2018, 11(5), 1068; https://doi.org/10.3390/en11051068
Received: 6 April 2018 / Revised: 22 April 2018 / Accepted: 23 April 2018 / Published: 26 April 2018
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Abstract
Water demand forecasting applies data supports for the scheduling and decision-making of urban water supply systems. In this study, a new dual-scale deep belief network (DSDBN) approach for daily urban water demand forecasting was proposed. Original daily water demand time series was decomposed
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Water demand forecasting applies data supports for the scheduling and decision-making of urban water supply systems. In this study, a new dual-scale deep belief network (DSDBN) approach for daily urban water demand forecasting was proposed. Original daily water demand time series was decomposed into several intrinsic mode functions (IMFs) and one residue component with ensemble empirical mode decomposition (EEMD) technique. Stochastic and deterministic terms were reconstructed through analyzing the frequency characteristics of IMFs and residue using generalized Fourier transform. The deep belief network (DBN) model was used for prediction using the two feature terms. The outputs of the double DBNs are summed as the final forecasting results. Historical daily water demand datasets from an urban waterworks in Zhuzhou, China, were investigated by the proposed DSDBN model. The mean absolute percentage error (MAPE), normalized root-mean-square error (NRMSE), correlation coefficient (CC) and determination coefficient (DC) were used as evaluation criteria. The results were compared with the autoregressive integrated moving average (ARIMA) model, feed forward neural network (FFNN) model, support vector regression (SVR) model, EEMD and their combinations, and single DBN model. The results obtained in the test period indicate that the proposed model has the smallest MAPE and NRMSE values of 1.291099 and 0.016625, respectively, and the largest CC and DC values of 0.976528 and 0.953512, respectively. Therefore, the proposed DSDBN method is a useful tool for daily urban water demand forecasting and outperforms other models in common use. Full article
(This article belongs to the Section Energy Storage and Application)
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Open AccessFeature PaperArticle Study of the Gas Distribution in a Multiphase Rotodynamic Pump Based on Interphase Force Analysis
Energies 2018, 11(5), 1069; https://doi.org/10.3390/en11051069
Received: 6 April 2018 / Revised: 20 April 2018 / Accepted: 24 April 2018 / Published: 26 April 2018
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Abstract
The performance of multiphase pumps has a remarkable influence on the related industrial application. In order to understand the flow field and gas-liquid phase interaction characteristics of a multiphase rotodynamic pump, detailed numerical analysis of the pump with a medium of air-water combination
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The performance of multiphase pumps has a remarkable influence on the related industrial application. In order to understand the flow field and gas-liquid phase interaction characteristics of a multiphase rotodynamic pump, detailed numerical analysis of the pump with a medium of air-water combination was carried out for the whole flow passage by means of a structured mesh using ICEM_CFD and TurboGrid. The results for 21% inlet gas void fraction (IGVF = 21%) condition showed that the magnitude ratio of non-drag forces to drag in impeller and guide vane passages was generally less than 1, whereas it was always less than 0.2 for the magnitude ratio of turbulent dispersion force to drag. When the IGVF was increased, the variation range of interphase forces in the impeller was greater than that in the guide vane. In addition, the gas in the impeller mainly accumulated near the suction surface in the outlet region. Further, with increased IGVF, the degree of aggregation increased as well as the gas inhomogeneity, and consequently the interphase forces in the impeller increased. Due to the divergent structure of the guide vane, obvious vortexes emerged at the hub and gradually moved toward the blade pressure surface along the streamwise direction. Full article
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Open AccessArticle Design Optimization of a Complex Polygeneration System for a Hospital
Energies 2018, 11(5), 1071; https://doi.org/10.3390/en11051071
Received: 11 February 2018 / Revised: 19 April 2018 / Accepted: 19 April 2018 / Published: 26 April 2018
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Abstract
Small-scale decentralized polygeneration systems have several energetic, economic and environmental benefits. However, using multiple energy sources and providing multiple energy services can lead to complicated studies which require advanced optimization techniques for determining optimal solutions. Furthermore, several parameters can influence the design and
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Small-scale decentralized polygeneration systems have several energetic, economic and environmental benefits. However, using multiple energy sources and providing multiple energy services can lead to complicated studies which require advanced optimization techniques for determining optimal solutions. Furthermore, several parameters can influence the design and performance of a polygeneration system. In this study, the effects of heat load, renewable generation and storage units on the optimal design and performance of a polygeneration system for a hypothetical hospital located in northern Italy are investigated. The polygeneration system shows higher performance compared to the reference system, which is based on the separate generation of heat and power. It reduces fuel consumption by 14–32%, CO2 emissions by 10–29% and annualized total cost by 7–19%, for various studied scenarios. The avoided fuel and electricity purchase of the polygeneration system has a positive impact on the economy. This, together with the environmental and energetic benefits if the renewable generation and use of storage devices, indicate the viability and competitiveness of the system. Full article
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Open AccessArticle The Maximum-Allowable Well Depth While Drilling of Extended-Reach Wells Targeting to Offshore Depleted Reservoirs
Energies 2018, 11(5), 1072; https://doi.org/10.3390/en11051072
Received: 24 February 2018 / Revised: 8 April 2018 / Accepted: 24 April 2018 / Published: 26 April 2018
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Abstract
In depleted offshore reservoirs, pore pressure declines and consequently horizontal in-situ stresses decrease as well. This causes a very limited well depth for extended-reach drilling targeting to offshore depleted reservoirs. In this paper, based on analyzing the safe mud weight window of the
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In depleted offshore reservoirs, pore pressure declines and consequently horizontal in-situ stresses decrease as well. This causes a very limited well depth for extended-reach drilling targeting to offshore depleted reservoirs. In this paper, based on analyzing the safe mud weight window of the depleted offshore reservoirs, a model of predicting the Maximum Allowable Measured Depth (MAMD) for extended-reach drilling targeting to offshore depleted reservoirs is developed. Meanwhile, the numerical method of the model is proposed, and the key affecting factors of the MAMD are also investigated. The results show the pore pressure depletion has obvious effects on the MAMD. With the depletion of pore pressure, the safe mud weight window appears narrower and even disappears, consequently the predicted MAMD becomes shorter. For a normal regime depositional environment in the depleted reservoirs, it may be impossible to drill with conventional drilling method in the nearby directions of the maximum horizontal in-situ stress, while it may be much safer and attain a long MAMD when drilling in the directions near the minimum horizontal in-situ stress. Moreover, the MAMD will decrease with the increase of Poisson’s ratio and Biot’s parameter, and its response to Poisson’s ratio is more obvious. For a specific target depleted reservoir, the extended-reach drilling with a high borehole inclination may have a longer MAMD than that with a low borehole inclination. This paper presents a method for promoting the design of extended-reach drilling targeting to offshore depleted reservoirs. Full article
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Open AccessArticle Online Internal Resistance Measurement Application in Lithium Ion Battery Capacity and State of Charge Estimation
Energies 2018, 11(5), 1073; https://doi.org/10.3390/en11051073
Received: 8 April 2018 / Revised: 17 April 2018 / Accepted: 20 April 2018 / Published: 26 April 2018
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Abstract
State of charge (SOC) and state of health (SOH) are two significant state parameters for the lithium ion batteries (LiBs). In obtaining these states, the capacity of the battery is an indispensable parameter that is hard to detect directly online. However, there is
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State of charge (SOC) and state of health (SOH) are two significant state parameters for the lithium ion batteries (LiBs). In obtaining these states, the capacity of the battery is an indispensable parameter that is hard to detect directly online. However, there is a strong correlation relationship between this parameter and battery internal resistance. This article first shows a simple and effective online internal resistance detection method. Secondly, the relationship between the measured internal resistance and the LiBs capacity is established by linear fitting. Finally, the capacity through internal resistance conversion is applied in SOC estimation. The estimation results show that this method can effectively enhance the SOC estimation accuracy regardless of temperature change and battery degradation. Full article
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Open AccessArticle Probabilistic Electricity Price Forecasting Models by Aggregation of Competitive Predictors
Energies 2018, 11(5), 1074; https://doi.org/10.3390/en11051074
Received: 8 March 2018 / Revised: 21 April 2018 / Accepted: 23 April 2018 / Published: 26 April 2018
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Abstract
This article presents original probabilistic price forecasting meta-models (PPFMCP models), by aggregation of competitive predictors, for day-ahead hourly probabilistic price forecasting. The best twenty predictors of the EEM2016 EPF competition are used to create ensembles of hourly spot price forecasts. For each hour,
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This article presents original probabilistic price forecasting meta-models (PPFMCP models), by aggregation of competitive predictors, for day-ahead hourly probabilistic price forecasting. The best twenty predictors of the EEM2016 EPF competition are used to create ensembles of hourly spot price forecasts. For each hour, the parameter values of the probability density function (PDF) of a Beta distribution for the output variable (hourly price) can be directly obtained from the expected and variance values associated to the ensemble for such hour, using three aggregation strategies of predictor forecasts corresponding to three PPFMCP models. A Reliability Indicator (RI) and a Loss function Indicator (LI) are also introduced to give a measure of uncertainty of probabilistic price forecasts. The three PPFMCP models were satisfactorily applied to the real-world case study of the Iberian Electricity Market (MIBEL). Results from PPFMCP models showed that PPFMCP model 2, which uses aggregation by weight values according to daily ranks of predictors, was the best probabilistic meta-model from a point of view of mean absolute errors, as well as of RI and LI. PPFMCP model 1, which uses the averaging of predictor forecasts, was the second best meta-model. PPFMCP models allow evaluations of risk decisions based on the price to be made. Full article
(This article belongs to the Special Issue Forecasting Models of Electricity Prices 2018)
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Open AccessArticle Analysis of Syngas Production from Biogas via the Tri-Reforming Process
Energies 2018, 11(5), 1075; https://doi.org/10.3390/en11051075
Received: 25 March 2018 / Revised: 19 April 2018 / Accepted: 25 April 2018 / Published: 27 April 2018
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Abstract
The tri-reforming process was employed for syngas production from biogas at elevated pressures in this study. In the tri-reforming process, air and water were added simultaneously as reactants in addition to the main biogas components. The effects of various operating parameters such as
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The tri-reforming process was employed for syngas production from biogas at elevated pressures in this study. In the tri-reforming process, air and water were added simultaneously as reactants in addition to the main biogas components. The effects of various operating parameters such as pressure, temperature and reactant composition on the reaction performance were studied numerically. From the simulated results, it was found that methane and carbon dioxide conversions can be enhanced and a higher hydrogen/carbon monoxide ratio can be obtained by increasing the amount of air. However, a decreased hydrogen yield could result due to the reverse water–gas shift reaction. A higher level of methane conversion and hydrogen/carbon monoxide ratio can be obtained with increased water addition. However, negative carbon dioxide conversion could result due to the water–gas shift and reverse carbon dioxide methanation reactions. The dry reforming reaction resulting in positive carbon dioxide conversion can only be found at a high reaction temperature. For all cases studied, low or negative carbon dioxide conversion was found because of carbon dioxide production from methane oxidation, water–gas shift, and reverse carbon dioxide methanation reactions. It was found that carbon dioxide conversion can be enhanced in the tri-reforming process by a small amount of added water. It was also found that first-law efficiency increased with increased reaction temperature because of higher hydrogen and carbon monoxide yields. Second-law efficiency was found to decrease with increased temperature because of higher exergy destruction due to a more complete chemical reaction at high temperatures. Full article
(This article belongs to the Special Issue Biofuel and Bioenergy Technology)
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Open AccessArticle Blood Volume Pulse Extraction for Non-Contact Heart Rate Measurement by Digital Camera Using Singular Value Decomposition and Burg Algorithm
Energies 2018, 11(5), 1076; https://doi.org/10.3390/en11051076
Received: 22 March 2018 / Revised: 18 April 2018 / Accepted: 23 April 2018 / Published: 27 April 2018
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Abstract
Conventional photoplesthymograph (PPG) measurements for heart rate (HR) determination require direct contact between the patient and the PPG device sensor. When using the conventional method, it is possible for users to suffer undesirable skin irritation, discomfort and soreness. Thus, the development of non-contact
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Conventional photoplesthymograph (PPG) measurements for heart rate (HR) determination require direct contact between the patient and the PPG device sensor. When using the conventional method, it is possible for users to suffer undesirable skin irritation, discomfort and soreness. Thus, the development of non-contact PPG has been investigated with various technologies and methods. One of the technologies that able to measure PPG in a non-contact way and at low cost is using digital cameras such as webcams. Various filters have been implemented to do non-contact PPG using digital cameras. This paper proposes a non-contact PPG filter system utilizing singular value decomposition (SVD) and Burg’s algorithm. The main role of SVD is for noise removal and as PPG signal extractor. As for the Burg algorithm, it was utilized for estimating the heart rate value from the filtered PPG signal. In this paper, we show and analyze an experiment for HR measurement using our method and a previous method that used independent component analysis (ICA). We compare and contrast both of them with HR measurements acquired by a commercial oximeter. The experiments were conducted at various distance between 30~110 cm and light intensities between 5~2000 lux. The estimated HR showed 2.25 bpm of mean error and 0.73 of Pearson correlation coefficient. The optimal distance between the mirror and user for HR measurement was 50 cm with medium light intensity, around 550 lux. Full article
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Open AccessArticle Numerical Study on the Effect of Distribution Plates in the Manifolds on the Flow Distribution and Thermal Performance of a Flat Plate Solar Collector
Energies 2018, 11(5), 1077; https://doi.org/10.3390/en11051077
Received: 7 December 2017 / Revised: 18 February 2018 / Accepted: 26 March 2018 / Published: 27 April 2018
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Abstract
Flow maldistribution represents a problem of particular interest in the engineering field for several thermal systems. In flat plate solar collectors, the thermal efficiency strongly depends on the flow distribution through the riser tubes, where a uniform distribution causes a uniform temperature distribution
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Flow maldistribution represents a problem of particular interest in the engineering field for several thermal systems. In flat plate solar collectors, the thermal efficiency strongly depends on the flow distribution through the riser tubes, where a uniform distribution causes a uniform temperature distribution and therefore a higher efficiency. In this work, a Computational Fluid Dynamics (CFD) numerical analysis has been carried out using the commercial software FLUENT®, in order to determine the flow distribution, pressure drop and hence the thermal efficiency of a solar collector with distribution flow plates inside the manifolds. The obtained numerical solution for this type of thermal systems has been validated with experimental results available in literature for laminar and turbulent flow. Four distribution plate configurations were analyzed. Results show that using two distribution plates in each of both manifolds improves the flow uniformity up to 40% under the same operating conditions when distribution plates are not used. Besides, it is shown that there exists an increase in the overall pressure drop which is practically negligible for the tilt angles commonly employed in the installation of flat plate solar collectors in Mexico. The use of closed end distribution plates on the dividing and combining manifolds allows the thermal efficiency to become close to the ideal thermal efficiency which is obtained with a uniform flow distribution. Full article
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Open AccessArticle Investigation of a Resonant dc–dc Converter for Light Rail Transportation Applications
Energies 2018, 11(5), 1078; https://doi.org/10.3390/en11051078
Received: 10 April 2018 / Revised: 20 April 2018 / Accepted: 24 April 2018 / Published: 27 April 2018
PDF Full-text (9358 KB) | HTML Full-text | XML Full-text
Abstract
A high efficiency dc–dc converter is studied for light rail transportation applications on DC microgrid systems. The adopted structure includes two series-connected resonant circuits with single isolated transformer from input 750 V to output 48 V. Two half-bridge resonant circuits and one voltage
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A high efficiency dc–dc converter is studied for light rail transportation applications on DC microgrid systems. The adopted structure includes two series-connected resonant circuits with single isolated transformer from input 750 V to output 48 V. Two half-bridge resonant circuits and one voltage balance capacitor are used to reduce voltage rating of active devices and to realize split voltages balance. Two series resonant circuits are connected with input-series by single transformer to reduce primary root-mean-square currents. Therefore, power devices with low voltage rating are selected in studied circuit to reduce power loss on sower devices and transformer winding of the isolated transformer. Frequency control approach is adopted to adjust load voltage under different voltage condition and current variations. Since the equivalent resonant tank of the studied circuit is activated under inductive load, active devices are easily operated at zero-voltage switching over wide voltage and current operation range. The feasibility of the studied circuit has been verified with a 1 kW prototype. Full article
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Open AccessArticle Triple Line-Voltage Cascaded VIENNA Converter Applied as the Medium-Voltage AC Drive
Energies 2018, 11(5), 1079; https://doi.org/10.3390/en11051079
Received: 5 April 2018 / Revised: 23 April 2018 / Accepted: 24 April 2018 / Published: 27 April 2018
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Abstract
A novel rectifier based on a triple line-voltage cascaded VIENNA converter (LVC-VC) was proposed. Compared to the conventional cascaded H-bridge converters, the switch voltage stress is lower, and the numbers of switches and dc capacitors are fewer under similar operating conditions in the
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A novel rectifier based on a triple line-voltage cascaded VIENNA converter (LVC-VC) was proposed. Compared to the conventional cascaded H-bridge converters, the switch voltage stress is lower, and the numbers of switches and dc capacitors are fewer under similar operating conditions in the proposed new multilevel converter. The modeling and control for the LVC-VC ware presented. Based on the analysis of the operation principle of the new converter, the power factor correction of the proposed converter was realized by employing a traditional one-cycle control strategy. The minimum average value and maximum harmonic components of the dc-link voltages of the three VIENNA rectifier modules ware calculated. Three VIENNA dc-link voltages were unbalanced under the unbalanced load conditions, so the zero sequence current was injected to the three inner currents for balancing three VIENNA dc-link voltages. Simulation and the results of the experiment verified the availability of the new proposed multilevel converter and the effectiveness of the corresponding control strategy applied. Full article
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