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Energies, Volume 10, Issue 2 (February 2017)

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Cover Story The development of distributed energy resources increases the needs of higher grid capacity. It is [...] Read more.
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Editorial

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Open AccessEditorial Forecasting Models of Electricity Prices
Energies 2017, 10(2), 160; doi:10.3390/en10020160
Received: 14 January 2017 / Revised: 20 January 2017 / Accepted: 20 January 2017 / Published: 29 January 2017
Cited by 1 | PDF Full-text (140 KB) | HTML Full-text | XML Full-text
(This article belongs to the Special Issue Forecasting Models of Electricity Prices) Printed Edition available

Research

Jump to: Editorial, Review

Open AccessArticle Decentralized Electric Vehicle Charging Strategies for Reduced Load Variation and Guaranteed Charge Completion in Regional Distribution Grids
Energies 2017, 10(2), 147; doi:10.3390/en10020147
Received: 10 November 2016 / Revised: 10 January 2017 / Accepted: 18 January 2017 / Published: 24 January 2017
Cited by 1 | PDF Full-text (2169 KB) | HTML Full-text | XML Full-text
Abstract
A novel, fully decentralized strategy to coordinate charge operation of electric vehicles is proposed in this paper. Based on stochastic switching control of on-board chargers, this strategy ensures high-efficiency charging, reduces load variations to the grid during charging periods, achieves charge completion with
[...] Read more.
A novel, fully decentralized strategy to coordinate charge operation of electric vehicles is proposed in this paper. Based on stochastic switching control of on-board chargers, this strategy ensures high-efficiency charging, reduces load variations to the grid during charging periods, achieves charge completion with high probability, and accomplishes approximate “valley-filling”. Further improvements on the core strategy, including individualized power management, adaptive strategies, and battery support systems, are introduced to further reduce power fluctuation variances and to guarantee charge completion. Stochastic analysis is performed to establish the main properties of the strategies and to quantitatively show the performance improvements. Compared with the existing decentralized charging strategies, the strategies proposed in this paper can be implemented without any information exchange between grid operators and electric vehicles (EVs), resulting in a communications cost reduction. Additionally, it is shown that by using stochastic charging rules, a grid-supporting battery system with a very small energy capacity can achieve substantial reduction of EV load fluctuations with high confidence. An extensive set of simulations and case studies with real-world data are used to demonstrate the benefits of the proposed strategies. Full article
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Open AccessArticle Influence of Tip Clearance on Pressure Fluctuation in Low Specific Speed Mixed-Flow Pump Passage
Energies 2017, 10(2), 148; doi:10.3390/en10020148
Received: 17 November 2016 / Revised: 16 January 2017 / Accepted: 18 January 2017 / Published: 24 January 2017
Cited by 2 | PDF Full-text (5273 KB) | HTML Full-text | XML Full-text
Abstract
To explore the influence of tip clearance on pressure fluctuation in a low specific speed mixed-flow pump, tip clearances δ of 0.25 mm, 0.75 mm and 1.00 mm, along with no tip clearance, were selected. The reliability of the simulation was verified by
[...] Read more.
To explore the influence of tip clearance on pressure fluctuation in a low specific speed mixed-flow pump, tip clearances δ of 0.25 mm, 0.75 mm and 1.00 mm, along with no tip clearance, were selected. The reliability of the simulation was verified by comparison with the experimental data of external characteristics and fluctuation in the guide vane passage. Through ANSYS-CFX, MATLAB code and fast Fourier transform (FFT) algorithm, pressure fluctuation characteristics in this pump were obtained. The results show that pressure fluctuation exists in all conditions due to the rotor-stator interaction. Under the no tip clearance and tip clearance conditions, the maximum fluctuation value was located near the guide inlet and impeller outlet, respectively. Clearance leakage had less influence on pressure fluctuation at the impeller inlet and central regions within a certain range of the clearance; beyond this range, fluctuations in the whole flow passage increased significantly, while the clearance variation had less effect on fluctuation in the guide vane. When the tip clearance value was 1.00 mm, pressure fluctuation of the shroud at the impeller inlet section suddenly increases, which was closely related to the obvious leakage vortexes and a larger low pressure area. Full article
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Open AccessArticle Fault Tolerant and Optimal Control of Wind Turbines with Distributed High-Speed Generators
Energies 2017, 10(2), 149; doi:10.3390/en10020149
Received: 3 October 2016 / Revised: 10 January 2017 / Accepted: 11 January 2017 / Published: 24 January 2017
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Abstract
In this paper, the control scheme of a distributed high-speed generator system with a total amount of 12 generators and nominal generator speed of 7000 min1 is studied. Specifically, a fault tolerant control (FTC) scheme is proposed to keep the turbine
[...] Read more.
In this paper, the control scheme of a distributed high-speed generator system with a total amount of 12 generators and nominal generator speed of 7000 min 1 is studied. Specifically, a fault tolerant control (FTC) scheme is proposed to keep the turbine in operation in the presence of up to four simultaneous generator faults. The proposed controller structure consists of two layers: The upper layer is the baseline controller, which is separated into a partial load region with the generator torque as an actuating signal and the full-load operation region with the collective pitch angle as the other actuating signal. In addition, the lower layer is responsible for the fault diagnosis and FTC characteristics of the distributed generator drive train. The fault reconstruction and fault tolerant control strategy are tested in simulations with several actuator faults of different types. Full article
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Open AccessArticle Application of Meta-Heuristic Techniques for Optimal Load Shedding in Islanded Distribution Network with High Penetration of Solar PV Generation
Energies 2017, 10(2), 150; doi:10.3390/en10020150
Received: 27 September 2016 / Revised: 5 December 2016 / Accepted: 17 January 2017 / Published: 24 January 2017
Cited by 1 | PDF Full-text (5693 KB) | HTML Full-text | XML Full-text
Abstract
Recently, several environmental problems are beginning to affect all aspects of life. For this reason, many governments and international agencies have expressed great interest in using more renewable energy sources (RESs). However, integrating more RESs with distribution networks resulted in several critical problems
[...] Read more.
Recently, several environmental problems are beginning to affect all aspects of life. For this reason, many governments and international agencies have expressed great interest in using more renewable energy sources (RESs). However, integrating more RESs with distribution networks resulted in several critical problems vis-à-vis the frequency stability, which might lead to a complete blackout if not properly treated. Therefore, this paper proposed a new Under Frequency Load Shedding (UFLS) scheme for islanding distribution network. This scheme uses three meta-heuristics techniques, binary evolutionary programming (BEP), Binary genetic algorithm (BGA), and Binary particle swarm optimization (BPSO), to determine the optimal combination of loads that needs to be shed from the islanded distribution network. Compared with existing UFLS schemes using fixed priority loads, the proposed scheme has the ability to restore the network frequency without any overshooting. Furthermore, in terms of execution time, the simulation results show that the BEP technique is fast enough to shed the optimal combination of loads compared with BGA and BPSO techniques. Full article
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Open AccessArticle Implementation and Assessment of a Decentralized Load Frequency Control: Application to Power Systems with High Wind Energy Penetration
Energies 2017, 10(2), 151; doi:10.3390/en10020151
Received: 12 October 2016 / Revised: 29 November 2016 / Accepted: 13 December 2016 / Published: 24 January 2017
Cited by 1 | PDF Full-text (3511 KB) | HTML Full-text | XML Full-text
Abstract
This paper describes and assesses a decentralized solution based on a wireless sensor-actuator network to provide primary frequency control from demand response in power systems with high wind energy penetration and, subsequently, with relevant frequency excursions. The proposed system is able to modify
[...] Read more.
This paper describes and assesses a decentralized solution based on a wireless sensor-actuator network to provide primary frequency control from demand response in power systems with high wind energy penetration and, subsequently, with relevant frequency excursions. The proposed system is able to modify the electrical power demand of a variety of thermostatically-controlled loads, maintaining minimum comfort levels and minimizing both infrastructure requirements and primary reserves from the supply side. This low-cost hardware solution avoids any additional wiring, extending the wireless sensor-actuator network technology towards small customers, which account for over a 30% share of the current power demand. Frequency excursions are collected by each individual load controller, considering not only the magnitude of the frequency deviation, but also their evolution over time. Based on these time-frequency excursion characteristics, controllers are capable of modifying the power consumption of thermostatically-controlled loads by switching them off and on, thus contributing to primary frequency control in power systems with higher generation unit oscillations as a consequence of relevant wind power integration. Field tests have been carried out in a laboratory environment to assess the load controller performance, as well as to evaluate the electrical and thermal response of individual loads under frequency deviations. These frequency deviations are estimated from power systems with a high penetration of wind energy, which are more sensitive to frequency oscillations and where demand response can significantly contribute to mitigate these frequency excursions. The results, also included in the paper, evaluate the suitability of the proposed load controllers and their suitability to decrease frequency excursions from the demand side in a decentralized manner. Full article
(This article belongs to the collection Smart Grid)
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Open AccessArticle Phase Change Material Based Accumulation Panels in Combination with Renewable Energy Sources and Thermoelectric Cooling
Energies 2017, 10(2), 152; doi:10.3390/en10020152
Received: 28 September 2016 / Revised: 3 January 2017 / Accepted: 17 January 2017 / Published: 24 January 2017
Cited by 2 | PDF Full-text (8328 KB) | HTML Full-text | XML Full-text
Abstract
The article deals with the use of modern materials and technologies that can improve the thermal comfort in buildings. The article describes the design and usage of a special accumulation device, which is composed of thermal panels based on phase change materials (PCMs).
[...] Read more.
The article deals with the use of modern materials and technologies that can improve the thermal comfort in buildings. The article describes the design and usage of a special accumulation device, which is composed of thermal panels based on phase change materials (PCMs). The thermal panels have an integrated tube heat exchanger and heating foils. The technology can be used as a passive or active system for heating and cooling. It is designed as a “green technology”, so it is able to use renewable energy sources, e.g., photovoltaic (PV) panels, solar thermal collectors and heat pumps. Moreover, an interesting possibility is the ability to use thermoelectric coolers. In the research, measurements of the different operating modes were made, and the results are presented in the text. The measurement approves that the technology improves the thermal capacity of the building, and it is possible to use it for active heating and cooling. Full article
(This article belongs to the Special Issue Advanced Heating and Cooling Techniques)
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Open AccessFeature PaperArticle Technology and Reliability of Normally-Off GaN HEMTs with p-Type Gate
Energies 2017, 10(2), 153; doi:10.3390/en10020153
Received: 28 November 2016 / Revised: 16 January 2017 / Accepted: 17 January 2017 / Published: 25 January 2017
Cited by 1 | PDF Full-text (4325 KB) | HTML Full-text | XML Full-text
Abstract
GaN-based transistors with p-GaN gate are commonly accepted as promising devices for application in power converters, thanks to the positive and stable threshold voltage, the low on-resistance and the high breakdown field. This paper reviews the most recent results on the technology and
[...] Read more.
GaN-based transistors with p-GaN gate are commonly accepted as promising devices for application in power converters, thanks to the positive and stable threshold voltage, the low on-resistance and the high breakdown field. This paper reviews the most recent results on the technology and reliability of these devices by presenting original data. The first part of the paper describes the technological issues related to the development of a p-GaN gate, and the most promising solutions for minimizing the gate leakage current. In the second part of the paper, we describe the most relevant mechanisms that limit the dynamic performance and the reliability of GaN-based normally-off transistors. More specifically, we discuss the following aspects: (i) the trapping effects specific for the p-GaN gate; (ii) the time-dependent breakdown of the p-GaN gate during positive gate stress and the related physics of failure; (iii) the stability of the electrical parameters during operation at high drain voltages. The results presented within this paper provide information on the current status of the performance and reliability of GaN-based E-mode transistors, and on the related technological issues. Full article
(This article belongs to the Special Issue Semiconductor Power Devices)
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Open AccessArticle A System Dynamics Analysis of Investment, Technology and Policy that Affect Natural Gas Exploration and Exploitation in China
Energies 2017, 10(2), 154; doi:10.3390/en10020154
Received: 24 September 2016 / Revised: 22 December 2016 / Accepted: 3 January 2017 / Published: 25 January 2017
Cited by 1 | PDF Full-text (2215 KB) | HTML Full-text | XML Full-text
Abstract
Natural gas has an increasing role in Chinese energy transformation. We present a system dynamics model of the natural gas industry in China. A new system dynamics model for natural gas companies based on reserve exploration and well construction as well as investment
[...] Read more.
Natural gas has an increasing role in Chinese energy transformation. We present a system dynamics model of the natural gas industry in China. A new system dynamics model for natural gas companies based on reserve exploration and well construction as well as investment dynamics is proposed. The contribution of the paper is to analyze the influence of technology, investment and policy factors on the natural gas industry. We found that the dynamics of the main variables, including gas policy, cost of investment, accounting depreciation and exploitation technology, are sensitive to the sustainable development of resources. The simulations and results presented here will be helpful for government to reform policies, and for upstream companies to make decisions. Full article
(This article belongs to the Special Issue Applied Energy System Modeling 2016)
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Open AccessArticle A Methodological Approach to Assess the Impact of Smarting Action on Electricity Transmission and Distribution Networks Related to Europe 2020 Targets
Energies 2017, 10(2), 155; doi:10.3390/en10020155
Received: 14 December 2016 / Revised: 13 January 2017 / Accepted: 19 January 2017 / Published: 26 January 2017
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Abstract
The achievement of the so-called 2020 targets requested by the European Union (EU) has determined a significant growth of proposals of solutions and of technical projects aiming at reducing the CO2 emissions and increasing the energy efficiency, as well as the penetration
[...] Read more.
The achievement of the so-called 2020 targets requested by the European Union (EU) has determined a significant growth of proposals of solutions and of technical projects aiming at reducing the CO2 emissions and increasing the energy efficiency, as well as the penetration of Renewable Energy Sources (RES) in the electric network. As many of them ask for funding from the EU itself, there is the necessity to define a methodology to rank them and decide which projects should be sponsored to obtain the maximum effect on the EU 2020 targets. The present paper aims at (i) defining a set of Key Performance Indicators (KPIs) to compare different proposals, (ii) proposing an analytical methodology to evaluate the defined KPIs and (iii) evaluating the maximum impact that the considered action is capable of producing. The proposed methodology is applied to a set of possible interventions performed on a benchmark transmission network test case, in order to show that the defined indicators can be either calculated or measured and that they are useful to rank different “smarting actions”. Full article
(This article belongs to the Special Issue Electric Power Systems Research 2017)
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Open AccessArticle Impact of Distributed Generation Grid Code Requirements on Islanding Detection in LV Networks
Energies 2017, 10(2), 156; doi:10.3390/en10020156
Received: 8 November 2016 / Revised: 20 December 2016 / Accepted: 19 January 2017 / Published: 26 January 2017
Cited by 7 | PDF Full-text (2056 KB) | HTML Full-text | XML Full-text
Abstract
The recent growing diffusion of dispersed generation in low voltage (LV) distribution networks is entailing new rules to make local generators participate in network stability. Consequently, national and international grid codes, which define the connection rules for stability and safety of electrical power
[...] Read more.
The recent growing diffusion of dispersed generation in low voltage (LV) distribution networks is entailing new rules to make local generators participate in network stability. Consequently, national and international grid codes, which define the connection rules for stability and safety of electrical power systems, have been updated requiring distributed generators and electrical storage systems to supply stabilizing contributions. In this scenario, specific attention to the uncontrolled islanding issue has to be addressed since currently required anti-islanding protection systems, based on relays locally measuring voltage and frequency, could no longer be suitable. In this paper, the effects on the interface protection performance of different LV generators’ stabilizing functions are analysed. The study takes into account existing requirements, such as the generators’ active power regulation (according to the measured frequency) and reactive power regulation (depending on the local measured voltage). In addition, the paper focuses on other stabilizing features under discussion, derived from the medium voltage (MV) distribution network grid codes or proposed in the literature, such as fast voltage support (FVS) and inertia emulation. Stabilizing functions have been reproduced in the DIgSILENT PowerFactory 2016 software environment, making use of its native programming language. Later, they are tested both alone and together, aiming to obtain a comprehensive analysis on their impact on the anti-islanding protection effectiveness. Through dynamic simulations in several network scenarios the paper demonstrates the detrimental impact that such stabilizing regulations may have on loss-of-main protection effectiveness, leading to an increased risk of unintentional islanding. Full article
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Open AccessArticle Improvement of Wind Energy Production through HVDC Systems
Energies 2017, 10(2), 157; doi:10.3390/en10020157
Received: 26 October 2016 / Revised: 19 December 2016 / Accepted: 10 January 2017 / Published: 27 January 2017
Cited by 2 | PDF Full-text (5793 KB) | HTML Full-text | XML Full-text
Abstract
Variable and non-programmable resources, such as solar and wind, have undergone a stunning growth in recent years and are likely to gain even more importance in the future. Their strong presence in the national electricity mix has created issues in many countries regarding
[...] Read more.
Variable and non-programmable resources, such as solar and wind, have undergone a stunning growth in recent years and are likely to gain even more importance in the future. Their strong presence in the national electricity mix has created issues in many countries regarding the secure operation of the power system. In order to guarantee the stability of the system, several TSOs have resorted to wind energy curtailment, which represents a waste of clean energy and an economic loss. In order to analyze this issue, a model of the Italian power system was developed, a program able to simulate the electricity dispatching mechanism. The model was, then, used to evaluate possible solutions to reduce wind curtailment. In particular, a proposal for the construction of an HVDC line linking Southern and Northern Italy was studied. Full article
(This article belongs to the Special Issue Innovative Methods for Smart Grids Planning and Management)
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Open AccessArticle The Impact of Shale Gas on the Cost and Feasibility of Meeting Climate Targets—A Global Energy System Model Analysis and an Exploration of Uncertainties
Energies 2017, 10(2), 158; doi:10.3390/en10020158
Received: 5 October 2016 / Revised: 13 January 2017 / Accepted: 17 January 2017 / Published: 27 January 2017
PDF Full-text (1903 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
There exists considerable uncertainty over both shale and conventional gas resource availability and extraction costs, as well as the fugitive methane emissions associated with shale gas extraction and its possible role in mitigating climate change. This study uses a multi-region energy system model,
[...] Read more.
There exists considerable uncertainty over both shale and conventional gas resource availability and extraction costs, as well as the fugitive methane emissions associated with shale gas extraction and its possible role in mitigating climate change. This study uses a multi-region energy system model, TIAM (TIMES integrated assessment model), to consider the impact of a range of conventional and shale gas cost and availability assessments on mitigation scenarios aimed at achieving a limit to global warming of below 2 °C in 2100, with a 50% likelihood. When adding shale gas to the global energy mix, the reduction to the global energy system cost is relatively small (up to 0.4%), and the mitigation cost increases by 1%–3% under all cost assumptions. The impact of a “dash for shale gas”, of unavailability of carbon capture and storage, of increased barriers to investment in low carbon technologies, and of higher than expected leakage rates, are also considered; and are each found to have the potential to increase the cost and reduce feasibility of meeting global temperature goals. We conclude that the extraction of shale gas is not likely to significantly reduce the effort required to mitigate climate change under globally coordinated action, but could increase required mitigation effort if not handled sufficiently carefully. Full article
(This article belongs to the Special Issue Low Carbon Economy)
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Open AccessArticle Effect of the Dendrimer Generation Used in the Synthesis of Pt-Ru Nanoparticles Supported on Carbon Nanofibers on the Catalytic Activity towards Methanol Oxidation
Energies 2017, 10(2), 159; doi:10.3390/en10020159
Received: 30 November 2016 / Revised: 12 January 2017 / Accepted: 19 January 2017 / Published: 28 January 2017
Cited by 2 | PDF Full-text (7140 KB) | HTML Full-text | XML Full-text
Abstract
Pt-Ru nanoparticles supported on carbon nanofibers (CNF) were synthesized by the sodium borohydride reduction method, using different generation dendrimers (zero, one, two and three generations). After the synthesis process, these materials were submitted to a heat treatment at 350 °C, in order to
[...] Read more.
Pt-Ru nanoparticles supported on carbon nanofibers (CNF) were synthesized by the sodium borohydride reduction method, using different generation dendrimers (zero, one, two and three generations). After the synthesis process, these materials were submitted to a heat treatment at 350 °C, in order to clean the nanoparticle surface of organic residues. TEM characterization showed that the Pt-Ru nanoparticles size ranged between 1.9 and 5.5 nm. The use of dendrimers did not totally avoid the formation of aggregates, although monodisperse sizes were observed. The heat treatment produces the desired surface cleaning, although promoted the formation of agglomerates and crystalline Ru oxides. The study of the electrochemical activity towards the methanol oxidation displayed some clues about the influence of both the dendrimer generation and the presence of Ru oxides. Moreover, the apparent activation energy Eap for this reaction was determined. The results showed a beneficial effect of the heat treatment on the methanol oxidation current densities for the materials synthesized with the biggest dendrimers, being the methanol deprotonation and COad diffusion the predominant rate determining steps (rds). Full article
(This article belongs to the Special Issue Direct Alcohol Fuel Cells)
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Open AccessArticle Numerical Investigation of the Production Behavior of Methane Hydrates under Depressurization Conditions Combined with Well-Wall Heating
Energies 2017, 10(2), 161; doi:10.3390/en10020161
Received: 2 December 2016 / Accepted: 19 January 2017 / Published: 30 January 2017
Cited by 1 | PDF Full-text (2775 KB) | HTML Full-text | XML Full-text
Abstract
In this study, a 2D hydrate dissociation simulator has been improved and verified to be valid in numerical simulations of the gas production behavior using depressurization combined with a well-wall heating method. A series of numerical simulations were performed and the results showed
[...] Read more.
In this study, a 2D hydrate dissociation simulator has been improved and verified to be valid in numerical simulations of the gas production behavior using depressurization combined with a well-wall heating method. A series of numerical simulations were performed and the results showed that well-wall heating had an influence enhancing the depressurization-induced gas production, but the influence was limited, and it was even gradually weakened with the increase of well-wall heating temperature. Meanwhile, the results of the sensitivity analysis demonstrated the gas production depended on the initial hydrate saturation, initial pressure and the thermal boundary conditions. The supply of heat for hydrate dissociation mainly originates from the thermal boundaries,whichcontrolthehydratedissociationandgasproductionbydepressurizationcombined with well-wall heating. However, the effect of initial temperature on the gas production could be nearly negligible under depressurization conditions combined with well-wall heating. Full article
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Open AccessArticle MACsec Layer 2 Security in HSR Rings in Substation Automation Systems
Energies 2017, 10(2), 162; doi:10.3390/en10020162
Received: 9 November 2016 / Accepted: 12 January 2017 / Published: 31 January 2017
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Abstract
The smart-grid concept takes the communications from the enclosed and protected environment of a substation to the wider city or nationwide area. In this environment, cyber security takes a key role in order to secure the communications. The challenge is to be able
[...] Read more.
The smart-grid concept takes the communications from the enclosed and protected environment of a substation to the wider city or nationwide area. In this environment, cyber security takes a key role in order to secure the communications. The challenge is to be able to secure the grid without impacting the latency while, at the same time, maintaining compatibility with older devices and non secure services. At the lower level, added security must not interfere with the redundancy and the latency required for the real-time substation automation communications. This paper studies how to integrate IEEE MAC Security standard (MACsec) in the substation environment, especially when used in substation system communications Full article
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Open AccessArticle Parallel Multi-Objective Genetic Algorithm for Short-Term Economic Environmental Hydrothermal Scheduling
Energies 2017, 10(2), 163; doi:10.3390/en10020163
Received: 15 November 2016 / Accepted: 13 January 2017 / Published: 31 January 2017
Cited by 10 | PDF Full-text (4345 KB) | HTML Full-text | XML Full-text
Abstract
With the increasingly serious energy crisis and environmental pollution, the short-term economic environmental hydrothermal scheduling (SEEHTS) problem is becoming more and more important in modern electrical power systems. In order to handle the SEEHTS problem efficiently, the parallel multi-objective genetic algorithm (PMOGA) is
[...] Read more.
With the increasingly serious energy crisis and environmental pollution, the short-term economic environmental hydrothermal scheduling (SEEHTS) problem is becoming more and more important in modern electrical power systems. In order to handle the SEEHTS problem efficiently, the parallel multi-objective genetic algorithm (PMOGA) is proposed in the paper. Based on the Fork/Join parallel framework, PMOGA divides the whole population of individuals into several subpopulations which will evolve in different cores simultaneously. In this way, PMOGA can avoid the wastage of computational resources and increase the population diversity. Moreover, the constraint handling technique is used to handle the complex constraints in SEEHTS, and a selection strategy based on constraint violation is also employed to ensure the convergence speed and solution feasibility. The results from a hydrothermal system in different cases indicate that PMOGA can make the utmost of system resources to significantly improve the computing efficiency and solution quality. Moreover, PMOGA has competitive performance in SEEHTS when compared with several other methods reported in the previous literature, providing a new approach for the operation of hydrothermal systems. Full article
(This article belongs to the Special Issue Sustainable and Renewable Energy Systems)
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Open AccessArticle Performance and Stability Enhancement of Perovskite-Type Nanomaterials Applied for Carbon Capture Utilizing Oxyfuel Combustion
Energies 2017, 10(2), 164; doi:10.3390/en10020164
Received: 17 October 2016 / Accepted: 18 January 2017 / Published: 1 February 2017
Cited by 1 | PDF Full-text (3170 KB) | HTML Full-text | XML Full-text
Abstract
A new series of Ba-Co-Operovskite-type oxygen carriers has been successfully synthesized by the microwave-assisted sol-gel method and further applied for producing an O2/CO2 mixture gas. The oxygen adsorption/desorption performance of synthesized samples was studied in a fixed-bed reactor system. Effects of A/B-site substitution
[...] Read more.
A new series of Ba-Co-Operovskite-type oxygen carriers has been successfully synthesized by the microwave-assisted sol-gel method and further applied for producing an O2/CO2 mixture gas. The oxygen adsorption/desorption performance of synthesized samples was studied in a fixed-bed reactor system. Effects of A/B-site substitution on the oxygen desorption performance of Ba-Co-O–based perovskites are also included. Furthermore, the effects of operating conditions including the adsorption time and temperature as well as the desorption temperature on oxygen production performance were investigated in detail. The results indicated that BaCoO3-δ exhibited an excellent oxygen desorption performance among the synthesized A/B-site–substituted ACoO3-δ and BaBO3-δ samples, and that the optimal adsorption time, adsorption temperature and desorption temperatureforBaCoO3-δ were determined to be 20min, 850◦Cand850◦C, respectively, in this study. Full article
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Open AccessArticle Voltage-Sensorless Control Scheme for a Grid Connected Inverter Using Disturbance Observer
Energies 2017, 10(2), 166; doi:10.3390/en10020166
Received: 1 November 2016 / Accepted: 23 January 2017 / Published: 2 February 2017
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Abstract
A grid connected inverter usually requires voltage and current measurements to control the active and reactive powers as well as the inverter output currents. While voltage sensors are essential to obtain reliable information on the phase angle, these additional components certainly increase the
[...] Read more.
A grid connected inverter usually requires voltage and current measurements to control the active and reactive powers as well as the inverter output currents. While voltage sensors are essential to obtain reliable information on the phase angle, these additional components certainly increase the production costs and complexity. In this paper, a voltage-sensorless control scheme for a grid connected inverter using a disturbance observer (DOB) is presented. The grid voltages are estimated by DOB in the stationary reference frame using the current measurements and reference signals. Even though the DOB estimates the grid voltages with reasonable accuracy in the presence of the uncertainty such as the unbalanced condition and harmonic distortion, the resultant waveform shows a phase lag depending on the estimation bandwidth. To overcome this limitation, a phase lead compensation is introduced. By using these techniques, the phase angle of grid voltages can be completely restored even if the phase angle of grid is initially unknown. The proposed scheme is simple and straightforward. In addition, it does not require any additional hardware. The feasibility of the proposed voltage-sensorless control scheme is demonstrated through simulations and experiments using 2 kVA prototype inverter. Full article
(This article belongs to the Special Issue Sustainable and Renewable Energy Systems)
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Open AccessArticle Adaptive Torque Estimation for an IPMSM with Cross-Coupling and Parameter Variations
Energies 2017, 10(2), 167; doi:10.3390/en10020167
Received: 30 September 2016 / Accepted: 23 January 2017 / Published: 27 January 2017
Cited by 1 | PDF Full-text (6029 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a new adaptive torque estimation algorithm for an interior permanent magnet synchronous motor (IPMSM) with parameter variations and cross-coupling between d- and q-axis dynamics. All cross-coupled, time-varying, or uncertain terms that are not part of the nominal flux equations are
[...] Read more.
This paper presents a new adaptive torque estimation algorithm for an interior permanent magnet synchronous motor (IPMSM) with parameter variations and cross-coupling between d- and q-axis dynamics. All cross-coupled, time-varying, or uncertain terms that are not part of the nominal flux equations are included in two equivalent mutual inductances, which are described using the equivalent d- and q-axis back electromotive forces (EMFs). The proposed algorithm estimates the equivalent d- and q-axis back EMFs in a recursive and stability-guaranteed manner, in order to compute the equivalent mutual inductances between the d- and q-axes. Then, it provides a more accurate and adaptive torque equation by adding the correction terms obtained from the computed equivalent mutual inductances. Simulations and experiments demonstrate that torque estimation errors are remarkably reduced by capturing and compensating for the inherent cross-coupling effects and parameter variations adaptively, using the proposed algorithm. Full article
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Open AccessArticle An N-k Analytic Method of Composite Generation and Transmission with Interval Load
Energies 2017, 10(2), 168; doi:10.3390/en10020168
Received: 2 October 2016 / Revised: 28 December 2016 / Accepted: 16 January 2017 / Published: 29 January 2017
Cited by 2 | PDF Full-text (1115 KB) | HTML Full-text | XML Full-text
Abstract
N-k contingency estimation plays a very important role in the operation and expansion planning of power systems, the method of which is traditionally based on heuristic screening. This paper stringently analyzes the best and worst states of power systems given the
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N-k contingency estimation plays a very important role in the operation and expansion planning of power systems, the method of which is traditionally based on heuristic screening. This paper stringently analyzes the best and worst states of power systems given the uncertainties of N-k contingency and interval load. For the sake of simplification and tractable computation, an approximate direct current (DC) power flow model was used. Rigorous optimization models were established for identifying the worst and best scenarios considering the contingencies of generators and transmission lines together with their uncertain loads. It is very useful to identify the worst N-k contingencies with interval loads. If the worst existing scenario meets security standards, all scenarios must satisfy it. The mathematical model established for finding the worst N-k contingency with interval load is a bi-level optimization model. In this paper, strong duality theory and mathematical linearization were applied to the solution of bi-level optimization. The computational results of standard cases validate the effectiveness of the proposed method and illustrate that generator contingency has more impact on minimum load shedding than transmission line contingency. Full article
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Open AccessArticle Multi-Agent-Based Controller for Voltage Enhancement in AC/DC Hybrid Microgrid Using Energy Storages
Energies 2017, 10(2), 169; doi:10.3390/en10020169
Received: 15 October 2016 / Revised: 4 January 2017 / Accepted: 18 January 2017 / Published: 3 February 2017
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Abstract
Development of renewable energies and DC loads have led microgrids toward the creation of DC networks. The predictions show that the hybrid microgrids will be used widely in the future. This article has studied the voltage stability in the presence of sources of
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Development of renewable energies and DC loads have led microgrids toward the creation of DC networks. The predictions show that the hybrid microgrids will be used widely in the future. This article has studied the voltage stability in the presence of sources of energy storage in AC/DC hybrid networks. However, because the different dynamics of hybrid networks applying centralized and distributed controllers will be faced with different problems, in this study, a multi-agent control for the microgrid has been used. A new structure referred to here as an event-driven microgrid control management (EDMCM) has been developed to control the microgrid. This method increases response speed and accuracy of decision making. Hybrid Network Simulation results confirm the validity of the developed model. Full article
(This article belongs to the Special Issue Microgrids 2016)
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Open AccessArticle Development of Propulsion Inverter Control System for High-Speed Maglev based on Long Stator Linear Synchronous Motor
Energies 2017, 10(2), 170; doi:10.3390/en10020170
Received: 19 September 2016 / Revised: 30 December 2016 / Accepted: 20 January 2017 / Published: 3 February 2017
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Abstract
In the case of a long-stator linear drive, unlike rotative drives for which speed or position sensors are a single unit attached to the shaft, these sensors extend along the guideway. The position signals transmitted from a maglev vehicle cannot meet the need
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In the case of a long-stator linear drive, unlike rotative drives for which speed or position sensors are a single unit attached to the shaft, these sensors extend along the guideway. The position signals transmitted from a maglev vehicle cannot meet the need of the real-time propulsion control in the on-ground inverter power substations. In this paper the design of the propulsion inverter control system with a position estimator for driving a long-stator synchronous motor in a high-speed maglev train is proposed. The experiments have been carried out at the 150 m long guideway at the O-song test track. To investigate the performance of the position estimator, the propulsion control system with, and without, the position estimator are compared. The result confirms that the proposed strategy can meet the dynamic property needs of the propulsion inverter control system for driving long-stator linear synchronous motors. Full article
(This article belongs to the Special Issue Power Electronics and Power Quality)
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Open AccessArticle Contribution Determination for Multiple Unbalanced Sources at the Point of Common Coupling
Energies 2017, 10(2), 171; doi:10.3390/en10020171
Received: 8 December 2016 / Revised: 20 January 2017 / Accepted: 20 January 2017 / Published: 4 February 2017
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Abstract
Three-phase unbalance is an important power quality issue that can cause many negative effects to the power system. Effective mitigation and management of voltage unbalance will benefit from the knowledge of how the unbalanced sources contribute to the voltage asymmetry at the point
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Three-phase unbalance is an important power quality issue that can cause many negative effects to the power system. Effective mitigation and management of voltage unbalance will benefit from the knowledge of how the unbalanced sources contribute to the voltage asymmetry at the point of evaluation (POE). In this paper, a method is proposed to assess the overall unbalance contribution of the multiple unbalanced sources at the point of common coupling (PCC). Firstly, the equivalent circuit for analysis is established and the unbalance contribution indices are proposed. Then a method is proposed to determine whether the dominant unbalanced polluter is at the upstream or downstream of POE. If the main unbalanced source is identified to be downstream of POE, a procedure is further proposed to determine the individual contribution of the multiple unbalanced sources. Moreover, for the multiple unbalanced source condition, the current flowing in each feeder is proposed to be used for the contribution estimation instead of the current actually emitted by the unbalanced source. Finally, a method is proposed to estimate the equivalent negative sequence impedance of the aggregate loads. Simulation and field analysis results validate the effectiveness and accuracy of the method. Full article
(This article belongs to the Special Issue Electric Power Systems Research 2017)
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Open AccessArticle Development of Middleware Applied to Microgrids by Means of an Open Source Enterprise Service Bus
Energies 2017, 10(2), 172; doi:10.3390/en10020172
Received: 30 September 2016 / Revised: 25 January 2017 / Accepted: 29 January 2017 / Published: 10 February 2017
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Abstract
The success of the smart grid relies heavily on the integration of Distributed Energy Resources (DERs) and interoperability among the hardware elements that are present as part of either the smart grid itself or in a smaller size deployment, such as a microgrid.
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The success of the smart grid relies heavily on the integration of Distributed Energy Resources (DERs) and interoperability among the hardware elements that are present as part of either the smart grid itself or in a smaller size deployment, such as a microgrid. Therefore, establishing an accurate design for software architectures that guarantee interoperability and are able to abstract hardware heterogeneity in this application domain, along with a clearly defined procedure on how to implement and test a solution like this, becomes a desirable objective. This paper describes the requirements needed to design a secure, decentralized and semantic middleware architecture for microgrids and the procedures used to develop it, so that the mandatory software components that have to be encased by the solution, as well as the steps that should be followed to make it happen, become clear for any designer, software architect or programmer that has to tackle similar challenges. In order to demonstrate the usability of the ideas put forward here, two successful pilots where middleware solutions were created according to these principles have been described. Full article
(This article belongs to the Special Issue Smart Microgrids: Developing the Intelligent Power Grid of Tomorrow)
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Open AccessArticle Parameter Identification with the Random Perturbation Particle Swarm Optimization Method and Sensitivity Analysis of an Advanced Pressurized Water Reactor Nuclear Power Plant Model for Power Systems
Energies 2017, 10(2), 173; doi:10.3390/en10020173
Received: 8 November 2016 / Revised: 16 December 2016 / Accepted: 22 January 2017 / Published: 4 February 2017
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Abstract
The ability to obtain appropriate parameters for an advanced pressurized water reactor (PWR) unit model is of great significance for power system analysis. The attributes of that ability include the following: nonlinear relationships, long transition time, intercoupled parameters and difficult obtainment from practical
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The ability to obtain appropriate parameters for an advanced pressurized water reactor (PWR) unit model is of great significance for power system analysis. The attributes of that ability include the following: nonlinear relationships, long transition time, intercoupled parameters and difficult obtainment from practical test, posed complexity and difficult parameter identification. In this paper, a model and a parameter identification method for the PWR primary loop system were investigated. A parameter identification process was proposed, using a particle swarm optimization (PSO) algorithm that is based on random perturbation (RP-PSO). The identification process included model variable initialization based on the differential equations of each sub-module and program setting method, parameter obtainment through sub-module identification in the Matlab/Simulink Software (Math Works Inc., Natick, MA, USA) as well as adaptation analysis for an integrated model. A lot of parameter identification work was carried out, the results of which verified the effectiveness of the method. It was found that the change of some parameters, like the fuel temperature and coolant temperature feedback coefficients, changed the model gain, of which the trajectory sensitivities were not zero. Thus, obtaining their appropriate values had significant effects on the simulation results. The trajectory sensitivities of some parameters in the core neutron dynamic module were interrelated, causing the parameters to be difficult to identify. The model parameter sensitivity could be different, which would be influenced by the model input conditions, reflecting the parameter identifiability difficulty degree for various input conditions. Full article
(This article belongs to the Special Issue Advances in Predictive Modeling of Nuclear Energy Systems)
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Open AccessArticle A Novel WPT System Based on Dual Transmitters and Dual Receivers for High Power Applications: Analysis, Design and Implementation
Energies 2017, 10(2), 174; doi:10.3390/en10020174
Received: 14 October 2016 / Revised: 30 December 2016 / Accepted: 19 January 2017 / Published: 4 February 2017
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Abstract
Traditional Wireless Power Transfer (WPT) systems only have one energy transmission path, which can hardly meet the power demand for high power applications, e.g., railway applications (electric trains and trams, etc.) due to the capacity constraints of power electronic devices. A novel WPT
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Traditional Wireless Power Transfer (WPT) systems only have one energy transmission path, which can hardly meet the power demand for high power applications, e.g., railway applications (electric trains and trams, etc.) due to the capacity constraints of power electronic devices. A novel WPT system based on dual transmitters and dual receivers is proposed in this paper to upgrade the power capacity of the WPT system. The reliability and availability of the proposed WPT system can be dramatically improved due to the four energy transmission paths. A three-dimensional finite element analysis (FEA) tool ANSYS MAXWELL (ANSYS, Canonsburg, PA, USA) is adopted to investigate the proposed magnetic coupling structure. Besides, the effects of the crossing coupling mutual inductances among the transmitters and receivers are analyzed. It shows that the same-side cross couplings will decrease the efficiency and transmitted power. Decoupling transformers are employed to mitigate the effects of the same-side cross couplings. Meanwhile, the output voltage in the secondary side can be regulated at its designed value with a fast response performance, and the system can continue work even with a faulty inverter. Finally, a scale-down experimental setup is provided to verify the proposed approach. The experimental results indicate that the proposed method could improve the transmitted power capacity, overall efficiency and reliability, simultaneously. The proposed WPT structure is a potential alternative for high power applications. Full article
(This article belongs to the Special Issue Wireless Power Transfer 2016)
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Open AccessArticle An Artificial Neural Network for Analyzing Overall Uniformity in Outdoor Lighting Systems
Energies 2017, 10(2), 175; doi:10.3390/en10020175
Received: 18 October 2016 / Revised: 19 January 2017 / Accepted: 20 January 2017 / Published: 4 February 2017
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Abstract
Street lighting installations are an essential service for modern life due to their capability of creating a welcoming feeling at nighttime. Nevertheless, several studies have highlighted that it is possible to improve the quality of the light significantly improving the uniformity of the
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Street lighting installations are an essential service for modern life due to their capability of creating a welcoming feeling at nighttime. Nevertheless, several studies have highlighted that it is possible to improve the quality of the light significantly improving the uniformity of the illuminance. The main difficulty arises when trying to improve some of the installation’s characteristics based only on statistical analysis of the light distribution. This paper presents a new algorithm that is able to obtain the overall illuminance uniformity in order to improve this sort of installations. To develop this algorithm it was necessary to perform a detailed study of all the elements which are part of street lighting installations. Because classification is one of the most important tasks in the application areas of artificial neural networks, we compared the performances of six types of training algorithms in a feed forward neural network for analyzing the overall uniformity in outdoor lighting systems. We found that the best algorithm that minimizes the error is “Levenberg-Marquardt back-propagation”, which approximates the desired output of the training pattern. By means of this kind of algorithm, it is possible to help to lighting professionals optimize the quality of street lighting installations. Full article
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Open AccessArticle An Estimate of the Uncertainty in the Grounding Resistance of Electrodes Buried in Two-Layered Soils with Non-Flat Surface
Energies 2017, 10(2), 176; doi:10.3390/en10020176
Received: 7 December 2016 / Revised: 13 January 2017 / Accepted: 24 January 2017 / Published: 4 February 2017
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Abstract
The influence of the irregular surface of a multi-layered soil on the estimation of the ground resistance of a complex electrode is studied. The electrode is placed in the first layer while the irregular surface is treated as the interface of an inhomogeneous
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The influence of the irregular surface of a multi-layered soil on the estimation of the ground resistance of a complex electrode is studied. The electrode is placed in the first layer while the irregular surface is treated as the interface of an inhomogeneous volume filled with air and embedded in the first layer. A wide sample of irregular soils is generated and the variation of the electrode grounding resistance, as a function of a parameter that measures the surface unevenness, is evaluated. A stochastic model of the grounding resistance is proposed for which the variation of the electrode grounding resistance with its horizontal position relative to the surface is studied. The model features allow us to explain the variability found, as we are able to estimate the part of the uncertainty about the electrode grounding resistance measurements due to the non-planar soil surface. Full article
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Open AccessArticle Mode Shift Control for a Hybrid Heavy-Duty Vehicle with Power-Split Transmission
Energies 2017, 10(2), 177; doi:10.3390/en10020177
Received: 15 December 2016 / Revised: 24 January 2017 / Accepted: 24 January 2017 / Published: 4 February 2017
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Abstract
Given that power-split transmission (PST) is considered to be a major powertrain technology for hybrid heavy-duty vehicles (HDVs), the development and application of PST in the HDVs make mode shift control an essential aspect of powertrain system design. This paper presents a shift
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Given that power-split transmission (PST) is considered to be a major powertrain technology for hybrid heavy-duty vehicles (HDVs), the development and application of PST in the HDVs make mode shift control an essential aspect of powertrain system design. This paper presents a shift schedule design and torque control strategy for a hybrid HDV with PST during mode shift, intended to reduce the output torque variation and improve the shift quality (SQ). Firstly, detailed dynamic models of the hybrid HDV are developed to analyze the mode shift characteristics. Then, a gear shift schedule calculation method including a dynamic shift schedule and an economic shift schedule is provided. Based on the dynamic models and the designed shift schedule, a mode shift performance simulator is built using MATLAB/Simulink, and simulations are carried out. Through analysis of the dynamic equations, it is seen that the inertia torques of the motor–generator lead to the occurrence of transition torque. To avoid the unwanted transition torque, we use a mode shift control strategy that coordinates the motor–generator torque to compensate for the transition torque. The simulation and experimental results demonstrate that the output torque variation during mode shift is effectively reduced by the proposed control strategy, thereby improving the SQ. Full article
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Open AccessCommunication Surface Assisted Combustion of Hydrogen-Oxygen Mixture in Nanobubbles Produced by Electrolysis
Energies 2017, 10(2), 178; doi:10.3390/en10020178
Received: 13 December 2016 / Revised: 26 January 2017 / Accepted: 2 February 2017 / Published: 4 February 2017
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Abstract
The spontaneous combustion of hydrogen–oxygen mixture observed in nanobubbles at room temperature is a puzzling phenomenon that has no explanation in the standard combustion theory. We suggest that the hydrogen atoms needed to ignite the reaction could be generated on charged sites at
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The spontaneous combustion of hydrogen–oxygen mixture observed in nanobubbles at room temperature is a puzzling phenomenon that has no explanation in the standard combustion theory. We suggest that the hydrogen atoms needed to ignite the reaction could be generated on charged sites at the gas–liquid interface. Equations of chemical kinetics augmented by the surface dissociation of hydrogen molecules are solved, keeping the dissociation probability as a parameter. It is predicted that in contrast with the standard combustion, the surface-assisted process can proceed at room temperature, resulting not only in water, but also in a perceptible amount of hydrogen peroxide in the final state. The combustion time for the nanobubbles with a size of about 100 nm is in the range of 1–100 ns, depending on the dissociation probability. Full article
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Open AccessArticle Risk-Based Probabilistic Voltage Stability Assessment in Uncertain Power System
Energies 2017, 10(2), 180; doi:10.3390/en10020180
Received: 28 October 2016 / Revised: 19 January 2017 / Accepted: 23 January 2017 / Published: 5 February 2017
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Abstract
The risk-based assessment is a new approach to the voltage stability assessment in power systems. Under several uncertainties, the security risk of static voltage stability with the consideration of wind power can be evaluated. In this paper, we first build a probabilistic forecast
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The risk-based assessment is a new approach to the voltage stability assessment in power systems. Under several uncertainties, the security risk of static voltage stability with the consideration of wind power can be evaluated. In this paper, we first build a probabilistic forecast model for wind power generation based on real historical data. Furthermore, we propose a new probability voltage stability approach based on Conditional Value-at-Risk (CVaR) and Quasi-Monte Carlo (QMC) simulation. The QMC simulation is used to speed up Monte Carlo (MC) simulation by improving the sampling technique. Our CVaR-based model reveals critical characteristics of static voltage stability. The distribution of the local voltage stability margin, which considers the security risk at a forecast operating time interval, is estimated to evaluate the probability voltage stability. Tested on the modified IEEE New England 39-bus system and the IEEE 118-bus system, results from the proposal are compared against the result of the conventional proposal. The effectiveness and advantages of the proposed method are demonstrated by the test results. Full article
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Open AccessArticle Interpolating and Estimating Horizontal Diffuse Solar Irradiation to Provide UK-Wide Coverage: Selection of the Best Performing Models
Energies 2017, 10(2), 181; doi:10.3390/en10020181
Received: 8 November 2016 / Revised: 16 January 2017 / Accepted: 21 January 2017 / Published: 5 February 2017
Cited by 2 | PDF Full-text (7719 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Plane-of-array (PoA) irradiation data is a requirement to simulate the energetic performance of photovoltaic devices (PVs). Normally, solar data is only available as global horizontal irradiation, for a limited number of locations, and typically in hourly time resolution. One approach to handling this
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Plane-of-array (PoA) irradiation data is a requirement to simulate the energetic performance of photovoltaic devices (PVs). Normally, solar data is only available as global horizontal irradiation, for a limited number of locations, and typically in hourly time resolution. One approach to handling this restricted data is to enhance it initially by interpolation to the location of interest; next, it must be translated to PoA data by separately considering the diffuse and the beam components. There are many methods of interpolation. This research selects ordinary kriging as the best performing technique by studying mathematical properties, experimentation and leave-one-out-cross validation. Likewise, a number of different translation models has been developed, most of them parameterised for specific measurement setups and locations. The work presented identifies the optimum approach for the UK on a national scale. The global horizontal irradiation will be split into its constituent parts. Divers separation models were tried. The results of each separation algorithm were checked against measured data distributed across the UK. It became apparent that while there is little difference between procedures (14 Wh/m2 mean bias error (MBE), 12 Wh/m2 root mean square error (RMSE)), the Ridley, Boland, Lauret equation (a universal split algorithm) consistently performed well. The combined interpolation/separation RMSE is 86 Wh/m2). Full article
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Open AccessArticle How Do Dietary Choices Influence the Energy-System Cost of Stabilizing the Climate?
Energies 2017, 10(2), 182; doi:10.3390/en10020182
Received: 9 December 2016 / Revised: 19 January 2017 / Accepted: 21 January 2017 / Published: 5 February 2017
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Abstract
We investigate how different global dietary scenarios affect the constraints on, and costs of, transforming the energy system to reach a global temperature stabilization limit of 2 °C above the pre-industrial level. A global food and agriculture model, World Food Supply Model (WOFSUM),
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We investigate how different global dietary scenarios affect the constraints on, and costs of, transforming the energy system to reach a global temperature stabilization limit of 2 °C above the pre-industrial level. A global food and agriculture model, World Food Supply Model (WOFSUM), is used to create three dietary scenarios and to calculate the CH4 and N2O emissions resulting from their respective food-supply chains. The diets are: (i) a reference diet based on current trends; (ii) a diet with high (reference-level) meat consumption, but without ruminant products (i.e., no beef, lamb, or dairy, only pork and poultry); and (iii) a vegan diet. The estimated CH4 and N2O emissions from food production are fed into a coupled energy and climate-system optimization model to quantify the energy system implications of the different dietary scenarios, given a 2 °C target. The results indicate that a phase-out of ruminant products substantially increases the emission space for CO2 by about 250 GtC which reduces the necessary pace of the energy system transition and cuts the net present value energy-system mitigation costs by 25%, for staying below 2 °C. Importantly, the additional cost savings with a vegan diet––beyond those achieved with a phase-out of ruminant products––are marginal (only one additional percentage point). This means that a general reduction of meat consumption is a far less effective strategy for meeting the 2 °C target than a reduction of beef and dairy consumption. Full article
(This article belongs to the Special Issue Applied Energy System Modeling 2016)
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Open AccessArticle Discrete Fracture Network Modelling in a Naturally Fractured Carbonate Reservoir in the Jingbei Oilfield, China
Energies 2017, 10(2), 183; doi:10.3390/en10020183
Received: 25 November 2016 / Revised: 15 January 2017 / Accepted: 16 January 2017 / Published: 6 February 2017
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Abstract
This paper presents an integrated approach of discrete fracture network modelling for a naturally fractured buried-hill carbonate reservoir in the Jingbei Oilfield by using a 3D seismic survey, conventional well logs, and core data. The ant tracking attribute, extracted from 3D seismic data,
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This paper presents an integrated approach of discrete fracture network modelling for a naturally fractured buried-hill carbonate reservoir in the Jingbei Oilfield by using a 3D seismic survey, conventional well logs, and core data. The ant tracking attribute, extracted from 3D seismic data, is used to detect the faults and large-scale fractures. Fracture density and dip angle are evaluated by observing drilling cores of seven wells. The fracture density distribution in spatiality was predicted in four steps; firstly, the ant tracking attribute was extracted as a geophysical log; then an artificial neural network model was built by relating the fracture density with logs, e.g., acoustic, gamma ray, compensated neutron, density, and ant tracking; then 3D distribution models of acoustic, gamma ray, compensated neutron and density were generated by using a Gaussian random function simulation; and, finally, the fracture density distribution in 3D was predicted by using the generated artificial neural network model. Then, different methods were used to build the discrete fracture network model for different types of fractures of which large-scale fractures were modelled deterministically and small-scale fractures were modelled stochastically. The results show that the workflow presented in this study is effective for building discrete fracture network models for naturally fractured reservoirs. Full article
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Open AccessArticle Investigating How an Artificial Neural Network Model Can Be Used to Detect Added Mass on a Non-Rotating Beam Using Its Natural Frequencies: A Possible Application for Wind Turbine Blade Ice Detection
Energies 2017, 10(2), 184; doi:10.3390/en10020184
Received: 20 December 2016 / Revised: 30 January 2017 / Accepted: 2 February 2017 / Published: 7 February 2017
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Abstract
Structures vibrate with their natural frequencies when disturbed from their equilibrium position. These frequencies reduce when an additional mass accumulates on their structures, like ice accumulation on wind turbines installed in cold climate sites. The added mass has two features: the location and
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Structures vibrate with their natural frequencies when disturbed from their equilibrium position. These frequencies reduce when an additional mass accumulates on their structures, like ice accumulation on wind turbines installed in cold climate sites. The added mass has two features: the location and quantity of mass. Natural frequencies of the structure reduce differently depending on these two features of the added mass. In this work, a technique based on an artificial neural network (ANN) model is proposed to identify added mass by training the neural network with a dataset of natural frequencies of the structure calculated using different quantities of the added mass at different locations on the structure. The proposed method is demonstrated on a non-rotating beam model fixed at one end. The length of the beam is divided into three zones in which different added masses are considered, and its natural frequencies are calculated using a finite element model of the beam. ANN is trained with this dataset of natural frequencies of the beam as an input and corresponding added masses used in the calculations as an output. ANN approximates the non-linear relationship between these inputs and outputs. An experimental setup of the cantilever beam is fabricated, and experimental modal analysis is carried out considering a few added masses on the beam. The frequencies estimated in the experiments are given as an input to the trained ANN model, and the identified masses are compared against the actual masses used in the experiments. These masses are identified with an error that varies with the location and the quantity of added mass. The reason for these errors can be attributed to the unaccounted stiffness variation in the beam model due to the added mass while generating the dataset for training the neural network. Therefore, the added masses are roughly estimated. At the end of the paper, an application of the current technique for detecting ice mass on a wind turbine blade is studied. A neural network model is designed and trained with a dataset of natural frequencies calculated using the finite element model of the blade considering different ice masses. The trained network model is tested to identify ice masses in four test cases that considers random mass distributions along the blade. The neural network model is able to roughly estimate ice masses, and the error reduces with increasing ice mass on the blade. Full article
(This article belongs to the Special Issue Wind Turbine 2017)
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Open AccessArticle Application of Liquid Hydrogen with SMES for Efficient Use of Renewable Energy in the Energy Internet
Energies 2017, 10(2), 185; doi:10.3390/en10020185
Received: 6 January 2017 / Revised: 1 February 2017 / Accepted: 2 February 2017 / Published: 8 February 2017
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Abstract
Considering that generally frequency instability problems occur due to abrupt variations in load demand growth and power variations generated by different renewable energy sources (RESs), the application of superconducting magnetic energy storage (SMES) may become crucial due to its rapid response features. In
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Considering that generally frequency instability problems occur due to abrupt variations in load demand growth and power variations generated by different renewable energy sources (RESs), the application of superconducting magnetic energy storage (SMES) may become crucial due to its rapid response features. In this paper, liquid hydrogen with SMES (LIQHYSMES) is proposed to play a role in the future energy internet in terms of its combination of the SMES and the liquid hydrogen storage unit, which can help to overcome the capacity limit and high investment cost disadvantages of SMES. The generalized predictive control (GPC) algorithm is presented to be appreciatively used to eliminate the frequency deviations of the isolated micro energy grid including the LIQHYSMES and RESs. A benchmark micro energy grid with distributed generators (DGs), electrical vehicle (EV) stations, smart loads and a LIQHYSMES unit is modeled in the Matlab/Simulink environment. The simulation results show that the proposed GPC strategy can reschedule the active power output of each component to maintain the stability of the grid. In addition, in order to improve the performance of the SMES, a detailed optimization design of the superconducting coil is conducted, and the optimized SMES unit can offer better technical advantages in damping the frequency fluctuations. Full article
(This article belongs to the Special Issue Advanced Energy Storage Technologies and Their Applications (AESA))
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Open AccessArticle k-Nearest Neighbor Neural Network Models for Very Short-Term Global Solar Irradiance Forecasting Based on Meteorological Data
Energies 2017, 10(2), 186; doi:10.3390/en10020186
Received: 24 November 2016 / Accepted: 1 February 2017 / Published: 8 February 2017
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Abstract
This paper proposes a novel methodology for very short term forecasting of hourly global solar irradiance (GSI). The proposed methodology is based on meteorology data, especially for optimizing the operation of power generating electricity from photovoltaic (PV) energy. This methodology is a combination
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This paper proposes a novel methodology for very short term forecasting of hourly global solar irradiance (GSI). The proposed methodology is based on meteorology data, especially for optimizing the operation of power generating electricity from photovoltaic (PV) energy. This methodology is a combination of k-nearest neighbor (k-NN) algorithm modelling and artificial neural network (ANN) model. The k-NN-ANN method is designed to forecast GSI for 60 min ahead based on meteorology data for the target PV station which position is surrounded by eight other adjacent PV stations. The novelty of this method is taking into account the meteorology data. A set of GSI measurement samples was available from the PV station in Taiwan which is used as test data. The first method implements k-NN as a preprocessing technique prior to ANN method. The error statistical indicators of k-NN-ANN model the mean absolute bias error (MABE) is 42 W/m2 and the root-mean-square error (RMSE) is 242 W/m2. The models forecasts are then compared to measured data and simulation results indicate that the k-NN-ANN-based model presented in this research can calculate hourly GSI with satisfactory accuracy. Full article
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Open AccessArticle Using a Reactive Transport Simulator to Simulate CH4 Production from Bear Island Basin in the Barents Sea Utilizing the Depressurization Method†
Energies 2017, 10(2), 187; doi:10.3390/en10020187
Received: 31 December 2016 / Accepted: 4 February 2017 / Published: 8 February 2017
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Abstract
The enormous amount of methane stored in natural gas hydrates (NGHs)worldwide offers a significant potential source of energy. NGHs will be generally unable to reach thermodynamic equilibrium at their in situ reservoir conditions due to the number of active phases involved. Lack of
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The enormous amount of methane stored in natural gas hydrates (NGHs)worldwide offers a significant potential source of energy. NGHs will be generally unable to reach thermodynamic equilibrium at their in situ reservoir conditions due to the number of active phases involved. Lack of reliable field data makes it difficult to predict the production potential and safety of CH4 production from NGHs. While the computer simulations will never be able to replace field data, one can apply state-of-the-artmodellingtechniquestoevaluateseveralpossiblelong-termscenarios. Realistic kinetic models for hydrate dissociation and reformation will be required, as well as analysis of all phase transition routes. This work utilizes our in-house extension of RetrasoCodeBright (RCB), a reactive transport simulator, to perform a gas hydrate production case study of the Bjørnøya (Bear Island) basin, a promising field with very limited geological data reported by available field studies. The use of a reactive transport simulator allowed us to implement non-equilibrium thermodynamics for analysisofCH4 production from the gas hydrates by treating each phase transition involving hydrates as a pseudo reaction. Our results showed a rapid propagation of the pressure drop through the reservoir following the imposition of pressure drawdown at the well. Consequently, gas hydrate dissociation and CH4 production began in the early stages of the five-year simulation period. Full article
(This article belongs to the Special Issue Methane Hydrate Research and Development)
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Open AccessArticle Fourier, Wavelet, and Hilbert-Huang Transforms for Studying Electrical Users in the Time and Frequency Domain
Energies 2017, 10(2), 188; doi:10.3390/en10020188
Received: 15 November 2016 / Revised: 30 January 2017 / Accepted: 3 February 2017 / Published: 8 February 2017
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Abstract
The analysis of electrical signals is a pressing requirement for the optimal design of power distribution. In this context, this paper illustrates how to use a variety of numerical tools, such as the Fourier, wavelet, and Hilbert-Huang transforms, to obtain information relating to
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The analysis of electrical signals is a pressing requirement for the optimal design of power distribution. In this context, this paper illustrates how to use a variety of numerical tools, such as the Fourier, wavelet, and Hilbert-Huang transforms, to obtain information relating to the active and reactive power absorbed by different types of users. In particular, the Fourier spectrum gives the most important frequency components of the electrical signals, and the wavelet analysis highlights the non-stationarity of those frequency contributions, whereas the Hilbert-Huang transform, by means of the Empirical Mode Decomposition, provides a more complete spectrum of frequencies. Full article
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Open AccessArticle On-Line Junction Temperature Monitoring of Switching Devices with Dynamic Compact Thermal Models Extracted with Model Order Reduction
Energies 2017, 10(2), 189; doi:10.3390/en10020189
Received: 6 September 2016 / Revised: 20 January 2017 / Accepted: 24 January 2017 / Published: 8 February 2017
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Abstract
Residual lifetime estimation has gained a key point among the techniques that improve the reliability and the efficiency of power converters. The main cause of failures are the junction temperature cycles exhibited by switching devices during their normal operation; therefore, reliable power converter
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Residual lifetime estimation has gained a key point among the techniques that improve the reliability and the efficiency of power converters. The main cause of failures are the junction temperature cycles exhibited by switching devices during their normal operation; therefore, reliable power converter lifetime estimation requires the knowledge of the junction temperature time profile. Since on-line dynamic temperature measurements are extremely difficult, in this work an innovative real-time monitoring strategy is proposed, which is capable of estimating the junction temperature profile from the measurement of the dissipated powers through an accurate and compact thermal model of the whole power module. The equations of this model can be easily implemented inside a FPGA, exploiting the control architecture already present in modern power converters. Experimental results on an IGBT power module demonstrate the reliability of the proposed method. Full article
(This article belongs to the Special Issue Semiconductor Power Devices)
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Open AccessArticle Assessment of an Adaptive Load Forecasting Methodology in a Smart Grid Demonstration Project
Energies 2017, 10(2), 190; doi:10.3390/en10020190
Received: 23 November 2016 / Revised: 13 January 2017 / Accepted: 19 January 2017 / Published: 8 February 2017
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Abstract
This paper presents the implementation of an adaptive load forecasting methodology in two different power networks from a smart grid demonstration project deployed in the region of Madrid, Spain. The paper contains an exhaustive comparative study of different short-term load forecast methodologies, addressing
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This paper presents the implementation of an adaptive load forecasting methodology in two different power networks from a smart grid demonstration project deployed in the region of Madrid, Spain. The paper contains an exhaustive comparative study of different short-term load forecast methodologies, addressing the methods and variables that are more relevant to be applied for the smart grid deployment. The evaluation followed in this paper suggests that the performance of the different methods depends on the conditions of the site in which the smart grid is implemented. It is shown that some non-linear methods, such as support vector machine with a radial basis function kernel and extremely randomized forest offer good performance using only 24 lagged load hourly values, which could be useful when the amount of data available is limited due to communication problems in the smart grid monitoring system. However, it has to be highlighted that, in general, the behavior of different short-term load forecast methodologies is not stable when they are applied to different power networks and that when there is a considerable variability throughout the whole testing period, some methods offer good performance in some situations, but they fail in others. In this paper, an adaptive load forecasting methodology is proposed to address this issue improving the forecasting performance through iterative optimization: in each specific situation, the best short-term load forecast methodology is chosen, resulting in minimum prediction errors. Full article
(This article belongs to the Special Issue Electric Power Systems Research 2017)
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Open AccessArticle Energy Performance and Flow Patterns of a Mixed-Flow Pump with Different Tip Clearance Sizes
Energies 2017, 10(2), 191; doi:10.3390/en10020191
Received: 6 November 2016 / Revised: 24 January 2017 / Accepted: 3 February 2017 / Published: 8 February 2017
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Abstract
Tip clearance between blade end and shroud is inevitable in pump operation and of great importance on pump energy performance and pressure fluctuation. As the tip clearance size increases, the head and efficiency of the mixed flow pump drop accordingly. The simulation results
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Tip clearance between blade end and shroud is inevitable in pump operation and of great importance on pump energy performance and pressure fluctuation. As the tip clearance size increases, the head and efficiency of the mixed flow pump drop accordingly. The simulation results show that the development of a leakage vortex is observed as the tip clearance increases, and the trajectory of this leakage vortex remains in the same direction along the blade suction side for different tip clearances. With the increase in tip clearance size, the intensity of the leakage vortex is enhanced, and the separation between the main leakage vortex and the secondary leakage vortex is also strengthened. The leakage separation angle near the blade tip remains at the same value of 10° for different tip clearance sizes. As for the spectrum analysis, the maximum amplitudes of pressure fluctuations dramatically increase in the impeller when the tip clearance increases from 0.0 mm to 1.0 mm, and the dominant frequencies go from 145 Hz to 184 Hz due to the considerable leakage flow. Full article
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Open AccessArticle Used Cooking Oils in the Biogas Chain: A Technical and Economic Assessment
Energies 2017, 10(2), 192; doi:10.3390/en10020192
Received: 29 November 2016 / Revised: 23 January 2017 / Accepted: 24 January 2017 / Published: 9 February 2017
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Abstract
The current concerns on global energy security, climate change, and environmental pollution represent some of the major elements of the growing interest on renewable energy. In this framework agro-food energy systems are at the center of a twofold debate: on the one hand
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The current concerns on global energy security, climate change, and environmental pollution represent some of the major elements of the growing interest on renewable energy. In this framework agro-food energy systems are at the center of a twofold debate: on the one hand they represent a key option for energy production while on the other their sustainability is threatened by the expansion of the bioenergy market that could lead to negative social and environmental consequences. The aim of this work is to evaluate—through a case study—the technical and economic feasibility of the replacement of energy crops (ECs) with used cooking oil (UCO) in an anaerobic digestion (AD) full-scale plant. At this purpose, a full-scale plant performing AD was monitored for two years. Three scenarios were developed and compared to evaluate the impacts and the potential benefits in terms of land saving in case of a substitution of ECs with UCO. Results highlighted a reduction of land use of over 50% if UCO is introduced in co-digestion with ECs. The lack of an appropriate legislative framework limits the utilization of used cooking oils (UCOs) in AD with a consequently missed opportunity for biogas owners that could find an important alternative in UCO. Full article
(This article belongs to the collection Bioenergy and Biofuel)
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Open AccessArticle Integration of Electric Springs and Multi-Port Transformers—A New Solution for AC Microgrids with Renewable Energy Sources
Energies 2017, 10(2), 193; doi:10.3390/en10020193
Received: 1 January 2017 / Revised: 24 January 2017 / Accepted: 4 February 2017 / Published: 9 February 2017
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Abstract
The new concept of integrating electric springs (ESs) and multi-port transformers (MTPs) as an active solution for energy management in alternating current (AC) microgrids is proposed. With an ES located at the port where storage devices previously were, the so-called critical flux is
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The new concept of integrating electric springs (ESs) and multi-port transformers (MTPs) as an active solution for energy management in alternating current (AC) microgrids is proposed. With an ES located at the port where storage devices previously were, the so-called critical flux is regulated to a constant value within the core of the transformer. The voltage on each winding is then clamped so that critical load (CL) voltage is regulated to a predefined value. The integration of ESs and MPTs can ensure a safer environment for ES utilization. Thus, the power generated by renewable energy sources can be safely used at residential locations with no need to worry about voltage fluctuations across CLs. Moreover, users can sell electricity to the power companies considered as CLs when the electricity generation of the AC microgrids or the home-installed renewable energy resources exceeds the personal consumption. In the paper, isolated topologies for ESs with three- and four-port transformers are examined, and a theoretical analysis of the ES operation is carried out. Then, equivalent circuits of the isolated ES topologies have been derived. Analysis of the ES operation and effectiveness of the isolated ES topologies are validated by both simulations and experiments. Full article
(This article belongs to the Special Issue Advanced Operation and Control of Smart Microgrids)
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Open AccessArticle Data-Reconciliation Based Fault-Tolerant Model Predictive Control for a Biomass Boiler
Energies 2017, 10(2), 194; doi:10.3390/en10020194
Received: 26 September 2016 / Revised: 22 January 2017 / Accepted: 25 January 2017 / Published: 9 February 2017
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Abstract
This paper presents a novel, effective method to handle critical sensor faults affecting a control system devised to operate a biomass boiler. In particular, the proposed method consists of integrating a data reconciliation algorithm in a model predictive control loop, so as to
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This paper presents a novel, effective method to handle critical sensor faults affecting a control system devised to operate a biomass boiler. In particular, the proposed method consists of integrating a data reconciliation algorithm in a model predictive control loop, so as to annihilate the effects of faults occurring in the sensor of the flue gas oxygen concentration, by feeding the controller with the reconciled measurements. Indeed, the oxygen content in flue gas is a key variable in control of biomass boilers due its close connections with both combustion efficiency and polluting emissions. The main benefit of including the data reconciliation algorithm in the loop, as a fault tolerant component, with respect to applying standard fault tolerant methods, is that controller reconfiguration is not required anymore, since the original controller operates on the restored, reliable data. The integrated data reconciliation–model predictive control (MPC) strategy has been validated by running simulations on a specific type of biomass boiler—the KPA Unicon BioGrate boiler. Full article
(This article belongs to the Special Issue Biomass for Energy Country Specific Show Case Studies)
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Open AccessArticle An Experimental Study on the Thermal Performance of Phase-Change Material and Wood-Plastic Composites for Building Roofs
Energies 2017, 10(2), 195; doi:10.3390/en10020195
Received: 25 November 2016 / Revised: 4 February 2017 / Accepted: 5 February 2017 / Published: 10 February 2017
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Abstract
We assessed the usefulness of phase-change material (PCM)-based thermal plates fabricated from wood-plastic composites (WPCs) in mitigating the urban heat island effect. The thermal performance of plates containing PCMs with two different melting temperatures and with two different albedo levels was evaluated. The
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We assessed the usefulness of phase-change material (PCM)-based thermal plates fabricated from wood-plastic composites (WPCs) in mitigating the urban heat island effect. The thermal performance of plates containing PCMs with two different melting temperatures and with two different albedo levels was evaluated. The results showed that the PCM with a melting temperature of 44 °C maintained lower surface and inner temperatures than the PCM with a melting temperature of 25 °C. Moreover, a higher surface albedo resulted in a lower surface temperature. However, the thermal performance of PCMs with different melting temperatures but the same surface albedo did not differ. Using PCM-based materials in roof finishing materials can reduce surface temperatures and improve thermal comfort. Full article
(This article belongs to the Special Issue PCM Applications in Building Energy)
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Open AccessArticle Energy Conservation in an Office Building Using an Enhanced Blind System Control
Energies 2017, 10(2), 196; doi:10.3390/en10020196
Received: 30 November 2016 / Revised: 17 January 2017 / Accepted: 1 February 2017 / Published: 10 February 2017
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Abstract
The two spaces office module is usually considered as a representative case-study to analyse the energetic improvement in office buildings. In this kind of buildings, the use of a model predictive control (MPC) scheme for the climate system control provides energy savings over
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The two spaces office module is usually considered as a representative case-study to analyse the energetic improvement in office buildings. In this kind of buildings, the use of a model predictive control (MPC) scheme for the climate system control provides energy savings over 15% in comparison to classic control policies. This paper focuses on the influence of solar radiation on the climate control of the office module under Belgian weather conditions. Considering MPC as main climate control, it proposes a novel distributed enhanced control for the blind system (BS) that takes into account part of the predictive information of the MPC. In addition to the savings that are usually achieved by MPC, it adds a potential 15% improvement in global energy use with respect to the usually proposed BS hysteresis control. Moreover, from the simulation results it can be concluded that the thermal comfort is also improved. The proposed BS scheme increases the energy use ratio between the thermally activated building system (TABS) and air-handling unit (AHU); therefore increasing the use of TABS and allowing economic savings, due to the use of more cost-effective thermal equipment. Full article
(This article belongs to the Special Issue Energy Conservation in Infrastructures 2016)
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Open AccessArticle Development of a General Package for Resolution of Uncertainty-Related Issues in Reservoir Engineering
Energies 2017, 10(2), 197; doi:10.3390/en10020197
Received: 20 November 2016 / Revised: 31 January 2017 / Accepted: 2 February 2017 / Published: 10 February 2017
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Abstract
Reservoir simulations always involve a large number of parameters to characterize the properties of formation and fluid, many of which are subject to uncertainties owing to spatial heterogeneity and insufficient measurements. To provide solutions to uncertainty-related issues in reservoir simulations, a general package
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Reservoir simulations always involve a large number of parameters to characterize the properties of formation and fluid, many of which are subject to uncertainties owing to spatial heterogeneity and insufficient measurements. To provide solutions to uncertainty-related issues in reservoir simulations, a general package called GenPack has been developed. GenPack includes three main functions required for full stochastic analysis in petroleum engineering, generation of random parameter fields, predictive uncertainty quantifications and automatic history matching. GenPack, which was developed in a modularized manner, is a non-intrusive package which can be integrated with any existing commercial simulator in petroleum engineering to facilitate its application. Computational efficiency can be improved both theoretically by introducing a surrogate model-based probabilistic collocation method, and technically by using parallel computing. A series of synthetic cases are designed to demonstrate the capability of GenPack. The test results show that the random parameter field can be flexibly generated in a customized manner for petroleum engineering applications. The predictive uncertainty can be reasonably quantified and the computational efficiency is significantly improved. The ensemble Kalman filter (EnKF)-based automatic history matching method can improve predictive accuracy and reduce the corresponding predictive uncertainty by accounting for observations. Full article
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Open AccessArticle Theoretical Analysis for Heat Transfer Optimization in Subcritical Electrothermal Energy Storage Systems
Energies 2017, 10(2), 198; doi:10.3390/en10020198
Received: 21 September 2016 / Revised: 17 November 2016 / Accepted: 11 January 2017 / Published: 10 February 2017
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Abstract
Electrothermal energy storage (ETES) provides bulk electricity storage based on heat pump and heat engine technologies. A subcritical ETES is described in this paper. Based on the extremum principle of entransy dissipation, a geometry model is developed for heat transfer optimization for subcritical
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Electrothermal energy storage (ETES) provides bulk electricity storage based on heat pump and heat engine technologies. A subcritical ETES is described in this paper. Based on the extremum principle of entransy dissipation, a geometry model is developed for heat transfer optimization for subcritical ETES. The exergy during the heat transfer process is deduced in terms of entropy production. The geometry model is validated by the extremum principle of entropy production. The theoretical analysis results show that the extremum principle of entransy dissipation is an effective criterion for the optimization, and the optimum heat transfer for different cases with the same mass flux or pressure has been discussed. The optimum heat transfer can be achieved by adjusting the mass flux and pressure of the working fluid. It also reveals that with the increase of mass flux, there is a minimum exergy in the range under consideration, and the exergy decreases with the increase of the pressure. Full article
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Open AccessArticle The Role of Smart Meters in Enabling Real-Time Energy Services for Households: The Italian Case
Energies 2017, 10(2), 199; doi:10.3390/en10020199
Received: 11 November 2016 / Revised: 17 January 2017 / Accepted: 31 January 2017 / Published: 10 February 2017
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Abstract
The Smart Meter (SM) is an essential tool for successful balancing the demand-offer energy curve. It allows the linking of the consumption and production measurements with the time information and the customer’s identity, enabling the substitution of flat-price billing with smarter solutions, such
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The Smart Meter (SM) is an essential tool for successful balancing the demand-offer energy curve. It allows the linking of the consumption and production measurements with the time information and the customer’s identity, enabling the substitution of flat-price billing with smarter solutions, such as Time-of-Use or Real-Time Pricing. In addition to sending data to the energy operators for billing and monitoring purposes, Smart Meters must be able to send the same data to customer devices in near-real-time conditions, enabling new services such as instant energy awareness and home automation. In this article, we review the ongoing situation in Europe regarding real-time services for the final customers. Then, we review the architectural and technological options that have been considered for the roll-out phase of the Italian second generation of Smart Meters. Finally, we identify a collection of use cases, along with their functional and performance requirements, and discuss what architectures and communications technologies can meet these requirements. Full article
(This article belongs to the Special Issue Smart Home Energy Management)
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Open AccessArticle Integration of Electric Vehicles into the Power Distribution Network with a Modified Capacity Allocation Mechanism
Energies 2017, 10(2), 200; doi:10.3390/en10020200
Received: 10 November 2016 / Accepted: 6 February 2017 / Published: 10 February 2017
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Abstract
The growing penetration of electric vehicles (EVs) represents an operational challenge to system operators, mainly at the distribution level by introducing congestion and voltage drop problems. To solve these potential problems, a two-level coordination approach is proposed in this study. An aggregation entity,
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The growing penetration of electric vehicles (EVs) represents an operational challenge to system operators, mainly at the distribution level by introducing congestion and voltage drop problems. To solve these potential problems, a two-level coordination approach is proposed in this study. An aggregation entity, i.e., an EV virtual power plant (EV-VPP), is used to facilitate the interaction between the distribution system operator (DSO) and EV owners considering the decentralized electricity market structure. In level I, to prevent the line congestion and voltage drop problems, the EV-VPP internally respects the line and voltage constraints when making optimal charging schedules. In level II, to avoid power transformer congestion problems, this paper investigates three different coordination mechanisms, or power transformer capacity allocation mechanisms, between the DSO and the EV-VPPs, considering the case of EVs charging and discharging. The three mechanisms include: (1) a market-based approach; (2) a pro-rata approach; and (3) a newly-proposed constrained market-based approach. A case study considering a 37-bus distribution network and high penetration of electric vehicles is presented to demonstrate the effectiveness of the proposed coordination mechanism, comparing with the existing ones. Full article
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Open AccessArticle Efficiency Analysis of the Main Components of a Vertical Closed-Loop System in a Borehole Heat Exchanger
Energies 2017, 10(2), 201; doi:10.3390/en10020201
Received: 22 November 2016 / Revised: 30 January 2017 / Accepted: 3 February 2017 / Published: 10 February 2017
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Abstract
In vertical closed-loop systems, it is common to use single or double U-tube heat exchangers separated by longitudinal spacers. In addition, the helical-shaped pipe is another configuration that requires lower drilling lengths but it is less used. The aim of the present research
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In vertical closed-loop systems, it is common to use single or double U-tube heat exchangers separated by longitudinal spacers. In addition, the helical-shaped pipe is another configuration that requires lower drilling lengths but it is less used. The aim of the present research is to study the influence of these components on the total efficiency of a borehole heat exchanger (BHE). Thus, the differences between using single/double U-tubes (with or without spacers) and helical pipes are analysed in terms of efficiency. Through different laboratory tests, a small vertical closed-loop system was simulated in order to analyse all these possible configurations. The grouting materials and the temperatures of the ground were modified at the same time in these tests. Regarding the heat exchange process between the ground and the heat carrier fluid, it must be highlighted that the best results were obtained for the helical-shaped pipe configuration. Some of the improvements offered by this heat exchanger typology with respect to the vertical configuration is that a lower drilling depth is required even it requires a larger diameter. This leads to significant economic savings in the performing drilling process. Finally, it is also worth noting the importance of using spacers in vertical U-tubes and that no improvements have been found regarding the use of single or double configuration of U-tubes. Thanks to the laboratory results derived from this study it is possible to establish the optimum behaviour pattern for the entire vertical closed-loop systems. Full article
(This article belongs to the Special Issue Low Enthalpy Geothermal Energy)
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Open AccessArticle From Theory to Econometrics to Energy Policy: Cautionary Tales for Policymaking Using Aggregate Production Functions
Energies 2017, 10(2), 203; doi:10.3390/en10020203
Received: 18 November 2016 / Revised: 16 January 2017 / Accepted: 24 January 2017 / Published: 10 February 2017
Cited by 4 | PDF Full-text (1735 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Development of energy policy is often informed by economic considerations via aggregate production functions (APFs). We identify a theory-to-policy process involving APFs comprised of six steps: (1) selecting a theoretical energy-economy framework; (2) formulating modeling approaches; (3) econometrically fitting an APF to historical
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Development of energy policy is often informed by economic considerations via aggregate production functions (APFs). We identify a theory-to-policy process involving APFs comprised of six steps: (1) selecting a theoretical energy-economy framework; (2) formulating modeling approaches; (3) econometrically fitting an APF to historical economic and energy data; (4) comparing and evaluating modeling approaches; (5) interpreting the economy; and (6) formulating energy and economic policy. We find that choices made in Steps 1–4 can lead to very different interpretations of the economy (Step 5) and policies (Step 6). To investigate these effects, we use empirical data (Portugal and UK) and the Constant Elasticity of Substitution (CES) APF to evaluate four modeling choices: (a) rejecting (or not) the cost-share principle; (b) including (or not) energy; (c) quality-adjusting (or not) factors of production; and (d) CES nesting structure. Thereafter, we discuss two revealing examples for which different upstream modeling choices lead to very different policies. In the first example, the (kl)e nesting structure implies significant investment in energy, while other nesting structures suggest otherwise. In the second example, unadjusted factors of production suggest balanced investment in labor and energy, while quality-adjusting suggests significant investment in labor over energy. Divergent outcomes provide cautionary tales for policymakers: greater understanding of upstream modeling choices and their downstream implications is needed. Full article
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Open AccessArticle Technical Feasibility Study of Thermal Energy Storage Integration into the Conventional Power Plant Cycle
Energies 2017, 10(2), 205; doi:10.3390/en10020205
Received: 7 December 2016 / Revised: 20 January 2017 / Accepted: 1 February 2017 / Published: 11 February 2017
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Abstract
The current load balance in the grid is managed mainly through peaking fossil-fuelled power plants that respond passively to the load changes. Intermittency, which comes from renewable energy sources, imposes additional requirements for even more flexible and faster responses from conventional power plants.
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The current load balance in the grid is managed mainly through peaking fossil-fuelled power plants that respond passively to the load changes. Intermittency, which comes from renewable energy sources, imposes additional requirements for even more flexible and faster responses from conventional power plants. A major challenge is to keep conventional generation running closest to the design condition with higher load factors and to avoid switching off periods if possible. Thermal energy storage (TES) integration into the power plant process cycle is considered as a possible solution for this issue. In this article, a technical feasibility study of TES integration into a 375-MW subcritical oil-fired conventional power plant is presented. Retrofitting is considered in order to avoid major changes in the power plant process cycle. The concept is tested based on the complete power plant model implemented in the ProTRAX software environment. Steam and water parameters are assessed for different TES integration scenarios as a function of the plant load level. The best candidate points for heat extraction in the TES charging and discharging processes are evaluated. The results demonstrate that the integration of TES with power plant cycle is feasible and provide a provisional guidance for the design of the TES system that will result in the minimal influence on the power plant cycle. Full article
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Open AccessArticle A Cell-to-Cell Equalizer Based on Three-Resonant-State Switched-Capacitor Converters for Series-Connected Battery Strings
Energies 2017, 10(2), 206; doi:10.3390/en10020206
Received: 23 December 2016 / Revised: 1 February 2017 / Accepted: 6 February 2017 / Published: 11 February 2017
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Abstract
Due to the low cost, small size, and ease of control, the switched-capacitor (SC) battery equalizers are promising among active balancing methods. However, it is difficult to achieve the full cell equalization for the SC equalizers due to the inevitable voltage drops across
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Due to the low cost, small size, and ease of control, the switched-capacitor (SC) battery equalizers are promising among active balancing methods. However, it is difficult to achieve the full cell equalization for the SC equalizers due to the inevitable voltage drops across Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET) switches. Moreover, when the voltage gap among cells is larger, the balancing efficiency is lower, while the balancing speed becomes slower as the voltage gap gets smaller. In order to soften these downsides, this paper proposes a cell-to-cell battery equalization topology with zero-current switching (ZCS) and zero-voltage gap (ZVG) among cells based on three-resonant-state SC converters. Based on the conventional inductor-capacitor (LC) converter, an additional resonant path is built to release the charge of the capacitor into the inductor in each switching cycle, which lays the foundations for obtaining ZVG among cells, improves the balancing efficiency at a large voltage gap, and increases the balancing speed at a small voltage gap. A four-lithium-ion-cell prototype is applied to validate the theoretical analysis. Experiment results demonstrate that the proposed topology has good equalization performances with fast equalization, ZCS, and ZVG among cells. Full article
(This article belongs to the Special Issue Advanced Energy Storage Technologies and Their Applications (AESA))
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Open AccessArticle Linear Formulation for Short-Term Operational Scheduling of Energy Storage Systems in Power Grids
Energies 2017, 10(2), 207; doi:10.3390/en10020207
Received: 11 July 2016 / Revised: 2 January 2017 / Accepted: 7 February 2017 / Published: 12 February 2017
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Abstract
This paper presents linear programming (LP) formulations for short-term energy time-shift operational scheduling with energy storage systems (ESSs) in power grids. In particular, it is shown that the conventional nonlinear formulations for electric bill minimization, peak shaving, and load leveling can be formulated
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This paper presents linear programming (LP) formulations for short-term energy time-shift operational scheduling with energy storage systems (ESSs) in power grids. In particular, it is shown that the conventional nonlinear formulations for electric bill minimization, peak shaving, and load leveling can be formulated in the LP framework. New variables for the peak and off-peak values are introduced in peak shaving and load leveling model, and the historical peak value for demand charge are considered in the electric bill minimization model. The LP formulations simplify computation while maintaining the accuracy for including linear technical constraints of ESSs, such as the state-of-charge, charging/discharging efficiency, output power range, and energy limit considering the life cycle of ESS. Proposed LP formulations have been implemented and verified in practical power systems and a large-scale industrial customer using historical data. Full article
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Open AccessArticle Peaking China’s CO2 Emissions: Trends to 2030 and Mitigation Potential
Energies 2017, 10(2), 209; doi:10.3390/en10020209
Received: 21 November 2016 / Revised: 16 January 2017 / Accepted: 18 January 2017 / Published: 11 February 2017
Cited by 3 | PDF Full-text (2405 KB) | HTML Full-text | XML Full-text
Abstract
China has submitted its nationally determined contribution to peak its energy-related emissions around 2030. To understand how China might develop its economy while controlling CO2 emissions, this study surveys a number of recent modeling scenarios that project the country’s economic growth, energy
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China has submitted its nationally determined contribution to peak its energy-related emissions around 2030. To understand how China might develop its economy while controlling CO2 emissions, this study surveys a number of recent modeling scenarios that project the country’s economic growth, energy mix, and associated emissions until 2050. Our analysis suggests that China’s CO2 emissions will continue to grow until 2040 or 2050 and will approximately double their 2010 level without additional policy intervention. The alternative scenario, however, suggests that peaking CO2 emissions around 2030 requires the emission growth rate to be reduced by 2% below the reference level. This step would result in a plateau in China’s emissions from 2020 to 2030. This paper also proposed a deep de-carbonization pathway for China that is consistent with China’s goal of peaking emissions by around 2030, which can best be achieved through a combination of improvements in energy and carbon intensities. Our analysis also indicated that the potential for energy intensity decline will be limited over time. Thus, the peaking will be largely dependent on the share of non-fossil fuel energy in primary energy consumption. Full article
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Open AccessArticle Recycling Possibility of the Salty Food Waste by Pyrolysis and Water Scrubbing
Energies 2017, 10(2), 210; doi:10.3390/en10020210
Received: 17 November 2016 / Revised: 19 January 2017 / Accepted: 4 February 2017 / Published: 13 February 2017
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Abstract
Salty food waste is difficult to manage with previous methods such as composting, anaerobic digestion, and incineration, due to the hindrance of salt and the additional burden to handle high concentrations of organic wastewater produced when raw materials are cleaned. This study presents
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Salty food waste is difficult to manage with previous methods such as composting, anaerobic digestion, and incineration, due to the hindrance of salt and the additional burden to handle high concentrations of organic wastewater produced when raw materials are cleaned. This study presents a possibility of recycling food waste as fuel without the burden of treatment washing with water by pyrolyzing and scrubbing. For this purpose, salty food waste with 3% NaCl was made using 10 materials and pyrolysis was conducted at temperature range between 200–400 °C. The result was drawn from elementary analysis (EA), X-ray photoelectron spectroscopy (XPS) analysis, atomic absorption spectrophotometry (AAS) analysis, water quality analysis and calorific value analysis of char, washed char, and washing water. The result of the EA showed that NaCl in food waste could be volatilized at a low pyrolysis temperature of 200–300 °C and it could be concentrated and fixed in char at a high pyrolysis temperature of 300–400 °C. The XPS analysis result showed that NaCl existed in form of chloride. Through the Na content result of the AAS analysis, NaCl remaining in char after water scrubbing was determined to be less than 2%. As the pyrolysis temperature increased, the chemical oxygen demand (COD) value of scrubbing water decreased rapidly, but the total phosphorus and nitrogen contents decreased gradually. The cleaned pyrolysis char showed an increase of higher heating value (HHV) approximately 3667–9920 J/g due to the removal of salt from the char and, especially at 300–400 °C, showed a similar HHV with normal fossil fuels. In conclusion, salty food waste, which is pyrolyzed at a temperature of 300–400 °C and cleaned by water, can be utilized as high-energy refuse derived fuel (RDF), without adverse effects, due to the volatilization of Cl and an additional process of contaminated water. Full article
(This article belongs to the Special Issue Pyrolysis of Biomass)
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Open AccessArticle Hydrothermal Carbonization of Waste Biomass: Process Design, Modeling, Energy Efficiency and Cost Analysis
Energies 2017, 10(2), 211; doi:10.3390/en10020211
Received: 23 December 2016 / Revised: 27 January 2017 / Accepted: 4 February 2017 / Published: 13 February 2017
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Abstract
In this paper, a hydrothermal carbonization (HTC) process is designed and modeled on the basis of experimental data previously obtained for two representative organic waste materials: off-specification compost and grape marc. The process accounts for all the steps and equipment necessary to convert
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In this paper, a hydrothermal carbonization (HTC) process is designed and modeled on the basis of experimental data previously obtained for two representative organic waste materials: off-specification compost and grape marc. The process accounts for all the steps and equipment necessary to convert raw moist biomass into dry and pelletized hydrochar. By means of mass and thermal balances and based on common equations specific to the various equipment, thermal energy and power consumption were calculated at variable process conditions: HTC reactor temperature T: 180, 220, 250 °C; reaction time θ: 1, 3, 8 h. When operating the HTC plant with grape marc (65% moisture content) at optimized process conditions (T = 220 °C; θ = 1 h; dry biomass to water ratio = 0.19), thermal energy and power consumption were equal to 1170 kWh and 160 kWh per ton of hydrochar produced, respectively. Correspondingly, plant efficiency was 78%. In addition, the techno-economical aspects of the HTC process were analyzed in detail, considering both investment and production costs. The production cost of pelletized hydrochar and its break-even point were determined to be 157 €/ton and 200 €/ton, respectively. Such values make the use of hydrochar as a CO2 neutral biofuel attractive. Full article
(This article belongs to the Special Issue Thermo-Chemical Conversion of Waste Biomass)
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Open AccessArticle Effect of Doubly Fed Induction GeneratorTidal Current Turbines on Stability of a Distribution Grid under Unbalanced Voltage Conditions
Energies 2017, 10(2), 212; doi:10.3390/en10020212
Received: 10 September 2016 / Revised: 30 January 2017 / Accepted: 1 February 2017 / Published: 13 February 2017
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Abstract
This paper analyses the effects of doubly fed induction generator (DFIG) tidal current turbines on a distribution grid under unbalanced voltage conditions of the grid. A dynamic model of an electrical power system under the unbalanced network is described in the paper, aiming
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This paper analyses the effects of doubly fed induction generator (DFIG) tidal current turbines on a distribution grid under unbalanced voltage conditions of the grid. A dynamic model of an electrical power system under the unbalanced network is described in the paper, aiming to compare the system performance when connected with and without DFIG at the same location in a distribution grid. Extensive simulations of investigating the effect of DFIG tidal current turbine on stability of the distribution grid are performed, taking into account factors such as the power rating, the connection distance of the turbine and the grid voltage dip. The dynamic responses of the distribution system are examined, especially its ability to ride through fault events under unbalanced grid voltage conditions. The research has shown that DFIG tidal current turbines can provide a good damping performance and that modern DFIG tidal current power plants, equipped with power electronics and low-voltage ride-through capability, can stay connected to weak electrical grids even under the unbalanced voltage conditions, whilst not reducing system stability. Full article
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Open AccessArticle Hybrid System Modeling and Full Cycle Operation Analysis of a Two-Stroke Free-Piston Linear Generator
Energies 2017, 10(2), 213; doi:10.3390/en10020213
Received: 16 December 2016 / Revised: 27 January 2017 / Accepted: 29 January 2017 / Published: 14 February 2017
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Abstract
Free-piston linear generators (FPLGs) have attractive application prospects for hybrid electric vehicles (HEVs) owing to their high-efficiency, low-emissions and multi-fuel flexibility. In order to achieve long-term stable operation, the hybrid system design and full-cycle operation strategy are essential factors that should be considered.
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Free-piston linear generators (FPLGs) have attractive application prospects for hybrid electric vehicles (HEVs) owing to their high-efficiency, low-emissions and multi-fuel flexibility. In order to achieve long-term stable operation, the hybrid system design and full-cycle operation strategy are essential factors that should be considered. A 25 kW FPLG consisting of an internal combustion engine (ICE), a linear electric machine (LEM) and a gas spring (GS) is designed. To improve the power density and generating efficiency, the LEM is assembled with two modular flat-type double-sided PM LEM units, which sandwich a common moving-magnet plate supported by a middle keel beam and bilateral slide guide rails to enhance the stiffness of the moving plate. For the convenience of operation processes analysis, the coupling hybrid system is modeled mathematically and a full cycle simulation model is established. Top-level systemic control strategies including the starting, stable operating, fault recovering and stopping strategies are analyzed and discussed. The analysis results validate that the system can run stably and robustly with the proposed full cycle operation strategy. The effective electric output power can reach 26.36 kW with an overall system efficiency of 36.32%. Full article
(This article belongs to the collection Electric and Hybrid Vehicles Collection)
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Open AccessArticle Stochastic Optimal Control of Parallel Hybrid Electric Vehicles
Energies 2017, 10(2), 214; doi:10.3390/en10020214
Received: 8 September 2016 / Revised: 4 February 2017 / Accepted: 7 February 2017 / Published: 13 February 2017
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Abstract
Energy management strategies (EMSs) in hybrid electric vehicles (HEVs) are highly related to the fuel economy and emission performances. However, EMS constitutes a challenging problem due to the complex structure of a HEV and the unknown or partially known driving cycles. To meet
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Energy management strategies (EMSs) in hybrid electric vehicles (HEVs) are highly related to the fuel economy and emission performances. However, EMS constitutes a challenging problem due to the complex structure of a HEV and the unknown or partially known driving cycles. To meet this problem, this paper adopts a stochastic dynamic programming (SDP) method for the EMS of a specially designed vehicle, a pre-transmission single-shaft torque-coupling parallel HEV. In this parallel HEV, the auto clutch output is connected to the transmission input through an electric motor, which benefits an efficient motor assist operation. In this EMS, demanded torque of driver is modeled as a one-state Markov process to represent the uncertainty of future driving situations. The obtained EMS has been evaluated with ADVISOR2002 over two standard government drive cycles and a self-defined one, and compared with a dynamic programming (DP) one and a rule-based one. Simulation results have shown the real-time performance of the proposed approach, and potential vehicle performance improvement relative to the rule-based one. Full article
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Open AccessArticle An Energy-Based Control Strategy for Battery Energy Storage Systems: A Case Study on Microgrid Applications
Energies 2017, 10(2), 215; doi:10.3390/en10020215
Received: 7 December 2016 / Accepted: 7 February 2017 / Published: 13 February 2017
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Abstract
Battery energy storage systems (BESSs) with proportional-integral (PI) control methods have been widely studied in microgrids (MGs). However, the performance of PI control methods might be unsatisfactory for BESSs due to the nonlinear characteristics of the system. To overcome this problem, an energy-based
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Battery energy storage systems (BESSs) with proportional-integral (PI) control methods have been widely studied in microgrids (MGs). However, the performance of PI control methods might be unsatisfactory for BESSs due to the nonlinear characteristics of the system. To overcome this problem, an energy-based (EB) control method is applied to control the converter of a BESS in this study. The EB method is a robust nonlinear control method based on passivity theory with good performance in both transient and steady states. The detailed design process of the EB method in the BESS by adopting an interconnection and damping assignment (IDA) strategy is described. The design process comprises three steps: the construction of the port-controlled Hamiltonian model, the determination of the equilibrium point and the solution of the undetermined matrix. In addition, integral action is combined to eliminate the steady state error generated by the model mismatch. To establish the correctness and validity of the proposed method, we implement several case simulation studies based on a test MG system and compare the control performance of the EB and PI methods carefully. The case simulation results demonstrate that the EB method has better tracking and anti-disturbance performance compared with the classic PI method. Moreover, the proposed EB method shows stronger robustness to the uncertainty of system parameters. Full article
(This article belongs to the Special Issue Advanced Operation and Control of Smart Microgrids)
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Open AccessArticle A Novel Electric Vehicle Powertrain System Supporting Multi-Path Power Flows: Its Architecture, Parameter Determination and System Simulation
Energies 2017, 10(2), 216; doi:10.3390/en10020216
Received: 10 November 2016 / Accepted: 6 February 2017 / Published: 13 February 2017
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Abstract
In this paper, a novel electric vehicle powertrain system is proposed. In the system, a coaxial magnetic gear (CMG), an electromagnetic clutch, a lock, and two electric machines (EMs) are adopted to achieve the power-split by controlling the states of the clutch and
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In this paper, a novel electric vehicle powertrain system is proposed. In the system, a coaxial magnetic gear (CMG), an electromagnetic clutch, a lock, and two electric machines (EMs) are adopted to achieve the power-split by controlling the states of the clutch and the lock, which enables electric vehicles (EVs) to work in four operation modes. The configuration, power flow paths and operation modes are depicted in detail. A dynamic model is established to help determine the parameters and build simulation models. The simple control strategy is adopted to achieve flexible power-splits. How to determine the relevant parameters to meet the drive requirements in the powertrain system is also elaborated. A dynamic simulation using MATLAB/Simulink is performed to take into account the control strategy and New European Drive Cycle. Finally, the simulation results demonstrate, in theory, the rationality of the determined parameters and the feasibility of the operation modes as well as the control strategy. Full article
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Open AccessArticle A Maximum Efficiency Point Tracking Control Scheme Based on Different Cross Coupling of Dual-Receiver Inductive Power Transfer System
Energies 2017, 10(2), 217; doi:10.3390/en10020217
Received: 15 October 2016 / Accepted: 7 February 2017 / Published: 13 February 2017
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Abstract
One of the most promising inductive power transfer applications is the wireless power supply for locomotives which may cancel the need for pantographs. In order to meet the dynamic and high power demands of wireless power supplies for locomotives, a relatively long transmitter
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One of the most promising inductive power transfer applications is the wireless power supply for locomotives which may cancel the need for pantographs. In order to meet the dynamic and high power demands of wireless power supplies for locomotives, a relatively long transmitter track and multiple receivers are usually adopted. However, during the dynamic charging, the mutual inductances between the transmitter and receivers vary and the load of the locomotives also changes randomly, which dramatically affects the system efficiency. A maximum efficiency point tracking control scheme is proposed to improve the system efficiency against the variation of the load and the mutual inductances between the transmitter and receivers while considering the cross coupling between receivers. Firstly, a detailed theoretical analysis on dual receivers is carried out. Then a control scheme with three control loops is proposed to regulate the receiver currents to be the same, to regulate the output voltage and to search for the maximum efficiency point. Finally, a 2 kW prototype is established to validate the performance of the proposed method. The overall system efficiency (DC-DC efficiency) reaches 90.6% at rated power and is improved by 5.8% with the proposed method under light load compared with the traditional constant output voltage control method. Full article
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Open AccessArticle Geospatial Analysis of Photovoltaic Mini-Grid System Performance
Energies 2017, 10(2), 218; doi:10.3390/en10020218
Received: 2 December 2016 / Revised: 20 January 2017 / Accepted: 2 February 2017 / Published: 15 February 2017
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Abstract
We present a geographic information system (GIS)-based tool for estimating the performance of photovoltaic (PV) mini-grid system over large geographical areas. The methodology consists of geospatial analysis and mapping of the energy output and reliability of PV mini-grid system. The algorithm uses a
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We present a geographic information system (GIS)-based tool for estimating the performance of photovoltaic (PV) mini-grid system over large geographical areas. The methodology consists of geospatial analysis and mapping of the energy output and reliability of PV mini-grid system. The algorithm uses a combination of hourly solar radiation data from satellites combined with measured data on PV module and battery performance and estimated electricity consumption data. The methods also make it possible to optimize the PV array and battery storage size for a given location. Results are presented for an area covering Africa and most of Southern and Central Asia. We also investigate the effects of using Li-ion batteries instead of the traditional lead-acid batteries. The use of our spatial analysis as decision support tool could help governments, local authorities and non-governmental organizations to investigate the suitability of PV mini-grids for electrification of regions where access to electricity is lacking. In this way it is possible to identify areas where PV mini-grids are most suitable. Full article
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Open AccessArticle Thermal Analysis of a Thermal Energy Storage Unit to Enhance a Workshop Heating System Driven by Industrial Residual Water
Energies 2017, 10(2), 219; doi:10.3390/en10020219
Received: 17 December 2016 / Revised: 7 February 2017 / Accepted: 8 February 2017 / Published: 14 February 2017
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Abstract
Various energy sources can be used for room heating, among which waste heat utilization has significantly improved in recent years. However, the majority of applicable waste heat resources are high-grade or stable thermal energy, while the low-grade or unstable waste heat resources, especially
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Various energy sources can be used for room heating, among which waste heat utilization has significantly improved in recent years. However, the majority of applicable waste heat resources are high-grade or stable thermal energy, while the low-grade or unstable waste heat resources, especially low-temperature industrial residual water (IRW), are insufficiently used. A thermal energy storage (TES) unit with paraffin wax as a phase change material (PCM) is designed to solve this problem in a pharmaceutical plant. The mathematical models are developed to simulate the heat storage and release processes of the TES unit. The crucial parameters in the recurrence formulae are determined: the phase change temperature range of the paraffin wax used is 47 to 56 °C, and the latent heat is 171.4 kJ/kg. Several thermal behaviors, such as the changes of melting radius, solidification radius, and fluid temperature, are simulated. In addition, the amount of heat transferred, the heat transfer rate, and the heat storage efficiency are discussed. It is presented that the medicine production unit could save 10.25% of energy consumption in the investigated application. Full article
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Open AccessArticle Robust Clamping Force Control of an Electro-Mechanical Brake System for Application to Commercial City Buses
Energies 2017, 10(2), 220; doi:10.3390/en10020220
Received: 15 December 2016 / Revised: 1 February 2017 / Accepted: 7 February 2017 / Published: 14 February 2017
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Abstract
This paper proposes a sensor-less robust force control method for improving the control performance of an electro-mechanical brake (EMB) which is applicable to commercial city buses. The EMB generates the accurate clamping force commanded by a driver through an independent motor control at
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This paper proposes a sensor-less robust force control method for improving the control performance of an electro-mechanical brake (EMB) which is applicable to commercial city buses. The EMB generates the accurate clamping force commanded by a driver through an independent motor control at each wheel instead of using existing mechanical components. In general, an EMB undergoes parameter variation and a backdrivability problem. For this reason, the cascade control strategy (e.g., force-position cascade control structure) is proposed and the disturbance observer is employed to enhance control robustness against model variations. Additionally, this paper proposed the clamping force estimation method for a sensor-less control, i.e., the clamping force observer (CFO). Finally, in order to confirm the performance and effectiveness of a proposed robust control method, several experiments are performed and analyzed. Full article
(This article belongs to the Special Issue Methods to Improve Energy Use in Road Vehicles)
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Open AccessArticle Computational Study of the Noise Radiation in a Centrifugal Pump When Flow Rate Changes
Energies 2017, 10(2), 221; doi:10.3390/en10020221
Received: 1 December 2016 / Revised: 7 February 2017 / Accepted: 8 February 2017 / Published: 14 February 2017
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Abstract
Noise radiation is of importance for the performance of centrifugal pumps. Aiming at exploring noise radiation patterns of a typical centrifugal pump at different flow rates, a three-dimensional unsteady hydro/aero acoustic model with large eddy simulation (LES) closure is developed. Specifically, the Ffowcs
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Noise radiation is of importance for the performance of centrifugal pumps. Aiming at exploring noise radiation patterns of a typical centrifugal pump at different flow rates, a three-dimensional unsteady hydro/aero acoustic model with large eddy simulation (LES) closure is developed. Specifically, the Ffowcs Williams-Hawkings model (FW-H) is employed to predict noise generation by the impeller and volute. The simulated flow fields reveal that the interactions of the blades with the volute induce root mean square (RMS) pressure and further lead to noise radiation. Moreover, it is found that the profiles of total sound pressure level (TSPL) regarding the directivity field for the impeller-generated noise demonstrate a typical dipole characteristic behavior, whereas strictly the volute-generated noise exhibits an apparently asymmetric behavior. Additionally, the design operation (Here, 1 Q represents the design operation) generates the lowest TSPL vis-a-vis the off-design operations for all the flow rates studied. In general, as the flow rates decrease from 1 Q to 0.25 Q, TSPL initially increases significantly before 0.75 Q and then levels off afterwards. A similar trend appears for cases having the larger flow rates (1–1.25 Q). The TSPL deviates with the radiation directivity and the maximum is about 50%. It is also found that TSPL by the volute and the blades can reach ~87 dB and ~70 dB at most, respectively. The study may offer a priori guidance for the experimental set up and the actual design layout. Full article
(This article belongs to the Special Issue Engineering Fluid Dynamics)
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