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Energies, Volume 12, Issue 16 (August-2 2019)

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Open AccessArticle
Experimental and Numerical Investigation of Wake Interactions of Marine Hydrokinetic Turbines
Energies 2019, 12(16), 3188; https://doi.org/10.3390/en12163188 (registering DOI)
Received: 30 July 2019 / Revised: 12 August 2019 / Accepted: 14 August 2019 / Published: 20 August 2019
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Abstract
To study the performance and environmental impacts of marine hydrokinetic (MHK) turbine arrays, we carry out an investigation based on laboratory experiments and numerical models able to resolve the dynamics of turbulent wake interactions and their effects on the river bed. We investigate [...] Read more.
To study the performance and environmental impacts of marine hydrokinetic (MHK) turbine arrays, we carry out an investigation based on laboratory experiments and numerical models able to resolve the dynamics of turbulent wake interactions and their effects on the river bed. We investigate a scaled Sabella D10 mounted on a mobile bed for a single and two aligned turbines, measuring the flow velocity, the rotor angular velocity, and the scour on the sediment bed. Numerical simulations are performed using a detached-eddy simulation (DES) turbulence model coupled with the blade-element momentum (BEM) approach, which can capture the mean flow and resolve the dynamics of turbulent coherent structures in the wakes. The simulations show a good agreement on the velocity statistics obtained experimentally. Power and thrust coefficients for the downstream turbine show an average decrease and a larger variability due to the turbulent intensity produced by the upstream turbine, as compared to the single turbine case. Results of this investigation also provide a framework to assess the predictive capabilities, scope, and applicability of computational models parameterizing the turbines using BEM, for testing different turbine designs and siting strategies within the MHK array. Full article
(This article belongs to the Special Issue Fluid Dynamics in Marine and Hydrokinetic Energy System)
Open AccessArticle
Optimization of Radio Interference Levels for 500 and 600 kV Bipolar HVDC Transmission Lines
Energies 2019, 12(16), 3187; https://doi.org/10.3390/en12163187 (registering DOI)
Received: 14 June 2019 / Revised: 31 July 2019 / Accepted: 2 August 2019 / Published: 20 August 2019
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Abstract
In this work, a method to compute the radio interference (RI) lateral profiles generated by corona discharge in high voltage direct current (HVDC) transmission lines is presented. The method is based on a transmission line model that considers the skin effect, through the [...] Read more.
In this work, a method to compute the radio interference (RI) lateral profiles generated by corona discharge in high voltage direct current (HVDC) transmission lines is presented. The method is based on a transmission line model that considers the skin effect, through the concept of complex penetration depth, in the conductors and in the ground plane. The attenuation constants are determined from the line parameters and the bipolar system is decoupled by using modal decomposition theory. As application cases, ±500 and ±600 kV bipolar transmission lines were analyzed. Afterwards, parametric sweeps of five variables that affect the RI levels are presented. Both the RI and the maximum electric field were calculated as a function of sub-conductor radius, bundle spacing, and the number of sub-conductors in the bundle. Additionally, the RI levels were also calculated as a function of the soil resistivity, and the RIV (radio interference voltage) frequency. Following this, vector optimization was applied to minimize the RI levels produced by the HVDC lines and differences between the designs with nominal and optimal values are discussed. Full article
Open AccessArticle
Research on Large-Signal Stability of DC Microgrid Based on Droop Control
Energies 2019, 12(16), 3186; https://doi.org/10.3390/en12163186 (registering DOI)
Received: 15 July 2019 / Revised: 16 August 2019 / Accepted: 19 August 2019 / Published: 20 August 2019
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Abstract
Ensuring the large signal stability of the DC microgrid is the premise of the safe operation of the DC microgrid, but the research on the large-signal stability of microgrids with multiple droop control micro-sources is still scarce. In this paper, a DC microgrid [...] Read more.
Ensuring the large signal stability of the DC microgrid is the premise of the safe operation of the DC microgrid, but the research on the large-signal stability of microgrids with multiple droop control micro-sources is still scarce. In this paper, a DC microgrid system model with multiple droop control micro-sources was established by appropriate simplification. Addressing the problem that most stability research methods cannot be quantitatively analyzed, the mixed potential function method was used to analyze the large signal stability of the system. However, the criterion obtained by the conventional mixed potential function method is complicated and contains multiple time-varying parameters, which is not convenient for analysis. Therefore, the simple form of the criterion was obtained through simplification and the analysis proved the rationality of the simplification. On this basis, a nonlinear droop control method was proposed to improve the anti-interference ability of the system. Finally, the accuracy of the large signal stability criterion and the effectiveness of nonlinear droop control on the system’s large signal stability were verified by simulation. Full article
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Open AccessArticle
Numerical Study of Variable Camber Continuous Trailing Edge Flap at Off-Design Conditions
Energies 2019, 12(16), 3185; https://doi.org/10.3390/en12163185 (registering DOI)
Received: 25 May 2019 / Revised: 22 July 2019 / Accepted: 2 August 2019 / Published: 20 August 2019
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Abstract
Numerical simulations are performed to study the outboard airfoil of advanced technology regional aircraft (ATRA) wings with five different variable camber continuous trailing edge flap (VCCTEF) configurations. The computational study aims to improve the aerodynamic efficiency of the airfoil under cruise conditions. The [...] Read more.
Numerical simulations are performed to study the outboard airfoil of advanced technology regional aircraft (ATRA) wings with five different variable camber continuous trailing edge flap (VCCTEF) configurations. The computational study aims to improve the aerodynamic efficiency of the airfoil under cruise conditions. The design of outboard airfoil complies with the hybrid laminar flow control design criteria. This work is unique in terms of analysis of the effects of VCCTEF on the ATRA wing’s outboard airfoil during the off-design condition. The Reynolds–Averaged Navier–Stokes equations coupled with the Spalart-Allmaras turbulence model are employed to perform the simulations for the baseline case and VCCTEF configurations. The current computational study is performed at an altitude of 10 km with a cruise Mach number of 0.77 and a Reynolds number of 2.16 × 107. Amongst all five configurations of VCCTEF airfoils studied, a flap having a parabolic profile (VCCTEF 123) configuration shows the maximum airfoil efficiency and resulted in an increase of 6.3% as compared to the baseline airfoil. Full article
(This article belongs to the Special Issue Modelling of Aerospace Vehicle Dynamics)
Open AccessArticle
Pre- and Post-Adoption Beliefs about the Diffusion and Continuation of Biogas-Based Cooking Fuel Technology in Pakistan
Energies 2019, 12(16), 3184; https://doi.org/10.3390/en12163184 (registering DOI)
Received: 30 June 2019 / Revised: 11 August 2019 / Accepted: 14 August 2019 / Published: 20 August 2019
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Abstract
A high level of acceptance and adoption is necessary to facilitate the widespread utilization of renewable energy technologies for cooking, as such utilization is essential for displacing the population’s massive dependence on fossil fuels and solid biomass. Economic and demographic aspects have been [...] Read more.
A high level of acceptance and adoption is necessary to facilitate the widespread utilization of renewable energy technologies for cooking, as such utilization is essential for displacing the population’s massive dependence on fossil fuels and solid biomass. Economic and demographic aspects have been the focus of recent literature in exploring the adoption phenomenon of biogas technology. However, literature to date has given little attention to the behavioral factors and the perceptions of the end-users. Our study does not only include behavioral factors, but it employs a hybrid model to explore the continued attentions of users based on their post-adoption beliefs and performance expectations. Using a survey conducted in Pakistan in 2017, the study conducts a multivariate analysis through structural equation modeling to measure the effect of pre- and post-adoption beliefs and expectation on adoption and the continuing intention of households towards biogas technology. Results show that the acceptance of the households towards biogas technology is highly influenced by their perceptions on the benefits, as well as their trust in the technology. The perceived cost and risk attached to the technology are found to be negatively correlated with the acceptance. Households’ intentions to continue the use of biogas technology is highly influenced by the satisfaction level of the users of biogas technology. With the integrated model of adoption and continuation, the study illustrates the dynamic process in obtaining a deeper understanding of a user’s behavior to better formulate the policies for increasing the rate of technology adoption. Full article
Open AccessArticle
Overpressure Generation Mechanisms and Its Distribution in the Paleocene Shahejie Formation in the Linnan Sag, Huimin Depression, Eastern China
Energies 2019, 12(16), 3183; https://doi.org/10.3390/en12163183 (registering DOI)
Received: 23 June 2019 / Revised: 5 August 2019 / Accepted: 15 August 2019 / Published: 20 August 2019
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Abstract
The Linnan Sag is one of the main oil-producing units in the Huimin Depression, Eastern China, and the pore pressure gradients obtained from drill stem tests (DSTs) range from 9.0 to 16.0 MPa/km. Uncertainty about the origin and distribution of abnormally high pressures [...] Read more.
The Linnan Sag is one of the main oil-producing units in the Huimin Depression, Eastern China, and the pore pressure gradients obtained from drill stem tests (DSTs) range from 9.0 to 16.0 MPa/km. Uncertainty about the origin and distribution of abnormally high pressures in the Linnan Sag has led to different interpretations of hydrocarbon accumulation and resource assessments, and it interferes with safe drilling. In the Linnan Sag, mudstone compaction curves are substantially affected by several non-compaction factors, and the normal trend of the compaction curve is difficult to determine. The determination of the origin and distribution of overpressure in the Linnan Sag is a challenge. In this study, the factors that may affect mudstone compaction—such as the shale volume, higher calcareous, and organic matter content—were carefully examined and processed. The pressures in the mudstones were estimated by the corrected mudstone compaction curves, which were compiled from acoustic, density, and neutron logs, and calibrated using DST and mud weight data. The log response–vertical effective stress and acoustic velocity-density crossplots were used to identify the mechanisms that generate overpressure. The comprehensive compaction curve shows that the mudstones in the overpressured layer exhibit clear disequilibrium compaction characteristics. The logging response crossplots demonstrate that those overpressured points were consistent with the loading curve. The findings suggest that, the fundamental mechanism resulting in overpressures is the disequilibrium compaction of thick Paleocene mudstones. Hydrocarbon generation and vertical transfer of overpressure may be the main unloading mechanisms, which corresponds to the overpressure points that deviate from the loading curves. Since organic matter cracking may occur in formations at depths greater than 4000 m (Ro > 1.0%), the contribution of hydrocarbon generation to overpressuring is expected to be limited. The transfer of overpressure through opening faults is therefore considered to be the main cause of higher overpressure in local sandstones. The overpressures in the mudstones are characterized by a gradual decrease from the center to the margin in the Linnan Sag. The pressure in the isolated sand bodies are generally similar to that in the surrounding mudstones, whereas it can be lower or higher when the overpressure in the sand bodies are vertically transferred by faults to other pressure systems. The results of this analysis provide an indication of the magnitude, mechanism, and distribution of overpressure in the Linnan Sag. This insight can be used to guide further exploration of the Linnan Sag and similar geological basins. Full article
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Open AccessArticle
Robust Direct Adaptive Controller Design for Photovoltaic Maximum Power Point Tracking Application
Energies 2019, 12(16), 3182; https://doi.org/10.3390/en12163182 (registering DOI)
Received: 12 July 2019 / Revised: 29 July 2019 / Accepted: 8 August 2019 / Published: 20 August 2019
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Abstract
Tracking the maximum output power of a photovoltaic (PV) cell is an important problem to harvest more energy at different weather and load conditions. This paper presents the design and simulation of a robust direct adaptive controller (RDAC) for maximum power point tracking [...] Read more.
Tracking the maximum output power of a photovoltaic (PV) cell is an important problem to harvest more energy at different weather and load conditions. This paper presents the design and simulation of a robust direct adaptive controller (RDAC) for maximum power point tracking (MPPT) device based on boost converter topology. A mathematical model is developed, and a suitable RDAC is designed for MPPT device, and simulations are performed using MATLAB/Simulink to verify the controller’s robustness at varying operating conditions. The real-time irradiance and temperature data are used on an hourly basis to test the suggested MPPT adaptive controller for a typical sunny day in summer and winter. The simulation results show that the RDAC performs excellent tracking under varying conditions such as irradiance, temperature, load, boost converter inductance, and capacitance. Full article
(This article belongs to the Section Solar Energy and Photovoltaic Systems)
Open AccessArticle
Active Fluidic Turn-Down Rectifier
Energies 2019, 12(16), 3181; https://doi.org/10.3390/en12163181
Received: 5 May 2019 / Revised: 24 June 2019 / Accepted: 27 June 2019 / Published: 19 August 2019
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Abstract
Paper discusses a device belonging into an interesting and yet little-known family of no-moving-part active fluidic rectifiers. The generated steady component of flow and pressure are driven by input alternating flow from an external source. The absence of moving components results in the [...] Read more.
Paper discusses a device belonging into an interesting and yet little-known family of no-moving-part active fluidic rectifiers. The generated steady component of flow and pressure are driven by input alternating flow from an external source. The absence of moving components results in the unique capability of unlimited life and reliability, especially useful for safety devices. In the experiment, the rectifier generated a pressure keeping dangerous liquid in the active zone. When the driving oscillation stops (like, e.g., due to coolant loss), the liquid leaves the zone under gravity, stopping the performed reaction. This safety facility is simple, inexpensive, and extremely reliable. Full article
(This article belongs to the Special Issue Fluid Mechanics and Thermodynamics: Theory, Methods and Applications)
Open AccessArticle
Robust Integral Backstepping Based Nonlinear MPPT Control for a PV System
Energies 2019, 12(16), 3180; https://doi.org/10.3390/en12163180
Received: 4 July 2019 / Revised: 9 August 2019 / Accepted: 12 August 2019 / Published: 19 August 2019
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Abstract
A photovoltaic system generates energy that depends on the environmental conditions such as temperature, irradiance and the variations in the load connected to it. To adapt to the consistently increasing interest of energy, the photovoltaic (PV) system must operate at maximum power point [...] Read more.
A photovoltaic system generates energy that depends on the environmental conditions such as temperature, irradiance and the variations in the load connected to it. To adapt to the consistently increasing interest of energy, the photovoltaic (PV) system must operate at maximum power point (MPP), however, it has the issue of low efficiency because of the varying climatic conditions. To increase its efficiency, a maximum power point technique is required to extract maximum power from the PV system. In this paper, a nonlinear fast and efficient maximum power point tracking (MPPT) technique is developed based on the robust integral backstepping (RIB) approach to harvest maximum power from a PV array using non-inverting DC-DC buck-boost converter. The study uses a NeuroFuzzy network to generate the reference voltage for MPPT. Asymptotic stability of the whole system is verified using Lyapunov stability criteria. The MATLAB/Simulink platform is used to test the proposed controller performance under varying meteorological conditions. The simulation results validate that the proposed controller effectively improves the MPPT in terms of tracking speed and efficiency. For further validation of the proposed controller performance, a comparative study is presented with backstepping controller, integral backstepping, robust backstepping and conventional MPPT algorithms (PID and P&O) under rapidly varying environmental conditions. Full article
(This article belongs to the Section Solar Energy and Photovoltaic Systems)
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Open AccessArticle
Economic Analysis of an Integrated Production–Inventory System under Stochastic Production Capacity and Energy Consumption
Energies 2019, 12(16), 3179; https://doi.org/10.3390/en12163179
Received: 1 June 2019 / Revised: 8 August 2019 / Accepted: 14 August 2019 / Published: 19 August 2019
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Abstract
Expensive power cost is a significant concern in today’s manufacturing world. Reduction in energy consumption is an ultimate measure towards achieving manufacturing efficiency and emissions control. In the existing literature of scheduling problems, the consumption of energy is considered uncertain under the dimensions [...] Read more.
Expensive power cost is a significant concern in today’s manufacturing world. Reduction in energy consumption is an ultimate measure towards achieving manufacturing efficiency and emissions control. In the existing literature of scheduling problems, the consumption of energy is considered uncertain under the dimensions of uncertain demand and supply. In reality, it is a random parameter that also depends on production capacity, manufacturing technology, and operational condition of the manufacturing system. As the unit production cost varies with production rate and reliability of the manufacturing system, the energy consumption of the system also varies accordingly. Therefore, this study investigated an unreliable manufacturing system under stochastic production capacities and energy consumption. A stochastic production–inventory policy is developed to optimize production quantity, production rate, and manufacturing reliability under variable energy consumption costs. As energy consumption varies in different operational states of manufacturing, we consider three specific states of power consumption, namely working, idle, and repair time, for an integrated production–maintenance model. The considered production system is subjected to stochastic failure and repair time, where productivity and manufacturing reliability is improved through additional technology investment. The robustness of the model is shown through numerical example, comparative study, and sensitivity analysis of model parameters. Several graphical illustrations are also provided to obtain meaningful managerial insights. Full article
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Open AccessArticle
Characteristic Analysis of DFIG Wind Turbine under Blade Mass Imbalance Fault in View of Wind Speed Spatiotemporal Distribution
Energies 2019, 12(16), 3178; https://doi.org/10.3390/en12163178
Received: 8 July 2019 / Revised: 13 August 2019 / Accepted: 14 August 2019 / Published: 19 August 2019
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Abstract
The blade mass imbalance fault is one of the common faults of the DFIG (Doubly-Fed Induction Generator) wind turbines (WTs). In this paper, considering the spatiotemporal distribution of natural wind speed and the influence of wind shear and tower shadow effect, the influence [...] Read more.
The blade mass imbalance fault is one of the common faults of the DFIG (Doubly-Fed Induction Generator) wind turbines (WTs). In this paper, considering the spatiotemporal distribution of natural wind speed and the influence of wind shear and tower shadow effect, the influence of blade mass imbalance faults on the electrical characteristics of DFIG WTs is analyzed. Firstly, the analytical expressions and variation characteristics of electromagnetic torque and electromagnetic power under blade mass imbalance are derived before and after consideration of the spatiotemporal distribution of wind speed. Then simulations on the MATLAB/Simulink platform were done to verify the theoretical analysis results. The theoretical analysis and simulation results show that, considering the spatiotemporal distribution of wind speed and the influence of wind shear and tower shadow effect, the blade mass imbalance fault will cause fluctuation at the frequency of 1P (P = the frequency of rotor rotation), 3P, and 6P on electromagnetic power. Fluctuation at 1P is caused by mass imbalance while fluctuation at 3P and 6P are caused by wind speed spatiotemporal distribution; the amplitude of fluctuation at 1P is proportional to the degree of the imbalance fault. Since the equivalent wind speed has been used in this paper instead of the average wind speed, the data is more suitable for the actual operation of the WT in the natural world and can be applied for fault diagnosis in field WT operation. Full article
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Open AccessFeature PaperArticle
Linearized Discrete Charge Balance Control with Simplified Algorithm for DCM Buck Converter
Energies 2019, 12(16), 3177; https://doi.org/10.3390/en12163177
Received: 29 July 2019 / Revised: 14 August 2019 / Accepted: 16 August 2019 / Published: 19 August 2019
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Abstract
In this paper, a linearized discrete charge balance (LDCB) control strategy is proposed for buck converter operating in discontinuous conduction mode (DCM). For DC-DC power converters, discrete charge balance (DCB) control is an attractive approach to improve the output voltage transient response. However, [...] Read more.
In this paper, a linearized discrete charge balance (LDCB) control strategy is proposed for buck converter operating in discontinuous conduction mode (DCM). For DC-DC power converters, discrete charge balance (DCB) control is an attractive approach to improve the output voltage transient response. However, as a non-linear control strategy, the algorithm is complex, which is difficult for implementation. To reduce the complexity, this paper proposes the LDCB control strategy that is derived through linearizing conventional DCB controller. By deriving the differential functions of the DCB control algorithm, the small signal relationship between the input and output of DCB controller is explored. Furthermore, based on the relationship, the LDCB controller is formed through three parallel feed loops to the duty ratio. As a linear control approach, the achieved LDCB controller is greatly simplified for implementation. This not only saves the hardware cost, but also reduces the calculation lag, which provides potential to improve the switching frequency. Besides, since the LDCB controller shares the same small signal model as that of DCB controller, it achieves similar control loop bandwidth and transient performance. Effectiveness of the proposed LDCB control is verified by zero/pole plots, transient analyses and experimental results. Full article
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Open AccessArticle
Proton Exchange Membrane Fuel Cell Stack Design Optimization Using an Improved Jaya Algorithm
Energies 2019, 12(16), 3176; https://doi.org/10.3390/en12163176
Received: 21 June 2019 / Revised: 12 August 2019 / Accepted: 12 August 2019 / Published: 19 August 2019
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Abstract
Fuel cell stack configuration optimization is known to be a problem that, in addition to presenting engineering challenges, is computationally hard. This paper presents an improved computational heuristic for solving the problem. The problem addressed in this paper is one of constrained optimization, [...] Read more.
Fuel cell stack configuration optimization is known to be a problem that, in addition to presenting engineering challenges, is computationally hard. This paper presents an improved computational heuristic for solving the problem. The problem addressed in this paper is one of constrained optimization, where the goal is to seek optimal (or near-optimal) values of (i) the number of proton exchange membrane fuel cells (PEMFCs) to be connected in series to form a group, (ii) the number of such groups to be connected in parallel, and (iii) the cell area, such that the PEMFC assembly delivers the rated voltage at the rated power while the cost of building the assembly is as low as possible. Simulation results show that the proposed method outperforms four of the best-known methods in the literature. The improvement in performance afforded by the proposed algorithm is validated with statistical tests of significance. Full article
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Open AccessArticle
Desiccant-Assisted Air Conditioning System Relying on Solar and Geothermal Energy during Summer and Winter
Energies 2019, 12(16), 3175; https://doi.org/10.3390/en12163175
Received: 19 July 2019 / Revised: 14 August 2019 / Accepted: 15 August 2019 / Published: 19 August 2019
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Abstract
At Hamburg University of Technology the combination of an open cycle desiccant-assisted air conditioning system and a geothermal system is investigated in the framework of different research projects for several years. The objective of this study is to investigate the energy efficiency of [...] Read more.
At Hamburg University of Technology the combination of an open cycle desiccant-assisted air conditioning system and a geothermal system is investigated in the framework of different research projects for several years. The objective of this study is to investigate the energy efficiency of the overall system and to evaluate the geothermal system during summer and winter mode, based on data measured for a temperate climate region. Monitoring results of the performance for dehumidification and remoistening of supply air are presented. Furthermore, the investigated system is compared to reference air conditioning processes. During summer mode, an average dehumidification efficiency of 1.15 is achieved. The electrical energy savings compared to a conventional reference system sum up to 50% for the investigated cooling period. System operation during winter shows an average moisture recovery efficiency of 0.75. The electrical energy demand for air humidification is reduced by 50% compared to a system with electric isothermal air humidification. The geothermal system is operated efficiently throughout the year for cooling and heating application. Besides the energetic system evaluation, measured data regarding the soil temperature and thermal comfort are presented. Full article
(This article belongs to the Special Issue Alternative Energy Systems in Buildings)
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Open AccessArticle
Design and Implementation of a Low Power Outer-Rotor Line-Start Permanent-Magnet Synchronous Motor for Ultra-Light Electric Vehicles
Energies 2019, 12(16), 3174; https://doi.org/10.3390/en12163174
Received: 5 July 2019 / Revised: 10 August 2019 / Accepted: 13 August 2019 / Published: 19 August 2019
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Abstract
Recently, while electric vehicles (EV) have substituted the fossil fuel vehicles, the design of the electrical motors with more efficient and less mechanical converters has become mandatory due to the weighting gears, mechanical differentials, and other cost-increasing parts. To overcome these problems, double [...] Read more.
Recently, while electric vehicles (EV) have substituted the fossil fuel vehicles, the design of the electrical motors with more efficient and less mechanical converters has become mandatory due to the weighting gears, mechanical differentials, and other cost-increasing parts. To overcome these problems, double electrical motors with low speed and high torque have been designed and used in the rear wheels of the EVs without any gearbox and mechanical differential. In this study, a novel outer rotor line-start hybrid synchronous motor is proposed as another solution. For this aim, four different hybrid rotor types, including magnets and rotor bars, have been designed and analyzed. Calculation and estimation of all parameters to design a motor are introduced. All of the analyses were carried out by Finite Elements Method (FEM). One of the analyzed motors, which is called Type-D was selected and implemented because of the best startup performance and better steady-state behavior under the rated load and overload. While holding this motor at synchronous speed under nominal load, in case of overloading, it remained in asynchronous mode, thus maintaining the sustainability of the system. Obtained results prove that the newly proposed outer rotor LSSM has the advantages of both synchronous motor and asynchronous motor. All of the experimental results validate the simulations well. The effects of the magnet alignments and dimensions on the performance of the motors are presented. Full article
(This article belongs to the Section Electric Vehicles)
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Open AccessArticle
Influence of Different Biofuels on the Efficiency of Gas Turbine Cycles for Prosumer and Distributed Energy Power Plants
Energies 2019, 12(16), 3173; https://doi.org/10.3390/en12163173
Received: 27 July 2019 / Revised: 14 August 2019 / Accepted: 16 August 2019 / Published: 19 August 2019
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Abstract
The efficiency of a gas turbine can be affected by the use of different biofuels usually with a relatively Lower Heating Value (LHV). The paper evaluates the impact of calorific value of fuel on turbine performance and analyzes the possibilities of optimizing turbine [...] Read more.
The efficiency of a gas turbine can be affected by the use of different biofuels usually with a relatively Lower Heating Value (LHV). The paper evaluates the impact of calorific value of fuel on turbine performance and analyzes the possibilities of optimizing turbine construction from the point of view of maximum efficiency for a particular fuel. The several variants of design of small power microturbines dedicated to various biofuels are analyzed. The calculations were carried out for: gas from biomass gasification (LHV = 4.4 MJ/kg), biogas (LHV = 17.5 MJ/kg) and methane (LHV = 50 MJ/kg). It is demonstrated that analyzed solution enables construction of several kW power microturbines that might be used on a local scale. Careful design of such devices allows for achieving high efficiency with appropriate choice of the turbine construction for specific fuel locally available. Such individually created generation systems might be applied in distributed generation systems assuring environmental profits. Full article
(This article belongs to the Special Issue Assessment of Energy–Environment–Economy Interrelations)
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Open AccessArticle
Pipeline Leak Detection and Location Based on Model-Free Isolation of Abnormal Acoustic Signals
Energies 2019, 12(16), 3172; https://doi.org/10.3390/en12163172
Received: 21 June 2019 / Revised: 8 August 2019 / Accepted: 16 August 2019 / Published: 18 August 2019
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Abstract
Pipeline leaks will lead to energy waste, environmental pollution and a threat to human safety. This paper proposes a pipeline leak detection and location method based on the model-free isolation of abnormal (leak and operation) signals. An acoustic signal is first decomposed into [...] Read more.
Pipeline leaks will lead to energy waste, environmental pollution and a threat to human safety. This paper proposes a pipeline leak detection and location method based on the model-free isolation of abnormal (leak and operation) signals. An acoustic signal is first decomposed into “sub-signals” according to its zero-crossing points. Then, based on the definition of signal-to-noise ratio (SNR), the function between the SNR of sub-signal and the number of abnormal sub-signals is established, following which the position of each abnormal sub-signal in the acoustic signal is obtained by tracing its index. Based on this and the cross-correlation analysis, the operation sub-signals can be filtered, which is helpful for the precise leak location. The experimental results demonstrate the computational efficiency and lower false/missing alarm rate of the proposed method that provides an innovative solution for pipeline leak detection. Full article
(This article belongs to the Section Energy Sources)
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Open AccessArticle
Power Output Enhancement of a Ducted Wind Turbine by Stabilizing Vortices around the Duct
Energies 2019, 12(16), 3171; https://doi.org/10.3390/en12163171
Received: 8 June 2019 / Revised: 7 August 2019 / Accepted: 14 August 2019 / Published: 18 August 2019
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Abstract
A brimmed-diffuser augmented turbine (called a wind lens turbine: WLT) actively uses vortices around the brim to enhance its power output. However, the vortices are usually unstable and asymmetric. This study attempted to stabilize the vortices to enhance the power output of a [...] Read more.
A brimmed-diffuser augmented turbine (called a wind lens turbine: WLT) actively uses vortices around the brim to enhance its power output. However, the vortices are usually unstable and asymmetric. This study attempted to stabilize the vortices to enhance the power output of a WLT. Then, we investigated new approaches using vortex stabilization plates and polygonal brims in wind tunnel experiments and numerical simulations. Both approaches achieved a 1.5–3.8% increase in power output compared with a standard WLT. Our numerical simulations revealed a periodicity existing in a fluctuating vortex structure on the circular brim. Importantly, vortex stabilization plates and polygonal brims must be the same periodic scale to suppress the vortex fluctuation and stabilize the vortices effectively. In addition, a larger brim tended to enhance the stabilizing effects. We believe that this discovery provides an easy way to increase the power output of existing wind turbines. It is particularly important in light of advances in wind energy technology and the increasing wind energy market. Full article
(This article belongs to the Section Wind, Wave and Tidal Energy)
Open AccessArticle
Vehicle Optimal Control Design to Meet the 1.5 °C Target: A Control Design Framework for Vehicle Subsystems
Energies 2019, 12(16), 3170; https://doi.org/10.3390/en12163170
Received: 26 June 2019 / Revised: 6 August 2019 / Accepted: 14 August 2019 / Published: 18 August 2019
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Abstract
Current studies have achieved energy savings of vehicle subsystems through various control strategies, but these control strategies lack a benchmark to measure whether these energy savings are sufficient. This work proposes a control design framework that uses the 1.5 °C target in the [...] Read more.
Current studies have achieved energy savings of vehicle subsystems through various control strategies, but these control strategies lack a benchmark to measure whether these energy savings are sufficient. This work proposes a control design framework that uses the 1.5 °C target in the Paris Agreement as a benchmark to measure the adequacy of energy savings of vehicle subsystems. This control design framework involves two points. One is the conversion of the 1.5 °C target into a constraint on the energy consumption of a vehicle subsystem. The other is the optimal control design of the vehicle subsystem under this constraint. To describe the specific application of this control design framework, we conduct a case study concerning the control design of active suspension in a battery electric light-duty vehicle. By comparison with a widely used linear quadratic regulator (LQR) method, we find that this control design framework can both ensure the performance comparable to the LQR method and help to meet the 1.5 °C target in the Paris Climate Agreement. In addition, a sensitivity analysis shows that the control effect is hardly changed by battery electric vehicle market share and electricity CO2 intensity. This work might provide insight on ways that the automotive industry could contribute to the Paris Agreement. Full article
(This article belongs to the Section Energy and Environment)
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Open AccessArticle
Contribution to the Energy Situation in Tajikistan by Using Residual Apricot Branches after Pruning as an Alternative Fuel
Energies 2019, 12(16), 3169; https://doi.org/10.3390/en12163169
Received: 25 July 2019 / Revised: 11 August 2019 / Accepted: 15 August 2019 / Published: 18 August 2019
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Abstract
A lack of access to energy in the rural areas of Tajikistan is one of the current problems of the country. Tajikistan’s goal is to reach energy independency, and the main prospects for the country’s energy sector, which relies on energy imports during [...] Read more.
A lack of access to energy in the rural areas of Tajikistan is one of the current problems of the country. Tajikistan’s goal is to reach energy independency, and the main prospects for the country’s energy sector, which relies on energy imports during the long heating periods, are: higher exploitations of hydropower and development of other renewables, mainly biofuels. Tajikistan is a highly agrarian country, where agriculture is the dominant source of income for the majority of the population. Apricot belongs to the primary agricultural commodities; however, the cultivation and management of apricot orchards is associated with the annual accumulation of significant amounts of wood waste (residual branches after pruning), which represent a source of easily available biomass. Thus, the main focus of the present research was to investigate the properties (physical, chemical and mechanical) of densified briquettes and pellets from the residual apricot tree branches through the laboratory measurements by the standard methodologies and to calculate the energy yield and potential of this material for Tajikistan as a similar study has not been conducted yet. The results showed a good quality of apricot-based biofuels characterised by the high calorific value (NCV dry basis of 19.3 MJ kg−1), relatively low ash content (1.7%) and suitable values of the main chemical elements that fulfil the standard requirement on graded wooden biofuels. The total yearly energy yield of residual apricot branches was calculated to be 3245 TJ. Full article
(This article belongs to the Special Issue Renewable energy solutions for the Baltic–Nordic region)
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Open AccessFeature PaperArticle
Modeling Future Energy Demand and CO2 Emissions of Passenger Cars in Indonesia at the Provincial Level
Energies 2019, 12(16), 3168; https://doi.org/10.3390/en12163168
Received: 9 July 2019 / Revised: 9 August 2019 / Accepted: 12 August 2019 / Published: 17 August 2019
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Abstract
The high energy demand and CO2 emissions in the road transport sector in Indonesia are mainly caused by the use of passenger cars. This situation is predicted to continue due to the increase in car ownership. Scenarios are arranged to examine the [...] Read more.
The high energy demand and CO2 emissions in the road transport sector in Indonesia are mainly caused by the use of passenger cars. This situation is predicted to continue due to the increase in car ownership. Scenarios are arranged to examine the potential reductions in energy demand and CO2 emissions in comparison with the business as usual (BAU) condition between 2016 and 2050 by controlling car intensity (fuel economy) and activity (vehicle-km). The intensity is controlled through the introduction of new car technologies, while the activity is controlled through the enactment of fuel taxes. This study aims to analyze the energy demand and CO2 emissions of passenger cars in Indonesia not only for a period in the past (2010–2015) but also based on projections through to 2050, by employing a provincially disaggregated bottom-up model. The provincially disaggregated model shows more accurate estimations for passenger car energy demands. The results suggest that energy demand and CO2 emissions in 2050 will be 50 million liter gasoline equivalent (LGE) and 110 million tons of CO2, respectively. The five provinces with the highest CO2 emissions in 2050 are projected to be West Java, Banten, East Java, Central Java, and South Sulawesi. The projected analysis for 2050 shows that new car technology and fuel tax scenarios can reduce energy demand from the BAU condition by 7.72% and 3.18% and CO2 emissions by 15.96% and 3.18%, respectively. Full article
(This article belongs to the Special Issue End-Users’ Perspectives on Energy Policy and Technology)
Open AccessReview
Phase Change Materials (PCM) for Solar Energy Usages and Storage: An Overview
Energies 2019, 12(16), 3167; https://doi.org/10.3390/en12163167
Received: 28 July 2019 / Revised: 14 August 2019 / Accepted: 15 August 2019 / Published: 17 August 2019
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Abstract
Solar energy is a renewable energy source that can be utilized for different applications in today’s world. The effective use of solar energy requires a storage medium that can facilitate the storage of excess energy, and then supply this stored energy when it [...] Read more.
Solar energy is a renewable energy source that can be utilized for different applications in today’s world. The effective use of solar energy requires a storage medium that can facilitate the storage of excess energy, and then supply this stored energy when it is needed. An effective method of storing thermal energy from solar is through the use of phase change materials (PCMs). PCMs are isothermal in nature, and thus offer higher density energy storage and the ability to operate in a variable range of temperature conditions. This article provides a comprehensive review of the application of PCMs for solar energy use and storage such as for solar power generation, water heating systems, solar cookers, and solar dryers. This paper will benefit the researcher in conducting further research on solar power generation, water heating system, solar cookers, and solar dryers using PCMs for commercial development. Full article
Open AccessArticle
Study of a Low-Power-Consumption Piezoelectric Energy Harvesting Circuit Based on Synchronized Switching Technology
Energies 2019, 12(16), 3166; https://doi.org/10.3390/en12163166
Received: 20 June 2019 / Revised: 2 August 2019 / Accepted: 15 August 2019 / Published: 17 August 2019
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Abstract
This paper presents a study of a piezoelectric energy harvesting circuit based on low-power-consumption synchronized switch technology. The proposed circuit includes a parallel synchronized switch harvesting on inductor interface circuit (P-SSHI) and a step-down DC-DC converter. The synchronized switch technology is applied to [...] Read more.
This paper presents a study of a piezoelectric energy harvesting circuit based on low-power-consumption synchronized switch technology. The proposed circuit includes a parallel synchronized switch harvesting on inductor interface circuit (P-SSHI) and a step-down DC-DC converter. The synchronized switch technology is applied to increase the conversion efficiency of the circuit. The DC-DC converter is used to accomplish the impedance matching for different loads. A low-power-consumption microcontroller and discrete components are used to build the P-SSHI interface circuit. The study starts with theoretical analysis and simulations of the P-SSHI interface circuit. Simulations and experiments were conducted to validate the theoretical analysis. The experimental results show that the maximum energy harvested by the system with a P-SSHI interface circuit is 231 μW, which is 2.89 times that of a system without the P-SSHI scheme. The power consumption of the P-SSHI interface circuit can be as low as 10.6 μW. Full article
(This article belongs to the Section Energy Sources)
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Open AccessArticle
Endoreversible Trigeneration Cycle Design Based on Finite Physical Dimensions Thermodynamics
Energies 2019, 12(16), 3165; https://doi.org/10.3390/en12163165
Received: 28 June 2019 / Revised: 15 August 2019 / Accepted: 16 August 2019 / Published: 17 August 2019
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Abstract
This paper focuses on the finite physical dimensions thermodynamics (FPDT)-based design of combined endoreversible power and refrigeration cycles (CCHP). Four operating schemes were analyzed, one for the summer season and three for the winter season. These basic CCHP cycles should define the reference [...] Read more.
This paper focuses on the finite physical dimensions thermodynamics (FPDT)-based design of combined endoreversible power and refrigeration cycles (CCHP). Four operating schemes were analyzed, one for the summer season and three for the winter season. These basic CCHP cycles should define the reference ones, having the maximum possible energy and exergy efficiencies considering real restrictive conditions. The FPDT design is an entropic approach because it defines and uses the dependences between the reference entropy and the control operational parameters characterizing the external energy interactions of CCHP subsystems. The FPDT introduces a generalization of CCHP systems design, due to the particular influences of entropy variations of the working fluids substituted with influences of four operational finite dimensions control parameters, i.e., two mean log temperature differences between the working fluids and external heat sources and two dimensionless thermal conductance inventories. Two useful energy interactions, power and cooling rate, were used as operational restrictive conditions. It was assumed that there are consumers required for the supplied heating rates depending on the energy operating scheme. The FPDT modeling evaluates main thermodynamic and heat transfer performances. The FPDT model presented in this paper is a general one, applicable to all endoreversible trigeneration cycles. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
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Open AccessArticle
Research on Double-Layer Optimal Scheduling Model of Integrated Energy Park Based on Non-Cooperative Game
Energies 2019, 12(16), 3164; https://doi.org/10.3390/en12163164
Received: 8 July 2019 / Revised: 6 August 2019 / Accepted: 14 August 2019 / Published: 16 August 2019
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Abstract
As the realization form of integrated energy system, integrated energy park is the key research object in the field of energy. Actual integrated energy parks are often partitioned internally. In order to take into account the interests of each zone in the optimal [...] Read more.
As the realization form of integrated energy system, integrated energy park is the key research object in the field of energy. Actual integrated energy parks are often partitioned internally. In order to take into account the interests of each zone in the optimal scheduling of integrated energy parks, a double-layer optimal scheduling model of integrated energy parks based on non-cooperative game theory is proposed. First, according to the operation of the integrated energy park, the output and cost model of the park is established. Second, with the minimum daily cost as the upper layer objective and the highest energy efficiency of the cogeneration system as the lower layer objective, a double-layer optimal scheduling model is established. Then based on non-cooperative game, the optimal operation strategy of each zone is obtained through the game among all the zones. An integrated energy park is taken as an example, the results show that the proposed model can make zones adjust their operation strategies more reasonably, thus helping to reduce the cost of the park and improve energy efficiency. Full article
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Open AccessArticle
A New Improved Voltage Stability Assessment Index-centered Integrated Planning Approach for Multiple Asset Placement in Mesh Distribution Systems
Energies 2019, 12(16), 3163; https://doi.org/10.3390/en12163163
Received: 16 July 2019 / Revised: 6 August 2019 / Accepted: 11 August 2019 / Published: 16 August 2019
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Abstract
This paper offers a new improved voltage stability assessment index (VSAI_B)-centered planning approach, aiming at the attainment of technical and cost related objectives with simultaneous multiple asset deployment in a mesh distribution systems (MDS). The assets such as multiple distributed generation [...] Read more.
This paper offers a new improved voltage stability assessment index (VSAI_B)-centered planning approach, aiming at the attainment of technical and cost related objectives with simultaneous multiple asset deployment in a mesh distribution systems (MDS). The assets such as multiple distributed generation (DG) and distributed static compensator (D-STATCOM) units have been utilized; aiming at voltage stabilization, loss minimization, and associated objectives. The proposed planning approach incorporates expressions of VSAI_B aiming at initial simultaneous assets placement followed by loss minimization conditions (LMC) for appropriate asset sizing, which is further utilized for performance evaluations. The VSAI_B-LMC-based integrated planning approach is applied to configured MDS models such as a 33-bus test distribution system (TDS) for detailed analysis. The performance evaluations with the presented approach have been conducted for different cases along with respective scenarios considering various technical and cost-economic performance metrics. First, three cases referring to multiple DGs sitting and sizing for various power factors have been presented, followed later by two cases of multiple DGs and D-STATCOMs with respective evaluation scenarios. Finally, benchmark analysis is conducted on a 69-bus TDS for validity demonstration of the proposed approach. The comparison of achieved results in comparison with the available literature points out toward the validity and improved performance of the proposed approach. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle
An Improved Assessment Method for FMEA for a Shipboard Integrated Electric Propulsion System Using Fuzzy Logic and DEMATEL Theory
Energies 2019, 12(16), 3162; https://doi.org/10.3390/en12163162
Received: 4 July 2019 / Revised: 4 August 2019 / Accepted: 14 August 2019 / Published: 16 August 2019
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Abstract
Shipboard integrated electric propulsion systems (IEPSs) are prone to suffer from system failures and security threats because of their complex functional structures and poor operational environments. An improved assessment method for failure mode and effects analysis (FMEA), integrating fuzzy logic and decision–making trial [...] Read more.
Shipboard integrated electric propulsion systems (IEPSs) are prone to suffer from system failures and security threats because of their complex functional structures and poor operational environments. An improved assessment method for failure mode and effects analysis (FMEA), integrating fuzzy logic and decision–making trial and evaluation laboratory (DEMATEL) theory, is proposed to enhance the system’s reliability and handle the correlation effects between failure modes and causes. In this method, information entropy and qualitative analysis are synthesized to determine the credibility weights of domain experts. Each risk factor and its relative importance are evaluated by linguistic terms and fuzzy ratings. The benchmark adjustment search algorithm is designed to obtain the alpha-level sets of fuzzy risk priority numbers (RPNs) for defuzzification. The defuzzified RPNs are regarded as the inputs for the DEMATEL technique to investigate the causal degrees of failure modes and causes. Accordingly, the risk levels of the failure modes are prioritized with respect to the causal degrees. The practical application to the typical failure modes of the propulsion subsystem is provided. The assessment results show that this system contributes to risk priority decision-making and disastrous accident prevention. Full article
(This article belongs to the Special Issue Reliability of Power Electronic Systems)
Open AccessArticle
Establishment, Validation, and Application of a Comprehensive Thermal Hydraulic Model for a Parabolic Trough Solar Field
Energies 2019, 12(16), 3161; https://doi.org/10.3390/en12163161
Received: 11 July 2019 / Revised: 5 August 2019 / Accepted: 9 August 2019 / Published: 16 August 2019
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Abstract
To better understand the thermal hydraulic characteristics of the parabolic trough solar field (PTSF), a comprehensive thermal hydraulic model (CTHM) based on a pilot plant is developed in this paper. All of the main components and thermal and hydraulic transients are considered in [...] Read more.
To better understand the thermal hydraulic characteristics of the parabolic trough solar field (PTSF), a comprehensive thermal hydraulic model (CTHM) based on a pilot plant is developed in this paper. All of the main components and thermal and hydraulic transients are considered in the CTHM, and the input parameters of the model are no longer dependent on the total flow rate. In this paper, we solve the CTHM by a novel numerical approach based on graph theory and the Newton-Raphson method, and then examine it by two tests conducted based on a pilot plant. Comparing the flow rate, temperature, and pressure drop results show good agreement and further validate the availability and accuracy of the CTHM under hydraulic and thermal disturbance. Besides, two applications of the CTHM are implemented for presenting its potential function. In the first application, two cases are simulated to reveal how the thermal effects influence the PTSF behavior, and in the second application, the CHTF is used for the study of control strategies under uniform and nonuniform solar irradiance. The results verify the feasibility of controlling the PTSF outlet temperature through the header and loop valves. Full article
(This article belongs to the Special Issue Research on Solar Collector)
Open AccessArticle
An Effective Passive Islanding Detection Algorithm for Distributed Generations
Energies 2019, 12(16), 3160; https://doi.org/10.3390/en12163160
Received: 1 July 2019 / Revised: 11 August 2019 / Accepted: 12 August 2019 / Published: 16 August 2019
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Abstract
Different issues will be raised and highlighted by emerging distributed generations (DGs) into modern power systems in which the islanding detection is the most important. In the islanding situation, a part of the system which consists of at least one DG, passive grid, [...] Read more.
Different issues will be raised and highlighted by emerging distributed generations (DGs) into modern power systems in which the islanding detection is the most important. In the islanding situation, a part of the system which consists of at least one DG, passive grid, and local load, becomes fully separated from the main grid. Several detection methods of islanding have been proposed in recent researches based on measured electrical parameters of the system. However, islanding detection based on local measurements suffers from the non-detection zone (NDZ) and undesirable detection during grid-connected events. This paper proposes a passive islanding detection algorithm for all types of DGs by appropriate combining the measured frequency, voltage, current, and phase angle and their rate of changes at the point of common coupling (PCC). The proposed algorithm detects the islanding situation, even with the exact zero power mismatches. Proposed algorithm discriminates between the islanding situation and non-islanding disturbances, such as short circuit faults, capacitor faults, and load switching in a proper time and without mal-operation. In addition, the performance of the proposed algorithm has been evaluated under different scenarios by performing the algorithm on the IEEE 13-bus distribution system. Full article
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Open AccessArticle
Study on Fault Current Characteristics and Current Limiting Method of Plug-In Devices in VSC-DC Distribution System
Energies 2019, 12(16), 3159; https://doi.org/10.3390/en12163159
Received: 19 June 2019 / Revised: 10 August 2019 / Accepted: 14 August 2019 / Published: 16 August 2019
Viewed by 207 | PDF Full-text (964 KB)
Abstract
The DC (Direct Current) distribution system based on the voltage source converter (VSC-DC) has become a research hotspot due to its various advantages. There are many plug-in devices in the VSC-DC distribution system, which may be damaged by the fault current. Therefore, studying [...] Read more.
The DC (Direct Current) distribution system based on the voltage source converter (VSC-DC) has become a research hotspot due to its various advantages. There are many plug-in devices in the VSC-DC distribution system, which may be damaged by the fault current. Therefore, studying the fault current characteristics and current limiting method is one of the key methods to ensure the safe and stable operation of the VSC-DC distribution system. Based on theoretical analysis and simulation calculations, this paper studies the causes, influencing factors, and current limiting methods of the fault current when the pole-to-pole fault occurs at the line side of plug-in devices in a ±10 kV VSC-DC distribution system. Firstly, based on the system topology, the decisive fault condition of fault current and the design principle of current limiting reactor value are analyzed. Secondly, the theoretical calculation methods of fault current and current limiting reactor value which satisfies the breaking capacity of DC circuit breaker are proposed. Finally, the accuracy of theoretical calculation methods is verified by simulation in PSCAD/EMTDC (Power Systems Computer Aided Design/ Electromagnetic Transients including DC). The research results could provide the theoretical calculation methods of the fault current and the current limiting reactor value of plug-in devices in the ±10 kV VSC-DC distribution system. Full article
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