Previous Issue

E-Mail Alert

Add your e-mail address to receive forthcoming issues of this journal:

Journal Browser

Journal Browser

Table of Contents

Energies, Volume 10, Issue 8 (August 2017)

  • Issues are regarded as officially published after their release is announced to the table of contents alert mailing list.
  • You may sign up for e-mail alerts to receive table of contents of newly released issues.
  • PDF is the official format for papers published in both, html and pdf forms. To view the papers in pdf format, click on the "PDF Full-text" link, and use the free Adobe Readerexternal link to open them.
Cover Story For a long time, the development of electric vehicles has run up against electrical storage [...] Read more.
View options order results:
result details:
Displaying articles 1-159
Export citation of selected articles as:

Research

Jump to: Review, Other

Open AccessArticle A Smart Forecasting Approach to District Energy Management
Energies 2017, 10(8), 1073; doi:10.3390/en10081073
Received: 15 May 2017 / Revised: 9 July 2017 / Accepted: 14 July 2017 / Published: 25 July 2017
PDF Full-text (6620 KB) | HTML Full-text | XML Full-text
Abstract
This study presents a model for district-level electricity demand forecasting using a set of Artificial Neural Networks (ANNs) (parallel ANNs) based on current energy loads and social parameters such as occupancy. A comprehensive sensitivity analysis is conducted to select the inputs of the
[...] Read more.
This study presents a model for district-level electricity demand forecasting using a set of Artificial Neural Networks (ANNs) (parallel ANNs) based on current energy loads and social parameters such as occupancy. A comprehensive sensitivity analysis is conducted to select the inputs of the ANN by considering external weather conditions, occupancy type, main income providers’ employment status and related variables for the fuel poverty index. Moreover, a detailed parameter tuning is conducted using various configurations for each individual ANN. The study also demonstrates the strength of the parallel ANN models in different seasons of the years. In the proposed district level energy forecasting model, the training and testing stages of parallel ANNs utilise dataset of a group of six buildings. The aim of each individual ANN is to predict electricity consumption and the aggregated demand in sub-hourly time-steps. The inputs of each ANN are determined using Principal Component Analysis (PCA) and Multiple Regression Analysis (MRA) methods. The accuracy and consistency of ANN predictions are evaluated using Pearson coefficient and average percentage error, and against four seasons: winter, spring, summer, and autumn. The lowest prediction error for the aggregated demand is about 4.51% for winter season and the largest prediction error is found as 8.82% for spring season. The results demonstrate that peak demand can be predicted successfully, and utilised to forecast and provide demand-side flexibility to the aggregators for effective management of district energy systems. Full article
(This article belongs to the Special Issue Zero-Carbon Buildings)
Figures

Figure 1

Open AccessFeature PaperArticle Parametric Investigation Using Computational Fluid Dynamics of the HVAC Air Distribution in a Railway Vehicle for Representative Weather and Operating Conditions
Energies 2017, 10(8), 1074; doi:10.3390/en10081074
Received: 26 June 2017 / Revised: 18 July 2017 / Accepted: 19 July 2017 / Published: 25 July 2017
PDF Full-text (5009 KB) | HTML Full-text | XML Full-text
Abstract
A computational fluid dynamics (CFD) analysis of air distribution in a representative railway vehicle equipped with a heating, ventilation, air conditioning (HVAC) system is presented in this paper. Air distribution in the passenger’s compartment is a very important factor to regulate temperature and
[...] Read more.
A computational fluid dynamics (CFD) analysis of air distribution in a representative railway vehicle equipped with a heating, ventilation, air conditioning (HVAC) system is presented in this paper. Air distribution in the passenger’s compartment is a very important factor to regulate temperature and air velocity in order to achieve thermal comfort. A complete CFD model, including the car’s geometry in detail, the passengers, the luminaires, and other the important features related to the HVAC system (air supply inlets, exhaust outlets, convectors, etc.) are developed to investigate eight different typical scenarios for Northern Europe climate conditions. The results, analyzed and discussed in terms of temperature and velocity fields in different sections of the tram, and also in terms of volumetric parameters representative of the whole tram volume, show an adequate behavior from the passengers’ comfort point of view, especially for summer climate conditions. Full article
(This article belongs to the Special Issue Engineering Fluid Dynamics)
Figures

Figure 1

Open AccessArticle Estimating Lithium-Ion Battery State of Charge and Parameters Using a Continuous-Discrete Extended Kalman Filter
Energies 2017, 10(8), 1075; doi:10.3390/en10081075
Received: 8 June 2017 / Revised: 21 July 2017 / Accepted: 22 July 2017 / Published: 25 July 2017
PDF Full-text (4826 KB) | HTML Full-text | XML Full-text
Abstract
A real-time determination of battery parameters is challenging because batteries are non-linear, time-varying systems. The transient behaviour of lithium-ion batteries is modelled by a Thevenin-equivalent circuit with two time constants characterising activation and concentration polarization. An experimental approach is proposed for directly determining
[...] Read more.
A real-time determination of battery parameters is challenging because batteries are non-linear, time-varying systems. The transient behaviour of lithium-ion batteries is modelled by a Thevenin-equivalent circuit with two time constants characterising activation and concentration polarization. An experimental approach is proposed for directly determining battery parameters as a function of physical quantities. The model’s parameters are a function of the state of charge and of the discharge rate. These can be expressed by regression equations in the model to derive a continuous-discrete extended Kalman estimator of the state of charge and of other parameters. This technique is based on numerical integration of the ordinary differential equations to predict the state of the stochastic dynamic system and the corresponding error covariance matrix. Then a standard correction step of the extended Kalman filter (EKF) is applied to increase the accuracy of estimated parameters. Simulations resulting from this proposed estimator model were compared with experimental results under a variety of operating scenarios—analysis of the results demonstrate the accuracy of the estimator for correctly identifying battery parameters. Full article
Figures

Figure 1

Open AccessArticle Real-Time Analysis of a Modified State Observer for Sensorless Induction Motor Drive Used in Electric Vehicle Applications
Energies 2017, 10(8), 1077; doi:10.3390/en10081077
Received: 5 May 2017 / Revised: 30 June 2017 / Accepted: 3 July 2017 / Published: 25 July 2017
PDF Full-text (9458 KB) | HTML Full-text | XML Full-text
Abstract
The purpose of this work is to present an adaptive sliding mode Luenberger state observer with improved disturbance rejection capability and better tracking performance under dynamic conditions. The sliding hyperplane is altered by incorporating the estimated disturbance torque with the stator currents. In
[...] Read more.
The purpose of this work is to present an adaptive sliding mode Luenberger state observer with improved disturbance rejection capability and better tracking performance under dynamic conditions. The sliding hyperplane is altered by incorporating the estimated disturbance torque with the stator currents. In addition, the effects of parameter detuning on the speed convergence are observed and compared with the conventional disturbance rejection mechanism. The entire drive system is first built in the Simulink environment. Then, the Simulink model is integrated with real-time (RT)-Lab blocksets and implemented in a relatively new real-time environment using OP4500 real-time simulator. Real-time simulation and testing platforms have succeeded offline simulation and testing tools due to their reduced development time. The real-time results validate the improvement in the proposed state observer and also correspond to the performance of the actual physical model. Full article
Figures

Figure 1

Open AccessArticle Heat Transfer Fluid Temperature Control in a Thermoelectric Solar Power Plant
Energies 2017, 10(8), 1078; doi:10.3390/en10081078
Received: 10 May 2017 / Revised: 17 July 2017 / Accepted: 21 July 2017 / Published: 25 July 2017
PDF Full-text (3924 KB) | HTML Full-text | XML Full-text
Abstract
Thermoelectric solar plants transform solar energy into electricity. Unlike photovoltaic plants, the sun’s energy heats a fluid (heat transfer fluid (HTF)) and this, in turn, exchanges its energy, generating steam. Finally, the steam generates electricity in a Rankine cycle. One of the main
[...] Read more.
Thermoelectric solar plants transform solar energy into electricity. Unlike photovoltaic plants, the sun’s energy heats a fluid (heat transfer fluid (HTF)) and this, in turn, exchanges its energy, generating steam. Finally, the steam generates electricity in a Rankine cycle. One of the main advantages of this double conversion (sun energy to heat in the HTF-Rankine cycle) is the fact that it facilitates energy storage without using batteries. It is possible to store the heat energy in melted salts in such a way that this energy will be recovered when necessary, i.e., during the night. These molten salts are stored in containers in a liquid state at high temperature. The HTF comes into the solar field at a given temperature and increases its energy thanks to the solar collectors. In order to optimize the sun to HTF energy transference, it is necessary to keep an adequate temperature control of the fluid at the output of the solar fields. This paper describes three different algorithms to control the HTF output temperature. Full article
(This article belongs to the Section Energy Storage and Application)
Figures

Figure 1

Open AccessArticle Analysis and Experiment of Hot-Spot Temperature Rise of 110 kV Three-Phase Three-Limb Transformer
Energies 2017, 10(8), 1079; doi:10.3390/en10081079
Received: 28 June 2017 / Revised: 15 July 2017 / Accepted: 18 July 2017 / Published: 25 July 2017
PDF Full-text (4569 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a fluid-thermal coupled analysis method to compute the temperature distribution in a 31.5 MVA/110 kV oil natural air natural (ONAN) three-phase three-limb transformer. The power losses of windings and core are measured by load-loss test and no-load test respectively. The
[...] Read more.
This paper presents a fluid-thermal coupled analysis method to compute the temperature distribution in a 31.5 MVA/110 kV oil natural air natural (ONAN) three-phase three-limb transformer. The power losses of windings and core are measured by load-loss test and no-load test respectively. The convective heat transfer process, radiation and oil flow inside the transformer are investigated by finite volume method (FVM). In order to validate the feasibility and accuracy of the presented method, the temperature measuring system based on fiber Brag grating (FBG) sensor is constructed for the temperature rise test of the 31.5 MVA/110 kV ONAN transformer. The simulation results deduced from the proposed method agree well with experimental data. This model can be applied to optimizing design and load scheduling. Full article
Figures

Figure 1

Open AccessArticle An Improved Droop Control Strategy Based on Changeable Reference in Low-Voltage Microgrids
Energies 2017, 10(8), 1080; doi:10.3390/en10081080
Received: 10 May 2017 / Revised: 9 June 2017 / Accepted: 20 July 2017 / Published: 26 July 2017
PDF Full-text (2193 KB) | HTML Full-text | XML Full-text
Abstract
This paper proposes an improved droop control strategy based on changeable reference in low-voltage microgrids. To restore running frequency of distributed generation to a rated value without affecting its reactive power output, changeable frequency reference, mainly compensating for frequency deviation, are proposed corresponding
[...] Read more.
This paper proposes an improved droop control strategy based on changeable reference in low-voltage microgrids. To restore running frequency of distributed generation to a rated value without affecting its reactive power output, changeable frequency reference, mainly compensating for frequency deviation, are proposed corresponding to various load demands. In terms of active power sharing inaccuracy associated with mismatched line impedance, changeable voltage amplitude reference is proposed to obtain a droop line suitable for the actual voltage of distributed generations. By further improvement of the active droop coefficient, power sharing is accurate with a difference in actual voltages of distributed generations. Virtual negative inductance is used to neutralize the redundant line inductance for strictly improving sharing accuracy. A robust control method based on Lyapunov function is used to handle the robustness problem in case of load variation. The control scheme is entirely decentralized, so communication links among distributed generations are redundant. Finally, simulation studies demonstrate the effectiveness of a control strategy. Full article
(This article belongs to the Special Issue Control and Communication in Distributed Generation Systems)
Figures

Figure 1

Open AccessArticle Automatic Faulted Feeder Section Location and Isolation Method for Power Distribution Systems Considering the Change of Topology
Energies 2017, 10(8), 1081; doi:10.3390/en10081081
Received: 30 March 2017 / Revised: 27 May 2017 / Accepted: 18 July 2017 / Published: 25 July 2017
PDF Full-text (6465 KB) | HTML Full-text | XML Full-text
Abstract
The increasing use of modern measuring devices, such as Feeder Terminal Units (FTUs), on power networks can provide multiple types of information for fault location on distribution systems. Using these devices, in this paper, a novel automatic matrix-based algorithm for the identification and
[...] Read more.
The increasing use of modern measuring devices, such as Feeder Terminal Units (FTUs), on power networks can provide multiple types of information for fault location on distribution systems. Using these devices, in this paper, a novel automatic matrix-based algorithm for the identification and isolation of faulted feeder sections on distribution systems is proposed. The algorithm works in two stages: the first stage automatically identifies the radial feeders that make up the whole system and represents the feeders’ topology in matrix form; and the second stage automatically identifies the faulted section of the identified feeder and opens the relevant switches to isolate it. The algorithm can be applied to single and multiple faults, as it operates using measuring device information and detecting the status of switch devices. It does not require any electrical parameters and it is not affected by the fault type or fault resistance. The algorithm was thoroughly tested using a large distribution system and was found to efficiently identify and isolate the faulted feeder section in each case. Full article
(This article belongs to the Section Electrical Power and Energy System)
Figures

Figure 1

Open AccessArticle Nonlinear Observer-Based Robust Passive Control of Doubly-Fed Induction Generators for Power System Stability Enhancement via Energy Reshaping
Energies 2017, 10(8), 1082; doi:10.3390/en10081082
Received: 20 May 2017 / Revised: 18 July 2017 / Accepted: 21 July 2017 / Published: 25 July 2017
PDF Full-text (4771 KB) | HTML Full-text | XML Full-text
Abstract
The large-scale penetration of wind power might lead to degradation of the power system stability due to its inherent feature of randomness. Hence, proper control designs which can effectively handle various uncertainties become very crucial. This paper designs a novel robust passive control
[...] Read more.
The large-scale penetration of wind power might lead to degradation of the power system stability due to its inherent feature of randomness. Hence, proper control designs which can effectively handle various uncertainties become very crucial. This paper designs a novel robust passive control (RPC) scheme of a doubly-fed induction generator (DFIG) for power system stability enhancement. The combinatorial effect of generator nonlinearities and parameter uncertainties, unmodelled dynamics, wind speed randomness, is aggregated into a perturbation, which is rapidly estimated by a nonlinear extended state observer (ESO) in real-time. Then, the perturbation estimate is fully compensated by a robust passive controller to realize a globally consistent control performance, in which the energy of the closed-loop system is carefully reshaped through output feedback passification, such that a considerable system damping can be injected to improve the transient responses of DFIG in various operation conditions of power systems. Six case studies are carried out while simulation results verify that RPC can rapidly stabilize the disturbed DFIG system much faster with less overshoot, as well as supress power oscillations more effectively compared to that of linear proportional-integral-derivative (PID) control and nonlinear feedback linearization control (FLC). Full article
(This article belongs to the Special Issue Sustainable Energy Technologies)
Figures

Figure 1

Open AccessFeature PaperArticle A Polar Fuzzy Control Scheme for Hybrid Power System Using Vehicle-To-Grid Technique
Energies 2017, 10(8), 1083; doi:10.3390/en10081083
Received: 12 May 2017 / Revised: 8 June 2017 / Accepted: 27 June 2017 / Published: 25 July 2017
PDF Full-text (2560 KB) | HTML Full-text | XML Full-text
Abstract
A novel polar fuzzy (PF) control approach for a hybrid power system is proposed in this research. The proposed control scheme remedies the issues of system frequency and the continuity of demand supply caused by renewable sources’ uncertainties. The hybrid power system consists
[...] Read more.
A novel polar fuzzy (PF) control approach for a hybrid power system is proposed in this research. The proposed control scheme remedies the issues of system frequency and the continuity of demand supply caused by renewable sources’ uncertainties. The hybrid power system consists of a wind turbine generator (WTG), solar photovoltaics (PV), a solar thermal power generator (STPG), a diesel engine generator (DEG), an aqua-electrolyzer (AE), an ultra-capacitor (UC), a fuel-cell (FC), and a flywheel (FW). Furthermore, due to the high cost of the battery energy storage system (BESS), a new idea of vehicle-to-grid (V2G) control is applied to use the battery of the electric vehicle (EV) as equivalent to large-scale energy storage units instead of small batteries to improve the frequency stability of the system. In addition, EV customers’ convenience is taken into account. A minimal-order observer is used to estimate the supply error. Then, the area control error (ACE) signal is calculated in terms of the estimated supply error and the frequency deviation. ACE is considered in the frequency domain. Two PF approaches are utilized in the intended system. The mission of each controller is to mitigate one frequency component of ACE. The responsibility for ACE compensation is shared among all parts of the system according to their speed of response. The performance of the proposed control scheme is compared to the conventional fuzzy logic control (FLC). The effectiveness and robustness of the proposed control technique are verified by numerical simulations under various scenarios. Full article
Figures

Figure 1

Open AccessArticle An Approach of Quantifying Gear Fatigue Life for Wind Turbine Gearboxes Using Supervisory Control and Data Acquisition Data
Energies 2017, 10(8), 1084; doi:10.3390/en10081084
Received: 27 June 2017 / Revised: 20 July 2017 / Accepted: 21 July 2017 / Published: 25 July 2017
PDF Full-text (9025 KB) | HTML Full-text | XML Full-text
Abstract
Quantifying wind turbine (WT) gearbox fatigue life is a critical problem for preventive maintenance when unsolved. This paper proposes a practical approach that uses ten minutes’ average wind speed of Supervisory Control and Data Acquisition (SCADA) data to quantify a WT gearbox’s gear
[...] Read more.
Quantifying wind turbine (WT) gearbox fatigue life is a critical problem for preventive maintenance when unsolved. This paper proposes a practical approach that uses ten minutes’ average wind speed of Supervisory Control and Data Acquisition (SCADA) data to quantify a WT gearbox’s gear fatigue life. Wind turbulence impacts on gearbox fatigue are studied thoroughly. Short-term fatigue assessment for the gearbox is then performed using linear fatigue theory by considering WT responses under external and internal excitation. The results shows that for a three stage gearbox, the sun gear in the first stage and pinions in the 2nd and 3rd stage are the most vulnerable parts. High mean wind speed, especially above the rated range, leads to a high risk of gearbox fatigue damage. Increase of wind turbulence may not increase fatigue damage as long as a WT has an instant response to external excitation. An approach of using SCADA data recorded every ten minutes to quantify gearbox long-term damages is presented. The calculation results show that the approach effectively presents gears’ performance degradation by quantifying their fatigue damage. This is critical to improve WT reliability and meaningful for WT gearbox fatigue assessment theory. The result provides useful tools for future wind farm prognostic maintenance. Full article
Figures

Figure 1

Open AccessArticle Correlation Characteristics Comparison of SF6 Decomposition versus Gas Pressure under Negative DC Partial Discharge Initiated by Two Typical Defects
Energies 2017, 10(8), 1085; doi:10.3390/en10081085
Received: 19 June 2017 / Revised: 15 July 2017 / Accepted: 21 July 2017 / Published: 25 July 2017
PDF Full-text (6316 KB) | HTML Full-text | XML Full-text
Abstract
Aimed to clarify the correlation characteristics between the internal partial discharge (PD) in negative direct current (DC) gas insulated system (GIS) and gas pressure initiated by two typical defects (i.e., free-metal particles and metal protrusion), this study on PD decomposition of sulfur hexafluoride
[...] Read more.
Aimed to clarify the correlation characteristics between the internal partial discharge (PD) in negative direct current (DC) gas insulated system (GIS) and gas pressure initiated by two typical defects (i.e., free-metal particles and metal protrusion), this study on PD decomposition of sulfur hexafluoride (SF6) was investigated under different pressures on the basis of constructing a SF6 decomposition experimental platform with DC PD. Free-metal particles and metal protrusion in a GIS were simulated using a spherical-bowl electrode and a needle-plate electrode, respectively. Trends and differences in the performance of SF6 decomposition components SOF2, SO2F2, CO2, and SO2 at different pressures were compared and analyzed by experiments under different defects. Based on gas microscopic ionization theory, the relationship between the decomposition component and gas pressure was deduced and verified. The concentrations of different decomposition components were found to vary with the change in gas pressure under different defects, whereas the characteristic ratios of decomposition components versus gas pressure showed a similar trend. Full article
Figures

Figure 1

Open AccessArticle Investigation on the Development of a Sliding Mode Controller for Constant Power Loads in Microgrids
Energies 2017, 10(8), 1086; doi:10.3390/en10081086
Received: 17 May 2017 / Revised: 22 June 2017 / Accepted: 18 July 2017 / Published: 26 July 2017
PDF Full-text (7156 KB) | HTML Full-text | XML Full-text
Abstract
To implement renewable energy resources, microgrid systems have been adopted and developed into the technology of choice to assure mass electrification in the next decade. Microgrid systems have a number of advantages over conventional utility grid systems, however, they face severe instability issues
[...] Read more.
To implement renewable energy resources, microgrid systems have been adopted and developed into the technology of choice to assure mass electrification in the next decade. Microgrid systems have a number of advantages over conventional utility grid systems, however, they face severe instability issues due to the continually increasing constant power loads. To improve the stability of the entire system, the load side compensation technique is chosen because of its robustness and cost effectiveness. In this particular occasion, a sliding mode controller is developed for a microgrid system in the presence of constant power loads to assure a certain control objective of keeping the output voltage constant at 480 V. After that, a robustness analysis of the sliding mode controller against parametric uncertainties was performed and the sliding mode controller’s robustness against parametric uncertainties, frequency variations, and additive white Gaussian noise (AWGN) are presented. Later, the performance of the proportional integral derivative (PID) and sliding mode controller are compared in the case of nonlinearity, parameter uncertainties, and noise rejection to justify the selection of the sliding mode controller over the PID controller. All the necessary calculations are reckoned mathematically and results are verified in a virtual platform such as MATLAB/Simulink with a positive outcome. Full article
(This article belongs to the Special Issue Innovative Methods for Smart Grids Planning and Management)
Figures

Figure 1

Open AccessArticle A Comparative Study of the Effect of Turbocompounding and ORC Waste Heat Recovery Systems on the Performance of a Turbocharged Heavy-Duty Diesel Engine
Energies 2017, 10(8), 1087; doi:10.3390/en10081087
Received: 31 May 2017 / Revised: 20 July 2017 / Accepted: 21 July 2017 / Published: 26 July 2017
PDF Full-text (3634 KB) | HTML Full-text | XML Full-text
Abstract
In this study the influence of utilization of two Waste Heat Recovery (WHR) strategies, namely organic Rankine cycle (ORC) and turbocompounding, have been investigated based on the performance of a heavy-duty diesel engine using 1-D simulation engine code (GT-Power) in terms of Brake
[...] Read more.
In this study the influence of utilization of two Waste Heat Recovery (WHR) strategies, namely organic Rankine cycle (ORC) and turbocompounding, have been investigated based on the performance of a heavy-duty diesel engine using 1-D simulation engine code (GT-Power) in terms of Brake Specific Fuel Consumptions (BSFC) at various engine speeds and Brake Mean Effective Pressures (BMEP). The model of a 6-cylinder turbocharged engine (Holset HDX55V) was calibrated using an experimental BSFC map to predict engine exhaust thermodynamic conditions such as exhaust mass flow rate and exhaust temperature under various operating conditions. These engine exhaust conditions were then utilized to feed the inlet conditions for both the ORC and turbocompounding models, evaluating the available exhaust energy to be recovered by each technology. Firstly the ORC system model was simulated to obtain the power that can be generated from the system. Having this additional power converted to useful work, the BSFC was observed to reduce around 2–5% depending upon engine’s speed and BMEP. The initial model of the engine was then modified by considering a second turbine representing turbocompounding heat recovery system. The BSFC was increased due to the back-pressure from the second turbine, but the energy generated from the turbine was sufficient to reduce the BSFC further. However, by application of turbocompounding no improvement in BSFC was achieved at low engine’s speeds. It is concluded that ORC heat recovery system produces a satisfactory results at low engine speeds with both low and high loads whereas at medium and high engine speeds turbocompounding heat recovery system causes higher BSFC reduction. Full article
(This article belongs to the Special Issue Automotive Engines Emissions and Control)
Figures

Figure 1

Open AccessArticle Power System Event Ranking Using a New Linear Parameter-Varying Modeling with a Wide Area Measurement System-Based Approach
Energies 2017, 10(8), 1088; doi:10.3390/en10081088
Received: 16 May 2017 / Revised: 28 June 2017 / Accepted: 19 July 2017 / Published: 26 July 2017
PDF Full-text (1929 KB) | HTML Full-text | XML Full-text
Abstract
Detecting critical power system events for Dynamic Security Assessment (DSA) is required for reliability improvement. The approach proposed in this paper investigates the effects of events on dynamic behavior during nonlinear system response while common approaches use steady-state conditions after events. This paper
[...] Read more.
Detecting critical power system events for Dynamic Security Assessment (DSA) is required for reliability improvement. The approach proposed in this paper investigates the effects of events on dynamic behavior during nonlinear system response while common approaches use steady-state conditions after events. This paper presents some new and enhanced indices for event ranking based on time-domain simulation and polytopic linear parameter-varying (LPV) modeling of a power system. In the proposed approach, a polytopic LPV representation is generated via linearization about some points of the nonlinear dynamic behavior of power system using wide-area measurement system (WAMS) concepts and then event ranking is done based on the frequency response of the system models on the vertices. Therefore, the nonlinear behaviors of the system in the time of fault occurrence are considered for events ranking. The proposed algorithm is applied to a power system using nonlinear simulation. The comparison of the results especially in different fault conditions shows the advantages of the proposed approach and indices. Full article
(This article belongs to the Section Electrical Power and Energy System)
Figures

Figure 1

Open AccessArticle An Improved Time-Frequency Analysis Method for Hydrocarbon Detection Based on EWT and SET
Energies 2017, 10(8), 1090; doi:10.3390/en10081090
Received: 6 July 2017 / Revised: 21 July 2017 / Accepted: 24 July 2017 / Published: 26 July 2017
PDF Full-text (2918 KB) | HTML Full-text | XML Full-text
Abstract
Oil and gas reservoirs can cause increased attenuation of seismic waves, which can be revealed by time-frequency analysis for direct detection of hydrocarbons. In this paper, a new method applying the empirical wavelet transform (EWT) in association with the synchroextracting transform (SET), named
[...] Read more.
Oil and gas reservoirs can cause increased attenuation of seismic waves, which can be revealed by time-frequency analysis for direct detection of hydrocarbons. In this paper, a new method applying the empirical wavelet transform (EWT) in association with the synchroextracting transform (SET), named EWT-SET, is proposed as an improved time-frequency analysis method for hydrocarbon detection. The SET is a novel time-frequency analysis method which can be considered as a post-processing procedure of short-time Fourier transform and can improve the energy concentration of the time-frequency representation by retaining only the time-frequency information most related to the signal time-varying features. Given the potential limitations of SET for broadband nonstationary seismic signals, using the EWT-SET method which applies SET to the signal after EWT decomposition, not only effectively extracts time-varying features of seismic signals but also improves the performance of SET in concentrating instantaneous energy. The preliminary model tests demonstrate that EWT-SET can effectively depict the location and extent of attenuation anomalies related to hydrocarbons with changing thicknesses of the gas-bearing layer. Application to field data further confirms the capacity for hydrocarbon detection of the presented method. Thus, the EWT-SET method shows significant application prospects and promotion value for hydrocarbon detection. Full article
Figures

Figure 1

Open AccessArticle Maintenance Tools applied to Electric Generators to Improve Energy Efficiency and Power Quality of Thermoelectric Power Plants
Energies 2017, 10(8), 1091; doi:10.3390/en10081091
Received: 14 June 2017 / Revised: 22 July 2017 / Accepted: 23 July 2017 / Published: 26 July 2017
PDF Full-text (7505 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a specific method to improve the reliability of the equipment and the quality of power supplied to the electrical systems with the frequency and voltage control of a thermoelectric plant, to guarantee a more stable system. The method has the
[...] Read more.
This paper presents a specific method to improve the reliability of the equipment and the quality of power supplied to the electrical systems with the frequency and voltage control of a thermoelectric plant, to guarantee a more stable system. The method has the novelty of combining Total Productive Maintenance (TPM) using only four pillars, with Electrical Predictive Maintenance based in failure analysis and diagnostic. It prevents voltage drops caused by excessive reactive consumption, thus guaranteeing the company a perfect functioning of its equipment and providing a longer life of them. The Maintenance Management Program (MMP) seeks to prevent failures from causing the equipment to be shut down from the electrical system, which means large financial losses, either by reducing billing or by paying fines to the regulatory agency, in addition to prejudice the reliability of the system. Using management tools, but applying only four TPM pillars, it was possible to achieve innovation in power plants with internal combustion engines. This study aims to provide maintenance with a more reliable process, through the implantation of measurement, control and diagnostic devices, thus allowing the management to reduce breakdown of plant equipment. Some results have been achieved after the implementation, such as reduction of annual maintenance cost, reduction of corrective maintenance, increase of MTBF (Mean Time between Failures) and reduction of MTTR (Mean Time to Repair) in all areas. Probabilistic models able to describe real processes in a more realistic way, and facilitate the optimization at maximum reliability or minimum costs are presented. Such results are reflected in more reliable and continual power generation. Full article
Figures

Figure 1

Open AccessArticle Nonlinear Synergetic Governor Controllers for Steam Turbine Generators to Enhance Power System Stability
Energies 2017, 10(8), 1092; doi:10.3390/en10081092
Received: 22 June 2017 / Revised: 17 July 2017 / Accepted: 24 July 2017 / Published: 26 July 2017
PDF Full-text (3245 KB) | HTML Full-text | XML Full-text
Abstract
This paper proposes a decentralized nonlinear synergetic governor controller (NSGC) for turbine generators to enhance power system stability by using synergetic control theory and the feedback linearization technique. The precise feedback linearization model of a turbine-generator with a steam valve control is obtained,
[...] Read more.
This paper proposes a decentralized nonlinear synergetic governor controller (NSGC) for turbine generators to enhance power system stability by using synergetic control theory and the feedback linearization technique. The precise feedback linearization model of a turbine-generator with a steam valve control is obtained, at first, by using a feedback linearization technique. Then based on this model, a manifold is defined as a linear combination of the deviation of the rotor angle, speed deviation, and speed derivative. The control law of the proposed NSGC is deduced and the stability condition of the whole closed-loop system is subsequently analyzed. According to the requirement of the primary frequency regulation, an additional proportional integral (PI) controller is designed to dynamically track the steady-state value of the rotor angle. Case studies are undertaken based on a single-machine infinite-bus system and the New England system, respectively. Simulation results show that the proposed NSGC can suppress the power oscillations and improve transient stability more effectively in comparison with the conventional proportional-integral-derivative (PID) governor controller. Moreover, the proposed NSGC is robust to the variations of the system operating conditions. Full article
(This article belongs to the Section Electrical Power and Energy System)
Figures

Figure 1

Open AccessArticle Hygrothermal Dynamic and Mould Growth Risk Predictions for Concrete Tiles by Using Least Squares Support Vector Machines
Energies 2017, 10(8), 1093; doi:10.3390/en10081093
Received: 3 July 2017 / Revised: 17 July 2017 / Accepted: 24 July 2017 / Published: 26 July 2017
PDF Full-text (7883 KB) | HTML Full-text | XML Full-text
Abstract
The hygrothermal analysis of roofs is relevant due to the large areas exposed to a wide range of weather conditions, these directly affecting the energy performance and thermal comfort of buildings. However, after a long life service, the solar absorptivity coatings of roofs
[...] Read more.
The hygrothermal analysis of roofs is relevant due to the large areas exposed to a wide range of weather conditions, these directly affecting the energy performance and thermal comfort of buildings. However, after a long life service, the solar absorptivity coatings of roofs can be altered by mould accumulation. Based on two well established mathematical models, one that adopts driving potentials to calculate temperature, moist air pressure and water vapor pressure gradients, and the other to estimate the mould growth risk on surfaces, this research introduces an approach to predict mould growth considering a reduced computational effort and simulation time. By adopting multiple MISO (Multiple-Input, Single-Output) Nonlinear AutoRegressive with eXogenous inputs (NARX) models, a machine learning technique known as Least Squares Support Vector Machines (LS-SVM), a maximum margin model based on structural risk minimization, was used to predict vapor flux, sensible heat flux, latent heat flux, and mould growth risk on roof surfaces. The proposed model was validated in terms of the Multiple Correlation Coefficient (R2R2R2), Mean Square Error (MSE) and Mean Absolute Error (MAE) performance indices considering as input the weather file from Curitiba city—Brazil, showing consistent precision when compared to the results of a validated numerical model. Full article
Figures

Figure 1

Open AccessArticle Numerical Investigations of the Combined Effects of Flow Rate and Methanol Concentration on DMFC Performance
Energies 2017, 10(8), 1094; doi:10.3390/en10081094
Received: 6 June 2017 / Revised: 7 July 2017 / Accepted: 13 July 2017 / Published: 26 July 2017
PDF Full-text (5656 KB) | HTML Full-text | XML Full-text
Abstract
A modified 3D numerical model on the energy conversion process in the anode side of a Direct Methanol Fuel Cell (DMFC) system was constructed and validated to published experimental results. Systematic simulations were performed to investigate the underlying mechanisms of the energy conversion
[...] Read more.
A modified 3D numerical model on the energy conversion process in the anode side of a Direct Methanol Fuel Cell (DMFC) system was constructed and validated to published experimental results. Systematic simulations were performed to investigate the underlying mechanisms of the energy conversion process, and the combined effects of inlet flow rate and input methanol concentration were summarized systematically. The increase of flow rate was found to be an effective strategy to accelerate the internal flow fields, while the diffusion layer was proposed to be a critical component in the design of high-performance DMFC. The frontier for optimal conditions of DMFC’s output was also determined, which can be helpful to improve the energy conversion performance of DMFC in practical applications. Full article
(This article belongs to the Special Issue Direct Alcohol Fuel Cells 2018)
Figures

Figure 1

Open AccessArticle Optimizing the District Heating Primary Network from the Perspective of Economic-Specific Pressure Loss
Energies 2017, 10(8), 1095; doi:10.3390/en10081095
Received: 20 June 2017 / Revised: 17 July 2017 / Accepted: 19 July 2017 / Published: 26 July 2017
PDF Full-text (2445 KB) | HTML Full-text | XML Full-text
Abstract
A district heating (DH) system is one of the most important components of infrastructures in cold areas. Proper DH network design should balance the initial investment and the heat distribution cost of the DH network. Currently, this design is often based on a
[...] Read more.
A district heating (DH) system is one of the most important components of infrastructures in cold areas. Proper DH network design should balance the initial investment and the heat distribution cost of the DH network. Currently, this design is often based on a recommended value for specific pressure loss (R = ∆P/L) in the main lines. This will result in a feasible network design, but probably not be optimal in most cases. The paper develops a novel optimization model to facilitate the design by considering the initial investment in the pipes and the heat distribution costs. The model will generate all possible network scenarios consisting of different series of diameters for each pipe in the flow direction of the network. Then, the annuity on the initial investment, the heat distribution cost, and the total annual cost will be calculated for each network scenario, taking into account the uncertainties of the material prices and the yearly operating time levels. The model is applied to a sample DH network and the results indicate that the model works quite well, clearly identifying the optimal network design and demonstrating that the heat distribution cost is more important than the initial investment in DH network design. Full article
Figures

Figure 1

Open AccessArticle Real-Time Distributed Economic Model Predictive Control for Complete Vehicle Energy Management
Energies 2017, 10(8), 1096; doi:10.3390/en10081096
Received: 15 June 2017 / Revised: 19 July 2017 / Accepted: 20 July 2017 / Published: 27 July 2017
PDF Full-text (1115 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, a real-time distributed economic model predictive control approach for complete vehicle energy management (CVEM) is presented using a receding control horizon in combination with a dual decomposition. The dual decomposition allows the CVEM optimization problem to be solved by solving
[...] Read more.
In this paper, a real-time distributed economic model predictive control approach for complete vehicle energy management (CVEM) is presented using a receding control horizon in combination with a dual decomposition. The dual decomposition allows the CVEM optimization problem to be solved by solving several smaller optimization problems. The receding horizon control problem is formulated with variable sample intervals, allowing for large prediction horizons with only a limited number of decision variables and constraints in the optimization problem. Furthermore, a novel on/off control concept for the control of the refrigerated semi-trailer, the air supply system and the climate control system is introduced. Simulation results on a low-fidelity vehicle model show that close to optimal fuel reduction performance can be achieved. The fuel reduction for the on/off controlled subsystems strongly depends on the number of switches allowed. By allowing up to 15-times more switches, a fuel reduction of 1.3% can be achieved. The approach is also validated on a high-fidelity vehicle model, for which the road slope is predicted by an e-horizon sensor, leading to a prediction of the propulsion power and engine speed. The prediction algorithm is demonstrated with measured ADASIS information on a public road around Eindhoven, which shows that accurate prediction of the propulsion power and engine speed is feasible when the vehicle follows the most probable path. A fuel reduction of up to 0.63% is achieved for the high-fidelity vehicle model. Full article
(This article belongs to the Special Issue Energy Management Control)
Figures

Figure 1

Open AccessArticle Optimizing the Structure of Distribution Smart Grids with Renewable Generation against Abnormal Conditions: A Complex Networks Approach with Evolutionary Algorithms
Energies 2017, 10(8), 1097; doi:10.3390/en10081097
Received: 16 May 2017 / Revised: 18 July 2017 / Accepted: 19 July 2017 / Published: 26 July 2017
PDF Full-text (4636 KB) | HTML Full-text | XML Full-text
Abstract
In this work, we describe an approach that allows for optimizing the structure of a smart grid (SG) with renewable energy (RE) generation against abnormal conditions (imbalances between generation and consumption, overloads or failures arising from the inherent SG complexity) by combining the
[...] Read more.
In this work, we describe an approach that allows for optimizing the structure of a smart grid (SG) with renewable energy (RE) generation against abnormal conditions (imbalances between generation and consumption, overloads or failures arising from the inherent SG complexity) by combining the complex network (CN) and evolutionary algorithm (EA) concepts. We propose a novel objective function (to be minimized) that combines cost elements, related to the number of electric cables, and several metrics that quantify properties that are beneficial for SGs (energy exchange at the local scale and high robustness and resilience). The optimized SG structure is obtained by applying an EA in which the chromosome that encodes each potential network (or individual) is the upper triangular matrix of its adjacency matrix. This allows for fully tailoring the crossover and mutation operators. We also propose a domain-specific initial population that includes both small-world and random networks, helping the EA converge quickly. The experimental work points out that the proposed method works well and generates the optimum, synthetic, small-world structure that leads to beneficial properties such as improving both the local energy exchange and the robustness. The optimum structure fulfills a balance between moderate cost and robustness against abnormal conditions. Our approach should be considered as an analysis, planning and decision-making tool to gain insight into smart grid structures so that the low level detailed design is carried out by using electrical engineering techniques. Full article
Figures

Figure 1

Open AccessArticle A Predictive Power Control Strategy for DFIGs Based on a Wind Energy Converter System
Energies 2017, 10(8), 1098; doi:10.3390/en10081098
Received: 7 June 2017 / Revised: 20 July 2017 / Accepted: 23 July 2017 / Published: 26 July 2017
PDF Full-text (4261 KB) | HTML Full-text | XML Full-text
Abstract
A feasible control strategy is proposed to control a doubly fed induction generator based on the wind energy converter system (DFIG-WECS). The main aim is to enhance the steady state and dynamic performance under the condition of the parameter perturbations and external disturbances
[...] Read more.
A feasible control strategy is proposed to control a doubly fed induction generator based on the wind energy converter system (DFIG-WECS). The main aim is to enhance the steady state and dynamic performance under the condition of the parameter perturbations and external disturbances and to satisfy the stator power response of the system. Within the proposed control method, the control scheme for the rotor side converter (RSC) is developed on the model predictive control. Firstly, the self-adaptive reference trajectory is established from the deduced discrete state-space equation of the generator. Then, the rotor voltage is calculated by minimizing the global performance index under the current prediction steps at the sampling instant. Through the control scheme for the grid side converter (GSC) and wind turbine, we have re-applied the conventional control. The effectiveness of the proposed control strategy is verified via time domain simulation of a 150 kW-575 V DFIG-WECS using Matlab/Simulink. The simulation result shows that the control of the DFIG with the proposed control method can enhance the steady and dynamic response capability better than the conventional ones when the system faces errors due to the parameter perturbations, external disturbances and the rotor speed. Full article
(This article belongs to the Special Issue Wind Generators Modelling and Control)
Figures

Figure 1

Open AccessArticle A Large Scale Grid Data Analysis Platform for DSOs
Energies 2017, 10(8), 1099; doi:10.3390/en10081099
Received: 7 June 2017 / Revised: 14 July 2017 / Accepted: 14 July 2017 / Published: 27 July 2017
PDF Full-text (6548 KB) | HTML Full-text | XML Full-text
Abstract
The number of fluctuating distributed energy resources (DER) in electricity grids is continuously rising. Due to the lack of operational information on low-voltage (LV) networks, conservative assumptions are necessary to assess the connection of generators to the grid. This paper introduces the hosting
[...] Read more.
The number of fluctuating distributed energy resources (DER) in electricity grids is continuously rising. Due to the lack of operational information on low-voltage (LV) networks, conservative assumptions are necessary to assess the connection of generators to the grid. This paper introduces the hosting capability (HC) as a measure to assess the amount of DER that can be integrated in LV-feeders. The HC of a feeder is the minimum amount of DER that can be hosted in a feeder without reinforcement needs for a given DER-scenario and for a given admissible voltage rise. The hosting capability assessment was performed on the entire LV-grid data of two Austrian Distribution System Operators (DSOs) with more than 36,000 LV-feeders. In total, 40 HC-scenarios were calculated with varying admissible voltage rise levels, DER-scenarios and reactive power control strategies. It turned out that only few feeder parameters such as the resistance at the end node and the lowest ampacity value of feeders show a high correlation with the calculated HC. Further, the impact of the DER-scenario on the share of voltage and loading constrained feeders is rather limited. The gathered results are suitable to validate equivalent LV-feeders models to perform integrated power flow studies on the transmission and distribution grids. Besides the results obtained for the network data of the two DSOs, a performant, modular and parallelizable tool has been developed to automatically analyze large LV network sets. Full article
Figures

Figure 1

Open AccessArticle Potential Arbitrage Revenue of Energy Storage Systems in PJM
Energies 2017, 10(8), 1100; doi:10.3390/en10081100
Received: 15 May 2017 / Revised: 20 July 2017 / Accepted: 21 July 2017 / Published: 27 July 2017
PDF Full-text (10204 KB) | HTML Full-text | XML Full-text
Abstract
The volatility of electricity prices is attracting interest in the opportunity of providing net revenue by energy arbitrage. We analyzed the potential revenue of a generic Energy Storage System (ESS) in 7395 different locations within the electricity markets of Pennsylvania-New Jersey-Maryland interconnection (PJM),
[...] Read more.
The volatility of electricity prices is attracting interest in the opportunity of providing net revenue by energy arbitrage. We analyzed the potential revenue of a generic Energy Storage System (ESS) in 7395 different locations within the electricity markets of Pennsylvania-New Jersey-Maryland interconnection (PJM), the largest U.S. regional transmission organization, using hourly locational marginal prices over the seven-year period 2008–2014. Assuming a price-taking ESS with perfect foresight in the real-time market, we optimized the charge-discharge profile to determine the maximum potential revenue for a 1 MW system as a function of energy/power ratio, or rated discharge duration, from 1 to 14 h, including a limited analysis of sensitivity to round-trip efficiency. We determined minimum potential revenue with a similar analysis of the day-ahead market. We presented the distribution over the set of nodes and years of price, price volatility, and maximum potential arbitrage revenue. From these results, we determined the breakeven overnight installed cost of an ESS below which arbitrage would be profitable, its dependence on rated discharge duration, its distribution over grid nodes, and its variation over the years. We showed that dispatch into real-time markets based on day-ahead market settlement prices is a simple, feasible method that raises the lower bound on the achievable arbitrage revenue. Full article
(This article belongs to the Section Energy Storage and Application)
Figures

Figure 1

Open AccessArticle Study on Electrode Potential of Zinc Nickel Single-Flow Battery during Charge
Energies 2017, 10(8), 1101; doi:10.3390/en10081101
Received: 21 June 2017 / Revised: 15 July 2017 / Accepted: 17 July 2017 / Published: 27 July 2017
PDF Full-text (3921 KB) | HTML Full-text | XML Full-text
Abstract
In this study of zinc nickel single-flow batteries (ZNB), the ion concentration of the convection area and the electrode surface of the battery runner were investigated first. Then, the relationships between the electrode over-potential (or equilibrium potential) and the charge time were studied.
[...] Read more.
In this study of zinc nickel single-flow batteries (ZNB), the ion concentration of the convection area and the electrode surface of the battery runner were investigated first. Then, the relationships between the electrode over-potential (or equilibrium potential) and the charge time were studied. This was based on the electrochemical reaction rate equation and the equilibrium potential equation, from which a mathematical model of the stack voltage (as affected by the internal parameters of the battery) was obtained. By comparison with experimental data, it was determined that the relative error of the simulated stack voltage of a 300 Ah battery was restricted to <0.62% while charging under the condition of 100 A constant-current charging. This shows that the mathematical model can accurately describe the dynamic characteristics of the battery stack voltage, and is very accurate for predicting the stack voltage of the battery during charging under 100 A constant-current charging conditions. Full article
(This article belongs to the Section Energy Storage and Application)
Figures

Figure 1

Open AccessArticle A New Methodology for Assessing the Energy Consumption of Building Stocks
Energies 2017, 10(8), 1102; doi:10.3390/en10081102
Received: 23 June 2017 / Revised: 18 July 2017 / Accepted: 24 July 2017 / Published: 27 July 2017
PDF Full-text (2809 KB) | HTML Full-text | XML Full-text
Abstract
The refurbishment of the existing building stocks represents a great potential for energy savings. To make the refurbishment effective, proper modeling of the current energy performance is needed. In most European countries, few and low quality data on the energy performance and on
[...] Read more.
The refurbishment of the existing building stocks represents a great potential for energy savings. To make the refurbishment effective, proper modeling of the current energy performance is needed. In most European countries, few and low quality data on the energy performance and on the refurbishment of building stocks are revealed, which increases the risk of not getting representative results. The article presents a new methodology for an effective bottom-up energy modeling, aimed at evaluating the current energy performance of housing stocks. The model is set up according to the IEE-EPISCOPE Project (Energy Performance Indicator Tracking Schemes for the Continuous Optimisation of Refurbishment Processes in European Housing Stocks, 2013–2016), which developed a framework of reliable data and clearly stated model assumptions, as to overcome the lack of data while guaranteeing transparency. The model, applied to an Italian region, is based on statistical data and uses the building typology approach. The energy performance is calculated by means of a quasi-steady state method. A correlation between the estimated and the real energy consumption is obtained. The model allows disaggregating the residential building stock in subsets to identify the main potential for energy savings in specific contexts. Improvements of the current data availability are strongly advisable to keep the model updated. Full article
Figures

Figure 1

Open AccessArticle A PMU-Based Method for Smart Transmission Grid Voltage Security Visualization and Monitoring
Energies 2017, 10(8), 1103; doi:10.3390/en10081103
Received: 26 June 2017 / Revised: 18 July 2017 / Accepted: 25 July 2017 / Published: 27 July 2017
PDF Full-text (3046 KB) | HTML Full-text | XML Full-text
Abstract
With the rapid growth of usage of phasor measurement units (PMUs) for modern power grids, the application of synchronized phasors (synchrophasors) to real-time voltage security monitoring has become an active research area. This paper presents a novel approach for fast determination of loading
[...] Read more.
With the rapid growth of usage of phasor measurement units (PMUs) for modern power grids, the application of synchronized phasors (synchrophasors) to real-time voltage security monitoring has become an active research area. This paper presents a novel approach for fast determination of loading margin using PMU data from a wide-area monitoring system (WAMS) to construct the voltage stability boundary (VSB) of a transmission grid. Specifically, a new approach for online loading margin estimation that considers system load trends is proposed based on the Thevenin equivalent (TE) technique and the Mobius transformation (MT) technique. A VSB is then computed by means of real-time PMU measurements and is presented in a complex load power space. VSB can be utilized as a visualization tool that is able to provide real-time visualization of the current voltage stability situation. The proposed method is fast and adequate for online voltage security assessment. Furthermore, it enables us to significantly increase a system operator’s situational awareness for operational decision making. Simulation studies were carried out using different sized power grid models under various operating conditions. The simulation results are shown to validate the capability of the proposed method. Full article
(This article belongs to the collection Smart Grid)
Figures

Figure 1

Open AccessArticle Assessment of Credible Capacity for Intermittent Distributed Energy Resources in Active Distribution Network
Energies 2017, 10(8), 1104; doi:10.3390/en10081104
Received: 26 April 2017 / Revised: 29 June 2017 / Accepted: 24 July 2017 / Published: 27 July 2017
PDF Full-text (2224 KB) | HTML Full-text | XML Full-text
Abstract
The irregularity and randomness of distributed energy sources’ (DERs) output power characteristic usually brings difficulties for grid analysis. In order to reliably and deterministically evaluate intermittent distributed generation’s active power output, a credible capacity index for active distribution network (ADN) is proposed. According
[...] Read more.
The irregularity and randomness of distributed energy sources’ (DERs) output power characteristic usually brings difficulties for grid analysis. In order to reliably and deterministically evaluate intermittent distributed generation’s active power output, a credible capacity index for active distribution network (ADN) is proposed. According to the definition, it is a certain interval that the stochastic active power output of DERs may fall in with larger probability in all kinds of possible dynamic and time varying operation scenarios. Based on the description and analysis on the time varying scenarios, multiple scenarios considered dynamic power flow method for and are proposed. The method to calculate and evaluate credible capacity based on dynamic power flow (DPF) result is illustrated. A study case of an active distribution network with DERs integrated and containing 32 nodes is selected; multiple operation scenarios with various fractal dimension are established and used. Results of calculated credible capacity based on several groups of scenarios have been analyzed, giving the variance analysis of groups of credible capacity values. A deterministic value with the maximum occurrence probability representing credible capacity is given. Based on the same network case, an application of credible capacity to grid extension planning is given, which contributes to expenditure and cost reduction. The effectiveness and significance of the proposed credible capacity and solution method have been demonstrated and verified. Full article
(This article belongs to the Special Issue Innovative Methods for Smart Grids Planning and Management)
Figures

Figure 1

Open AccessArticle Effects of Combined Sorbitan Monolaurate Anti-Agglomerants on Viscosity of Water-in-Oil Emulsion and Natural Gas Hydrate Slurry
Energies 2017, 10(8), 1105; doi:10.3390/en10081105
Received: 9 May 2017 / Revised: 7 July 2017 / Accepted: 24 July 2017 / Published: 27 July 2017
PDF Full-text (2773 KB) | HTML Full-text | XML Full-text
Abstract
Hydrate plugging is the major challenge in the flow assurance of deep-sea pipelines. For water-in-oil emulsions, this risk could be significantly reduced with the addition of anti-agglomerants (AAs). Hydrates often form from water-in-oil emulsions and the measurement of emulsion and slurry viscosity constitutes
[...] Read more.
Hydrate plugging is the major challenge in the flow assurance of deep-sea pipelines. For water-in-oil emulsions, this risk could be significantly reduced with the addition of anti-agglomerants (AAs). Hydrates often form from water-in-oil emulsions and the measurement of emulsion and slurry viscosity constitutes the basis for the application of hydrate slurry flow technology. In this work, using a novel high-pressure viscometer, emulsion and slurry viscosity with different AAs for water content ranging from 5% to 30% was obtained. The viscosity-temperature curves of emulsions were determined and correlated. The variation of system viscosity during hydrate formation from water-in-oil emulsions was examined, the sensitivity of stable slurry viscosity to water cut and the effects of temperature on annealed slurry viscosity were investigated. The results indicated that the variation of viscosity during hydrate formation relies on the conversion ratio. It also implied that the sensitivity of slurry viscosity to change in its water cut or temperature was reduced with AA addition. Full article
Figures

Figure 1

Open AccessArticle Design, Implementation and Demonstration of Embedded Agents for Energy Management in Non-Residential Buildings
Energies 2017, 10(8), 1106; doi:10.3390/en10081106
Received: 4 June 2017 / Revised: 18 July 2017 / Accepted: 21 July 2017 / Published: 29 July 2017
PDF Full-text (1277 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
With the building sector being responsible for 30% of the total final energy consumption, great interest lies in implementing adequate policies and deploying efficient technologies that would decrease this number. However, building comfort and energy management systems (BCEM) are challenging to manage on
[...] Read more.
With the building sector being responsible for 30% of the total final energy consumption, great interest lies in implementing adequate policies and deploying efficient technologies that would decrease this number. However, building comfort and energy management systems (BCEM) are challenging to manage on account of their increasing complexity with regard to the integration of renewable energy sources or the connection of electrical, thermal and gas grids. Multi-agent~systems (MAS) deal well with such complex issues. This paper presents an MAS for non-residential buildings from the design, implementation and demonstration, both simulation based and in a field test. Starting from an ontology and an attached data model for BCEM application, we elaborated use cases for developing and testing the MAS framework. The building and technical equipment are modeled using the modeling language Modelica under Dymola. The agents are programmed in JADE and communicate with Dymola via TCP/IP and with the real devices via BACnet. Operatively, the~agents can take on different control strategies: normal operation with no optimization, optimization of energy costs, where energy is delivered through the room through the devices that have the lowest operating costs, and relaxation of the comfort constraint, where the costs of the productivity loss under sub-optimal comfort conditions is taken into account during optimization. Comfort is expressed as a function of indoor air temperature. Simulation, including a comparison with a benchmark system, and field test results are presented to demonstrate the features of the proposed BCEM. Full article
(This article belongs to the Special Issue ICT for Energy)
Figures

Figure 1

Open AccessArticle The Effect of Hydrogen Addition on the Combustion Characteristics of RP-3 Kerosene/Air Premixed Flames
Energies 2017, 10(8), 1107; doi:10.3390/en10081107
Received: 19 April 2017 / Revised: 2 June 2017 / Accepted: 18 July 2017 / Published: 30 July 2017
PDF Full-text (13686 KB) | HTML Full-text | XML Full-text
Abstract
Experimental studies have been performed to investigate the effects of hydrogen addition on the combustion characteristics of Chinese No.3 jet fuel (RP-3 kerosene/air premixed flames. Experiments were carried out in a constant volume chamber and the influences of the initial temperatures of 390
[...] Read more.
Experimental studies have been performed to investigate the effects of hydrogen addition on the combustion characteristics of Chinese No.3 jet fuel (RP-3 kerosene/air premixed flames. Experiments were carried out in a constant volume chamber and the influences of the initial temperatures of 390 and 420 K, initial pressures of 0.1 and 0.3 MPa, equivalence ratios of 0.6–1.6 and hydrogen additions of 0.0–0.5 on the laminar burning velocities, and Markstein numbers of Hydrogen (H2)/RP-3/air mixtures were investigated. The results show that the flame front surfaces of RP-3/air mixtures remain smooth throughout the entire flame propagation process at a temperature of 390 K, pressure of 0.3 MPa, equivalence ratio of 1.3 and without hydrogen addition, but when the hydrogen addition increases from 0.0 to 0.5 under the same conditions, flaws and protuberances occur at the flame surfaces. It was also found that with the increase of the equivalence ratio from 0.9 to 1.5, the laminar burning velocities of the mixtures increase at first and then decrease, and the highest laminar burning velocity was measured at an equivalence ratio of 1.2. Meanwhile, with the increase of hydrogen addition, laminar burning velocities of H2/RP-3/air mixtures increase. However, the Markstein numbers of H2/RP-3/air mixtures decrease with the increase of hydrogen addition, which means that the flames of H2/RP-3/air mixtures become unstable with the increase of hydrogen addition. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
Figures

Figure 1

Open AccessArticle Optimization of Active Current for Large-Scale Wind Turbines Integrated into Weak Grids for Power System Transient Stability Improvement
Energies 2017, 10(8), 1108; doi:10.3390/en10081108
Received: 20 June 2017 / Revised: 15 July 2017 / Accepted: 26 July 2017 / Published: 31 July 2017
PDF Full-text (2170 KB) | HTML Full-text | XML Full-text
Abstract
Power system transient stability is a challenge when integrating large-scale wind turbines into weak grids. This paper addresses the issue of transient stability in such situations by optimizing a wind turbine’s active current behavior. A wind turbine’s active current reference controller and its
[...] Read more.
Power system transient stability is a challenge when integrating large-scale wind turbines into weak grids. This paper addresses the issue of transient stability in such situations by optimizing a wind turbine’s active current behavior. A wind turbine’s active current reference controller and its setting optimization method are proposed based on analyses of two associated problems: the mechanism for improving transient stability of a single (synchronous) machine infinite bus (SMIB) system, as well as the various physical factor dependencies dictating how active and reactive wind turbine currents affect the swing dynamics of synchronous machines. Analysis of the first problem guided the design of the controller’s main structure. Analysis of the second problem guided selection of the control object within a wind turbine’s active and reactive currents, as well as helped recognition of the influential physical factors that must be considered in the parameter setting process. The efficiency of the controller and the validity of the analyses were verified by case studies using Kundur’s two-area system. Full article
(This article belongs to the Section Electrical Power and Energy System)
Figures

Figure 1

Open AccessArticle Evaporation and Ignition Characteristics of Water Emulsified Diesel under Conventional and Low Temperature Combustion Conditions
Energies 2017, 10(8), 1109; doi:10.3390/en10081109
Received: 14 April 2017 / Revised: 29 June 2017 / Accepted: 11 July 2017 / Published: 31 July 2017
PDF Full-text (12673 KB) | HTML Full-text | XML Full-text
Abstract
The combination of emulsified diesel and low temperature combustion (LTC) technology has great potential in reducing engine emissions. A visualization study on the spray and combustion characteristics of water emulsified diesel was conducted experimentally in a constant volume chamber under conventional and LTC
[...] Read more.
The combination of emulsified diesel and low temperature combustion (LTC) technology has great potential in reducing engine emissions. A visualization study on the spray and combustion characteristics of water emulsified diesel was conducted experimentally in a constant volume chamber under conventional and LTC conditions. The effects of ambient temperature on the evaporation, ignition and combustion characteristics of water emulsified diesel were studied under cold, evaporating and combustion conditions. Experimental results showed that the ambient temperature had little effect on the spray structures, in terms of the liquid core length, the spray shape and the spray area. However, higher ambient temperature slightly reduced the Sauter Mean Diameter (SMD) of the spray droplets. The auto-ignition delay time increased significantly with the decrease of the ambient temperature. The ignition process always occurred at the entrainment region near the front periphery of the liquid core. This entrainment region was evolved from the early injected fuel droplets which were heated and mixed by the continuous entrainment until the local temperature and equivalence ratio reached the ignition condition. The maximum value of integrated natural flame luminosity (INFL) reduced by 60% when the ambient temperature dropped from 1000 to 800 K, indicating a significant decrease of the soot emissions could be achieved by LTC combustion mode than the conventional diesel engines. Full article
(This article belongs to the Special Issue Internal Combustion Engines)
Figures

Figure 1

Open AccessArticle Characterization of Particle and Gaseous Emissions from Marine Diesel Engines with Different Fuels and Impact of After-Treatment Technology
Energies 2017, 10(8), 1110; doi:10.3390/en10081110
Received: 4 June 2017 / Revised: 8 July 2017 / Accepted: 27 July 2017 / Published: 31 July 2017
PDF Full-text (4602 KB) | HTML Full-text | XML Full-text
Abstract
The International Maritime Organization (IMO) Marine Environment Protection Committee (MEPC) and some countries have gradually strengthened the laws regulating ship exhaust emissions. The aim of this paper is to estimate the impact of an after-treatment technology exhaust gas cleaning (EGC) system on marine
[...] Read more.
The International Maritime Organization (IMO) Marine Environment Protection Committee (MEPC) and some countries have gradually strengthened the laws regulating ship exhaust emissions. The aim of this paper is to estimate the impact of an after-treatment technology exhaust gas cleaning (EGC) system on marine diesel engine emissions and the cost advantage compared to using low-sulfur fuel oil. The emission characteristics of SO2 and particulate matter (PM) produced from high sulfur oil and low sulfur oil in a low-speed two-stroke marine diesel engine were also presented. The removal efficiency of SO2 has been tested and the PM removal efficiency was also predicted in this study. When using high sulfur oil, the emission factor of SO2 and PM were from 8.73 g/kWh to 11.6 g/kWh and 2.0 g/kWh to 2.7 g/kWh, respectively. These values are significantly higher than the emission values from using low sulfur oil. The fuel sulfur content (FSC) was the key factor affecting the emission factors of SO2 and PM. The fuel change could reduce the mass emission factor of PM, which is above 90% for the total particle emission with the two fuels. When using the EGC system, the desulfurization efficiencies were above 99%. The pH values at a 25, 39, 53, and 67% load were also stabilized to be around 7.5, 7.6, 7.7, and 8, respectively. The EGC system can also capture part of the primary PM and secondary PM formed from SO2. The EGC system was more effective for PM of the size larger than 1 μm. Thus, according to this study, the usage of low sulfur oil and EGC will also substantially decrease the emission of currently unregulated hazardous chemical species in the exhaust gas of ships in addition to satisfying future emissions regulations of ship. Furthermore, the EGC system also had a significant cost advantage compared to using low-sulfur fuel oil. Full article
Figures

Figure 1

Open AccessArticle Optimal Dynamic Analysis of Electrical/Electronic Components in Wind Turbines
Energies 2017, 10(8), 1111; doi:10.3390/en10081111
Received: 23 May 2017 / Revised: 28 June 2017 / Accepted: 18 July 2017 / Published: 31 July 2017
PDF Full-text (3931 KB) | HTML Full-text | XML Full-text
Abstract
Electrical and electronic components are very important subcomponents in modern industrial wind turbines. Complex multimegawatt wind turbines are continuously being installed both onshore and offshore, continuously increasing the demand for sophisticated electronic and electrical components. In this work, most critical electrical and electronic
[...] Read more.
Electrical and electronic components are very important subcomponents in modern industrial wind turbines. Complex multimegawatt wind turbines are continuously being installed both onshore and offshore, continuously increasing the demand for sophisticated electronic and electrical components. In this work, most critical electrical and electronic components in industrial wind turbines have been identified and the applicability of appropriate condition monitoring processes simulated. A fault tree dynamic analysis has been carried out by binary decision diagrams to obtain the system failure probability over time and using different time increments to evaluate the system. This analysis allows critical electrical and electronic components of the converters to be identified in different conditions. The results can be used to develop a scheduled maintenance that improves the decision making and reduces the maintenance costs. Full article
(This article belongs to the collection Wind Turbines)
Figures

Figure 1

Open AccessArticle Study of a High-Pressure External Gear Pump with a Computational Fluid Dynamic Modeling Approach
Energies 2017, 10(8), 1113; doi:10.3390/en10081113
Received: 30 May 2017 / Revised: 26 July 2017 / Accepted: 27 July 2017 / Published: 31 July 2017
PDF Full-text (9070 KB) | HTML Full-text | XML Full-text
Abstract
A study on the internal fluid dynamic of a high-pressure external gear pump is described in this paper. The pump has been analyzed with both numerical and experimental techniques. Starting from a geometry of the pump, a three-dimensional computational fluid dynamics (CFD) model
[...] Read more.
A study on the internal fluid dynamic of a high-pressure external gear pump is described in this paper. The pump has been analyzed with both numerical and experimental techniques. Starting from a geometry of the pump, a three-dimensional computational fluid dynamics (CFD) model has been built up using the commercial code PumpLinx®. All leakages have been taken into account in order to estimate the volumetric efficiency of the pump. Then the pump has been tested on a test bench of Casappa S.p.A. Model results like the volumetric efficiency, absorbed torque, and outlet pressure ripple have been compared with the experimental data. The model has demonstrated the ability to predict with good accuracy the performance of the real pump. The CFD model has been also used to evaluate the effect on the pump performance of clearances in the meshing area. With the validated model the pressure inside the chambers of both driving and driven gears have been studied underlining cavitation in meshing fluid volume of the pump. For this reason, the model has been implemented in order to predict the cavitation phenomena. The analysis has allowed the detection of cavitating areas, especially at high rotation speeds and delivery pressure. Isosurfaces of the fluid volume have been colored as a function of the total gas fraction to underline where the cavitation occurs. Full article
(This article belongs to the Special Issue Engineering Fluid Dynamics)
Figures

Figure 1

Open AccessArticle The Optimal Generation Cost-Based Tariff Rates for Onshore Wind Energy in Malaysia
Energies 2017, 10(8), 1114; doi:10.3390/en10081114
Received: 20 June 2017 / Revised: 21 July 2017 / Accepted: 25 July 2017 / Published: 31 July 2017
PDF Full-text (1598 KB) | HTML Full-text | XML Full-text
Abstract
The government of Malaysia has recently decided to explore the feasibility of wind energy to generate electricity in the country. Their ambition is to achieve a measureable target in the percentage contribution of electricity generated by renewable energy technology in the national electricity
[...] Read more.
The government of Malaysia has recently decided to explore the feasibility of wind energy to generate electricity in the country. Their ambition is to achieve a measureable target in the percentage contribution of electricity generated by renewable energy technology in the national electricity generation mix. As part of this initiative, a study of wind energy policy has been conducted by identifying the optimal feed-in tariff (FiT) rates to support the development of wind energy in the country. The aim of this paper is to calculate the optimal level of tariff that is suitable with local wind conditions. A closed-form equation for optimal feed-in tariff rate of wind energy with consideration of the availability of capital allowance has been developed. The focus is on small- and utility-scale wind turbine installations. As a result, by considering the availability of capital allowance, the optimal FiT rates for small-scale wind turbines in Malaysia are between 0.9245–1.1313 RM/kWh, while utility-scale rates are between 0.7396 and 0.9050 RM/kWh. The level of FiT is changed with the changing value of economic parameters. Kudat, in northern Borneo, has been identified as a prime site for wind energy development in the country; however, more work needs to be conducted, including the development of a regional wind map and measurement of wind data at more new potential sites. Full article
(This article belongs to the Section Energy Sources)
Figures

Figure 1

Open AccessArticle A Current Frequency Component-Based Fault-Location Method for Voltage-Source Converter-Based High-Voltage Direct Current (VSC-HVDC) Cables Using the S Transform
Energies 2017, 10(8), 1115; doi:10.3390/en10081115
Received: 5 July 2017 / Revised: 24 July 2017 / Accepted: 28 July 2017 / Published: 31 July 2017
PDF Full-text (2719 KB) | HTML Full-text | XML Full-text
Abstract
This paper proposes a fault-location method for voltage-source converter (VSC)-based high-voltage direct current (VSC-HVDC) systems. This method relies on the current frequency components generated by faults in the cable, and requires the arrival time of the frequency components at two terminals. The S
[...] Read more.
This paper proposes a fault-location method for voltage-source converter (VSC)-based high-voltage direct current (VSC-HVDC) systems. This method relies on the current frequency components generated by faults in the cable, and requires the arrival time of the frequency components at two terminals. The S transform is a time–frequency analysis tool that is superior to the wavelet transform in some respects. Therefore, the S transform was employed to determine the arrival time in this paper. To obtain a reliable criterion, a novel phase-mode transform method for bipolar cables was developed, and the propagation characteristics of the current frequency components through out the cable were analyzed. A two-terminal VSC-HVDC system was modeled in power system computer aided design/electromagnetic transients including DC (PSCAD/EMTDC). Various faults under different conditions were simulated on the basis of this model, and the simulation results verified a high accuracy, robustness against fault-resistance, and noise immunity of the proposed method. Full article
(This article belongs to the Section Electrical Power and Energy System)
Figures

Figure 1

Open AccessArticle A DC Microgrid Coordinated Control Strategy Based on Integrator Current-Sharing
Energies 2017, 10(8), 1116; doi:10.3390/en10081116
Received: 10 July 2017 / Revised: 23 July 2017 / Accepted: 25 July 2017 / Published: 1 August 2017
PDF Full-text (4429 KB) | HTML Full-text | XML Full-text
Abstract
The DC microgrid has become a new trend for microgrid study with the advantages of high reliability, simple control and low losses. With regard to the drawbacks of the traditional droop control strategies, an improved DC droop control strategy based on integrator current-sharing
[...] Read more.
The DC microgrid has become a new trend for microgrid study with the advantages of high reliability, simple control and low losses. With regard to the drawbacks of the traditional droop control strategies, an improved DC droop control strategy based on integrator current-sharing is introduced. In the strategy, the principle of eliminating deviation through an integrator is used, constructing the current-sharing term in order to make the power-sharing between different distributed generation (DG) units uniform and reasonable, which can reduce the circulating current between DG units. Furthermore, at the system coordinated control level, a hierarchical/droop control strategy based on the DC bus voltage is proposed. In the strategy, the operation modes of the AC main network and micro-sources are determined through detecting the DC voltage variation, which can ensure the power balance of the DC microgrid under different operating conditions. Meanwhile, communication is not needed between different DG units, while each DG unit needs to sample the DC bus voltage, which retains the plug-and-play feature of the DC microgrid. The proposed control strategy is validated by simulation on a DC microgrid with permanent magnet synchronous generator-based wind turbines, solar arrays and energy storage batteries, which can be applied to small commercial or residential buildings. Full article
(This article belongs to the collection Wind Turbines)
Figures

Figure 1

Open AccessFeature PaperArticle Energy Refurbishment of an Office Building with Hybrid Photovoltaic System and Demand-Side Management
Energies 2017, 10(8), 1117; doi:10.3390/en10081117
Received: 16 June 2017 / Revised: 25 July 2017 / Accepted: 26 July 2017 / Published: 1 August 2017
PDF Full-text (8430 KB) | HTML Full-text | XML Full-text
Abstract
On-site photovoltaic (PV) and battery systems intend to improve buildings energy performance, however battery costs and monetary incentives are a major drawback for the introduction of these technologies into the electricity grids. This paper proposes an energy refurbishment of an office building based
[...] Read more.
On-site photovoltaic (PV) and battery systems intend to improve buildings energy performance, however battery costs and monetary incentives are a major drawback for the introduction of these technologies into the electricity grids. This paper proposes an energy refurbishment of an office building based on multi-objective simulations. An innovative demand-side management approach is analyzed through the PV and battery control with the purpose of reducing grid power peaks and grid imported energy, as well as improving the project economy. Optimization results of load matching and grid interaction parameters, complemented with an economic analysis, are investigated in different scenarios. By means of battery use, the equivalent use of the grid connection is reduced by 12%, enhancing the grid interaction potential, and 10% of load matching rates can be increased. Project improvements indicate the grid connection capacity can be reduced by 13% and significant savings of up to 48% are achieved on yearly bills. The economy demonstrates the grid parity is only achieved for battery costs below 100 €/kWh and the payback period is large: 28 years. In the case with only PV system, the grid parity achieves better outcomes and the payback time is reduced by a half, making this a more attractive option. Full article
(This article belongs to the Special Issue Energy Conservation in Infrastructures 2016)
Figures

Figure 1

Open AccessArticle Investigation on a Power Coupling Steering System for Dual-Motor Drive Tracked Vehicles Based on Speed Control
Energies 2017, 10(8), 1118; doi:10.3390/en10081118
Received: 24 June 2017 / Revised: 26 July 2017 / Accepted: 28 July 2017 / Published: 1 August 2017
PDF Full-text (4979 KB) | HTML Full-text | XML Full-text
Abstract
Double-motor drive tracked vehicles (2MDTV) are widely used in the tracked vehicle industry due to the development of electric vehicle drive systems. The aim of this paper is to solve the problem of insufficient propulsion motor torque in low-speed, small-radius steering and insufficient
[...] Read more.
Double-motor drive tracked vehicles (2MDTV) are widely used in the tracked vehicle industry due to the development of electric vehicle drive systems. The aim of this paper is to solve the problem of insufficient propulsion motor torque in low-speed, small-radius steering and insufficient power in high-speed large-radius steering. In order to do this a new type of steering system with a coupling device is designed and a closed-loop control strategy based on speed is adopted to improve the lateral stability of the vehicle. The work done entails modeling and simulating the 2MDTV and the proposed control strategy in RecurDyn and Matlab/Simulink. The simulation results show that the 2MDTV with the coupling device outputs more torque and power in both steering cases compared to the 2MDTV without the coupling device, and the steering stability of the vehicle is improved by using the strategy based on speed. Full article
(This article belongs to the Special Issue Methods to Improve Energy Use in Road Vehicles)
Figures

Figure 1

Open AccessArticle Using SF6 Decomposed Component Analysis for the Diagnosis of Partial Discharge Severity Initiated by Free Metal Particle Defect
Energies 2017, 10(8), 1119; doi:10.3390/en10081119
Received: 20 June 2017 / Revised: 27 July 2017 / Accepted: 28 July 2017 / Published: 1 August 2017
PDF Full-text (2826 KB) | HTML Full-text | XML Full-text
Abstract
The decomposition characteristics of a SF6 gas-insulated medium were used to diagnose the partial discharge (PD) severity in DC gas-insulated equipment (DC-GIE). First, the PD characteristics of the whole process were studied from the initial PD to the breakdown initiated by a
[...] Read more.
The decomposition characteristics of a SF6 gas-insulated medium were used to diagnose the partial discharge (PD) severity in DC gas-insulated equipment (DC-GIE). First, the PD characteristics of the whole process were studied from the initial PD to the breakdown initiated by a free metal particle defect. The average discharge magnitude in a second was used to characterize the PD severity and the PD was divided into three levels: mild PD, medium PD, and dangerous PD. Second, two kinds of voltage in each of the above PD levels were selected for the decomposition experiments of SF6. Results show that the negative DC-PD in these six experiments decomposes the SF6 gas and generates five stable decomposed components, namely, CF4, CO2, SO2F2, SOF2, and SO2. The concentrations and concentration ratios of the SF6 decomposed components can be associated with the PD severity. A minimum-redundancy-maximum-relevance (mRMR)-based feature selection algorithm was used to sort the concentrations and concentration ratios of the SF6 decomposed components. Back propagation neural network (BPNN) and support vector machine (SVM) algorithms were used to diagnose the PD severity. The use of C(CO2)/CT1, C(CF4)/C(SO2), C(CO2)/C(SOF2), and C(CF4)/C(CO2) shows good performance in diagnosing PD severity. This finding serves as a foundation in using the SF6 decomposed component analysis (DCA) method to diagnose the insulation faults in DC-GIE and assess its insulation status. Full article
Figures

Figure 1

Open AccessArticle Proposal of Physical-Statistical Model of Thermal Aging Respecting Threshold Value
Energies 2017, 10(8), 1120; doi:10.3390/en10081120
Received: 26 June 2017 / Revised: 21 July 2017 / Accepted: 24 July 2017 / Published: 2 August 2017
PDF Full-text (4634 KB) | HTML Full-text | XML Full-text
Abstract
The aging of electrical insulation material or a system is a main issue for designers of high-voltage (HV) machines. Precise determination of the life cycle of electrical insulation is one way of improving the efficiency of electrical machines involved in the production and
[...] Read more.
The aging of electrical insulation material or a system is a main issue for designers of high-voltage (HV) machines. Precise determination of the life cycle of electrical insulation is one way of improving the efficiency of electrical machines involved in the production and transmission of electrical energy. Much effort has been devoted to preparing statistical or physical methods of Electrical Insulating System (EIS) life time estimation in the real operation of electrical machinery. The main aim of this paper is to introduce a new physical-statistical model of thermal aging respecting the threshold value. This model is based on thermal aging model and the main difference between this model and previously published models is taking into account the threshold value of degradation factor. The complete design of this model is presented in this paper, including functions defining the threshold value of the effect of the degradation factor depending on the temperature. Proposed model was verified by accelerated thermal aging test at selected temperatures (160, 170, 180 °C) and time intervals (0, 120, 240 h) on a commonly used transformer board. The breakdown voltage was set as an indicating parameter of the level of thermal aging and was measured according to standard IEC 60243-1. Collected data from these measurements were used for threshold value determination (431.23 K) and verification of proposed physical-statistical model of thermal aging respecting the threshold value. Full article
Figures

Figure 1

Open AccessArticle Analysis of Low Temperature Preheating Effect Based on Battery Temperature-Rise Model
Energies 2017, 10(8), 1121; doi:10.3390/en10081121
Received: 13 May 2017 / Revised: 22 June 2017 / Accepted: 27 July 2017 / Published: 1 August 2017
PDF Full-text (3253 KB) | HTML Full-text | XML Full-text
Abstract
It is difficult to predict the heating time and power consumption associated with the self-heating process of lithium-ion batteries at low temperatures. A temperature-rise model considering the dynamic changes in battery temperature and state of charge is thus proposed. When this model is
[...] Read more.
It is difficult to predict the heating time and power consumption associated with the self-heating process of lithium-ion batteries at low temperatures. A temperature-rise model considering the dynamic changes in battery temperature and state of charge is thus proposed. When this model is combined with the ampere-hour integral method, the quantitative relationship among the discharge rate, heating time, and power consumption, during the constant-current discharge process in an internally self-heating battery, is realized. Results show that the temperature-rise model can accurately reflect actual changes in battery temperature. The results indicate that the discharge rate and the heating time present an exponential decreasing trend that is similar to the discharge rate and the power consumption. When a 2 C discharge rate is selected, the battery temperature can rise from −10 °C to 5 °C in 280 s. In this scenario, power consumption of the heating process does not exceed 15% of the rated capacity. As the discharge rate gradually reduced, the heating time and power consumption of the heating process increase slowly. When the discharge rate is 1 C, the heating time is more than 1080 s and the power consumption approaches 30% of the rated capacity. The effect of discharge rate on the heating time and power consumption during the heating process is significantly enhanced when it is less than 1 C. Full article
(This article belongs to the Special Issue Advanced Energy Storage Technologies and Their Applications (AESA))
Figures

Open AccessArticle Electret Length Optimization of Output Power for Double-End Fixed Beam Out-of-Plane Electret-Based Vibration Energy Harvesters
Energies 2017, 10(8), 1122; doi:10.3390/en10081122
Received: 15 May 2017 / Revised: 26 June 2017 / Accepted: 16 July 2017 / Published: 1 August 2017
PDF Full-text (3896 KB) | HTML Full-text | XML Full-text
Abstract
Thanks to miniaturization, it is now possible to imagine self-powered systems that can harvest energy from the environment to produce electrical energy. Out-of-plane electret-based vibration energy harvesters (E-EVHs) are an effective and inexpensive energy harvester type that has attracted much attention. Increasing the
[...] Read more.
Thanks to miniaturization, it is now possible to imagine self-powered systems that can harvest energy from the environment to produce electrical energy. Out-of-plane electret-based vibration energy harvesters (E-EVHs) are an effective and inexpensive energy harvester type that has attracted much attention. Increasing the capacitance of variable capacitors is an effective way to improve the output power of E-EVHs. In this paper, firstly an accurate capacitance theoretical model of a double-ended fixed beam out-of-plane E-EVHs which has 97% reliability compared with FEM (COMSOL Multiphysics) results is presented. A comparison of capacitance between the double-ended fixed beam structure and a cantilever structure of the same size indicates that the double-ended fixed beam structure has greater capacitance and capacitance variation. We apply this theoretical capacitance model to the mechanical-electrical coupling model of double-ended fixed beam out-of-plane E-EVHs and study harvesters’ output performances for different electret lengths by numerical and experimental method, respectively. There exists an optimal electret length to harvest maximum power in our simulation results. Enhanced electrostatic forces with increasing the electret length emphasizes the soft spring effect, which widens the half power bandwidth and lowers the resonance frequency. Increasing the length of the electret can reduce the resistance of the optimum load. The experimental results show trend consistent with the numerical predictions. The maximum output power can reach 404 µW (134.66 µW/cm2/g) at the electret length of 40 mm when the external acceleration and the frequency were 5 m/s2 and 74 Hz, respectively. The maximum bandwidth reaches 2.5 Hz at the electret length of 60 mm. Therefore, the electret length should be placed between 40 mm and 60 mm, while ensuring a higher output power and also get a larger bandwidth in practical applications. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
Figures

Figure 1

Open AccessArticle Techno-Economic Assessment of Heat Transfer Fluid Buffering for Thermal Energy Storage in the Solar Field of Parabolic Trough Solar Thermal Power Plants
Energies 2017, 10(8), 1123; doi:10.3390/en10081123
Received: 13 April 2017 / Revised: 17 July 2017 / Accepted: 24 July 2017 / Published: 1 August 2017
PDF Full-text (2465 KB) | HTML Full-text | XML Full-text
Abstract
Currently, operating parabolic trough (PT) solar thermal power plants, either solar-only or with thermal storage block, use the solar field as a heat transfer fluid (HTF) thermal storage system to provide extra thermal capacity when it is needed. This is done by circulating
[...] Read more.
Currently, operating parabolic trough (PT) solar thermal power plants, either solar-only or with thermal storage block, use the solar field as a heat transfer fluid (HTF) thermal storage system to provide extra thermal capacity when it is needed. This is done by circulating heat transfer fluid into the solar field piping in order to create a heat fluid buffer. In the same way, by oversizing the solar field, it can work as an alternative thermal energy storage (TES) system to the traditionally applied methods. This paper presents a solar field TES model for a standard solar field from a 50-MWe solar power plant. An oversized solar model is analyzed to increase the capacity storage system (HTF buffering). A mathematical model has been developed and different simulations have been carried out over a cycle of one year with six different solar multiples considered to represent the different oversized solar field configurations. Annual electricity generation and levelized cost of energy (LCOE) are calculated to find the solar multiple (SM) which makes the highest solar field thermal storage capacity possible within the minimum LCOE. Full article
(This article belongs to the Section Energy Storage and Application)
Figures

Figure 1

Open AccessCommunication The Performance of a Direct Borohydride/Peroxide Fuel Cell Using Graphite Felts as Electrodes
Energies 2017, 10(8), 1124; doi:10.3390/en10081124
Received: 24 June 2017 / Revised: 20 July 2017 / Accepted: 25 July 2017 / Published: 1 August 2017
PDF Full-text (2444 KB) | HTML Full-text | XML Full-text
Abstract
A direct borohydride/peroxide fuel cell (DBPFC) generates electrical power by recirculating liquid anolyte and catholyte between the stack and reservoirs, which is similar to the operation of flow batteries. To enhance the accessibility of the catalyst layer to the liquid anolyte/catholyte, graphite felts
[...] Read more.
A direct borohydride/peroxide fuel cell (DBPFC) generates electrical power by recirculating liquid anolyte and catholyte between the stack and reservoirs, which is similar to the operation of flow batteries. To enhance the accessibility of the catalyst layer to the liquid anolyte/catholyte, graphite felts are employed as the porous diffusion layer of a single-cell DBPFC instead of carbon paper/cloth. The effects of the type of anode alkaline solution and operating conditions, including flow rate and temperature of the anolyte/catholyte, on DBPFC performance are investigated and discussed. The durability of the DBPFC is also evaluated by galvanostatic discharge at 0.1 A∙cm−2 for over 50 h. The results of this preliminary study show that a DBPFC with porous graphite electrodes can provide a maximum power density of 0.24 W∙cm−2 at 0.8 V. The performance of the DBPFC drops slightly after 50 h of operation; however, the discharge capacity shows no significant decrease. Full article
(This article belongs to the Special Issue Polymer Electrolyte Membrane Fuel Cells 2017)
Figures

Figure 1

Open AccessArticle The Coupled Effect of Fines Mobilization and Salt Precipitation on CO2 Injectivity
Energies 2017, 10(8), 1125; doi:10.3390/en10081125
Received: 6 June 2017 / Revised: 20 July 2017 / Accepted: 26 July 2017 / Published: 1 August 2017
PDF Full-text (2367 KB) | HTML Full-text | XML Full-text
Abstract
In terms of storage capacity and containment efficiency, deep saline aquifers are among the best candidates for CO2 storage. However, salt precipitation in the wellbore vicinity and fines mobilization ensued from in situ mineral dissolution could impair CO2 injectivity and reduce
[...] Read more.
In terms of storage capacity and containment efficiency, deep saline aquifers are among the best candidates for CO2 storage. However, salt precipitation in the wellbore vicinity and fines mobilization ensued from in situ mineral dissolution could impair CO2 injectivity and reduce the quality and capacity of deep saline reservoirs for CO2 storage. The mechanisms of salt precipitation and its impact on CO2 injectivity have been studied, but the effects of fines mobilization have not been properly investigated. We conducted core-flood experiments and theoretical studies to investigate the impact of fines mobilization on CO2 injectivity, the relative contribution of fines mobilization and salt precipitation to injectivity impairment, and the coupled effect of salt precipitation and fines mobilization. We found that, mineral dissolution and transport effects could induce up to about 26% injectivity impairment. The findings also suggest that about 0.3 wt % particle concentration in the pore fluid could induce over twofold injectivity impairment compared to about 10 wt % of total dissolved salt in the formation water. Salt precipitation was also found to compound injectivity impairment induced by fines mobilization. The present study provides important insight, and could serve as a foundation to inspire further experimental and theoretical investigation into the effects of mineral dissolution and fines mobilization in the context of CO2 injectivity. Full article
Figures

Figure 1

Open AccessArticle An Energy Efficient Lighting Design Strategy to Enhance Visual Comfort in Offices with Windows
Energies 2017, 10(8), 1126; doi:10.3390/en10081126
Received: 12 June 2017 / Revised: 24 July 2017 / Accepted: 28 July 2017 / Published: 1 August 2017
PDF Full-text (2471 KB) | HTML Full-text | XML Full-text
Abstract
A high luminance contrast between windows and surrounding surfaces can increase the risk of discomfort glare, which can diminish office workers’ satisfaction and productivity. Accordingly, it can lead to occupant interventions, such as drawing window blinds or increasing electric light levels, which are
[...] Read more.
A high luminance contrast between windows and surrounding surfaces can increase the risk of discomfort glare, which can diminish office workers’ satisfaction and productivity. Accordingly, it can lead to occupant interventions, such as drawing window blinds or increasing electric light levels, which are intended to enhance indoor visual comfort but counterproductively act to increase energy consumption. Increasing the luminance of the areas surrounding the windows using a supplementary lighting system, such as wall-washing with light emitting diode (LED) linear luminaires, could reduce discomfort glare arising from windowed walls. This paper reports on the results of a study in a typical office room in Brisbane, Australia. The outcomes of this study indicate that creating a luminance contrast of between 11:1 and 12:1 on the window wall in an office room with a 45% window-to-exterior-wall ratio using a supplementary LED system leads to improved subjective assessments of window appearance. The results suggest that such an enhancement could significantly reduce discomfort glare from windows, as well as diminishing the likelihood of the users intending to turn on the ceiling lights or to move the blinds. Full article
(This article belongs to the Special Issue Smart Lighting Environments: Sensing and Control)
Figures

Figure 1

Open AccessArticle A Demand-Side Perspective on Developing a Future Electricity Generation Mix: Identifying Heterogeneity in Social Preferences
Energies 2017, 10(8), 1127; doi:10.3390/en10081127
Received: 17 May 2017 / Revised: 23 July 2017 / Accepted: 26 July 2017 / Published: 1 August 2017
PDF Full-text (611 KB) | HTML Full-text | XML Full-text
Abstract
Public support is an important factor in failure or success of the government decisions with respect to the electricity generation mix, which highlights the necessity of developing an electricity mix that reflects social preferences and acceptance. This study explores heterogeneity in social preferences
[...] Read more.
Public support is an important factor in failure or success of the government decisions with respect to the electricity generation mix, which highlights the necessity of developing an electricity mix that reflects social preferences and acceptance. This study explores heterogeneity in social preferences for power sources and develops an electricity mix from a demand-side perspective. The study utilizes the choice-based conjoint survey and latent class model, and bases its empirical analysis on South Korea’s electric power sector. Results demonstrate that preferences for power sources in Korean society consist of two classes: one that is sensitive to the environment and one that is sensitive to risk. An electricity mix for Korea that reflects social preferences is 16.5–19.8% coal-fired, 13.3–24.9% liquefied natural gas (LNG), 9.0–11.2% oil, 22.3–32.9% nuclear, and 18.5–38.9% renewables, depending on the scenario. The study confirms that renewables are the power source with the least potential to cause social conflict, compared to nuclear and coal-fired sources. Moreover, increasing the proportion of renewables (currently only 3.9%) while decreasing the proportion of coal-fired power sources (currently 39.9%) to less than half its current level will result in an electricity mix that is accordance with social preferences in the long run. Full article
(This article belongs to the Section Energy Sources)
Figures

Figure 1

Open AccessArticle A New Combined Boost Converter with Improved Voltage Gain as a Battery-Powered Front-End Interface for Automotive Audio Amplifiers
Energies 2017, 10(8), 1128; doi:10.3390/en10081128
Received: 18 April 2017 / Revised: 4 June 2017 / Accepted: 28 July 2017 / Published: 1 August 2017
PDF Full-text (10688 KB) | HTML Full-text | XML Full-text
Abstract
High boost DC/DC voltage conversion is always indispensable in a power electronic interface of certain battery-powered electrical equipment. However, a conventional boost converter works for a wide duty cycle for such high voltage gain, which increases power consumption and has low reliability problems.
[...] Read more.
High boost DC/DC voltage conversion is always indispensable in a power electronic interface of certain battery-powered electrical equipment. However, a conventional boost converter works for a wide duty cycle for such high voltage gain, which increases power consumption and has low reliability problems. In order to solve this issue, a new battery-powered combined boost converter with an interleaved structure consisting of two phases used in automotive audio amplifier is presented. The first phase uses a conventional boost converter; the second phase employs the inverted type. With this architecture, a higher boost voltage gain is able to be achieved. A derivation of the operating principles of the converter, analyses of its topology, as well as a closed-loop control designs are performed in this study. Furthermore, simulations and experiments are also performed using input voltage of 12 V for a 120 W circuit. A reasonable duty cycle is selected to reach output voltage of 60 V, which corresponds to static voltage gain of five. The converter achieves a maximum measured conversion efficiency of 98.7% and the full load efficiency of 89.1%. Full article
Figures

Figure 1

Open AccessArticle Investigation of the Dynamic Melting Process in a Thermal Energy Storage Unit Using a Helical Coil Heat Exchanger
Energies 2017, 10(8), 1129; doi:10.3390/en10081129
Received: 18 June 2017 / Revised: 27 July 2017 / Accepted: 28 July 2017 / Published: 1 August 2017
PDF Full-text (9057 KB) | HTML Full-text | XML Full-text
Abstract
In this study, the dynamic melting process of the phase change material (PCM) in a vertical cylindrical tube-in-tank thermal energy storage (TES) unit was investigated through numerical simulations and experimental measurements. To ensure good heat exchange performance, a concentric helical coil was inserted
[...] Read more.
In this study, the dynamic melting process of the phase change material (PCM) in a vertical cylindrical tube-in-tank thermal energy storage (TES) unit was investigated through numerical simulations and experimental measurements. To ensure good heat exchange performance, a concentric helical coil was inserted into the TES unit to pipe the heat transfer fluid (HTF). A numerical model using the computational fluid dynamics (CFD) approach was developed based on the enthalpy-porosity method to simulate the unsteady melting process including temperature and liquid fraction variations. Temperature measurements using evenly spaced thermocouples were conducted, and the temperature variation at three locations inside the TES unit was recorded. The effects of the HTF inlet parameters were investigated by parametric studies with different temperatures and flow rate values. Reasonably good agreement was achieved between the numerical prediction and the temperature measurement, which confirmed the numerical simulation accuracy. The numerical results showed the significance of buoyancy effect for the dynamic melting process. The system TES performance was very sensitive to the HTF inlet temperature. By contrast, no apparent influences can be found when changing the HTF flow rates. This study provides a comprehensive solution to investigate the heat exchange process of the TES system using PCM. Full article
(This article belongs to the Special Issue Solar Technologies for Buildings)
Figures

Figure 1

Open AccessArticle Advanced Measurement and Simulation Procedure for the Identification of Heat and Mass Transfer Parameters in Dynamic Adsorption Experiments
Energies 2017, 10(8), 1130; doi:10.3390/en10081130
Received: 27 April 2017 / Revised: 30 June 2017 / Accepted: 23 July 2017 / Published: 2 August 2017
PDF Full-text (3589 KB) | HTML Full-text | XML Full-text
Abstract
Thermally-driven heat pumps can help to mitigate CO2 emissions by enhancing the efficiency of heating systems or by driving cooling systems with waste or solar heat. In order to make the thermally-driven systems more attractive for the end consumer, these systems need
[...] Read more.
Thermally-driven heat pumps can help to mitigate CO2 emissions by enhancing the efficiency of heating systems or by driving cooling systems with waste or solar heat. In order to make the thermally-driven systems more attractive for the end consumer, these systems need a higher power density. A higher power density can be achieved by intensifying the heat and mass transfer processes within the adsorption heat exchanger. For the optimization of this key component, a numerical model of the non-isothermal adsorption dynamics can be applied. The calibration of such a model can be difficult, since heat and mass transfer processes are strongly coupled. We present a measurement and simulation procedure that makes it possible to calibrate the heat transfer part of the numerical model separately from the mass transfer part. Furthermore, it is possible to identify the parts of the model that need to be improved. For this purpose, a modification of the well-known large temperature jump method is developed. The newly-introduced measurements are conducted under an inert N2 atmosphere, and the surface temperature of the sample is measured with an infrared sensor. We show that the procedure is applicable for two completely different types of samples: a loose grains configuration and a fibrous structure that is directly crystallized. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
Figures

Figure 1

Open AccessArticle Demand Side Management in Nearly Zero Energy Buildings Using Heuristic Optimizations
Energies 2017, 10(8), 1131; doi:10.3390/en10081131
Received: 29 June 2017 / Revised: 25 July 2017 / Accepted: 29 July 2017 / Published: 2 August 2017
PDF Full-text (890 KB) | HTML Full-text | XML Full-text
Abstract
Today’s buildings are responsible for about 40% of total energy consumption and 30–40% of carbon emissions, which are key concerns for the sustainable development of any society. The excessive usage of grid energy raises sustainability issues in the face of global changes, such
[...] Read more.
Today’s buildings are responsible for about 40% of total energy consumption and 30–40% of carbon emissions, which are key concerns for the sustainable development of any society. The excessive usage of grid energy raises sustainability issues in the face of global changes, such as climate change, population, economic growths, etc. Traditionally, the power systems that deliver this commodity are fuel operated and lead towards high carbon emissions and global warming. To overcome these issues, the recent concept of the nearly zero energy building (nZEB) has attracted numerous researchers and industry for the construction and management of the new generation buildings. In this regard, this paper proposes various demand side management (DSM) programs using the genetic algorithm (GA), teaching learning-based optimization (TLBO), the enhanced differential evolution (EDE) algorithm and the proposed enhanced differential teaching learning algorithm (EDTLA) to manage energy and comfort, while taking the human preferences into consideration. Power consumption patterns of shiftable home appliances are modified in response to the real-time price signal in order to get monetary benefits. To further improve the cost and user discomfort objectives along with reduced carbon emission, renewable energy sources (RESs) are also integrated into the microgrid (MG). The proposed model is implemented in a smart residential complex of multiple homes under a real-time pricing environment. We figure out two feasible regions: one for electricity cost and the other for user discomfort. The proposed model aims to deal with the stochastic nature of RESs while introducing the battery storage system (BSS). The main objectives of this paper include: (1) integration of RESs; (2) minimization of the electricity bill (cost) and discomfort; and (3) minimizing the peak to average ratio (PAR) and carbon emission. Additionally, we also analyze the tradeoff between two conflicting objectives, like electricity cost and user discomfort. Simulation results validate both the implemented and proposed techniques. Full article
(This article belongs to the Special Issue Battery Energy Storage Applications in Smart Grid)
Figures

Figure 1

Open AccessArticle Design of a Control System for a Maglev Planar Motor Based on Two-Dimension Linear Interpolation
Energies 2017, 10(8), 1132; doi:10.3390/en10081132
Received: 6 June 2017 / Revised: 23 July 2017 / Accepted: 27 July 2017 / Published: 2 August 2017
PDF Full-text (9310 KB) | HTML Full-text | XML Full-text
Abstract
In order to realize the high speed and high-precision control of a maglev planar motor, a high-precision electromagnetic model is needed in the first place, which can also contribute to meeting the real-time running requirements. Traditionally, the electromagnetic model is based on analytical
[...] Read more.
In order to realize the high speed and high-precision control of a maglev planar motor, a high-precision electromagnetic model is needed in the first place, which can also contribute to meeting the real-time running requirements. Traditionally, the electromagnetic model is based on analytical calculations. However, this neglects the model simplification and the manufacturing errors, which may bring certain errors to the model. Aiming to handle this inaccuracy, this paper proposes a novel design method for a maglev planar motor control system based on two-dimensional linear interpolation. First, the magnetic field is divided into several regions according to the symmetry of the Halbach magnetic array, and the uniform grid method is adopted to partition one of these regions. Second, targeting this region, it is possible to sample the electromagnetic forces and torques on each node of the grid and obtain the complete electromagnetic model in this region through the two-dimensional linear interpolation method. Third, the whole electromagnetic model of the maglev planar motor can be derived according to the symmetry of the magnetic field. Finally, the decoupling method and controller are designed according to this electromagnetic model, and thereafter, the control model can be established. The designed control system is demonstrated through simulations and experiments to feature better accuracy and meet the requirements of real-time control. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
Figures

Figure 1

Open AccessArticle Model Predictive Direct Power Control for Nonredundant Fault Tolerant Grid-Connected Bidirectional Voltage Source Converter
Energies 2017, 10(8), 1133; doi:10.3390/en10081133
Received: 7 July 2017 / Revised: 27 July 2017 / Accepted: 28 July 2017 / Published: 2 August 2017
PDF Full-text (7870 KB) | HTML Full-text | XML Full-text
Abstract
This paper proposes a model predictive direct power control scheme for nonredundant fault tolerant grid-connected bidirectional voltage source converter (BVSC) with balanced dc-link split capacitor voltage and high reliability. Based on the operation analysis of fault-tolerant BVSC with phase leg faults, a power
[...] Read more.
This paper proposes a model predictive direct power control scheme for nonredundant fault tolerant grid-connected bidirectional voltage source converter (BVSC) with balanced dc-link split capacitor voltage and high reliability. Based on the operation analysis of fault-tolerant BVSC with phase leg faults, a power predictive model of three-phase four-switch fault-tolerant topology in αβ coordinates is established, and the space voltage vectors with unbalanced dc-link split capacitor voltage are analyzed. According to the power predictive model and cost function, the optimal space voltage vector is selected to achieve a flexible, smooth transition between inverter and rectifier mode with direct power control. Pulse width modulation and phase locked loop are not required in the proposed method. The constraint of dc-link voltage constraint is designed for the cost function to achieve a central point of dc-link voltage offset suppression, which can reduce the risk of electrolytic capacitor failure for over-voltage operation. With the proposed control method, the converter can work continuously in both inverter mode and rectifier mode, even if phase leg faults occur. The simulation and experimental results show good steady-state and dynamic performance of the proposed control scheme to enhance the reliability of bidirectional power conversion. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
Figures

Figure 1

Open AccessArticle Improving the Traffic Model to Be Used in the Optimisation of Mass Transit System Electrical Infrastructure
Energies 2017, 10(8), 1134; doi:10.3390/en10081134
Received: 20 June 2017 / Revised: 20 July 2017 / Accepted: 28 July 2017 / Published: 2 August 2017
PDF Full-text (5032 KB) | HTML Full-text | XML Full-text
Abstract
Among the different approaches for minimising the energy consumption of mass transit systems (MTSs), a common concern for MTS operators is the improvement of the electrical infrastructure. The traffic on the lines under analysis is one of the most important inputs to the
[...] Read more.
Among the different approaches for minimising the energy consumption of mass transit systems (MTSs), a common concern for MTS operators is the improvement of the electrical infrastructure. The traffic on the lines under analysis is one of the most important inputs to the studies devoted to improving MTS infrastructure, since it represents where and how frequently it is possible to save energy. However, on the one hand, MTS electrical studies usually simplify the traffic model, which may lead to a misrepresentation of the energy interactions between trains. On the other hand, if the stochastic traffic is rigorously modelled, the size of the simulation problem could grow excessively, which in turn could make the time to obtain results unmanageable. To cope with this issue, this paper presents a method to obtain a reduced-size set of representative scenarios. Firstly, a traffic model including the most representative stochastic traffic variables is developed. Secondly, a function highly correlated with energy savings is proposed to make it possible to properly characterise the traffic scenarios. Finally, this function is used to select the most representative scenarios. The representative scenario set obtained by the application of this method is shown to be sufficiently accurate with a limited number of scenarios. The traffic approach in this paper improves the accuracy with respect to the usual traffic approach used in the literature. Full article
(This article belongs to the Section Electrical Power and Energy System)
Figures

Figure 1

Open AccessArticle Transformer Paper Expected Life Estimation Using ANFIS Based on Oil Characteristics and Dissolved Gases (Case Study: Indonesian Transformers)
Energies 2017, 10(8), 1135; doi:10.3390/en10081135
Received: 7 June 2017 / Revised: 24 July 2017 / Accepted: 27 July 2017 / Published: 2 August 2017
PDF Full-text (3250 KB) | HTML Full-text | XML Full-text
Abstract
This article presents an algorithm for modelling an Adaptive Neuro Fuzzy Inference System (ANFIS) for power transformer paper conditions in order to estimate the transformer’s expected life. The dielectric characteristics, dissolved gasses, and furfural of 108 running transformers were collected, which were divided
[...] Read more.
This article presents an algorithm for modelling an Adaptive Neuro Fuzzy Inference System (ANFIS) for power transformer paper conditions in order to estimate the transformer’s expected life. The dielectric characteristics, dissolved gasses, and furfural of 108 running transformers were collected, which were divided into 76 training datasets and another 32 testing datasets. The degree of polymerization (DP) of the transformer paper was predicted using the ANFIS model based on using the dielectric characteristics and dissolved gases as input. These inputs were analyzed, and the best combination was selected, whereas CO + CO2, acidity, interfacial tension, and color were correlated with the paper’s deterioration condition and were chosen as the input variables. The best combination of input variables and membership function was selected to build the optimal ANFIS model, which was then compared and evaluated. The proposed ANFIS model has 89.07% training accuracy and 85.75% testing accuracy and was applied to a transformer paper insulation assessment and an estimation of the expected life of four Indonesian transformers for which furfural data is unavailable. This proposed algorithm can be used as a furfural alternative for the general assessment of transformer paper conditions and the estimation of expected life and provides a helpful assistance for experts in transformer condition assessment. Full article
Figures

Figure 1

Open AccessArticle Computational Fluid Dynamics Simulation Study of a Novel Membrane Contactor for Simultaneous Carbon Dioxide Absorption and Stripping
Energies 2017, 10(8), 1136; doi:10.3390/en10081136
Received: 4 July 2017 / Revised: 28 July 2017 / Accepted: 31 July 2017 / Published: 2 August 2017
PDF Full-text (9140 KB) | HTML Full-text | XML Full-text
Abstract
Physical absorption is a potential technology for economic carbon capture due to its low energy consumption, however, the absorption efficiency of current systems must be improved. In this study, novel hybrid absorption/stripping membrane contactors (HASMCs) for physical solvent carbon capture are proposed. The
[...] Read more.
Physical absorption is a potential technology for economic carbon capture due to its low energy consumption, however, the absorption efficiency of current systems must be improved. In this study, novel hybrid absorption/stripping membrane contactors (HASMCs) for physical solvent carbon capture are proposed. The simultaneous absorption and stripping within one module provides instant regeneration of the solvent and results in the enhancement of absorption. HASMCs with parallel-flow and cross-flow configurations and using empty or spacer-filled channels are investigated by rigorous computational fluid dynamics simulation. The internal profiles of transmembrane mass fluxes reveal that cross-flow HASMCs are much more effective than the parallel-flow ones and the modules using spacer-filled channels give better performance than the ones using empty channels. The mass transfer coefficients of HASMCs are much higher than predicted by correlations in the literature. Full article
Figures

Figure 1

Open AccessArticle Development of the IBSAL-SimMOpt Method for the Optimization of Quality in a Corn Stover Supply Chain
Energies 2017, 10(8), 1137; doi:10.3390/en10081137
Received: 28 June 2017 / Revised: 31 July 2017 / Accepted: 31 July 2017 / Published: 3 August 2017
PDF Full-text (7694 KB) | HTML Full-text | XML Full-text
Abstract
Variability on the physical characteristics of feedstock has a relevant effect on the reactor’s reliability and operating cost. Most of the models developed to optimize biomass supply chains have failed to quantify the effect of biomass quality and preprocessing operations required to meet
[...] Read more.
Variability on the physical characteristics of feedstock has a relevant effect on the reactor’s reliability and operating cost. Most of the models developed to optimize biomass supply chains have failed to quantify the effect of biomass quality and preprocessing operations required to meet biomass specifications on overall cost and performance. The Integrated Biomass Supply Analysis and Logistics (IBSAL) model estimates the harvesting, collection, transportation, and storage cost while considering the stochastic behavior of the field-to-biorefinery supply chain. This paper proposes an IBSAL-SimMOpt (Simulation-based Multi-Objective Optimization) method for optimizing the biomass quality and costs associated with the efforts needed to meet conversion technology specifications. The method is developed in two phases. For the first phase, a SimMOpt tool that interacts with the extended IBSAL is developed. For the second phase, the baseline IBSAL model is extended so that the cost for meeting and/or penalization for failing in meeting specifications are considered. The IBSAL-SimMOpt method is designed to optimize quality characteristics of biomass, cost related to activities intended to improve the quality of feedstock, and the penalization cost. A case study based on 1916 farms in Ontario, Canada is considered for testing the proposed method. Analysis of the results demonstrates that this method is able to find a high-quality set of non-dominated solutions. Full article
(This article belongs to the Special Issue Biomass for Energy Country Specific Show Case Studies)
Figures

Figure 1

Open AccessArticle Evaluation of Voltage Control Approaches for Future Smart Distribution Networks
Energies 2017, 10(8), 1138; doi:10.3390/en10081138
Received: 14 June 2017 / Revised: 29 July 2017 / Accepted: 31 July 2017 / Published: 3 August 2017
PDF Full-text (1865 KB) | HTML Full-text | XML Full-text
Abstract
This paper evaluates meta-heuristic and deterministic approaches for distribution network voltage control. As part of this evaluation, a novel meta-heuristic algorithm, Cuckoo Search, is applied for distribution network voltage control and compared with a deterministic voltage control algorithm, the oriented discrete coordinate decent
[...] Read more.
This paper evaluates meta-heuristic and deterministic approaches for distribution network voltage control. As part of this evaluation, a novel meta-heuristic algorithm, Cuckoo Search, is applied for distribution network voltage control and compared with a deterministic voltage control algorithm, the oriented discrete coordinate decent method (ODCDM). ODCDM has been adopted in a state-of-the-art industrial product and applied in real distribution networks. These two algorithms have been evaluated under a set of test cases, which were generated to represent the voltage control problems in current and future distribution networks. Sampled test results have been presented, and findings have been discussed regarding the adoption of different optimization algorithms for current and future distribution networks. Full article
(This article belongs to the Section Electrical Power and Energy System)
Figures

Figure 1

Open AccessArticle Passivity-Based Control of a Doubly Fed Induction Generator System under Unbalanced Grid Voltage Conditions
Energies 2017, 10(8), 1139; doi:10.3390/en10081139
Received: 23 May 2017 / Revised: 17 July 2017 / Accepted: 31 July 2017 / Published: 3 August 2017
PDF Full-text (1364 KB) | HTML Full-text | XML Full-text
Abstract
According to the theory of passivity-based control (PBC), this paper establishes a port-controlled Hamiltonian system with dissipation (PCHD) model for a doubly fed induction generator (DFIG) system under unbalanced grid voltage conditions and proposes a method of interconnection and damping assignment passivity-based control
[...] Read more.
According to the theory of passivity-based control (PBC), this paper establishes a port-controlled Hamiltonian system with dissipation (PCHD) model for a doubly fed induction generator (DFIG) system under unbalanced grid voltage conditions and proposes a method of interconnection and damping assignment passivity-based control (IDA-PBC) of the system under such conditions. By using this method, the rotor-side converter and grid-side converter can be controlled simultaneously in order to improve fault ride-through capability of the DFIG system. Simulation results indicate that this IDA-PBC strategy effectively suppresses fluctuations of output current and power in the DFIG system during unbalanced grid voltage sag/swell, enhances dynamic performance, and improves the robustness of the system. Full article
(This article belongs to the Section Energy Sources)
Figures

Figure 1

Open AccessArticle Windbreak Effects Within Infinite Wind Farms
Energies 2017, 10(8), 1140; doi:10.3390/en10081140
Received: 9 May 2017 / Revised: 14 July 2017 / Accepted: 27 July 2017 / Published: 3 August 2017
PDF Full-text (3818 KB) | HTML Full-text | XML Full-text
Abstract
Building upon a recent study that showed windbreaks to be effective in increasing the power output of a wind turbine, the potential of windbreaks in a large wind farm is explored using simplified formulations. A top-down boundary layer approach is combined with methods
[...] Read more.
Building upon a recent study that showed windbreaks to be effective in increasing the power output of a wind turbine, the potential of windbreaks in a large wind farm is explored using simplified formulations. A top-down boundary layer approach is combined with methods of estimating both the roughness effects of windbreaks and the induced inviscid speed-up for nearby turbines to investigate power production impact for several layouts of infinite wind farms. Results suggest that the negative impact of windbreak wakes for an infinite wind farm will outweigh the local inviscid speed-up for realistic inter-turbine spacings, with the break-even point expected at a spacing of ∼25 rotor diameters. However, the possibility that windbreaks may be applicable in finite and other wind farm configurations remains open. Inspection of the windbreak porosity reveals an impact on the magnitude of power perturbation, but not whether the change is positive or negative. Predictions from the boundary-layer approach are validated with power measurements from large-eddy simulations. Full article
(This article belongs to the collection Wind Turbines)
Figures

Figure 1

Open AccessFeature PaperArticle A Simplified Microgrid Model for the Validation of Islanded Control Logics
Energies 2017, 10(8), 1141; doi:10.3390/en10081141
Received: 19 June 2017 / Revised: 25 July 2017 / Accepted: 30 July 2017 / Published: 3 August 2017
PDF Full-text (12467 KB) | HTML Full-text | XML Full-text
Abstract
Microgrids (MGs) may represent a solution in the near future to many problems in the energy and electric world scenarios; such as pollution, high reliability, efficiency and so on. In particular, MGs’ capability to work in an islanded configuration represents one of their
[...] Read more.
Microgrids (MGs) may represent a solution in the near future to many problems in the energy and electric world scenarios; such as pollution, high reliability, efficiency and so on. In particular, MGs’ capability to work in an islanded configuration represents one of their most interesting features in terms of the improvement of the reliability of the system, the integration of renewable energy sources and the exploitation of the quick response and flexibility of power electronic devices in a stand-alone system. In order to study and validate innovative solutions and control strategies for islanded operation, there is a need to develop models for MG structures that can be reliable and sufficiently simple to be used for the purpose of the design and validation of innovative control systems. This paper proposes a simplified, first harmonic model for a generic structure of MG characterized by its use of only electronic power converter interfaced generation. The main advantages of the proposed method lie in the model’s simplicity and its reduced solving time, thanks to the limited number of necessary parameters to describe the system. Moreover, the developed formulation allows the avoidance of specific (and often licensed) software to simulate the system. The performances of the proposed model have been validated by means of a comparative analysis of the results obtained against a more accurate representation of the system performed in the power system CAD—electromagnetic transient and DC (PSCAD—EMTDC) environment, which allows for the representation of each component with a very high level of detail. Such comparison has been performed using the University of Genoa Savona Campus Smart Polygeneration Microgrid testbed facility, due to the availability of all the necessary numerical values. Full article
Figures

Figure 1

Open AccessArticle Design and Construction of 1 MW Class Floating PV Generation Structural System Using FRP Members
Energies 2017, 10(8), 1142; doi:10.3390/en10081142
Received: 22 May 2017 / Revised: 11 July 2017 / Accepted: 1 August 2017 / Published: 3 August 2017
PDF Full-text (7084 KB) | HTML Full-text | XML Full-text
Abstract
The paper investigates overview of construction process of a 1 MW class floating photovoltaic (PV) generation structural system fabricated with fiber reinforced polymer (FRP) members. The floating PV generation system consists of unit structures linked by a hinge type connection of which the
[...] Read more.
The paper investigates overview of construction process of a 1 MW class floating photovoltaic (PV) generation structural system fabricated with fiber reinforced polymer (FRP) members. The floating PV generation system consists of unit structures linked by a hinge type connection of which the effect of bending moment between the unit structures, induced by the unstable movement of the water surface, was minimized. Moreover, the unit structures were classified into three types of structures by combining the floating PV generation system and pontoon bridges, which are constructed to install the electrical equipment and a route of movement for workers. The structural safety of the connection system among the unit structures and/or the mooring system is confirmed by referring to the relevant design codes. In addition, structural analysis using the finite element method was performed to ensure the safety of the floating PV generation structure, and commercial viability evaluation was performed based on the construction cost. The FRP member shows superior performance in construction and cost effectiveness in a floating PV generation system. Full article
(This article belongs to the Special Issue PV System Design and Performance)
Figures

Figure 1

Open AccessArticle AC Transmission Emulation Control Strategies for the BTB VSC HVDC System in the Metropolitan Area of Seoul
Energies 2017, 10(8), 1143; doi:10.3390/en10081143
Received: 31 May 2017 / Revised: 30 July 2017 / Accepted: 31 July 2017 / Published: 3 August 2017
PDF Full-text (3851 KB) | HTML Full-text | XML Full-text
Abstract
In the Korean power system, growing power loads have recently created the problems of voltage instability and fault current in the Seoul Capital Area (SCA). Accordingly, the back-to-back (BTB) voltage source converter (VSC) high-voltage direct-current (HVDC) system is emerging to resolve such problems
[...] Read more.
In the Korean power system, growing power loads have recently created the problems of voltage instability and fault current in the Seoul Capital Area (SCA). Accordingly, the back-to-back (BTB) voltage source converter (VSC) high-voltage direct-current (HVDC) system is emerging to resolve such problems with grid segmentation. However, non-convergence problems occur in this metropolitan area, due to the large change of power flow in some contingencies. Therefore, this paper proposes two kinds of AC transmission emulation control (ATEC) strategies to improve the metropolitan transient stability, and to resolve the non-convergence problem. The proposed ATEC strategies are able to mitigate possible overloading of adjacent AC transmission, and maintain power balance between metropolitan regions. The first ATEC strategy uses a monitoring system that permits the reverse power flow of AC transmission, and thus effectively improves the grid stability based on the power transfer equation. The second ATEC strategy emulates AC transmission with DC link capacitors in a permissible DC-link voltage range according to angle difference, and securely improves the gird stability, without requiring grid operator schedule decisions. This paper compares two kinds of ATEC schemes: it demonstrates the first ATEC strategy with specific fault scenario with PSS/E (Power Transmission System Planning Software), and evaluates the second ATEC strategy with internal controller performance with PSCAD/EMTDC (Power System Electromagnetic Transients Simulation Software). Full article
(This article belongs to the Section Electrical Power and Energy System)
Figures

Figure 1