Next Issue
Volume 10, August
Previous Issue
Volume 10, June

Table of Contents

Energies, Volume 10, Issue 7 (July 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 (view full-size image) Alternative fuels are an important aspect of transportation and energy production. The study of [...] Read more.
Order results
Result details
Select all
Export citation of selected articles as:
Open AccessEditorial
Energy and Waste Management
Energies 2017, 10(7), 1072; https://doi.org/10.3390/en10071072 - 24 Jul 2017
Cited by 4 | Viewed by 1278
Abstract
Waste management and energy systems are often interlinked, either directly by waste-to-energy technologies, or indirectly as processes for recovery of resources—such as materials, oils, manure, or sludge—use energy in their processes or substitute conventional production of the commodities for which the recycling processes [...] Read more.
Waste management and energy systems are often interlinked, either directly by waste-to-energy technologies, or indirectly as processes for recovery of resources—such as materials, oils, manure, or sludge—use energy in their processes or substitute conventional production of the commodities for which the recycling processes provide raw materials. A special issue in Energies on the topic of “Energy and Waste Management” attained a lot of attention from the scientific community. In particular, papers contributing to improved understanding of the combined management of waste and energy were invited. In all, 9 papers were published out of 24 unique submissions. The papers cover technical topics such as leaching of heavy metals, pyrolysis, and production of synthetic natural gas in addition to different systems assessments of horse manure, incineration, and complex future scenarios at a national level. All papers except one focused on energy recovery from waste. That particular paper focused on waste management of infrastructure in an energy system (wind turbines). Published papers illustrate research in the field of energy and waste management on both a current detailed process level as well as on a future system level. Knowledge gained on both types is necessary to be able to make progress towards a circular economy. Full article
(This article belongs to the Special Issue Energy and Waste Management)
Open AccessArticle
Research on Capacitance Current Compensation Scheme of Current Differential Protection of Complex Four-Circuit Transmission Lines on the Same Tower
Energies 2017, 10(7), 1071; https://doi.org/10.3390/en10071071 - 23 Jul 2017
Cited by 1 | Viewed by 1334
Abstract
Current differential protection is the main protection of transmission lines which include multi-circuit lines on the same tower, and whose sensitivity and reliability of differential protection is mainly affected by the distributed capacitive current. For the four-circuit line on the same tower, due [...] Read more.
Current differential protection is the main protection of transmission lines which include multi-circuit lines on the same tower, and whose sensitivity and reliability of differential protection is mainly affected by the distributed capacitive current. For the four-circuit line on the same tower, due to the influence of coupling between the loop road, the distributed capacitance current increases significantly when compared with ordinary lines, affecting the sensitivity of the current differential protection, especially for different voltage levels throughout the four-circuit lines on the same tower. The relationship of the electrostatic coupling between the circuits is more complex, and increases the difficulty of the compensating the distributed capacitance current. This paper is based on the electrostatic coupling principle of four-circuit lines on the same tower, establishes the distributed parameter model of four-circuit transmission lines on the same tower, and discusses the effect of circuit operation mode on the compensation of capacitance current differential protection when different faults occur on the complex four-circuit transmission lines on the same tower. A new compensation scheme suitable for capacitive current compensation is proposed. Simulation results show that this capacitive current compensation scheme can effectively improve the performance of current differential protection. Full article
(This article belongs to the Section Electrical Power and Energy System)
Show Figures

Figure 1

Open AccessArticle
Influence of the Steam Addition on Premixed Methane Air Combustion at Atmospheric Pressure
Energies 2017, 10(7), 1070; https://doi.org/10.3390/en10071070 - 23 Jul 2017
Cited by 1 | Viewed by 1608
Abstract
Steam-diluted combustion in gas turbine systems is an effective approach to control pollutant emissions and improve the gas turbine efficiency. The primary purpose of the present research is to analyze the influence of steam dilution on the combustion stability, flame structures, and CO [...] Read more.
Steam-diluted combustion in gas turbine systems is an effective approach to control pollutant emissions and improve the gas turbine efficiency. The primary purpose of the present research is to analyze the influence of steam dilution on the combustion stability, flame structures, and CO emissions of a swirl-stabilized gas turbine model combustor under atmospheric pressure conditions. The premixed methane/air/steam flame was investigated with three preheating temperatures (384 K/434 K/484 K) and the equivalence ratio was varied from stoichiometric conditions to the flammability limits where the flame was physically blown out from the combustor. In order to represent the steam dilution intensity, the steam fraction Ω defined as the steam to air mass flow rate ratio was used in this work. Exhaust gases were sampled with a water-cooled emission probe which was mounted at the combustor exit. A 120 mm length quartz liner was used which enabled the flame visualization and optical measurement. Time-averaged CH chemiluminescence imaging was conducted to characterize the flame location and it was further analyzed with the inverse Abel transform method. Chemical kinetics calculation was conducted to support and analyze the experimental results. It was found that the LBO (lean blowout) limits were increased with steam fraction. CH chemiluminescence imaging showed that with a high steam fraction, the flame length was elongated, but the flame structure was not altered. CO emissions were mapped as a function of the steam fraction, inlet air temperature, and equivalence ratios. Stable combustion with low CO emission can be achieved with an appropriate steam fraction operation range. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
Show Figures

Figure 1

Open AccessArticle
A Novel Workflow for Geothermal Prospectively Mapping Weights-of-Evidence in Liaoning Province, Northeast China
Energies 2017, 10(7), 1069; https://doi.org/10.3390/en10071069 - 22 Jul 2017
Cited by 2 | Viewed by 1419
Abstract
Geological faults are highly developed in the eastern Liaoning Province in China, where Mesozoic granitic intrusions and Archean and Paleoproterozoic metamorphic rocks are widely distributed. Although the heat flow value in eastern Liaoning Province is generally low, the hot springs are very developed. [...] Read more.
Geological faults are highly developed in the eastern Liaoning Province in China, where Mesozoic granitic intrusions and Archean and Paleoproterozoic metamorphic rocks are widely distributed. Although the heat flow value in eastern Liaoning Province is generally low, the hot springs are very developed. It is obvious that the faults have significant control over the distribution of hot springs, and traditional methods of spatial data analysis such as WofE (weight of evidence) usually do not take into account the direction of the distribution of geothermal resources in the geothermal forecast process, which seriously affects the accuracy of the prediction results. To overcome the deficiency of the traditional evidence weight method, wherein it does not take the direction of evidence factor into account, this study put forward a combination of the Fry and WofE methods, Fry-WofE, based on geological observation, gravity, remote sensing, and DEM (digital elevation model) multivariate data. This study takes eastern Liaoning Province in China as an example, and the geothermal prospect was predicted respectively by the Fry-WofE and WofE methods from the statistical data on the spatial distribution of the exposed space of geothermal anomalies the surface. The result shows that the Fry-WofE method can achieve better prediction results when comparing the accuracy of these two methods. Based on the results of Fry-WofE prediction and water system extraction, 13 favorable geothermal prospect areas are delineated in eastern Liaoning Province. The Fry-WofE method is effective in study areas where the geothermal distribution area is obviously controlled by the fault. We provide not only a new method for solving the similar issue of geothermal exploration, but also a new insight into the distribution of geothermal resources in Liaoning Province. Full article
(This article belongs to the Section Energy Sources)
Show Figures

Figure 1

Open AccessArticle
Modeling Noise Sources and Propagation in External Gear Pumps
Energies 2017, 10(7), 1068; https://doi.org/10.3390/en10071068 - 22 Jul 2017
Cited by 6 | Viewed by 2351
Abstract
As a key component in power transfer, positive displacement machines often represent the major source of noise in hydraulic systems. Thus, investigation into the sources of noise and discovering strategies to reduce noise is a key part of improving the performance of current [...] Read more.
As a key component in power transfer, positive displacement machines often represent the major source of noise in hydraulic systems. Thus, investigation into the sources of noise and discovering strategies to reduce noise is a key part of improving the performance of current hydraulic systems, as well as applying fluid power systems to a wider range of applications. The present work aims at developing modeling techniques on the topic of noise generation caused by external gear pumps for high pressure applications, which can be useful and effective in investigating the interaction between noise sources and radiated noise and establishing the design guide for a quiet pump. In particular, this study classifies the internal noise sources into four types of effective load functions and, in the proposed model, these load functions are applied to the corresponding areas of the pump case in a realistic way. Vibration and sound radiation can then be predicted using a combined finite element and boundary element vibro-acoustic model. The radiated sound power and sound pressure for the different operating conditions are presented as the main outcomes of the acoustic model. The noise prediction was validated through comparison with the experimentally measured sound power levels. Full article
(This article belongs to the Special Issue Energy Efficiency and Controllability of Fluid Power Systems)
Show Figures

Figure 1

Open AccessArticle
Control Strategy for a Grid-Connected Inverter under Unbalanced Network Conditions—A Disturbance Observer-Based Decoupled Current Approach
Energies 2017, 10(7), 1067; https://doi.org/10.3390/en10071067 - 22 Jul 2017
Cited by 11 | Viewed by 2041
Abstract
This paper proposes a new approach on the novel current control strategy for grid-tied voltage-source inverters (VSIs) with circumstances of asymmetrical voltage conditions. A standard grid-connected inverter (GCI) allows the degree of freedom to integrate the renewable energy system to enhance the penetration [...] Read more.
This paper proposes a new approach on the novel current control strategy for grid-tied voltage-source inverters (VSIs) with circumstances of asymmetrical voltage conditions. A standard grid-connected inverter (GCI) allows the degree of freedom to integrate the renewable energy system to enhance the penetration of total utility power. However, restrictive grid codes require that renewable sources connected to the grid must support stability of the grid under grid faults. Conventional synchronously rotating frame dq current controllers are insufficient under grid faults due to the low bandwidth of proportional-integral (PI) controllers. Hence, this work proposes a proportional current controller with a first-order low-pass filter disturbance observer (DOb). The proposed controller establishes independent control on positive, as well as negative, sequence current components under asymmetrical grid voltage conditions. The approach is independent of parametric component values, as it estimates nonlinear feed-forward terms with the low-pass filter DOb. A numerical simulation model of the overall power system was implemented in a MATLAB/Simulink (2014B, MathWorks, Natick, MA, USA). Further, particular results show that double-frequency active power oscillations are suppressed by injecting appropriate negative-sequence currents. Moreover, a set of simulation results provided in the article matches the developed theoretical background for its feasibility. Full article
Show Figures

Figure 1

Open AccessArticle
Thermal and Performance Analysis of a Gasification Boiler and Its Energy Efficiency Optimization
Energies 2017, 10(7), 1066; https://doi.org/10.3390/en10071066 - 22 Jul 2017
Cited by 3 | Viewed by 1615
Abstract
The purpose of this study was to determine a method for multi-parametric output regulation of a gasification boiler especially designed for heating or for hot water heating in buildings. A new method of regulation is offered, namely more parametric regulation via proportional-integral-derivative (PID) [...] Read more.
The purpose of this study was to determine a method for multi-parametric output regulation of a gasification boiler especially designed for heating or for hot water heating in buildings. A new method of regulation is offered, namely more parametric regulation via proportional-integral-derivative (PID) controllers that are capable of controlling the calculated values of pressure, temperature and fan speed. These values of pressure, temperature and fan speed are calculated in a completely new way, and calculations of setpoints for determination of optimal parameters lead to an increase in boilers efficiency and power output. Results of measurements show that changes at the mouth of the stack draft due atmospheric influences occur in times with high intensity and high frequency, while power parameters, or boiler power output amplitudes and fan speed automatically “copy” those changes proportionally due to instantaneous fan speed changes. The proposed method of regulation of the gasification boiler power output according to the technical solution enables a simple, cheap, express and continuous maintenance of high power output at low concentrations of the exhaust gases of the gasification boilers from the viewpoint of the boiler user, as well as from the perspective of development and production it allows a continuous control monitoring of these parameters. Full article
(This article belongs to the Section Energy Sources)
Show Figures

Figure 1

Open AccessArticle
Effects of Anisotropic Thermal Conductivity and Lorentz Force on the Flow and Heat Transfer of a Ferro-Nanofluid in a Magnetic Field
Energies 2017, 10(7), 1065; https://doi.org/10.3390/en10071065 - 22 Jul 2017
Cited by 7 | Viewed by 2455
Abstract
In this paper, we study the effects of the Lorentz force and the induced anisotropic thermal conductivity due to a magnetic field on the flow and the heat transfer of a ferro-nanofluid. The ferro-nanofluid is modeled as a single-phase fluid, where the viscosity [...] Read more.
In this paper, we study the effects of the Lorentz force and the induced anisotropic thermal conductivity due to a magnetic field on the flow and the heat transfer of a ferro-nanofluid. The ferro-nanofluid is modeled as a single-phase fluid, where the viscosity depends on the concentration of nanoparticles; the thermal conductivity shows anisotropy due to the presence of the nanoparticles and the external magnetic field. The anisotropic thermal conductivity tensor, which depends on the angle of the applied magnetic field, is suggested considering the principle of material frame indifference according to Continuum Mechanics. We study two benchmark problems: the heat conduction between two concentric cylinders as well as the unsteady flow and heat transfer in a rectangular channel with three heated inner cylinders. The governing equations are made dimensionless, and the flow and the heat transfer characteristics of the ferro-nanofluid with different angles of the magnetic field, Hartmann number, Reynolds number and nanoparticles concentration are investigated systematically. The results indicate that the temperature field is strongly influenced by the anisotropic behavior of the nanofluids. In addition, the magnetic field may enhance or deteriorate the heat transfer performance (i.e., the time-spatially averaged Nusselt number) in the rectangular channel depending on the situations. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
Show Figures

Figure 1

Open AccessArticle
Utilizing Non-Equilibrium Thermodynamics and Reactive Transport to Model CH4 Production from the Nankai Trough Gas Hydrate Reservoir
Energies 2017, 10(7), 1064; https://doi.org/10.3390/en10071064 - 22 Jul 2017
Cited by 1 | Viewed by 1410
Abstract
The ongoing search for new sources of energy has brought natural gas hydrate (NGH) reservoirs to the forefront of attention in both academia and the industry. The amount of gas reserves trapped within these reservoirs surpasses all of the conventional fossil fuel sources [...] Read more.
The ongoing search for new sources of energy has brought natural gas hydrate (NGH) reservoirs to the forefront of attention in both academia and the industry. The amount of gas reserves trapped within these reservoirs surpasses all of the conventional fossil fuel sources explored so far, which makes it of utmost importance to predict their production potential and safety. One of the challenges facing those attempting to analyse their behaviour is that the large number of involved phases make NGHs unable to ever reach equilibrium in nature. Field-scale experiments are expensive and time consuming. However, computer simulations have now become capable of modelling different gas production scenarios, as well as production optimization analyses. In addition to temperature and pressure, independent thermodynamic parameters for hydrate stabilization include the hydrate composition and concentrations for all co-existing phases. It is therefore necessary to develop and implement realistic kinetic models accounting for all significant routes for dissociation and reformation. The reactive transport simulator makes it easy to deploy nonequilibrium thermodynamics for the study of CH4 production from hydrate-bearing sediments by considering each hydrate-related transition as a separate pseudo reaction. In this work, we have used the expanded version of the RetrasoCodeBright (RCB) reactive transport simulator to model exploitation of the methane hydrate (MH) reservoir located in the Nankai Trough, Japan. Our results showed that higher permeabilities in the horizontal direction dominated the pressure drop propagation throughout the hydrate layers and affected their hydrate dissociation rates. Additionally, the comparison of the vertical well versus the horizontal well pattern indicated that hydrate dissociation was slightly higher in the vertical well scenario compared to the horizontal. Full article
(This article belongs to the Special Issue Methane Hydrate Research and Development)
Show Figures

Figure 1

Open AccessArticle
Adaptive Model Predictive Control-Based Energy Management for Semi-Active Hybrid Energy Storage Systems on Electric Vehicles
Energies 2017, 10(7), 1063; https://doi.org/10.3390/en10071063 - 22 Jul 2017
Cited by 16 | Viewed by 1590
Abstract
This paper deals with the energy management strategy (EMS) for an on-board semi-active hybrid energy storage system (HESS) composed of a Li-ion battery (LiB) and ultracapacitor (UC). Considering both the nonlinearity of the semi-active structure and driving condition uncertainty, while ensuring HESS operation [...] Read more.
This paper deals with the energy management strategy (EMS) for an on-board semi-active hybrid energy storage system (HESS) composed of a Li-ion battery (LiB) and ultracapacitor (UC). Considering both the nonlinearity of the semi-active structure and driving condition uncertainty, while ensuring HESS operation within constraints, an adaptive model predictive control (AMPC) method is adopted to design the EMS. Within AMPC, LiB Ah-throughput is minimized online to extend its life. The proposed AMPC determines the optimal control action by solving a quadratic programming (QP) problem at each control interval, in which the QP solver receives control-oriented model matrices and current states for calculation. The control-oriented model is constructed by linearizing HESS online to approximate the original nonlinear model. Besides, a time-varying Kalman filter (TVKF) is introduced as the estimator to improve the state estimation accuracy. At the same time, sampling time, prediction horizon and scaling factors of AMPC are determined through simulation. Compared with standard MPC, TVKF reduces the estimation error by 1~3 orders of magnitude, and AMPC reduces LiB Ah-throughput by 4.3% under Urban Dynamometer Driving Schedule (UDDS) driving cycle condition, indicating superior model adaptivity. Furthermore, LiB Ah-throughput of AMPC under various classical driving cycles differs from that of dynamic programming by an average of 6.5% and reduces by an average of 10.6% compared to rule-based strategy of LiB Ah-throughput, showing excellent adaptation to driving condition uncertainty. Full article
(This article belongs to the Section Energy Storage and Application)
Show Figures

Graphical abstract

Open AccessArticle
An Optimization Framework for Investment Evaluation of Complex Renewable Energy Systems
Energies 2017, 10(7), 1062; https://doi.org/10.3390/en10071062 - 22 Jul 2017
Cited by 2 | Viewed by 1934
Abstract
Enhancing the role of renewable energies in existing power systems is one of the most crucial challenges that society faces today. However, the high variability of their generation potential and the temporal disparity between the demand and the generation potential represent technological and [...] Read more.
Enhancing the role of renewable energies in existing power systems is one of the most crucial challenges that society faces today. However, the high variability of their generation potential and the temporal disparity between the demand and the generation potential represent technological and operational gaps that burden the massive incorporation of renewable sources into power systems. Energy storage technologies are an alternative to tackle this gap; nonetheless, their incorporation within large-scale power grids calls for decision-making tools that ensure an appropriate design and sizing of power systems that exploit the benefits of incorporating storage facilities along with renewable generation power. In this paper, we present an optimization framework for aiding the evaluation of the strategic design of complex renewable power systems. The developed tool relies on an optimization problem, the generation, transmission, storage energy location and sizing problem, which allows one to compute economically-attractive investment plans given by the location and sizing of generation and storage energy systems, along with the corresponding layout of transmission lines. Results on a real case study (located in the central region of Chile), characterized by carefully-curated data, show the potential of the developed tool for aiding long-term investment planning. Full article
(This article belongs to the Special Issue Energy Production Systems)
Show Figures

Figure 1

Open AccessArticle
Biomass Production from Crops Residues: Ranking of Agro-Energy Regions
Energies 2017, 10(7), 1061; https://doi.org/10.3390/en10071061 - 22 Jul 2017
Cited by 5 | Viewed by 1175
Abstract
The aim of the paper is to rank the agro-energy regions according to their potentials of biomass production in the Region of Central Macedonia (RCM). For this reason, a model of Multi-Criteria Analysis (MCDA) is developed with the ELimination and Et Choix Traduisant [...] Read more.
The aim of the paper is to rank the agro-energy regions according to their potentials of biomass production in the Region of Central Macedonia (RCM). For this reason, a model of Multi-Criteria Analysis (MCDA) is developed with the ELimination and Et Choix Traduisant la REalite (ELECTRE) ΙΙΙ method, with the construction of outranking relations. The aim is to compare in a comprehensive way each pair of action, in our case the agro-energy regions of the RCM, in order to satisfy the main goal which is to rank the seven regions as regards their biomass production. The final goal is to select the optimal crop plan as a pilot case for biomass production in the region. In the case of ELECTRE III multicriteria model, we used several conflicting criteria such as the farm income, the biomass production from crop residues, the variable costs, and the production of thermal energy and electrical energy. Alongside a technical and economic analysis of the study area is conducted for the existent crop plans of each agro-energy region. The results show that agro-energy regions with cereals and arable crops have better results than regions with fruit trees and other crops. Full article
Show Figures

Figure 1

Open AccessArticle
Linking the Power and Transport Sectors—Part 1: The Principle of Sector Coupling
Energies 2017, 10(7), 956; https://doi.org/10.3390/en10070956 - 21 Jul 2017
Cited by 42 | Viewed by 3107
Abstract
The usage of renewable energy sources (RESs) to achieve greenhouse gas (GHG) emission reduction goals requires a holistic transformation across all sectors. Due to the fluctuating nature of RESs, it is necessary to install more wind and photovoltaics (PVs) generation in terms of [...] Read more.
The usage of renewable energy sources (RESs) to achieve greenhouse gas (GHG) emission reduction goals requires a holistic transformation across all sectors. Due to the fluctuating nature of RESs, it is necessary to install more wind and photovoltaics (PVs) generation in terms of nominal power than would otherwise be required in order to ensure that the power demand can always be met. In a near fully RES-based energy system, there will be times when there is an inadequate conventional load to meet the overcapacity of RESs, which will lead to demand regularly being exceeded and thereby a surplus. One approach to making productive use of this surplus, which would lead to a holistic transformation of all sectors, is “sector coupling” (SC). This paper describes the general principles behind this concept and develops a working definition intended to be of utility to the international scientific community. Furthermore, a literature review provides an overview of relevant scientific papers on the topic. Due to the challenge of distinguishing between papers with or without SC, the approach adopted here takes the German context as a case study that can be applied to future reviews with an international focus. Finally, to evaluate the potential of SC, an analysis of the linking of the power and transport sectors on a worldwide, EU and German level has been conducted and is outlined here. Full article
(This article belongs to the Section Electrical Power and Energy System)
Show Figures

Figure 1

Open AccessArticle
Comparison of the Performance of Artificial Neural Networks and Fuzzy Logic for Recognizing Different Partial Discharge Sources
Energies 2017, 10(7), 1060; https://doi.org/10.3390/en10071060 - 21 Jul 2017
Cited by 6 | Viewed by 1795
Abstract
This paper compared the capabilities of the artificial neural network (ANN) and the fuzzy logic (FL) approaches for recognizing and discriminating partial discharge (PD) fault classes. The training and testing parameters for the ANN and FL comprise statistical fingerprints from different phase-amplitude-number ( [...] Read more.
This paper compared the capabilities of the artificial neural network (ANN) and the fuzzy logic (FL) approaches for recognizing and discriminating partial discharge (PD) fault classes. The training and testing parameters for the ANN and FL comprise statistical fingerprints from different phase-amplitude-number (φ-q-n) measurements. Two PD fault classes considered are internal discharges in voids and surface discharges. In the void class, there are single voids, serial voids and parallel voids in polyethylene terephthalate (PET), while the surface discharge class comprises four different surface discharge arrangements on pressboard in oil at different voltages and angular positioning of the ground electrode on the respective pressboards. Previously, the ANN and FL have been investigated for PD classification, but there is no work reported in the literature that compares their performance, specifically when applied for real time PD detection problem. As expected, both the ANN and FL can recognize PD defect classes, but the results show that the ANN appears to be more robust as compared to the FL, but these conclusions required to be further investigated with complex PD examples. Finally, both the ANN and FL were assessed as practical PD classification. Despite of the limitations of the ANN, it is concluded that the ANN is better suited for practical PD recognition because of its ability to provide accurate recognition values and the severity level of PD defects. Full article
Show Figures

Figure 1

Open AccessArticle
Pole-to-Ground Fault Analysis and Fast Protection Scheme for HVDC Based on Overhead Transmission Lines
Energies 2017, 10(7), 1059; https://doi.org/10.3390/en10071059 - 21 Jul 2017
Cited by 12 | Viewed by 1837
Abstract
Flexible direct current (DC) transmission network technology is an effective method for large capacity clean energy access to power grids, but the DC short-circuit fault detection for it is a difficult problem. In this paper, the pole-to-ground fault transient characteristics in a multi-terminal [...] Read more.
Flexible direct current (DC) transmission network technology is an effective method for large capacity clean energy access to power grids, but the DC short-circuit fault detection for it is a difficult problem. In this paper, the pole-to-ground fault transient characteristics in a multi-terminal DC power grid, based on overhead transmission lines and DC circuit breakers, are analyzed firstly. Then, a fast protection scheme is proposed according to the fault transient characteristics. Only local information is utilized for fault detection and location in the proposed scheme. Moreover, the scheme is verified to have the advantages of fast action speed, high reliability and the ability to resist the transition resistance. A four terminal DC power grid model based on actual engineering parameters is established in PSCAD/EMTDC, and the validity of the protection scheme under different fault conditions is verified by simulation results. Full article
(This article belongs to the Section Electrical Power and Energy System)
Show Figures

Figure 1

Open AccessArticle
A Novel Multi-Point Excitation Fatigue Testing Method for Wind Turbine Rotor Blades
Energies 2017, 10(7), 1058; https://doi.org/10.3390/en10071058 - 21 Jul 2017
Cited by 1 | Viewed by 1357
Abstract
Wind turbine blades have to withstand the rigorous test of 20–25 years of service. Fatigue testing is an accurate method used to verify blade reliability. Multi-point excitation could better fit the fatigue damage distribution, which reduces the power output of a single exciter [...] Read more.
Wind turbine blades have to withstand the rigorous test of 20–25 years of service. Fatigue testing is an accurate method used to verify blade reliability. Multi-point excitation could better fit the fatigue damage distribution, which reduces the power output of a single exciter and saves testing energy consumption. The amplitude, phase, and frequency characteristics of the fatigue test system and, moreover, the relationship between the excitation force, damping, and the amplitude variation of the blade, are analyzed by the Lagrangian equation and the finite element simulation method. The full-scale fatigue test of an equivalent full cycle life in the flapwise direction is carried out by multi-excitation. When the frequency and phase of the multi-point exciters are consistent, the maximum vibration effect can be exerted. When the phase difference of the dual exciters is 180°, the vibration effect produced by the dual exciters can be equivalent to each other. The blade amplitude is proportional to excitation forces, while inversely proportional to the damping ratio. The bending moment deviation of the blade is controlled within 9.2%; moreover, the energy consumption is 40% lower than that of the single-point excitation. The use of multi-point excitation allows loading the blade with high precision, stable operation, and low cost, which provides the theoretical and experimental basis for the fatigue test of large wind turbine blades. Full article
(This article belongs to the Special Issue Wind Turbine 2017)
Show Figures

Figure 1

Open AccessArticle
Analysis of Overlying Strata Movement and Behaviors in Caving and Solid Backfilling Mixed Coal Mining
Energies 2017, 10(7), 1057; https://doi.org/10.3390/en10071057 - 21 Jul 2017
Cited by 8 | Viewed by 1485
Abstract
Based on techniques of close upper protective coal-rock layer mining, relieved gas extraction, and underground gangue washing-discharging-backfilling, this paper initiates the concept of mixed fully-mechanized coal mining, which combines a solid backfilling method and a caving method (hereinafter referred to as “backfill and [...] Read more.
Based on techniques of close upper protective coal-rock layer mining, relieved gas extraction, and underground gangue washing-discharging-backfilling, this paper initiates the concept of mixed fully-mechanized coal mining, which combines a solid backfilling method and a caving method (hereinafter referred to as “backfill and caving mixed mining”). After the principle and key techniques are introduced, a physical simulation experiment and a numerical simulation are used to study the characteristics of the overlying strata’s fracture development, the main roof subsidence, the stress field and its influence area in the transition area with the length ratios of the backfilling section and the caving section, and the advancing distance of the mixed longwall face. Thus, the lengths of the caving section and the backfilling section, the parameters of the support system in the transition section, and the design process of the mixed longwall face are presented. In practice, the mixed longwall face Ji15-31010 in Ping-dingshan No. 12 Colliery proves that the designed lengths of 120 m and 100 m for the backfilling section and the caving section, respectively, are appropriate. The monitoring results of the hydraulic support working resistance show that the supports were working well in general; the maximum growth height of the overlying strata fracture is 18 m; the gas drainage efficiency is up to 80% and the average gas concentration is 0.1 g/m3; a large quantity of gangue generated in the Ji14 seam is disposed underground; coal and gas are extracted simultaneously; and significant environmental and economic benefits are realized. Full article
Show Figures

Figure 1

Open AccessEditor’s ChoiceReview
State of the Art and Trends in the Monitoring, Detection and Diagnosis of Failures in Electric Induction Motors
Energies 2017, 10(7), 1056; https://doi.org/10.3390/en10071056 - 21 Jul 2017
Cited by 22 | Viewed by 2119
Abstract
Despite the complex mathematical models and physical phenomena on which it is based, the simplicity of its construction, its affordability, the versatility of its applications and the relative ease of its control have made the electric induction motor an essential element in a [...] Read more.
Despite the complex mathematical models and physical phenomena on which it is based, the simplicity of its construction, its affordability, the versatility of its applications and the relative ease of its control have made the electric induction motor an essential element in a considerable number of processes at the industrial and domestic levels, in which it converts electrical energy into mechanical energy. The importance of this type of machine for the continuity of operation, mainly in industry, is such that, in addition to being an important part of the study programs of careers related to this branch of electrical engineering, a large number of investigations into monitoring, detecting and quickly diagnosing its incipient faults due to a variety of factors have been conducted. This bibliographic research aims to analyze the conceptual aspects of the first discoveries that served as the basis for the invention of the induction motor, ranging from the development of the Fourier series, the Fourier transform mathematical formula in its different forms and the measurement, treatment and analysis of signals to techniques based on artificial intelligence and soft computing. This research also includes topics of interest such as fault types and their classification according to the engine, software and hardware parts used and modern approaches or maintenance strategies. Full article
(This article belongs to the Special Issue Electric Machines and Drives for Renewable Energy Harvesting 2017)
Show Figures

Figure 1

Open AccessArticle
Effect of Altitude on the Audible Noise Level of AC Power lines
Energies 2017, 10(7), 1055; https://doi.org/10.3390/en10071055 - 21 Jul 2017
Cited by 5 | Viewed by 1296
Abstract
The audible noise (AN) induced by corona discharge of AC transmission lines is more severe at high altitudes than at low altitudes; this has become a crucial limiting factor for the structural design of power lines and their environmental impact assessment. To determine [...] Read more.
The audible noise (AN) induced by corona discharge of AC transmission lines is more severe at high altitudes than at low altitudes; this has become a crucial limiting factor for the structural design of power lines and their environmental impact assessment. To determine the altitude effect and correction of AN level for AC power lines, a corona cage test system was used to measure the acoustic power level of four bundled conductors at five elevations, namely Wuhan (23 m), Tianshui (1100 m), Xining (2261 m), Gonghe (2943 m), and Yangbajain (4300 m). We obtained the AN characteristics for different altitudes, bundle numbers, and subconductor diameters through a statistical analysis of measured data. The analysis and comparison results indicate that the actual AN correction values are slightly less than the Bonneville Power Administration term of 1 dB/300 m at altitudes below 3200 m. Above 3200 m, the difference increases gradually. A correction term 2.85 dB/1000 m is recommended for more accurate evaluation. Full article
(This article belongs to the Section Electrical Power and Energy System)
Show Figures

Figure 1

Open AccessArticle
RTV Silicone Rubber Degradation Induced by Temperature Cycling
Energies 2017, 10(7), 1054; https://doi.org/10.3390/en10071054 - 21 Jul 2017
Cited by 6 | Viewed by 1789
Abstract
Room temperature vulcanized (RTV) silicone rubber is extensively used in power system due to its hydrophobicity and hydrophobicity transfer ability. Temperature has been proven to markedly affect the performance of silicone rubbers. This research investigated the degradation of RTV silicone rubber under temperature [...] Read more.
Room temperature vulcanized (RTV) silicone rubber is extensively used in power system due to its hydrophobicity and hydrophobicity transfer ability. Temperature has been proven to markedly affect the performance of silicone rubbers. This research investigated the degradation of RTV silicone rubber under temperature cycling treatment. Hydrophobicity and its transfer ability, hardness, functional groups, microscopic appearance, and thermal stability were analyzed using the static contact angle method, a Shore A durometer, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetry (TG), respectively. Some significant conclusions were drawn. After the temperature was cycled between −25 °C and 70 °C, the hydrophobicity changed modestly, but its transfer ability changed remarkably, which may result from the competition between the formation of more channels for the transfer of low molecular weight (LMW) silicone fluid and the reduction of LMW silicone fluid in the bulk. A hardness analysis and FTIR analysis demonstrated that further cross-linking reactions occurred during the treatment. SEM images showed the changes in roughness of the RTV silicone rubber surfaces. TG analysis also demonstrated the degradation of RTV silicone rubber by presenting evidence that the content of organic materials decreased during the temperature cycling treatment. Full article
Show Figures

Figure 1

Open AccessArticle
High-Precision Spectral Decomposition Method Based on VMD/CWT/FWEO for Hydrocarbon Detection in Tight Sandstone Gas Reservoirs
Energies 2017, 10(7), 1053; https://doi.org/10.3390/en10071053 - 21 Jul 2017
Viewed by 1266
Abstract
Seismic time-frequency analysis methods can be used for hydrocarbon detection because of the phenomena of energy and abnormal attenuation of frequency when the seismic waves travel across reservoirs. A high-resolution method based on variational mode decomposition (VMD), continuous-wavelet transform (CWT) and frequency-weighted energy [...] Read more.
Seismic time-frequency analysis methods can be used for hydrocarbon detection because of the phenomena of energy and abnormal attenuation of frequency when the seismic waves travel across reservoirs. A high-resolution method based on variational mode decomposition (VMD), continuous-wavelet transform (CWT) and frequency-weighted energy operator (FWEO) is proposed for hydrocarbon detection in tight sandstone gas reservoirs. VMD can decompose seismic signals into a set of intrinsic mode functions (IMF) in the frequency domain. In order to avoid meaningful frequency loss, the CWT method is used to obtain the time-frequency spectra of the selected IMFs. The energy separation algorithm based on FWEO can improve the resolution of time-frequency spectra and highlight abnormal energy, which is applied to track the instantaneous energy in the time-frequency spectra. The difference between the high-frequency section and low-frequency section acquired by applying the proposed method is utilized to detect hydrocarbons. Applications using the model and field data further demonstrate that the proposed method can effectively detect hydrocarbons in tight sandstone reservoirs, with good anti-noise performance. The newly-proposed method can be used as an analysis tool to detect hydrocarbons. Full article
Show Figures

Figure 1

Open AccessArticle
A Chaos-Embedded Gravitational Search Algorithm for the Identification of Electrical Parameters of Photovoltaic Cells
Energies 2017, 10(7), 1052; https://doi.org/10.3390/en10071052 - 21 Jul 2017
Cited by 7 | Viewed by 1662
Abstract
Solar energy is used worldwide to alleviate the daily increasing demands for electric power. Photovoltaic (PV) cells, which are used to convert solar energy into electricity, can be represented as equivalent circuit models, in which a series of electrical parameters must be identified [...] Read more.
Solar energy is used worldwide to alleviate the daily increasing demands for electric power. Photovoltaic (PV) cells, which are used to convert solar energy into electricity, can be represented as equivalent circuit models, in which a series of electrical parameters must be identified in order to determine their operating characteristics under different test conditions. Intelligent approaches, like those based in population-based optimization algorithms like Particle Swarm Optimization (PSO), Genetic Algorithms (GAs), and Simulated Annealing (SA), have been demonstrated to be powerful methods for the accurate identification of such parameters. Recently, chaos theory have been highlighted as a promising alternative to increase the performance of such approaches; as a result, several chaos-based optimization methods have been devised to solve many different and complex engineering problems. In this paper, the Chaotic Gravitational Search Algorithm (CGSA) is proposed to solve the problem of accurate PV cell parameter estimation. To prove the feasibility of the proposed approach, a series of comparative experiments against other similar parameters extraction methods were performed. As shown by our experimental results, our proposed approach outperforms all other methods compared in this work, and proves to be an excellent alternative to tackle the challenging problem of solar cell parameters identification. Full article
Show Figures

Graphical abstract

Open AccessArticle
Non-Convex Economic Dispatch of a Virtual Power Plant via a Distributed Randomized Gradient-Free Algorithm
Energies 2017, 10(7), 1051; https://doi.org/10.3390/en10071051 - 21 Jul 2017
Cited by 6 | Viewed by 1236
Abstract
The economic dispatch problem of a virtual power plant (VPP) is becoming non-convex for distributed generators’ characteristics of valve-point loading effects, prohibited operating zones, and multiple fuel options. In this paper, the economic dispatch model of VPP is established and then solved by [...] Read more.
The economic dispatch problem of a virtual power plant (VPP) is becoming non-convex for distributed generators’ characteristics of valve-point loading effects, prohibited operating zones, and multiple fuel options. In this paper, the economic dispatch model of VPP is established and then solved by a distributed randomized gradient-free algorithm. To deal with the non-smooth objective function, its Gauss approximation is used to construct distributed randomized gradient-free oracles in optimization iterations. A projection operator is also introduced to solve the discontinuous variable space problem. An example simulation is implemented on a modified IEEE-34 bus test system, and the results demonstrate the effectiveness and applicability of the proposed algorithm. Full article
(This article belongs to the Section Electrical Power and Energy System)
Show Figures

Figure 1

Open AccessArticle
Total-Factor Energy Efficiency (TFEE) Evaluation on Thermal Power Industry with DEA, Malmquist and Multiple Regression Techniques
Energies 2017, 10(7), 1039; https://doi.org/10.3390/en10071039 - 21 Jul 2017
Cited by 6 | Viewed by 1267
Abstract
Under the background of a new round of power market reform, realizing the goals of energy saving and emission reduction, reducing the coal consumption and ensuring the sustainable development are the key issues for thermal power industry. With the biggest economy and energy [...] Read more.
Under the background of a new round of power market reform, realizing the goals of energy saving and emission reduction, reducing the coal consumption and ensuring the sustainable development are the key issues for thermal power industry. With the biggest economy and energy consumption scales in the world, China should promote the energy efficiency of thermal power industry to solve these problems. Therefore, from multiple perspectives, the factors influential to the energy efficiency of thermal power industry were identified. Based on the economic, social and environmental factors, a combination model with Data Envelopment Analysis (DEA) and Malmquist index was constructed to evaluate the total-factor energy efficiency (TFEE) in thermal power industry. With the empirical studies from national and provincial levels, the TFEE index can be factorized into the technical efficiency index (TECH), the technical progress index (TPCH), the pure efficiency index (PECH) and the scale efficiency index (SECH). The analysis showed that the TFEE was mainly determined by TECH and PECH. Meanwhile, by panel data regression model, unit coal consumption, talents and government supervision were selected as important indexes to have positive effects on TFEE in thermal power industry. In addition, the negative indexes, such as energy price and installed capacity, were also analyzed to control their undesired effects. Finally, considering the analysis results, measures for improving energy efficiency of thermal power industry were discussed widely, such as strengthening technology research and design (R&D), enforcing pollutant and emission reduction, distributing capital and labor rationally and improving the government supervision. Relative study results and suggestions can provide references for Chinese government and enterprises to enhance the energy efficiency level. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
Show Figures

Figure 1

Open AccessArticle
Linking the Power and Transport Sectors—Part 2: Modelling a Sector Coupling Scenario for Germany
Energies 2017, 10(7), 957; https://doi.org/10.3390/en10070957 - 20 Jul 2017
Cited by 42 | Viewed by 2250
Abstract
“Linking the power and transport sectors—Part 1” describes the general principle of “sector coupling” (SC), develops a working definition intended of the concept to be of utility to the international scientific community, contains a literature review that provides an overview of relevant scientific [...] Read more.
“Linking the power and transport sectors—Part 1” describes the general principle of “sector coupling” (SC), develops a working definition intended of the concept to be of utility to the international scientific community, contains a literature review that provides an overview of relevant scientific papers on this topic and conducts a rudimentary analysis of the linking of the power and transport sectors on a worldwide, EU and German level. The aim of this follow-on paper is to outline an approach to the modelling of SC. Therefore, a study of Germany as a case study was conducted. This study assumes a high share of renewable energy sources (RES) contributing to the grid and significant proportion of fuel cell vehicles (FCVs) in the year 2050, along with a dedicated hydrogen pipeline grid to meet hydrogen demand. To construct a model of this nature, the model environment “METIS” (models for energy transformation and integration systems) we developed will be described in more detail in this paper. Within this framework, a detailed model of the power and transport sector in Germany will be presented in this paper and the rationale behind its assumptions described. Furthermore, an intensive result analysis for the power surplus, utilization of electrolysis, hydrogen pipeline and economic considerations has been conducted to show the potential outcomes of modelling SC. It is hoped that this will serve as a basis for researchers to apply this framework in future to models and analysis with an international focus. Full article
(This article belongs to the Section Electrical Power and Energy System)
Show Figures

Figure 1

Open AccessArticle
The Potential of Smart Technologies and Micro-Generation in UK SMEs
Energies 2017, 10(7), 1050; https://doi.org/10.3390/en10071050 - 20 Jul 2017
Cited by 2 | Viewed by 1463
Abstract
Small-to-medium-sized enterprises (SMEs) make up 99% of businesses and contribute 13% of energy demand globally. However, much of the demand-side energy research and policy attention to date has focused on the domestic, large commercial and industrial sectors. Previous research on SMEs has primarily [...] Read more.
Small-to-medium-sized enterprises (SMEs) make up 99% of businesses and contribute 13% of energy demand globally. However, much of the demand-side energy research and policy attention to date has focused on the domestic, large commercial and industrial sectors. Previous research on SMEs has primarily concentrated on the drivers and barriers to the adoption of energy efficiency measures. However, less attention has been given to other areas of demand-side management in SMEs, such as the role of ‘smart’ technologies and micro-generation. The paper aims to contribute to filling this gap. To analyse the potential of smart technologies in UK SMEs, a quantitative model is developed to assess seven categories of smart technologies in ten non-domestic sectors. Overall, the results suggest that smart technologies within the UK SME market offer significant estimated annual energy savings potential of ~£8.6 billion against an estimated energy spend of ~£49.7 billion (representing ~17% savings potential on energy expenditures). From the smart technology categories examined, fleet management, integrated building management systems and smart meters have the potential to offer the greatest energy savings to SMEs, providing estimated total energy savings of ~£7.5 billion annually. To analyse the potential of micro-generation in UK SMEs, interview-based qualitative research was undertaken with 17 SMEs to explore the drivers and barriers to its adoption. The research found that the initial costs, technical feasibility and planning permission on historical buildings were the main barriers, and that the ‘green’ marketing potential of micro-generation, coupled with ethical reasons and feed-in tariffs, were the main drivers. Full article
(This article belongs to the Special Issue From Smart Metering to Demand Side Management)
Show Figures

Figure 1

Open AccessArticle
A Heuristic Algorithm to Compute Multimodal Criterial Function Weights for Demand Management in Residential Areas
Energies 2017, 10(7), 1049; https://doi.org/10.3390/en10071049 - 20 Jul 2017
Cited by 5 | Viewed by 956
Abstract
We present the conceptual design of a collective control scheme for appliances within a smart home. Based on the relevant energy acquisition procedures, three appliance groups are defined, modeled, and completed with an energy storage as well as a generator using renewable sources. [...] Read more.
We present the conceptual design of a collective control scheme for appliances within a smart home. Based on the relevant energy acquisition procedures, three appliance groups are defined, modeled, and completed with an energy storage as well as a generator using renewable sources. At the following stage, a mixed quadratic optimization problem is presented, with the solution consisting in a time plan to regulate the operation of the individual devices. Importantly, the paper also proposes a heuristic algorithm securing consistent functionality of the computational process even despite the varying input and user conditions given in the receding horizon. Full article
(This article belongs to the Section Electrical Power and Energy System)
Show Figures

Figure 1

Open AccessArticle
A Study on the Effects of Starches on the Properties of Alkali-Activated Cement and the Potential of Starch as a Self-Degradable Additive
Energies 2017, 10(7), 1048; https://doi.org/10.3390/en10071048 - 20 Jul 2017
Cited by 2 | Viewed by 967
Abstract
An urgent problem of geothermal energy source development is how to cut down the production costs. The use of temporary sealing materials can reduce the costs associated with the circulation lost by plugging, and increase the production by self-degradation. Based on the utilization [...] Read more.
An urgent problem of geothermal energy source development is how to cut down the production costs. The use of temporary sealing materials can reduce the costs associated with the circulation lost by plugging, and increase the production by self-degradation. Based on the utilization of starches as self-degradable additives in the medical field, this paper investigated the effects of three kinds of starches, namely corn starch (CS), hydroxypropyl starch (HPS) and carboxymethyl starch (CMS) on the properties of alkali-activated cement (AAC). In addition, the thermal properties of starch, the compressive strength and microstructures of the cement with starch were tested, to evaluate the potentiality of starch as self-degradable additive for geothermal cement. The analysis showed that: (1) all the starches have the effect of increasing the apparent viscosity, prolonging the setting time and reducing the static fluid loss of alkali-activated cement; (2) the addition of starch increased the number of pores in 200 °C-heated cement, facilitated the leaching process, and thus promoted the self-degradation; and (3) among the three starches, CMS has the most potential as a self-degradable additive. Full article
Show Figures

Figure 1

Open AccessArticle
Improved Linear Active Disturbance Rejection Control for Microgrid Frequency Regulation
Energies 2017, 10(7), 1047; https://doi.org/10.3390/en10071047 - 20 Jul 2017
Cited by 7 | Viewed by 1664
Abstract
The frequency regulation has become one of the major subjects in microgrid power system due to the complexity structure of microgrid. In order to solve this problem, this paper proposes an improved linear active disturbance rejection control algorithm (ILADRC) that can significantly improve [...] Read more.
The frequency regulation has become one of the major subjects in microgrid power system due to the complexity structure of microgrid. In order to solve this problem, this paper proposes an improved linear active disturbance rejection control algorithm (ILADRC) that can significantly improve system performances through changing feedback control law to reduce the disturbance estimation error of extended state observer. Then, the proposed algorithm is employed in microgrid power system frequency regulation problem, which demonstrates its effectiveness. The parameters of controllers are optimized by particle swarm optimization (PSO) algorithm improved by genetic algorithm (GA). Simulations with different disturbances including sudden and stochastic change of load demand and wind turbine generation are carried out in comparison with previous studies. And robustness testing based on Monte-Carlo approach also shows better performance. So frequency stability of microgrid power system can be well guaranteed by proposed control algorithm. Full article
(This article belongs to the Special Issue Advanced Operation and Control of Smart Microgrids)
Show Figures

Figure 1

Open AccessArticle
Optimal Power Transmission of Offshore Wind Power Using a VSC-HVdc Interconnection
Energies 2017, 10(7), 1046; https://doi.org/10.3390/en10071046 - 20 Jul 2017
Cited by 1 | Viewed by 1846
Abstract
High-voltage dc transmission based on voltage-source converter (VSC-HVdc) is quickly increasing its power rating, and it can be the most appropriate link for the connection of offshore wind farms (OWFs) to the grid in many locations. This paper presents a steady-state operation model [...] Read more.
High-voltage dc transmission based on voltage-source converter (VSC-HVdc) is quickly increasing its power rating, and it can be the most appropriate link for the connection of offshore wind farms (OWFs) to the grid in many locations. This paper presents a steady-state operation model to calculate the optimal power transmission of an OWF connected to the grid through a VSC-HVdc link. The wind turbines are based on doubly fed induction generators (DFIGs), and a detailed model of the internal OWF grid is considered in the model. The objective of the optimization problem is to maximize the active power output of the OWF, i.e., the reduction of losses, by considering the optimal reactive power allocation while taking into account the restrictions imposed by the available wind power, the reactive power capability of the DFIG, the DC link model, and the operating conditions. Realistic simulations are performed to evaluate the proposed model and to execute optimal operation analyses. The results show the effectiveness of the proposed method and demonstrate the advantages of using the reactive control performed by DFIG to achieve the optimal operation of the VSC-HVdc. Full article
(This article belongs to the Special Issue Wind Generators Modelling and Control)
Show Figures

Figure 1

Previous Issue
Next Issue
Back to TopTop