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Energies, Volume 9, Issue 11 (November 2016)

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Cover Story We investigated the possibility of using soundless cracking demolition agents (SCDAs) as an [...] Read more.
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Editorial

Jump to: Research, Review

Open AccessEditorial Simulation of Polygeneration Systems
Energies 2016, 9(11), 925; doi:10.3390/en9110925
Received: 1 November 2016 / Revised: 3 November 2016 / Accepted: 3 November 2016 / Published: 8 November 2016
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Abstract
This Special Issue aims at collecting the recent studies dealing with polygeneration systems, with a special focus on the possible integration of different technologies into a single system, able to convert one or multiple energy sources into energy services (electricity, heat and cooling)
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This Special Issue aims at collecting the recent studies dealing with polygeneration systems, with a special focus on the possible integration of different technologies into a single system, able to convert one or multiple energy sources into energy services (electricity, heat and cooling) and other useful products (e.g., desalinized water, hydrogen, glycerin, ammonia, etc.). Renewable sources (solar, wind, hydro, biomass and geothermal), as well as fossil fuels, feeding advanced energy systems such as fuel cells and cogeneration systems, are considered. Special attention is paid to control strategies and to the management of the systems in general. Studies including thermoeconomic analyses and system optimizations are presented. Full article
(This article belongs to the Special Issue Simulation of Polygeneration Systems)

Research

Jump to: Editorial, Review

Open AccessArticle A Generalized SOC-OCV Model for Lithium-Ion Batteries and the SOC Estimation for LNMCO Battery
Energies 2016, 9(11), 900; doi:10.3390/en9110900
Received: 19 August 2016 / Revised: 19 October 2016 / Accepted: 26 October 2016 / Published: 1 November 2016
Cited by 3 | PDF Full-text (3710 KB) | HTML Full-text | XML Full-text
Abstract
A state-of-charge (SOC) versus open-circuit-voltage (OCV) model developed for batteries should preferably be simple, especially for real-time SOC estimation. It should also be capable of representing different types of lithium-ion batteries (LIBs), regardless of temperature change and battery degradation. It must therefore be
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A state-of-charge (SOC) versus open-circuit-voltage (OCV) model developed for batteries should preferably be simple, especially for real-time SOC estimation. It should also be capable of representing different types of lithium-ion batteries (LIBs), regardless of temperature change and battery degradation. It must therefore be generic, robust and adaptive, in addition to being accurate. These challenges have now been addressed by proposing a generalized SOC-OCV model for representing a few most widely used LIBs. The model is developed from analyzing electrochemical processes of the LIBs, before arriving at the sum of a logarithmic, a linear and an exponential function with six parameters. Values for these parameters are determined by a nonlinear estimation algorithm, which progressively shows that only four parameters need to be updated in real time. The remaining two parameters can be kept constant, regardless of temperature change and aging. Fitting errors demonstrated with different types of LIBs have been found to be within 0.5%. The proposed model is thus accurate, and can be flexibly applied to different LIBs, as verified by hardware-in-the-loop simulation designed for real-time SOC estimation. Full article
(This article belongs to the Special Issue Advanced Energy Storage Technologies and Their Applications (AESA))
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Open AccessArticle Auto-Mapping and Configuration Method of IEC 61850 Information Model Based on OPC UA
Energies 2016, 9(11), 901; doi:10.3390/en9110901
Received: 24 June 2016 / Revised: 9 October 2016 / Accepted: 20 October 2016 / Published: 1 November 2016
Cited by 3 | PDF Full-text (5106 KB) | HTML Full-text | XML Full-text
Abstract
The open-platform communication (OPC) unified architecture (UA) (IEC62541) is introduced as a key technology for realizing a variety of smart grid (SG) use cases enabling relevant automation and control tasks. The OPC UA can expand interoperability between power systems. The top-level SG management
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The open-platform communication (OPC) unified architecture (UA) (IEC62541) is introduced as a key technology for realizing a variety of smart grid (SG) use cases enabling relevant automation and control tasks. The OPC UA can expand interoperability between power systems. The top-level SG management platform needs independent middleware to transparently manage the power information technology (IT) systems, including the IEC 61850. To expand interoperability between the power system for a large number of stakeholders and various standards, this paper focuses on the IEC 61850 for the digital substation. In this paper, we propose the interconnection method to integrate communication with OPC UA and convert OPC UA AddressSpace using system configuration description language (SCL) of IEC 61850. We implemented the mapping process for the verification of the interconnection method. The interconnection method in this paper can expand interoperability between power systems for OPC UA integration for various data structures in the smart grid. Full article
(This article belongs to the Special Issue Advances in Power System Operations and Planning)
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Open AccessArticle The Impact and Determinants of Environmental Taxation on Economic Growth Communities in Romania
Energies 2016, 9(11), 902; doi:10.3390/en9110902
Received: 17 August 2016 / Revised: 21 October 2016 / Accepted: 25 October 2016 / Published: 1 November 2016
Cited by 3 | PDF Full-text (256 KB) | HTML Full-text | XML Full-text
Abstract
Environmental taxation represents a key influence on sustainable development in post-transition countries. Romania has experienced important transformations of environmental policy, including taxation, due to sustained reliance on traditional energy sources to satisfy its energy needs. The aim of this paper is to show
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Environmental taxation represents a key influence on sustainable development in post-transition countries. Romania has experienced important transformations of environmental policy, including taxation, due to sustained reliance on traditional energy sources to satisfy its energy needs. The aim of this paper is to show a possible causal relationship between the Romanian GDP and several explanatory variables related to taxation of environmental damage and energy generation and consumption in the country. In order to do this, the authors make use of several statistical tests to verify the existence of a meaningful relationship between economic variables expressed in time series. The study has also attempted to identify the influence of environmental taxation on ensuring green economic development, starting from the premise that for emergent economies these taxes provide both a GDP increase and prevent environmental degradation by decreasing the pollution and environmentally harmful supplies and practices. Full article
Open AccessArticle Using CPE Function to Size Capacitor Storage for Electric Vehicles and Quantifying Battery Degradation during Different Driving Cycles
Energies 2016, 9(11), 903; doi:10.3390/en9110903
Received: 27 August 2016 / Revised: 1 October 2016 / Accepted: 24 October 2016 / Published: 2 November 2016
Cited by 1 | PDF Full-text (8701 KB) | HTML Full-text | XML Full-text
Abstract
Range anxiety and battery cycle life are two major factors which restrict the development of electric vehicles. Battery degradation can be reduced by adding supercapacitors to create a Hybrid Energy Storage System. This paper proposes a systematic approach to configure the hybrid energy
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Range anxiety and battery cycle life are two major factors which restrict the development of electric vehicles. Battery degradation can be reduced by adding supercapacitors to create a Hybrid Energy Storage System. This paper proposes a systematic approach to configure the hybrid energy storage system and quantifies the battery degradation for electric vehicles when using supercapacitors. A continuous power-energy function is proposed to establish supercapacitor size based on national household travel survey statistics. By analyzing continuous driving action in standard driving cycles and special driving phases (start up and acceleration), the supercapacitor size is calculated to provide a compromise between the capacitor size and battery degradation. Estimating the battery degradation after 10 years, the battery capacity loss value decreases 17.55% and 21.6%, respectively, under the urban dynamometer driving schedule and the US06. Furthermore, the battery lifespan of the continuous power-energy configured system is prolonged 28.62% and 31.39%, respectively, compared with the battery alone system. Full article
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Open AccessArticle A Novel Flux Focusing Magnetically Geared Machine with Reduced Eddy Current Loss
Energies 2016, 9(11), 904; doi:10.3390/en9110904
Received: 18 July 2016 / Revised: 26 October 2016 / Accepted: 27 October 2016 / Published: 2 November 2016
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Abstract
This paper proposes a novel flux focusing magnetically geared (MG) machine for wind power generation, considering the permanent magnets (PMs) eddy current loss and the balance between the pull-out torque of MG machine and the back-electromotive force (EMF)of the PM brushless machine. The
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This paper proposes a novel flux focusing magnetically geared (MG) machine for wind power generation, considering the permanent magnets (PMs) eddy current loss and the balance between the pull-out torque of MG machine and the back-electromotive force (EMF)of the PM brushless machine. The PM eddy current loss in the two rotors of the conventional surface-mounted MG machine is calculated and analyzed by using finite-element method. By adopting serial-spoke structure in the inner rotor, a novel rotor structure for a MG machine is proposed to reduce the PM eddy current loss. Moreover, in order to balance the pull-out torque and the back-EMF, several serial-spoke structures and the main design parameters are investigated. Then, a quantitative comparison between the proposed topology and the conventional surface-mounted MG machine is performed. The analysis results indicate that the PM eddy current loss of the proposed MG machine can be significantly reduced and its pull-out torque and back-EMF can be balanced well. Full article
(This article belongs to the Special Issue Electric Machines and Drives for Renewable Energy Harvesting)
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Open AccessArticle Basic Characteristics and Design of a Novel Hybrid Magnetic Bearing for Wind Turbines
Energies 2016, 9(11), 905; doi:10.3390/en9110905
Received: 8 September 2016 / Revised: 20 October 2016 / Accepted: 20 October 2016 / Published: 2 November 2016
Cited by 1 | PDF Full-text (6681 KB) | HTML Full-text | XML Full-text
Abstract
This paper proposes a five-degree-of-freedom (5-DOF) hybrid magnetic bearing (HMB) for direct-drive wind turbines, which can realize suspension in the 4-DOF radial and 1-DOF axial directions. Only two sets of radial control windings are employed in the proposed HMB because only one set
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This paper proposes a five-degree-of-freedom (5-DOF) hybrid magnetic bearing (HMB) for direct-drive wind turbines, which can realize suspension in the 4-DOF radial and 1-DOF axial directions. Only two sets of radial control windings are employed in the proposed HMB because only one set of radial control windings can achieve the 2-DOF suspension in the radial direction. Unlike the traditional active thrust magnetic bearings, this paper uses a cylindrical rotor core without a large thrust disc in the novel HMB. The numbers of the controller, power amplifier and system volume can be reduced in the magnetic suspension system. This paper also presents the structure and basic characteristics of the proposed magnetic bearing. A precision equivalent magnetic circuit analysis of the permanent magnet ring and control magnetic field is conducted in this study, in consideration of the non-uniform distribution of magnetic density. Accordingly, the mathematical models, including the suspension force expression, are derived based on the accurate equivalent magnetic circuit. The basic principle of the structure parameter design is presented, based on the given key parameters. The accuracy of the analytical method is further validated by 3D finite element analysis. Full article
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Open AccessArticle Cost-Effectiveness Comparison of Coupler Designs of Wireless Power Transfer for Electric Vehicle Dynamic Charging
Energies 2016, 9(11), 906; doi:10.3390/en9110906
Received: 9 July 2016 / Revised: 2 October 2016 / Accepted: 26 October 2016 / Published: 2 November 2016
Cited by 5 | PDF Full-text (5644 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a cost-effectiveness comparison of coupler designs for wireless power transfer (WPT), meant for electric vehicle (EV) dynamic charging. The design comparison of three common types of couplers is first based on the raw material cost, output power, transfer efficiency, tolerance
[...] Read more.
This paper presents a cost-effectiveness comparison of coupler designs for wireless power transfer (WPT), meant for electric vehicle (EV) dynamic charging. The design comparison of three common types of couplers is first based on the raw material cost, output power, transfer efficiency, tolerance of horizontal offset, and flux density. Then, the optimal cost-effectiveness combination is selected for EV dynamic charging. The corresponding performances of the proposed charging system are compared and analyzed by both simulation and experimentation. The results verify the validity of the proposed dynamic charging system for EVs. Full article
(This article belongs to the Special Issue Wireless Power Transfer 2016)
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Open AccessArticle Numerical Investigation of Wind Conditions for Roof-Mounted Wind Turbines: Effects of Wind Direction and Horizontal Aspect Ratio of a High-Rise Cuboid Building
Energies 2016, 9(11), 907; doi:10.3390/en9110907
Received: 6 September 2016 / Revised: 23 October 2016 / Accepted: 25 October 2016 / Published: 3 November 2016
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Abstract
From the viewpoint of installing small wind turbines (SWTs) on rooftops, this study investigated the effects of wind direction and horizontal aspect ratio (HAR = width/length) of a high-rise cuboid building on wind conditions above the roof by conducting large eddy simulations (LESs).
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From the viewpoint of installing small wind turbines (SWTs) on rooftops, this study investigated the effects of wind direction and horizontal aspect ratio (HAR = width/length) of a high-rise cuboid building on wind conditions above the roof by conducting large eddy simulations (LESs). The LES results confirmed that as HAR decreases (i.e., as the building width decreases), the variation in wind velocity over the roof tends to decrease. This tendency is more prominent as the angle between the wind direction and the normal vector of the building’s leeward face with longer roof edge increases. Moreover, at windward corners of the roof, wind conditions are generally favorable at relatively low heights. In contrast, at the midpoint of the roof's windward edge, wind conditions are generally not favorable at relatively low heights. At leeward representative locations of the roof, the bottoms of the height range of favorable wind conditions are typically higher than those at the windward representative locations, but the favorable wind conditions are much better at the leeward representative locations. When there is no prevailing wind direction, the center of the roof is more favorable for installing SWTs than the corners or the edge midpoints of the roof. Full article
(This article belongs to the collection Wind Turbines)
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Open AccessArticle Promise and Challenges of High-Voltage SiC Bipolar Power Devices
Energies 2016, 9(11), 908; doi:10.3390/en9110908
Received: 11 October 2016 / Revised: 27 October 2016 / Accepted: 28 October 2016 / Published: 3 November 2016
PDF Full-text (2814 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Although various silicon carbide (SiC) power devices with very high blocking voltages over 10 kV have been demonstrated, basic issues associated with the device operation are still not well understood. In this paper, the promise and limitations of high-voltage SiC bipolar devices are
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Although various silicon carbide (SiC) power devices with very high blocking voltages over 10 kV have been demonstrated, basic issues associated with the device operation are still not well understood. In this paper, the promise and limitations of high-voltage SiC bipolar devices are presented, taking account of the injection-level dependence of carrier lifetimes. It is shown that the major limitation of SiC bipolar devices originates from band-to-band recombination, which becomes significant at a high-injection level. A trial of unipolar/bipolar hybrid operation to reduce power loss is introduced, and an 11 kV SiC hybrid (merged pin-Schottky) diodes is experimentally demonstrated. The fabricated diodes with an epitaxial anode exhibit much better forward characteristics than diodes with an implanted anode. The temperature dependence of forward characteristics is discussed. Full article
(This article belongs to the Special Issue Semiconductor Power Devices)
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Open AccessArticle Multi-Objective Distribution Network Expansion Incorporating Electric Vehicle Charging Stations
Energies 2016, 9(11), 909; doi:10.3390/en9110909
Received: 31 August 2016 / Revised: 21 October 2016 / Accepted: 27 October 2016 / Published: 3 November 2016
Cited by 2 | PDF Full-text (4005 KB) | HTML Full-text | XML Full-text
Abstract
The paper develops a multi-objective planning framework for distribution network expansion with electric vehicle charging stations. Charging loads are modeled in the first place, and then integrated into the optimal distribution network expansion planning. The formulation is extended from the single objective of
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The paper develops a multi-objective planning framework for distribution network expansion with electric vehicle charging stations. Charging loads are modeled in the first place, and then integrated into the optimal distribution network expansion planning. The formulation is extended from the single objective of the economic cost minimization into three objectives with the additional maximization of the charging station utilization, and maximization of the reliability level. Compared with the existing models, it captures the interactive impacts between charging infrastructures planning and distribution network planning from the aspects of economy, utilization, and reliability. A multi-stage search strategy is designed to solve the multi-objective problem. The models and the strategy are demonstrated by the test case. The results show that the proposed planning framework can make a trade-off among the three objectives, and offer a perspective to effectively integrate the network constraints from both the transportation network and distribution network. Full article
(This article belongs to the collection Smart Grid)
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Open AccessArticle Thermal Cracking of Jatropha Oil with Hydrogen to Produce Bio-Fuel Oil
Energies 2016, 9(11), 910; doi:10.3390/en9110910
Received: 24 September 2016 / Revised: 26 October 2016 / Accepted: 28 October 2016 / Published: 3 November 2016
Cited by 1 | PDF Full-text (1307 KB) | HTML Full-text | XML Full-text
Abstract
This study used thermal cracking with hydrogen (HTC) to produce bio-fuel oil (BFO) from jatropha oil (JO) and to improve its quality. We conducted HTC with different hydrogen pressures (PH2; 0–2.07 MPa or 0–300 psig), retention times (tr
[...] Read more.
This study used thermal cracking with hydrogen (HTC) to produce bio-fuel oil (BFO) from jatropha oil (JO) and to improve its quality. We conducted HTC with different hydrogen pressures (PH2; 0–2.07 MPa or 0–300 psig), retention times (tr; 40–780 min), and set temperatures (TC; 623–683 K). By applying HTC, the oil molecules can be hydrogenated and broken down into smaller molecules. The acid value (AV), iodine value, kinematic viscosity (KV), density, and heating value (HV) of the BFO produced were measured and compared with the prevailing standards for oil to assess its suitability as a substitute for fossil fuels or biofuels. The results indicate that an increase in PH2 tends to increase the AV and KV while decreasing the HV of the BFO. The BFO yield (YBFO) increases with PH2 and tr. The above properties decrease with increasing TC. Upon HTC at 0.69 MPa (100 psig) H2 pressure, 60 min time, and 683 K temperature, the YBFO was found to be 86 wt%. The resulting BFO possesses simulated distillation characteristics superior to those of boat oil and heavy oil while being similar to those of diesel oil. The BFO contains 15.48% light naphtha, 35.73% heavy naphtha, 21.79% light gas oil, and 27% heavy gas oil and vacuum residue. These constituents can be further refined to produce gasoline, diesel, lubricants, and other fuel products. Full article
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Open AccessArticle Solar Resource for Urban Communities in the Baja California Peninsula, Mexico
Energies 2016, 9(11), 911; doi:10.3390/en9110911
Received: 21 July 2016 / Revised: 26 October 2016 / Accepted: 27 October 2016 / Published: 3 November 2016
Cited by 1 | PDF Full-text (14080 KB) | HTML Full-text | XML Full-text
Abstract
Several studies have determined that Mexico has great renewable energy potential, and one of its most abundant resources is solar energy, a source that could be exploited to provide development opportunities to its population, however it is necessary to calculate the amount of
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Several studies have determined that Mexico has great renewable energy potential, and one of its most abundant resources is solar energy, a source that could be exploited to provide development opportunities to its population, however it is necessary to calculate the amount of this source available. The aim of this study was to assess solar irradiance at urban communities in the Baja California Peninsula. For this purpose data recorded every 10 min during 6 years (2010–2015) by the Automatic Meteorological Stations (AMSs) and Synoptic Automatic Meteorological Stations (SAMSs) of the National Meteorological System of Mexico (NMS) were analyzed. Satellite data from the Surface and Meteorology Energy System (SMSE) were also used, and a linear regression was performed to compare the measured and satellite data. The highest R-square value found was 0.97 and the lowest was 0.82. Daily patterns show that Cabo San Lucas had the highest average solar irradiation/day, with 1000 W/m2. Considering the urban areas, total solar irradiation reaching the Peninsula is about 447 × 106 kWh, which represents around 447 times the total Baja California Peninsula yearly energy consumption. Geographic Information System (GIS) helped to identify the zones and months with higher solar resources. May is the month registering the highest irradiation, more than 8.1 kWh/m2/day, while the average solar resource for the whole Peninsula is 5.7 kWh/m2/day. Full article
(This article belongs to the Special Issue Urban Generation of Renewable Energy and Sustainable Cities)
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Open AccessArticle Experimental Optimization of Passive Cooling of a Heat Source Array Flush-Mounted on a Vertical Plate
Energies 2016, 9(11), 912; doi:10.3390/en9110912
Received: 12 July 2016 / Revised: 30 October 2016 / Accepted: 1 November 2016 / Published: 4 November 2016
Cited by 2 | PDF Full-text (9628 KB) | HTML Full-text | XML Full-text
Abstract
Heat sources, such as power electronics for offshore power, could be cooled passively—mainly by conduction and natural convection. The obvious advantage of this strategy is its high reliability. However, it must be implemented in an efficient manner (i.e., the area needs to be
[...] Read more.
Heat sources, such as power electronics for offshore power, could be cooled passively—mainly by conduction and natural convection. The obvious advantage of this strategy is its high reliability. However, it must be implemented in an efficient manner (i.e., the area needs to be kept low to limit the construction costs). In this study, the placement of multiple heat sources mounted on a vertical plate was studied experimentally for optimization purposes. We chose a regular distribution, as this is likely to be the preferred choice in the construction process. We found that optimal spacing can be determined for a targeted source density by tuning the vertical and horizontal spacing between the heat sources. The optimal aspect ratio was estimated to be around two. Full article
(This article belongs to the Special Issue Renewable Energy Technologies for Small Scale Applications)
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Open AccessArticle A Principal Component Analysis in Switchgrass Chemical Composition
Energies 2016, 9(11), 913; doi:10.3390/en9110913
Received: 28 July 2016 / Revised: 18 October 2016 / Accepted: 25 October 2016 / Published: 4 November 2016
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Abstract
In recent years, bioenergy has become a promising renewable energy source that can potentially reduce the greenhouse emissions and generate economic growth in rural areas. Gaining understanding and controlling biomass chemical composition contributes to an efficient biofuel generation. This paper presents a principal
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In recent years, bioenergy has become a promising renewable energy source that can potentially reduce the greenhouse emissions and generate economic growth in rural areas. Gaining understanding and controlling biomass chemical composition contributes to an efficient biofuel generation. This paper presents a principal component analysis (PCA) that shows the influence and relevance of selected controllable factors over the chemical composition of switchgrass and, therefore, in the generation of biofuels. The study introduces the following factors: (1) storage days; (2) particle size; (3) wrap type; and (4) weight of the bale. Results show that all the aforementioned factors have an influence in the chemical composition. The number of days that bales have been stored was the most significant factor regarding changes in chemical components due to its effect over principal components 1 and 2 (PC1 and PC2, approximately 80% of the total variance). The storage days are followed by the particle size, the weight of the bale and the type of wrap utilized to enclose the bale. An increment in the number of days (from 75–150 days to 225 days) in storage decreases the percentage of carbohydrates by −1.03% while content of ash increases by 6.56%. Full article
(This article belongs to the collection Bioenergy and Biofuel)
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Open AccessArticle Definition and Experimental Validation of a Simplified Model for a Microgrid Thermal Network and its Integration into Energy Management Systems
Energies 2016, 9(11), 914; doi:10.3390/en9110914
Received: 29 August 2016 / Revised: 27 October 2016 / Accepted: 2 November 2016 / Published: 4 November 2016
Cited by 1 | PDF Full-text (2532 KB) | HTML Full-text | XML Full-text
Abstract
The present paper aims at defining a simplified but effective model of a thermal network that links the thermal power generation with the resulting temperature time profile in a heated or refrigerated environment. For this purpose, an equivalent electric circuit is proposed together
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The present paper aims at defining a simplified but effective model of a thermal network that links the thermal power generation with the resulting temperature time profile in a heated or refrigerated environment. For this purpose, an equivalent electric circuit is proposed together with an experimental procedure to evaluate its input parameters. The paper also highlights the simplicity of implementation of the proposed model into a microgrid Energy Management System. This allows the optimal operation of the thermal network to be achieved on the basis of available data (desired temperature profile) instead of a less realistic basis (such as the desired thermal power profile). The validation of the proposed model is performed on the Savona Campus Smart Polygeneration Microgrid (SPM) with the following steps: (i) identification of the parameters involved in the equivalent circuit (performed by minimizing the difference between the temperature profile, as calculated with the proposed model, and the measured one in a set of training days); (ii) test of the model accuracy on a set of testing days (comparing the measured temperature profiles with the calculated ones); (iii) implementation of the model into an Energy Management System in order to optimize the thermal generation starting from a desired temperature hourly profile. Full article
(This article belongs to the Special Issue Thermally Driven Systems)
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Open AccessArticle A Procedure to Perform Multi-Objective Optimization for Sustainable Design of Buildings
Energies 2016, 9(11), 915; doi:10.3390/en9110915
Received: 14 September 2016 / Revised: 27 October 2016 / Accepted: 31 October 2016 / Published: 4 November 2016
Cited by 1 | PDF Full-text (7984 KB) | HTML Full-text | XML Full-text
Abstract
When dealing with sustainable design concepts in new construction or in retrofitting existing buildings, it is useful to define both economic and environmental performance indicators, in order to select the optimal technical solutions. In most of the cases, the definition of the optimal
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When dealing with sustainable design concepts in new construction or in retrofitting existing buildings, it is useful to define both economic and environmental performance indicators, in order to select the optimal technical solutions. In most of the cases, the definition of the optimal strategy is not trivial because it is necessary to solve a multi-objective problem with a high number of the variables subjected to nonlinear constraints. In this study, a powerful multi-objective optimization genetic algorithm, NSGAII (Non-dominated Sorting Genetic Algorithm-II), is used to derive the Pareto optimal solutions, which can illustrate the whole trade-off relationship between objectives. A method is then proposed, to introduce uncertainty evaluation in the optimization procedure. A new university building is taken as a case study to demonstrate how each step of the optimization process should be performed. The results achieved turn out to be reliable and show the suitableness of this procedure to define both economic and environmental performance indicators. Similar analysis on a set of buildings representatives of a specific region might be used to assist local/national administrations in the definition of appropriate legal limits that will permit a strategic optimized extension of renewable energy production. Finally, the proposed approach could be applied to similar optimization models for the optimal planning of sustainable buildings, in order to define the best solutions among non-optimal ones. Full article
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Open AccessArticle Comparison of Degradation on Aluminum Reflectors for Solar Collectors due to Outdoor Exposure and Accelerated Aging
Energies 2016, 9(11), 916; doi:10.3390/en9110916
Received: 28 September 2016 / Revised: 31 October 2016 / Accepted: 1 November 2016 / Published: 5 November 2016
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Abstract
Reflectors for concentrated solar thermal technologies need to withstand 20 or even 30 years of outdoor exposure without significant loss of solar specular reflectance. In order to test the durability of innovative reflectors within a shorter period of time, an accelerated aging methodology
[...] Read more.
Reflectors for concentrated solar thermal technologies need to withstand 20 or even 30 years of outdoor exposure without significant loss of solar specular reflectance. In order to test the durability of innovative reflectors within a shorter period of time, an accelerated aging methodology is required. The problem with accelerated testing is that poor correlation between laboratory and field test results has been achieved in the past. This is mainly because unrealistic degradation mechanisms are accelerated in the weathering chambers. In order to define a realistic testing procedure, a high number of accelerated aging tests have been performed on differently coated aluminum reflectors. The degradation mechanisms of the accelerated tests have been classified and systematically compared to samples that have been exposed at nine different exposure sites outdoors. Besides the standardized aging tests, innovative aging procedures have been developed in such way that the agreement to the degradation pattern observed outdoors is increased. Although degradation depends on materials and location, five generic degradation mechanisms were detected. Standardized tests only reproduced one or two of the five mechanisms detected outdoors. Additionally, several degradation effects that were not observed outdoors appeared. The innovative accelerated aging tests of artificially soiled samples were able to reproduce three of the five mechanisms observed outdoors, presenting a much more realistic overall degradation pattern. Full article
(This article belongs to the Special Issue Urban Generation of Renewable Energy and Sustainable Cities)
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Open AccessArticle Comparing Apples to Apples: Why the Net Energy Analysis Community Needs to Adopt the Life-Cycle Analysis Framework
Energies 2016, 9(11), 917; doi:10.3390/en9110917
Received: 22 April 2016 / Revised: 20 June 2016 / Accepted: 8 October 2016 / Published: 5 November 2016
Cited by 1 | PDF Full-text (980 KB) | HTML Full-text | XML Full-text
Abstract
How do we know which energy technologies or resources are worth pursuing and which aren’t? One way to answer that question is to compare the energy return of a certain technology—i.e., how much energy is remaining after accounting for the amount of energy
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How do we know which energy technologies or resources are worth pursuing and which aren’t? One way to answer that question is to compare the energy return of a certain technology—i.e., how much energy is remaining after accounting for the amount of energy expended in the production and delivery process. Such energy return ratios (the most famous of which is energy return on investment (EROI)) fall within the field of net energy analysis (NEA), and provide an easy way to determine which technology is “better”; i.e., higher Energy Return Ratios (ERRs) are, certeris paribus, better than lower ERRs. Although useful as a broad measure of energy profitability, comparisons can also be misleading, particularly if the units being compared are different. For example, the energy content of electricity produced from a photovoltaic cell is different than the energy content of coal at the mine-mouth, yet these are often compared directly within the literature. These types of inconsistencies are common within the NEA literature. In this paper, we offer life cycle assessment (LCA) and the LCA methodology as a possible solution to the persistent methodological issues within the NEA community, and urge all NEA practitioners to adopt this methodology in the future. Full article
(This article belongs to the Special Issue Life-Cycle Assessment of Energy Systems in Current and Evolving Grids)
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Open AccessArticle Minimization of Cogging Force in Fractional-Slot Permanent Magnet Linear Motors with Double-Layer Concentrated Windings
Energies 2016, 9(11), 918; doi:10.3390/en9110918
Received: 27 July 2016 / Revised: 25 October 2016 / Accepted: 3 November 2016 / Published: 5 November 2016
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Abstract
Permanent magnet linear motors (PMLMs) with double-layer concentrated windings generally show significant cogging forces due to the introduction of auxiliary teeth for eliminating the end-effect induced phase unbalance, even when the fractional-slot technology is applied. This paper presents a novel approach to reduce
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Permanent magnet linear motors (PMLMs) with double-layer concentrated windings generally show significant cogging forces due to the introduction of auxiliary teeth for eliminating the end-effect induced phase unbalance, even when the fractional-slot technology is applied. This paper presents a novel approach to reduce the cogging force by adjusting the armature core dimensions in fractional-slot PMLMs with double-layer concentrated windings, together with magnet skewing. It is shown that the proposed technique is capable of reducing the cogging force of the motor in an effective way, with the peak value minimized to less than 0.4% of the rated thrust force in the case study. Such a technique can also be applicable to other linear motors with appropriate changes. Full article
(This article belongs to the Special Issue Electric Machines and Drives for Renewable Energy Harvesting)
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Open AccessArticle A Supervisory Control Algorithm of Hybrid Electric Vehicle Based on Adaptive Equivalent Consumption Minimization Strategy with Fuzzy PI
Energies 2016, 9(11), 919; doi:10.3390/en9110919
Received: 30 May 2016 / Revised: 27 September 2016 / Accepted: 29 September 2016 / Published: 8 November 2016
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Abstract
This paper presents a new energy management system based on equivalent consumption minimization strategy (ECMS) for hybrid electric vehicles. The aim is to enhance fuel economy and impose state of charge (SoC) charge-sustainability. First, the relationship between the equivalent factor (EF)
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This paper presents a new energy management system based on equivalent consumption minimization strategy (ECMS) for hybrid electric vehicles. The aim is to enhance fuel economy and impose state of charge (SoC) charge-sustainability. First, the relationship between the equivalent factor (EF) of ECMS and the co-state of pontryagin’s minimum principle (PMP) is derived. Second, a new method of implementing the adaptation law using fuzzy proportional plus integral (PI) controller is developed to adjust EF for ECMS in real-time. This adaptation law is more robust than one with constant EF due to the variation of EF as well as driving cycle. Finally, simulations for two driving cycles using ECMS are conducted as opposed to the commonly used rule-based (RB) control strategy, indicating that the proposed adaptation law can provide a promising blend in terms of fuel economy and charge-sustainability. The results confirm that ECMS with Fuzzy PI adaptation law is more robust than ECMS with constant EF as well as PI adaptation law and it achieves significant improvements compared with RB in terms of fuel economy, which is enhanced by 4.44% and 14.7% for china city bus cycle and economic commission of Europe (ECE) cycle, respectively. Full article
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Open AccessArticle Combustion and Emission Characteristics According to the Fuel Injection Ratio of an Ultra-Lean LPG Direct Injection Engine
Energies 2016, 9(11), 920; doi:10.3390/en9110920
Received: 27 June 2016 / Revised: 5 October 2016 / Accepted: 1 November 2016 / Published: 7 November 2016
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Abstract
The effect of the fuel injection ratio on the combustion and emission characteristics of stratified lean mixture combustion was investigated for a spray-guided liquefied petroleum gas (LPG) direct injection engine. Inter-injection spark-ignition combustion—a specially designed combustion strategy for LPG fuel derived from a
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The effect of the fuel injection ratio on the combustion and emission characteristics of stratified lean mixture combustion was investigated for a spray-guided liquefied petroleum gas (LPG) direct injection engine. Inter-injection spark-ignition combustion—a specially designed combustion strategy for LPG fuel derived from a two-staged injection—was employed to maximize the improvement in thermal efficiency when combustion stability is secured. When changing the fuel injection ratio, the optimum spark advance and fuel injection timings were experimentally determined to maximize the thermal efficiency based on sweeping timings. The optimum fuel injection ratio with the highest thermal efficiency (42.76%) and stable operation was 60%/40%, with the optimization of the spark advance and fuel injection timing, because of the locally rich mixture region in the recirculation zone. NOx emissions were at their highest level with a fuel injection ratio of 60%/40% because of the high combustion temperature, and the levels of total hydrocarbon and CO emissions with 50%/50% and 60%/40% fuel injection ratios were similar, whereas emissions at 70%/30% were significantly higher because of fuel wetting and the formation of over-lean mixture. Full article
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Open AccessArticle Measurement Research on the Decoupling Effect of Industries’ Carbon Emissions—Based on the Equipment Manufacturing Industry in China
Energies 2016, 9(11), 921; doi:10.3390/en9110921
Received: 15 July 2016 / Revised: 9 October 2016 / Accepted: 17 October 2016 / Published: 8 November 2016
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Abstract
Economic development usually leads to increased energy consumption, which in turn will result in an increase in carbon emissions. To break the relationship between economic development and carbon emissions, scholars have turned their attention to the phenomenon of decoupling. In this paper, we
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Economic development usually leads to increased energy consumption, which in turn will result in an increase in carbon emissions. To break the relationship between economic development and carbon emissions, scholars have turned their attention to the phenomenon of decoupling. In this paper, we studied the decoupling relationship between carbon emissions and economic growth of the equipment manufacturing industry in China from 2000 to 2014. We adapted the LMDI decomposition method, and we used the Tapio decoupling evaluation model to analyze our data. We found that the decoupling relationship between carbon emissions and economic growth of China’s equipment manufacturing industry is weak, which indicates the industry is experiencing faster economic growth than carbon emission growth. We found the economic output is the factor that has the strongest influence on the industry’s carbon emission, and energy consumption intensity has the strongest relationship with the decoupling of economic growth and carbon emission. The indicators of the industry’s decoupling-effort are all less than 1.0, which indicates that the industry is in the state of weak decoupling, and we also observed an annual decreasing trend in the industry’s indicators. Toward the end of this paper, we used the Grey forecasting model to predict the decoupling relationship between carbon emission and economic growth for 2015–2024, and we discussed the implications of our research. Full article
(This article belongs to the Special Issue Energy-Efficient and Sustainable Networking)
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Open AccessArticle Biomass Residues to Renewable Energy: A Life Cycle Perspective Applied at a Local Scale
Energies 2016, 9(11), 922; doi:10.3390/en9110922
Received: 21 June 2016 / Revised: 7 October 2016 / Accepted: 1 November 2016 / Published: 8 November 2016
Cited by 4 | PDF Full-text (1977 KB) | HTML Full-text | XML Full-text
Abstract
Italy, like every country member of the European Union (EU), will have to achieve the objectives required by the Energy Roadmap 2050. The purpose of the study was to evaluate the environmental impacts of residue recovery arising from the management of public and
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Italy, like every country member of the European Union (EU), will have to achieve the objectives required by the Energy Roadmap 2050. The purpose of the study was to evaluate the environmental impacts of residue recovery arising from the management of public and private green feedstocks, activity of the cooperative “Green City” in the Bologna district, and usage in a centralized heating system to produce thermal energy for public buildings. Results, obtained using the ReCipe impact assessment method, are compared with scores achieved by a traditional methane boiler. The study shows some advantages of the biomass-based system in terms of greenhouse gases (GHGs) emissions and consumption of non-renewable fuels, which affect climate change (−41%) and fossil resources depletion (−40%), compared to the use of natural gas (NG). Moreover, scores from network analysis denote the great contribution of feedstock transportation (98% of the cumulative impact). The main reason is attributable to all requirements to cover distances, in particular due to stages involved in the fuel supply chains. Therefore, it is clear that greater environmental benefits could be achieved by reducing supply transport distances or using more sustainable engines. Full article
(This article belongs to the Special Issue Renewable Energy Technologies for Small Scale Applications)
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Open AccessArticle Analysis and Speed Ripple Mitigation of a Space Vector Pulse Width Modulation-Based Permanent Magnet Synchronous Motor with a Particle Swarm Optimization Algorithm
Energies 2016, 9(11), 923; doi:10.3390/en9110923
Received: 17 August 2016 / Revised: 19 October 2016 / Accepted: 27 October 2016 / Published: 8 November 2016
Cited by 2 | PDF Full-text (576 KB) | HTML Full-text | XML Full-text
Abstract
A method is proposed for reducing speed ripple of permanent magnet synchronous motors (PMSMs) controlled by space vector pulse width modulation (SVPWM). A flux graph and mathematics are used to analyze the speed ripple characteristics of the PMSM. Analysis indicates that the 6P
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A method is proposed for reducing speed ripple of permanent magnet synchronous motors (PMSMs) controlled by space vector pulse width modulation (SVPWM). A flux graph and mathematics are used to analyze the speed ripple characteristics of the PMSM. Analysis indicates that the 6P (P refers to pole pairs of the PMSM) time harmonic of rotor mechanical speed is the main harmonic component in the SVPWM control PMSM system. To reduce PMSM speed ripple, harmonics are superposed on a SVPWM reference signal. A particle swarm optimization (PSO) algorithm is proposed to determine the optimal phase and multiplier coefficient of the superposed harmonics. The results of a Fourier decomposition and an optimized simulation model verified the accuracy of the analysis as well as the effectiveness of the speed ripple reduction methods, respectively. Full article
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Open AccessArticle SoC-Based Output Voltage Control for BESS with a Lithium-Ion Battery in a Stand-Alone DC Microgrid
Energies 2016, 9(11), 924; doi:10.3390/en9110924
Received: 25 August 2016 / Revised: 26 October 2016 / Accepted: 3 November 2016 / Published: 8 November 2016
Cited by 2 | PDF Full-text (5680 KB) | HTML Full-text | XML Full-text
Abstract
This paper proposes a new DC output voltage control for a battery energy storage system (BESS) with a lithium-ion battery based on the state of charge (SoC). The proposed control scheme was verified through computer simulations for a typical stand-alone DC microgrid, which
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This paper proposes a new DC output voltage control for a battery energy storage system (BESS) with a lithium-ion battery based on the state of charge (SoC). The proposed control scheme was verified through computer simulations for a typical stand-alone DC microgrid, which consists of a BESS, photovoltaic (PV) panel, engine generator (EG), and DC load. A scaled hardware prototype for a stand-alone DC microgrid was set up in the lab, in which the proposed control scheme was loaded in a DSP controller. The experimental results were compared with the simulation results for performance verification. The proposed control scheme provides relatively lower variation of the DC grid voltage than the conventional droop control. Full article
(This article belongs to the Special Issue Microgrids 2016)
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Open AccessArticle Modeling and Experimental Validation of a Low-Cost Radiation Sensor Based on the Photovoltaic Effect for Building Applications
Energies 2016, 9(11), 926; doi:10.3390/en9110926
Received: 29 June 2016 / Revised: 24 October 2016 / Accepted: 31 October 2016 / Published: 8 November 2016
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Abstract
The energy consumed to cool buildings is very elevated and solar gains represent a high percentage of these cooling loads. To minimize the thermal load it is necessary to control external shading systems. This control requires continuous measurement of solar radiation in different
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The energy consumed to cool buildings is very elevated and solar gains represent a high percentage of these cooling loads. To minimize the thermal load it is necessary to control external shading systems. This control requires continuous measurement of solar radiation in different locations of the building. However, for such applications the use of conventional irradiance sensors increases the cost and reduces the profitability of the installation. This paper is focused on the development, modeling, and experimental validation of low cost irradiation sensors based on photovoltaic effect in order to reduce the costs of dynamic external shading devices and to improve the profitability of the system. With this proposal, firstly, small commercial photovoltaic cells have been adapted for use as an irradiation measurement device. Subsequently, quasi-stationary and continuous experimental measurements of these silicon cells, facing south and installed horizontally, have been carried out in Jaén (Spain) in 2009 and 2010. Finally, a nonlinear multiparameter function has been developed to evaluate the irradiance using the electric current generated by the cell, cell temperature, ambient temperature, and absolute humidity. A favorable agreement between the model predictions and experimental data has been observed with a coefficient of determination around 0.996 for all cells. Full article
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Open AccessArticle Power Quality Disturbances Feature Selection and Recognition Using Optimal Multi-Resolution Fast S-Transform and CART Algorithm
Energies 2016, 9(11), 927; doi:10.3390/en9110927
Received: 24 August 2016 / Revised: 26 October 2016 / Accepted: 2 November 2016 / Published: 9 November 2016
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Abstract
In order to improve the recognition accuracy and efficiency of power quality disturbances (PQD) in microgrids, a novel PQD feature selection and recognition method based on optimal multi-resolution fast S-transform (OMFST) and classification and regression tree (CART) algorithm is proposed. Firstly, OMFST is
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In order to improve the recognition accuracy and efficiency of power quality disturbances (PQD) in microgrids, a novel PQD feature selection and recognition method based on optimal multi-resolution fast S-transform (OMFST) and classification and regression tree (CART) algorithm is proposed. Firstly, OMFST is carried out according to the frequency domain characteristic of disturbance signal, and 67 features are extracted by time-frequency analysis to construct the original feature set. Subsequently, the optimal feature subset is determined by Gini importance and sorted according to an embedded feature selection method based on the Gini index. Finally, one standard error rule subtree evaluation methods were applied for cost complexity pruning. After pruning, the optimal decision tree (ODT) is obtained for PQD classification. The experiments show that the new method can effectively improve the classification efficiency and accuracy with feature selection step. Simultaneously, the ODT can be constructed automatically according to the ability of feature classification. In different noise environments, the classification accuracy of the new method is higher than the method based on probabilistic neural network, extreme learning machine, and support vector machine. Full article
(This article belongs to the Special Issue Microgrids 2016)
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Open AccessArticle Comparison of Cooling System Designs for an Exhaust Heat Recovery System Using an Organic Rankine Cycle on a Heavy Duty Truck
Energies 2016, 9(11), 928; doi:10.3390/en9110928
Received: 30 August 2016 / Revised: 27 October 2016 / Accepted: 1 November 2016 / Published: 9 November 2016
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Abstract
A complex simulation model of a heavy duty truck, including an Organic Rankine Cycle (ORC) based waste heat recovery system and a vehicle cooling system, was applied to determine the system fuel economy potential in a typical drive cycle. Measures to increase the
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A complex simulation model of a heavy duty truck, including an Organic Rankine Cycle (ORC) based waste heat recovery system and a vehicle cooling system, was applied to determine the system fuel economy potential in a typical drive cycle. Measures to increase the system performance were investigated and a comparison between two different cooling system designs was derived. The base design, which was realized on a Mercedes-Benz Actros vehicle revealed a fuel efficiency benefit of 2.6%, while a more complicated design would generate 3.1%. Furthermore, fully transient simulation results were performed and are compared to steady state simulation results. It is shown that steady state simulation can produce comparable results if averaged road data are used as boundary conditions. Full article
(This article belongs to the Special Issue Waste Heat Recovery)
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Open AccessArticle New Requirements of the Voltage/VAR Function for Smart Inverter in Distributed Generation Control
Energies 2016, 9(11), 929; doi:10.3390/en9110929
Received: 19 July 2016 / Revised: 19 October 2016 / Accepted: 4 November 2016 / Published: 9 November 2016
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Abstract
International Electronical Committee (IEC) 61850-90-7 is a part of the IEC 61850 series which specifies the advanced functions and object models for power converter based Distributed Energy Resources (DERs). One of its functions, the Voltage/VAR (V/V) control function, is used to enhance the
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International Electronical Committee (IEC) 61850-90-7 is a part of the IEC 61850 series which specifies the advanced functions and object models for power converter based Distributed Energy Resources (DERs). One of its functions, the Voltage/VAR (V/V) control function, is used to enhance the stability and the reliability of the voltage in the distribution system. The conventional V/V function acts mainly for flattening the voltage profile as for a basic grid support function. Currently, other objectives such as the minimization of line loss and the operational costs reduction are coming into the spotlight. In order to attain these objectives, the V/V function and hence the DER units shall actively respond to the change of distribution system conditions. In this paper, the modification of V/V function and new requirements are proposed. To derive new requirements of V/V function, loss minimization is applied to a particle swarm optimization (PSO) algorithm where the condition of voltage constraint is considered not to deteriorate the voltage stability of the distribution system. Full article
(This article belongs to the Special Issue Electric Power Systems Research 2017)
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Open AccessArticle Horizontal Air-Ground Heat Exchanger Performance and Humidity Simulation by Computational Fluid Dynamic Analysis
Energies 2016, 9(11), 930; doi:10.3390/en9110930
Received: 7 June 2016 / Revised: 1 November 2016 / Accepted: 3 November 2016 / Published: 10 November 2016
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Abstract
Improving energy efficiency in buildings and promoting renewables are key objectives of European energy policies. Several technological measures are being developed to enhance the energy performance of buildings. Among these, geothermal systems present a huge potential to reduce energy consumption for mechanical ventilation
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Improving energy efficiency in buildings and promoting renewables are key objectives of European energy policies. Several technological measures are being developed to enhance the energy performance of buildings. Among these, geothermal systems present a huge potential to reduce energy consumption for mechanical ventilation and cooling, but their behavior depending on varying parameters, boundary and climatic conditions is not fully established. In this paper a horizontal air-ground heat exchanger (HAGHE) system is studied by the development of a computational fluid dynamics (CFD) model. Summer and winter conditions representative of the Mediterranean climate are analyzed to evaluate operation and thermal performance differences. A particular focus is given to humidity variations as this parameter has a major impact on indoor air quality and comfort. Results show the benefits that HAGHE systems can provide in reducing energy consumption in all seasons, in summer when free-cooling can be implemented avoiding post air treatment using heat pumps. Full article
(This article belongs to the Special Issue Energy Conservation in Infrastructures 2016)
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Open AccessArticle Forecasting Electricity Market Risk Using Empirical Mode Decomposition (EMD)—Based Multiscale Methodology
Energies 2016, 9(11), 931; doi:10.3390/en9110931
Received: 15 July 2016 / Revised: 7 October 2016 / Accepted: 25 October 2016 / Published: 9 November 2016
Cited by 1 | PDF Full-text (2761 KB) | HTML Full-text | XML Full-text
Abstract
The electricity market has experienced an increasing level of deregulation and reform over the years. There is an increasing level of electricity price fluctuation, uncertainty, and risk exposure in the marketplace. Traditional risk measurement models based on the homogeneous and efficient market assumption
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The electricity market has experienced an increasing level of deregulation and reform over the years. There is an increasing level of electricity price fluctuation, uncertainty, and risk exposure in the marketplace. Traditional risk measurement models based on the homogeneous and efficient market assumption no longer suffice, facing the increasing level of accuracy and reliability requirements. In this paper, we propose a new Empirical Mode Decomposition (EMD)-based Value at Risk (VaR) model to estimate the downside risk measure in the electricity market. The proposed model investigates and models the inherent multiscale market risk structure. The EMD model is introduced to decompose the electricity time series into several Intrinsic Mode Functions (IMF) with distinct multiscale characteristics. The Exponential Weighted Moving Average (EWMA) model is used to model the individual risk factors across different scales. Experimental results using different models in the Australian electricity markets show that EMD-EWMA models based on Student’s t distribution achieves the best performance, and outperforms the benchmark EWMA model significantly in terms of model reliability and predictive accuracy. Full article
(This article belongs to the Special Issue Energy Time Series Forecasting)
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Open AccessArticle The Coupling Fields Characteristics of Cable Joints and Application in the Evaluation of Crimping Process Defects
Energies 2016, 9(11), 932; doi:10.3390/en9110932
Received: 14 September 2016 / Revised: 23 October 2016 / Accepted: 1 November 2016 / Published: 9 November 2016
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Abstract
The internal defects of cable joints always accelerate the deterioration of insulation, until finally accidents can arise due to the explosion of the joints. The formation process of this damage often involves changes in the electromagnetic, temperature and stress distribution of the cable
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The internal defects of cable joints always accelerate the deterioration of insulation, until finally accidents can arise due to the explosion of the joints. The formation process of this damage often involves changes in the electromagnetic, temperature and stress distribution of the cable joint, therefore, it is necessary to analyze the electromagnetic-thermal-mechanical distribution of cable joints. Aiming at solving this problem, the paper sets up a 3-D electromagnetic-thermal-mechanical coupling model of cable joints under crimping process defects. Based on the model, the electromagnetic losses distribution, temperature distribution and stress distribution of a cable joint and body are calculated. Then, the coupling fields characteristics in different contact coefficient k, ambient temperature Tamb and load current I were analyzed, and according to the thermal-mechanical characteristics of a cable joint under internal defects, the temperature difference ΔTf and stress difference Δσf of cable surface are applied to evaluate the internal cable joint defects. Finally, a simplified model of the cable joint is set up to verify the accuracy of the coupling field model proposed in this paper, which indicates that the model can be used to analyze the coupling fields characteristics of cable joints and the method can be applied to evaluate crimping process defects of cable joints. Full article
(This article belongs to the Special Issue Advanced Thermal Simulation of Energy Systems)
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Open AccessArticle Analysis of Power Quality Signals Using an Adaptive Time-Frequency Distribution
Energies 2016, 9(11), 933; doi:10.3390/en9110933
Received: 19 August 2016 / Revised: 17 October 2016 / Accepted: 26 October 2016 / Published: 9 November 2016
Cited by 1 | PDF Full-text (1271 KB) | HTML Full-text | XML Full-text
Abstract
Spikes frequently occur in power quality (PQ) disturbance signals due to various causes such as switching of the inductive loads and the energization of the capacitor bank. Such signals are difficult to analyze using existing time-frequency (TF) methods as these signals have two
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Spikes frequently occur in power quality (PQ) disturbance signals due to various causes such as switching of the inductive loads and the energization of the capacitor bank. Such signals are difficult to analyze using existing time-frequency (TF) methods as these signals have two orthogonal directions in a TF plane. To address this issue, this paper proposes an adaptive TF distribution (TFD) for the analysis of PQ signals. In the proposed adaptive method, the smoothing kernel’s direction is locally adapted based on the direction of energy in the joint TF domain, and hence an improved TF resolution can be obtained. Furthermore, the performance of the proposed adaptive technique in analyzing electrical PQ is thoroughly studied for both synthetic and real world electrical power signals with the help of extensive simulations. The simulation results (specially for empirical data) indicate that the adaptive TFD method achieves high energy concentration in the TF domain for signals composed of tones and spikes. Moreover, the local adaptation of the smoothing kernel in the adaptive TFD enables the extraction of TF signature of spikes from TF images, which further helps in measuring the energy of spikes in a given signal. This new measure can be used to both detect the spikes as well as to quantify the extent of distortion caused by the spikes in a given signal. Full article
(This article belongs to the Special Issue Power Electronics in Power Quality)
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Open AccessArticle Analysis and Design of an Active Stabilizer for a Boost Power Converter System
Energies 2016, 9(11), 934; doi:10.3390/en9110934
Received: 2 August 2016 / Revised: 2 November 2016 / Accepted: 4 November 2016 / Published: 10 November 2016
Cited by 1 | PDF Full-text (7585 KB) | HTML Full-text | XML Full-text
Abstract
In electrical power converter systems, the presence of an LC input filter can efficiently reduce the Electromagnetic Interference (EMI) effect, and at the same time protect the converter and the load from being impacted by sharp input impulse voltages. However, for transportation applications,
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In electrical power converter systems, the presence of an LC input filter can efficiently reduce the Electromagnetic Interference (EMI) effect, and at the same time protect the converter and the load from being impacted by sharp input impulse voltages. However, for transportation applications, the weight and size limitations of input LC filters for power converters have to be taken into consideration. The reduction of LC filter size may impair the system stability margin and dynamic response. In serve cases, the system may even become unstable. Thus, in order to ensure the system stability while minimizing the input LC filter size, the implementation of a stabilizer for the system control is needed. In this paper, a novel digital stabilizer design method is proposed for a boost power converter with a small input LC filter. The proposed method is based on input filter inductance current measurements and DSP (Digital Signal Processor) -based digital stabilizer design. Simulation and experimentation confirm the validity of the proposed approach. Full article
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Open AccessArticle Application of a Method for Intelligent Multi-Criteria Analysis of the Environmental Impact of Tailing Ponds in Northern Kosovo and Metohija
Energies 2016, 9(11), 935; doi:10.3390/en9110935
Received: 27 May 2016 / Revised: 31 October 2016 / Accepted: 3 November 2016 / Published: 10 November 2016
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Abstract
The technological process of exploitation of mineral resources and processing of mined ores to cater to the market results, among other things, in a large amount of tailings deposed on tailing ponds. Because of the chemical composition of the material, the increasing amount
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The technological process of exploitation of mineral resources and processing of mined ores to cater to the market results, among other things, in a large amount of tailings deposed on tailing ponds. Because of the chemical composition of the material, the increasing amount of waste, and the mismanagement of recovery and reclamation of ponds, these ponds have become a significant element of negative impact on the surrounding ecosystem. Economics was behind the discharging of this material, resulting in tailing ponds created in inappropriate areas. There is an ongoing process of depositing tailings on old tailing ponds, although no special attention has been paid to the subsequent effect on the environment. Application of intelligent multi-criteria analysis AHP and PROMETHEE has been performed in this paper for the purpose of ranking the degree of negative impact on the environment of tailing ponds. Analysis is performed for five tailing ponds of MMCC (Mining Metallurgy Chemical Combine) “Trepča”, whereby two of the ponds are active and three inactive. The ponds are in relatively close proximity to the municipalities of Zvečan and Kosovska Mitrovica, to the north of Kosovo and Metohija, Republic of Serbia. In order to achieve the most objective results, the AHP and PROMETHEE methods were applied. By using these methods for calculations, the following ranking for the flotation tailing waste deposits was obtained, regarding their environmental impact: Žitkovac, Tvrđanski Do, Bostanište, Gornje Polje and Žarkov Potok. This result can contribute to the decision-making process of a prioritizing strategy for rehabilitation and remediation of these five flotation tailings. The analysis illustrates that application of intelligent multi-criteria analysis is a useful environmental management tool to be included in the decision-making process. Full article
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Open AccessArticle Analysis of Power Network for Line Reactance Variation to Improve Total Transmission Capacity
Energies 2016, 9(11), 936; doi:10.3390/en9110936
Received: 25 July 2016 / Revised: 29 September 2016 / Accepted: 2 November 2016 / Published: 10 November 2016
Cited by 1 | PDF Full-text (3349 KB) | HTML Full-text | XML Full-text
Abstract
The increasing growth in power demand and the penetration of renewable distributed generations in competitive electricity market demands large and flexible capacity from the transmission grid to reduce transmission bottlenecks. The bottlenecks cause transmission congestion, reliability problems, restrict competition, and limit the maximum
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The increasing growth in power demand and the penetration of renewable distributed generations in competitive electricity market demands large and flexible capacity from the transmission grid to reduce transmission bottlenecks. The bottlenecks cause transmission congestion, reliability problems, restrict competition, and limit the maximum dispatch of low cost generations in the network. The electricity system requires efficient utilization of the current transmission capability to improve the Available Transfer Capability (ATC). To improve the ATC, power flow among the lines can be managed by using Flexible AC Transmission System (FACTS) devices as power flow controllers, which alter the parameters of power lines. It is important to place FACTS devices on suitable lines to vary the reactance for improving Total Transmission Capacity (TTC) of the network and provide flexibility in the power flow. In this paper a transmission network is analyzed based on line parameters variation to improve TTC of the interconnected system. Lines are selected for placing FACTS devices based on real power flow Performance Index (PI) sensitivity factors. TTC is computed using the Repeated Power Flow (RPF) method using the constraints of lines thermal limits, bus voltage limits and generator limits. The reactance of suitable lines, selected on the basis of PI sensitivity factors are changed to divert the power flow to other lines with enough transfer capacity available. The improvement of TTC using line reactance variation is demonstrated with three IEEE test systems with multi-area networks. The results show the variation of the selected lines’ reactance in improving TTC for all the test networks with defined contingency cases. Full article
(This article belongs to the Special Issue Electric Power Systems Research 2017)
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Open AccessArticle Coil Design for High Misalignment Tolerant Inductive Power Transfer System for EV Charging
Energies 2016, 9(11), 937; doi:10.3390/en9110937
Received: 8 August 2016 / Revised: 22 October 2016 / Accepted: 25 October 2016 / Published: 10 November 2016
Cited by 2 | PDF Full-text (3399 KB) | HTML Full-text | XML Full-text
Abstract
The inductive power transfer (IPT) system for electric vehicle (EV) charging has acquired more research interest in its different facets. However, the misalignment tolerance between the charging coil (installed in the ground) and pick-up coil (mounted on the car chassis), has been a
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The inductive power transfer (IPT) system for electric vehicle (EV) charging has acquired more research interest in its different facets. However, the misalignment tolerance between the charging coil (installed in the ground) and pick-up coil (mounted on the car chassis), has been a challenge and fundamental interest in the future market of EVs. This paper proposes a new coil design QDQ (Quad D Quadrature) that maintains the high coupling coefficient and efficient power transfer during reasonable misalignment. The QDQ design makes the use of four adjacent circular coils and one square coil, for both charging and pick-up side, to capture the maximum flux at any position. The coil design has been modeled in JMAG software for calculation of inductive parameters using the finite element method (FEM), and its hardware has been tested experimentally at various misaligned positions. The QDQ coils are shown to be capable of achieving good coupling coefficient and high efficiency of the system until the misalignment displacement reaches 50% of the employed coil size. Full article
(This article belongs to the collection Electric and Hybrid Vehicles Collection)
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Open AccessArticle Flow Induced Vibration and Energy Extraction of an Equilateral Triangle Prism at Different System Damping Ratios
Energies 2016, 9(11), 938; doi:10.3390/en9110938
Received: 25 August 2016 / Revised: 23 October 2016 / Accepted: 3 November 2016 / Published: 10 November 2016
Cited by 1 | PDF Full-text (5786 KB) | HTML Full-text | XML Full-text
Abstract
The flow induced vibration and energy extraction of an equilateral triangle prism elastically mounted in a water channel are investigated experimentally at different system damping ratios ζtotal with the constant oscillating mass Mosc and system stiffness K. A power take-off
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The flow induced vibration and energy extraction of an equilateral triangle prism elastically mounted in a water channel are investigated experimentally at different system damping ratios ζtotal with the constant oscillating mass Mosc and system stiffness K. A power take-off system with a variable damping function is developed. The translation-rotation equation of the vibration system deduced in the study indicates that the total oscillating mass includes the material mass, and the equivalent mass due to the rotation of the gears and rotor. Besides, increasing load resistance can result in a decrease in ζtotal when K and Mosc remain unchanged. The prism experiences, in turn, soft galloping, hard galloping 1 and hard galloping 2 with increasing ζtotal. As ζtotal increases up to 0.335, only the vortex-induced vibration is observed because the extremely high ζtotal prevents the prism from galloping. The response amplitude decreases with the increasing ζtotal. In addition, higher ζtotal promotes the galloping to start at a higher reduced velocity. The galloping characteristics of the prism, including large amplitude responses in an extremely large range of flow velocities, excellent vibration stationarity, and steady vibration frequencies, are beneficial for improving energy conversion. The prism can extract hydraulic energy for the flow velocity U > 0.610 m/s. The harnessed power Pout and the energy conversion efficiency ηout increase with increasing ζtotal in the galloping zone. The maximum Pout and ηout reach 53.56 W and 40.44%, respectively. The optimal system damping ratio for extracting energy is the maximum system damping ratio that the prism can overcome to experience stable galloping. Full article
(This article belongs to the Special Issue Sustainable Energy Technologies)
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Open AccessArticle Perturb and Observe Control for an Embedded Point Pivoted Absorber
Energies 2016, 9(11), 939; doi:10.3390/en9110939
Received: 1 August 2016 / Revised: 4 November 2016 / Accepted: 8 November 2016 / Published: 10 November 2016
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Abstract
Marine energy sources represent an attractive and inexhaustible reservoir able to contribute to the fulfillment of the world energy demand in accordance with climate/energy regulatory frameworks. Wave energy converter (WEC) integration into the main grid requires both the maximization of the harvested energy
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Marine energy sources represent an attractive and inexhaustible reservoir able to contribute to the fulfillment of the world energy demand in accordance with climate/energy regulatory frameworks. Wave energy converter (WEC) integration into the main grid requires both the maximization of the harvested energy and the proper management of the generation variability. The present paper focuses on both these mentioned issues. More specifically, it presents an embedded point pivoted absorber (PPA) and its related control strategy aimed at maximizing the harvested energy. Experimental and numerical investigations have been carried out in a wave/towing tank facility in order to derive the design characteristics of the full-scale model and demonstrate the validity and effectiveness of the proposed control strategy. Full article
(This article belongs to the Special Issue Numerical Modelling of Wave and Tidal Energy)
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Open AccessArticle Effect of Air Staging Ratios on the Burning Rate and Emissions in an Underfeed Fixed-Bed Biomass Combustor
Energies 2016, 9(11), 940; doi:10.3390/en9110940
Received: 8 September 2016 / Revised: 31 October 2016 / Accepted: 4 November 2016 / Published: 11 November 2016
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Abstract
This experimental work studies a small-scale biomass combustor (5–12 kW) with an underfed fixed bed using low air staging ratios (15%–30%). This document focuses on the influence of the operative parameters on the combustion process, so gaseous emissions and the distribution and concentration
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This experimental work studies a small-scale biomass combustor (5–12 kW) with an underfed fixed bed using low air staging ratios (15%–30%). This document focuses on the influence of the operative parameters on the combustion process, so gaseous emissions and the distribution and concentration of particulate matter have also been recorded. The facility shows good stability and test repeatability. For the studied airflow ranges, the results show that increasing the total airflow rate does not increase the overall air excess ratio because the burning rate is proportionally enhanced (with some slight differences that depend on the air staging ratio). Consequently, the heterogeneous reactions at the bed remain in the so-called oxygen-limited region, and thus the entire bed operates under sub-stoichiometric conditions with regards of the char content of the biomass. In addition, tests using only primary air (no staging) may increase the fuel consumption, but in a highly incomplete way, approaching a gasification regime. Some measured burning rates are almost 40% higher than previous results obtained in batch combustors due to the fixed position of the ignition front. The recorded concentration of particulate matter varies between 15 and 75 mg/Nm3, with a main characteristic diameter between 50 and 100 nm. Full article
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Open AccessArticle Analysis and Modeling for China’s Electricity Demand Forecasting Using a Hybrid Method Based on Multiple Regression and Extreme Learning Machine: A View from Carbon Emission
Energies 2016, 9(11), 941; doi:10.3390/en9110941
Received: 8 October 2016 / Revised: 3 November 2016 / Accepted: 4 November 2016 / Published: 11 November 2016
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Abstract
The power industry is the main battlefield of CO2 emission reduction, which plays an important role in the implementation and development of the low carbon economy. The forecasting of electricity demand can provide a scientific basis for the country to formulate a
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The power industry is the main battlefield of CO2 emission reduction, which plays an important role in the implementation and development of the low carbon economy. The forecasting of electricity demand can provide a scientific basis for the country to formulate a power industry development strategy and further promote the sustained, healthy and rapid development of the national economy. Under the goal of low-carbon economy, medium and long term electricity demand forecasting will have very important practical significance. In this paper, a new hybrid electricity demand model framework is characterized as follows: firstly, integration of grey relation degree (GRD) with induced ordered weighted harmonic averaging operator (IOWHA) to propose a new weight determination method of hybrid forecasting model on basis of forecasting accuracy as induced variables is presented; secondly, utilization of the proposed weight determination method to construct the optimal hybrid forecasting model based on extreme learning machine (ELM) forecasting model and multiple regression (MR) model; thirdly, three scenarios in line with the level of realization of various carbon emission targets and dynamic simulation of effect of low-carbon economy on future electricity demand are discussed. The resulting findings show that, the proposed model outperformed and concentrated some monomial forecasting models, especially in boosting the overall instability dramatically. In addition, the development of a low-carbon economy will increase the demand for electricity, and have an impact on the adjustment of the electricity demand structure. Full article
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Open AccessArticle Simple Design Approach for Low Torque Ripple and High Output Torque Synchronous Reluctance Motors
Energies 2016, 9(11), 942; doi:10.3390/en9110942
Received: 11 September 2016 / Revised: 27 October 2016 / Accepted: 7 November 2016 / Published: 11 November 2016
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Abstract
The rotor design of Synchronous Reluctance Motors (SynRMs) has a large effect on their efficiency, torque density and torque ripple. In order to achieve a good compromise between these three goals, an optimized rotor geometry is necessary. A finite element method (FEM) is
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The rotor design of Synchronous Reluctance Motors (SynRMs) has a large effect on their efficiency, torque density and torque ripple. In order to achieve a good compromise between these three goals, an optimized rotor geometry is necessary. A finite element method (FEM) is a good tool for the optimization. However, the computation time is an obstacle as there are many geometrical parameters to be optimized. The flux-barrier widths and angles are the two most crucial parameters for the SynRM output torque and torque ripple. This paper proposes an easy-to-use set of parametrized equations to select appropriate values for these two rotor parameters. With these equations, the reader can design a SynRM of distributed windings with a low torque ripple and with a better average torque. The methodology is valid for a wide range of SynRMs. To check the validity of the proposed equations, the sensitivity analysis for the variation of these two parameters on the SynRM torque and torque ripple is carried out. In addition, the analysis in this paper gives insight into the behavior of the machine as a function of these two parameters. Furthermore, the torque and torque ripple of SynRMs having a rotor with three, four and five flux-barriers are compared with three literature approaches. The comparison shows that the proposed equations are effective in choosing the flux-barrier angles and widths for low torque ripple and better average torque. Experimental results have been obtained to confirm the FEM results and to validate the methodology for choosing the rotor parameters. Full article
(This article belongs to the Special Issue Electric Machines and Drives for Renewable Energy Harvesting)
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Open AccessArticle Conventional P-ω/Q-V Droop Control in Highly Resistive Line of Low-Voltage Converter-Based AC Microgrid
Energies 2016, 9(11), 943; doi:10.3390/en9110943
Received: 2 August 2016 / Revised: 25 October 2016 / Accepted: 3 November 2016 / Published: 11 November 2016
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Abstract
In low-voltage converter-based alternating current (AC) microgrids with resistive distribution lines, the P-V droop with Q-f boost (VPD/FQB) is the most common method for load sharing. However, it cannot achieve the active power sharing proportionally. To overcome this drawback,
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In low-voltage converter-based alternating current (AC) microgrids with resistive distribution lines, the P-V droop with Q-f boost (VPD/FQB) is the most common method for load sharing. However, it cannot achieve the active power sharing proportionally. To overcome this drawback, the conventional P-ω/Q-V droop control is adopted in the low-voltage AC microgrid. As a result, the active power sharing among the distributed generators (DGs) is easily obtained without communication. More importantly, this study clears up the previous misunderstanding that conventional P-ω/Q-V droop control is only applicable to microgrids with highly inductive lines, and lays a foundation for the application of conventional droop control under different line impedances. Moreover, in order to guarantee the accurate reactive power sharing, a guide for designing Q-V droop gains is given, and virtual resistance is adopted to shape the desired output impedance. Finally, the effects of power sharing and transient response are verified through simulations and experiments in converter-based AC Microgrid. Full article
(This article belongs to the Special Issue Microgrids 2016)
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Open AccessArticle The Recent Change in the Italian Policies for Photovoltaics: Effects on the Energy Demand Coverage of Grid-Connected PV Systems Installed in Urban Contexts
Energies 2016, 9(11), 944; doi:10.3390/en9110944
Received: 28 September 2016 / Revised: 28 October 2016 / Accepted: 8 November 2016 / Published: 12 November 2016
Cited by 3 | PDF Full-text (22502 KB) | HTML Full-text | XML Full-text
Abstract
In July 2013, the Italian photovoltaic (PV) support policies changed the feed-in tariff (FIT) mechanism and turned to a tax credits program, which is currently in force. The aim of this paper is to investigate how such a radical change has influenced the
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In July 2013, the Italian photovoltaic (PV) support policies changed the feed-in tariff (FIT) mechanism and turned to a tax credits program, which is currently in force. The aim of this paper is to investigate how such a radical change has influenced the electricity demand coverage of the PV systems installed in urban contexts. A methodology, which connects the economic assessment to a detailed architectural and energy suitability analysis, was applied to some case studies to analyse the relationships between the physical parameters related to multi-storey buildings (roof shapes, number of floors and area of flats) and the most relevant economic and financial features affecting the viability of rooftop PV systems. The study, which considers only the electricity produced by the PV systems that are economically profitable, highlighted that the tax credits scheme is even more effective in covering the electrical consumption of densely urbanised Italian city districts. The results, which are significantly influenced by the latitude of the analysed districts, underline the opportunity for governments to adopt PV promoting policies that are more sensitive to the amount of solar energy available in the different regions of their national territory. Full article
(This article belongs to the Special Issue Grid-Connected Photovoltaic Systems)
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Open AccessArticle Long Term Expected Revenue of Wind Farms Considering the Bidding Admission Uncertainty
Energies 2016, 9(11), 945; doi:10.3390/en9110945
Received: 4 September 2016 / Revised: 25 October 2016 / Accepted: 6 November 2016 / Published: 19 November 2016
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Abstract
As a long term bidding behavior, bid shading is exhibited by wind farms participating in real Uniform Price (UP) markets. This signifies that the wind farm owners bid far below their true long run marginal cost. In this paper, a method is proposed
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As a long term bidding behavior, bid shading is exhibited by wind farms participating in real Uniform Price (UP) markets. This signifies that the wind farm owners bid far below their true long run marginal cost. In this paper, a method is proposed to consider the uncertainty of bidding admission in the long term expected revenue of wind farms. We show that this consideration could perfectly explain the observed bid shading behavior of wind farm owners. We use a novel market price model with a stochastic model of a wind farm to derive indices describing the uncertainty of bidding admission. The optimal behavior of the wind farm is then obtained by establishing a multi objective optimization problem and subsequently solved using genetic algorithm. The method is applied to the analysis of long term bidding behavior of a wind farm participating in a Pay-as-Bid (PAB) auction such as Iran Electricity Market (IEM). The results demonstrate that wind farm owners change their bid shading behavior in a PAB Auction. However, the expected revenue of the wind farm will also decrease in a PAB auction. As a result, it is not recommended to make an obligation for the wind farms to participate in a PAB auction as a normal market player. Full article
(This article belongs to the Special Issue Energy Policy and Climate Change 2016)
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Open AccessArticle Raman Spectral Characteristics of Oil-Paper Insulation and Its Application to Ageing Stage Assessment of Oil-Immersed Transformers
Energies 2016, 9(11), 946; doi:10.3390/en9110946
Received: 9 August 2016 / Revised: 27 October 2016 / Accepted: 8 November 2016 / Published: 12 November 2016
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Abstract
The aging of oil-paper insulation in power transformers may cause serious power failures. Thus, effective monitoring of the condition of the transformer insulation is the key to prevent major accidents. The purpose of this study was to explore the feasibility of confocal laser
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The aging of oil-paper insulation in power transformers may cause serious power failures. Thus, effective monitoring of the condition of the transformer insulation is the key to prevent major accidents. The purpose of this study was to explore the feasibility of confocal laser Raman spectroscopy (CLRS) for assessing the aging condition of oil-paper insulation. Oil-paper insulation samples were subjected to thermal accelerated ageing at 120 °C for up to 160 days according to the procedure described in the IEEE Guide. Meanwhile, the dimension of the Raman spectrum of the insulation oil was reduced by principal component analysis (PCA). The 160 oil-paper insulation samples were divided into five aging stages as training samples by clustering analysis and with the use of the degree of polymerization of the insulating papers. In addition, the features of the Raman spectrum were used as the inputs of a multi-classification support vector machine. Finally, 105 oil-paper insulation testing samples aged at a temperature of 130 °C were used to further test the diagnostic capability and universality of the established algorithm. Results demonstrated that CLRS in conjunction with the PCA-SVM technique provides a new way for aging stage assessment of oil-paper insulation equipment in the field. Full article
(This article belongs to the Special Issue Power Transformer Diagnostics, Monitoring and Design Features)
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Open AccessArticle Exergy Accounting: A Quantitative Comparison of Methods and Implications for Energy-Economy Analysis
Energies 2016, 9(11), 947; doi:10.3390/en9110947
Received: 29 September 2016 / Revised: 4 November 2016 / Accepted: 10 November 2016 / Published: 14 November 2016
Cited by 2 | PDF Full-text (3663 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Assessments of the feasibility of decoupling energy consumption from economic growth could benefit from an improved understanding of the size, nature and value of different energy flows. This understanding may be enhanced by focusing upon so-called “useful exergy”—a measure of both the quantity
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Assessments of the feasibility of decoupling energy consumption from economic growth could benefit from an improved understanding of the size, nature and value of different energy flows. This understanding may be enhanced by focusing upon so-called “useful exergy”—a measure of both the quantity and “quality” of energy (defined here as its thermodynamic ability to perform physical work) at the “useful” stage of the energy conversion chain. Useful exergy flows within national economies are increasingly being quantified and their role in economic activity explored. However, this so-called “exergy economics” field currently lacks a consistent methodology. This paper contributes to the development of a more consistent approach. By constructing a “useful exergy account” for the United Kingdom covering the period 1960–2012, we explore how different methodological choices influence estimates of useful exergy for different categories of end-use as well as estimates of total national useful exergy consumption. Specifically, we evaluate the sensitivity of estimates to: (a) the method of estimating the exergy efficiency of different end-uses; (b) the boundaries between end-use categories; and (c) the method of estimating the primary exergy associated with renewable electricity. We also improve upon the current method of accounting for industrial uses of heat. This leads to suggestions for best practice when constructing useful exergy accounts, and the identification of areas where further methodological development is required. Full article
(This article belongs to the Special Issue Low Carbon Economy)
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Open AccessArticle Spray Formation of a Liquid Carbon Dioxide-Water Mixture at Elevated Pressures
Energies 2016, 9(11), 948; doi:10.3390/en9110948
Received: 6 September 2016 / Revised: 8 November 2016 / Accepted: 8 November 2016 / Published: 14 November 2016
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Abstract
Liquid carbon dioxide-assisted (LCO2-assisted) atomization can be used in coal-water slurry gasification plants to prevent the agglomeration of coal particles. It is essential to understand the atomization behavior of the water-LCO2 mixture leaving the injector nozzle under various conditions, including
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Liquid carbon dioxide-assisted (LCO2-assisted) atomization can be used in coal-water slurry gasification plants to prevent the agglomeration of coal particles. It is essential to understand the atomization behavior of the water-LCO2 mixture leaving the injector nozzle under various conditions, including the CO2 blending ratio, injection pressure, and chamber pressure. In this study, the flash-atomization behavior of a water-LCO2 mixture was evaluated with regard to the spray angle and penetration length during a throttling process. The injector nozzle was mounted downstream of a high-pressure spray-visualization system. Based on the results, the optimal condition for the effective transport of coal particles was proposed. Full article
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Open AccessArticle Experimental Investigation on Wall Film Distribution of Dimethyl Ether/Diesel Blended Fuels Formed during Spray Wall Impingement
Energies 2016, 9(11), 949; doi:10.3390/en9110949
Received: 5 October 2016 / Revised: 4 November 2016 / Accepted: 8 November 2016 / Published: 16 November 2016
Cited by 2 | PDF Full-text (4557 KB) | HTML Full-text | XML Full-text
Abstract
Dimethyl ether (DME)/diesel blended fuels are used to improve the emissions caused by spray wall impingement during the early injection period. However, experimental results have showed that the spray wall impingement still cannot be avoided due to the engine structure and low density
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Dimethyl ether (DME)/diesel blended fuels are used to improve the emissions caused by spray wall impingement during the early injection period. However, experimental results have showed that the spray wall impingement still cannot be avoided due to the engine structure and low density of the in-cylinder charge at the early injection timing. Furthermore, the wall film formed in the spray wall impingement process directly affects fuel/air mixture formation, combustion, exhaust emissions and oil quality subsequently. In this paper, the wall film distribution of DME/diesel blended fuels formed during the spray wall impingement process has been experimentally investigated. The variations of wall film distribution, wall film area and average thickness with different injection pressures, impingement distances, impingement angles and blending ratios have been discussed under both dry wall and wet wall conditions. Results showed that the wall film distribution styles were mainly determined by the spray impingement momentum. The variation of the wall film area and average thickness were affected by three factors including the impingement momentum, wall film mass and fuel properties. Correlation analysis was introduced in order to evaluate the effect of each impact factor on the variation of wall film area and average thickness. Full article
(This article belongs to the Special Issue Automotive Engines Emissions and Control)
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Open AccessArticle A Novel Algorithm for Efficient Downlink Packet Scheduling for Multiple-Component-Carrier Cellular Systems
Energies 2016, 9(11), 950; doi:10.3390/en9110950
Received: 23 September 2016 / Revised: 20 October 2016 / Accepted: 8 November 2016 / Published: 15 November 2016
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Abstract
The simultaneous aggregation of multiple component carriers (CCs) for use by a base station constitutes one of the more promising strategies for providing substantially enhanced bandwidths for packet transmissions in 4th and 5th generation cellular systems. To the best of our knowledge, however,
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The simultaneous aggregation of multiple component carriers (CCs) for use by a base station constitutes one of the more promising strategies for providing substantially enhanced bandwidths for packet transmissions in 4th and 5th generation cellular systems. To the best of our knowledge, however, few previous studies have undertaken a thorough investigation of various performance aspects of the use of a simple yet effective packet scheduling algorithm in which multiple CCs are aggregated for transmission in such systems. Consequently, the present study presents an efficient packet scheduling algorithm designed on the basis of the proportional fair criterion for use in multiple-CC systems for downlink transmission. The proposed algorithm includes a focus on providing simultaneous transmission support for both real-time (RT) and non-RT traffic. This algorithm can, when applied with sufficiently efficient designs, provide adequate utilization of spectrum resources for the purposes of transmissions, while also improving energy efficiency to some extent. According to simulation results, the performance of the proposed algorithm in terms of system throughput, mean delay, and fairness constitute substantial improvements over those of an algorithm in which the CCs are used independently instead of being aggregated. Full article
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Open AccessArticle Optimization of Electrochemically Deposited Highly Doped ZnO Bilayers on Ga-Rich Chalcopyrite Selenide for Cost-Effective Photovoltaic Device Technology
Energies 2016, 9(11), 951; doi:10.3390/en9110951
Received: 30 August 2016 / Revised: 1 November 2016 / Accepted: 1 November 2016 / Published: 15 November 2016
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Abstract
High quality polycrystalline bilayers of aluminium doped ZnO (Al:ZnO) were successively electrodeposited in the form of columnar structures preferentially oriented along the (101¯1) crystallographic direction from aqueous solution of zinc nitrate (Zn(NO3)2) at negative
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High quality polycrystalline bilayers of aluminium doped ZnO (Al:ZnO) were successively electrodeposited in the form of columnar structures preferentially oriented along the ( 10 1 ¯ 1 ) crystallographic direction from aqueous solution of zinc nitrate (Zn(NO3)2) at negative electrochemical potential of EC = (−0.8)–(−1.2) V and moderate temperature of 80 °C on gallium rich (30% Ga) chalcopyrite selenide Cu(In,Ga)Se2 (CIGS) with chemically deposited ZnSe buffer (ZnSe/Cu(In,Ga)Se2/Mo/glass). The aluminium doped ZnO layer properties have initially been probed by deposition of Al:ZnO/i-ZnO bilayers directly on Mo/glass substrates. The band-gap energy of the Al:ZnO/i-ZnO reference layers was found to vary from 3.2 to 3.7 eV by varying the AlCl3 solute dopant concentration from 1 to 20 mM. The electrical resistivity of indium-pellet contacted highly doped Al:ZnO sheet of In/Al:ZnO/i-ZnO/Mo/glass reference samples was of the order ρ ~10−5 Ω·cm; the respective carrier concentration of the order 1022 cm−3 is commensurate with that of sputtered Al:ZnO layers. For crystal quality optimization of the bilayers by maintenance of the volatile selenium content of the chalcopyrite, they were subjected to 2-step annealing under successive temperature raise and N2 flux regulation. The hydrostatic compressive strain due to Al3+ incorporation in the ZnO lattice of bilayers processed successively with 5 and 12 mM AlCl3 dopant was εh = −0.046 and the respective stress σh = −20 GPa. The surface reflectivity of maximum 5% over the scanned region of 180–900 nm and the (optical) band gap of Eg = 3.67 eV were indicative of the high optical quality of the electrochemically deposited (ECD) Al:ZnO bilayers. Full article
(This article belongs to the Special Issue Nano-Structured Solar Cells)
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Open AccessArticle Retrofitted Solar Domestic Hot Water Systems for Swedish Single-Family Houses—Evaluation of a Prototype and Life-Cycle Cost Analysis
Energies 2016, 9(11), 953; doi:10.3390/en9110953
Received: 30 August 2016 / Revised: 7 November 2016 / Accepted: 8 November 2016 / Published: 15 November 2016
Cited by 1 | PDF Full-text (5852 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
According to recent technology road maps, system cost reductions and development of standardised plug-and-function systems are some of the most important goals for solar heating technology development. Retrofitting hot water boilers in single-family houses when installing solar collectors has the potential to significantly
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According to recent technology road maps, system cost reductions and development of standardised plug-and-function systems are some of the most important goals for solar heating technology development. Retrofitting hot water boilers in single-family houses when installing solar collectors has the potential to significantly reduce both material and installation costs. Previous studies have investigated such retrofitting, using theoretical simulations and laboratory tests, but no actual installations were made and tested in practice. This article describes the installation, measured performance and cost effectiveness of a retrofitting solution that converts existing domestic hot water heaters to a solar domestic hot water system. The measured performance is characterised by the monthly and annual solar fractions. The cost effectiveness is evaluated by a life-cycle cost analysis, comparing the retrofitted system to a conventional solar domestic hot water system and the case without any solar heating system. Measurements showed that approximately 50% of the 5000 kWh/year of domestic hot water consumption was saved by the retrofitted system in south Sweden. Such savings are in agreement with previous estimations and are comparable to the energy savings when using a conventional solar domestic hot water system. The life-cycle cost analysis showed that, according to the assumptions and given climate, the return on investment of the retrofitted system is approximately 17 years, while a conventional system does not reach profitability during its lifetime of 25 years. Full article
(This article belongs to the Special Issue Solar Cooling and Heating)
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Open AccessArticle Study on Insulator Flashover Voltage Gradient Correction Considering Soluble Pollution Constituents
Energies 2016, 9(11), 954; doi:10.3390/en9110954
Received: 11 September 2016 / Revised: 24 October 2016 / Accepted: 8 November 2016 / Published: 15 November 2016
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Abstract
Natural polluted insulator surfaces are always coated with various kinds of soluble constituents, and those constituents affect flashover performance differentially. Currently, this fact is not considered either in laboratory experiments or field pollution degree measurements, causing the existing insulation selection method to be
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Natural polluted insulator surfaces are always coated with various kinds of soluble constituents, and those constituents affect flashover performance differentially. Currently, this fact is not considered either in laboratory experiments or field pollution degree measurements, causing the existing insulation selection method to be deficient. In this paper, a systematic study on insulator flashover voltage gradient correction involving different types of soluble pollution constituents is presented. Using a typical type glass insulator as the sample, its flashover tests, polluted by typical soluble chemicals (NaCl, NaNO3, KNO3, NH4NO3, MgSO4, Ca(NO3)2 and CaSO4), were carried out. Then, the flashover gradient correction was made by combining the flashover performance of each soluble constituent, the equivalent salt deposit density (ESDD) contribution of the seven constituents, and the saturation performance of CaSO4. The correction agreed with the flashover test results of insulator polluted by three types of soluble mixture. Research results indicate that the flashover gradient correction method proposed in this paper performs well in reducing the calculating error. It is recommended to carry out component measurements and flashover gradient correction to better select outdoor insulation configuration. Full article
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Open AccessArticle The Demand Side Management Potential to Balance a Highly Renewable European Power System
Energies 2016, 9(11), 955; doi:10.3390/en9110955
Received: 3 July 2016 / Revised: 6 November 2016 / Accepted: 8 November 2016 / Published: 15 November 2016
Cited by 4 | PDF Full-text (738 KB) | HTML Full-text | XML Full-text
Abstract
Shares of renewables continue to grow in the European power system. A fully renewable European power system will primarily depend on the renewable power sources of wind and photovoltaics (PV), which are not dispatchable but intermittent and therefore pose a challenge to the
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Shares of renewables continue to grow in the European power system. A fully renewable European power system will primarily depend on the renewable power sources of wind and photovoltaics (PV), which are not dispatchable but intermittent and therefore pose a challenge to the balancing of the power system. To overcome this issue, several solutions have been proposed and investigated in the past, including storage, backup power, reinforcement of the transmission grid, and demand side management (DSM). In this paper, we investigate the potential of DSM to balance a simplified, fully renewable European power system. For this purpose, we use ten years of weather and historical load data, a power-flow model and the implementation of demand side management as a storage equivalent, to investigate the impact of DSM on the need for backup energy. We show that DSM has the potential to reduce the need for backup energy in Europe by up to one third and can cover the need for backup up to a renewable share of 67%. Finally, it is demonstrated that the optimal mix of wind and PV is shifted by the utilisation of DSM towards a higher share of PV, from 19% to 36%. Full article
(This article belongs to the Special Issue Control of Energy Storage)
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Open AccessArticle Distributed Generation Islanding Effect on Distribution Networks and End User Loads Using the Load Sharing Islanding Method
Energies 2016, 9(11), 956; doi:10.3390/en9110956
Received: 28 July 2016 / Revised: 23 October 2016 / Accepted: 8 November 2016 / Published: 16 November 2016
Cited by 1 | PDF Full-text (12756 KB) | HTML Full-text | XML Full-text
Abstract
In this paper a realistic medium voltage (MV) network with four different distributed generation technologies (diesel, gas, hydro and wind) along with their excitation and governor control systems is modelled and simulated. Moreover, an exponential model was used to represent the loads in
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In this paper a realistic medium voltage (MV) network with four different distributed generation technologies (diesel, gas, hydro and wind) along with their excitation and governor control systems is modelled and simulated. Moreover, an exponential model was used to represent the loads in the network. The dynamic and steady state behavior of the four distributed generation technologies was investigated during grid-connected operation and two transition modes to the islanding situation, planned and unplanned. This study aims to address the feasibility of planned islanding operation and to investigate the effect of unplanned islanding. The load sharing islanding method has been used for controlling the distributed generation units during grid-connected and islanding operation. The simulation results were validated through various case studies and have shown that properly planned islanding transition could provide support to critical loads at the event of utility outages. However, a reliable protection scheme would be required to mitigate the adverse effect of unplanned islanding as all unplanned sub-cases returned severe negative results. Full article
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Open AccessArticle Robust Unit Commitment Including Frequency Stability Constraints
Energies 2016, 9(11), 957; doi:10.3390/en9110957
Received: 31 August 2016 / Revised: 5 November 2016 / Accepted: 10 November 2016 / Published: 16 November 2016
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Abstract
An increased use of variable generation technologies such as wind power and photovoltaic generation can have important effects on system frequency performance during normal operation as well as contingencies. The main reasons are the operational principles and inherent characteristics of these power plants
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An increased use of variable generation technologies such as wind power and photovoltaic generation can have important effects on system frequency performance during normal operation as well as contingencies. The main reasons are the operational principles and inherent characteristics of these power plants like operation at maximum power point and no inertial response during power system imbalances. This has led to new challenges for Transmission System Operators in terms of ensuring system security during contingencies. In this context, this paper proposes a Robust Unit Commitment including a set of additional frequency stability constraints. To do this, a simplified dynamic model of the initial system frequency response is used in combination with historical frequency nadir data during contingencies. The proposed approach is especially suitable for power systems with cost-based economic dispatch like those in most Latin American countries. The study is done considering the Northern Interconnected System of Chile, a 50-Hz medium size isolated power system. The results obtained were validated by means of dynamic simulations of different system contingencies. Full article
(This article belongs to the Special Issue Advances in Power System Operations and Planning)
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Open AccessArticle Cooperative Energy Management of Hybrid DC Renewable Grid Using Decentralized Control Strategies
Energies 2016, 9(11), 859; doi:10.3390/en9110859
Received: 30 July 2016 / Revised: 3 October 2016 / Accepted: 17 October 2016 / Published: 25 October 2016
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Abstract
This paper attempted to control a hybrid DC microgrid in islanded operation mode using decentralized power management strategies. Proposed adaptive I/V characteristic for hybrid photovoltaic (PV) and battery energy storage system (BESS) and wind turbine generator (WTG) adapts the distributed energy resources (DER)
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This paper attempted to control a hybrid DC microgrid in islanded operation mode using decentralized power management strategies. Proposed adaptive I/V characteristic for hybrid photovoltaic (PV) and battery energy storage system (BESS) and wind turbine generator (WTG) adapts the distributed energy resources (DER) behavior independently in accordance with the load demand. Hence, the PV module can spend its maximum power on load demand and spend the extra power for charging the BESS, which will regulate DC bus voltage and maintain the power balance within the microgrid. When load demand is beyond the maximum generation power of PV unit, WTG will supply the energy shortage. The proposed control system was applied on the DC microgrid in order to achieve control objectives through a decentralized procedure, without telecommunication links. In order to validate the proposed strategies, the control system was implemented on a DC microgrid within MATLAB/SIMULINK, where the simulation results were analyzed and validated. Full article
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Open AccessArticle Parametric Density Recalibration of a Fundamental Market Model to Forecast Electricity Prices
Energies 2016, 9(11), 959; doi:10.3390/en9110959
Received: 18 August 2016 / Revised: 3 October 2016 / Accepted: 11 November 2016 / Published: 17 November 2016
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Abstract
This paper proposes a new approach to hybrid forecasting methodology, characterized as the statistical recalibration of forecasts from fundamental market price formation models. Such hybrid methods based upon fundamentals are particularly appropriate to medium term forecasting and in this paper the application is
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This paper proposes a new approach to hybrid forecasting methodology, characterized as the statistical recalibration of forecasts from fundamental market price formation models. Such hybrid methods based upon fundamentals are particularly appropriate to medium term forecasting and in this paper the application is to month-ahead, hourly prediction of electricity wholesale prices in Spain. The recalibration methodology is innovative in seeking to perform the recalibration into parametrically defined density functions. The density estimation method selects from a wide diversity of general four-parameter distributions to fit hourly spot prices, in which the first four moments are dynamically estimated as latent functions of the outputs from the fundamental model and several other plausible exogenous drivers. The proposed approach demonstrated its effectiveness against benchmark methods across the full range of percentiles of the price distribution and performed particularly well in the tails. Full article
(This article belongs to the Special Issue Forecasting Models of Electricity Prices) Printed Edition available
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Open AccessArticle Simplified Minimum Copper Loss Remedial Control of a Five-Phase Fault-Tolerant Permanent-Magnet Vernier Machine under Short-Circuit Fault
Energies 2016, 9(11), 860; doi:10.3390/en9110860
Received: 9 July 2016 / Revised: 2 October 2016 / Accepted: 13 October 2016 / Published: 25 October 2016
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Abstract
A fault-tolerant permanent-magnet vernier (FT-PMV) machine incorporates the merits of high fault-tolerant capability and high torque density. In this paper, a new remedial control is proposed for a five-phase FT-PMV machine with short-circuit fault of stator windings. Based on the principle of copper
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A fault-tolerant permanent-magnet vernier (FT-PMV) machine incorporates the merits of high fault-tolerant capability and high torque density. In this paper, a new remedial control is proposed for a five-phase FT-PMV machine with short-circuit fault of stator windings. Based on the principle of copper loss minimization, the aims of the proposed control strategy are to keep magnetic motive force (MMF) unchanged and minimize torque ripple. The proposed remedial control strategy contains two parts. Firstly, the remedial currents of the healthy phases are used to compensate for the ripple of MMF caused by the short-circuit current. Secondly, an open-circuit fault-tolerant control strategy is used to compensate for the lack of normal torque in the fault phase. Finally, the vector sum of two parts is adopted to derive the remedial currents. The final expression of the proposed remedial current is simpler than that than these previous methods. In addition, the proposed remedial currents are sinusoidal, which can reduce the reactive component in instantaneous power produced by pulsating torque and iron loss of a sine back-EMF machine. A FT-PMV prototype is built. The simulations and the experiments verify the effectiveness of the proposed strategy. Full article
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Open AccessArticle Estimation of Energy Consumption and Greenhouse Gas Emissions of Transportation in Beef Cattle Production
Energies 2016, 9(11), 960; doi:10.3390/en9110960
Received: 24 August 2016 / Revised: 7 November 2016 / Accepted: 11 November 2016 / Published: 18 November 2016
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Abstract
Accounting for transportation is an important part of the life cycle analysis (LCA) of beef cattle production because it is associated with energy consumption and greenhouse gas emissions. This paper describes the development and application of a model that estimates energy consumption and
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Accounting for transportation is an important part of the life cycle analysis (LCA) of beef cattle production because it is associated with energy consumption and greenhouse gas emissions. This paper describes the development and application of a model that estimates energy consumption and greenhouse gas emissions of transport in beef cattle production. The animal transport model is based on the weight and number of animals in each weight category, type of trailer, vehicle, and fuel used. The energy consumption and greenhouse gas emission estimates of animal feed transportation are based on the weight of a truckload and the number of truckloads of feed transported. Our results indicate that a truckload is travelling approximately 326 km in connection with beef cattle production in the study region. The fuel consumption amounts to 24 L of fossil fuel per 1000 kg of boneless beef. The corresponding greenhouse gas emission is 83 kg. It appears from our results that the majority of energy consumption and greenhouse gas emissions are associated with sending the finished cattle to slaughterhouses and bringing feeder cattle to feedlots. Our results point out appreciable reductions in energy consumption and greenhouse gas emissions by changing from conventional fuel to bio-fuel. Full article
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Open AccessArticle An Adaptive Speed Control Approach for DC Shunt Motors
Energies 2016, 9(11), 961; doi:10.3390/en9110961
Received: 2 July 2016 / Revised: 18 October 2016 / Accepted: 8 November 2016 / Published: 17 November 2016
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Abstract
A B-spline neural networks-based adaptive control technique for angular speed reference trajectory tracking tasks with highly efficient performance for direct current shunt motors is proposed. A methodology for adaptive control and its proper training procedure are introduced. This algorithm sets the control signal
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A B-spline neural networks-based adaptive control technique for angular speed reference trajectory tracking tasks with highly efficient performance for direct current shunt motors is proposed. A methodology for adaptive control and its proper training procedure are introduced. This algorithm sets the control signal without using a detailed mathematical model nor exact values of the parameters of the nonlinear dynamic system. The proposed robust adaptive tracking control scheme only requires measurements of the velocity output signal. Thus, real-time measurements or estimations of acceleration, current and disturbance signals are avoided. Experimental results confirm the efficient and robust performance of the proposed control approach for highly demanding motor operation conditions exposed to variable-speed reference trajectories and completely unknown load torque. Hence, laboratory experimental tests on a direct current shunt motor prove the viability of the proposed adaptive output feedback trajectory tracking control approach. Full article
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Open AccessArticle Linearization and Control of Series-Series Compensated Inductive Power Transfer System Based on Extended Describing Function Concept
Energies 2016, 9(11), 962; doi:10.3390/en9110962
Received: 9 August 2016 / Revised: 1 November 2016 / Accepted: 11 November 2016 / Published: 17 November 2016
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Abstract
The extended describing function (EDF) is a well-known method for modelling resonant converters due to its high accuracy. However, it requires complex mathematical formulation effort. This paper presents a simplified non-linear mathematical model of series-series (SS) compensated inductive power transfer (IPT) system, considering
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The extended describing function (EDF) is a well-known method for modelling resonant converters due to its high accuracy. However, it requires complex mathematical formulation effort. This paper presents a simplified non-linear mathematical model of series-series (SS) compensated inductive power transfer (IPT) system, considering zero-voltage switching in the inverter. This simplified mathematical model permits the user to derive the small-signal model using the EDF method, with less computational effort, while maintaining the accuracy of an actual physical model. The derived model has been verified using a frequency sweep method in PLECS. The small-signal model has been used to design the voltage loop controller for a SS compensated IPT system. The designed controller was implemented on a 3.6 kW experimental setup, to test its robustness. Full article
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Open AccessArticle Influence of Icing on the Modal Behavior of Wind Turbine Blades
Energies 2016, 9(11), 862; doi:10.3390/en9110862
Received: 14 June 2016 / Revised: 14 September 2016 / Accepted: 14 October 2016 / Published: 26 October 2016
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Abstract
Wind turbines installed in cold climate sites accumulate ice on their structures. Icing of the rotor blades reduces turbine power output and increases loads, vibrations, noise, and safety risks due to the potential ice throw. Ice accumulation increases the mass distribution of the
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Wind turbines installed in cold climate sites accumulate ice on their structures. Icing of the rotor blades reduces turbine power output and increases loads, vibrations, noise, and safety risks due to the potential ice throw. Ice accumulation increases the mass distribution of the blade, while changes in the aerofoil shapes affect its aerodynamic behavior. Thus, the structural and aerodynamic changes due to icing affect the modal behavior of wind turbine blades. In this study, aeroelastic equations of the wind turbine blade vibrations are derived to analyze modal behavior of the Tjaereborg 2 MW wind turbine blade with ice. Structural vibrations of the blade are coupled with a Beddoes-Leishman unsteady attached flow aerodynamics model and the resulting aeroelastic equations are analyzed using the finite element method (FEM). A linearly increasing ice mass distribution is considered from the blade root to half-length and thereafter constant ice mass distribution to the blade tip, as defined by Germanischer Lloyd (GL) for the certification of wind turbines. Both structural and aerodynamic properties of the iced blades are evaluated and used to determine their influence on aeroelastic natural frequencies and damping factors. Blade natural frequencies reduce with ice mass and the amount of reduction in frequencies depends on how the ice mass is distributed along the blade length; but the reduction in damping factors depends on the ice shape. The variations in the natural frequencies of the iced blades with wind velocities are negligible; however, the damping factors change with wind velocity and become negative at some wind velocities. This study shows that the aerodynamic changes in the iced blade can cause violent vibrations within the operating wind velocity range of this turbine. Full article
(This article belongs to the Special Issue Modeling and Simulation for Wind Turbine Loads Analysis)
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Open AccessArticle Expert Opinion Analysis on Renewable Hydrogen Storage Systems Potential in Europe
Energies 2016, 9(11), 963; doi:10.3390/en9110963
Received: 5 October 2016 / Revised: 3 November 2016 / Accepted: 8 November 2016 / Published: 18 November 2016
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Abstract
Among the several typologies of storage technologies, mainly on different physical principles (mechanical, electrical and chemical), hydrogen produced by power to gas (P2G) from renewable energy sources complies with chemical storage principle and is based on the conversion of electrical energy into chemical
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Among the several typologies of storage technologies, mainly on different physical principles (mechanical, electrical and chemical), hydrogen produced by power to gas (P2G) from renewable energy sources complies with chemical storage principle and is based on the conversion of electrical energy into chemical energy by means of the electrolysis of water which does not produce any toxic or climate-relevant emission. This paper aims to pinpoint the potential uses of renewable hydrogen storage systems in Europe, analysing current and potential locations, regulatory framework, governments’ outlooks, economic issues, and available renewable energy amounts. The expert opinion survey, already used in many research articles on different topics including energy, has been selected as an effective method to produce realistic results. The obtained results highlight strategies and actions to optimize the storage of hydrogen produced by renewables to face varying electricity demand and generation-driven fluctuations reducing the negative effects of the increasing share of renewables in the energy mix of European Countries. Full article
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Open AccessArticle Quantification of the Lifecycle Greenhouse Gas Emissions from Nuclear Power Generation Systems
Energies 2016, 9(11), 863; doi:10.3390/en9110863
Received: 5 July 2016 / Revised: 16 October 2016 / Accepted: 19 October 2016 / Published: 25 October 2016
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Abstract
This paper statistically quantifies the lifecycle greenhouse gas (GHG) emissions from six distinct reactor-based (boiling water reactor (BWR), pressurized water reactor (PWR), light water reactor (LWR), heavy-water-moderated reactor (HWR), gas-cooled reactor (GCR), fast breeder reactor (FBR)) nuclear power generation systems by following a
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This paper statistically quantifies the lifecycle greenhouse gas (GHG) emissions from six distinct reactor-based (boiling water reactor (BWR), pressurized water reactor (PWR), light water reactor (LWR), heavy-water-moderated reactor (HWR), gas-cooled reactor (GCR), fast breeder reactor (FBR)) nuclear power generation systems by following a two-step approach that included (a) performing a review of the lifecycle assessment (LCA) studies on the reactor-based nuclear power generation systems; and (b) statistically evaluating the lifecycle GHG emissions (expressed in grams of carbon dioxide equivalent per kilowatt hour, gCO2e/kWh) for each of the reactor-based nuclear power generation systems to assess the role of different types of nuclear reactors in the reduction of the lifecycle GHG emissions. Additionally, this study quantified the impacts of fuel enrichment methods (centrifuge, gaseous diffusion) on GHG emissions. The mean lifecycle GHG emissions resulting from the use of BWR (sample size, N = 15), PWR (N = 21), LWR (N = 7), HWR (N = 3), GCR (N = 1), and FBR (N = 2) in nuclear power generation systems are 14.52 gCO2e/kWh, 11.87 gCO2e/kWh, 20.5 gCO2e/kWh, 28.2 gCO2e/kWh, 8.35 gCO2e/kWh, and 6.26 gCO2e/kWh, respectively. The FBR nuclear power generation systems produced the minimum lifecycle GHGs. The centrifuge enrichment method produced lower GHG emissions than the gaseous diffusion enrichment method. Full article
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Open AccessArticle Control Optimization of Solar Thermally Driven Chillers
Energies 2016, 9(11), 864; doi:10.3390/en9110864
Received: 3 August 2016 / Revised: 13 September 2016 / Accepted: 13 October 2016 / Published: 25 October 2016
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Abstract
Many installed solar thermally driven cooling systems suffer from high auxiliary electric energy consumption which makes them not more efficient than conventional compression cooling systems. A main reason for this is the use of non-efficient controls with constant set points that do not
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Many installed solar thermally driven cooling systems suffer from high auxiliary electric energy consumption which makes them not more efficient than conventional compression cooling systems. A main reason for this is the use of non-efficient controls with constant set points that do not allow a chiller power modulation at partial-load and therefore lead to unnecessary high power consumption of the parasitics. The aims of this paper are to present a method to control efficiently solar thermally driven chillers, to demonstrate experimentally its applicability and to quantify the benefits. It has been shown that the cooling capacity of a diffusion absorption chiller can be modulated very effectively by adjusting both the temperature and the flow rate of the cooling water. With the developed approach and the use of optimization algorithms, both the temperature and the flow rate can be controlled simultaneously in a way that the cooling load is matched and the electricity consumption is minimized. Depending on the weather and operating conditions, electricity savings between 20% and 60% can be achieved compared to other tested control approaches. The highest savings are obtained when the chiller is operated at partial load. The presented method is not restricted to solar cooling systems and can also be applied to other conventional heating ventilation and air conditioning (HVAC) systems. Full article
(This article belongs to the Special Issue Solar Cooling and Heating)
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Open AccessArticle Novel Auto-Reclosing Blocking Method for Combined Overhead-Cable Lines in Power Networks
Energies 2016, 9(11), 964; doi:10.3390/en9110964
Received: 25 June 2016 / Revised: 18 October 2016 / Accepted: 15 November 2016 / Published: 17 November 2016
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Abstract
This paper presents a novel auto-reclosing blocking method for combined overhead-cable lines in power distribution networks that are solidly or impedance grounded, with distribution transformers in a delta connection in their high-voltage sides. The main contribution of this new technique is that it
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This paper presents a novel auto-reclosing blocking method for combined overhead-cable lines in power distribution networks that are solidly or impedance grounded, with distribution transformers in a delta connection in their high-voltage sides. The main contribution of this new technique is that it can detect whether a ground fault has been produced at the overhead line side or at the cable line side, thus improving the performance of the auto-reclosing functionality. This localization technique is based on the measurements and analysis of the argument differences between the load currents in the active conductors of the cable and the currents in the shields at the cable end where the transformers in delta connection are installed, including a wavelet analysis. This technique has been verified through computer simulations and experimental laboratory tests. Full article
(This article belongs to the Special Issue Control and Communication in Distributed Generation Systems)
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Open AccessArticle The Effect of Biogas Production on Farmland Rental Prices: Empirical Evidences from Northern Italy
Energies 2016, 9(11), 965; doi:10.3390/en9110965
Received: 8 June 2016 / Revised: 23 October 2016 / Accepted: 25 October 2016 / Published: 18 November 2016
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Abstract
In the last decade, increased environmental awareness has prompted the adoption of incentives for exploiting renewable energy sources. Among these, biogas production has received a certain attention in developed countries. Nonetheless, the subsidies provided have posed the problem of an activity (the production
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In the last decade, increased environmental awareness has prompted the adoption of incentives for exploiting renewable energy sources. Among these, biogas production has received a certain attention in developed countries. Nonetheless, the subsidies provided have posed the problem of an activity (the production of bioenergy) that engages in direct competition with food and feed production for limited resources, like agricultural land. Even if this competition may be softened by allocating marginal land and/or using dedicated non-agricultural crops, empirical evidence shows that biogas plants have been developed in highly-productive agricultural areas, using increasing amounts of maize silage as feedstock. Thus, studies aimed at measuring the effect of biogas production on agricultural activities are needed in order to avoid this socially undesirable outcome. The paper presents an econometric estimation of the impact of biogas plants on farmland rental values of a Northern Italian rural area. Results show that biogas has a non-linear effect on rental prices, suggesting that incentive schemes specifically accounting for plants’ dimensions and technologies would improve the social sustainability of the bioenergy sector and its coexistence with agricultural activity. Full article
(This article belongs to the Special Issue Economics of Bioenergy 2016)
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Open AccessArticle Modeling of a Pouch Lithium Ion Battery Using a Distributed Parameter Equivalent Circuit for Internal Non-Uniformity Analysis
Energies 2016, 9(11), 865; doi:10.3390/en9110865
Received: 18 August 2016 / Revised: 9 October 2016 / Accepted: 10 October 2016 / Published: 25 October 2016
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Abstract
A battery model that has the capability of analyzing the internal non-uniformity of local state variables, including the state of charge (SOC), temperature and current density, is proposed in this paper. The model is built using a set of distributed parameter equivalent circuits.
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A battery model that has the capability of analyzing the internal non-uniformity of local state variables, including the state of charge (SOC), temperature and current density, is proposed in this paper. The model is built using a set of distributed parameter equivalent circuits. In order to validate the accuracy of the model, a customized battery with embedded T-type thermocouple sensors inside the battery is tested. The simulated temperature conforms well with the measured temperature at each test point, and the maximum difference is less than 1 °C. Then, the model is applied to analyze the evolution processes of local state variables’ distribution inside the battery during the discharge process. The simulation results demonstrate drastic distribution changes of the local state variables inside the battery during the discharge process. The internal non-uniformity is originally caused by the resistance of positive and negative foils, while also influenced by the change rate of open circuit voltage and the total resistance of the battery. Hence, the factors that affect the distribution of the local state variables are addressed. Full article
(This article belongs to the Special Issue Advanced Energy Storage Technologies and Their Applications (AESA))
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Open AccessArticle Study on the Static Load Capacity and Synthetic Vector Direct Torque Control of Brushless Doubly Fed Machines
Energies 2016, 9(11), 966; doi:10.3390/en9110966
Received: 27 June 2016 / Revised: 7 November 2016 / Accepted: 8 November 2016 / Published: 18 November 2016
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Abstract
Compared to the doubly fed machine, the brushless doubly fed machine (BDFM) has high reliability and low maintenance requirements. First, by taking the negative conjugation of the control motor variables in rotor reference frame, a state-space model of BDFM is derived. It is
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Compared to the doubly fed machine, the brushless doubly fed machine (BDFM) has high reliability and low maintenance requirements. First, by taking the negative conjugation of the control motor variables in rotor reference frame, a state-space model of BDFM is derived. It is then transformed into synchronous reference frame, called synchronous reference frame state-space model (SSSM). In this way, all the variables of the SSSM are DC under the static state. Second, on the basis of the analysis of static equations, the possible output torque limits are obtained. Third, the causes of losing control are analyzed by the flux and the torque derivatives. A new control strategy called synthetic vector direct torque control (SVDTC) is proposed to solve the losing control problems of the conventional direct torque control (DTC). Finally, the correctness of the results of this paper is verified by calculation examples and simulation results, the losing control problems can be solved, and the theoretical output capacity limits can be reached using SVDTC. Full article
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Open AccessArticle Energy Efficiency Strategies for Ecological Greenhouses: Experiences from Murcia (Spain)
Energies 2016, 9(11), 866; doi:10.3390/en9110866
Received: 2 August 2016 / Revised: 12 October 2016 / Accepted: 18 October 2016 / Published: 25 October 2016
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Abstract
There has been a continuous growth in ecological agriculture (EA) in recent years. It is recognized as a production system with rational energy use and low demand for fossil fuels. There are many studies relating to this subject, in contrast to the few
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There has been a continuous growth in ecological agriculture (EA) in recent years. It is recognized as a production system with rational energy use and low demand for fossil fuels. There are many studies relating to this subject, in contrast to the few studies regarding the use of energy and its impact on the environment in ecological greenhouses. This article analyzes the strategies adopted by a Transformational Agricultural Society (Sociedad Agraria de Transformación) in order to improve energy efficiency in ecological greenhouses, with regards to the use of fossil fuels. The methodology is based on the Working With People (WWP) Model, which involves social learning processes over 30 years in one of the largest regions of ecological crops in Spain. The results show that the measures taken to manage the greenhouses have achieved a decrease of over 80% in terms of fossil fuel consumption. The experience demonstrates that EA, as opposed to conventional agriculture (CA), is a system with great potential when it comes to reducing energy consumption and environmental improvements through various strategies. Full article
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Open AccessArticle A Detailed Assessment of the Wave Energy Resource at the Atlantic Marine Energy Test Site
Energies 2016, 9(11), 967; doi:10.3390/en9110967
Received: 18 July 2016 / Revised: 7 November 2016 / Accepted: 9 November 2016 / Published: 18 November 2016
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Abstract
Wave characteristic assessments of wave energy test sites provide a greater understanding of prevailing wave conditions and are therefore extremely important to both wave energy test site operators and clients as they can inform wave energy converter des