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Energies, Volume 11, Issue 4 (April 2018)

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Open AccessArticle Value of Residential Investment in Photovoltaics and Batteries in Networks: A Techno-Economic Analysis
Energies 2018, 11(4), 1022; https://doi.org/10.3390/en11041022
Received: 7 April 2018 / Revised: 19 April 2018 / Accepted: 20 April 2018 / Published: 24 April 2018
Cited by 1 | PDF Full-text (6811 KB) | HTML Full-text | XML Full-text
Abstract
Australia has one of the highest rates of residential photovoltaics penetration in the world. The willingness of households to privately invest in energy infrastructure, and the maturing of battery technology, provides significant scope for more efficient energy networks. The purpose of this paper
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Australia has one of the highest rates of residential photovoltaics penetration in the world. The willingness of households to privately invest in energy infrastructure, and the maturing of battery technology, provides significant scope for more efficient energy networks. The purpose of this paper is to evaluate the scope for promoting distributed generation and storage from within existing network spending. In this paper, a techno-economic analysis is conducted to evaluate the economic impacts on networks of private investment in energy infrastructure. A highly granular probabilistic model of households within a test area was developed and an economic evaluation of both household and network sectors performed. Results of this paper show that PV only installations carry the greatest private return and, at current battery prices, the economics of combined PV and battery systems is marginal. However, when network benefits arising from reducing residential evening peaks, improved reliability, and losses avoided are considered, this can more than compensate for private economic losses. The main conclusion of this paper is that there is significant scope for network benefits in retrofitting existing housing stock through the incentivization of a policy of a more rapid adoption of distributed generation and residential battery storage. Full article
(This article belongs to the collection Smart Grid)
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Open AccessReview A Review on Battery Charging and Discharging Control Strategies: Application to Renewable Energy Systems
Energies 2018, 11(4), 1021; https://doi.org/10.3390/en11041021
Received: 23 March 2018 / Revised: 17 April 2018 / Accepted: 18 April 2018 / Published: 23 April 2018
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Abstract
Energy storage has become a fundamental component in renewable energy systems, especially those including batteries. However, in charging and discharging processes, some of the parameters are not controlled by the battery’s user. That uncontrolled working leads to aging of the batteries and a
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Energy storage has become a fundamental component in renewable energy systems, especially those including batteries. However, in charging and discharging processes, some of the parameters are not controlled by the battery’s user. That uncontrolled working leads to aging of the batteries and a reduction of their life cycle. Therefore, it causes an early replacement. Development of control methods seeks battery protection and a longer life expectancy, thus the constant-current–constant-voltage method is mostly used. However, several studies show that charging time can be reduced by using fuzzy logic control or model predictive control. Another benefit is temperature control. This paper reviews the existing control methods used to control charging and discharging processes, focusing on their impacts on battery life. Classical and modern methods are studied together in order to find the best approach to real systems. Full article
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Open AccessArticle Investigation of Pumped Storage Hydropower Power-Off Transient Process Using 3D Numerical Simulation Based on SP-VOF Hybrid Model
Energies 2018, 11(4), 1020; https://doi.org/10.3390/en11041020
Received: 24 March 2018 / Revised: 11 April 2018 / Accepted: 17 April 2018 / Published: 23 April 2018
Cited by 1 | PDF Full-text (5116 KB) | HTML Full-text | XML Full-text
Abstract
The transient characteristic of the power-off process is investigated due to its close relation to hydraulic facilities’ safety in a pumped storage hydropower (PSH). In this paper, power-off transient characteristics of a PSH station in pump mode was studied using a three-dimensional (3D)
[...] Read more.
The transient characteristic of the power-off process is investigated due to its close relation to hydraulic facilities’ safety in a pumped storage hydropower (PSH). In this paper, power-off transient characteristics of a PSH station in pump mode was studied using a three-dimensional (3D) unsteady numerical method based on a single-phase and volume of fluid (SP-VOF) coupled model. The computational domain covered the entire flow system, including reservoirs, diversion tunnel, surge tank, pump-turbine unit, and tailrace tunnel. The fast changing flow fields and dynamic characteristic parameters, such as unit flow rate, runner rotate speed, pumping lift, and static pressure at measuring points were simulated, and agreed well with experimental results. During the power-off transient process, the PSH station underwent pump mode, braking mode, and turbine mode, with the dynamic characteristics and inner flow configurations changing significantly. Intense pressure fluctuation occurred in the region between the runner and guide vanes, and its frequency and amplitude were closely related to the runner’s rotation speed and pressure gradient, respectively. While the reversed flow rate of the PSH unit reached maximum, some parameters, such as static pressure, torque, and pumping lift would suddenly jump significantly, due to the water hammer effect. The moment these marked jumps occurred was commonly considered as the most dangerous moment during the power-off transient process, due to the blade passages being clogged by vortexes, and chaos pressure distribution on the blade surfaces. The results of this study confirm that 3D SP-VOF hybrid simulation is an effective method to reveal the hydraulic mechanism of the PSH transient process. Full article
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Open AccessArticle Single-Phase Shunt Active Power Filter Based on a 5-Level Converter Topology
Energies 2018, 11(4), 1019; https://doi.org/10.3390/en11041019
Received: 14 March 2018 / Revised: 12 April 2018 / Accepted: 16 April 2018 / Published: 22 April 2018
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Abstract
This paper presents a single-phase Shunt Active Power Filter (SAPF) with a multilevel converter based on an asymmetric full-bridge topology capable of producing five distinct voltage levels. The calculation of the SAPF compensation current is based on the Generalized Theory of Instantaneous Reactive
[...] Read more.
This paper presents a single-phase Shunt Active Power Filter (SAPF) with a multilevel converter based on an asymmetric full-bridge topology capable of producing five distinct voltage levels. The calculation of the SAPF compensation current is based on the Generalized Theory of Instantaneous Reactive Power (p-q theory) modified to work in single-phase installations, complemented by a Phase-Locked Loop algorithm and by a dedicated algorithm to regulate the voltages in the DC-link capacitors. The control of the SAPF uses a closed loop predictive current control, followed by a multilevel Sinusoidal Pulse-Width Modulation technique with two vertical distributed carriers, which were specially conceived to deal with the asymmetric nature of the converter legs. Along the paper, some simulation results are used to show the main characteristics of the 5-level converter and control algorithms, and the hardware topology and control algorithms are described in detail. In order to demonstrate the feasibility and performance of the proposed SAPF based on a 5-level converter, a laboratory prototype was developed and experimental results obtained under diverse conditions of operation, with linear and non-linear loads, are presented and discussed in this paper. Full article
(This article belongs to the Special Issue Power Electronics and Power Quality)
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Open AccessArticle Optimal Sizing and Location of Distributed Generators Based on PBIL and PSO Techniques
Energies 2018, 11(4), 1018; https://doi.org/10.3390/en11041018
Received: 27 February 2018 / Revised: 23 March 2018 / Accepted: 27 March 2018 / Published: 22 April 2018
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Abstract
The optimal location and sizing of distributed generation is a suitable option for improving the operation of electric systems. This paper proposes a parallel implementation of the Population-Based Incremental Learning (PBIL) algorithm to locate distributed generators (DGs), and the use of Particle Swarm
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The optimal location and sizing of distributed generation is a suitable option for improving the operation of electric systems. This paper proposes a parallel implementation of the Population-Based Incremental Learning (PBIL) algorithm to locate distributed generators (DGs), and the use of Particle Swarm Optimization (PSO) to define the size those devices. The resulting method is a master-slave hybrid approach based on both the parallel PBIL (PPBIL) algorithm and the PSO, which reduces the computation time in comparison with other techniques commonly used to address this problem. Moreover, the new hybrid method also reduces the active power losses and improves the nodal voltage profiles. In order to verify the performance of the new method, test systems with 33 and 69 buses are implemented in Matlab, using Matpower, for evaluating multiple cases. Finally, the proposed method is contrasted with the Loss Sensitivity Factor (LSF), a Genetic Algorithm (GA) and a Parallel Monte-Carlo algorithm. The results demonstrate that the proposed PPBIL-PSO method provides the best balance between processing time, voltage profiles and reduction of power losses. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle Theoretical and Experimental Investigation of the Voltage Ripple across Flying Capacitors in the Interleaved Buck Converter with Extended Duty Cycle
Energies 2018, 11(4), 1017; https://doi.org/10.3390/en11041017
Received: 25 March 2018 / Revised: 17 April 2018 / Accepted: 18 April 2018 / Published: 21 April 2018
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Abstract
The interleaved buck converter with an extended duty cycle is analyzed in terms of unexplored parasitic switching states that diminish the switch utilization and its safety due to high-magnitude charging and discharging currents. The analysis explains the origin of the states and their
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The interleaved buck converter with an extended duty cycle is analyzed in terms of unexplored parasitic switching states that diminish the switch utilization and its safety due to high-magnitude charging and discharging currents. The analysis explains the origin of the states and their effects and demonstrates their correlation with the existing voltage ripple on flying capacitors. The article further demonstrates that the voltage ripple can no longer be arbitrarily chosen as parasitic states emerge whenever the ripple exceeds an identified critical value being equal to the twofold voltage drop on the diode. A simple design criterion for flying capacitance is proposed. For a limited set of battery-powered DC–DC converters, a solution permitting the use of smaller capacitance by adding an extra switch is proposed. The derived findings are verified using experimental and simulation results. Full article
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Open AccessFeature PaperArticle Comparison of Different Approaches to Predict the Performance of Pumps As Turbines (PATs)
Energies 2018, 11(4), 1016; https://doi.org/10.3390/en11041016
Received: 18 March 2018 / Revised: 18 April 2018 / Accepted: 18 April 2018 / Published: 21 April 2018
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Abstract
This paper deals with the comparison of different methods which can be used for the prediction of the performance curves of pumps as turbines (PATs). The considered approaches are four, i.e., one physics-based simulation model (“white box” model), two “gray box” models, which
[...] Read more.
This paper deals with the comparison of different methods which can be used for the prediction of the performance curves of pumps as turbines (PATs). The considered approaches are four, i.e., one physics-based simulation model (“white box” model), two “gray box” models, which integrate theory on turbomachines with specific data correlations, and one “black box” model. More in detail, the modeling approaches are: (1) a physics-based simulation model developed by the same authors, which includes the equations for estimating head, power, and efficiency and uses loss coefficients and specific parameters; (2) a model developed by Derakhshan and Nourbakhsh, which first predicts the best efficiency point of a PAT and then reconstructs their complete characteristic curves by means of two ad hoc equations; (3) the prediction model developed by Singh and Nestmann, which predicts the complete turbine characteristics based on pump shape and size; (4) an Evolutionary Polynomial Regression model, which represents a data-driven hybrid scheme which can be used for identifying the explicit mathematical relationship between PAT and pump curves. All approaches are applied to literature data, relying on both pump and PAT performance curves of head, power, and efficiency over the entire range of operation. The experimental data were provided by Derakhshan and Nourbakhsh for four different turbomachines, working in both pump and PAT mode with specific speed values in the range 1.53–5.82. This paper provides a quantitative assessment of the predictions made by means of the considered approaches and also analyzes consistency from a physical point of view. Advantages and drawbacks of each method are also analyzed and discussed. Full article
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Open AccessArticle Advanced One-Dimensional Entrained-Flow Gasifier Model Considering Melting Phenomenon of Ash
Energies 2018, 11(4), 1015; https://doi.org/10.3390/en11041015
Received: 3 March 2018 / Revised: 17 April 2018 / Accepted: 17 April 2018 / Published: 21 April 2018
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Abstract
A one-dimensional model is developed to represent the ash-melting phenomenon, which was not considered in the previous one-dimensional (1-D) entrained-flow gasifier model. We include sensible heat of slag and the fusion heat of ash in the heat balance equation. To consider the melting
[...] Read more.
A one-dimensional model is developed to represent the ash-melting phenomenon, which was not considered in the previous one-dimensional (1-D) entrained-flow gasifier model. We include sensible heat of slag and the fusion heat of ash in the heat balance equation. To consider the melting of ash, we propose an algorithm that calculates the energy balance for three scenarios based on temperature. We also use the composition and the thermal properties of anorthite mineral to express ash. gPROMS for differential equations is used to solve this algorithm in a simulation; the results include coal conversion, gas composition, and temperature profile. Based on the Texaco pilot plant gasifier, we validate our model. Our results show good agreement with previous experimental data. We conclude that the sensible heat of slag and the fusion heat of ash must be included in the entrained flow gasifier model. Full article
(This article belongs to the Special Issue Biomass Chars: Elaboration, Characterization and Applications Ⅱ)
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Open AccessArticle Numerical Research of the Effect of Surface Biomimetic Features on the Efficiency of Tidal Turbine Blades
Energies 2018, 11(4), 1014; https://doi.org/10.3390/en11041014
Received: 12 March 2018 / Revised: 17 April 2018 / Accepted: 19 April 2018 / Published: 21 April 2018
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Abstract
Horizontal-axis axial flow tidal current turbine is regularly used to exploit the kinematic energy in tidal currents. However, the scaling up of tidal current turbine is very difficult. This is because strong tidal current only exists in the underwater region close to water
[...] Read more.
Horizontal-axis axial flow tidal current turbine is regularly used to exploit the kinematic energy in tidal currents. However, the scaling up of tidal current turbine is very difficult. This is because strong tidal current only exists in the underwater region close to water surface, which implies that scaling up by enlarging rotor size is not always applicable to tidal current turbines. Hence, scaling up by improving the energy capture efficiency of the tidal turbine blade becomes a plausible choice. For this reason, apart from the numerous researches based on conventional aerodynamic and hydrodynamic theories, improving efficiency by biomimetic method is attracting increasing interest in recent years. It has been proved that leading-edge tubercles have positive contribution to improving the efficiency of tidal turbine blade. However, leading-edge tubercles can be made on blade only in the manufacturing process, as the post-production of them is quite difficult. Thus, how to improve the energy capture efficiency of the existing blades becomes a challenging issue. To address this issue, numerical research of the effect of surface biomimetic features on blade efficiency is conducted in this paper. For the sake of simplicity, surface bumps are investigated in this preliminary research in order to obtain a basic understanding of the effect of surface biomimetic features. In the research, the influences of surface bumps on blade surface pressure and the ratio of lift to drag forces are investigated in different bump array scenarios and at different tidal current speeds and the angles of attack. The calculation results have shown that surface bumps do improve the ratio of lift to drag forces of the blade in spite of their array arrangement, the angle of attack and tidal current speed. This suggests that the energy capture efficiency of both new and existing blades can be further improved if appropriate biomimetic features are deployed on the blade surfaces. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
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Open AccessArticle Flexible, Heat-Resistant, and Flame-Retardant Glass Fiber Nonwoven/Glass Platelet Composite Separator for Lithium-Ion Batteries
Energies 2018, 11(4), 999; https://doi.org/10.3390/en11040999
Received: 26 March 2018 / Revised: 11 April 2018 / Accepted: 13 April 2018 / Published: 20 April 2018
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Abstract
A new type of high-temperature stable and self-supporting composite separator for lithium-ion batteries was developed consisting of custom-made ultrathin micrometer-sized glass platelets embedded in a glass fiber nonwoven together with a water-based sodium alginate binder. The physical and electrochemical properties were investigated and
[...] Read more.
A new type of high-temperature stable and self-supporting composite separator for lithium-ion batteries was developed consisting of custom-made ultrathin micrometer-sized glass platelets embedded in a glass fiber nonwoven together with a water-based sodium alginate binder. The physical and electrochemical properties were investigated and compared to commercial polymer-based separators. Full-cell configuration cycling tests at different current rates were performed using graphite and lithium iron phosphate as electrode materials. The glass separator was high-temperature tested and showed a stability up to at least 600 °C without significant shrinking. Furthermore, it showed an exceptional wettability for non-aqueous electrolytes. The electrochemical performance was excellent compared to commercially available polymer-based separators. The results clearly show that glass platelets integrated into a glass fiber nonwoven performs remarkably well as a separator material in lithium-ion batteries and show high-temperature stability. Full article
(This article belongs to the Section Energy Storage and Application)
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Open AccessArticle Classification Method to Define Synchronization Capability Limits of Line-Start Permanent-Magnet Motor Using Mesh-Based Magnetic Equivalent Circuit Computation Results
Energies 2018, 11(4), 998; https://doi.org/10.3390/en11040998
Received: 21 March 2018 / Revised: 15 April 2018 / Accepted: 18 April 2018 / Published: 20 April 2018
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Abstract
Line start permanent magnet synchronous motors (LS-PMSM) are energy-efficient synchronous motors that can start asynchronously due to a squirrel cage in the rotor. The drawback, however, with this motor type is the chance of failure to synchronize after start-up. To identify the problem,
[...] Read more.
Line start permanent magnet synchronous motors (LS-PMSM) are energy-efficient synchronous motors that can start asynchronously due to a squirrel cage in the rotor. The drawback, however, with this motor type is the chance of failure to synchronize after start-up. To identify the problem, and the stable operation limits, the synchronization at various parameter combinations is investigated. For accurate knowledge of the operation limits to assure synchronization with the utility grid, an accurate classification of parameter combinations is needed. As for this, many simulations have to be executed, a rapid evaluation method is indispensable. To simulate the dynamic behavior in the time domain, several modeling methods exist. In this paper, a discussion is held with respect to different modeling methods. In order to include spatial factors and magnetic nonlinearities, on the one hand, and to restrict the computation time on the other hand, a magnetic equivalent circuit (MEC) modeling method is developed. In order to accelerate numerical convergence, a mesh-based analysis method is applied. The novelty in this paper is the implementation of support vector machine (SVM) to classify the results of simulations at various parameter combinations into successful or unsuccessful synchronization, in order to define the synchronization capability limits. It is explained how these techniques can benefit the simulation time and the evaluation process. The results of the MEC modeling correspond to those obtained with finite element analysis (FEA), despite the reduced computation time. In addition, simulation results obtained with MEC modeling are experimentally validated. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle Assessment of Collective Production of Biomethane from Livestock Waste for Urban Transportation Mobility in Brazil and the United States
Energies 2018, 11(4), 997; https://doi.org/10.3390/en11040997
Received: 25 January 2018 / Revised: 27 March 2018 / Accepted: 18 April 2018 / Published: 20 April 2018
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Abstract
Water, energy, and food are essential elements for human life, but face constant pressure resulting from economic development, climate change, and other global processes. Predictions of rapid economic growth, increasing population, and urbanization in the coming decades point to rapidly increasing demand for
[...] Read more.
Water, energy, and food are essential elements for human life, but face constant pressure resulting from economic development, climate change, and other global processes. Predictions of rapid economic growth, increasing population, and urbanization in the coming decades point to rapidly increasing demand for all three. In this context, improved management of the interactions among water, energy, and food requires an integrated “nexus” approach. This paper focuses on a specific nexus case: biogas generated from organic waste, a renewable source of energy created in livestock production, which can have water-quality impacts if waste enters water bodies. An innovative model is presented to make biogas and biomethane systems feasible, termed “biogas condominiums” (based on collective action given that small- and medium-scale farms on their own cannot afford the necessary investments). Based on the “farm to fuel” concept, animal waste and manure are converted into electrical and thermal energy, biofuel for transportation, and high-quality biofertilizer. This nexus approach provides multiple economic, environmental, and social benefits in both rural and urban areas, including reduction of ground and surface water pollution, decrease of fossil fuels dependence, and mitigation of greenhouse gases emissions, among others. The research finds that biogas condominiums create benefits for the whole biogas supply chain, which includes farmers, agroindustry, input providers, and local communities. The study estimated that biomethane potential in Brazil could substitute the country’s entire diesel and gasoline imports as well as 44% of the total diesel demand. In the United States, biomethane potential can meet 16% of diesel demand and significantly diversify the energy matrix. Full article
(This article belongs to the Special Issue The Nexus of Renewable Energy, Water, and Food Systems)
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Open AccessArticle Installation, Commissioning and Tests of Four Fast Switching Units of up to 20 kA for the JT-60SA Nuclear Fusion Experiment
Energies 2018, 11(4), 996; https://doi.org/10.3390/en11040996
Received: 13 February 2018 / Revised: 17 April 2018 / Accepted: 18 April 2018 / Published: 20 April 2018
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Abstract
The nuclear fusion project JT-60SA is presently under construction in Naka (Japan) as a joint collaboration between Europe and Japan, within the framework of the Broader Approach Agreement. According to such agreement, the various JT-60SA systems are supplied by European and Japanese institutions.
[...] Read more.
The nuclear fusion project JT-60SA is presently under construction in Naka (Japan) as a joint collaboration between Europe and Japan, within the framework of the Broader Approach Agreement. According to such agreement, the various JT-60SA systems are supplied by European and Japanese institutions. In particular, the Italian Agency ENEA was in charge for the procurement of the four Switching Network Units (SNUs) for the JT-60SA Central Solenoid (CS). The main SNU function is to interrupt a DC current up to 20 kA in a short time (less than 1 ms) in order to produce an overvoltage of up to 5 kV, crucial to generate and sustain the fusion plasma. The SNU design, manufacturing and factory test activities have been completed in 2016. After the delivery in Naka, the four SNUs have been installed and successfully commissioned in 2017. After an overview on the main technical characteristics of the SNUs and the key aspects of their design, this paper describes the activities performed on-site, highlighting the results obtained during the final acceptance tests and comparing them with the design simulation and the factory test results. Full article
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Open AccessArticle A Novel Intelligent Method for the State of Charge Estimation of Lithium-Ion Batteries Using a Discrete Wavelet Transform-Based Wavelet Neural Network
Energies 2018, 11(4), 995; https://doi.org/10.3390/en11040995
Received: 2 April 2018 / Revised: 13 April 2018 / Accepted: 16 April 2018 / Published: 20 April 2018
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Abstract
State of charge (SOC) estimation is becoming increasingly important, along with electric vehicle (EV) rapid development, while SOC is one of the most significant parameters for the battery management system, indicating remaining energy and ensuring the safety and reliability of EV. In this
[...] Read more.
State of charge (SOC) estimation is becoming increasingly important, along with electric vehicle (EV) rapid development, while SOC is one of the most significant parameters for the battery management system, indicating remaining energy and ensuring the safety and reliability of EV. In this paper, a hybrid wavelet neural network (WNN) model combining the discrete wavelet transform (DWT) method and adaptive WNN is proposed to estimate the SOC of lithium-ion batteries. The WNN model is trained by Levenberg-Marquardt (L-M) algorithm, whose inputs are processed by discrete wavelet decomposition and reconstitution. Compared with back-propagation neural network (BPNN), L-M based BPNN (LMBPNN), L-M based WNN (LMWNN), DWT with L-M based BPNN (DWTLMBPNN) and extend Kalman filter (EKF), the proposed intelligent SOC estimation method is validated and proved to be effective. Under the New European Driving Cycle (NEDC), the mean absolute error and maximum error can be reduced to 0.59% and 3.13%, respectively. The characteristics of high accuracy and strong robustness of the proposed method are verified by comparison study and robustness evaluation results (e.g., measurement noise test and untrained driving cycle test). Full article
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Open AccessArticle Study on Variation of Internal Heat Gain in Office Buildings by Chronology
Energies 2018, 11(4), 1013; https://doi.org/10.3390/en11041013
Received: 19 March 2018 / Revised: 11 April 2018 / Accepted: 17 April 2018 / Published: 20 April 2018
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Abstract
The additional process of load calculation during the retrofit of heating, ventilation, and air conditioning (HVAC) equipment has been generally omitted in Korea, in recent years. Instead, a simple replacement of HVAC equipment, based on existing HVAC capacities, has been used, which is
[...] Read more.
The additional process of load calculation during the retrofit of heating, ventilation, and air conditioning (HVAC) equipment has been generally omitted in Korea, in recent years. Instead, a simple replacement of HVAC equipment, based on existing HVAC capacities, has been used, which is limited when taking the variation of internal heat gain into consideration, due to changes in the consumption power due to light and office automation (OA) equipment in recent years. Thus, this study aimed to identify a change in internal heat gains over 30 years, from 1985 to 2015, study investigated actual measurement-based academic papers and catalogs about OA equipment, lighting, and the number of occupants per unit area. The heat load produced from OA equipment has increased by approximately 49.6% in 2015 compared to that of 1980, and the heat load from lighting equipment has decreased by 47% compared to that of fluorescent-based lighting, and the heat load from human bodies was approximately 10 W/m2 on average, which showed a minimal change over the past 30 years. The internal heat gain calculated for 30,000 m2 of total floor area has increased constantly for the last 30 years. Note that the internal heat gains were designed excessively, as the values used in literature was approximately 17% to 50% smaller than the value used normally in the case of pre-2000 designs, and the values used after 2000 were approximately 35% to 50% smaller than the design standard value. Full article
(This article belongs to the Section Sustainable Energy)
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