Next Issue
Previous Issue

E-Mail Alert

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

Journal Browser

Journal Browser

Table of Contents

Energies, Volume 10, Issue 1 (January 2017)

  • Issues are regarded as officially published after their release is announced to the table of contents alert mailing list.
  • You may sign up for e-mail alerts to receive table of contents of newly released issues.
  • PDF is the official format for papers published in both, html and pdf forms. To view the papers in pdf format, click on the "PDF Full-text" link, and use the free Adobe Readerexternal link to open them.
Cover Story An easy-to-parametrize micro gas turbine (MGT) model which is applicable in the concept phase of [...] Read more.
View options order results:
result details:
Displaying articles 1-146
Export citation of selected articles as:

Editorial

Jump to: Research, Review, Other

Open AccessEditorial Acknowledgement to Reviewers of Energies in 2016
Energies 2017, 10(1), 106; doi:10.3390/en10010106
Received: 17 January 2017 / Accepted: 17 January 2017 / Published: 17 January 2017
PDF Full-text (251 KB) | HTML Full-text | XML Full-text

Research

Jump to: Editorial, Review, Other

Open AccessArticle The Effect of Distributed Parameters on Conducted EMI from DC-Fed Motor Drive Systems in Electric Vehicles
Energies 2017, 10(1), 1; doi:10.3390/en10010001
Received: 18 August 2016 / Revised: 9 December 2016 / Accepted: 12 December 2016 / Published: 22 December 2016
PDF Full-text (6480 KB) | HTML Full-text | XML Full-text
Abstract
The large dv/dt and di/dt outputs of power devices in DC-fed motor drive systems in electric vehicles (EVs) always introduce conducted electromagnetic interference (EMI) emissions and may lead to motor drive system energy transmission losses. The effect of distributed parameters on conducted EMI
[...] Read more.
The large dv/dt and di/dt outputs of power devices in DC-fed motor drive systems in electric vehicles (EVs) always introduce conducted electromagnetic interference (EMI) emissions and may lead to motor drive system energy transmission losses. The effect of distributed parameters on conducted EMI from the DC-fed high voltage motor drive systems in EVs is studied. A complete test for conducted EMI from the direct current fed(DC-fed) alternating current (AC) motor drive system in an electric vehicle (EV) under load conditions is set up to measure the conducted EMI of high voltage DC cables and the EMI noise peaks due to resonances in a frequency range of 150 kHz–108 MHz. The distributed parameters of the motor can induce bearing currents under low frequency sine wave operation. However the impedance of the distributed parameters of the motor is very high at resonance frequencies of 500 kHz and 30 MHz, and the effect of the bearing current can be ignored, so the research mainly focuses on the distributed parameters in inverters and cables at 500 kHz and 30 MHz, not the effect of distributed parameters of the motor on resonances. The corresponding equivalent circuits for differential mode (DM) and common mode (CM) EMI at resonance frequencies of 500 kHz and 30 MHz are established to determine the EMI propagation paths and analyze the effect of distributed parameters on conducted EMI. The dominant distributed parameters of elements responsible for the appearing resonances at 500 kHz and 30 MHz are determined. The effect of the dominant distributed parameters on conducted EMI are presented and verified by simulation and experiment. The conduced voltage at frequencies from 150 kHz to 108 MHz can be mitigated to below the limit level-3 of CISPR25 by changing the dominant distributed parameters. Full article
(This article belongs to the Special Issue Advances in Electric Vehicles and Plug-in Hybrid Vehicles 2017)
Figures

Figure 1

Open AccessArticle Torque Distribution Characteristics of a Novel Double-Stator Permanent Magnet Generator Integrated with a Magnetic Gear
Energies 2017, 10(1), 2; doi:10.3390/en10010002
Received: 25 October 2016 / Revised: 12 December 2016 / Accepted: 12 December 2016 / Published: 22 December 2016
Cited by 1 | PDF Full-text (21249 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a novel double-stator permanent-magnet machine integrated with a triple rotor magnetic gear structure, which is proposed to address problems of mechanical geared generators for low-speed applications. Torque transmission is based on three rotors consisting of prime permanent-magnet (PM) poles in
[...] Read more.
This paper presents a novel double-stator permanent-magnet machine integrated with a triple rotor magnetic gear structure, which is proposed to address problems of mechanical geared generators for low-speed applications. Torque transmission is based on three rotors consisting of prime permanent-magnet (PM) poles in the middle rotor and field PM poles in the inner and outer rotors. The proposed machine combines the functions of magnetic gearing and electrical power generation. The operating principles of the magnetic gear and generator are discussed and the torque distribution characteristics of the integrated machine are analysed using the 2D finite-element method (2D FEM). Also the power, torque, and speed characteristics are reported. A prototype is fabricated and tested experimentally. The predicted and measured results validate the proposed machine design. Full article
Figures

Figure 1a

Open AccessArticle Deep Neural Network Based Demand Side Short Term Load Forecasting
Energies 2017, 10(1), 3; doi:10.3390/en10010003
Received: 15 July 2016 / Revised: 25 November 2016 / Accepted: 16 December 2016 / Published: 22 December 2016
Cited by 5 | PDF Full-text (2576 KB) | HTML Full-text | XML Full-text
Abstract
In the smart grid, one of the most important research areas is load forecasting; it spans from traditional time series analyses to recent machine learning approaches and mostly focuses on forecasting aggregated electricity consumption. However, the importance of demand side energy management, including
[...] Read more.
In the smart grid, one of the most important research areas is load forecasting; it spans from traditional time series analyses to recent machine learning approaches and mostly focuses on forecasting aggregated electricity consumption. However, the importance of demand side energy management, including individual load forecasting, is becoming critical. In this paper, we propose deep neural network (DNN)-based load forecasting models and apply them to a demand side empirical load database. DNNs are trained in two different ways: a pre-training restricted Boltzmann machine and using the rectified linear unit without pre-training. DNN forecasting models are trained by individual customer’s electricity consumption data and regional meteorological elements. To verify the performance of DNNs, forecasting results are compared with a shallow neural network (SNN), a double seasonal Holt–Winters (DSHW) model and the autoregressive integrated moving average (ARIMA). The mean absolute percentage error (MAPE) and relative root mean square error (RRMSE) are used for verification. Our results show that DNNs exhibit accurate and robust predictions compared to other forecasting models, e.g., MAPE and RRMSE are reduced by up to 17% and 22% compared to SNN and 9% and 29% compared to DSHW. Full article
(This article belongs to the Special Issue Energy Time Series Forecasting)
Figures

Figure 1

Open AccessArticle Modeling of a Photovoltaic-Powered Electric Vehicle Charging Station with Vehicle-to-Grid Implementation
Energies 2017, 10(1), 4; doi:10.3390/en10010004
Received: 18 July 2016 / Revised: 7 November 2016 / Accepted: 13 December 2016 / Published: 22 December 2016
Cited by 1 | PDF Full-text (414 KB) | HTML Full-text | XML Full-text
Abstract
This paper is aimed at modelling of a distinct smart charging station for electric vehicles (EVs) that is suitable for DC quick EV charging while ensuring minimum stress on the power grid. Operation of the charging station is managed in such a way
[...] Read more.
This paper is aimed at modelling of a distinct smart charging station for electric vehicles (EVs) that is suitable for DC quick EV charging while ensuring minimum stress on the power grid. Operation of the charging station is managed in such a way that it is either supplied by photovoltaic (PV) power or the power grid, and the vehicle-to-grid (V2G) is also implemented for improving the stability of the grid during peak load hours. The PV interfaced DC/DC converter and grid interfaced DC/AC bidirectional converter share a DC bus. A smooth transition of one operating mode to another demonstrates the effectiveness of the employed control strategy. Modelling and control of the different components are explained and are implemented in Simulink. Simulations illustrate the feasible behaviour of the charging station under all operating modes in terms of the four-way interaction among PV, EVs and the grid along with V2G operation. Additionally, a business model is discussed with comprehensive analysis of cost estimation for the deployment of charging facilities in a residential area. It has been recognized that EVs bring new opportunities in terms of providing regulation services and consumption flexibility by varying the recharging power at a certain time instant. The paper also discusses the potential financial incentives required to inspire EV owners for active participation in the demand response mechanism. Full article
Figures

Figure 1

Open AccessArticle Improved Battery Parameter Estimation Method Considering Operating Scenarios for HEV/EV Applications
Energies 2017, 10(1), 5; doi:10.3390/en10010005
Received: 3 October 2016 / Revised: 7 December 2016 / Accepted: 13 December 2016 / Published: 22 December 2016
Cited by 2 | PDF Full-text (7886 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents an improved battery parameter estimation method based on typical operating scenarios in hybrid electric vehicles and pure electric vehicles. Compared with the conventional estimation methods, the proposed method takes both the constant-current charging and the dynamic driving scenarios into account,
[...] Read more.
This paper presents an improved battery parameter estimation method based on typical operating scenarios in hybrid electric vehicles and pure electric vehicles. Compared with the conventional estimation methods, the proposed method takes both the constant-current charging and the dynamic driving scenarios into account, and two separate sets of model parameters are estimated through different parts of the pulse-rest test. The model parameters for the constant-charging scenario are estimated from the data in the pulse-charging periods, while the model parameters for the dynamic driving scenario are estimated from the data in the rest periods, and the length of the fitted dataset is determined by the spectrum analysis of the load current. In addition, the unsaturated phenomenon caused by the long-term resistor-capacitor (RC) network is analyzed, and the initial voltage expressions of the RC networks in the fitting functions are improved to ensure a higher model fidelity. Simulation and experiment results validated the feasibility of the developed estimation method. Full article
(This article belongs to the Special Issue Advanced Energy Storage Technologies and Their Applications (AESA))
Figures

Figure 1

Open AccessArticle Performance Study on a Single-Screw Expander for a Small-Scale Pressure Recovery System
Energies 2017, 10(1), 6; doi:10.3390/en10010006
Received: 30 September 2016 / Revised: 1 December 2016 / Accepted: 2 December 2016 / Published: 22 December 2016
PDF Full-text (4486 KB) | HTML Full-text | XML Full-text
Abstract
A single-screw expander with 195 mm diameter is developed to recover pressure energy in letdown stations. An experiment system is established using compressed air as a working fluid instead of natural gas. Experiments are conducted via measurements for important parameters, such as inlet
[...] Read more.
A single-screw expander with 195 mm diameter is developed to recover pressure energy in letdown stations. An experiment system is established using compressed air as a working fluid instead of natural gas. Experiments are conducted via measurements for important parameters, such as inlet and outlet temperature and pressure, volume flow rate and power output. The influence of inlet pressure and rotational speed on the performance are also analyzed. Results indicate that the single-screw expander achieved good output characteristics, in which 2800 rpm is considered the best working speed. The maximum volumetric efficiency, isentropic efficiency, overall efficiency, and the lowest air-consumption are 51.1 kW, 83.5%, 66.4%, 62.2%, and 44.1 kg/(kW·h), respectively. If a single-screw expander is adopted in a pressure energy recovery system applied in a certain domestic natural gas letdown station, the isentropic efficiency of the single-screw expander and overall efficiency of the system are found to be 66.4% and 62.2%, respectively. Then the system performances are predicted, in which the lowest methane consumption is 27.3 kg/(kW·h). The installed capacity is estimated as 204.7 kW, and the annual power generation is 43.3 MWh. In the next stage, a pressure energy recovery demonstration project that recycles natural gas will be established within China, with the single-screw expander serving as the power machine. Full article
(This article belongs to the Special Issue Electric Machines and Drives for Renewable Energy Harvesting)
Figures

Figure 1

Open AccessArticle Correlation Feature Selection and Mutual Information Theory Based Quantitative Research on Meteorological Impact Factors of Module Temperature for Solar Photovoltaic Systems
Energies 2017, 10(1), 7; doi:10.3390/en10010007
Received: 2 September 2016 / Revised: 10 December 2016 / Accepted: 15 December 2016 / Published: 22 December 2016
PDF Full-text (4311 KB) | HTML Full-text | XML Full-text
Abstract
The module temperature is the most important parameter influencing the output power of solar photovoltaic (PV) systems, aside from solar irradiance. In this paper, we focus on the interdisciplinary research that combines the correlation analysis, mutual information (MI) and heat transfer theory, which
[...] Read more.
The module temperature is the most important parameter influencing the output power of solar photovoltaic (PV) systems, aside from solar irradiance. In this paper, we focus on the interdisciplinary research that combines the correlation analysis, mutual information (MI) and heat transfer theory, which aims to figure out the correlative relations between different meteorological impact factors (MIFs) and PV module temperature from both quality and quantitative aspects. The identification and confirmation of primary MIFs of PV module temperature are investigated as the first step of this research from the perspective of physical meaning and mathematical analysis about electrical performance and thermal characteristic of PV modules based on PV effect and heat transfer theory. Furthermore, the quantitative description of the MIFs influence on PV module temperature is mathematically formulated as several indexes using correlation-based feature selection (CFS) and MI theory to explore the specific impact degrees under four different typical weather statuses named general weather classes (GWCs). Case studies for the proposed methods were conducted using actual measurement data of a 500 kW grid-connected solar PV plant in China. The results not only verified the knowledge about the main MIFs of PV module temperatures, more importantly, but also provide the specific ratio of quantitative impact degrees of these three MIFs respectively through CFS and MI based measures under four different GWCs. Full article
(This article belongs to the Special Issue Innovative Methods for Smart Grids Planning and Management)
Figures

Figure 1

Open AccessArticle An Economic and Policy Analysis of a District Heating System Using Corn Straw Densified Fuel: A Case Study in Nong’an County in Jilin Province, China
Energies 2017, 10(1), 8; doi:10.3390/en10010008
Received: 23 November 2016 / Revised: 14 December 2016 / Accepted: 16 December 2016 / Published: 23 December 2016
PDF Full-text (6268 KB) | HTML Full-text | XML Full-text
Abstract
The development of district heating systems of corn straw densified fuel (CSDF-DHS) is an important option to promote the use of bioenergy on a large scale for sustainable development, especially in China. At present, China’s biomass densified solid fuel (BSDF) development lags behind
[...] Read more.
The development of district heating systems of corn straw densified fuel (CSDF-DHS) is an important option to promote the use of bioenergy on a large scale for sustainable development, especially in China. At present, China’s biomass densified solid fuel (BSDF) development lags behind previously planned target, main barriers of which are economic and policy support problems. Accurate case studies are key to analyze these problems. This manuscript takes Nong’an County in Jilin Province of China as an example to establish a techno-economic model to evaluate the economic performance of a CSDF-DHS under two policy scenarios. It calculates the economic performance under a benchmark market scenario (BMS) and the current policy scenario (CPS) and analyzes the influence of various policy instruments, including subsidies, carbon trading, and preferential taxation. The results indicate that: (1) The CSDF-DHS option is not competitive under the BMS or CPS compared to the traditional energy system based mainly on coal and liquefied petroleum gas; (2) Comparatively, the economic performance of corn straw briquette fuel (CSBF) is better than that of corn straw pellet fuel (CSPF); and (3) further policy support can make CSDF-DHSs competitive in the market, especially with subsidies for concentrated heating services and CSDF, carbon trading, and economic compensation to reduce the profit margin of enterprises, which can make both CSPF-DHSs and CSBF-DHSs competitive. The research results could provide scientific basis for relevant policy making and project decision. Full article
(This article belongs to the Special Issue Biomass for Energy Country Specific Show Case Studies)
Figures

Figure 1

Open AccessArticle Hybrid Off-Grid SPV/WTG Power System for Remote Cellular Base Stations Towards Green and Sustainable Cellular Networks in South Korea
Energies 2017, 10(1), 9; doi:10.3390/en10010009
Received: 21 August 2016 / Revised: 25 October 2016 / Accepted: 16 December 2016 / Published: 23 December 2016
Cited by 3 | PDF Full-text (7939 KB) | HTML Full-text | XML Full-text
Abstract
This paper aims to address the sustainability of power resources and environmental conditions for telecommunication base stations (BSs) at off-grid sites. Accordingly, this study examined the feasibility of using a hybrid solar photovoltaic (SPV)/wind turbine generator (WTG) system to feed the remote Long
[...] Read more.
This paper aims to address the sustainability of power resources and environmental conditions for telecommunication base stations (BSs) at off-grid sites. Accordingly, this study examined the feasibility of using a hybrid solar photovoltaic (SPV)/wind turbine generator (WTG) system to feed the remote Long Term Evolution-macro base stations at off-grid sites of South Korea the energy necessary to minimise both the operational expenditure and greenhouse gas emissions. Three key aspects have been discussed: (i) optimal system architecture; (ii) energy yield analysis; and (iii) economic analysis. In addition, this study compares the feasibility of using a hybrid SPV/WTG system vs. a diesel generator. The simulation results show that by applying the proposed SPV/WTG system scheme to the cellular system, the total operational expenditure can be up to 48.52% more efficient and sustainability can be ensured with better planning by providing cleaner energy. Full article
(This article belongs to the Special Issue Hybrid Renewable Energy Systems in Remote Sites)
Figures

Figure 1

Open AccessArticle A Causal and Real-Time Capable Power Management Algorithm for Off-Highway Hybrid Propulsion Systems
Energies 2017, 10(1), 10; doi:10.3390/en10010010
Received: 28 September 2016 / Revised: 8 December 2016 / Accepted: 16 December 2016 / Published: 26 December 2016
PDF Full-text (3359 KB) | HTML Full-text | XML Full-text
Abstract
Hybrid propulsion systems allow for a reduction of fuel consumption and pollutant emissions of future off-highway applications. A challenging aspect of a hybridization is the larger number of system components that further increases both the complexity and the diversification of such systems. Hence,
[...] Read more.
Hybrid propulsion systems allow for a reduction of fuel consumption and pollutant emissions of future off-highway applications. A challenging aspect of a hybridization is the larger number of system components that further increases both the complexity and the diversification of such systems. Hence, beside a standardization on the hardware side for off-highway systems, a high flexibility and modularity of the control schemes is required to employ them in as many different applications as possible. In this paper, a causal optimization-based power management algorithm is introduced to control the power split between engine and electric machine in a hybrid powertrain. The algorithm optimizes the power split to achieve the maximum power supply efficiency and, thereby, considers the energy cost for maintaining the battery charge. Furthermore, the power management provides an optional function to control the battery state of charge in such a way that a target value is attained. In a simulation case study, the potential and the benefits of the proposed power management for the hybrid powertrain—aiming at a reduction of the fuel consumption of a DMU (diesel multiple unit train) operated on a representative track—will be shown. Full article
Figures

Figure 1

Open AccessArticle Generic Combined Heat and Power (CHP) Model for the Concept Phase of Energy Planning Process
Energies 2017, 10(1), 11; doi:10.3390/en10010011
Received: 7 November 2016 / Revised: 7 December 2016 / Accepted: 9 December 2016 / Published: 23 December 2016
Cited by 2 | PDF Full-text (904 KB) | HTML Full-text | XML Full-text
Abstract
Micro gas turbines (MGTs) are regarded as combined heat and power (CHP) units which offer high fuel utilization and low emissions. They are applied in decentralized energy generation. To facilitate the planning process of energy systems, namely in the context of the increasing
[...] Read more.
Micro gas turbines (MGTs) are regarded as combined heat and power (CHP) units which offer high fuel utilization and low emissions. They are applied in decentralized energy generation. To facilitate the planning process of energy systems, namely in the context of the increasing application of optimization techniques, there is a need for easy-to-parametrize component models with sufficient accuracy which allow a fast computation. In this paper, a model is proposed where the non-linear part load characteristics of the MGT are linearized by means of physical insight of the working principles of turbomachinery. Further, it is shown that the model can be parametrized by the data usually available in spec sheets. With this model a uniform description of MGTs from several manufacturers covering an electrical power range from 30 k W to 333 k W can be obtained. The MGT model was implemented by means of Modelica/Dymola. The resulting MGT system model, comprising further heat exchangers and hydraulic components, was validated using the experimental data of a 65 k W MGT from a trigeneration energy system. Full article
Figures

Figure 1

Open AccessArticle A New Dynamic Injection System of Urea-Water Solution for a Vehicular Select Catalyst Reduction System
Energies 2017, 10(1), 12; doi:10.3390/en10010012
Received: 28 September 2016 / Revised: 4 December 2016 / Accepted: 9 December 2016 / Published: 23 December 2016
PDF Full-text (2716 KB) | HTML Full-text | XML Full-text
Abstract
Since the Euro-ІІІ standard was adopted, the main methods to inhibit NOx production in diesel engines are exhaust gas recirculation (EGR) and select catalyst reduction (SCR). On these methods SCR offers great fuel economy, so it has received wide attention. However, there
[...] Read more.
Since the Euro-ІІІ standard was adopted, the main methods to inhibit NOx production in diesel engines are exhaust gas recirculation (EGR) and select catalyst reduction (SCR). On these methods SCR offers great fuel economy, so it has received wide attention. However, there also exists a trade-off law between NOx conversion efficiency and NH3 slip under dynamic conditions. To inhibit NH3 slip with high NOx conversion efficiency, a dynamic control method for a urea water solution (UWS) injection was investigated. The variation phenomena of SCR conversion efficiency with respect to the cross-sensitivity characteristics of the NOx sensor to NH3 have been thoroughly analyzed. The methodology of “uncertain conversion efficiency curve tangent analysis” has been applied to estimate the concentration of the slipped NH3. The correction factor “φ” of UWS injection is obtained by a comparative calculation of the NOx conversion ability and subsequent NH3 slip. It also includes methods of flow compensation and flow reduction. The proposed control method has been authenticated under dynamic conditions. In low frequency dynamic experiments, this control method has accurately justified the NH3 slip process and inhibits the NH3 emission to a lower level thereby improving the conversion efficiency to a value closer to the target value. The results of European transient cycle (ETC) experiments indicate that NH3 emissions are reduced by 90.8% and the emission level of NOx is close to the Euro-Ѵ standard. Full article
(This article belongs to the Special Issue Automotive Engines Emissions and Control)
Figures

Figure 1

Open AccessArticle Risk Assessment Method of UHV AC/DC Power System under Serious Disasters
Energies 2017, 10(1), 13; doi:10.3390/en10010013
Received: 10 November 2016 / Revised: 14 December 2016 / Accepted: 17 December 2016 / Published: 23 December 2016
PDF Full-text (1989 KB) | HTML Full-text | XML Full-text
Abstract
Based on the theory of risk assessment, the risk assessment method for an ultra-high voltage (UHV) AC/DC hybrid power system under severe disaster is studied. Firstly, considering the whole process of cascading failure, a fast failure probability calculation method is proposed, and the
[...] Read more.
Based on the theory of risk assessment, the risk assessment method for an ultra-high voltage (UHV) AC/DC hybrid power system under severe disaster is studied. Firstly, considering the whole process of cascading failure, a fast failure probability calculation method is proposed, and the whole process risk assessment model is established considering the loss of both fault stage and recovery stage based on Monte Carlo method and BPA software. Secondly, the comprehensive evaluation index system is proposed from the aspects of power system structure, fault state and economic loss, and the quantitative assessment of system risk is carried out by an entropy weight model. Finally, the risk assessment of two UHV planning schemes are carried out and compared, which proves the effectiveness of the research work. Full article
(This article belongs to the Special Issue Advances in Power System Operations and Planning)
Figures

Figure 1

Open AccessArticle A Feedback Passivation Design for DC Microgrid and Its DC/DC Converters
Energies 2017, 10(1), 14; doi:10.3390/en10010014
Received: 22 October 2016 / Revised: 27 November 2016 / Accepted: 13 December 2016 / Published: 23 December 2016
PDF Full-text (2818 KB) | HTML Full-text | XML Full-text
Abstract
There are difficulties in analyzing the stability of microgrids since they are located on various network structures. However, considering that the network often consists of passive elements, the passivity theory is applied in this paper to solve the above-mentioned problem. It has been
[...] Read more.
There are difficulties in analyzing the stability of microgrids since they are located on various network structures. However, considering that the network often consists of passive elements, the passivity theory is applied in this paper to solve the above-mentioned problem. It has been formerly shown that when the network is weakly strictly positive real (WSPR), the DC microgrid is stable if all interfaces between the microgrid and converters are made to be passive, which is called interface passivity. Then, the feedback passivation method is proposed for the controller design of various DC–DC converters to achieve the interface passivity. The interface passivity is different from the passivity of closed-loop systems on which the passivity based control (PBC) concentrates. The feedback passivation design is detailed for typical buck converters and boost converters in terms of conditions that the controller parameters should satisfy. The theoretical results are verified by a hardware-in-loop real-time labotray (RTLab) simulation of a DC microgrid with four generators. Full article
(This article belongs to the collection Smart Grid)
Figures

Figure 1

Open AccessArticle Thermo-Economic Comparison and Parametric Optimizations among Two Compressed Air Energy Storage System Based on Kalina Cycle and ORC
Energies 2017, 10(1), 15; doi:10.3390/en10010015
Received: 25 September 2016 / Revised: 12 December 2016 / Accepted: 14 December 2016 / Published: 23 December 2016
PDF Full-text (4714 KB) | HTML Full-text | XML Full-text
Abstract
The compressed air energy storage (CAES) system, considered as one method for peaking shaving and load-levelling of the electricity system, has excellent characteristics of energy storage and utilization. However, due to the waste heat existing in compressed air during the charge stage and
[...] Read more.
The compressed air energy storage (CAES) system, considered as one method for peaking shaving and load-levelling of the electricity system, has excellent characteristics of energy storage and utilization. However, due to the waste heat existing in compressed air during the charge stage and exhaust gas during the discharge stage, the efficient operation of the conventional CAES system has been greatly restricted. The Kalina cycle (KC) and organic Rankine cycle (ORC) have been proven to be two worthwhile technologies to fulfill the different residual heat recovery for energy systems. To capture and reuse the waste heat from the CAES system, two systems (the CAES system combined with KC and ORC, respectively) are proposed in this paper. The sensitivity analysis shows the effect of the compression ratio and the temperature of the exhaust on the system performance: the KC-CAES system can achieve more efficient operation than the ORC-CAES system under the same temperature of exhaust gas; meanwhile, the larger compression ratio can lead to the higher efficiency for the KC-CAES system than that of ORC-CAES with the constant temperature of the exhaust gas. In addition, the evolutionary multi-objective algorithm is conducted between the thermodynamic and economic performances to find the optimal parameters of the two systems. The optimum results indicate that the solutions with an exergy efficiency of around 59.74% and 53.56% are promising for KC-CAES and ORC-CAES system practical designs, respectively. Full article
Figures

Figure 1

Open AccessArticle The Effect of Two Types of Biochars on the Efficacy, Emission, Degradation, and Adsorption of the Fumigant Methyl Isothiocyanate
Energies 2017, 10(1), 16; doi:10.3390/en10010016
Received: 7 September 2016 / Revised: 2 December 2016 / Accepted: 19 December 2016 / Published: 23 December 2016
PDF Full-text (1137 KB) | HTML Full-text | XML Full-text
Abstract
Biochar (BC) is increasingly applied in agriculture; however, due to its adsorption and degradation properties, biochar may also affect the efficacy of fumigant in amended soil. Our research is intended to study the effects of two types of biochars (BC-1 and BC-2) on
[...] Read more.
Biochar (BC) is increasingly applied in agriculture; however, due to its adsorption and degradation properties, biochar may also affect the efficacy of fumigant in amended soil. Our research is intended to study the effects of two types of biochars (BC-1 and BC-2) on the efficacy and emission of methyl isothiocyanate (MITC) in biochar amendment soil. Both types of biochars can significantly reduce MITC emission losses, but, at the same time, decrease the concentration of MITC in the soil. The efficacy of MITC for controlling soil-borne pests (Meloidogyne spp., Fusarium spp. Phytophthora spp., Abutilon theophrasti and Digitaria sanguinalis) was reduced when the biochar (BC-1 and BC-2) was applied at a rate of higher than 1% and 0.5% (on a weight basis) (on a weight basis), respectively. However, increased doses of dazomet (DZ) were able to offset decreases in the efficacy of MITC in soils amended with biochars. Biochars with strong adsorption capacity (such as BC-1) substantially reduced MITC degradation rate by 6.2 times, and increased by 4.1 times following amendment with biochar with high degradability (e.g., BC-2), compared to soil without biochar amendment. This is due to the adsorption and degradation of biochar that reduces MITC emission losses and pest control. Full article
(This article belongs to the Special Issue Biomass Chars: Elaboration, Characterization and Applications)
Figures

Open AccessArticle Operation Optimization of Steam Accumulators as Thermal Energy Storage and Buffer Units
Energies 2017, 10(1), 17; doi:10.3390/en10010017
Received: 7 November 2016 / Revised: 4 December 2016 / Accepted: 16 December 2016 / Published: 23 December 2016
Cited by 1 | PDF Full-text (7464 KB) | HTML Full-text | XML Full-text
Abstract
Although steam is widely used in industrial production, there is often an imbalance between steam supply and demand, which ultimately results in steam waste. To solve this problem, steam accumulators (SAs) can be used as thermal energy storage and buffer units. However, it
[...] Read more.
Although steam is widely used in industrial production, there is often an imbalance between steam supply and demand, which ultimately results in steam waste. To solve this problem, steam accumulators (SAs) can be used as thermal energy storage and buffer units. However, it is difficult to promote the application of SAs due to high investment costs, which directly depend on the usage volume. Thus, the operation of SAs should be optimized to reduce initial investment through volume minimization. In this work, steam sources (SSs) are classified into two types: controllable steam sources (CSSs) and uncontrollable steam sources (UCSSs). A basic oxygen furnace (BOF) was selected as an example of a UCSS to study the optimal operation of an SA with a single BOF and sets of parallel-operating BOFs. In another case, a new method whereby CSSs cooperate with SAs is reported, and the mathematical model of the minimum necessary thermal energy storage capacity (NTESC) is established. A solving program for this mathematical model is also designed. The results show that for UCSSs, applying an SA in two parallel-operating SSs requires less capacity than that required between a single SS and its consumer. For CSSs, the proposed minimum NTESC method can effectively find the optimal operation and the minimum volume of an SA. The optimized volume of an SA is smaller than that used in practice, which results in a better steam storage effect. Full article
Figures

Figure 1

Open AccessArticle Experimental Investigation on a Thermal Model for a Basin Solar Still with an External Reflector
Energies 2017, 10(1), 18; doi:10.3390/en10010018
Received: 13 October 2016 / Revised: 24 November 2016 / Accepted: 6 December 2016 / Published: 24 December 2016
PDF Full-text (2762 KB) | HTML Full-text | XML Full-text
Abstract
In this study, a thermal model for estimating the efficiency of a basin solar still with an external reflector was introduced using the energy balance equations of different parts of the solar still. Then, in order to verify the precision and accuracy of
[...] Read more.
In this study, a thermal model for estimating the efficiency of a basin solar still with an external reflector was introduced using the energy balance equations of different parts of the solar still. Then, in order to verify the precision and accuracy of this model, a basin solar still with an external reflector was constructed and some experiments were performed. The hourly temperature values for different places of the still and amount of distilled water were calculated using the thermal model and compared with experimental measurements. Comparisons show that the thermal model of the still is in good agreement with the experimental results. Therefore, it can be concluded that the introduced thermal model can be used reliably to estimate the amount of distilled water and efficiency of the basin solar still with an external reflector. Results also revealed that the efficiency of the solar still is low in the early hours, while it was enhanced 44% in the afternoon. Furthermore, it was concluded that the accumulated distilled water is 4600 mL/day and 4300 mL/day for theoretical and experimental examinations, respectively. Full article
Figures

Figure 1

Open AccessArticle A Simple Method for the Detection of Long-Chain Fatty Acids in an Anaerobic Digestate Using a Quartz Crystal Sensor
Energies 2017, 10(1), 19; doi:10.3390/en10010019
Received: 20 September 2016 / Revised: 14 December 2016 / Accepted: 15 December 2016 / Published: 24 December 2016
PDF Full-text (1175 KB) | HTML Full-text | XML Full-text
Abstract
In anaerobic digestion (AD), long-chain fatty acids (LCFAs) produced by hydrolysis of lipids, exhibit toxicity against microorganisms when their concentration exceeds several millimolar. An absorption detection system using a quartz crystal microbalance (QCM) was developed to monitor the LCFA concentration during an anaerobic
[...] Read more.
In anaerobic digestion (AD), long-chain fatty acids (LCFAs) produced by hydrolysis of lipids, exhibit toxicity against microorganisms when their concentration exceeds several millimolar. An absorption detection system using a quartz crystal microbalance (QCM) was developed to monitor the LCFA concentration during an anaerobic digester’s operation treating oily organic waste. The dissociation of the LCFAs considerably improved the sensor response and, moreover, enabled it to specifically detect LCFA from the mixture of LCFA and triglyceride. Under alkaline conditions, the frequency-shift rates of the QCM sensor linearly increased in accordance with palmitic acid concentration in the range of 0–100 mg/L. Frequency changes caused by anaerobic digestate samples were successfully measured after removing suspended solids and adjusting the pH to 10.7. Finally, the QCM measurements for digestate samples demonstrated that frequency-shift rates are highly correlated with LCFA concentrations, which confirmed that the newly developed QCM sensor is helpful for LCFA monitoring in terms of rapidness and usability. Full article
(This article belongs to the collection Bioenergy and Biofuel)
Figures

Figure 1

Open AccessArticle Analysis of the Primary Constraint Conditions of an Efficient Photovoltaic-Thermoelectric Hybrid System
Energies 2017, 10(1), 20; doi:10.3390/en10010020
Received: 27 October 2016 / Revised: 13 December 2016 / Accepted: 20 December 2016 / Published: 24 December 2016
Cited by 1 | PDF Full-text (5941 KB) | HTML Full-text | XML Full-text
Abstract
Electrical efficiency can be increased by combining photovoltaic (PV) and the thermoelectric (TE) systems. However, a simple and cursory combination is unsuitable because the negative impact of temperature on PV may be greater than its positive impact on TE. This study analyzed the
[...] Read more.
Electrical efficiency can be increased by combining photovoltaic (PV) and the thermoelectric (TE) systems. However, a simple and cursory combination is unsuitable because the negative impact of temperature on PV may be greater than its positive impact on TE. This study analyzed the primary constraint conditions based on the hybrid system model consisting of a PV and a TE generator (TEG), which includes TE material with temperature-dependent properties. The influences of the geometric size, solar irradiation and cold side temperature on the hybrid system performance is discussed based on the simulation. Furthermore, the effective range of parameters is demonstrated using the image area method, and the change trend of the area with different parameters illustrates the constraint conditions of an efficient PV-TE hybrid system. These results provide a benchmark for efficient PV-TEG design. Full article
Figures

Figure 1

Open AccessArticle Development of a Numerical Weather Analysis Tool for Assessing the Precooling Potential at Any Location
Energies 2017, 10(1), 21; doi:10.3390/en10010021
Received: 12 August 2016 / Revised: 11 November 2016 / Accepted: 17 December 2016 / Published: 24 December 2016
PDF Full-text (2557 KB) | HTML Full-text | XML Full-text
Abstract
Precooling a building overnight during the summer is a low cost practice that may provide significant help in decreasing energy demand and shaving peak loads in buildings. The effectiveness of precooling depends on the weather patterns at the location, however research in this
[...] Read more.
Precooling a building overnight during the summer is a low cost practice that may provide significant help in decreasing energy demand and shaving peak loads in buildings. The effectiveness of precooling depends on the weather patterns at the location, however research in this field is predominantly focused in the building thermal response alone. This paper proposes an analytical tool for assessing the precooling potential through simulations from real data in a numerical weather prediction platform. Three dimensionless ratios are developed based on the meteorological analysis and the concept of degree hours that provide an understanding of the precooling potential, utilization and theoretical value. Simulations were carried out for five sites within the Sydney (Australia) metro area and it was found that they have different responses to precooling, depending on their proximity to the ocean, vegetation coverage, and urban density. These effects cannot be detected when typical meteorological year data or data from weather stations at a distance from the building were used. Results from simulations in other Australian capitals suggest that buildings in continental and temperate climates have the potential to cover substantial parts of the cooling loads with precooling, assuming appropriate infrastructure is in place. Full article
(This article belongs to the Special Issue Selected Papers from 2nd Energy Future Conference)
Figures

Figure 1

Open AccessArticle Understanding Inertial Response of Variable-Speed Wind Turbines by Defined Internal Potential Vector
Energies 2017, 10(1), 22; doi:10.3390/en10010022
Received: 29 September 2016 / Revised: 9 December 2016 / Accepted: 12 December 2016 / Published: 25 December 2016
PDF Full-text (3920 KB) | HTML Full-text | XML Full-text
Abstract
With the rapid development of wind power generation, the inertial response of wind turbines (WTs) has become a topic of wide concern recently, due to its influence on grid frequency dynamics and stability. This paper proposes and defines the inner potential to summarize
[...] Read more.
With the rapid development of wind power generation, the inertial response of wind turbines (WTs) has become a topic of wide concern recently, due to its influence on grid frequency dynamics and stability. This paper proposes and defines the inner potential to summarize and understand the inertia control methods and inertial response of type-3 and type-4 WTs, which is analogous to typical synchronous generators (SGs), to make it more easy to understand by system operators and engineers with a traditional power system background. The dynamics of the defined inner potential of the wind turbine without any inertia control is different from SGs, thus the electromechanical inertia is completely hidden. The rapid power control loop and synchronization control loop are the major reasons that the WT’s inertial response is disenabled. On the basis of the defined inner potential’s dynamic, the existing inertia control method for WTs are reviewed and summarized as three approaches, i.e., optimizing the power control or synchronization control or both. At last, the main challenges and issues of these inertia controls are attempted to explain and address. Full article
(This article belongs to the Special Issue Wind Turbine 2017)
Figures

Figure 1

Open AccessArticle A Transient Fault Recognition Method for an AC-DC Hybrid Transmission System Based on MMC Information Fusion
Energies 2017, 10(1), 23; doi:10.3390/en10010023
Received: 29 August 2016 / Revised: 2 December 2016 / Accepted: 19 December 2016 / Published: 26 December 2016
PDF Full-text (7433 KB) | HTML Full-text | XML Full-text
Abstract
At present, the research is still in the primary stage in the process of fault disturbance energy transfer in the multilevel modular converter based high voltage direct current (HVDC-MMC). An urgent problem is how to extract and analyze the fault features hidden in
[...] Read more.
At present, the research is still in the primary stage in the process of fault disturbance energy transfer in the multilevel modular converter based high voltage direct current (HVDC-MMC). An urgent problem is how to extract and analyze the fault features hidden in MMC electrical information in further studies on the HVDC system. Aiming at the above, this article analyzes the influence of AC transient disturbance on electrical signals of MMC. At the same time, it is found that the energy distribution of electrical signals in MMC is different for different arms in the same frequency bands after the discrete wavelet packet transformation (DWPT). Renyi wavelet packet energy entropy (RWPEE) and Renyi wavelet packet time entropy (RWPTE) are proposed and applied to AC transient fault feature extraction from electrical signals in MMC. Using the feature extraction results of Renyi wavelet packet entropy (RWPE), a novel recognition method is put forward to recognize AC transient faults using the information fusion technology. Theoretical analysis and experimental results show that the proposed method is available to recognize transient AC faults. Full article
(This article belongs to the Special Issue Electric Power Systems Research 2017)
Figures

Figure 1

Open AccessArticle Novel Frequency Swapping Technique for Conducted Electromagnetic Interference Suppression in Power Converter Applications
Energies 2017, 10(1), 24; doi:10.3390/en10010024
Received: 9 August 2016 / Revised: 30 November 2016 / Accepted: 19 December 2016 / Published: 27 December 2016
PDF Full-text (21772 KB) | HTML Full-text | XML Full-text
Abstract
Quasi-resonant flyback (QRF) converters have been widely applied as the main circuit topology in power converters because of their low cost and high efficiency. Conventional QRF converters tend to generate higher average conducted electromagnetic interference (EMI) in the low-frequency domain due to the
[...] Read more.
Quasi-resonant flyback (QRF) converters have been widely applied as the main circuit topology in power converters because of their low cost and high efficiency. Conventional QRF converters tend to generate higher average conducted electromagnetic interference (EMI) in the low-frequency domain due to the switching noise generated by power switches, resulting in the fact they can exceed the EMI standards of the European Standard 55022 Class-B emission requirements. The presented paper develops a novel frequency swapping control method that spreads spectral energy to reduce the amplitude of sub-harmonics, thereby lowering average conducted EMI in the low-frequency domain. The proposed method is implemented in a control chip, which requires no extra circuit components and adds zero cost. The proposed control method is verified using a 24 W QRF converter. Experimental results reveals that conducted EMI has been reduced by approximately 13.24 dBμV at 498 kHz compared with a control method without the novel frequency swapping technique. Thus, the proposed method can effectively improve the flyback system to easily meet the CISPR 22/EN55022 standards. Full article
(This article belongs to the Special Issue Power Electronics Optimal Design and Control)
Figures

Figure 1

Open AccessArticle Analysis of Micronized Charcoal for Use in a Liquid Fuel Slurry
Energies 2017, 10(1), 25; doi:10.3390/en10010025
Received: 21 September 2016 / Revised: 16 December 2016 / Accepted: 19 December 2016 / Published: 27 December 2016
PDF Full-text (2550 KB) | HTML Full-text | XML Full-text
Abstract
Yellow poplar (Liriodendron tulipifera) was chosen as the woody biomass for the production of charcoal for use in a liquid fuel slurry. Charcoal produced from this biomass resulted in a highly porous structure similar to the parent material. Micronized particles were
[...] Read more.
Yellow poplar (Liriodendron tulipifera) was chosen as the woody biomass for the production of charcoal for use in a liquid fuel slurry. Charcoal produced from this biomass resulted in a highly porous structure similar to the parent material. Micronized particles were produced from this charcoal using a multi-step milling process and verified using a scanning electron microscope and laser diffraction system. Charcoal particles greater than 50 µm exhibited long needle shapes much like the parent biomass while particles less than 50 µm were produced with aspect ratios closer to unity. Laser diffraction measurements indicated D10, D50, and D90 values of 4.446 µm, 15.83 µm, and 39.69 µm, respectively. Moisture content, ash content, absolute density, and energy content values were also measured for the charcoal particles produced. Calculated volumetric energy density values for the charcoal particles exceeded the No. 2 diesel fuel that would be displaced in a liquid fuel slurry. Full article
(This article belongs to the Special Issue Biomass Chars: Elaboration, Characterization and Applications)
Figures

Figure 1

Open AccessArticle Experimental and Numerical Study of the Radiant Induction-Unit and the Induction Radiant Air-Conditioning System
Energies 2017, 10(1), 26; doi:10.3390/en10010026
Received: 4 November 2016 / Revised: 18 December 2016 / Accepted: 19 December 2016 / Published: 27 December 2016
PDF Full-text (1370 KB) | HTML Full-text | XML Full-text
Abstract
In this paper we proposed the novel air-conditioning system which combined induction ventilation and radiant air-conditioning. The indoor terminal device is the radiant induction-unit (RIDU). The RIDU is the induction unit combined with the pore radiant panel on which the copper pipes with
[...] Read more.
In this paper we proposed the novel air-conditioning system which combined induction ventilation and radiant air-conditioning. The indoor terminal device is the radiant induction-unit (RIDU). The RIDU is the induction unit combined with the pore radiant panel on which the copper pipes with rigid aluminum diffusion fins are installed. The two-stage evaporator chiller with the non-azeotropic mixture refrigerant is utilized in the system to reduce the initial investment in equipment. With the performance test and the steady state heat transfer model based on the theory of radiative heat transfer, the relationship between the induction ratio of the RIDU and the characteristic of the air supply was studied. Based on this, it is verified that the RIDU has a lower dew-point temperature and better anti-condensation performance than a traditional plate-type radiant panel. The characteristics of the radiation and convection heat transfer of the RIDU were studied. The total heat exchange of the RIDU can be 16.5% greater than that of the traditional plate-type radiant terminal. Full article
Figures

Figure 1

Open AccessArticle Balanced Current Control Strategy for Current Source Rectifier Stage of Indirect Matrix Converter under Unbalanced Grid Voltage Conditions
Energies 2017, 10(1), 27; doi:10.3390/en10010027
Received: 1 September 2016 / Revised: 8 December 2016 / Accepted: 20 December 2016 / Published: 27 December 2016
PDF Full-text (14611 KB) | HTML Full-text | XML Full-text
Abstract
This paper proposes a balanced current control strategy for the current source rectifier (CSR) stage of an indirect matrix converter (IMC) under unbalanced grid voltage conditions. If the three-phase grid connected to the voltage source inverter (VSI) of the IMC has unbalanced voltage
[...] Read more.
This paper proposes a balanced current control strategy for the current source rectifier (CSR) stage of an indirect matrix converter (IMC) under unbalanced grid voltage conditions. If the three-phase grid connected to the voltage source inverter (VSI) of the IMC has unbalanced voltage conditions, it affects the currents of the CSR stage and VSI stage, and the currents are distorted. Above all, the distorted currents of the CSR stage cause instability in the overall system, which can affect the life span of the system. Therefore, in this paper, a control strategy for balanced currents in the CSR stage is proposed. To achieve balanced currents in the CSR stage, the VSI stage should receive DC power without ripple components from the CSR stage. This is implemented by controlling the currents in the VSI stage. Therefore, the proposed control strategy decouples the positive and negative phase-sequence components existing in the unbalanced voltages and currents of the VSI stage. Using the proposed control strategy under unbalanced grid voltage conditions, the stability and life span of the overall system can be improved. The effectiveness of the proposed control strategy is verified by simulation and experimental results. Full article
(This article belongs to the Special Issue Microgrids 2016)
Figures

Figure 1

Open AccessArticle Multi-Agent System Fault Protection with Topology Identification in Microgrids
Energies 2017, 10(1), 28; doi:10.3390/en10010028
Received: 11 October 2016 / Revised: 15 December 2016 / Accepted: 20 December 2016 / Published: 27 December 2016
PDF Full-text (43598 KB) | HTML Full-text | XML Full-text
Abstract
Data acquisition and supervisory control are usually performed using client-server architecture and centralized control in conventional power systems. However, the message transmission and fault clearing are too slow for large-scale complex power systems. Microgrid systems have various types of distributed energy resources (DERs)
[...] Read more.
Data acquisition and supervisory control are usually performed using client-server architecture and centralized control in conventional power systems. However, the message transmission and fault clearing are too slow for large-scale complex power systems. Microgrid systems have various types of distributed energy resources (DERs) which are quite different in characteristics and capacities, thus, the client-server architecture and centralized control are inadequate to control and operate in microgrids. Based on MATLAB/Simulink (ver.R2012a) simulation software and Java Agent Development Framework (JADE) (JADE 4.1.1-revision 6532), this paper proposes a novel fault protection technology that used multi-agent system (MAS) to perform fault detection, fault isolation and service restoration in microgrids. A new topology identification method using the YBus Matrix Algorithm is presented to successfully recognize the network configurations. The identification technology can respond to microgrid variations. Furthermore, the interactive communications among intelligent electronic devices (IEDs), circuit breakers (CBs), and agents are clarified during fault occurrence. The simulation results show that the proposed MAS-based microgrids can promptly isolate faults and protect the system against faults in real time. Full article
(This article belongs to the Special Issue Smart Microgrids: Developing the Intelligent Power Grid of Tomorrow)
Figures

Figure 1

Open AccessArticle Bioenergy from Low-Intensity Agricultural Systems: An Energy Efficiency Analysis
Energies 2017, 10(1), 29; doi:10.3390/en10010029
Received: 28 October 2016 / Revised: 12 December 2016 / Accepted: 20 December 2016 / Published: 28 December 2016
Cited by 3 | PDF Full-text (5824 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
In light of possible future restrictions on the use of fossil fuel, due to climate change obligations and continuous depletion of global fossil fuel reserves, the search for alternative renewable energy sources is expected to be an issue of great concern for policy
[...] Read more.
In light of possible future restrictions on the use of fossil fuel, due to climate change obligations and continuous depletion of global fossil fuel reserves, the search for alternative renewable energy sources is expected to be an issue of great concern for policy stakeholders. This study assessed the feasibility of bioenergy production under relatively low-intensity conservative, eco-agricultural settings (as opposed to those produced under high-intensity, fossil fuel based industrialized agriculture). Estimates of the net energy gain (NEG) and the energy return on energy invested (EROEI) obtained from a life cycle inventory of the energy inputs and outputs involved reveal that the energy efficiency of bioenergy produced in low-intensity eco-agricultural systems could be as much as much as 448.5–488.3 GJ·ha−1 of NEG and an EROEI of 5.4–5.9 for maize ethanol production systems, and as much as 155.0–283.9 GJ·ha−1 of NEG and an EROEI of 14.7–22.4 for maize biogas production systems. This is substantially higher than for industrialized agriculture with a NEG of 2.8–52.5 GJ·ha−1 and an EROEI of 1.2–1.7 for maize ethanol production systems, as well as a NEG of 59.3–188.7 GJ·ha−1 and an EROEI of 2.2–10.2 for maize biogas production systems. Bioenergy produced in low-intensity eco-agricultural systems could therefore be an important source of energy with immense net benefits for local and regional end-users, provided a more efficient use of the co-products is ensured. Full article
Figures

Figure 1

Open AccessArticle Real-Time Velocity Optimization to Minimize Energy Use in Passenger Vehicles
Energies 2017, 10(1), 30; doi:10.3390/en10010030
Received: 11 November 2016 / Revised: 11 December 2016 / Accepted: 15 December 2016 / Published: 27 December 2016
PDF Full-text (9688 KB) | HTML Full-text | XML Full-text
Abstract
Energy use in internal combustion engine passenger vehicles contributes directly to CO2 emissions and fuel consumption, as well as producing a number of air pollutants. Optimizing the vehicle velocity by utilising upcoming road information is an opportunity to minimize vehicle energy use
[...] Read more.
Energy use in internal combustion engine passenger vehicles contributes directly to CO 2 emissions and fuel consumption, as well as producing a number of air pollutants. Optimizing the vehicle velocity by utilising upcoming road information is an opportunity to minimize vehicle energy use without requiring mechanical design changes. Dynamic programming is capable of such an optimization task and is shown in simulation to produce fuel savings, on average 12%, compared to real driving data; however, in this paper it is also applied in real time on a Raspberry Pi, a low cost miniature computer, in situ in a vehicle. A test drive was undertaken with driver feedback being provided by a dynamic programming algorithm, and the results are compared to a simulated intelligent cruise control system that can follow the algorithm results precisely. An 8% reduction in fuel with no loss in time is reported compared to the test driver. Full article
(This article belongs to the collection Electric and Hybrid Vehicles Collection)
Figures

Figure 1

Open AccessArticle Analysis on Filling Ratio and Shield Supporting Pressure for Overburden Movement Control in Coal Mining with Compacted Backfilling
Energies 2017, 10(1), 31; doi:10.3390/en10010031
Received: 13 November 2016 / Revised: 20 December 2016 / Accepted: 22 December 2016 / Published: 30 December 2016
Cited by 5 | PDF Full-text (9092 KB) | HTML Full-text | XML Full-text
Abstract
Since the weight of overburden is sustained by both the backfill body and the unmined solid coal in coal mining with compacted backfilling (CMCB) panels, the stress and deformation characteristics of the surrounding rocks in coal mining are radically changed. The overburden movement
[...] Read more.
Since the weight of overburden is sustained by both the backfill body and the unmined solid coal in coal mining with compacted backfilling (CMCB) panels, the stress and deformation characteristics of the surrounding rocks in coal mining are radically changed. The overburden movement control mechanism by coordinating with backfill body and shield in CMCB was studied systematically in this paper. Based on the analysis of deformational and structural characteristics of surrounding rock in CMCB panels, the methods of theoretical analysis, numerical simulation and engineering test are employed. The results show that the fracture of the main roof is mainly controlled by the filling ratio φ and is non-correlated to the shield supporting pressure p. However, p has a significant control effect on the deflection of roof within the shield canopy length, and adversely affects the filling ratio. With the increase of the filling ratio of the gob, the maximum sagging of the immediate and the main roofs, the peak front and the influence range of the abutment pressures are gradually reduced. Correspondingly, the stable period of internal pressure of backfill body in the gob is shortened. Engineering practice shows that the sagging of the gob roof, the distribution of the abutment pressure, the distribution of the internal pressure in the backfill body, and the ground surface sagging results obtained by the in-situ measurement are approximately corresponding to the theoretical analysis and numerical simulation results. Full article
Figures

Figure 1

Open AccessArticle Prognosis of the Remaining Useful Life of Bearings in a Wind Turbine Gearbox
Energies 2017, 10(1), 32; doi:10.3390/en10010032
Received: 13 September 2016 / Revised: 5 December 2016 / Accepted: 21 December 2016 / Published: 31 December 2016
Cited by 1 | PDF Full-text (4217 KB) | HTML Full-text | XML Full-text
Abstract
Predicting the remaining useful life (RUL) of critical subassemblies can provide an advanced maintenance strategy for wind turbines installed in remote regions. This paper proposes a novel prognostic approach to predict the RUL of bearings in a wind turbine gearbox. An artificial neural
[...] Read more.
Predicting the remaining useful life (RUL) of critical subassemblies can provide an advanced maintenance strategy for wind turbines installed in remote regions. This paper proposes a novel prognostic approach to predict the RUL of bearings in a wind turbine gearbox. An artificial neural network (NN) is used to train data-driven models and to predict short-term tendencies of feature series. By combining the predicted and training features, a polynomial curve reflecting the long-term degradation process of bearings is fitted. Through solving the intersection between the fitted curve and the pre-defined threshold, the RUL can be deduced. The presented approach is validated by an operating wind turbine with a faulty bearing in the gearbox. Full article
(This article belongs to the Special Issue Wind Turbine 2017)
Figures

Figure 1

Open AccessArticle Experimental Study on Specific Heat of Concrete at High Temperatures and Its Influence on Thermal Energy Storage
Energies 2017, 10(1), 33; doi:10.3390/en10010033
Received: 18 September 2016 / Revised: 21 December 2016 / Accepted: 23 December 2016 / Published: 29 December 2016
Cited by 1 | PDF Full-text (4157 KB) | HTML Full-text | XML Full-text
Abstract
Using concrete as a thermal energy storage (TES) material is a promising option for large-scale solar-thermal resource development and utilization. Specific heat is one of the most important characteristics for TES performance. In this paper, the half-open dynamic method based on the mixing
[...] Read more.
Using concrete as a thermal energy storage (TES) material is a promising option for large-scale solar-thermal resource development and utilization. Specific heat is one of the most important characteristics for TES performance. In this paper, the half-open dynamic method based on the mixing principle is proposed and applied to measure concrete-specific heat at temperatures up to 600 °C. Measurement of the specific heat of corundum ceramic (99% Al2O3) is first performed, and the test results illustrate the accuracy and efficiency of the proposed test method. Furthermore, concrete-specific heat tests are carried out at high temperatures. It found that the specific heat increases as the temperature rises, especially, linearly in the range of 300–600 °C, in which the concrete TES module is expected to be in operation. Finally, the effect of concrete-specific heat changes with temperature on its TES capacity is investigated, demonstrating that specific heat is of great significance for concrete TES design for concentrating solar power. Full article
Figures

Figure 1

Open AccessArticle Power Control of Low Frequency AC Transmission Systems Using Cycloconverters with Virtual Synchronous Generator Control
Energies 2017, 10(1), 34; doi:10.3390/en10010034
Received: 6 September 2016 / Revised: 28 November 2016 / Accepted: 19 December 2016 / Published: 28 December 2016
Cited by 2 | PDF Full-text (4560 KB) | HTML Full-text | XML Full-text
Abstract
This paper is focused on the application of a multi-terminal line-commutated converter-type low frequency AC transmission system (MTLF) using a cycloconverter by applying a new power control scheme for multi-terminal operation. With the virtual synchronous generator (VSG) control scheme, the transmitting power among
[...] Read more.
This paper is focused on the application of a multi-terminal line-commutated converter-type low frequency AC transmission system (MTLF) using a cycloconverter by applying a new power control scheme for multi-terminal operation. With the virtual synchronous generator (VSG) control scheme, the transmitting power among the multi-terminal system can be accomplished without a communication link for frequency synchronization in each terminal. The details of the proposed control scheme are explained in order to understand the advantages of this method. The configuration of a two-phase low frequency AC transmission system (LFAC) is adopted to examine with the proposed control scheme. Simulation results are provided to illustrate the proposed control scheme with respect to the LFAC system’s performance. Full article
Figures

Figure 1

Open AccessArticle Optimization of Reducing Sugar Production from Manihot glaziovii Starch Using Response Surface Methodology
Energies 2017, 10(1), 35; doi:10.3390/en10010035
Received: 14 June 2016 / Revised: 30 August 2016 / Accepted: 4 September 2016 / Published: 1 January 2017
Cited by 1 | PDF Full-text (2053 KB) | HTML Full-text | XML Full-text
Abstract
Bioethanol is known as a viable alternative fuel to solve both energy and environmental crises. This study used response surface methodology based on the Box-Behnken experimental design to obtain the optimum conditions for and quality of bioethanol production. Enzymatic hydrolysis optimization was performed
[...] Read more.
Bioethanol is known as a viable alternative fuel to solve both energy and environmental crises. This study used response surface methodology based on the Box-Behnken experimental design to obtain the optimum conditions for and quality of bioethanol production. Enzymatic hydrolysis optimization was performed with selected hydrolysis parameters, including substrate loading, stroke speed, α-amylase concentration and amyloglucosidase concentration. From the experiment, the resulting optimum conditions are 23.88% (w/v) substrate loading, 109.43 U/g α-amylase concentration, 65.44 U/mL amyloglucosidase concentration and 74.87 rpm stroke speed, which yielded 196.23 g/L reducing sugar. The fermentation process was also carried out, with a production value of 0.45 g ethanol/g reducing sugar, which is equivalent to 88.61% of ethanol yield after fermentation by using Saccharomyces cerevisiae (S. cerevisiae). The physical and chemical properties of the produced ethanol are within the specifications of the ASTM D4806 standard. The good quality of ethanol produced from this study indicates that Manihot glaziovii (M. glaziovii) has great potential as bioethanol feedstock. Full article
(This article belongs to the collection Bioenergy and Biofuel)
Figures

Figure 1

Open AccessArticle An Indicator-Based Approach for Analyzing the Resilience of Transitions for Energy Regions. Part I: Theoretical and Conceptual Considerations
Energies 2017, 10(1), 36; doi:10.3390/en10010036
Received: 14 November 2016 / Revised: 22 December 2016 / Accepted: 23 December 2016 / Published: 1 January 2017
PDF Full-text (421 KB) | HTML Full-text | XML Full-text
Abstract
The transition of our current energy system from a fossil-based system to a system based on renewables is likely to be one of the most complex and long-term societal transitions in history. The need for a fundamental system transformation raises the question of
[...] Read more.
The transition of our current energy system from a fossil-based system to a system based on renewables is likely to be one of the most complex and long-term societal transitions in history. The need for a fundamental system transformation raises the question of how to measure the continuing progress and the resilience of this process over time. This paper aims at developing the conceptualization and operationalization of resilience for energy systems in transition with regard to both social and technical aspects. Based on the resilience concept in social-ecological systems literature, we propose to conceptualize resilience for energy systems building on two core attributes of resilience, namely diversity and connectivity. We present an indicator set to operationalize these key attributes in social and technical systems using: (i) definitions and measurements for three fundamental diversity properties—variety, balance and disparity—and (ii) basic connectivity properties from the social network analysis literature—path length, centrality and modularity. Finally, we reflect on possibilities for an application of these indicators in the social and technical system’s spheres and discuss the added value of the approach for energy transition research. Full article
(This article belongs to the Special Issue Resilience of Energy Systems)
Figures

Figure 1

Open AccessArticle Multi-Time Scale Control of Demand Flexibility in Smart Distribution Networks
Energies 2017, 10(1), 37; doi:10.3390/en10010037
Received: 13 October 2016 / Revised: 16 December 2016 / Accepted: 19 December 2016 / Published: 1 January 2017
Cited by 3 | PDF Full-text (3286 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a multi-timescale control strategy to deploy electric vehicle (EV) demand flexibility for simultaneously providing power balancing, grid congestion management, and economic benefits to participating actors. First, an EV charging problem is investigated from consumer, aggregator, and distribution system operator’s perspectives.
[...] Read more.
This paper presents a multi-timescale control strategy to deploy electric vehicle (EV) demand flexibility for simultaneously providing power balancing, grid congestion management, and economic benefits to participating actors. First, an EV charging problem is investigated from consumer, aggregator, and distribution system operator’s perspectives. A hierarchical control architecture (HCA) comprising scheduling, coordinative, and adaptive layers is then designed to realize their coordinative goal. This is realized by integrating multi-time scale controls that work from a day-ahead scheduling up to real-time adaptive control. The performance of the developed method is investigated with high EV penetration in a typical residential distribution grid. The simulation results demonstrate that HCA efficiently utilizes demand flexibility stemming from EVs to solve grid unbalancing and congestions with simultaneous maximization of economic benefits to the participating actors. This is ensured by enabling EV participation in day-ahead, balancing, and regulation markets. For the given network configuration and pricing structure, HCA ensures the EV owners to get paid up to five times the cost they were paying without control. Full article
(This article belongs to the Special Issue Smart Microgrids: Developing the Intelligent Power Grid of Tomorrow)
Figures

Figure 1

Open AccessArticle Theoretical Analysis of Shrouded Horizontal Axis Wind Turbines
Energies 2017, 10(1), 38; doi:10.3390/en10010038
Received: 26 September 2016 / Revised: 13 December 2016 / Accepted: 20 December 2016 / Published: 1 January 2017
PDF Full-text (10155 KB) | HTML Full-text | XML Full-text
Abstract
Numerous analytical studies for power augmentation systems can be found in the literature with the goal to improve the performance of wind turbines by increasing the energy density of the air at the rotor. All methods to date are only concerned with the
[...] Read more.
Numerous analytical studies for power augmentation systems can be found in the literature with the goal to improve the performance of wind turbines by increasing the energy density of the air at the rotor. All methods to date are only concerned with the effects of a diffuser as the power augmentation, and this work extends the semi-empirical shrouded wind turbine model introduced first by Foreman to incorporate a converging-diverging nozzle into the system. The analysis is based on assumptions and approximations of the conservation laws to calculate optimal power coefficients and power extraction, as well as augmentation ratios. It is revealed that the power enhancement is proportional to the mass stream rise produced by the nozzle diffuser-augmented wind turbine (NDAWT). Such mass flow rise can only be accomplished through two essential principles: the increase in the area ratios and/or by reducing the negative back pressure at the exit. The thrust coefficient for optimal power production of a conventional bare wind turbine is known to be 8/9, whereas the theoretical analysis of the NDAWT predicts an ideal thrust coefficient either lower or higher than 8/9 depending on the back pressure coefficient at which the shrouded turbine operates. Computed performance expectations demonstrate a good agreement with numerical and experimental results, and it is demonstrated that much larger power coefficients than for traditional wind turbines are achievable. Lastly, the developed model is very well suited for the preliminary design of a shrouded wind turbine where typically many trade-off studies need to be conducted inexpensively. Full article
(This article belongs to the Special Issue Wind Turbine 2017)
Figures

Figure 1

Open AccessArticle Sensor Fault Diagnosis for Aero Engine Based on Online Sequential Extreme Learning Machine with Memory Principle
Energies 2017, 10(1), 39; doi:10.3390/en10010039
Received: 5 September 2016 / Revised: 18 December 2016 / Accepted: 20 December 2016 / Published: 1 January 2017
Cited by 2 | PDF Full-text (1502 KB) | HTML Full-text | XML Full-text
Abstract
The on-board sensor fault detection and isolation (FDI) system is essential to guarantee the reliability and safety of an aero engine. In this paper, a novel online sequential extreme learning machine with memory principle (MOS-ELM) is proposed for detecting, isolating, and reconstructing the
[...] Read more.
The on-board sensor fault detection and isolation (FDI) system is essential to guarantee the reliability and safety of an aero engine. In this paper, a novel online sequential extreme learning machine with memory principle (MOS-ELM) is proposed for detecting, isolating, and reconstructing the fault sensor signal of aero engines. In many practical online applications, the sequentially coming data chunk usually possesses a characteristic of timeliness, and the overdue training data may mislead the subsequent learning process. The proposed MOS-ELM can improve the training process by introducing the concept of memory principle into the online sequential extreme learning machine (OS-ELM) to tackle the timeliness of the data chunk. Simulations on some time series problems and some benchmark databases show that MOS-ELM performs better in generalization performance, stability, and prediction accuracy than OS-ELM. The experiment results of the MOS-ELM-based sensor fault diagnosis system also verify the excellent generalization performance of MOS-ELM and indicate the effectiveness and feasibility of the developed diagnosis system. Full article
Figures

Figure 1

Open AccessArticle Short-Term Forecasting of Electric Loads Using Nonlinear Autoregressive Artificial Neural Networks with Exogenous Vector Inputs
Energies 2017, 10(1), 40; doi:10.3390/en10010040
Received: 14 November 2016 / Revised: 6 December 2016 / Accepted: 22 December 2016 / Published: 1 January 2017
Cited by 2 | PDF Full-text (773 KB) | HTML Full-text | XML Full-text
Abstract
Short-term load forecasting is crucial for the operations planning of an electrical grid. Forecasting the next 24 h of electrical load in a grid allows operators to plan and optimize their resources. The purpose of this study is to develop a more accurate
[...] Read more.
Short-term load forecasting is crucial for the operations planning of an electrical grid. Forecasting the next 24 h of electrical load in a grid allows operators to plan and optimize their resources. The purpose of this study is to develop a more accurate short-term load forecasting method utilizing non-linear autoregressive artificial neural networks (ANN) with exogenous multi-variable input (NARX). The proposed implementation of the network is new: the neural network is trained in open-loop using actual load and weather data, and then, the network is placed in closed-loop to generate a forecast using the predicted load as the feedback input. Unlike the existing short-term load forecasting methods using ANNs, the proposed method uses its own output as the input in order to improve the accuracy, thus effectively implementing a feedback loop for the load, making it less dependent on external data. Using the proposed framework, mean absolute percent errors in the forecast in the order of 1% have been achieved, which is a 30% improvement on the average error using feedforward ANNs, ARMAX and state space methods, which can result in large savings by avoiding commissioning of unnecessary power plants. The New England electrical load data are used to train and validate the forecast prediction. Full article
Figures

Figure 1

Open AccessArticle A Novel Voltage Control Scheme for Low-Voltage DC Distribution Systems Using Multi-Agent Systems
Energies 2017, 10(1), 41; doi:10.3390/en10010041
Received: 10 August 2016 / Revised: 7 December 2016 / Accepted: 21 December 2016 / Published: 1 January 2017
PDF Full-text (5763 KB) | HTML Full-text | XML Full-text
Abstract
Low-voltage direct current (LVDC) distribution systems have been evolving into interesting ways of integrating distributed energy resources (DERs) and power electronics loads to local distribution networks. In LVDC distribution systems, voltage regulation is one of the most important issues, whereas AC systems have
[...] Read more.
Low-voltage direct current (LVDC) distribution systems have been evolving into interesting ways of integrating distributed energy resources (DERs) and power electronics loads to local distribution networks. In LVDC distribution systems, voltage regulation is one of the most important issues, whereas AC systems have concerns such as frequency, power factor, reactive power, harmonic distortion and so on. This paper focuses on a voltage control method for a LVDC distribution system based on the concept of multi-agent system (MAS), which can deploy intelligence and decision-making abilities to local areas. This paper proposes a distributed power flow analysis method using local information refined by local agents and communication between agents based on MAS. This paper also proposes a voltage control method by coordinating the main AC/DC converter and multiple DERs. By using the proposed method, we can effectively maintain the line voltages in a pre-defined normal range. The performance of the proposed voltage control method is evaluated by case studies and compared to conventional methods. Full article
Figures

Figure 1

Open AccessArticle Lobatto-Milstein Numerical Method in Application of Uncertainty Investment of Solar Power Projects
Energies 2017, 10(1), 43; doi:10.3390/en10010043
Received: 5 August 2016 / Revised: 6 December 2016 / Accepted: 21 December 2016 / Published: 3 January 2017
Cited by 2 | PDF Full-text (2217 KB) | HTML Full-text | XML Full-text
Abstract
Recently, there has been a growing interest in the production of electricity from renewable energy sources (RES). The RES investment is characterized by uncertainty, which is long-term, costly and depends on feed-in tariff and support schemes. In this paper, we address the real
[...] Read more.
Recently, there has been a growing interest in the production of electricity from renewable energy sources (RES). The RES investment is characterized by uncertainty, which is long-term, costly and depends on feed-in tariff and support schemes. In this paper, we address the real option valuation (ROV) of a solar power plant investment. The real option framework is investigated. This framework considers the renewable certificate price and, further, the cost of delay between establishing and operating the solar power plant. The optimal time of launching the project and assessing the value of the deferred option are discussed. The new three-stage numerical methods are constructed, the Lobatto3C-Milstein (L3CM) methods. The numerical methods are integrated with the concept of Black–Scholes option pricing theory and applied in option valuation for solar energy investment with uncertainty. The numerical results of the L3CM, finite difference and Monte Carlo methods are compared to show the efficiency of our methods. Our dataset refers to the Arab Republic of Egypt. Full article
Figures

Figure 1

Open AccessArticle Hybrid Forecasting Approach Based on GRNN Neural Network and SVR Machine for Electricity Demand Forecasting
Energies 2017, 10(1), 44; doi:10.3390/en10010044
Received: 8 November 2016 / Revised: 19 December 2016 / Accepted: 25 December 2016 / Published: 3 January 2017
Cited by 1 | PDF Full-text (27192 KB) | HTML Full-text | XML Full-text
Abstract
Accurate electric power demand forecasting plays a key role in electricity markets and power systems. The electric power demand is usually a non-linear problem due to various unknown reasons, which make it difficult to get accurate prediction by traditional methods. The purpose of
[...] Read more.
Accurate electric power demand forecasting plays a key role in electricity markets and power systems. The electric power demand is usually a non-linear problem due to various unknown reasons, which make it difficult to get accurate prediction by traditional methods. The purpose of this paper is to propose a novel hybrid forecasting method for managing and scheduling the electricity power. EEMD-SCGRNN-PSVR, the proposed new method, combines ensemble empirical mode decomposition (EEMD), seasonal adjustment (S), cross validation (C), general regression neural network (GRNN) and support vector regression machine optimized by the particle swarm optimization algorithm (PSVR). The main idea of EEMD-SCGRNN-PSVR is respectively to forecast waveform and trend component that hidden in demand series to substitute directly forecasting original electric demand. EEMD-SCGRNN-PSVR is used to predict the one week ahead half-hour’s electricity demand in two data sets (New South Wales (NSW) and Victorian State (VIC) in Australia). Experimental results show that the new hybrid model outperforms the other three models in terms of forecasting accuracy and model robustness. Full article
Figures

Open AccessArticle Optimal Load Shedding for Maximizing Satisfaction in an Islanded Microgrid
Energies 2017, 10(1), 45; doi:10.3390/en10010045
Received: 3 August 2016 / Revised: 29 December 2016 / Accepted: 29 December 2016 / Published: 3 January 2017
Cited by 1 | PDF Full-text (3627 KB) | HTML Full-text | XML Full-text
Abstract
A microgrid (MG) is a discrete energy system that can operate either in parallel with or independently from a main power grid. It is designed to enhance reliability, carbon emission reduction, diversification of energy sources, and cost reduction. When a power fault occurs
[...] Read more.
A microgrid (MG) is a discrete energy system that can operate either in parallel with or independently from a main power grid. It is designed to enhance reliability, carbon emission reduction, diversification of energy sources, and cost reduction. When a power fault occurs in a grid, an MG operates in an islanded manner from the grid and protects its power generations and loads from disturbance by means of intelligent load shedding. A load shedding is a control procedure that results in autonomous decrease of the power demands of loads in an MG. In this study, we propose a load shedding algorithm for the optimization problem to maximize the satisfaction of system components. The proposed algorithm preferentially assigns the power to the subdemand with a high preference to maximize the satisfaction of power consumers. In addition, the algorithm assigns the power to maximize the power sale and minimize the power surplus for satisfaction of power suppliers. To verify the performance of our algorithm, we implement a multi-agent system (MAS) on top of a conventional development framework and assess the algorithm’s adaptability, satisfaction metric, and running time. Full article
(This article belongs to the Special Issue Smart Microgrids: Developing the Intelligent Power Grid of Tomorrow)
Figures

Figure 1

Open AccessArticle Conjugate Image Theory Applied on Capacitive Wireless Power Transfer
Energies 2017, 10(1), 46; doi:10.3390/en10010046
Received: 14 October 2016 / Revised: 14 December 2016 / Accepted: 26 December 2016 / Published: 3 January 2017
Cited by 2 | PDF Full-text (4149 KB) | HTML Full-text | XML Full-text
Abstract
Wireless power transfer using a magnetic field through inductive coupling is steadily entering the market in a broad range of applications. However, for certain applications, capacitive wireless power transfer using electric coupling might be preferable. In order to obtain a maximum power transfer
[...] Read more.
Wireless power transfer using a magnetic field through inductive coupling is steadily entering the market in a broad range of applications. However, for certain applications, capacitive wireless power transfer using electric coupling might be preferable. In order to obtain a maximum power transfer efficiency, an optimal compensation network must be designed at the input and output ports of the capacitive wireless link. In this work, the conjugate image theory is applied to determine this optimal network as a function of the characteristics of the capacitive wireless link, as well for the series as for the parallel topology. The results are compared with the inductive power transfer system. Introduction of a new concept, the coupling function, enables the description of the compensation network of both an inductive and a capacitive system in two elegant equations, valid for the series and the parallel topology. This approach allows better understanding of the fundamentals of the wireless power transfer link, necessary for the design of an efficient system. Full article
(This article belongs to the Special Issue Wireless Power Transfer 2016)
Figures

Open AccessArticle Effects of a Dual-Loop Exhaust Gas Recirculation System and Variable Nozzle Turbine Control on the Operating Parameters of an Automotive Diesel Engine
Energies 2017, 10(1), 47; doi:10.3390/en10010047
Received: 23 September 2016 / Revised: 3 November 2016 / Accepted: 21 December 2016 / Published: 4 January 2017
PDF Full-text (3182 KB) | HTML Full-text | XML Full-text
Abstract
Reduction of NOX emissions and fuel consumption are the main topics in engine development, forcing the adoption of complex techniques and components, whose interactions have to be clearly understood for proper and reliable operations and management of the whole system. The investigation
[...] Read more.
Reduction of NOX emissions and fuel consumption are the main topics in engine development, forcing the adoption of complex techniques and components, whose interactions have to be clearly understood for proper and reliable operations and management of the whole system. The investigation presented in this paper aimed at the development of integrated control strategies of turbocharging, high pressure (HP) and low pressure (LP) exhaust gas recirculation (EGR) systems for better NOX emissions and fuel consumption, while analyzing their reciprocal influence and the resulting variations of engine quantities. The study was based on an extended experimental program in three part load engine operating conditions. In the paper a comparison of the behavior of the main engine sub-systems (intake and exhaust circuits, turbocharger turbine and compressor, HP and LP EGR loops) in a wide range of operating modes is presented and discussed, considering open and closed loop approaches for variable nozzle turbine (VNT) control, and showing how these affect engine performance and emissions. The potential of significant decrease in NOX emissions through the integration of HP and LP EGR was confirmed, while a proper VNT management allowed for improved fuel consumption level, if an open loop control scheme is followed. At higher engine speed and load, further actions have to be applied to compensate for observed soot emissions increase. Full article
Figures

Figure 1

Open AccessArticle The Influence of Acoustic Field Induced by HRT on Oscillation Behavior of a Single Droplet
Energies 2017, 10(1), 48; doi:10.3390/en10010048
Received: 21 October 2016 / Revised: 25 December 2016 / Accepted: 29 December 2016 / Published: 4 January 2017
Cited by 1 | PDF Full-text (6349 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents an experimental and theoretical study on the effects of an acoustic field induced by Hartmann Resonance Tube (HRT) on droplet deformation behavior. The characteristics of the acoustic field generated by HRT are investigated. Results show that the acoustic frequency decreases
[...] Read more.
This paper presents an experimental and theoretical study on the effects of an acoustic field induced by Hartmann Resonance Tube (HRT) on droplet deformation behavior. The characteristics of the acoustic field generated by HRT are investigated. Results show that the acoustic frequency decreases with the increase of the resonator length, the sound pressure level (SPL) increases with the increase of nozzle pressure ratio (NPR), and it is also noted that increasing resonator length can cause SPL to decrease, which has rarely been reported in published literature. Further theoretical analysis reveals that the resonance frequency of a droplet has several modes, and when the acoustic frequency equals the droplet’s frequency, heightened droplet responses are observed with the maximum amplitude of the shape oscillation. The experimental results for different resonator cavity lengths, nozzle pressure ratios and droplet diameters confirm the non-linear nature of this problem, and this conclusion is in good agreement with theoretical analysis. Measurements by high speed camera have shown that the introduction of an acoustic field can greatly enhance droplet oscillation, which means with the use of an ultrasonic atomizer based on HRT, the quality of atomization and combustion can be highly improved. Full article
(This article belongs to the Special Issue Combustion and Propulsion)
Figures

Figure 1

Open AccessArticle Wireless DC Motor Drives with Selectability and Controllability
Energies 2017, 10(1), 49; doi:10.3390/en10010049
Received: 7 November 2016 / Revised: 20 December 2016 / Accepted: 26 December 2016 / Published: 4 January 2017
Cited by 2 | PDF Full-text (12397 KB) | HTML Full-text | XML Full-text
Abstract
This paper proposes and implements the concept of wireless DC motor drives, which can achieve the abilities of selective driving and controllable speed. Due to different resonant frequencies of the multiple energy receivers of the associated DC motor drives, the transmitter can be
[...] Read more.
This paper proposes and implements the concept of wireless DC motor drives, which can achieve the abilities of selective driving and controllable speed. Due to different resonant frequencies of the multiple energy receivers of the associated DC motor drives, the transmitter can be purposely tuned to the specified resonant frequency which matches with the specified receiver, hence driving the specified motor selectively. In the meantime, the burst fire control is used to regulate the operating speed of the motor working at the resonant frequency, hence retaining the maximum power transmission efficiency. Both finite element analysis and experimentation are given to verify the validity of the proposed wireless DC motor drive system. For exemplification, three different resonant frequencies, namely 60 kHz, 100 kHz and 140 kHz, are selected to energize three DC motors. Under the burst fire control method, the speed of each motor can be regulated separately and the wireless power transfer (WPT) system can achieve the measured power transmission efficiency of about 60%. Full article
(This article belongs to the Special Issue Wireless Power Transfer 2016)
Figures

Figure 1

Open AccessArticle Thermal Impact Analysis of Circulating Current in High Power Modular Online Uninterruptible Power Supplies Application
Energies 2017, 10(1), 50; doi:10.3390/en10010050
Received: 17 October 2016 / Revised: 23 December 2016 / Accepted: 26 December 2016 / Published: 4 January 2017
PDF Full-text (4274 KB) | HTML Full-text | XML Full-text
Abstract
In modular uninterruptible power supplies (UPSs), several DC/AC modules are required to work in parallel. This structure allows the system to be more reliable and flexible. These DC/AC modules share the same DC bus and AC critical bus. Module differences, such as filter
[...] Read more.
In modular uninterruptible power supplies (UPSs), several DC/AC modules are required to work in parallel. This structure allows the system to be more reliable and flexible. These DC/AC modules share the same DC bus and AC critical bus. Module differences, such as filter inductor, filter capacitor, control parameters, and so on, will make it possible for the potential zero sequence current to flow among the modules. This undesired type of circulating current will bring extra losses to the power semiconductor devices in the system, which should be paid special attention in high power application scenarios. In this paper, plug’n’play modules and cycle control are discussed and validated through experimental results. Moreover, potential zero sequence circulating current impact on power semiconductor devices thermal performance is also analyzed in this paper. Full article
Figures

Figure 1

Open AccessArticle Energy Rebound as a Potential Threat to a Low-Carbon Future: Findings from a New Exergy-Based National-Level Rebound Approach
Energies 2017, 10(1), 51; doi:10.3390/en10010051
Received: 30 September 2016 / Revised: 13 December 2016 / Accepted: 19 December 2016 / Published: 7 January 2017
Cited by 3 | PDF Full-text (2846 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
150 years ago, Stanley Jevons introduced the concept of energy rebound: that anticipated energy efficiency savings may be “taken back” by behavioural responses. This is an important issue today because, if energy rebound is significant, this would hamper the effectiveness of energy efficiency
[...] Read more.
150 years ago, Stanley Jevons introduced the concept of energy rebound: that anticipated energy efficiency savings may be “taken back” by behavioural responses. This is an important issue today because, if energy rebound is significant, this would hamper the effectiveness of energy efficiency policies aimed at reducing energy use and associated carbon emissions. However, empirical studies which estimate national energy rebound are rare and, perhaps as a result, rebound is largely ignored in energy-economy models and associated policy. A significant difficulty lies in the components of energy rebound assessed in empirical studies: most examine direct and indirect rebound in the static economy, excluding potentially significant rebound of the longer term structural response of the national economy. In response, we develop a novel exergy-based approach to estimate national energy rebound for the UK and US (1980–2010) and China (1981–2010). Exergy—as “available energy”—allows a consistent, thermodynamic-based metric for national-level energy efficiency. We find large energy rebound in China, suggesting that improvements in China’s energy efficiency may be associated with increased energy consumption (“backfire”). Conversely, we find much lower (partial) energy rebound for the case of the UK and US. These findings support the hypothesis that producer-sided economies (such as China) may exhibit large energy rebound, reducing the effectiveness of energy efficiency, unless other policy measures (e.g., carbon taxes) are implemented. It also raises the prospect we need to deploy renewable energy sources faster than currently planned, if (due to rebound) energy efficiency policies cannot deliver the scale of energy reduction envisaged to meet climate targets. Full article
(This article belongs to the Special Issue Low Carbon Economy)
Figures

Figure 1

Open AccessArticle Low-Carbon Energy Development in Indonesia in Alignment with Intended Nationally Determined Contribution (INDC) by 2030
Energies 2017, 10(1), 52; doi:10.3390/en10010052
Received: 29 September 2016 / Revised: 26 December 2016 / Accepted: 27 December 2016 / Published: 5 January 2017
PDF Full-text (2049 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
This study analyzed the role of low-carbon energy technologies in reducing the greenhouse gas emissions of Indonesia’s energy sector by 2030. The aim of this study was to provide insights into the Indonesian government’s approach to developing a strategy and plan for mitigating
[...] Read more.
This study analyzed the role of low-carbon energy technologies in reducing the greenhouse gas emissions of Indonesia’s energy sector by 2030. The aim of this study was to provide insights into the Indonesian government’s approach to developing a strategy and plan for mitigating emissions and achieving Indonesia’s emission reduction targets by 2030, as pledged in the country’s Intended Nationally Determined Contribution. The Asia-Pacific Integrated Model/Computable General Equilibrium (AIM/CGE) model was used to quantify three scenarios that had the same socioeconomic assumptions: baseline, countermeasure (CM)1, and CM2, which had a higher emission reduction target than that of CM1. Results of the study showed that an Indonesian low-carbon energy system could be achieved with two pillars, namely, energy efficiency measures and deployment of less carbon-intensive energy systems (i.e., the use of renewable energy in the power and transport sectors, and the use of natural gas in the power sector and in transport). Emission reductions would also be satisfied through the electrification of end-user consumption where the electricity supply becomes decarbonized by deploying renewables for power generation. Under CM1, Indonesia could achieve a 15.5% emission reduction target (compared to the baseline scenario). This reduction could be achieved using efficiency measures that reduce final energy demand by 4%; This would require the deployment of geothermal power plants at a rate six times greater than the baseline scenario and four times the use of hydropower than that used in the baseline scenario. Greater carbon reductions (CM2; i.e., a 27% reduction) could be achieved with similar measures to CM1 but with more intensive penetration. Final energy demand would need to be cut by 13%, deployment of geothermal power plants would need to be seven times greater than at baseline, and hydropower use would need to be five times greater than the baseline case. Carbon prices under CM1 and CM2 were US$16 and US$63 (2005)/tCO2, respectively. The mitigation scenarios for 2030 both had a small positive effect on gross domestic product (GDP) compared to the baseline scenario (0.6% and 0.3% for CM1 and CM2, respectively). This is mainly due to the combination of two assumptions. The first is that there would be a great increase in coal-fired power in the baseline scenario. The other assumption is that there is low productivity in coal-related industries. Eventually, when factors such as capital and labor shift from coal-related industries to other low-carbon-emitting sectors in the CM cases are put in place, the total productivity of the economy would offset low-carbon investment. Full article
(This article belongs to the Special Issue Low Carbon Economy)
Figures

Figure 1

Open AccessArticle Multi-Objective Optimization of Thin-Film Silicon Solar Cells with Metallic and Dielectric Nanoparticles
Energies 2017, 10(1), 53; doi:10.3390/en10010053
Received: 20 September 2016 / Revised: 7 December 2016 / Accepted: 26 December 2016 / Published: 4 January 2017
PDF Full-text (2114 KB) | HTML Full-text | XML Full-text
Abstract
Thin-film solar cells enable a strong reduction of the amount of silicon needed to produce photovoltaic panels but their efficiency lowers. Placing metallic or dielectric nanoparticles over the silicon substrate increases the light trapping into the panel thanks to the plasmonic scattering from
[...] Read more.
Thin-film solar cells enable a strong reduction of the amount of silicon needed to produce photovoltaic panels but their efficiency lowers. Placing metallic or dielectric nanoparticles over the silicon substrate increases the light trapping into the panel thanks to the plasmonic scattering from nanoparticles at the surface of the cell. The goal of this paper is to optimize the geometry of a thin-film solar cell with silver and silica nanoparticles in order to improve its efficiency, taking into account the amount of silver. An efficient evolutionary algorithm is applied to perform the optimization with a reduced computing time. Full article
(This article belongs to the Special Issue Key Developments in Thin Film Solar Cells)
Figures

Figure 1

Open AccessArticle A Dynamic Control Strategy for Hybrid Electric Vehicles Based on Parameter Optimization for Multiple Driving Cycles and Driving Pattern Recognition
Energies 2017, 10(1), 54; doi:10.3390/en10010054
Received: 5 August 2016 / Revised: 24 December 2016 / Accepted: 26 December 2016 / Published: 5 January 2017
Cited by 1 | PDF Full-text (6642 KB) | HTML Full-text | XML Full-text
Abstract
The driving pattern has an important influence on the parameter optimization of the energy management strategy (EMS) for hybrid electric vehicles (HEVs). A new algorithm using simulated annealing particle swarm optimization (SA-PSO) is proposed for parameter optimization of both the power system and
[...] Read more.
The driving pattern has an important influence on the parameter optimization of the energy management strategy (EMS) for hybrid electric vehicles (HEVs). A new algorithm using simulated annealing particle swarm optimization (SA-PSO) is proposed for parameter optimization of both the power system and control strategy of HEVs based on multiple driving cycles in order to realize the minimum fuel consumption without impairing the dynamic performance. Furthermore, taking the unknown of the actual driving cycle into consideration, an optimization method of the dynamic EMS based on driving pattern recognition is proposed in this paper. The simulation verifications for the optimized EMS based on multiple driving cycles and driving pattern recognition are carried out using Matlab/Simulink platform. The results show that compared with the original EMS, the former strategy reduces the fuel consumption by 4.36% and the latter one reduces the fuel consumption by 11.68%. A road test on the prototype vehicle is conducted and the effectiveness of the proposed EMS is validated by the test data. Full article
(This article belongs to the Special Issue Advanced Energy Storage Technologies and Their Applications (AESA))
Figures

Figure 1

Open AccessArticle Study on the Tribological Characteristics of Australian Native First Generation and Second Generation Biodiesel Fuel
Energies 2017, 10(1), 55; doi:10.3390/en10010055
Received: 11 October 2016 / Revised: 21 December 2016 / Accepted: 22 December 2016 / Published: 5 January 2017
PDF Full-text (2741 KB) | HTML Full-text | XML Full-text
Abstract
Biodiesels are a renewable energy source, and they have the potential to be used as alternatives to diesel fuel. The aim of this study is to investigate the wear and friction characteristics of Australian native first generation and second generation biodiesels using a
[...] Read more.
Biodiesels are a renewable energy source, and they have the potential to be used as alternatives to diesel fuel. The aim of this study is to investigate the wear and friction characteristics of Australian native first generation and second generation biodiesels using a four-ball tribo tester. The biodiesel was produced through a two-step transesterification process and characterized according to the American Society for Testing and Materials (ASTM) standards. The tribological experiment was carried out at a constant 1800 rpm and different loads and temperatures. In addition, the surface morphology of the ball was tested by scanning electron microscope (SEM)/energy dispersive X-ray spectroscopy (EDX) analysis. The test results indicated that biodiesel fuels have a lower coefficient of frictions (COF) and lower wear scar diameter (WSD) up to 83.50% and 41.28%, respectively, compared to conventional diesel fuel. The worn surface area results showed that biodiesel fuel has a minimum percentage of C and O, except Fe, compared to diesel. In addition, the worn surface area for diesel was found (2.20%–27.92%) to be higher than biodiesel. The findings of this study indicated that both first and second generation biodiesel fuels have better tribological performance than diesel fuel, and between the biodiesel fuels, macadamia biodiesel showed better lubrication performance. Full article
(This article belongs to the collection Bioenergy and Biofuel)
Figures

Figure 1

Open AccessArticle Coordinated Control of Superconducting Fault Current Limiter and Superconducting Magnetic Energy Storage for Transient Performance Enhancement of Grid-Connected Photovoltaic Generation System
Energies 2017, 10(1), 56; doi:10.3390/en10010056
Received: 23 September 2016 / Revised: 13 December 2016 / Accepted: 26 December 2016 / Published: 5 January 2017
PDF Full-text (6638 KB) | HTML Full-text | XML Full-text
Abstract
In regard to the rapid development of renewable energy sources, more and more photovoltaic (PV) generation systems have been connected to main power networks, and it is critical to enhance their transient performance under short-circuit faults conditions. This paper proposes and studies the
[...] Read more.
In regard to the rapid development of renewable energy sources, more and more photovoltaic (PV) generation systems have been connected to main power networks, and it is critical to enhance their transient performance under short-circuit faults conditions. This paper proposes and studies the coordinated control of a flux-coupling-type superconducting fault current limiter (SFCL) and a superconducting magnetic energy storage (SMES), to improve the fault ride through (FRT) capability and smooth the power fluctuation of a grid-connected PV generation system. Theoretical analyses of the device structure, operating principle and control strategy are conducted, and a detailed simulation model of 100 kW class PV generation system is built in MATLAB/SIMULINK. During the simulations of the symmetrical and asymmetrical faults, the maximum power point tracking (MPPT) control is disabled, and four different cases including without auxiliary, with SFCL, with SMES, and with SFCL-SMES, are compared. From the demonstrated results, the combination of without MPPT and with SFCL-SMES can more efficiently improve the point of common coupling (PCC) voltage sag, inhibit the DC-link overvoltage and alleviate the power fluctuation. Finally, a preliminary parameter optimization method is suggested for the SFCL and the SMES, and it is helpful to promote their future application in the real PV projects. Full article
(This article belongs to the Special Issue Grid-Connected Photovoltaic Systems)
Figures

Figure 1

Open AccessArticle Energy Performance and Radial Force of a Mixed-Flow Pump with Symmetrical and Unsymmetrical Tip Clearances
Energies 2017, 10(1), 57; doi:10.3390/en10010057
Received: 26 October 2016 / Revised: 28 December 2016 / Accepted: 29 December 2016 / Published: 5 January 2017
Cited by 4 | PDF Full-text (8262 KB) | HTML Full-text | XML Full-text
Abstract
The energy performance and radial force of a mixed flow pump with symmetrical and unsymmetrical tip clearance are investigated in this paper. As the tip clearance increases, the pump head and efficiency both decrease. The center of the radial force on the principal
[...] Read more.
The energy performance and radial force of a mixed flow pump with symmetrical and unsymmetrical tip clearance are investigated in this paper. As the tip clearance increases, the pump head and efficiency both decrease. The center of the radial force on the principal axis is located at the coordinate origin when the tip clearance is symmetrical, and moves to the third quadrant when the tip clearance is unsymmetrical. Analysis results show that the total radial force on the principal axis is closely related to the fluctuation of mass flow rate in each single flow channel. Unsteady simulations show that the dominant frequencies of radial force on the hub and blade correspond to the blade number, vane number, or double blade number because of the rotor stator interaction. The radial force on the blade pressure side decreases with the tip clearance increase because of leakage flow. The unsymmetrical tip clearances in an impeller induce uneven leakage flow rate and then result in unsymmetrical work ability of each blade and flow pattern in each channel. Thus, the energy performance decreases and the total radial force increases for a mixed flow pump with unsymmetrical tip clearance. Full article
Figures

Figure 1

Open AccessArticle Design Parameters of Vortex Pumps: A Meta-Analysis of Experimental Studies
Energies 2017, 10(1), 58; doi:10.3390/en10010058
Received: 14 November 2016 / Revised: 27 December 2016 / Accepted: 29 December 2016 / Published: 5 January 2017
PDF Full-text (6592 KB) | HTML Full-text | XML Full-text
Abstract
Vortex pumps can impel solid-containing fluids and are therefore widely applied, from wastewater transport to the food industry. Despite constant efforts to improve vortex pumps, however, they have remained relatively inefficient compared to conventional centrifugal pumps. To find an optimized design of vortex
[...] Read more.
Vortex pumps can impel solid-containing fluids and are therefore widely applied, from wastewater transport to the food industry. Despite constant efforts to improve vortex pumps, however, they have remained relatively inefficient compared to conventional centrifugal pumps. To find an optimized design of vortex pumps, this paper provides a systematic analysis on experimental studies that investigated how variations in geometric parameters influence vortex pump characteristics, in particular the pump head, the pressure coefficient and the efficiency for best point operation. To this end, an extensive literature search was conducted, and eighteen articles with 53 primary investigations were identified and meta-integrated. This showed that it is not yet clarified how vortex pumps operate. Two different assumptions of the underlying operating principle of a vortex pump lead to diverging design principles. From the results of this meta-analysis, we deduce recommendations for a more efficient design of a vortex pump and emphasize further aspects on the underlying operating principle of a vortex pump. Full article
Figures

Figure 1

Open AccessArticle Development of an Nearly Zero Emission Building (nZEB) Life Cycle Cost Assessment Tool for Fast Decision Making in the Early Design Phase
Energies 2017, 10(1), 59; doi:10.3390/en10010059
Received: 11 October 2016 / Revised: 16 December 2016 / Accepted: 22 December 2016 / Published: 6 January 2017
Cited by 1 | PDF Full-text (3231 KB) | HTML Full-text | XML Full-text
Abstract
An economic feasibility optimization method for the life cycle cost (LCC) has been developed to apply energy saving techniques in the early design stages of a building. The method was developed using default data (e.g., operation schedules), energy consumption prediction equations and cost
[...] Read more.
An economic feasibility optimization method for the life cycle cost (LCC) has been developed to apply energy saving techniques in the early design stages of a building. The method was developed using default data (e.g., operation schedules), energy consumption prediction equations and cost prediction equations utilizing design variables considered in the early design phase. With certain equations developed, an LCC model was constructed using the computational program MATLAB, to create an automated optimization process. To verify the results from the newly developed assessment tool, a case study on an office building was performed to outline the results of the designer’s proposed model and the cost optimal model. Full article
(This article belongs to the Special Issue Zero-Carbon Buildings)
Figures

Figure 1

Open AccessArticle Battery Internal Temperature Estimation for LiFePO4 Battery Based on Impedance Phase Shift under Operating Conditions
Energies 2017, 10(1), 60; doi:10.3390/en10010060
Received: 17 November 2016 / Revised: 26 December 2016 / Accepted: 3 January 2017 / Published: 6 January 2017
Cited by 1 | PDF Full-text (5051 KB) | HTML Full-text | XML Full-text
Abstract
An impedance-based temperature estimation method is investigated considering the electrochemical non-equilibrium with short-term relaxation time for facilitating the vehicular application. Generally, sufficient relaxation time is required for battery electrochemical equilibrium before the impedance measurement. A detailed experiment is performed to investigate the regularity
[...] Read more.
An impedance-based temperature estimation method is investigated considering the electrochemical non-equilibrium with short-term relaxation time for facilitating the vehicular application. Generally, sufficient relaxation time is required for battery electrochemical equilibrium before the impedance measurement. A detailed experiment is performed to investigate the regularity of the battery impedance in short-term relaxation time after switch-off current excitation, which indicates that the impedance can be measured and also has systematical decrement with the relaxation time growth. Based on the discussion of impedance variation in electrochemical perspective, as well as the monotonic relationship between impedance phase shift and battery internal temperature in the electrochemical equilibrium state, an exponential equation that accounts for both measured phase shift and relaxation time is established to correct the measuring deviation caused by electrochemical non-equilibrium. Then, a multivariate linear equation coupled with ambient temperature is derived considering the temperature gradients between the active part and battery surface. Equations stated above are all identified with the embedded thermocouple experimentally. In conclusion, the temperature estimation method can be a valuable alternative for temperature monitoring during cell operating, and serve the functionality as an efficient implementation in battery thermal management system for electric vehicles (EVs) and hybrid electric vehicles (HEVs). Full article
(This article belongs to the Special Issue Advanced Energy Storage Technologies and Their Applications (AESA))
Figures

Figure 1

Open AccessArticle Ion Migration in the Process of Water Freezing under Alternating Electric Field and Its Impact on Insulator Flashover
Energies 2017, 10(1), 61; doi:10.3390/en10010061
Received: 2 September 2016 / Revised: 15 November 2016 / Accepted: 30 December 2016 / Published: 6 January 2017
PDF Full-text (14627 KB) | HTML Full-text | XML Full-text
Abstract
Ice flashover threatens the security and reliability of power transmission. However, the ice flashover mechanism of insulators remains poorly understood. This study analyses water droplet freezing and ion distribution in ice layer under alternating electric field. It also investigates ion migration during icing
[...] Read more.
Ice flashover threatens the security and reliability of power transmission. However, the ice flashover mechanism of insulators remains poorly understood. This study analyses water droplet freezing and ion distribution in ice layer under alternating electric field. It also investigates ion migration during icing process of insulator string under alternating electric field and its effects on insulator flashover. Results showed that the average freezing time of water droplets was related to electric field strength. The extent of ion migration during freezing decreased with increasing electric field strength. The maximal melting water conductivity of the ice layer and icicle of the insulator formed under energized condition was higher than the corresponding freezing water conductivity but lower than that under non-energized condition. Furthermore, the hanging location of each insulator significantly affected the melting water conductivity of the ice layer. The surface conductivity of the ice layer increased because of the conductive ion migration in freezing water during freezing, which was an important factor that decreased the flashover voltage of the ice-covered insulator. The existence of alternating electric field would impact the extent of ion migration. This study may serve as a reference for updating prediction flashover model of ice-covered insulators during the melting period. Full article
Figures

Figure 1

Open AccessArticle Investigation of Ethanol Production Potential from Lignocellulosic Material without Enzymatic Hydrolysis Using the Ultrasound Technique
Energies 2017, 10(1), 62; doi:10.3390/en10010062
Received: 25 November 2016 / Revised: 27 December 2016 / Accepted: 30 December 2016 / Published: 6 January 2017
Cited by 1 | PDF Full-text (3047 KB) | HTML Full-text | XML Full-text
Abstract
This research investigates ethanol production from waste lignocellulosic material (sugarcane bagasse). The bagasse was first pretreated using chemicals and ultrasound techniques. These pretreatment techniques were applied separately and combined. The pretreated bagasse was then fermented anaerobically for biofuel production without enzymatic hydrolysis. The
[...] Read more.
This research investigates ethanol production from waste lignocellulosic material (sugarcane bagasse). The bagasse was first pretreated using chemicals and ultrasound techniques. These pretreatment techniques were applied separately and combined. The pretreated bagasse was then fermented anaerobically for biofuel production without enzymatic hydrolysis. The results showed higher ethanol production than those reported in the literature. The maximum ethanol production of 820 mg/L was achieved with a combination of ultrasound (60 amplitude level, 127 W) and acid (3% H2SO4 concentration). The combination of two-step pretreatment such as an ultrasound (50 amplitude level, 109 W) with acid (3% H2SO4 concentration) and then an ultrasound with alkaline (23% NaOH concentration) generated 911 mg/L of ethanol. Full article
Figures

Figure 1

Open AccessArticle Non-Linear Behavioral Modeling for DC-DC Converters and Dynamic Analysis of Distributed Energy Systems
Energies 2017, 10(1), 63; doi:10.3390/en10010063
Received: 30 November 2016 / Revised: 28 December 2016 / Accepted: 29 December 2016 / Published: 6 January 2017
PDF Full-text (6393 KB) | HTML Full-text | XML Full-text
Abstract
In modern distributed energy systems (DES), focus is shifting from the conventional centralized approach towards distributed architectures. However, modeling and analysis of these systems is more complex, as it involves the interface of multiple energy sources with many different type of loads through
[...] Read more.
In modern distributed energy systems (DES), focus is shifting from the conventional centralized approach towards distributed architectures. However, modeling and analysis of these systems is more complex, as it involves the interface of multiple energy sources with many different type of loads through power electronics converters. The integration of power electronics converters allows distributed renewable energy sources to become part of modern electronics power distribution systems (EPDS). It will also facilitate the ongoing research towards DC-based DES which is mostly composed of commercial DC-DC converters whose internal structure and parameters are unknown. For the system level analysis, the behavioral modeling technique is the only choice. Since most power electronics converters are non-linear systems and linear models can’t model their dynamics to a desired level of accuracy, hence non-linear modeling is required for accurate modeling. The non-linear modeling approach presented here aims to develop behavioral models that can predict the response of the system over the entire operating range. In this work, either a lookup table or a polytopic structure-based modeling technique is used. The technique is further applied to cascade and parallel connected converters, being two DES scenarios. First the procedure is verified via application to switching models in a simulation and then validated for commercial converters via experiments. The results show that the developed behavioral models accurately predict both the transient and steady state response. Full article
Figures

Figure 1

Open AccessArticle Power Consumption Analysis of Electrical Installations at Healthcare Facility
Energies 2017, 10(1), 64; doi:10.3390/en10010064
Received: 22 November 2016 / Revised: 21 December 2016 / Accepted: 31 December 2016 / Published: 6 January 2017
Cited by 1 | PDF Full-text (6615 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a methodology for power consumption estimation considering harmonic and interharmonic content and then it is compared to the power consumption estimation commonly done by commercial equipment based on the fundamental frequency, and how they can underestimate the power consumption considering
[...] Read more.
This paper presents a methodology for power consumption estimation considering harmonic and interharmonic content and then it is compared to the power consumption estimation commonly done by commercial equipment based on the fundamental frequency, and how they can underestimate the power consumption considering power quality disturbances (PQD). For this purpose, data of electrical activity at the electrical distribution boards in a healthcare facility is acquired for a long time period with proprietary equipment. An analysis in the acquired current and voltage signals is done, in order to compare the power consumption centered in the fundamental frequency with the generalized definition of power consumption. The results obtained from the comparison in the power consumption estimation show differences between 4% and 10% of underestimated power consumption. Thus, it is demonstrated that the presence of harmonic and interharmonic content provokes a significant underestimation of power consumption using only the power consumption centered at the fundamental frequency. Full article
Figures

Open AccessArticle Thermal Performance for Wet Cooling Tower with Different Layout Patterns of Fillings under Typical Crosswind Conditions
Energies 2017, 10(1), 65; doi:10.3390/en10010065
Received: 2 December 2016 / Revised: 3 January 2017 / Accepted: 3 January 2017 / Published: 6 January 2017
PDF Full-text (1004 KB) | HTML Full-text | XML Full-text
Abstract
A thermal-state model experimental study was performed in lab to investigate the thermal performance of a wet cooling tower with different kinds of filling layout patterns under windless and 0.4 m/s crosswind conditions. In this paper, the contrast analysis was focused on comparing
[...] Read more.
A thermal-state model experimental study was performed in lab to investigate the thermal performance of a wet cooling tower with different kinds of filling layout patterns under windless and 0.4 m/s crosswind conditions. In this paper, the contrast analysis was focused on comparing a uniform layout pattern and one kind of optimal non-uniform layout pattern when the environmental crosswind speed is 0 m/s and 0.4 m/s. The experimental results proved that under windless conditions, the heat transfer coefficient and total heat rejection of circulating water for the optimal non-uniform layout pattern can enhance by approximately 40% and 28%, respectively, compared with the uniform layout pattern. It was also discovered that the optimal non-uniform pattern can dramatically relieve the influence of crosswind on the thermal performance of the tower when the crosswind speed is equal to 0.4 m/s. For the uniform layout pattern, the heat transfer coefficient under 0.4 m/s crosswind conditions decreased by 9.5% compared with the windless conditions, while that value lowered only by 2.0% for the optimal non-uniform layout pattern. It has been demonstrated that the optimal non-uniform layout pattern has the better thermal performance under 0.4 m/s crosswind condition. Full article
Figures

Figure 1

Open AccessArticle Assessment against Experiments of Devolatilization and Char Burnout Models for the Simulation of an Aerodynamically Staged Swirled Low-NOx Pulverized Coal Burner
Energies 2017, 10(1), 66; doi:10.3390/en10010066
Received: 6 December 2016 / Revised: 27 December 2016 / Accepted: 30 December 2016 / Published: 7 January 2017
PDF Full-text (5742 KB) | HTML Full-text | XML Full-text
Abstract
In the next few years, even though there will be a continuous growth of renewables and a loss of the share of fossil fuel, energy production will still be strongly dependent on fossil fuels. It is expected that coal will continue to play
[...] Read more.
In the next few years, even though there will be a continuous growth of renewables and a loss of the share of fossil fuel, energy production will still be strongly dependent on fossil fuels. It is expected that coal will continue to play an important role as a primary energy source in the next few decades due to its lower cost and higher availability with respect to other fossil fuels. However, in order to improve the sustainability of energy production from fossil fuels, in terms of pollutant emissions and energy efficiency, the development of advanced investigation tools is crucial. In particular, computational fluid dynamics (CFD) simulations are needed in order to support the design process of low emission burners. Even if in the literature several combustion models can be found, the assessment of their performance against detailed experimental measurements on full-scale pulverized coal burners is lacking. In this paper, the numerical simulation of a full-scale low-NO x , aerodynamically-staged, pulverized coal burner for electric utilities tested in the 48 MW th plant at the Combustion Environment Research Centre (CCA - Centro Combustione e Ambiente) of Ansaldo Caldaie S.p.A. in Gioia del Colle (Italy) is presented. In particular, this paper is focused on both devolatilization and char burnout models. The parameters of each model have been set according to the coal characteristics without any tuning based on the experimental data. Thanks to a detailed description of the complex geometry of the actual industrial burner and, in particular, of the pulverized coal inlet distribution (considering the entire primary air duct, in order to avoid any unrealistic assumption), a correct selection of both devolatilization and char burnout models and a selection of suited parameters for the NO x modeling, accurate results have been obtained in terms of NO x formation. Since the model parameters have been evaluated a priori, the numerical approach proposed here could be suitable to be applied as a performance prediction tool in the design of pulverized coal burners. Full article
Figures

Figure 1

Open AccessArticle Performance Analysis of Data-Driven and Model-Based Control Strategies Applied to a Thermal Unit Model
Energies 2017, 10(1), 67; doi:10.3390/en10010067
Received: 27 November 2016 / Revised: 8 December 2016 / Accepted: 24 December 2016 / Published: 7 January 2017
Cited by 2 | PDF Full-text (563 KB) | HTML Full-text | XML Full-text
Abstract
The paper presents the design and the implementation of different advanced control strategies that are applied to a nonlinear model of a thermal unit. A data-driven grey-box identification approach provided the physically–meaningful nonlinear continuous-time model, which represents the benchmark exploited in this work.
[...] Read more.
The paper presents the design and the implementation of different advanced control strategies that are applied to a nonlinear model of a thermal unit. A data-driven grey-box identification approach provided the physically–meaningful nonlinear continuous-time model, which represents the benchmark exploited in this work. The control problem of this thermal unit is important, since it constitutes the key element of passive air conditioning systems. The advanced control schemes analysed in this paper are used to regulate the outflow air temperature of the thermal unit by exploiting the inflow air speed, whilst the inflow air temperature is considered as an external disturbance. The reliability and robustness issues of the suggested control methodologies are verified with a Monte Carlo (MC) analysis for simulating modelling uncertainty, disturbance and measurement errors. The achieved results serve to demonstrate the effectiveness and the viable application of the suggested control solutions to air conditioning systems. The benchmark model represents one of the key issues of this study, which is exploited for benchmarking different model-based and data-driven advanced control methodologies through extensive simulations. Moreover, this work highlights the main features of the proposed control schemes, while providing practitioners and heating, ventilating and air conditioning engineers with tools to design robust control strategies for air conditioning systems. Full article
(This article belongs to the Special Issue Energy Management Control)
Figures

Figure 1

Open AccessArticle Impact of Battery Energy Storage System Operation Strategy on Power System: An Urban Railway Load Case under a Time-of-Use Tariff
Energies 2017, 10(1), 68; doi:10.3390/en10010068
Received: 24 October 2016 / Revised: 12 December 2016 / Accepted: 3 January 2017 / Published: 7 January 2017
Cited by 1 | PDF Full-text (2497 KB) | HTML Full-text | XML Full-text
Abstract
Customer-owned battery energy storage systems (BESS) have been used to reduce electricity costs of energy storage owners (ESOs) under a time-of-use (TOU) tariff in Korea. However, the current TOU tariff can unintentionally induce customer’s electricity usage to have a negative impact on power
[...] Read more.
Customer-owned battery energy storage systems (BESS) have been used to reduce electricity costs of energy storage owners (ESOs) under a time-of-use (TOU) tariff in Korea. However, the current TOU tariff can unintentionally induce customer’s electricity usage to have a negative impact on power systems. This paper verifies the impact of different BESS operation strategies on power systems under a TOU tariff by analyzing the TOU tariff structure and the customer’s load pattern. First, several BESS operation strategies of ESO are proposed to reduce the electricity cost. In addition, a degradation cost calculation method for lithium ion batteries is considered for the ESO to determine the optimal BESS operation strategy that maximizes both electricity cost and annual investment cost. The optimal BESS operation strategy that maximizes ESO’s net benefit is illustrated by simulation using an urban railway load data from Namgwangju Station, Korea. The results show that BESS connected to urban railway loads can negative impact power system operation. This is due to the high BESS degradation costs and lack of incentive of differential rates in TOU tariff that can effectively induce proper demand response. Full article
Figures

Figure 1

Open AccessArticle Stability Analysis and Stability Enhancement Based on Virtual Harmonic Resistance for Meshed DC Distributed Power Systems with Constant Power Loads
Energies 2017, 10(1), 69; doi:10.3390/en10010069
Received: 24 November 2016 / Revised: 16 December 2016 / Accepted: 2 January 2017 / Published: 9 January 2017
PDF Full-text (3401 KB) | HTML Full-text | XML Full-text
Abstract
This paper addresses the stability issue of the meshed DC distributed power systems (DPS) with constant power loads (CPLs) and proposes a stability enhancement method based on virtual harmonic resistance. In previous researches, the network dynamics of the meshed DC DPS are often
[...] Read more.
This paper addresses the stability issue of the meshed DC distributed power systems (DPS) with constant power loads (CPLs) and proposes a stability enhancement method based on virtual harmonic resistance. In previous researches, the network dynamics of the meshed DC DPS are often ignored, which affects the derivation of the equivalent system impendence. In addition, few of them have considered the meshed DC