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Showing records 26 to 50 of 155. [First] Page: 1 2 3 4 5 6 Last
Experimental Investigation on Wall Film Distribution of Dimethyl Ether/Diesel Blended Fuels Formed during Spray Wall Impingement
Hanzhengnan Yu, Xingyu Liang, Gequn Shu, Xu Wang, Yuesen Wang, Hongsheng Zhang
February 5, 2019 (v1)
Keywords: dimethyl ether (DME)/diesel blended fuels, early injection, lubricating oil film, spray wall impingement, wall film characteristics
Dimethyl ether (DME)/diesel blended fuels are used to improve the emissions caused by spray wall impingement during the early injection period. However, experimental results have showed that the spray wall impingement still cannot be avoided due to the engine structure and low density of the in-cylinder charge at the early injection timing. Furthermore, the wall film formed in the spray wall impingement process directly affects fuel/air mixture formation, combustion, exhaust emissions and oil quality subsequently. In this paper, the wall film distribution of DME/diesel blended fuels formed during the spray wall impingement process has been experimentally investigated. The variations of wall film distribution, wall film area and average thickness with different injection pressures, impingement distances, impingement angles and blending ratios have been discussed under both dry wall and wet wall conditions. Results showed that the wall film distribution styles were mainly determined by t... [more]
Study on Insulator Flashover Voltage Gradient Correction Considering Soluble Pollution Constituents
Dongdong Zhang, Zhijin Zhang, Xingliang Jiang, Zhongyi Yang, Jiayao Zhao, Yongfu Li
February 5, 2019 (v1)
Subject: Other
Keywords: equivalent salt deposit density (ESDD), flashover voltage gradient, insulator, pollution flashover, soluble constituent
Natural polluted insulator surfaces are always coated with various kinds of soluble constituents, and those constituents affect flashover performance differentially. Currently, this fact is not considered either in laboratory experiments or field pollution degree measurements, causing the existing insulation selection method to be deficient. In this paper, a systematic study on insulator flashover voltage gradient correction involving different types of soluble pollution constituents is presented. Using a typical type glass insulator as the sample, its flashover tests, polluted by typical soluble chemicals (NaCl, NaNO₃, KNO₃, NH₄NO₃, MgSO₄, Ca(NO₃)₂ and CaSO₄), were carried out. Then, the flashover gradient correction was made by combining the flashover performance of each soluble constituent, the equivalent salt deposit density (ESDD) contribution of the seven constituents, and the saturation performance of CaSO₄. The correction agreed with the flashover test results of insulator poll... [more]
Retrofitted Solar Domestic Hot Water Systems for Swedish Single-Family Houses—Evaluation of a Prototype and Life-Cycle Cost Analysis
Luis Ricardo Bernardo, Henrik Davidsson, Erik Andersson
February 5, 2019 (v1)
Subject: Energy Policy
Keywords: domestic hot water, life cycle cost, retrofit, single-family houses, Solar Thermal
According to recent technology road maps, system cost reductions and development of standardised plug-and-function systems are some of the most important goals for solar heating technology development. Retrofitting hot water boilers in single-family houses when installing solar collectors has the potential to significantly reduce both material and installation costs. Previous studies have investigated such retrofitting, using theoretical simulations and laboratory tests, but no actual installations were made and tested in practice. This article describes the installation, measured performance and cost effectiveness of a retrofitting solution that converts existing domestic hot water heaters to a solar domestic hot water system. The measured performance is characterised by the monthly and annual solar fractions. The cost effectiveness is evaluated by a life-cycle cost analysis, comparing the retrofitted system to a conventional solar domestic hot water system and the case without any so... [more]
Optimization of Electrochemically Deposited Highly Doped ZnO Bilayers on Ga-Rich Chalcopyrite Selenide for Cost-Effective Photovoltaic Device Technology
Dimitra N. Papadimitriou, Georgios Roupakas, Georgios G. Roumeliotis, Patrick Vogt, Tristan Köhler
February 5, 2019 (v1)
Subject: Materials
Keywords: annealing T-threshold, CIGS photovoltaics, current-voltage measurements, ECD process optimization, oriented Al:ZnO bilayers, scanning electron microscopy, transmittance/reflectance spectroscopy, van der Pauw measurement techniques, X-ray diffraction
High quality polycrystalline bilayers of aluminium doped ZnO (Al:ZnO) were successively electrodeposited in the form of columnar structures preferentially oriented along the ( 10 1 ¯ 1 ) crystallographic direction from aqueous solution of zinc nitrate (Zn(NO₃)₂) at negative electrochemical potential of EC = (−0.8)⁻(−1.2) V and moderate temperature of 80 °C on gallium rich (30% Ga) chalcopyrite selenide Cu(In,Ga)Se₂ (CIGS) with chemically deposited ZnSe buffer (ZnSe/Cu(In,Ga)Se₂/Mo/glass). The aluminium doped ZnO layer properties have initially been probed by deposition of Al:ZnO/i-ZnO bilayers directly on Mo/glass substrates. The band-gap energy of the Al:ZnO/i-ZnO reference layers was found to vary from 3.2 to 3.7 eV by varying the AlCl₃ solute dopant concentration from 1 to 20 mM. The electrical resistivity of indium-pellet contacted highly doped Al:ZnO sheet of In/Al:ZnO/i-ZnO/Mo/glass reference samples was of the order ρ ~10−5 Ω·cm; the respective carrier concentratio... [more]
The Demand Side Management Potential to Balance a Highly Renewable European Power System
Alexander Kies, Bruno U. Schyska, Lueder von Bremen
February 5, 2019 (v1)
Keywords: demand side management, energy system modelling, European power system, renewable energy systems, solar energy, wind energy
Shares of renewables continue to grow in the European power system. A fully renewable European power system will primarily depend on the renewable power sources of wind and photovoltaics (PV), which are not dispatchable but intermittent and therefore pose a challenge to the balancing of the power system. To overcome this issue, several solutions have been proposed and investigated in the past, including storage, backup power, reinforcement of the transmission grid, and demand side management (DSM). In this paper, we investigate the potential of DSM to balance a simplified, fully renewable European power system. For this purpose, we use ten years of weather and historical load data, a power-flow model and the implementation of demand side management as a storage equivalent, to investigate the impact of DSM on the need for backup energy. We show that DSM has the potential to reduce the need for backup energy in Europe by up to one third and can cover the need for backup up to a renewable... [more]
A Novel Algorithm for Efficient Downlink Packet Scheduling for Multiple-Component-Carrier Cellular Systems
Yao-Liang Chung
February 5, 2019 (v1)
Keywords: 4G/5G cellular systems, efficiency, multiple component carriers, proportional fair
The simultaneous aggregation of multiple component carriers (CCs) for use by a base station constitutes one of the more promising strategies for providing substantially enhanced bandwidths for packet transmissions in 4th and 5th generation cellular systems. To the best of our knowledge, however, few previous studies have undertaken a thorough investigation of various performance aspects of the use of a simple yet effective packet scheduling algorithm in which multiple CCs are aggregated for transmission in such systems. Consequently, the present study presents an efficient packet scheduling algorithm designed on the basis of the proportional fair criterion for use in multiple-CC systems for downlink transmission. The proposed algorithm includes a focus on providing simultaneous transmission support for both real-time (RT) and non-RT traffic. This algorithm can, when applied with sufficiently efficient designs, provide adequate utilization of spectrum resources for the purposes of trans... [more]
Spray Formation of a Liquid Carbon Dioxide-Water Mixture at Elevated Pressures
Hakduck Kim, Changyeon Kim, Heechang Lim, Juhun Song
February 5, 2019 (v1)
Keywords: coal gasification, flash atomization, liquid carbon dioxide (LCO2), solubility, water-LCO2 mixture
Liquid carbon dioxide-assisted (LCO₂-assisted) atomization can be used in coal-water slurry gasification plants to prevent the agglomeration of coal particles. It is essential to understand the atomization behavior of the water-LCO₂ mixture leaving the injector nozzle under various conditions, including the CO₂ blending ratio, injection pressure, and chamber pressure. In this study, the flash-atomization behavior of a water-LCO₂ mixture was evaluated with regard to the spray angle and penetration length during a throttling process. The injector nozzle was mounted downstream of a high-pressure spray-visualization system. Based on the results, the optimal condition for the effective transport of coal particles was proposed.
Exergy Accounting: A Quantitative Comparison of Methods and Implications for Energy-Economy Analysis
Jack Miller, Timothy J. Foxon, Steve Sorrell
February 5, 2019 (v1)
Keywords: decoupling, economic growth, Energy, Energy Efficiency, Exergy
Assessments of the feasibility of decoupling energy consumption from economic growth could benefit from an improved understanding of the size, nature and value of different energy flows. This understanding may be enhanced by focusing upon so-called “useful exergy”—a measure of both the quantity and “quality” of energy (defined here as its thermodynamic ability to perform physical work) at the “useful” stage of the energy conversion chain. Useful exergy flows within national economies are increasingly being quantified and their role in economic activity explored. However, this so-called “exergy economics” field currently lacks a consistent methodology. This paper contributes to the development of a more consistent approach. By constructing a “useful exergy account” for the United Kingdom covering the period 1960⁻2012, we explore how different methodological choices influence estimates of useful exergy for different categories of end-use as well as estimates of total national useful exer... [more]
The Recent Change in the Italian Policies for Photovoltaics: Effects on the Energy Demand Coverage of Grid-Connected PV Systems Installed in Urban Contexts
Aldo Orioli, Vincenzo Franzitta, Alessandra Di Gangi, Ferdinando Foresta
February 5, 2019 (v1)
Subject: Energy Policy
Keywords: feed-in tariff, photovoltaic, tax credit
In July 2013, the Italian photovoltaic (PV) support policies changed the feed-in tariff (FIT) mechanism and turned to a tax credits program, which is currently in force. The aim of this paper is to investigate how such a radical change has influenced the electricity demand coverage of the PV systems installed in urban contexts. A methodology, which connects the economic assessment to a detailed architectural and energy suitability analysis, was applied to some case studies to analyse the relationships between the physical parameters related to multi-storey buildings (roof shapes, number of floors and area of flats) and the most relevant economic and financial features affecting the viability of rooftop PV systems. The study, which considers only the electricity produced by the PV systems that are economically profitable, highlighted that the tax credits scheme is even more effective in covering the electrical consumption of densely urbanised Italian city districts. The results, which a... [more]
Raman Spectral Characteristics of Oil-Paper Insulation and Its Application to Ageing Stage Assessment of Oil-Immersed Transformers
Jingxin Zou, Weigen Chen, Fu Wan, Zhou Fan, Lingling Du
February 5, 2019 (v1)
Keywords: aging stage, clustering analysis, degree of polymerization, power transformers, principal component analysis, Raman spectroscopy, support vector machine
The aging of oil-paper insulation in power transformers may cause serious power failures. Thus, effective monitoring of the condition of the transformer insulation is the key to prevent major accidents. The purpose of this study was to explore the feasibility of confocal laser Raman spectroscopy (CLRS) for assessing the aging condition of oil-paper insulation. Oil-paper insulation samples were subjected to thermal accelerated ageing at 120 °C for up to 160 days according to the procedure described in the IEEE Guide. Meanwhile, the dimension of the Raman spectrum of the insulation oil was reduced by principal component analysis (PCA). The 160 oil-paper insulation samples were divided into five aging stages as training samples by clustering analysis and with the use of the degree of polymerization of the insulating papers. In addition, the features of the Raman spectrum were used as the inputs of a multi-classification support vector machine. Finally, 105 oil-paper insulation testing sam... [more]
Conventional P-ω/Q-V Droop Control in Highly Resistive Line of Low-Voltage Converter-Based AC Microgrid
Xiaochao Hou, Yao Sun, Wenbin Yuan, Hua Han, Chaolu Zhong, Josep M. Guerrero
February 5, 2019 (v1)
Keywords: droop control, low-voltage alternating current (AC) microgrid, power sharing, small signal stability
In low-voltage converter-based alternating current (AC) microgrids with resistive distribution lines, the P-V droop with Q-f boost (VPD/FQB) is the most common method for load sharing. However, it cannot achieve the active power sharing proportionally. To overcome this drawback, the conventional P-ω/Q-V droop control is adopted in the low-voltage AC microgrid. As a result, the active power sharing among the distributed generators (DGs) is easily obtained without communication. More importantly, this study clears up the previous misunderstanding that conventional P-ω/Q-V droop control is only applicable to microgrids with highly inductive lines, and lays a foundation for the application of conventional droop control under different line impedances. Moreover, in order to guarantee the accurate reactive power sharing, a guide for designing Q-V droop gains is given, and virtual resistance is adopted to shape the desired output impedance. Finally, the effects of power sharing and transient... [more]
Simple Design Approach for Low Torque Ripple and High Output Torque Synchronous Reluctance Motors
Mohamed Nabil Fathy Ibrahim, Peter Sergeant, Essam Rashad
February 5, 2019 (v1)
Keywords: design, finite element method (FEM), flux-barriers, sensitivity analysis, synchronous reluctance motor, torque ripple
The rotor design of Synchronous Reluctance Motors (SynRMs) has a large effect on their efficiency, torque density and torque ripple. In order to achieve a good compromise between these three goals, an optimized rotor geometry is necessary. A finite element method (FEM) is a good tool for the optimization. However, the computation time is an obstacle as there are many geometrical parameters to be optimized. The flux-barrier widths and angles are the two most crucial parameters for the SynRM output torque and torque ripple. This paper proposes an easy-to-use set of parametrized equations to select appropriate values for these two rotor parameters. With these equations, the reader can design a SynRM of distributed windings with a low torque ripple and with a better average torque. The methodology is valid for a wide range of SynRMs. To check the validity of the proposed equations, the sensitivity analysis for the variation of these two parameters on the SynRM torque and torque ripple is c... [more]
Analysis and Modeling for China’s Electricity Demand Forecasting Using a Hybrid Method Based on Multiple Regression and Extreme Learning Machine: A View from Carbon Emission
Yi Liang, Dongxiao Niu, Ye Cao, Wei-Chiang Hong
February 5, 2019 (v1)
Keywords: carbon emission, electricity demand forecasting, extreme learning machine (ELM), grey relation degree (GRD), induced ordered weighted harmonic averaging operator (IOWHA), multiple regression (MR)
The power industry is the main battlefield of CO₂ emission reduction, which plays an important role in the implementation and development of the low carbon economy. The forecasting of electricity demand can provide a scientific basis for the country to formulate a power industry development strategy and further promote the sustained, healthy and rapid development of the national economy. Under the goal of low-carbon economy, medium and long term electricity demand forecasting will have very important practical significance. In this paper, a new hybrid electricity demand model framework is characterized as follows: firstly, integration of grey relation degree (GRD) with induced ordered weighted harmonic averaging operator (IOWHA) to propose a new weight determination method of hybrid forecasting model on basis of forecasting accuracy as induced variables is presented; secondly, utilization of the proposed weight determination method to construct the optimal hybrid forecasting model base... [more]
Effect of Air Staging Ratios on the Burning Rate and Emissions in an Underfeed Fixed-Bed Biomass Combustor
Araceli Regueiro, David Patiño, Jacobo Porteiro, Enrique Granada, José Luis Míguez
February 5, 2019 (v1)
Subject: Biosystems
Keywords: air staging, bed stoichiometry, biomass combustion, burning rate, fixed-bed
This experimental work studies a small-scale biomass combustor (5⁻12 kW) with an underfed fixed bed using low air staging ratios (15%⁻30%). This document focuses on the influence of the operative parameters on the combustion process, so gaseous emissions and the distribution and concentration of particulate matter have also been recorded. The facility shows good stability and test repeatability. For the studied airflow ranges, the results show that increasing the total airflow rate does not increase the overall air excess ratio because the burning rate is proportionally enhanced (with some slight differences that depend on the air staging ratio). Consequently, the heterogeneous reactions at the bed remain in the so-called oxygen-limited region, and thus the entire bed operates under sub-stoichiometric conditions with regards of the char content of the biomass. In addition, tests using only primary air (no staging) may increase the fuel consumption, but in a highly incomplete way, appro... [more]
Flow Induced Vibration and Energy Extraction of an Equilateral Triangle Prism at Different System Damping Ratios
Jun Zhang, Fang Liu, Jijian Lian, Xiang Yan, Quanchao Ren
February 5, 2019 (v1)
Subject: Other
Keywords: damping ratio, energy extraction, equilateral triangle prism, flow induced vibration, galloping, vortex induced vibration
The flow induced vibration and energy extraction of an equilateral triangle prism elastically mounted in a water channel are investigated experimentally at different system damping ratios ζtotal with the constant oscillating mass Mosc and system stiffness K. A power take-off system with a variable damping function is developed. The translation-rotation equation of the vibration system deduced in the study indicates that the total oscillating mass includes the material mass, and the equivalent mass due to the rotation of the gears and rotor. Besides, increasing load resistance can result in a decrease in ζtotal when K and Mosc remain unchanged. The prism experiences, in turn, soft galloping, hard galloping 1 and hard galloping 2 with increasing ζtotal. As ζtotal increases up to 0.335, only the vortex-induced vibration is observed because the extremely high ζtotal prevents the prism from galloping. The response amplitude decreases with the increasing ζtotal. In addition, higher ζtotal pr... [more]
Perturb and Observe Control for an Embedded Point Pivoted Absorber
Gianluca Brando, Domenico Pietro Coiro, Marino Coppola, Adolfo Dannier, Andrea Del Pizzo, Ivan Spina
February 5, 2019 (v1)
Keywords: marine, maximum power point tracking (MPPT), perturb and observe (P&, Q), scale model, wave energy converter (WEC)
Marine energy sources represent an attractive and inexhaustible reservoir able to contribute to the fulfillment of the world energy demand in accordance with climate/energy regulatory frameworks. Wave energy converter (WEC) integration into the main grid requires both the maximization of the harvested energy and the proper management of the generation variability. The present paper focuses on both these mentioned issues. More specifically, it presents an embedded point pivoted absorber (PPA) and its related control strategy aimed at maximizing the harvested energy. Experimental and numerical investigations have been carried out in a wave/towing tank facility in order to derive the design characteristics of the full-scale model and demonstrate the validity and effectiveness of the proposed control strategy.
Analysis of Power Network for Line Reactance Variation to Improve Total Transmission Capacity
Ikram Ullah, Wolfgang Gawlik, Peter Palensky
February 5, 2019 (v1)
Keywords: Available Transfer Capability (ATC), FACTS, PTDF, real power flow Performance Index sensitivity
The increasing growth in power demand and the penetration of renewable distributed generations in competitive electricity market demands large and flexible capacity from the transmission grid to reduce transmission bottlenecks. The bottlenecks cause transmission congestion, reliability problems, restrict competition, and limit the maximum dispatch of low cost generations in the network. The electricity system requires efficient utilization of the current transmission capability to improve the Available Transfer Capability (ATC). To improve the ATC, power flow among the lines can be managed by using Flexible AC Transmission System (FACTS) devices as power flow controllers, which alter the parameters of power lines. It is important to place FACTS devices on suitable lines to vary the reactance for improving Total Transmission Capacity (TTC) of the network and provide flexibility in the power flow. In this paper a transmission network is analyzed based on line parameters variation to impr... [more]
Coil Design for High Misalignment Tolerant Inductive Power Transfer System for EV Charging
Kafeel Ahmed Kalwar, Saad Mekhilef, Mehdi Seyedmahmoudian, Ben Horan
February 5, 2019 (v1)
Subject: Other
Keywords: electric vehicle (EV), inductive power transfer (IPT), misalignment tolerance
The inductive power transfer (IPT) system for electric vehicle (EV) charging has acquired more research interest in its different facets. However, the misalignment tolerance between the charging coil (installed in the ground) and pick-up coil (mounted on the car chassis), has been a challenge and fundamental interest in the future market of EVs. This paper proposes a new coil design QDQ (Quad D Quadrature) that maintains the high coupling coefficient and efficient power transfer during reasonable misalignment. The QDQ design makes the use of four adjacent circular coils and one square coil, for both charging and pick-up side, to capture the maximum flux at any position. The coil design has been modeled in JMAG software for calculation of inductive parameters using the finite element method (FEM), and its hardware has been tested experimentally at various misaligned positions. The QDQ coils are shown to be capable of achieving good coupling coefficient and high efficiency of the system... [more]
Application of a Method for Intelligent Multi-Criteria Analysis of the Environmental Impact of Tailing Ponds in Northern Kosovo and Metohija
Gordana Milentijević, Blagoje Nedeljković, Milena Lekić, Zoran Nikić, Ivica Ristović, Jelena Djokić
February 5, 2019 (v1)
Keywords: ecology, environment, multi-criteria analysis, tailing pond, Trepča
The technological process of exploitation of mineral resources and processing of mined ores to cater to the market results, among other things, in a large amount of tailings deposed on tailing ponds. Because of the chemical composition of the material, the increasing amount of waste, and the mismanagement of recovery and reclamation of ponds, these ponds have become a significant element of negative impact on the surrounding ecosystem. Economics was behind the discharging of this material, resulting in tailing ponds created in inappropriate areas. There is an ongoing process of depositing tailings on old tailing ponds, although no special attention has been paid to the subsequent effect on the environment. Application of intelligent multi-criteria analysis AHP and PROMETHEE has been performed in this paper for the purpose of ranking the degree of negative impact on the environment of tailing ponds. Analysis is performed for five tailing ponds of MMCC (Mining Metallurgy Chemical Combine... [more]
Analysis and Design of an Active Stabilizer for a Boost Power Converter System
Yigeng Huangfu, Shengzhao Pang, Babak Nahid-Mobarakeh, Akshay Rathore, Fei Gao, Dongdong Zhao
February 5, 2019 (v1)
Subject: Other
Keywords: boost power converter, input filter, stabilizer
In electrical power converter systems, the presence of an LC input filter can efficiently reduce the Electromagnetic Interference (EMI) effect, and at the same time protect the converter and the load from being impacted by sharp input impulse voltages. However, for transportation applications, the weight and size limitations of input LC filters for power converters have to be taken into consideration. The reduction of LC filter size may impair the system stability margin and dynamic response. In serve cases, the system may even become unstable. Thus, in order to ensure the system stability while minimizing the input LC filter size, the implementation of a stabilizer for the system control is needed. In this paper, a novel digital stabilizer design method is proposed for a boost power converter with a small input LC filter. The proposed method is based on input filter inductance current measurements and DSP (Digital Signal Processor) -based digital stabilizer design. Simulation and expe... [more]
Horizontal Air-Ground Heat Exchanger Performance and Humidity Simulation by Computational Fluid Dynamic Analysis
Paolo Maria Congedo, Caterina Lorusso, Maria Grazia De Giorgi, Riccardo Marti, Delia D’Agostino
February 5, 2019 (v1)
Keywords: computational fluid dynamic (CFD), cooling, efficiency, ground heat exchanger, ground source heat pump, heating, humidity, ventilation, zero energy building (ZEB)
Improving energy efficiency in buildings and promoting renewables are key objectives of European energy policies. Several technological measures are being developed to enhance the energy performance of buildings. Among these, geothermal systems present a huge potential to reduce energy consumption for mechanical ventilation and cooling, but their behavior depending on varying parameters, boundary and climatic conditions is not fully established. In this paper a horizontal air-ground heat exchanger (HAGHE) system is studied by the development of a computational fluid dynamics (CFD) model. Summer and winter conditions representative of the Mediterranean climate are analyzed to evaluate operation and thermal performance differences. A particular focus is given to humidity variations as this parameter has a major impact on indoor air quality and comfort. Results show the benefits that HAGHE systems can provide in reducing energy consumption in all seasons, in summer when free-cooling can b... [more]
The Coupling Fields Characteristics of Cable Joints and Application in the Evaluation of Crimping Process Defects
Fan Yang, Kai Liu, Peng Cheng, Shaohua Wang, Xiaoyu Wang, Bing Gao, Yalin Fang, Rong Xia, Irfan Ullah
February 5, 2019 (v1)
Keywords: coupling fields, defects characteristics, evaluation of internal defects, power cable joint, stress field, temperature field
The internal defects of cable joints always accelerate the deterioration of insulation, until finally accidents can arise due to the explosion of the joints. The formation process of this damage often involves changes in the electromagnetic, temperature and stress distribution of the cable joint, therefore, it is necessary to analyze the electromagnetic-thermal-mechanical distribution of cable joints. Aiming at solving this problem, the paper sets up a 3-D electromagnetic-thermal-mechanical coupling model of cable joints under crimping process defects. Based on the model, the electromagnetic losses distribution, temperature distribution and stress distribution of a cable joint and body are calculated. Then, the coupling fields characteristics in different contact coefficient k, ambient temperature Tamb and load current I were analyzed, and according to the thermal-mechanical characteristics of a cable joint under internal defects, the temperature difference ΔTf and stress difference Δσ... [more]
Analysis of Power Quality Signals Using an Adaptive Time-Frequency Distribution
Nabeel A. Khan, Faisal Baig, Syed Junaid Nawaz, Naveed Ur Rehman, Shree K. Sharma
February 5, 2019 (v1)
Keywords: distribution, power quality, power signals, smoothing, time-frequency
Spikes frequently occur in power quality (PQ) disturbance signals due to various causes such as switching of the inductive loads and the energization of the capacitor bank. Such signals are difficult to analyze using existing time-frequency (TF) methods as these signals have two orthogonal directions in a TF plane. To address this issue, this paper proposes an adaptive TF distribution (TFD) for the analysis of PQ signals. In the proposed adaptive method, the smoothing kernel’s direction is locally adapted based on the direction of energy in the joint TF domain, and hence an improved TF resolution can be obtained. Furthermore, the performance of the proposed adaptive technique in analyzing electrical PQ is thoroughly studied for both synthetic and real world electrical power signals with the help of extensive simulations. The simulation results (specially for empirical data) indicate that the adaptive TFD method achieves high energy concentration in the TF domain for signals composed of... [more]
Forecasting Electricity Market Risk Using Empirical Mode Decomposition (EMD)—Based Multiscale Methodology
Kaijian He, Hongqian Wang, Jiangze Du, Yingchao Zou
February 5, 2019 (v1)
Keywords: electricity market risk, Empirical Mode Decomposition (EMD), Exponential Weighted Moving Average (EWMA), Value at Risk (VaR)
The electricity market has experienced an increasing level of deregulation and reform over the years. There is an increasing level of electricity price fluctuation, uncertainty, and risk exposure in the marketplace. Traditional risk measurement models based on the homogeneous and efficient market assumption no longer suffice, facing the increasing level of accuracy and reliability requirements. In this paper, we propose a new Empirical Mode Decomposition (EMD)-based Value at Risk (VaR) model to estimate the downside risk measure in the electricity market. The proposed model investigates and models the inherent multiscale market risk structure. The EMD model is introduced to decompose the electricity time series into several Intrinsic Mode Functions (IMF) with distinct multiscale characteristics. The Exponential Weighted Moving Average (EWMA) model is used to model the individual risk factors across different scales. Experimental results using different models in the Australian electric... [more]
Comparison of Cooling System Designs for an Exhaust Heat Recovery System Using an Organic Rankine Cycle on a Heavy Duty Truck
Nicolas Stanzel, Thomas Streule, Markus Preißinger, Dieter Brüggemann
February 5, 2019 (v1)
Keywords: 1-D simulation, cooling system, Ethanol, heat recovery, heavy-duty truck, Organic Rankine Cycle (ORC)
A complex simulation model of a heavy duty truck, including an Organic Rankine Cycle (ORC) based waste heat recovery system and a vehicle cooling system, was applied to determine the system fuel economy potential in a typical drive cycle. Measures to increase the system performance were investigated and a comparison between two different cooling system designs was derived. The base design, which was realized on a Mercedes-Benz Actros vehicle revealed a fuel efficiency benefit of 2.6%, while a more complicated design would generate 3.1%. Furthermore, fully transient simulation results were performed and are compared to steady state simulation results. It is shown that steady state simulation can produce comparable results if averaged road data are used as boundary conditions.
Showing records 26 to 50 of 155. [First] Page: 1 2 3 4 5 6 Last