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HEMS-enabled transactive flexibility in real-time operation of three-phase unbalanced distribution systems

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Journal of Modern Power Systems and Clean Energy 2019年第6期7卷 1434-1449页

作者： Mohammad Nazif FAQIRY Li WANG Hongyu WU Department of Electrical and Computer Engineering Kansas State UniversityManhattanKSUSA

This paper proposes a coordinated two-stage real-time market mechanism in an unbalanced distribution system which can utilize flexibility service from home energy management system(HEMS)to alleviate line congestion,voltage violation,and substation-level power *** the grid level,the distribution system operator(DSO)computes the distribution locational marginal prices(DLMPs)and its energy,loss,congestion,and voltage violation components through comprehensive sensitivity *** using the DLMP components in a firststage optimization problem,the DSO generates two price signals and sends them to HEMS to seek flexibility *** response to the request of DSO,each home-level HEMS computes a flexibility range by incorporating the prices of DSO in its own optimization *** to future uncertainties,the HEMS optimization problem is modeled as an adaptive dynamic programming(ADP)to minimize the total expected cost and discomfort of the household over a forward-looking *** flexibility range of each HEMS is then used by the DSO in a second-stage optimization problem to determine new optimal dispatch points which ensure the efficient,reliable,and congestionfree operation of the distribution ***,the second-stage dispatch points are used by each HEMS to constrain its maximum consumption level in a final ADP to assign consumption level of major appliances such as energy storage,heating,ventilation and air-conditioning,and water *** proposed method is validated on an IEEE 69-bus system with a large number of regular and HEMS-equipped homes in each phase.

关键词： Distribution locational marginal price Real-time market Congestion Home energy management system unbalanced distribution system Energy storage Adaptive dynamic programming

Balance control of grid currents for UPQC under unbalanced loads based on matching-ratio compensation algorithm

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Journal of Modern Power Systems and Clean Energy 2018年第6期6卷 1319-1331页

作者： Xiaojun ZHAO Chunjiang ZHANG Xiuhui CHAI Jinlong ZHANG Fanqi LIU Zhe ZHANG Department of Electrical Engineering Yanshan University Department of Electrical Engineering Technical University of Denmark

In three-phase four-wire systems, unbalanced loads can cause grid currents to be unbalanced, and this may cause the neutral point potential on the grid side to shift. The neutral point potential shift will worsen the control precision as well as the performance of the threephase four-wire unified power quality conditioner(UPQC),and it also leads to unbalanced three-phase output voltage,even causing damage to electric equipment. To deal with unbalanced loads, this paper proposes a matching-ratio compensation algorithm(MCA) for the fundamental active component of load currents, and by employing this MCA,balanced three-phase grid currents can be realized under 100% unbalanced loads. The steady-state fluctuation and the transient drop of the DC bus voltage can also be restrained. This paper establishes the mathematical model of the UPQC, analyzes the mechanism of the DC bus voltage fluctuations, and elaborates the interaction between unbalanced grid currents and DC bus voltage fluctuations;two control strategies of UPQC under three-phase stationary coordinate based on the MCA are given, and finally, the feasibility and effectiveness of the proposed control strategy are verified by experiment results.

关键词： Unified power quality conditioner(UPQC) unbalanced loads Matching-ratio compensation Balance control DC bus voltage fluctuations

A Nonlinear Control Strategy for Vienna Rectifier Under unbalanced Input Voltage

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Transactions of Nanjing University of Aeronautics and Astronautics 2019年第5期36卷 703-714页

作者： REN Xiaoyong CHEN Yu TONG Dan ZHANG Zhiliang CHEN Qianhong Aero-Power Sci-Tech Center College of Electronic EngineeringNanjing University of Aeronautics and Astronautics

The Vienna rectifier with unbalanced input voltage and load transient is analyzed.A nonlinear control strategy for Vienna rectifier under unbalanced input is *** the view of positive and negative sequence components,the proposed nonlinear control strategy suppresses the twice frequency ripple and guarantees the dynamic response characteristic at the same *** to the proposed nonlinear control strategy,the DC bus capacitor can be reduced a lot since the voltage ripple and drop can be suppressed.A 10 kW Vienna rectifier is built to verify the proposed control *** applying the proposed nonlinear control strategy,the voltage ripple is only7 V and decreases over 75%over the traditional PI control when the unbalanced degree is 20%.The voltage drop can be reduced about 80%than former control strategy which is helpful to reduce the DC bus capacitor and achieve higher power *** volume of the capacitor can be reduced by 83.3%with the new control method.

关键词： Vienna rectifier radars unbalanced input voltage nonlinear control strategy DC bus capacitance

Modeling method of sequence admittance for three-phase voltage source converter under unbalanced grid condition

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Journal of Modern Power Systems and Clean Energy 2018年第3期6卷 595-606页

作者： Yang CEN Meng HUANG Xiaoming ZHA School of Electrical Engineering Wuhan University

The admittance is a strong tool for stability analysis and assessment of the three-phase voltage source converters(VSCs) especially in grid-connected ***, the sequence admittance is hard to calculate when the VSC is operating under unbalanced grid voltage conditions. In this paper, a simple and direct modeling method is proposed for a three-phase VSC taking the unbalanced grid voltage as a new variable for the *** coupling in the three-phase system can be calculated by applying the harmonic linearization method. The calculated admittance of three-phase VSCs is verified by detailed circuit simulations.

关键词： unbalanced grid voltage Three-phase voltage source converter Harmonic linearization Positive and negative sequence admittance Stability

Constructing an unbalanced structure toward high working voltage for improving energy density of non-aqueous carbon-based electrochemical capacitors

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Chinese Chemical Letters 2020年第3期31卷 903-908页

作者： Junsheng Zheng Nan Qin Liming Jin Xin Guo Chao Shen Qiang Wu Jim PZheng Clean Energy Automotive Engineering Center Tongji University(Jiading Campus)Shanghai 201804China School of Automotive Studies Tongji University(Jiading Campus)Shanghai 201804China Department of Electrical and Computer Engineering Florida A&M University-Florida State University College of EngineeringFL 32304United States

The energy density of non-aqueous carbon-based electrochemical capacitors(cEC)is mainly determined by the specific capacitance and operational voltage *** this study,we propose to construct an unbalanced structure to make full use of stable voltage range for improving energy *** stable voltage range is firstly carefully explored using cyclic *** an unbalanced carbon-based electrochemical capacitor(ucEC)is constructed with an optimized positive electrode to negative electrode weight ratio and voltage *** electrochemical performance is comprehensively investigated,including energy density,power density as well as cycle *** ucEC is capable to deliver an improved energy density up to 64.9 Wh/kg(1.4 times as high as a general cEC)without sacrificing the power density and cycle *** electrode properties after cycling are also analyzed,illustrating the change of electrode potential caused by unbalanced *** proposed structure demonstrates a great potential for improving the energy density at little cost of electrode design and cell configuration.

关键词： unbalanced electrochemical capacitor Non-aqueous electrolyte High working voltage Practical application High energy density

Flexible unbalanced control with peak current limitation for virtual synchronous generator under voltage sags

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Journal of Modern Power Systems and Clean Energy 2018年第1期6卷 61-72页

作者： Tianwen ZHENG Laijun CHEN Yan GUO Shengwei MEI State Key Laboratory of Control and Simulation of Power Systems and Generation Equipments Department of Electrical Engineering Tsinghua University Qinghai Key Lab of Efficient Utilization of Clean Energy New Energy Photovoltaic Industry Research Center Qinghai University

Virtual synchronous generator(VSG)is gridfriendly for integrating distributed generations(DGs)since it can emulate the operation mechanism of traditional synchronous generator(SG).However,the traditional VSG control strategy,which is mainly suitable for balanced voltage conditions,may lead to power oscillations,current unbalance and even overcurrent under unbalanced voltage *** overcome this difficulty,a flexible unbalanced control with peak current limitation for VSG under unbalanced operating conditions is *** on the basic VSG control algorithm,the control strategy integrates two novel control modules,which are current reference generator(CRG)and power reference generator(PRG).The proposed control strategy can flexibly meet different operation demands,which includes current balancing,constant active or reactive *** the injected currents are kept within safety values for a better utilization of the VSG power ***,the experimental platform is *** results demonstrate the validness and effectiveness of the proposed control strategy.

关键词： Virtual synchronous generator unbalanced control Current reference generator Power reference generator Voltage sags

An LCC-HVDC Adaptive Emergency Power Support Strategy Based on unbalanced Power On-Line Estimation

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Journal of Harbin Institute of Technology(New Series) 2020年第2期27卷 87-96页

作者： Congshan Li Jian Guo Ping He Yukun Tao Cunxiang Yang Youyi Wang School of Electrical and Information Engineering Zhengzhou University of Light IndustryZhengzhou 450002China School of Electrical&Electronic Engineering Nanyang Technological UniversitySingapore 639798Singapore

HVDC auxiliary power control can significantly improve the transient stability of AC/DC power *** HVDC adaptive emergency power support method based on unbalanced power on line estimation is proposed in this *** establishing the extended state equation of the system,the on line dynamic estimation of unbalanced power of the system was *** this basis,power support was realized based on the principle of the ladder *** optimal DC was selected by the power support factor,and the emergency power support controller was installed on the *** emergency power support method can realize dynamic optimal power support with minimized control *** three infeed HVDC system was built on *** simulation results show the effectiveness of the proposed method.

关键词： emergency power support unbalanced power extended state observer ladder increasing principle multi infeed HVDC system

unbalanced World:An Eco-feminist Approach to A Thousand Acres

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Journal of Literature and Art Studies 2020年第4期10卷 290-295页

作者： LIU Yuan Wuhan University of Technology WuhanChina

Jane Smiley is one of the most famous female novelists in the contemporary literary *** far,she has published more than a dozen novels,and the most famous one is her novel A Thousand Acres published in 1991.A Thousand Acres received extensive attention once it was published and won the Pulitzer Prize and the National Book Critics Circle Award in *** the same time,this work also laid the foundation of Jane Smiley in the contemporary American literary *** novel mainly depicts the agricultural life of the American *** A Thousand Acres,Smiley combines ecological themes with feminist issues,which coincides with the theoretical pursuit of ecofeminism that emerged in the 20th *** the perspective of ecofeminism,this paper interprets women’s struggle and revolt against nature under men’s control and suppression in a patriarchal society depicted in the *** also hopes to awaken people to realizethe supposedly harmonious relationship between them and nature,and between men and women.

关键词： ecofeminism nature female unbalanced

unbalanced Regressions and Spurious Inference

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Open Journal of Statistics 2012年第3期2卷 297-299页

作者： Daniel Ventosa-Santaularia Centro de Investigación y Docencia Económicas CIDE Mexico City Mexico

Spurious regression has been extensively studied in time series econometrics since Granger and Newbold’s seminal paper. Recently, it has been advanced that this phenomenon is due to a mistreatment of short-range autocorrelation in the residuals of the regression when at least one of the variables in a bivariate regression is stationary. HAC errors, feasible GLS and Cochrane-Orcutt-type procedures are then proposed to draw correct inference. Such a proposal should be cautiously considered, since nonsense inference might also be due to deterministic trend mechanisms, structural breaks, and long range dependence. In these cases, standard autocorrelation correction procedures would not solve the problem of spurious regression. We aim to make the later argument clear.

关键词： Spurious Regression Stationarity unbalanced Regression Unit Root