Research On Harmonic Treatment Of Electric Vehicles Access To Micro-grid

The shortage of the fossil energy resources and environmental pollution have promoted the rapid developments of renewable energy sources,such as wind power,photovoltaics and electric vehicles(EVs).However,in distribution network,the uncontrollability of distributed generations(DGs)affects the power balance,and the charging of EVs causes harmonic pollution.Microgrid(MG),which integrates DGs with EVs to form an autonomous and self-control system,not only absorbs distributed energy but also ensures power supply reliability of EVs charging,and improves the stability and economy of distribution network.This paper studies harmonics caused by EVs access to MG and designs a multi-functional energy storage inverter that can realize the synchronous treatment of power fluctuations and harmonics.It has certain theoretical research and engineering instructional significance.Firstly,the characteristics,principles and mathematical models of wind turbine generation system(WTGS),photovoltaic generation system(PVGS)and energy storage system(ESS)in MG are studied;the structural model of electric vehicle chargers(stations)is established through introducing nonlinear resistance with negative impedance characteristics.According to the actual data collection of wind speed and light radiation in Xinzhou,Shanxi,the model on MG is built by PSCAD/EMTDC.The changes of voltage and current in WTGS,PVGS,single and multiple EVs charging system,are simulated respectively and analyzed on harmonic simulation.Secondly,the compensation principles and design schemes of passive filter and active power filter(APF)are summarized.Mathematical model of power systems in different distortion states are established.Five harmonic detection schemes are studied:p-qtheory andi_p-i_qtheory based on instantaneous reactive power theory,FBD theory,inproved FBD theory,and CPT theory.Through the analysis of mathematical theory,it is concluded from the comparisons of harmonic current decomposition and detection accuracy that the harmonic detection scheme based on CPT theory is more effective when current distortion is serious.Multiple electric vehicle charging models are simulated by PSCAD/EMTDC to verify the correctness of related conclusions.Thirdly,harmonic current amplification effect of parallel active power filter(P-APF)participating in harmonic compensation system of electric vehicle charging station(EVCS)is analyzed.And the equivalent circuit of harmonic compensation system is established.Based on circuit theory analysis,mathematical expressions of the harmonic current amplification effect of P-APF with system current detection control and load current detection control is deduced respectively.The suppression measures on harmonic current amplification effect are proposed.The effectiveness of these proposed methods is verified by PSCAD/EMTDC simulation examples.Finally,according to the similarity of APF topology,a multi-functional energy storage inverter based on CPT detection theory is designed.The synchronization control principles on power fluctuations and harmonics of inverter are analyzed,and the rated capacity of energy storage is determined.Through the research on current repeated control,an improved PQ control strategybasedonfeedforwardrepeatitivecontrolisproposed.PSCAD/EMTDCsimulationexamples verifytheeffectivenessof multi-functional energy storage inverter and its control strategy.