Research On Harmonic Of Electric Vehicle Charging Station

Electric vehicle is an important means to solve the problem of energy crisis and environmental pollution,also is the new direction of automobile industry development in the future.As the point connecting large-scale distrbuted EVs and power grid,the chargers with nonlinear load characteristic would produce a large amount of harmonic current into the power system.And these harmonic current will result in waveform distortion and affecting power quality.Hence,carrying out the research on harmonic of electric vehicle charging station has theoretical and practical significance.Building a reasonable harmonic model of chargers is the valid approach to research the harmonic of electric vehicle charging station.And the key to analyse the harmonic model is to study the harmonic characteristics of the process of power battery charging.Firstly,the harmonic coupling mathematical relationship between AC side and DC side of converter is deduced in detail in the frequency domain.Then through regarding the converter as a two-port network based on hybrid parameters,establishing a mathematical relationship of voltage and current in each converter stage,modulating with switching function and solving with Fourier transform,the hybrid parameters matrix are derived.Then a new fully coupled harmonics model of converter is proposed,as well as its reduced form.Then analysing the equivalent circuit of chargers deeply,the power converter of charges is equivalent to a discrete and nonlinear time-varying resistance which has the chage characteristics of power battery.When the parameters of chargers and transformer,the harmonic model of chargers is got in each period.Each matrix corresponding based on hybrid parameters could be calculated with the value of resistance one by one in each period.Thus the harmonic model of single charger in charging station is built,which could describe the harmonic characteristic of the process of charging.Time-domain simulation model in Simulink verifies the accuracy and applicability of the harmonic model.Lastly,the harmonic characteristics in a charge cycle of several chargers in charging station are explored.And the rationality about the charge mode of "interval input" will reducing the harmonic current effectively is analysed briefly.