Research On Harmonic Characteristics Analysis And Harmonic Suppression Measures Of Electric Vehicle Charging Station

With the development of electric vehicles,the construction scale of charging stations is also expanding.The charging equipment of charging stations contains a large number of power electronic components,which will generate a large number of harmonic currents and reduce the power quality of the power system.Therefore,it is particularly important to carry out research on the harmonic characteristics of charging stations and take certain suppression measures.The structure of electric vehicle charging stations,the types of chargers,and the charging methods are analyzed.The three-phase uncontrollable rectifier chargers are selected as research objects.Based on the analysis of the charger structure,the equivalent circuit of the charger is obtained,and a simulation model of a single charger and the entire charging station is built based on MATLAB / Simulink.It can easily simulate and analyze the complete process of the charging cycle of the charger and the charging station.The harmonic characteristics of the charger are theoretically analyzed.Based on the simulation model,the operation of a single charger and multiple chargers are analyzed,the variation law of harmonic currents and total harmonic distortion rate in each charging cycle are studied;The phenomenon of harmonic cancellation when multiple chargers are running at the same time is analyzed.The variation rule of the size of harmonics of charging station and the total harmonic distortion rate with the number of chargers are obtained.In view of the harmonic characteristics of electric vehicle charging stations,Active Power Filter(APF)is selected as a measure to suppress harmonics,and the mathematical model of APF is derived..Traditional Hysteresis control as current tracking control will lead to insufficient compensation capacity or excessive compensation current.Aiming at this deficiency,a variable loop wide hysteresis current control based on fuzzy theory is designed.The difference between the command current and the actual current and its rate of change are used as input,and the ring width is modified in real time by the fuzzy controller to realize the tracking control of the current.Due to the shortcomings of traditional PI control such as large overshoot and poor robustness,it is optimized.Sliding mode PI composite control method is used to control the DC-side voltage.The switching surface of sliding mode control and the output function of PI parameters are designed.The simulation results show that the proposed variable-loop-wide hysteresis current control based on fuzzy theory can track the command current changes better than the fixed-loop-width hysteresis control.It also can reduce the switching frequency of the switching device.The control effect of the DC voltage under three operating conditions(reference voltage and charging station load remain constant,reference voltage changes,charging station load changes)is analyzed.Compared with the traditional PI control of the DC side voltage,the sliding mode PI composite control strategy is adopted to make the DC side capacitor voltage response faster and more robust,and the harmonic suppression effect of the charging station is better.