| With the development of electric vehicles,the construction scale of electric vehicle charging stations is also expanding.However,as a high-power power electronic load,the State Grid has strict requirements for harmonics in charging stations.Power factor(PF)and harmonic distortion rate(THD)of charging stations are important indicators to measure harmonics of charging stations.Charging stations with too low power factor and too high harmonic distortion rate are not allowed to be connected to the grid.Therefore,it is particularly important to control the harmonics of charging stations,improve the harmonic pollution to the power grid,and take effective restraining measures.The power factor and harmonic distortion rate of the charging station are affected by the power factor and harmonic distortion rate of a single charging pile.At the same time,it is also related to the working state,load size and other factors when multiple charging piles work at the same time.In order to improve the power factor of the charging station and reduce the harmonic distortion rate,the following two aspects are studied.The first is to improve the power factor of a single charging pile and reduce the harmonic distortion rate.The charging pile structure with source power factor correction is adopted.The distortion of the input current is reduced and the input current follows the phase change of the input voltage by means of average current method and double closed-loop PI control of voltage and current.The second is to synchronously start each charging pile through orderly control,so that the same harmonics generated by multiple charging piles can be maximized to offset each other when superimposed,thus reducing the total harmonic distortion rate of the charging station and improving the power factor.The controller of orderly start adopts ARM-STM32 microcontroller.By sampling the working condition and PWM wave of each charging pile,the PWM wave synchronization between the starting of charging pile and the working charging pile is controlled.In order to verify the effectiveness of the control strategy,the simulation of the control strategy is carried out in the MATLAB/Simulink simulation environment.The simulation results show that the power factor of single charging pile and charging station reaches more than 0.998.The hardware circuit design and software programming of the front stage AC-DC of the charging pile are completed.The experimental results show that the power factor of the front stage rectifier circuit of a single charging pile reaches 0.96.The comparison and verification of the equivalent charging station consisting of three AC-DC parts of the front stage of the charging pile are carried out.The total power factor of the charging station is at least 0.92 in the case of disordered start,and at least 0.96 in the case of ordered start.The power factor of ordered start is significantly improved than that of disordered start.The experimental results verify the correctness of the theoretical derivation and the effectiveness of the control strategy. |
