Research On Harmonic Suppression Measures Of Electric Vehicle Charging Stations Based On Three-level APF

The construction scale of electric vehicle charging stations continues to expand with the popularity of electric vehicles,and the charging equipment o f charging stations contains a large number of nonlinear power components.During the working process,a large amount of harmonic currents will be generated,seriously affecting the power quality of the power grid and the safety of electrical equipment.On the basis of analyzing the harmonic characteristics of charging equipment,this article proposes the application of three-level APF to improve the power quality of charging stations,and conducts research on its harmonic detection and control strategy.Th e feasibility of the proposed method is verified through simulation.The specific content includes:Firstly,taking a three-phase uncontrollable rectifier charger as the research object,the equivalent model of the charger was obtained by analyzing its in ternal structure;analyze the harmonic characteristics of the charging device and build a simulation model of the charger.Simulate a complete charging process of the charging device,and obtain the time-varying resistance R_c,output power P₀,and the variation law of each harmonic current with charging time.Secondly,the mathematical model of three-level APF was derived,and the i_p-i_q method was used as the harmonic detection method for APF.A filter based on the integral mean principle was proposed to address the shortcomings of the low-pass filter in the i_p-i_q method,which cannot balance real-time performance and accuracy.Through simulation verification,the i_p-i_q detection method can accurately detect harmonic currents in the power grid under differen t voltage conditions,and the integrated mean filter has better real-time performance and more thorough filtering of harmonic components compared to traditional low-pass filters;in view of the shortcomings of PI control that can not achieve accurate track ing of command current and rapid and stable control of DC side voltage when the load changes suddenly,the traditional double closed loop PI control strategy is improved by introducing repetitive control in the inner current loop control and Sliding mode control in the outer voltage loop control to achieve accurate tracking of command current and rapid stability of DC side voltage.The simulation results show that the improved control strategy has improved the steady-state and dynamic performance of the system compared to the traditional PI control strategy,with higher harmonic compensation accuracy and faster DC side voltage response speed;adopting SVPWM modulation technology and introducing adjustment factors to control the action time of each small vect or,achieving balance of midpoint potential.Finally,the parameters of the charging station system and the main components of the APF were designed,and the harmonic suppression results during the operation of a single and multiple chargers were analyzed in the simulation platform.The simulation results showed that after the three-level APF was put into operation,the grid current waveform was good,and the average total harmonic current distortion rate was about 3%,meeting the demand for harmonic suppression in daily work of the charging station.