Research Of Multi-mode Pulse Width Modulation Of AC Speed Regulating System Based On SHEPWM

In the recent years,PMSM have been widely used in high-power rail traction systems because of their advantages of simple structure,high reliability,and wide speed range.However,due to the limitations of switching losses and heat dissipation conditions,the switching frequency of power devices in traction system is usually low,making the system carrier wave ratio low.In this case,if using the single modulation mode,the harmonic content of the inverter voltage will be higher,especially the Low-order harmonics will have a greater impact on the performance of the traction motor and equipment.Therefore,the multi-mode modulation method is very important to reducing the harmonic content of the traction system.This article takes the permanent magnet synchronous motor as the research object,the multi-mode pulse width modulation method using asynchronous space vector pulse width modulation(SVPWM)at low frequencies and synchronous segment Selective Harmonic elimination pulse width modulation(SHEPWM)at medium and high frequencies is designed.The vector control system of permanent magnet synchronous motor is constructed based on the maximum torque per ampere control,and the harmonic characteristics of the system are simulated and analyzed.In order to solve the SHEPWM nonlinear equations,this paper first uses GA and PSO algorithm to solve the problem to avoid the traditional numerical methods rely too much on the initial value.Secondly,for the premature convergence problem of GA,an improved GA is designed.This method improves the accuracy of the optimal solution by switching the search mode.What’s more,based on the advantages of GA and PSO,a hybrid GA-PSO algorithm was designed.The hybrid algorithm also has the advantages of GA’s strict population evolution mechanism and PSO’s fast convergence speed by simulation analysis.In addition,in order to solve the problem of switching between different frequency bands in the multi-modulation mode.This paper analyzes the smooth switching conditions and derives the switching phase angle that satisfies the conditions to achieve a smooth transition between multi-mode pulse width modulation.Based on the MATLAB / Simulink platform,this paper builds a simulation model of the multi-mode pulse width modulation method for permanent magnet synchronous motors.The simulation results verify the effectiveness of multi-mode modulation in terms of motor stator current,torque,dynamic response performance and current harmonic content.In addition,each switching point has a smooth transition,which verifies the correctness of the theory.