Research On Hybrid Method Of SVPWM And SHEPWM Applied On Three-level Topology-based PMSM Traction System

Multi-level inverters have been widely applied in power drive field of high-voltage large-capacity AC drive system.Since the limitation of switching loss and heat dissipation of power device,it is better to limit the switching frequency to no more than 1000 Hertz.Meanwhile,in the whole speed range of traction system,it is difficult to satisfy the demand of quick response in low-speed condition and low loss in high-speed condition through a single method of modulation.In order to solve these problems,permanent magnet synchronous machine(PMSM)is employed as traction motor.Neutral-point-clamped(NPC)three level topology,id=0 control strategy and hybrid method of SVPWM and SHEPWM is proposed and adapted in this paper.The main contents of this paper are as follows:First of all,sector calculation,vector selection and calculation of duty cycle was calculated while the computational method and initial value of selective harmonic eliminated nonlinear equations was analyzed.Newton iteration method was applied to calculate the switching angles based on different values of modulation ratio and numbers of switching angle.The hybrid method of SVPWM and SHEPWM based on three-level topology is studied and simulated by MATLAB/SIMULINK,simulation results verify the availability and feasibility of the proposed control method.In addition,the smooth operation method based on different modulation methods and same modulation method with different numbers of switching angles was analyzed.A method of realizing the smooth operation included different modulation methods and same modulation method with different numbers of switching angles in PMSM traction system was proposed through analyzing the harmonic characteristic of phase current.This method unify the switching point based on same modulation method with different numbers of switching angle and different modulations into the current zero-crossing point which is easy to realize in engineering.id=0 control strategy is chosen for this system through analyzing.These methods were simulated by MATLAB/SIMULINK.Simulation results of SVPWM show that quick response in low-speed condition can be achieved through this method.Simulation results of hybrid method show that having N switching angles per quarter cycle,up to N-1 harmonics can be eliminated and low loss characteristics of current can be achieved in high-speed condition compared to SVPWM modulation method.At last,in order to carry out studies about PMSM traction system based on three-level topology,the software of hybrid method of SVPWM and SHEPWM applied on three-Level topology-based PMSM traction system is completed by CCS.The experimental results show that this proposed method can satisfy the demand of quick response in low-speed condition,low loss in high-speed condition and the smooth transition of speed and torque during modulations or number of angles switching,N switching angles per quarter cycle,up to N-1 harmonics can be eliminated.Beside,the smooth operation included different modulations and same modulation with different numbers of switching angle in PMSM control system can be achieved.