Research On The Influence Of Pulse Width Modulation On Efficiency Of Electric Traction System

In high-power traction drive system,considering the constraints of switching losses and heat dissipation conditions,the switching frequency of the inverter should not exceed 1kHz.When the carrier ratio is relatively low,the low-order harmonic content of the output voltage waveform of the traction inverter that is not conducive to the operation of the motor will significantly increase,so that the harmonic loss of the motor increases,and the efficiency of the motor decreases.Different pulse width modulation strategies have different effects on traction inverter and motor losses.In this paper,the traction inverter-motor system is used as the research object to study the influence of pulse width modulation strategy on the system loss.The minimum loss modulation strategy is adopted to improve system efficiency.This paper studies the two-part loss of traction inverter-motor system.Firstly,the calculation methods and their mathematical models of several iron loss are analyzed.The equivalent circuit of the motor and equivalent resistance model of iron loss are studied.Based on the harmonic equivalent circuit calculation model of the motor loss is established,and the mathematical formulas of harmonic iron loss and copper loss are derived.Secondly,the research status of the inverter loss is described,and the loss of the two-level inverter is studied.The calculation model of switching losses and on-state losses is given,and the main factors of influence of the inverter losses are discussed.Finally,in view of the shortcomings of the traditional space vector pulse width modulation strategy to reduce the switching loss,the zero vector cross allocation method is used to optimize it,and four kinds of optimization strategies are compared and analyzed to reduce the switching loss and the harmonic content.In the Matlab/Simulink software platform,the loss model of the traction inverter-motor system is built.Then the simulation analysis of the SVPWM optimization strategy is completed,and the correctness of the theory and the switching loss model is verified by the simulation results.By comparing the simulation data,the effects of different SVPWM modulation strategies on inverter switching losses and motor harmonic losses are analyzed.In addition,based on the study of segmented synchronous switching under segmented synchronous modulation,several switching point selection schemes are designed.Through simulation data,the total system loss under different PWM strategies is quantitatively analyzed.From the point of the optimal total loss of the system,the selection of switching points and modulation strategies under different modes is given in order to improve the energy utilization rate of the inverter and the motor.