| In the control system of the high power AC electrical locomotive, the high switch freq of the inverter is nearly some hundreds Hz, for the limitation of the element switch freq and heat elimination. Because of the large-scale change of the locomotive speed, the carrier ratio has a large area. Under this situation, the multi-mode PWM effectively improves the output of the inverter and meets the need of operation on low switch freq and large speed scale. In addition, in order to improve the control performance of the motor, the vector control has been commonly used, so the control method based on the Multi-mode PWM modulation and vector control, not only meet the need of high speed and low switch freq, but also improve the output of the torque and control performance.This paper research the vector control of Multi-mode PWM modulation based on low switch freq. For the optimization PWM, this paper emphatically point out the principle and realization method of selected harmonic elimination PWM, this paper also instruct the calculation method of switch angle based on the Matlab and curve fitting. Based on the control of rotor flux amplitude and its angle, it can achieve accurate control of the electromagnetic torque under different modulation methods or inaccurate parameters which can lead to incorrect field orientation. This paper builds the 7.5KW asynchronous motor experiment table, and verifies the Transition strategy of SHEPWM on open loop VVVF system by simulation and experiment. This paper also generates the pulse of three-level SHEPWM by DSP. This paper also builds the vector control model based on Multi-mode PWM by Matlab/Simulink, and carries out experiment on the machine experiment table by TMS320F28335. Simulation and experimental results are given to verify the validity of the proposed theoretical analyze.
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