Closed-Loop Current Control Extended to Six-Step Operation With Varying Sample-Control Frequency for PMSM Traction System

Abstract

Six-step operation can enhance the torque output capability and maximum power utilization and decrease the switching frequency for the PMSM traction system. The main problems of closed-loop current control extended to six-step operation are voltage error disturbances from current controller windup and low-order harmonics current under the low ratio of switching frequency to fundamental frequency. The problem of low-order harmonics current is alleviated by the hybrid synchronized PWM (HSPWM) schemes, but the sample-control frequency is time-varying with speed and fluctuated to keep synchronization. A complex vector current controller (CVCC) with time-varying and stable active resistances to improve the disturbance rejection, including delay time compensation and anti-windup, is designed to be combined with HSPWM. The accurate torque control and closed-loop current control extended to six-step operation are realized. Simulations and experiments are carried out to validate the effectiveness of the proposed control scheme.