Smooth Transition of Multimode Synchronous Modulation for IPMSM Sensorless Drives in Rail-Transit Applications

In rail-transit application, the multimode synchronous pulsewidth modulation (PWM) strategy is widely used to achieve better control performance in middle- or high-speed region, which brings challenges to sensorless control that can enhance the system robustness. Within the synchronous modulation, a regular 21-pulse space vector PWM and a selective harmonic elimination PWM are selected to analysis the influence of PWM modes transition on an interior permanent magnet synchronous machine (IPMSM) sensorless drives. When the carrier ratio is less than 10, as the transition occurs between different PWM modes, the amplitude and phase of low-order harmonics change obviously and affects the position estimation accuracy severely. Here, a fast central ${60^\circ }$ transition method for three-phase pulses is designed, then the smooth transition can be achieved in half fundamental period and the estimated position fluctuation is eliminated. In addition, small changes in the fundamental-frequency results in frequent transition between different PWM modes, which deteriorates the sensorless control performance. A frequency hysteresis zone is set and the effect of load-disturbance is also considered. Finally, the feasibility of the proposed sensorless method is verified on a 3.7-kW IPMSM drive platform.