Torque Pulsation Reduction During Magnetization in Variable Flux Machines

Abstract

This paper proposes two methods to minimize the pulsating torque during magnetization in a variable flux - permanent magnet synchronous machine (VF-PMSM). The VF-PMSM is demagnetized and remagnetized by injecting a current pulse to achieve the high speed and high torque requirements. During demagnetization and remagnetization, a d – axis current pulse is injected to change the magnetization state (MS). These MS changing current pulses will change the magnet flux linkage based on the amplitude of the pulse. However, the injected d – axis current abruptly changes the magnet torque as well as reluctance torque and results in a pulsating torque. Since the remagnetization current is much higher than the machine rated current, the pulsating torque is more severe during the remagnetization process. Thus, it is preferred to magnetize the magnet at zero speed and unloaded conditions. To solve this problem, a q – axis current reference during the remagnetization is determined by two different methods: voltage limit method and load torque method. The derived q – axis current reduces the torque pulsation during the remagnetization. The effectiveness of the proposed scheme is experimentally verified on a manufactured VF-PMSM prototype.