Average torque distribution strategy for low speed operation of three-phase SRM with low-resolution rotor position sensor

Abstract

An average torque distribution (ATD) strategy for low-speed operation of three-phase switched reluctance motor (SRM) with hall-effect rotor position sensor, as well as a calibration method for the sensor, are proposed. The sensor can only detect unaligned and aligned positions of all phases, and these positions evenly divides an electrical cycle into six position sectors. These positions are fully utilized by shaping a phase current as a four-step waveform and controlling motor average torque in each sector. In commutation sectors, a motor average torque reference is distributed into two phase average torque references. The distribution is optimized offline to minimize torque ripple and copper losses based on the phase torque characteristics. Compared with the torque control schemes using square-wave current references, the proposal can greatly reduce torque ripple without or with only a small penalty on copper losses. Based on difference among the aligned position detection errors of the hall-effect sensor, a calibration procedure for the sensor is developed. This procedure can ensure the absolute value of the average of these errors less than the maximum difference among these errors without high-resolution position signal as reference. Experimental results demonstrate effectiveness of the proposed ATD strategy and the calibration.