Optimal design of a spoke-type permanent magnet motor with phase-group concentrated-coil windings to minimize torque pulsations

This paper proposes a multi-step design and optimization strategy to minimize torque pulsations in a spoke-type PM motor with phase-group concentrated-coil windings. Different from the conventional techniques that work on the motor itself, in the first step (interim model I), an auxiliary inner stator is adopted to suppress the torque pulsations. In the second step (interim model II), the optimization by using the Kriging method and genetic algorithm, is then applied to the auxiliary inner stator to further reduce cogging torque and torque ripple. In the third step (final model III), the harmonic injected current is utilized to suppress torque ripple by maintaining the required power, while the optimal input current waveform is optimized by the aforementioned algorithms based on the harmonic analysis of back EMF. As a result, the cogging torque and torque ripple of the final model are significantly reduced by 95.7% and 70.0%, respectively, when compared to those of the initial model.

I. Introduction

Spoke-type permanent magnet (PM) motors with a phase-group concentrated-coil (PGCC) winding have been examined to have the advantages of higher winding factor and copper packing factor, as well as the enhanced flux focus effects, thus for greatly improved torque and efficiency [1]. However, when designing for a single-airgap spoke-type PM motor with PGCC windings, it exhibits tremendous cogging torque and torque ripple. In this paper, a multi-step optimal design strategy, without optimizing the initial motor itself, is proposed to minimize cogging torque and torque ripple in a 5kW spoke-type PM motor with the PGCC windings.