A Novel Dual Three-Phase Permanent Magnet Synchronous Motor With Asymmetric Stator Winding

Although three-phase permanent magnet (PM) motors are dominant in industry, multi-phase PM synchronous motors present higher torque-to-weight ratios, better efficiency, and low torque ripple compared with three-phase conventional PM motors. These features make fault-tolerant multi-phase PM motors become attractive for safety-critical applications. In this paper, a novel PM multi-phase motor design with a dual three-phase asymmetric stator winding is proposed. The winding structure of the proposed motor is unconventional due to selected slot-pole combinations. Therefore, an asymmetric winding is needed. The detailed finite-element analysis of the proposed motor and a performance comparison between the conventional integer-slot (72-slot/12-pole motor) with symmetric winding and the unconventional fractional-slot (78-slot/12-pole motor) PM motors with asymmetric windings is performed to see the benefits of the proposed motor. It was shown that the novel unconventional multi-phase PM motor has excellent torque quality and slightly higher torque density levels.

I. Introduction

After the development of the fault-tolerant permanent magnet (PM) motor drives, a growing interest has been shown to multi-phase (phase number greater than 3) PM machines in special applications. Although three-phase motors have a broad market in industry, multi-phase PM synchronous machines offer higher torque-to-weight ratios and power densities, and better efficiency compared with three-phase PM motors. Moreover, increasing the phase number by keeping the input voltage and power the same decreases the per-phase current. Thus, it helps to reduce the thermal stresses on power devices and provides the employment of smaller converters. Most importantly, reliability and redundancy are the key features for multi-phase machines with multiples of three, so that the machine can continue to operate even with one or more unhealthy stator winding sets [1]. These features make the fault-tolerant multi-phase PM motors become more attractive for safety-critical applications, such as space, traction, military, and so on.