High Torque Density Spoke-Type Ferrite Permanent Magnet Synchronous Machine Assisted by Rare-Earth Magnets for Traction Applications

This paper proposes a new high torque density ferrite spoke-type permanent magnet synchronous machine assisted by rare-earth magnets to improve the utilization of rare-earth magnet and reduce the material cost. The topology of the proposed machine and design is introduced firstly. The influence of different key rotor design parameters on torque performance is investigated to maximize the average torque. Some design techniques are adopted to reduce the torque pulsation of the proposed machine, including rotor pole shaping and rotor skewing. The electromagnetic performance of the proposed design is verified and compared to a conventional spoke-type ferrite permanent magnet machine. The torque capability can be enhanced significantly by using rare-earth magnets assistance. Finally, the torque capability of the proposed design is compared to conventional interior permanent magnet traction motor using high-strength rare-earth magnets only. The mass of rare-earth magnet reduces from 1.23kg to 0.48kg to produce the same average torque. The utilization of rare-earth magnets extremely enhances and the material cost significantly reduces as well. The proposed machine is an attractive and practical alternative for electric vehicle traction applications with high torque density and low-cost features.