Effect of Combination Between Stator-Slot and Rotor-Pole Numbers on the Performance of Multi-Phase Spoke-Type PM Motors for Vehicle Traction Applications

Abstract

Tangential Flux Permanent Magnet (TFPM) or Spoke-Type Permanent Magnet (STPM) motors are a competitive topology in vehicle traction applications due to high airgap flux and torque densities. In this paper, the effect of combination between the stator-slot and rotor-pole numbers on the performance of multi-phase STPM motors for electric vehicles (EVs) is presented. Three-, five- and nine-phase STPM motors are designed with different stator-slot number and rotor-pole combinations using Finite Element Method (FEM). The proposed designs consist of 12/16 and 24/32 stator-slot number and rotor- pole combination for the three-phase STPM motors referred as (3P-12/16) and (3P-24/32) respectively, 20/32 and 40/64 stator-slot number and rotor-pole combination for the five-phase STPM motors referred as (5P-20/32) and (5P-40/64) respectively, and 18/28 and 36/56 stator-slot number and rotor-pole combination for the nine-phase STPM motors referred as (9P-18/28) and (9P-36/56) respectively. The 2D Finite Element Models of all six motors were run for ac magnetic transient solution at the speed of 3000 rpm to analyse the back EMFs, the torque characteristics, the speed range, and other performance parameters of interests. From the Finite Element Analysis (FEA) results, all six motors have shown to have a high torque per rotor volume, and they produced a high torque density. Furthermore, the effects of phase number, combination of stator slot and rotor pole numbers are well noticeable on the speed range capability, toque quality, efficiency and power factor of the STPM motors analysed in this paper. The results clearly evidenced that the highest peak torque of ± 243 Nm was achieved by the 5P-20/32 and 9P-18/28 motors, and the lowest cogging torque of ± 1.2% was realized by the 9P-36/56 motor, followed by the 9P-18/28 motor which has attained a low cogging torque of ± 1.92%. The 9P-18/28 motor had the highest efficiency of about 94.856%, and a wide speed range. The 9P18/28 motor is found to have an outstanding performance by accomplishing less torque ripple content, low cogging torque, high average torque, high torque per rotor volume, high peak power and torque, high average torque, high efficiency, and wide speed range capability.