Slot-Pole Combination Analysis of FSCW-PMVM on Magnetic Field Modulation Performance

The impact of slot-pole combinations on the magnetic field modulation performance of permanent magnet vernier machines (PMVM) is analyzed in this article. First, the working principle of PMVM is analyzed, slot-pole combination constraints are formulated, and a topology group is constructed. Then, the relationship between slot-pole combinations, modulation ratios, magnetic field modulation harmonics, and harmonic torque contribution is examined. Further, a design method for a multidegree of freedom modulator is proposed to maximize the torque output capacity. Due to the improved airgap permeance, the magnetic field modulation capability of low modulation ratio topologies is significantly enhanced, achieving a 40% increase in output torque. Thus, the high-torque PMVM could be realized with low pole pairs which eases manufacturing and control. Finally, a similar torque performance of the low modulation ratio machine 18s50p and the high modulation ratio machine 18s56p is successfully achieved by global parameter optimization. The two prototype motors are manufactured and tested to verify the correctness of the analysis.