Torque characteristics of dual stator permanent magnet vernier machine with different pole/slot combinations

Traditional direct-drive permanent magnet synchronous machine (PMSM) suffers from large bulk and complex topology structure, which extremely limits its industrial applications. As a novel embranchment of PMSM, PM vernier machine (PMVM) incorporates the magnetic gear effects into conventional PMSM producing high torque at a relatively low speed, which is desirable for direct-drive applications. Recently, the specific magnetic field modulation effect and high output torque ability have been subtly incorporated into PMVM, which simultaneously enables the sinusoidal back-EMF waveform, high power density, efficient thermal dissipation. However, the torque characteristics of PMVMs with different pole-slot combinations and gear ratios have not been studied systemically as yet. In this paper, two representative dual stator PMVMs are designed to analyze the torque characteristics in detail with particular emphasis on the dominant influence of pole-slot combinations. In addition, gear ratio selecting is also investigated through the analysis of the electromagnetic characteristics of the designed PMVMs, which provides further unique insights into the design and optimization of PMVMs.