Comprehensive Analysis and Practical Design Guidelines for High-Performance Surface Permanent Magnet Vernier Machines With Halbach Array

Permanent magnet vernier machines (PMVMs) exhibit the feature of high torque density, which makes them a compelling candidate for gearless direct-drive applications. However, the long end winding, caused by overlaps and large coil pitch, significantly reduces the efficiency and torque density for motors of short stack length. This paper investigates the performance metrics of PMVMs with Halbach magnet array for different slot/pole combinations and winding layouts (short-pitch, fractional-slot, odd number of slot or pole). Motor configurations with various winding layouts are analyzed and the performance metrics are modeled with theoretical method, including torque ripple and radial force. Some promising structures are selected according to the theoretical analysis. The performance comparison is based on winding configuration, torque, optimal PM parameter and physical air gap length. Performance metrics are then discussed in detail according to different operating conditions and motor size. Finally, a balanced performance prototype is fabricated to verify the assumptions, and the specific frequency current injection approach is proposed to reduce the torque ripple resulting from the manufacturing tolerance.