Synthesis of fractional-slot vernier permanent magnet machines

Vernier permanent magnet (VPM) machines have gained growing interest in recent years due to several advantages, including high torque density and simple mechanical structure. This paper presents a thorough investigation on the nature of fractional slot vernier permanent magnet (FS-VPM) machines with regular stator topology. Through analytical derivation, the configuration and performance of two winding types, i.e., fractional slot concentrated winding (FSCW) and FS winding with two-slot coil pitch are evaluated for VPM machines. The FS winding VPM machine with two-slot coil pitch is newly proposed, and turns out a promising candidate in direct-drive application with competitive torque density and improved power factor. All the electromagnetic performances are calculated and compared through finite element analysis (FEA).