Quantitative Comparison of Two Typical Field-Modulated Permanent Magnet Machines: Unidirectional Field Modulation Effect versus Bidirectional Field Modulation Effect

Field-modulated permanent-magnet machines (FMPMs) have been becoming prominent candidates for direct-drive applications due to their high torque densities. The purpose of this paper is to compare the performance and characteristics of two typical FMPMs quantitatively, namely, permanent-magnet vernier machine (PMVM) and dual-permanent-magnet-excited machine (DPMEM). The former machine works on the unidirectional field modulation effect (UFME), while the latter one operates with the bi-directional field modulation effect (BFME). The field distributions in two machines, as well as their torque capabilities, Back-EMFs, power factors, power losses and efficiencies are calculated by using finite element method (FEM). The results indicate that DPMEM takes notable advantages over PMVM.