Design and Analysis of a Modular Permanent Magnet Vernier Machine for Electric Vehicle Application

In this manuscript, a modular dual-rotor axial-flux permanent magnet vernier machine was designed and analyzed for the electric vehicle (EV) drive system, namely the dual-rotor axial-flux aligned permanent magnet vernier machine (DR-AFAPMVM). By adopting the dual-rotor topology, the machine can achieve higher torque density than the single-rotor one due to the modular multi-layer double flux filed design in both sides. In order to highlight the advantages of the proposed machine, two types of one-stator one-rotor vernier machines with surface-mounted and spoke-type magnets were compared firstly, which verified that spoke-type magnets had the so called "flux focusing" ability to increase air gap flux density. Compared to the above single air gap machine, the axial-direction electromagnetic force of rotor in the double-stator machine was largely reduced, which was significant for the axial-flux machine. Furthermore, in order to increase the electromagnetic torque density significantly, two types of three-stator two-rotor machines were designed, where comparative evaluation of the proposed DR-AFAPMVM and the dual-rotor axial-flux unaligned permanent magnet vernier machine (DR-AFUPMVM) were performed by using finite element analysis. In detail, a flux calibration coefficient considering magnet air gap leakage flux and radial direction leakage flux was proposed to contribute to the analytical model. Performance of the proposed machines was compared by both analytical method and finite element analysis, which verified the accuracy of the improved analytical method. Finally, the performance of DR-AFAPMVM, such as efficiency map, speed range and operation points, was verified by simulation to illustrate its drive ability in EV application. © 2021 Chin. Soc. for Elec. Eng.