Comparative Study of Torque Production Mechanism in Rotor-PM and Stator-PM Vernier Machines

In recent years, permanent magnet vernier (PMV) machines have gained more and more research interest owing to their superior torque density. However, rotor-PM vernier (RPMV) and stator-PM vernier (SPMV) machines, differing in the position of PMs, exhibit significant differences in torque performance. To reveal the underlying cause, this study begins with an analysis of the phase characteristics of three basic parts: the armature, flux modulator, and PMs, with particular attention to the phase angles of the resulting air-gap flux density harmonics. Then, based on the Maxwell stress tensor (MST) method, the torque contributions of the dominant harmonics in RPMV and SPMV machines, such as thePath,Pmth, and (Pm+Z)th harmonics, are quantified to display their torque differences. The results indicate that torque in RPMV machines is primarily generated by thePmth harmonic, while both thePath andPmth harmonics contribute torque together in SPMV machines. In addition, the torque generated by thePmth harmonic in RPMV machines markedly exceeds that in SPMV machines. To verify these theoretical findings, two representative machines with the same winding pole-pair number and machine dimension are compared. Finally, a prototype of the RPMV machine is tested to confirm the accuracy of the analytical and simulation results.