I. Introduction
Recently, a surface-mounted permanent-magnet vernier machine (SPMVM) has been gaining more attention due to the features of high torque density and low torque ripple. In the SPMVM, the lower spatial harmonic of the armature magnetic field is modulated into the higher spatial harmonic by flux modulation poles (FMPs), which are formed on the stator [1]. Then, the resulting higher spatial harmonic produces the torque by synchronizing with the rotor PM magnetic field of the same spatial order. Thus, many researchers of the SPMSM have focused on improving the torque density based on the magnetic-field modulation.