Scaling Effect on Electromagnetic Performance of Surface-Mounted Permanent-Magnet Vernier Machine

This article investigates the impact of scaling on the electromagnetic performance of surface-mounted permanent-magnet Vernier (SPM-V) machines with a main focus on open-circuit induced Electro Motive Force (EMF). Three different power ratings, i.e., 3 kW, 500 kW, and 3 MW, have been chosen for this article. For each power rating, the SPM-V machines are analyzed for different slot/pole number combinations to compare their optimal performance with a conventional SPM machine. Step-by-step development of an analytical equation is presented for the prediction of induced EMF taking into account the interpole leakage of rotor permanent-magnets. 2-D finite-element analysis (FEA) has been used to validate the analytical equation across different power ratings. The analytical equation is thereafter utilized to study the influence of different geometric parameters on the performance of the SPM-V machines. It reveals that the back EMF and torque of SPM-V machines, for a given normalized pole pitch (rotor pole pitch to magnetic airgap length), are unaffected by the increase in airgap length due to scaling. However, the power factor of SPM-V, unlike the conventional SPM, reduces significantly with the increase in electrical loading due to the scaling effect. The analytical model for induced EMF and the 2-D FEA predicted results are validated by experiments using conventional SPM and SPM-V machine prototypes.