A New Perspective on the PM Vernier Machine Mechanism

Permanent magnet vernier (PMV) machines have attracted more and more attention for their merits of high torque density and simple structure. Also, the principle of electromechanical energy conversion is the most common way to investigate the PMV machine by calculating back electromotive force and electromagnetic torque. In this paper, a new perspective on the mechanism of PMV machines based on the Maxwell stress tensor method is presented to deepen the insight into the reason why the force on the rotor of a PMV machine is larger than that of an surface permanent magnet (SPM) machine. Based on the finite element analysis (FEA) method, three machines with exactly the same rotor are analyzed and compared, namely 24-slot/20-pole SPM, 12-slot/20-pole surface PMV, and 6-slot/20-pole split-tooth PMV machines. The radial and tangential flux densities and force distributions along the airgap are illustrated. The influence of pole ratio on the performance of PMV machines is also investigated. It is shown that the improvement of tangential flux density in the PMV machine plays a primary role in the higher torque density, which shows a promising way to improve the torque density of machines.