A New Vernier Machine With Compensatory Permanent Magnet Array

Vernier machines (VM) are widely used in direct drive field for its simple structure and high torque density at low operation speed. In order to increase torque quality furtherly and reduce the cogging torque and torque ripple, pole-shaping has been an alternative approach applied in VM. However, pole shaping brings manufacturing difficulty, which limits the development of pole-shaping in machine design. A new VM with compensatory PM array (CPMVM) is proposed, which can provide high quality torque production. The compensatory PM array consists of several PMs with different thickness, which is used to optimize the airgap flux density for high quality torque. Compared to the conventional pole-shaping, the proposed machine can achieve high sinusoidal airgap flux density distribution without increasing equivalent airgap length in magnetic circuit. The proposed CPMVM and the conventional VM are designed sharing the identical key design parameters and optimized by multi-objective evolutionary algorithm. The back electromagnetic force and torque production of the designed machines are analyzed using finite element analysis (FEA). The FEA-predicted results indicate that the proposed CPMVMs exhibit good inhibitory capacity for torque ripple and have high PM utilization.