Effects of Magnet Shape on Torque Capability of Surface-Mounted Permanent Magnet Machine for Servo Applications

This paper proposes three new methods to improve torque capability for the surface-mounted permanent magnet machine in a servo system. The key to the proposed methods is to explore various magnet shape designs via sufficient attempts of harmonic combinations. Such techniques serve to avoid a significant drop in the average torque when reducing the torque ripple. The effect of analytical harmonic compensation on output torques is investigated by the finite-element method, and diverse torques are evaluated by a predefined objective function, which as an evaluation criterion of the torque performance is established. Comparisons of the proposed and the existing methods are carried out, showing the higher average torque and the lower torque ripple of the proposed method. Finally, a prototype machine designed with one of the proposed methods is fabricated and tested for validation.