Mitigation of torque ripple in interior permanent magnet motors by optimal shape design

Optimal shape design of an interior permanent-magnet (IPM) synchronous motor can substantially reduce its torque pulsation. However, the shape design variations should be feasible and practical. We report on an optimal shape design obtained by drilling small circular holes in the rotor. We found that an optimal location and radius of the holes effectively suppresses the torque pulsation of the IPM drive for various loads under steady-state conditions. The optimal design at rated load is considered as the final design. We use a transient finite-element analysis that is coupled with motion and adequate electric excitation for optimization purposes. An evaluation of the optimal design at various operating conditions showed torque ripple reduction and average torque improvement under all load conditions. The optimal design also shows improvement in the field-weakening region for high-speed operation.