Design Optimization using Asymmetric Rotor in IPMSM for Torque Ripple Reduction considering Forward and Reverse Directions

In the interior permanent magnet synchronous motor (IPMSM), an asymmetric rotor is used as a design method to reduce torque ripple or cogging torque by adjusting the saturation of the rotor core. The advantage of an asymmetric rotor is that it can reduce torque ripple or cogging torque in the forward direction while maintaining the average torque or output power. However, when driving in the reverse direction, the torque ripple or cogging torque can be increased. Therefore, the asymmetric rotor produces different characteristics in the forward and reverse directions. In this study, the asymmetric rotor shape is designed using an optimization technique taking into consideration the rotating direction. The optimum design is performed based on the symmetric rotor as the base model. When rotating in the forward direction, the asymmetric rotor has a lower torque ripple than the symmetric rotor, and when rotating in the reverse direction, the asymmetric and symmetric rotors are designed to be similar. The kriging surrogate model was used to determine the optimum design point that satisfied the constraints. Finally, a symmetric and asymmetric rotor was manufactured and evaluated through tests.