Optimization of a Double-Layer Flared-Shaped IPMSM for Torque Ripple Reduction

Interior permanent magnet synchronous motors (IPMSMs) offer high torque density. However, they are expensive owing to the rising prices of rare earth elements used in permanent magnets (PMs). This study proposes a double-layer flared-shaped IPMSM (DF-IPMSM) that achieves equivalent output torque and reduced torque ripple, while minimizing PM usage. It achieves flux concentration using C-type ferrite PMs arranged in a flared configuration and enhances reluctance torque by increasing the difference between L_d and L_q using a double-layer PM arrangement. Finite element analysis (FEA) under rated load and drive conditions demonstrates that the DF-IPMSM achieves output torque and efficiency equivalent to those of a single-layer flared-shaped IPMSM (SF-IPMSM) despite the reduced PM usage. To verify the structural advantages of the DF-IPMSM, it was compared with three alternatives, namely, SF-IPMSM, double-bar type IPMSM (DB-IPMSM), and double-spoke type IPMSM (DS-IPMSM), under rated load conditions. The FEA results indicated that the DF-IPMSM achieves the highest reluctance torque at equivalent output torque and efficiency. Although DF-IPMSM utilizes the reluctance torque more effectively than SF-IPMSM, it has the disadvantage of increasing torque ripple due to magnetic saturation and harmonic distortion. We performed an optimization rotor geometry design to improve this drawback. Sample points were generated using Latin Hypercube Sampling (LHS) and constructed a Kriging-based surrogate model. Subsequently, a genetic algorithm (GA) was employed to determine the optimal values for minimizing torque ripple. Finally, the FEA results of the optimized model were compared with the prototype measurements to verify the validity of the proposed DF-IPMSM. The proposed DF-IPMSM design offers a cost-effective alternative to conventional IPMSMs by significantly reducing reliance on rare earth PMs while maintaining high torque performance and efficiency.