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Interior permanent magnet synchronous machines (IPMSMs) are extensively used in electric drives due to their high-power density and wide-speed operation capability. In order to improve the performance of the drive application, low torque ripple of the IPMSM is valuable and necessary. However, as far as the existing analytical models are concerned, it is difficult to establish a direct relationship between the structural parameters and the torque ripple law of IPMSMs due to the complexity of their flux circuits, and therefore, it is not easy to achieve a directional suppression of the torque ripple by means of design. With this in mind, this article establishes a general analytical model for electromagnetic torque and its ripples (including synchronous torque, reluctance torque, and cogging torque) based on the harmonic interaction effects. Thereby, a novel and simple design method to reduce torque ripple is proposed, and its principle is to change the rotor surface shape to artificially construct the specific number of reluctance harmonics. As a result, it is verified by finite element method and experiments that the proposed method can precisely eliminate the specific torque ripple and reduce the overall torque ripple.

Permanent magnet (PM) machines garner significant attention due to their high-power density and high efficiency. As research progresses, high-end motor applications are placing higher and more comprehensive performance demands on PM machines, driving the need for multifaceted and synergistic motor design optimization. In response to this demand, this article proposes a multi-objective optimization design process aimed at improving the overall electromagnetic performance of PM machines. The objectives include enhancing torque density, suppressing torque ripple, and reducing vibration and noise. The optimization process utilizes a meta-model fitted to the numerical model solved by the finite element method, leading to a substantial acceleration of the overall optimization process. Furthermore, an optimization approach is employed to optimize several key structural parameters of a double layer interior PM machine using an evolutionary algorithm. The resulting optimized motor is fabricated and tested, and both numerical simulations and experiments validate that the optimized motor exhibits enhanced torque, low torque ripple, and avoids resonance vibration noise near the rated speed. This comprehensive validation confirms the effectiveness of the structural design and the optimization process.