Optimal shape design to improve torque characteristics of interior permanent magnet synchronous motor for small electric vehicles

This study focused on optimizing the stator and rotor shapes of a 30 kW electric vehicle interior permanent magnet synchronous motor (IPMSM) to enhance its torque characteristics. Twelve design variables for both stator and rotor were selected for the optimization process. Metamodels, generated using an optimal Latin hypercube design, were employed to obtain the optimal IPMSM solution. Parametric sensitivity analysis performed the adjustment of design variable ranges, leading to the optimal solution through the progressive quadratic response surface method (PQRSM). Verification was carried out through finite element analysis, encompassing electromagnetic, demagnetization, and structural analyses. The optimal model maintained the same rated torque and efficiency as the initial model but reduced torque ripple by 19.4% and peak-to-peak cogging torque by 40.2%. Fast Fourier transform analysis revealed an increased fundamental frequency component in the back electromotive force (back EMF) of the optimal model compared to that of the initial model. Furthermore, demagnetization analysis demonstrated that the IPMSM can be operated even at 150 °C. Structural analysis indicated a 26.1% reduction in von Mises stress on the barrier between two permanent magnets. Efficiency analysis under maximum torque per ampere control yielded an efficiency of 96.7% at a rated torque of 95.5 Nm and a rated speed of 3000 rpm. These results show that the proposed optimal design process significantly improve the torque characteristics of IPMSM.