Multi-Objective Optimal Design of an Axial Flux Permanent Magnet Motor for In-Wheel Drive Considering Torque Ripple Reduction

This study proposes an optimal design approach incorporating rotor skew to reduce torque ripple in a 5 kW in-wheel axial flux permanent magnet (AFPM) motor. Nine design variables, including the skew angle, were selected for optimization. The variation ranges of these variables were defined, and sample points were generated using the optimal Latin hypercube design (OLHD). Response data corresponding to the sample points were obtained through three-dimensional finite element method (3D FEM) analysis. Metamodels were then constructed using five different methods and evaluated based on the root mean square error (RMSE). The optimization results showed that the average torque of the optimized model increased by 2.3% compared with the initial design, reaching 48.85 Nm. Torque ripple was reduced by 42.01% to 2.83 Nm, while peak-to-peak cogging torque decreased by 42.76% to 2.61 Nm. In addition, efficiency improved by 0.07% to 95.53%, and the total harmonic distortion (THD) of the back-EMF waveform was reduced by 50.72% to 2.4%. These findings demonstrate that the proposed method provides an effective and systematic design strategy for enhancing the performance of AFPM motors.