Optimisation of a permanent magnet-assisted synchronous reluctance motor with hybrid magnets and segmented air-gap rotor using the A-NSGA-III algorithm

Purpose This paper aims to address large torque ripple and high production costs in neodymium-iron-boron (NdFeB) permanent magnet-assisted synchronous reluctance motors (PMaSynRMs), which typically feature high torque density. To this end, a novel rotor structure integrated with segmented non-uniform air gaps and hybrid ferrite-NdFeB magnets is proposed. Design/methodology/approach The electromagnetic characteristics of four motors with different rotor structures are compared: NdFeB rotor, hybrid magnet rotor and non-uniform air-gap rotor. The reason for larger torque ripple in hybrid magnet motors is elucidated. A Gaussian process regression (GPR) surrogate model with average torque, torque ripple, efficiency and permanent magnet cost as objectives is established. The 15 geometric parameters are co-optimised using the adaptive non-dominated sorting genetic algorithm III (A-NSGA-III). Findings For the optimised motor, NdFeB consumption is reduced by 27.12%, torque ripple is decreased from 16.66% to 7.17% and efficiency remains at 89.39%. Average torque is maintained at 28.19 N·m, permanent magnet cost is reduced by 10.18%. Originality/value This paper proposes a novel rotor structure integrating segmented non-uniform air gaps with hybrid ferrite-NdFeB magnets. Through the multi-objective co-optimisation of the GPR surrogate model and the A-NSGA-III algorithm, the motor manufacturing cost is reduced, while its electromagnetic performance is significantly enhanced. This study provides an effective engineering solution for the development of low-cost, high-performance and low-torque-ripple PMaSynRMs.