This paper proposes a ferrite permanent magnet–based double-layer spoke-type permanent magnet synchronous motor for ultra-compact electric vehicle traction applications, aiming to achieve high torque density while reducing cost and dependence on rare-earth materials. By adopting a double-layer spoke rotor structure, the q-axis inductance is increased, enabling effective utilization of reluctance torque to enhance overall performance. Although the double-layer spoke-type rotor structure is effective in enhancing reluctance torque utilization, it tends to exacerbate cogging torque, torque ripple, and harmonic distortion. Therefore, a core skew technique is employed to alleviate these undesirable effects. Key design parameters such as magnet thickness, rotor radius, I-core thickness, and tooth thickness are systematically optimized based on the required torque–speed operating region derived from vehicle driving conditions, and an integrated performance index incorporating cogging torque, torque ripple ratio, and line voltage total harmonic distortion (THD) under load is employed to determine the optimal design. The proposed motor is evaluated through two-dimensional and three-dimensional finite element analysis and validated experimentally using a prototype and dynamometer testing. Experimental results demonstrate that the proposed design achieves a cogging torque reduction of approximately 95 %, a torque ripple reduction of 37 %p , and a decrease of about 14 %p in line voltage THD under load compared to a conventional Nd-based motor, while the measured average torque and torque ripple agree with the analysis results within 1 % error, confirming the validity and reliability of the proposed design methodology.
Nam et al. (Thu,) studied this question.