Comparative Study on Electromagnetic Performance of Slotted and Slotless PM Synchronous Motors According to Aspect Ratios

Permanent magnet synchronous motors (PMSMs) are widely used in industrial applications due to their high torque density. PMSM are generally classified into slotted and slotless types, each offering distinct advantages. A key design parameter of PMSM is the aspect ratio, defined as the ratio of the stator outer diameter to the stack length, which significantly affects electromagnetic performance and application suitability. In this article, a comparative study of 1.35 kW slotted and slotless PMSM is proposed based on aspect ratios under the same volume, using a finite element analysis (FEAs). Although the volume of PMSM primarily determines electromagnetic performance, such as electromagnetic torque and loss, the aspect ratio is also crucial because of its impact on magnetic leakage flux. Constraints, including the volume of PMSM, magnet thickness, and current density, are selected to compare electromagnetic performances based on aspect ratio. Optimal models of slotted and slotless PMSM are designed, and their electromagnetic performances are compared. The optimal slotless PMSM achieves a torque ripple approximately 31.08%p lower than that of the optimal slotted PMSM. Furthermore, the total harmonic distortion (THD) of the induced voltage is reduced by approximately 20.16%p. To verify this study, the 1.35 kW optimal slotless PMSM is manufactured and experimentally tested, showing errors of less than 5% compared to FEA results.