Torque analysis of a permanent magnet synchronous motor using flux densities in air gap

Permanent magnet synchronous motors (PMSMs) having high power density and high efficiency are rigorously researched in various premium applications. Among PMSMs, many studies have been conducted on interior permanent magnet synchronous motors (IPMSMs) to improve torque ripple, but its accurate estimation is not straightforward. Therefore, a six-pole nine-slot (6p/9s) IPMSM is adopted as a base model due to its popularity in academia and industries, and other two pole/slot combinations (8p/12s and 10p/15s) are additionally selected to investigate the influence of a pole/slot combination on torque ripple. Torque performance is easily identified by analyzing tangential force due to their direct proportional relation. In this paper, magnetic flux densities in radial and tangential direction are systematically analyzed since tangential force is determined by the product of the two magnetic flux densities. The modification of a stator pole regarding its tip thickness is chosen as a key parameter in 6p/9s IPMSM. The thickness of a stator pole tip opposite to the direction of spin is more critical in torque ripple improvement. It is verified that the proposed method is sufficient for accurate torque prediction.