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Torque Analysis in Permanent-Magnet Synchronous Motors: A Comparative Study

This paper examines the torque ripple and cogging-torque variation in permanent-magnet synchronous motors (PMSMs). The effect of slot number and magnet skewing on electromagnetic motor torque, has been analyzed in different 20-pole, three-phase, PMSM configurations having the same envelop dimensions and output requirements. Finite-element technique is used for machine characteristics computation. Maxwell-stress tensor is used to find torque. Finite-element analysis results show that: 1) motors with fractional-slot winding have lower torque ripple but show a reduction of the average torque and 2) in step-skew magnet motors, torque-ripple reduction is significant only for a certain step number and magnet-skew angle.