Influence of magnet shape on the cogging torque of a surface-mounted permanent magnet motor

The influence of bread-loaf shaped magnet poles under parallel magnetization on the cogging torque of surface-mounted permanent magnet (SPM) motors is studied. For the SPM motors having magnetic poles with eccentricity and sine harmonic compensation, the electromagnetic performances of integer and fractional slot motors are compared. It is found that the cogging torque and torque ripple of the integer and fractional slot motors can be reduced with the same eccentric magnet pole. The cogging torque and torque ripple of a fractional slot motor can be decreased by sine harmonic compensation, however, the same sine harmonic compensation has a small influence in integer slot motors. By varying the magnetic poles, the contribution of the field harmonics (k = (2n + 1) p), which are a direct result of magnet magnetization, to the cogging torque also changes. The electromagnetic performance of a 3 kW prototype is tested, and it is found that the experimental results validate the theoretical investigation.