In the permanent magnet motor of the surface-inserted rotor structure, Fig. 1 shows a typical structure of a bread-shaped permanent magnet. The outer diameter of the permanent magnet is Rr, and the bottom surface of the permanent magnet is linear rather than curved, which is advantageous for generating a sinusoidal air gap magnetic density distribution. The maximum thickness of the permanent magnet is hm, and the width of the pole arc is αm, which is parallel magnetization. Between the adjacent magnetic poles, the iron core has a convex portion, which is advantageous for fixing the permanent magnet, so the permanent magnet is surface-inserted.
In this paper, the motor shown in Fig. 1 is used as a reference. The influence of the iron core opening auxiliary groove under the permanent magnet and the auxiliary opening of the permanent magnet bottom on the torque ripple of the motor during load operation will be studied. In the subsequent studies of this paper, the finite element method is used to calculate the electromagnetic torque of the motor, and the same three-phase symmetrical sinusoidal rated current is applied to the motor. When the rated current (51.6 Arms) is applied to the reference motor, the average electromagnetic torque is 52.3 Nm, and the torque ripple (defined herein as the ratio of the peak-to-peak torque to the average torque) is 21.4%. It can be seen that although the bread-shaped permanent magnet is used, the torque ripple is still serious, and it is necessary to further optimize the design to reduce the torque ripple.
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