permanent magnet bottom auxiliary slot
In addition to the auxiliary groove for the rotor core, an auxiliary groove can be opened at the bottom of the permanent magnet. Firstly, the two semi-circular grooves of symmetry are studied. As shown in Fig. 9, the position and size of the auxiliary groove are constrained by two parameters of x1 and r1, and the results shown in Fig. 10 are obtained through optimization analysis. It can be seen that the addition of a suitable auxiliary groove to the permanent magnet can effectively attenuate the torque ripple, but the improper positioning of the auxiliary groove can greatly deteriorate the torque ripple of the motor. When x1 = 3 mm and r1 = 1.5 mm, the torque ripple is optimally 8.2%, and the average torque is 50.4 Nm.
When the outer tank is optimal, a pair of inner tanks is added, as shown in Fig. 11, and the inner tank is optimized by two parameters of x2 and r2, and the result shown in Fig. 12 is obtained. It can be seen that the provision of a suitable internal auxiliary groove is advantageous for further weakening the motor torque ripple. When the inner auxiliary groove radius r2 is constant, the torque ripple first decreases and then increases as the inner auxiliary groove position x2 becomes larger. When x2 = 2.5 mm and r2 = 1.5 mm, the torque ripple can be reduced to 4.8%, while the average torque at this time is 48.0 Nm.
If the third pair of slots is continued to be opened at the bottom of the permanent magnet, the finite element calculation shows that the torque ripple is not weakened, but deteriorates, and detailed calculation results are not given here.
5 Conclusion
In this paper, the influence of the rotor auxiliary groove on the torque ripple of the surface-inserted permanent magnet motor during load operation is studied. Firstly, a rectangular and semi-circular auxiliary groove is built on the rotor core below the permanent magnet, and the influence of the size, position and quantity of the auxiliary groove on the motor torque ripple is studied. When the auxiliary groove of the rotor core is a symmetric double rectangular groove, the torque ripple of the motor tends to decrease with the increase of the depth of the rectangular groove, and decreases first and then increases with the increase of the groove width. When a pair of inner rectangular grooves is added, the appropriate inner groove can further weaken the torque ripple of the motor; when the inner groove size is fixed, the torque ripple increases as the distance from the inner groove to the outer groove increases. Opening more rectangular slots no longer reduces torque ripple. When the auxiliary groove of the rotor core is a semi-circular groove and the groove position is fixed, the torque pulsation decreases first and then increases with the groove radius. When a pair of inner grooves is added, it is found that the torque ripple increases as the distance between the inner grooves becomes larger. Finally, the influence of the auxiliary groove on the bottom of the bread-shaped permanent magnet is studied. When a pair of semi-circular grooves is opened, if the groove size is fixed, the torque ripple will increase first when the distance between the edge of the groove and the edge of the permanent magnet increases. Decrease the trend after increasing. When a pair of inner grooves is added, it is found that the torque pulsation decreases first and then increases with the distance between the two grooves. In general, the arrangement of the inner slots helps to reduce torque ripple. When the permanent magnets open the third pair of semicircular auxiliary grooves, the torque ripple is deteriorated.
Based on the above analysis and research, it can be known that the reasonable design of the auxiliary groove on the rotor core or the permanent magnet can effectively weaken the torque ripple, and of course the average torque will also decrease.
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