Torque Ripple Improvement of Interior Permanent Magnet Motors by Magnet Asymmetry Considering Wide Speed Range of Operation

This paper proposes torque ripple reduction method for 3 phase 48 slot 8 pole IPM machine. Asymmetry is created between pole and pole pairs in the conventional rotor to minimize the effect of interactional magneto motive forces (MMF). Initially, the symmetry between the poles and pole pairs is altered for one pole, followed by the introduction of asymmetry between the pole pairs. The MMF for both conventional and asymmetric rotor types are obtained on the slotless stator model, and then the torque waveform is mathematically calculated by using the Lorentz force law. A comparison is made between the mathematically obtained waveform and the FEA method. Once the interactional MMF harmonics are minimized in the slotless stator model, the model is transferred to the slotted model. Detailed analyses of torque waveforms are conducted for all rotor types by considering constant torque and field weakening operation. Finally torquespeed curves are obtained for all rotor types. The effects of the rotor pole asymmetries on the speed range of the motor are investigated. Preliminary results indicates that significant improvement for extended speed operation would be possible when the correct asymmetry is employed for the rotor poles. © 2023 IEEE.