Sinusoidal PWM Techniques in Rotor Pole Segmentation to Reduce Permanent Magnet Synchronous Machine Torque Ripple

Abstract

Torque ripples can cause mechanical stress in electrical machines, among otherproblems. The present paper proposes three methods to reduce these ripples in the permanent magnets synchronous machine considering rotor poles design. These methods consist in segmenting the rotor poles, with width and distances between segments obtained by SPWM techniques. The modulating wave is a sinwave which has the same frequency as the air gap flux density fundamental harmonic. Method 1 contemplates the unipolar SPWM technique, whereas methods 1 and 2 used the bipolar SWPM technique. Furthermore, the equations used to predict the cogging torque behavior are presented and verified by means of a finite element analysis. The torque ripple reduction is achieved due to the elimination of back-electromotive force harmonics and the decrease in the cogging torque peak. Method 1 has proved to be the most effective, reducing the torque ripple by 51.38% and 76.61% for the 4-pole and 8-pole machines, respectively. In addition, the magnet volume utilized has been reduced by 22.55% for the 4-pole machine, but the average torque value has been reduced by 18.7%. It is worth mentioning that the proposed methods do not require skewing to reduce the torque ripple.