A Novel Region-Refinement Pulse Width Modulation Method for Torque Ripple Reduction of Brushless DC Motors

Brushless dc motors (BLDCMs) exhibit relatively large torque ripple due to the current pulsation during the commutation process. In this paper, first, the production mechanism of the commutation torque ripple is analyzed in detail, where the diode freewheeling in the inactive phase winding and the non-commutation torque ripple under the existing PWM modulation modes are compared for a three-phase six-switch inverter-fed BLDCM drive. The torque ripple expression of each PWM mode is derived analytically. Thereafter, a new region-refinement PWM method is proposed, in which a normal operation region of 60° is refined into two 30° sub-regions, and PWM-ON and ON-PWM modulation method is suitable to be employed, respectively, in the former and latter 30° regions. To verify the effectiveness of reducing the non-commutation torque ripple, both simulations and experiments are conducted on a three-phase prototyped BLDCM. The results demonstrate that the torque ripple under the proposed PWM mode can be reduced significantly.