A modulation method to decrease commutation torque ripple of brushless DC motors

Brushless DC motors have great power density and torque output. However, they have the problem of commutation torque ripple due to structural characteristics and conventional commutation method. In order to decrease the commutation torque ripple, a new commutation control method based on PWM_ON is applied in this paper. In non-commutation interval, the PWM_ON modulation is used; in commutation interval, the three-phase corporative modulation is used, and the duty cycle of each phase is calculated to keep the current slope of off-going phase and on-going phase equal. The method is simple and decreases the commutation torque ripple obviously. The process to calculate the duty cycle of off-going phase and on-going phase in commutation interval is presented, and their relationship is proposed. The experimental results show the correctness and validity of the commutation control method.