Torque Ripple Reduction of Brushless DC Motors by PWM Modes

The steady commutation process of brushless DC motor by PWM modes was analyzed,and realized phase conversion torque ripple compensation control under both low speed and high speed operation by PWM control in commutation period,and confirmed commutation time to hold amplitude of current in commutation period.The effect by PWM modes on a three-phase six-state 120°conduction brushless DC motor was analyzed,and proposed torque ripple compensation control in PWM_ON_PWM mode,which can not only entirely eliminate torque ripple resulted from the current emerging in the turn-off phase during non-commutation period but also compensate torque ripple caused by the commutation current during commutation period.The torque ripple can be effectively reduced under both low speed and high speed operation using torque ripple compensation control in PWM_ON_PWM mode.