The Suppression of Commutation Torque Ripple in Brushless DC Motors Based on Segmental Duty Cycle Distribution

During the commutation process of brushless direct current (BLDC) motors, significant commutation torque pulsations occur, which degrade the operational performance and efficiency of the motor. Conventional overlapping commutation methods can effectively suppress commutation torque pulsations; however, they are susceptible to issues related to control fail areas. In response to this challenge, the paper presents an improved segmented duty cycle allocation method for overlapping commutation, which effectively suppresses commutation torque pulsations during the braking process across a wide range of speeds. This commutation method employs a PWM-OFF-PWM modulation technique, which allocates differing duty cycles based on the high and low speed segments during the commutation period. Each speed segment independently undergoes pulse width modulation for either the conducting phase or the non-conducting phase, ensuring that the rate of current rise in the conducting phase is matched by the rate of current decline in the non-conducting phase during commutation. This synchronization allows for a smooth transition of non-commutating phase currents during the commutation period, thereby reducing commutation torque pulsations. Compared to conventional overlapping commutation methods, the proposed technique not only eliminates the control fail area issue induced by delayed control strategies, but also decreases the switching frequency of the power switch transistors, thus reducing switching losses. The feasibility, effectiveness and superiority of the proposed method are demonstrated in experiments.