Commutation Torque Ripple Reduction for Brushless DC Motor Based on an Auxiliary Step-Up Circuit

There exists torque ripple in the commutation process of brushless DC motor (BLDCM), which seriously restricts its application in the high-performance field. This paper proposes an auxiliary step-up circuit to suppress the commutation torque ripple of BLDCM, and the auxiliary step-up circuit consists of a transformer, a capacitor and a switch circuit. For effective suppression of the commutation torque ripple, the capacitor is charged in the non-commutation period. When the commutation occurs, the charged capacitor is added on the power source through a switch circuit to step up the dc-bus voltage in the commutation period, and the three-phase inverter is regulated to make the motor's input voltage is equal to four times the back electromotive force (back EMF) amplitude. The auxiliary step-up circuit only transfers partial power required in the commutation process of the motor, and the capacity of the power components is reduced accordingly. The inductive energy stored in the transformer is returned to the power source in each switching cycle, which improves the energy utilization rate. In addition, this method can also shorten the commutation time. The validity and effectiveness of the proposed method is verified through experimental results.