A Torque Control Strategy for Torque Ripple Reduction of Brushless DC Motor With Nonideal Back Electromotive Force

This paper proposes a new torque control strategy to reduce torque ripple of brushless dc motor. All possible combinations of terminal voltages are obtained from different switching states of the inverter during normal conduction period and commutation period. Moreover, the expressions of torque variation rates, corresponding to different terminal voltages, are derived to analyze the sign and the magnitude of the torque variation rates. Based on this analysis, two switching tables with main vector (MV) and subsidiary vector (SV) in these two periods are established, respectively. Through the combined effect of MV and SV in each control cycle, the torque ripple caused by both nonideal back electromotive force and current commutation can be reduced effectively. Meanwhile, dynamic performance of torque and switching times are taken into account. Especially in the commutation period, a unified vector selection table is applied over the entire speed range without distinguishing high speed and low speed. Finally, the effectiveness of the proposed strategy is verified by experimental results.