Coordinated suppression commutation torque ripple for brushless DC motor with commutation time

Abstract

A commutation torque ripple suppression strategy for the brushless DC motor (BLDCM) with commutation time is proposed. First, a torque model considering back electromotive force (back-EMF) variation is presented, and the cause of commutation torque ripple is analysed. The results show that the commutation torque ripple of BLDCM is inevitable even if the non-commutation current remains steady. On this basis, the influence and quantitative relationships of non-commutation current and commutation time on commutation torque ripple are studied. Furthermore, two impact factors are proposed to comprehensively consider their effects on commutation torque ripple. The three-phase windings are modulated in the commutation process at individual duty cycles. The comprehensive optimisation index of commutation torque ripple for different working conditions is obtained by calculating the relative relationship of the impact factors. The optimisation index determines the proper modulation duty cycles. Therefore, the motor parameters and working conditions do not limit the strategy. Finally, the experimental results verify the correctness of the theoretical analysis and the feasibility of the proposed strategy. The proposed strategy can reduce the commutation torque ripple by 16.28% and 21.80% and shorten the commutation time by 50.00% and 36.67% at low speed and high speed, respectively, compared with the conventional strategy.