New Method to Eliminate Commutation Torque Ripple of Brushless DC Motor With Minimum Commutation Time

Commutation torque ripple of brushless DC motor (BLDCM) is caused by the different current slew rates between switching-in phase and switching-out phase. If the slew rates were equal, commutation torque ripple could be eliminated. A simple full speed range method was presented in this paper to eliminate commutation torque ripple by dividing each pulsewidth modulation (PWM) period into three segments during commutation time. By selecting proper proportions of these three segments, the average current slew rate of switching-in phase can be kept equal with the average rate of switching-out phase in each PWM period. Because the commutation time is controllable in the presented method, commutation process which is bad for the operation of BLDCM can be finished in its highest speed. The theoretical derivation is given, the experimental results show that the commutation torque ripple can be eliminated in the minimum commutation time, and output power of BLDCM under rated load can be improved.