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A study about reducing torque ripple of brushless DC motor

Owing to the inductance in the stator winding of brushless DC motor, the current can't respond immediately. During the commutation interval, the non-commutation phase current ripple and commutation torque ripple are emerged. This paper presents a novel voltage compensation topology, including four switches, one power diode and one capacitor. By controlling switches sequences, in the non-commutation period, the voltage source charges to the capacitor, simultaneously, during the commutation interval, the voltage source is in series with the capacitor, keeping the driving voltage is equal to four times of the back EMF amplitude, leading to the falling rate of outgoing phase current matches with the rising rate of incoming phase current. The non-commutation phase current ripple and commutation torque ripple are reduced significantly. Furthermore, taking account of the voltage of the capacitor will drop as time going during commutation, which causing the driving voltage decreases and the commutation torque ripple still exists. Combining with overlap commutation strategy can keep the non-commutation current constant by delaying the time of the outgoing phase. At last, the proposed method is demonstrated effectively by simulation in MATLAB.