Commutating Current Modulation Method of Brushless Direct Current Motor under Non-ideal Back Electromotive Force

Abstract

A phase current modulation method that suppresses commutating torque pulsation of brushless direct current motor under non-ideal back EMF was proposed to solve commutating toque ripple problem. This method calculates the duty cycle and commutation time by acquiring the line voltage in real time, and controls the modulation of different duty cycles of the power device to ensure that the on-phase and off-phase current changes at the same rate during commutation, and finally suppresses non-commutation phase current pulsates. It assures the consistent change rate of conducting-phase and shut-off phase currents at commutation, and thereby suppresses non-commutation torque ripple. Moreover, the proposed method realized indirect observation of non-ideal back EMF through real-time acquisition of line voltage, which prevents the difficulty and poor accuracy of observation of back EMF. Comparing with phase current modulation method considering armature resistance, the proposed method can control non-commutation current control at the commutation moment more accurately. The experimental results show that the phase current ripple coefficient is only 11.1% at 1000r/min and 13.9% at 2000 r/min, while the phase current ripple coefficient under contrast method control is 15.3% at 1000r/min and 19.4% at 2000r/min. The ripple of non-commutation current and commutation torque is smaller at the commutation moment.