A pulse-width modulation technique for BLDC motor drive system to reduce commutation time

摘要

Commutations occurring in brushless DC motor (BLDCM) drive system cause failure of a sensorless drive based on zero-crossing detection of back-electromotive force (BEMF) when the commutation angle reaches or exceeds 30°. On the other hand, increasing the load on the motor slows down falling process of outgoing phase current during commutation. This paper presents a new method for complete vanishing of outgoing phase current before BEMF zero-crossing point, using a pulse-width modulation (PWM) mode in which an adaptive pattern is inserted to H-PWML-ON mode synchronously with commutation time. The proposed PWM mode can be used for sensorless drive based on direct BEMF zero-crossing detection method. The proposed method is applied to a 14 kW/220 V BLDCM with constant v/f control, and the results show that as the duty cycle of PWM is reduced, commutation time becomes shorter and the transferred power to motor is increased compared to H-PWM_L-ON mode.