Commutation point correction method of sensorless BLDC motor based on back emf detection

Abstract

For sensorless brushless DC (BLDC) motors, whose rotor position is calculated by the applied estimation techniques, the estimation accuracy is hence a critical factor for the motors’ operating performance. In this paper, respective effects of the estimated rotor position error on the phase current and terminal voltage are analyzed theoretically. Accordingly, a novel commutation point correction method is proposed, which allows the automatic symmetrical modulation of the terminal voltage. In particularly, the commutation point is adjusted on-line by means of closed-loop control of the delayed angle. The proposed technique presents several valuable advantages: 1) it requires no additional hardware implementation; 2) guarantees accuracy and stability of method in the high speed range. The above-mentioned features are verified experimentally on a 4-pole sensorless BLDC motor.