A Full-Speed Range Sensorless Control Scheme of Brushless DC Motor Based on Saliency Effects

As for a Brushless DC Motor(BLDCM) with saliency pole structured rotor, the self-inductance and mutual inductance vary according to the rotor position. As a result, the difference between terminal voltage samples of floating phases during PWM on and free-wheeling period shows a regular change, which makes it possible to detect the rotor position. Based on the principle above, the initial rotor position detection is realized. A new sensorless commutation technique is proposed by comparing the terminal voltage sample difference with commutation thresholds. When the PWM duty cycle approaches 100%, a complementary rotor position detection method suitable for the extreme situation is applied. Thus, the rotor position can be detected in full-speed range. Experiment results verify that the saliency-based sensorless strategy is simple and effective.