A closed loop control method to correct position phase for sensorless Brushless DC motor

The paper detail analyzes the relationship between position phase error and free-wheel current of inactive phase. It is found that free-wheel current error can exactly reflect position phase error, and a novel closed loop control method to correct position phase is proposed. In order to keep free-wheel current of the inactive phase symmetrical, free-wheel current error is inputted to PI controller, and delay angel after zero-crossing is adjusted in time with PI controller. Thus the phase error is corrected immediately. The validity of the method is verified by experiments.