Study of position detection method for sensorless brushless DC electromotor

This paper presents a new method to detect the position of a sensorless brushless DC motor´s rotor by using a special microcontroller. The rotor´s position is detected using the induced voltage wave of the stator winding. The method provides the following features: the induced voltage modes are detected and converted after the power transistor of the upper bridge in the inducting phase has been turned off for 15 degrees of electric angle; the measurement is synchronized with the carrier wave, and it should avoid meeting with the moment of the peak interference; and the process of using the prediction and evaluation method to estimate the next mode switchover time can rectify the factual value and also insert value accurately when the position signal is lost, so the precision and reliability of the detection are improved