Abstract: To solve the difficulty in determining the rotor position of sensorless brushless DC in zero speed or low speed, the paper presents a new method for detecting the initial rotor position and its startup without reversing based on variation of winding inductances. For the magnetic saturation effect of the stator core, the winding inductances vary with the rotor in different positions. The initial rotor position is located by three short pulses and the winding voltage is detected. After that the motor speeds up until the back EMF can be detected stably. And it can switch to the control by back EMF. The proposed method validated by experiment proves to be effective.

Key words: rotor position, sensorless brushless DC, stator winding inductances, magnetic saturation effect, speedup strategy