A Novel Method of Detecting for Rotor Position of a Sensorless Brushless DC Motor

In this paper, the author introduces a new rotor position detecting method for the sensorless control of brushless DC motor (BLDCM). It applies a new circuit to get fundamental wave from three phase terminal voltage. A special switched capacitor filter is designed to achieve constant delay 90 electrical degrees. Since the phase lag is not related to the speed of the rotor, it needn't phase compensation. The filtered signal can be converted to six commutation signals for BLDCM just through zero-crossing comparator and decoder, so the detection circuit is simplified. The hardware-implemented system has low cost and high reliability, which is suitable for oil well detecting.