A novel method of detecting for rotor position of a sensorless brushless DC motor

It is a valuable research to design high temperature brushless DC (BLDCM) motor drive and control system for oil well detecting. In this paper, a new rotor position detecting method for the sensorless control of brushless DC motor is introduced. A novel circuit is designed to obtain fundamental harmonic from three-phase terminal voltage. A switched-capacitor filter which makes a fixed phase delay is researched. And the lag in phase is not related to the speed of the rotor. Since the phase is constant delay 90 electrical degree when the motor speed is changed, a rotor position signal which needn't phase compensation is obtained. It realizes a hardware-implemented sensorless BLDCM driver system and applies in well logging high temperature and speed BLDCM system successfully. The experimental results show that this method is simple and practical.