Using phase-current sensing circuit as the position sensor for brushless DC motors without shaft position sensor

The authors present a prototype phase-current sensing circuit to detect and process phase-current waveforms for obtaining exact rotor position signals. Without an additional phase-calibration loop for processed signals, the output signals of this circuit can keep in phase with the signals of a Hall sensor for a wide range of speed variations. Furthermore, with the nearly exact rotor position signals this prototype sensing circuit, better torque operation can be obtained. Experimental results obtained with this circuit are given and compared with the signals from the Hall sensor of a brushless DC motor.