Sensorless brushless DC motor drive with EMF constant identifier

This paper presents the position and speed sensorless drive of a brushless DC motor with a sinusoidal flux distribution. Since the motor with a ferrite magnet rotor presents the EMF constant variation due to a temperature rise, sensorless drive characteristics must be robust against variations of EMF constant. The features of the proposed scheme are the simultaneous identifications of position, speed and EMF constant. The estimation is based on the current difference between the actual motor and the model. By using this current difference, estimations of speed and EMF constant are performed and the position is obtained as an integration of the estimated speed. The effectiveness of the proposed scheme is confirmed by experiments using 1.2 kW brushless DC motors