Sensorless drive of brushless DC motor with 180-degree commutation

To drive trapezoidal back-EMF type of brushless DC motor, for 120-degree commutation, the winding without phase current in each conduction interval can be considered as a sensor for back-EMF detection. However, in the case of 180-degree commutation, the back-EMF detection can not be realized because all the three windings are driven with current. Sensorless algorithm of indirect back-EMF determination is necessary to be used. In this paper, 180-degree commutation gate switching pattern is analysed. An enhanced sensorless algorithm is developed for 180-degree commutation. PWM soft chopping technique is carried out for supplied voltage adjustment. The simulation results based on Matlab/Simulink prove that the proposed sensorless drive of 180-degree commutation works properly.