Design of a control system for sensorless brushless DC motor using the dsPIC

This paper presents the design of a control system for sensorless brushless DC motor. The system directly extracts the true back EMF zero crossing point by detecting the voltage difference between the floating phase terminal and the midpoint in the DC link. The commutation signal of the floating phase is obtained by lagging the back EMF zero crossing point 30 electrical degrees. And two motor starting methods are implemented in the system. The experiment shows good motor performance over a wide speed range. Experimental results from a prototype of brushless DC motor control system verify the analytical results and confirm the validity of the system.