Sensorless speed control of BLDC motor using six step square wave and rotor position detection

This paper presents a brushless DC motor (BLDCM) control system that does not require Hall sensor and speed encoder for an air conditioner fan motor. Using low cost circuits, the zero-crossing points are detected to estimate the commutated timing and speed information. Hall element shortcoming can therefore be eliminated. A modified six-step square wave pattern with pulse-width modulation is developed to simplify the conventional coordinate transformations technique. To verify the proposed method, a prototype fan motor controller is constructed and tested. Experimental results show that the proposed method has high efficiency and good performance.