Abstract
In recent years, sensorless drive schemes have been proposed widely and most of them are based on the ZCP (Zero Crossing Point) detection of the BEMF (Back Electro-Motive Force). These schemes have two main problems. One is that ZCP may not be detected at low speed and thus a forced drive is required. The other problem is that there is $30^{\circ}$ phase difference between ZCP and the motor commutation instant and to ensure proper operation, this gap should be accounted for. To solve these problems a circuit is devised for detecting ZCP of the BEMF difference through the line voltage difference. Experimental results show that the output of this circuit is identical to that of the Hall sensor signal, and velocity control of a BLDC motor is possible without the sensor.
