Implementation of the back EMF zero crossing detection for BLDC motor

Brushless DC (BLDC) motors are increasingly replacing brushed DC motors due to their efficiency, long life smooth torque delivery and high speed operation. Usually, BLDC motors are commutated in six-step pattern with commutation controlled by position sensors. The implementation of sensorless control gives possibility to reduce cost and complexity of the motor control system. In the paper implementation of a back electromotive force (EMF) detection method for sensorless BLDC drives is discussed. Usually the neutral wire of the motor is not accessible therefore the back EMF of the floating phase is detected during off time of the corresponding transistor. The back EMF sensing method and sensorless BLDC drive control system are implemented by using low cost microcontroller.