Indirect Back-EMF Zero Crossing Detection for Sensorless BLDC Motor Operation

Brushless DC (BLDC) Motors are widely used in industrial and consumer appliances due to their high efficiency, high power density, low maintenance and silent operation. However the need for position sensors makes the drive less reliable and expensive. Sensorless control is therefore gaining importance now-a-days. This paper proposes an indirect way of detecting the zero crossing instant of the back-EMF from the three terminal voltages without using the neutral potential. Inaccuracies due to device drops have been eliminated. This scheme is simple to implement. Simulation results show the validity of this scheme.