Enhanced sensorless control of brushless drives using back emf mapping

An enhanced inexpensive algorithm is presented in this paper for sensorless control of brushless DC motors (BLDCMs) based on the back EMF (BEMF) sensing techniques. The algorithm determines the switching point of power between phases, which is calculated with reasonable accuracy in simple mathematical equations utilizing the slope of the BEMF which is mapped back to reference values. Simulation of the method is presented for verification. Predictably, this eliminates using speed dependant filters, comparators, and the delays called through look up tables after the detection of the zero crossing point (ZCP).