Modelling of an electronically commutated (Brushless DC) motor drives with back-emf sensing

Brushless DC (BLDC) motors and their drives are penetrating the market of home appliances and HVAC industry in recent years because of their high efficiency, silent operation, high reliability and low maintenance requirement. Conventionally, BLDC motors are commutated in six-step pattern with commutation controlled by position sensors. To reduce cost and complexity of the drive system, sensorless drive is preferred. The existing sensorless control scheme with the conventional back EMF sensing based on motor neutral voltage for BLDC has certain drawbacks, which limit its applications. This paper presents a circuit model of an electronically commutated motor drive with back emf sensing. The circuit model was simulated using LTspice and the results obtained were compared with the experimental results. The value of the motor constant and the back emf measured from the experiment agreed with the simulated model.