Commutation circuit for a sensorless three-phase brushless direct curent motor

摘要

A commutation circuit for a sensorless three-phase BLDC motor enables soft switching in the commutation process without the need for a complex delay circuit and generates signals separate from the back EMF signals of the stator to start the rotation of the motor rotor. The commutation circuit includes a starting circuit adapted to generate a starting clock signal to forcibly start the motor without information associated with the position of the motor rotor and generates first, second and third reference clock signals that are used to drive the motor in constant velocity operation. The commutation circuit also includes a constant velocity controlling circuit that compares the voltages from each of the phases to the neutral voltage of the stator and a stair/common voltage generating circuit that provides a first group of stair voltages and a common voltage to forcibly start rotation of the rotor or, alternatively, a second group of stair voltages with a second common voltage to optimally commutate the phases when the rotor is accelerating is turning at a constant operational speed.