Sensorless accurate commutation method and device of brushless DC motor

The invention discloses a sensorless accurate commutation method and device of a brushless DC motor. The sensorless accurate commutation method comprises the steps of respectively connecting an A-phase voltage line, a B-phase voltage line and a C-phase voltage line of the brushless DC motor to corresponding voltage acquisition devices, triggering commutation service interrupt by jump edges of induction voltage waveforms of three phases A, B and C; entering commutation service interrupt if the jump edges are descending edges, and changing states of corresponding MOS tubes and IGBTs to achieve commutation after delaying by 30 electrical angels; performing triggering by ascending edges if the jump edges are ascending edges, starting to count in a circulation way from 0, entering commutation service interrupt when a counting value is 2, changing the states of the corresponding MOS tubes and IGBTs to achieve commutation after delaying by 30 electrical angels, and resetting the counter. Thecommutation method has the advantages of high interrupt service trigger and good reliability, a commutation misjudgment accident of the brushless DC motor is prevented under the interference of a demagnetization accident, and the commutation moment is scientifically and simply judged.