Method and device for position-free control of brushless direct current motor

The invention discloses a position-free control method and device for a brushless direct current motor. The method comprises the steps that a signal obtained after a back electromotive force zero crossing point signal of the brushless direct current motor is processed through a low-pass filter is obtained; reconstructing the filtered back electromotive force zero-crossing signal according to the comparison of the filtered back electromotive force zero-crossing signal and a preset value signal to obtain a reconstructed back electromotive force zero-crossing signal; according to the transfer function of the low-pass filter and the electrical angular velocity of the brushless direct current motor, calculating the electrical angle of the reconstructed back electromotive force zero crossing point signal leading or lagging behind the commutation point of the brushless direct current motor; selecting different compensation modes according to the range of the electrical angle, and combining the electrical angle speed