The invention discloses a brushless
direct current motor rotor position detecting device based on the counter EMF
triple frequency harmonic and a phase changing method suitable for the brushless
direct current motor rotor position detecting device. The brushless
direct current motor rotor position detecting device is composed of a Y-shaped connecting three-phase symmetrical resistance network, a
voltage bleeder circuit, a band-pass filtering circuit, a zero passage comparison circuit and an optoelectronic isolation circuit. According to the detecting device, the
simulation neutral points are built through the star-shaped three-phase symmetrical resistance network, the counter EMF
triple frequency harmonic component is extracted from the
simulation neutral points, zero passage signals of the counter EMF
triple frequency harmonic component are obtained by comparing the counter EMF triple frequency harmonic component with the grounding end, and a
microprocessor calculates the zero passage time of the three-phase counter EMF of a brushless direct current motor according to the two times of zero passage signals of the detecting device and the last action time of a switch tube and controls the phase changing according to the zero passage time. By means of the detecting method, the number of components of the rotor position detecting device can be reduced, and the reliability of detecting can be improved.