Method for detecting initial position of sensorless permanent magnet synchronous motor

The invention relates to a method for detecting the initial position of a sensorless permanent magnet synchronous motor. On the basis of ensuring the static state of the motor, open-loop control is carried out on current, the initial position of a rotor is initialized, estimated high-frequency alternating axial current is extracted by injecting high-frequency cosine voltage signals into an estimation direct axis of an estimated synchronous rotating coordinate system, and signal processing and adjusting are carried on the high-frequency alternating axial current to obtain the estimated initial value of the initial position of the rotor; then a plurality of high-frequency cosine voltage signals of the determined period are continuously injected into the estimation direct axis, and the magnetic polarity is judged and the accurate initial position of the rotor is obtained by judging whether an integral value of the direct axis current is positive or negative. Motor parameters do not need to be obtained, the problem that as an existing rotor initial position detecting method possibly causes motor rotation, identification signals are difficult to detect is effectively avoided, hardware does not need to be additionally arranged, implementation is convenient, and the initial position of any rotor magnetic pole can be accurately obtained when the motor is in the static state.