Well-known methods of vector control of permanent magnet synchronous motor suppose that before starting the motion the initial position of the rotor magnetic axis with respect to the stator magnetic field have to be determined and thereafter depending on the reference frame the motor is started in the speed control or positioning mode. Traditional method of determining initial position of the motor shaft is carried out by means of Hall sensors and\or a position sensor. In the paper method of starting the synchronous motor with unknown initial position of the rotor magnetic axis with respect to the stator magnetic field using incremental encoder is proposed and studied.