An improved method of initial rotor position estimation and magnetic polarity identification for surface permanent magnet synchronous motor

A position sensor is required in a Permanent magnet synchronous machines(PMSM) system, which will raise cost and reduced reliability. Sensorless control of PMSM drive overcome these difficul-ties. In the start-up control of sensorless PMSM, may cause a starting failure due to unknown rotor initial position[1].a voltage pulse injection method based on magnetic saturation effect has been proposed[2].A series of pulse voltage vectors with certain angular difference are injected into Surface mounted PMSM, and the rotor position can be judged by the response currents which are different from each other caused by the difference of magnetic saturation. The voltage vector angle needs to be divided continuously for high accuracy to avoid increasing error after the angle is smaller than a certain extent. The more situation is that the judgment of the rotor pole may be wrong due to small size of rotor poles, the difference of inductance between poles is unobvious, it makes the judgment of rotor poles become difficult and inaccurate[3]. If the judgment is wrong, the motor rotates reversely in machine tools and robot applications, it could be unacceptable.