Initial rotor position estimation method for PM motors

This paper presents a method to detect the rotor position of permanent-magnet motors at standstill, which is suitable to avoid temporary reverse rotation at startup or starting failure. The approach is based on the investigation of the stator inductance variation as a function of the rotor magnets position and the stator current space vector. It involves the application of a proper sequence of voltage pulses to the stator windings, and the measurement of the peak values of the resulting current in order to achieve the rotor position estimation. Actually, the current measurements show significant uncertainties which affect the rotor position detection. In order to avoid these problems, the authors propose a novel procedure which combines an iterative sequence of voltage pulses with a fuzzy logic processing of the current responses and phase currents derivation based on the dc-link current measurements. The proposed method has been implemented on a muC digital signal processor (TMS320F240). The obtained results confirm the effectiveness of the proposed solution. It can be applied in sensorless drives, in drives equipped with nonabsolute position transducers, with a wide range of motors, and it does not require the knowledge of any of the motor parameters.