Initial rotor position detection in PMSM based on low frequency harmonic current injection

This paper presents an approach for the initial rotor position detection in permanent magnet synchronous machine (PMSM) drives. It is based on injection of low frequency current and excitation of small rotor speed oscillations. In this way information about spatial position of the rotor flux can be retrieved from the stator voltage response regardless of the rotor (average) speed. The method presented is based on the standard synchronous reference frame proportional-integral (SRF PI) current controller augmented by a bank of harmonic integral (I) controllers. Such expanded current controller typically used in selective active filters provides simultaneously precise control of the harmonic current injection and spectral decomposition of the applied stator voltage. In the theoretical analyses presented relationships between the rotor flux position information and outputs of the harmonic I controllers are established. Based on this analysis a simple rotor position tracking and magnet flux polarity detection system is constructed. Experimental results presented demonstrate feasibility of this approach for initial rotor position detection in PMSM drives.