Influence of stator current and machine saliency on sensorless control performance based on third-harmonic back-EMF

This presentation investigates the influence of stator current and machine saliency on the rotor position estimation of a permanent-magnet synchronous machine (PMSM) based on third-harmonic back-EMF which is contained in windings irrespective of the operational mode and parameters. Due to machine saliency and saturation of the air gap flux-linkage, the amplitude and phase angle of the third-harmonic back-EMF will be affected by the stator current. Several experimental analyses, carried out based on a dSPACE platform with a laboratory PMSM, validate that the machine speed and q-axis current does not affect the phase angle of the third-harmonic back-EMF, whereas is does exhibit a rotor position estimation error when a negative d-axis current is applies, and with a large positive d-axis current, the third-harmonic back-EMF is seriously distorted due to critical air-gap saturation.