Reduced-order flux observer for speed-sensorless induction motor drives: Gain selection for better noise rejection

This paper deals with the reduced-order flux observer for speed-sensorless induction motor (IM) drives, which shows stable operation even at very low speeds. However, noise appears in the estimated flux in higher speeds (starting around 0.5 p.u.) in the motoring mode. An analytical solution for the observer gain that improves noise rejection of the observer in higher speeds is derived. The proposed gain selection is compared with the original one using a 45-kW IM drive; improved noise rejection with the proposed gain selection is demonstrated.