A nonlinear observer for rotor flux estimation considering magnetic saturation effects in induction motor drives

This paper proposes a non-linear observer for In- duction Machine (IM) drives which takes into consideration the saturation effects. The non-linear observer is based on an original formulation of the dynamic model of the IM taking into consideration the magnetic saturation of the iron core. A Lyapunov based convergence analysis is proposed in order to suitably compute the observer gain guaranteeing the stability of the observer. The proposed non-linear observer has been tested in numerical simulation and experimentally on a suitably developed test set-up. Its behaviour has been compared to that obtained with a classic Full-Order Luenberger Observer (FOLO) in variable flux working conditions, in terms of accuracy of the amplitude and phase of both the rotor flux linkage and the stator currents space vectors. Results have shown the capability of the proposed non-linear observer to correctly estimate the rotor flux linkage amplitude and phase under flux varying conditions including strong variation of the saturation of the iron path with accuracy in the flux estimation much higher than that obtained with the classic FOLO.