Sensorless Induction Machine Drive for Fly-Wheel Energy Storage Systems with a TLS-based Non-linear Observer

This paper proposes a sensorless technique for an induction machine Flywheel Energy Storage System (FESS) based on a non-linear observer integrated with a total least-squares speed estimator taking into consideration the IM (Induction Machine) saturation effects. The nonlinear observer is based on an original formulation of the dynamic model of the IM including the magnetic saturation, rearranged in a space-state form, after assuming as state variables the stator current and the rotor magnetizing current space-vectors in the stator reference frame. The choice of the observer gain has been made by the use of Lyapunov's method. The speed signal needed by the non-linear observer for the flux estimation is provided by the Total Least Square (TLS) based speed estimator, which itself takes into consideration the magnetic saturation for the speed estimation. The proposed nonlinear observer has been tested in numerical simulation and verified experimentally on a suitably developed test set-up, demonstrating its applicability as far as FESS is concerned.