Induction motor sensorless observer aligned with rotor flux derivative

A novel observer is proposed to reconstruct rotor speed and rotor flux vector in induction motors. The presented solution is characterized by a simple structure, based on a rotating reference frame which is pushed toward perfect alignment with the time-derivative of the rotor flux vector with respect to the stator windings reference frame. This approach allows to derive rotor speed and flux estimations without relying on pure integration of the stator flux dynamics and without using typical adaptive schemes which exploit the product between flux components and speed in the back-EMF of the stator current dynamics. Therefore, very good robustness is achieved with respect to voltage and current measurement uncertainties. Stability analysis is carried out by singular perturbation arguments, guaranteeing semiglobal practical asymptotic convergence. Effective tuning rules are derived considering a meaningful linearization of the proposed nonlinear observer. Simulations are presented to show the effectiveness of the solution.