Cascade and high-gain observers comparison for sensorless closed-loop induction motor control

Cascade and high-gain observers based on interconnected form to estimate the mechanical and magnetic states of sensorless induction motor drives are considered. Furthermore, a flux and speed sliding-mode controller is proposed and combined with the observers to achieve the tracking of rotor flux and mechanical speed for induction motor without the need of flux, speed and load torque measurements. On the basis of the Lyapunov theory, the stability analysis of the proposed observers, the controller and the closed-loop ´observer + controller´ are given. The observers, combined with the controller in closed loop, are compared in terms of their speed-tracking capability and their sensitivity to parameter variations on reference trajectories of a sensorless induction motor control benchmark, particularly when the induction motor state is unobservable. This benchmark is applied on an experimental set-up located at IRCCyN (Nantes, France).