A double-manifold sliding mode observer for the speed and flux of the induction motor using an alternative state-space model

The paper presents a sensorless double-manifold sliding mode observer for the induction motor (IM) drive. The observer is designed using an alternative state-space model of the IM - it estimates the speed and the stationary frame fluxes of the motor. These are typically needed in an IM direct field orientation control scheme. First, the paper presents the alternative state-space model of the IM that is obtained from the traditional one using a change of variable. Based on this model, a Sliding Mode (SM) observer is designed. Sliding mode existence, observer convergence and gain design are discussed. The estimate of the speed is obtained by filtering one of the switching manifolds of the observer. Simulations show that the speed and flux estimates are fairly accurate. A sensitivity analysis with respect to the rotor and stator resistances and the magnetizing inductance is presented.