Design of a double manifold Sliding Mode observer for speed and state estimation of the induction motor

The paper discusses the problem of speed and state estimation for the induction motor (IM) drive and presents a double-manifold Sliding Mode observer. This is obtained by adding extra feedback terms to a single-manifold observer design. Both designs are based on the model of the IM in the stationary reference frame. The observer uses compound manifolds which are constructed as a combination of the estimated states and mismatches. Observers with compound manifolds have not been widely investigated because they cannot be designed using a standard procedure; however, they may have very interesting properties. The paper investigates the behavior of a single-manifold observer first; it is shown that this only converges partially and provides an approximate speed estimate. Based on this, a double-manifold observer is designed. This estimates the fluxes, drives the current mismatches to zero and yields an accurate speed estimate. The method is applicable in a sensorless IM drive control algorithm where the speed, the flux magnitude and the rotor flux angle are needed. The theoretical developments are supported with simulations.