Design of Sliding Mode observers with single compound manifolds for state estimation of the induction motor drive

The paper discusses the problem of state/rotor flux angle estimation for the induction motor (IM) drive and presents a series of Sliding Mode (SM) observers that are constructed using compound manifolds. The observers use the model of the IM in the stationary reference frame - their behavior and estimation properties are discussed. Observers with compound manifolds have not been widely investigated because they cannot be designed using a standard procedure; however, they have interesting properties. The paper shows candidate manifolds and explains the approach for designing IM observers with compound manifolds. A class of observers and their versions are presented. In the paper, several sensored SM observers are presented first. Then, it is attempted to transform them into sensorless observers by replacing the measured speed with a speed estimate (which is assumed inaccurate). The paper finds a certain design has desirable properties - using an improper speed value, its estimated fluxes are in phase with the real fluxes. Using direct field orientation, the rotor flux angle obtained is accurate and this can be used for sensorless field orientation.