Single and double compound manifold sliding mode observers for flux and speed estimation of the induction motor drive

The study discusses the problem of speed and flux estimation for the induction motor (IM) drive and presents the design of two sliding mode observers (SMO) with compound manifolds. Both observers are developed using the IM model in the stationary reference frame. The first observer is a single-manifold SMO - it estimates the motor fluxes and yields an approximate value of the speed; however, it is not a converging observer. The single-manifold design is transformed into a double-manifold observer by adding extra feedback terms - this leads to a fully convergent observer that also yields an accurate estimate of the speed. The observers are designed using compound manifolds, which are chosen as a combination of the estimated fluxes and current mismatches. Observers with compound manifolds have been rarely investigated because they cannot be designed using a standard procedure; however, they are shown to have interesting properties. Observer uniqueness is also discussed. The methods proposed are suited to 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 and experiments.