Induction motor sliding mode estimators with known fluxes

Direct field orientation (DFO) is a widely used method to control the induction motor (IM) drive. In DFO, the stationary frame fluxes are estimated using an observer and are fed in the tan^–1 function to obtain the field orientation angle. This angle affects the stability and performance of the drive and no computational effort should be spared to ensure the accuracy of the fluxes. A flux observer may be augmented with parameter estimation schemes; also, the fluxes may be corrected to reduce the errors caused by non-ideal integration. If the fluxes are fully accurate, they can be viewed as an extra set of measurements and can now be used as input quantities into observers that estimate the other quantities of interest in IM control: speed, load torque, inverse of the rotor time constant. This paper shows what IM quantities can be estimated when the fluxes are known and presents a series of observer designs. The estimation mathematics is validated with simulations and experiments.