Full-order estimator for induction motor states and parameters

In direct vector control of induction machines, the instantaneous rotor flux vector is measured using sensors, estimators or a combination of both. Since the basic Kalman filter is a state estimator, its use in vector-controlled schemes has received much attention, including reduced-order variants. The paper describes the application of the Kalman filter to rotor current estimators for the direct scheme. The method used is termed full order, and is advocated as an alternative to reduced-order schemes which have been developed to aid realtime implementation. A novel approximate full-order form using steady-state gain values is shown to give encouraging results while yielding a useful computational saving. Also described is the application of the full extended Kalman filter algorithm to the online estimation of rotor resistance in an induction motor drive, required for the slip-calculation algorithm of indirect vector control. Temperature variations in rotor resistance can be tracked as they occur. These performance advantages are illustrated by experimental results from a typical open-loop-controlled drive.