Adaptive flux observer of induction motor and its stability

Abstract

The indirect field oriented control of an induction motor is widely used. This methbd has a disadvantage which is sensitivity to the motor parameter variation. Especially, resistance depends on the motor temperature. On the other hand, the direct field oriented control method is robust against the motor parameter variation because the measured motor flux is fed back to the reference. The disadvantage of this method is that the installation of a flux sensor is necessary. Therefore, flux estimation from the terminal variables is usually used instead of the flux measurement. However, flux estimation is also sensitive to the motor parameter variation.Recently, flux observers have been proposed for flux estimation. The sensitivity of the flux observers to the rotor resistance variation is much lower than that of the conventional flux, estimator. However, the sensitivity of these observers cannot be completely zero.To solve these problems, a new rotor flux observer with parameter adaption scheme is proposed in this paper. Parameters identified adaptively are the stator and rotor resistance which are dependent upon the motor temperature. A stability of the proposed adaptive flux observer is proved by the Lyapunov's theorem.