Nonlinear flux observer with on-line parameter tuning for wide speed operation of induction machines

Abstract

A closed-loop rotor flux observer with a nonlinear speed dependent gain is presented. The observer is used in a rotor flux regulated, rotor flux oriented induction machine drive that also makes provisions for on-line parameter tuning using a model reference adaptive system (MRAS). The closed-loop observer is based on using two different open-loop observers. The current and voltage model rotor flux observers are blended together using a nonlinear gain function. The nonlinear gain function determines the bandwidth of the closed-loop observer and allows for a transition to take place from the current model to voltage model rotor flux estimating attributes. The implementation of the closed-loop observer and parameter tuning algorithm is less complicated than previous designs and yet, theoretically, the performance of the motor drive system is improved.