Variable structure robust state and parameter estimator

The problem of simultaneous robust state and parameters estimation for a cl ass of SISO non-linear systems under mixed uncertainties (unmodelled dynami cs as well as observation noises) is addressed. A non-linear variable structure robust 'observer-identifier' is introduced to obtain the corresponding estimates. Lie derivative technique is used to obtain the observability conditions for the equivalent extended non-linear system. It is shown that, in general, the extended system can lose the glob al observability property and a special procedure is needed to work well in this situation. The suggested adaptive observer has the non-linear high-ga in observer structure with adjusted parameters that provides 'a good' upper bound for the identification error performance index. The van der Monde tr ansformation is used to derive this bound which turns out to be tight. Thre e examples dealing with a simple pendulum, the Duffing equation and the van del Pol oscillator are considered to illustrate the effectiveness of the s uggested approach. Copyright (C) 2001 John Wiley & Sons, Ltd.