REDUCED-ORDER ADAPTIVE OBSERVATION WITH NONSPECIFIC ADAPTIVE LAW

The robustness of adaptive observers whose order is less than that of the plant is addressed. It is shown that residuals (unmodeled states) with finite energy over a finite time interval, together with a definitely exciting plant input, are sufficient to insure ultimate boundedness of the parameter and state errors, regardless of the plant stability or input boundedness. In the absence of definite excitation, the errors are shown to increase at a maximum rate which is proportional to t1/2.