Universal lambda-tracking for nonlinearly-perturbed systems without restrictions on the relative degree

This paper presents a universal output-feedback tracking strategy for minim um phase linear systems of arbitrary but known relative degree with a class of nonlinear perturbations and output measurement noises. Some information , such as the state dimension, the sign of high-frequency gain and the rela tive degree of nonlinearly perturbed systems, are not known a priori. It is proved that the tracking error is guaranteed asymptotic to the interval [- lambda, lambda] subset of R with arbitrary prescribed lambda > 0. (C) 1999 Elsevier Science Ltd. All rights reserved.