Observer-based adaptive robust control of a class of nonlinear systems with dynamic uncertainties

In this paper, a discontinuous projection-based adaptive robust control (AR C) scheme is constructed for a class of nonlinear systems in an extended se mi-strict feedback form by incorporating a nonlinear observer and a dynamic normalization signal. The form allows for parametric uncertainties, uncert ain nonlinearities, and dynamic uncertainties. The unmeasured states associ ated with the dynamic uncertainties are assumed to enter the system equatio ns in an affine fashion. A novel nonlinear observer is first constructed to estimate the unmeasured states for a less conservative design. Estimation errors of dynamic uncertainties, as well as other model uncertainties, are dealt with effectively via certain robust feedback control terms for a guar anteed robust performance. In contrast with existing conservative robust ad aptive control schemes, the proposed ARC method makes full use of the avail able structural information on the unmeasured state dynamics and the prior knowledge on the bounds of parameter variations for high performance. The r esulting ARC controller achieves a prescribed output tracking transient per formance and final tracking accuracy in the sense that the upper bound on t he absolute value of the output tracking error over entire time-history is given and related to certain controller design parameters in a known form. Furthermore, in the absence of uncertain nonlinearities, asymptotic output tracking is also achieved. Copyright (C) 2001 John Wiley & Sons, Ltd.