Robust control of nonlinear systems by estimating time variant uncertainties

In this note, robust control design is considered for nonlinear systems with time variant uncertainties. Instead of assuming that bounding function on uncertainties is either known or parameterizable in terms of unknown constants, uncertainties or their bounding functions are estimated. It is shown that bounded uncertainties from a known or partially known exo-system can be estimated as a part of a globally stabilizing robust control. The proposed method extends the existing results of adaptive robust control, and it makes robust control more applicable by requiring less information on uncertainties.