Asymptotic rejection of unmatched nonlinear disturbances for a class of nonlinear output-feedback systems

This paper deals with asymptotic disturbance rejection for nonlinear output feedback systems with unmatched disturbances that are generated from nonlinear exosystems. Nonlinear observer design techniques are exploited for the internal model design. A new strategy for internal model design is proposed, based on a dynamic extension of an existing nonlinear observer design for the nonlinear exosystem from the nonlinear term of the exosystem state which is injected in the nonlinear system. Additional filters are used to estimate the invariant manifold in the state space subject to the nonlinear exosystem, and other parts of the desired feedforward input. The proposed design for the internal model and the control ensures that the state variable asymptotically converges to the invariant manifold, which implies that the output asymptotically converges to zero. Copyright © 2010 Watam Press.