Adaptive feedforward disturbance rejection in nonlinear systems

This paper investigates the problem of adaptive feedforward compensation for a class of nonlinear systems, namely that of input-to-state (and locally exponentially) convergent systems. It is shown how, under suitable assumptions, the proposed scheme succeeds in achieving disturbance rejection of a harmonic disturbance at the input of a convergent nonlinear system, with a semi-global domain of convergence. The effectiveness of the proposed solution is demonstrated by combining results from averaging analysis with techniques for semi-global stabilization. An illustrative example shows the effectiveness of the scheme.