Asymptotic attenuation of a class of nonlinear systems with unknown sinusoidal disturbances

Abstract

In this paper, nonlinear observers are incorporated into the adaptive control to synthesize controllers for a class of uncertain nonlinear systems with unknown sinusoidal disturbances which are presented in matched and unmatched forms. In addition to magnitudes and phases, frequencies of the sinusoidal disturbances need not be known as well, so long as the overall order is known. Nonlinear observers are constructed to eliminate the effect of unknown sinusoidal disturbances to improve the steady-state output tracking performance-asymptotic output tracking is achieved. The adaptation law is used to obtain the estimate of all unknown parameters. The presented disturbance decoupling algorithms can deal with matched and unmatched unknown sinusoidal disturbances.