Output-Feedback Adaptive Control for Systems with Time-Varying Parameters

This paper investigates the output-feedback adaptive control problem, exploiting the so-called congelation of variables method, to achieve output regulation for systems with time-varying parameters. To overcome the coupling between the input and the time-varying parameters, a strong minimum-phase property, i.e. input-to-state stability (ISS) of the inverse dynamics, is assumed. This property allows replacing the original coupling with a new coupling between the output and the varying parameters, which can be dominated via backstepping. A set of high-gain Kreisselmeier filters is then designed to guarantee that the state estimation error dynamics are also ISS. Finally, implementing the backstepping controller with a strengthened nonlinear damping term guarantees that all trajectories of the closed-loop system are bounded and that the output converges to zero asymptotically. (C) 2019, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.