Binary robust adaptive control with monitoring functions for systems under unknown high‐frequency‐gain sign, parametric uncertainties and unmodeled dynamics

In this paper, we propose an adaptive output-feedback controller for uncertain linear systems without a priori knowledge of the plant high-frequency-gain sign. To deal with parametric uncertainties and unmodeled dynamics, we consider a robust adaptive strategy named binary model reference adaptive control, which has the good transient properties and robustness of sliding mode control with the important advantage of having a continuous control signal free of chattering. The effective way of tackling unknown high-frequency-gain sign is employing monitoring functions. The developed adaptive control guarantees global exponential stability of the closed-loop error system with respect to a compact residual set. Moreover, in the absence of unmodeled dynamics, exact tracking of a reference signal can be achieved. Numerical simulations illustrate the efficacy of the proposed approach. Copyright © 2015 John Wiley & Sons, Ltd.