Binary robust adaptive control for global tracking of uncertain systems with unknown high-frequency-gain sign

An adaptive output-feedback controller is proposed for uncertain linear systems without a priori knowledge of the plant high-frequency-gain sign. The system parametric uncertainties are compensated by a robust adaptive strategy named binary adaptive control which combines the good transient properties and robustness of Sliding Mode Control with the desirable steady-state properties of parameter adaptive systems. An important advantage with respect to sliding mode control is that the proposed controller generates a continuous signal so that control chattering is avoided. The effective way of tackling unknown high-frequency-gain sign is employing monitoring functions. The developed adaptive control guarantees global stability of the closed-loop system and exact tracking of a reference signal. Numerical simulations illustrate the efficacy of the proposed approach.