A robust controller for a class of uncertain systems: with unknown bound of uncertainty

A robust control scheme with nonlinear feedback is proposed for a class of time-varying systems with uncertainty. The bound of the uncertainty is not necessarily known for the controller design. The controller is simple in the structure, and yet it guarantees the systems to converge exponentially, with a prescribed degree, towards its equilibrium or a residual ball centered at the equilibrium, depending on whether the actual magnitude of the uncertainty is less or larger than its estimated bound