Output-Constrained Robust Adaptive Control for Uncertain Nonlinear MIMO Systems With Unknown Control Directions

This letter proposes a new output-constrained robust adaptive controller for a class of uncertain multi-input multi-output nonlinear systems. In the adaptive control synthesis, Nussbaum gain is introduced, which not only ensures the closed-loop stability of the system in presence of unknown control directions but also enforces the asymptotic tracking of the reference signal under non-parametric plant uncertainties. The output constraints are enforced by carrying out a novel transformation, which transforms the constrained system into an equivalent unconstrained system. It is proven that the closed-loop system is asymptotic stable in the sense of Lyapunov and the output of the system will remain bounded by the imposed output constraints. The effectiveness of the proposed control design is demonstrated through extensive simulations.