Constrained robust output regulation for a class of nonlinear systems with unknown control direction

This paper addresses a constrained robust output regulation problem for a class of output feedback systems with unknown control direction. The problem is firstly transformed into a constrained stabilization problem by introducing the internal model principle. Then a robust adaptive feedback control law for the system is proposed to solve the constrained stabilization problem by incorporating the techniques of Barrier Lyapunov Function and Nussbaum gain. Such a design leads to the solution of the constrained robust output regulation problem of the original system in the sense that the output tracking error is constrained within the prescribed barrier limit while asymptotically approaching to zero and the closed loop signals are all bounded for all the time. A numerical example is provided to illustrate the performance of the proposed control.