Constrained set-point tracking control via output feedback for a class of nonlinear cascaded systems

This article proposes a constrained set-point tracking control scheme via output feedback for a class of nonlinear cascaded systems. The system in question allows for input-to-state stable (ISS) unmodelled dynamics, uncertain nonlinearities, and additive nonvanishing disturbances in the input channel. A reduced-order extended state observer (RESO) is delicately constructed to observe unmeasured states and to estimate the external disturbances. ISS changing supply rates technique with uncertain supply pair is developed to deal with the unmodelled dynamics. The tan-type Barrier Lyapunov function (BLF) is introduced to guarantee the tracking error converge to the origin without violation of the output constraint and all the closed-loop signals are bounded in the semi-global sense. The numerical example of a simple-link robot arm (SLRA) with and without an output constraint illustrates our theoretical results.