Tracking of piecewise constant references for constrained nonlinear systems

The paper addresses tracking of a piecewise constant reference for a nonlinear system subject to control and/or state constraints. The proposed controller, called dual-mode, extends to the nonlinear case an approach formerly introduced for linear systems. The dual-mode controller is based on the knowledge of the set of feasible state-setpoint pairs and operates in two different modes: as a regulator if the current state is feasible for the desired set-point, or attempts to recover feasibility as quickly as possible whenever feasibility is lost due to a set-point change. The difficulty of constructing the feasibility set in the state-setpoint space for a nonlinear system is overcome by embedding the original system into a family of uncertain (polytopic) linear systems.