A robust override scheme enforcing strict output constraints for a class of strictly proper systems

This paper presents an override controller which ensures that constrained output variables retain certain prescribed strict bounds. The class of nominal closed loop systems considered for the constrained output regulation problem is strictly proper and minimum phase, assuming for each output measurement constraint one available actuator and the first Markov parameter to be full rank. This necessitates the open-loop plant to have the same input-toconstrained-output characteristics. The advantage of the considered class of nominal systems is that an output constraint translates directly into a state constraint for which it is possible to use a particular non-smooth Lyapunov function. The non-smooth Lyapunov function is defined by the level of the output constraint creating an invariant set for which the strict output constraints are satisfied. The override strategy is designed to retain a minimal effect on the nominal control loop in case no output constraint is violated. Copyright 2005 IFAC