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

An override controller is presented which ensures that constrained output variables retain prescribed strict bounds. The class of nominal closed loop systems considered for the constrained output regulation problem is strictly proper & minimum phase, assuming for each output constraint one available actuator & the first Markov parameter to be full rank. This needs the plant to have the same input-to-constrained-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 nonsmooth Lyapunov function. This Lyapunov function is defined by the level of the output constraint creating an invariant set for which the strict constraints are satisfied. The override strategy retains a minimal effect on the nominal control loop in case no constraint is violated