Safe controller changes with additional guaranteed model reference performance improvement for the unknown plant

A safe controller change is a change, from a current stabilising controller to a new controller, with guaranteed stability of the real closed loop system (i.e. the closed loop system formed by the new controller and the physical plant), even if the true transfer function of the physical plant is not exactly known. In a previous contribution, we characterised safe controller changes, with guaranteed bounds on the stability margin of the real dosed loop system, on the basis of uncertain closed loop models. In this paper, we introduce additional conditions which guarantee safety and also performance improvement of the real closed loop system.