Stability in the presence of persistent plant changes

In this paper we consider the use of periodic controllers for simultaneous stabilization and performance, including the case when there is an occasional, though persistent, plant change. We consider the case of a finite set of admissible models; we provide a design procedure which yields a controller which stabilizes each such model and provides near optimal LQR performance, and then demonstrate that it has the facility to tolerate occasional (but persistent) switches between these models. The controller is periodic with a slight nonlinearity.