Design of robust multivariable feedback control systems using pole assignment and positivity concepts

The fact that the feedback interconnection of strictly positive real (spr) systems leads to an asymptotically stable closed loop can be used for the synthesis of robust observer-based state-space controllers. Since most control plants originally are not spr structural modifications must be done to establish this property even under parameter variations. Going that way one gets a modified spr plant that should be fed back by a controller that is also spr. In the present paper we use state-space controllers that are based on reduced-order observers: The closed-loop dynamics are designed by pole assignment and additional degrees of freedom that remain in the controller´s transfer matrix are used in order to render the controller spr.