On plant and LQG controller continuity questions (Q1298271)

Using the dual Youla parametrizations of controller-based coprime factor plant perturbations and plant-based coprime factor controller perturbations, the LQG plant-controller continuity question is studied. It is shown that it is possible to calculate a new optimal LQG controller from a previous one when the plant is slightly changed and to quantify the change in the controller as a function of the change in the plant. The degradation in the achieved LQG cost when the LQG controller is computed on the basis of a perturbation of the real plant is also determined. As a by-product, the set of all plants that have the same optimal LQG controller is characterized.