The robustness of a new class of two-degree-of-freedom controllers

We consider a new approach in designing a two-degree-of-freedom controller for a class of uncertain linear systems. To tackle the structured uncertainty in the plant, we utilise the notion of quadratic guaranteed cost control. Such scheme guarantees that the closed loop system is quadratically stable and an associated cost function is bounded. In the reference control part we apply a novel method called a hybrid reference control (HRC). For the unperturbed plant, this control scheme improves the transient response performance. We focus on the application of the HRC when the underlying system is perturbed as well as in the robustness of the improved performance. It is shown that the perturbed systems do not necessarily enjoy the benefits of HRC in improving the performance