Hakki Ulas Ünal

Robust Controller Design:: Systems with Multiple Uncertain Time-delays Hakki Ulas Ünal

Since an actual plant can not be modelled perfectly, robust controllers are needed due to the existing uncertainties. The uncertain part of the model may be non-causal if the plant has time-delays possessing time-varying uncertainties. Note that, most of the robust controller design methods are based on the ``small-gain theorem'', which assumes the causality of the connected sub-systems. Because of this, some limitations on the plant may be required to ensure the causality of the uncertain part to design a robust controller. However, such an approach results in a conservative controller. In this study, allowing non-causal uncertain parts, optimal robust controller design problem for systems with multiple time-delays possessing time-varying uncertainties is considered. The problem is difficult, since these systems are infinite-dimensional and the uncertain parts are allowed to be non-causal. Since unstable controllers are not desired in practice, however, designed optimal controllers may be unstable, stable robust controller design algorithms are also considered. As a case study, the flow control problem in data-communication systems is handled.