Robust PI controller desing for a time-delay process

The paper presents an approach to PI controller design for time-delay systems which can be interpreted as systems with the interval parametric uncertainty. It is supposed that the controlled system is described by the transfer function with time-delay with parameters lying in certain intervals. The transfer function of the controlled system is modified by approximation of the time-delay term by its Pade expansion. PI controllers, that are able to assure robust stability of the feedback closed loop with the modified controlled system are found by the graphical method. Then the pole-placement method is used to specify those controller parameters, which assure certain quality of the control performance.