Control of process with time delay

In this paper the robustness of the Smith predictor is discussed. An extension of the time delay tolerance is given for systems presenting an open-loop frequency response with multiple unity gain crossover frequencies. A two-degree-of-freedom decoupling scheme is proposed to independently adjust set point and load disturbance responses. Classical design tools (PI, PID) can be used to design the feedback part of the controller. The effectiveness of the method is demonstrated on a numerical example which shows that the nominal performance of our design is similar to the Smith predictor performance but with better robustness properties.