A new control strategy for integrating and unstable time delay processes

This paper presents a novel control strategy for open-loop integrating and unstable processes with time delay and shows that on it the Smith predictors are not absolutely necessary to overcome the control problems caused by long dead time in these processes. An inner feedback loop with a proportional (P) or proportional and derivative (PD) controller plays an important role in stabilizing the integrating and unstable processes. Then the feedforward controller in the outer loop is designed to control the stabilized process efficiently. Simple tuning formulae have been derived for the controllers based on user-specified gain and phase margins. A comparison of the performance of the proposed design settings with those given by earlier workers is presented.