Modified internal model control for chemical unstable processes with time-delay

Aiming at unstable processes with large time delay in chemical industry, a modified internal model control method is proposed based on internal model control (IMC). The structure of new control method consists of inner-loop control and outerloop control. The separately design step is used to design forward-feedback controller for disturbance rejection and the IMC controller for set-point tracking. Meanwhile, a method of choosing the inner-loop controller is presented. Simulation results show that the method presented is not only effective for the dynamics and the stability of control system but also effective for the process robustness. Since the robustness can be improved by tuning the filter time constant when the model mismatch exits between the process model and plant.