Two-degree-of-freedom IMC structure and controller design for integrating processes based on gain and phase-margin specifications

In industrial practice, controller designs are usually performed based on an approximate model. The parameters of the physical systems can vary with operating conditions and time. Therefore it is essential to design a control system that shows a robust performance in the case of the aforementioned situations. Gain and phase margins are well-known measures for maintaining the robustness of a control system. There are many publications considering controller designs for stable processes based on gain and phase-margin specifications. However, for integrating processes, controller designs with user-specified gain and phase margins are very rare. A new two-degree-of-freedom internal model control structure is presented with simple tuning rules to design and tune PD controllers for integrating processes with a dead time to meet specified gain and phase margins. Simulation examples illustrate that the proposed design method can give better closed-loop system performance than existing design methods based on user-specified gain and phase margins. Simulation results for an assumed perturbation in the process parameters are also given to illustrate the robustness of the proposed controller structure and design method.