Extension of IMC tuning to improve controller performance

Rivera et al. (1986) introduced a PID controller design method based on internal model control (IMC) that is attractive to industrial users because it has only one tuning parameter. The parameter relates directly to the closed loop speed of response and the robustness of the control loop. For a system with deadtime, if used as an approximation for the time delay, the IMC controller includes implicitly integral action and has a PID structure in cascade with a filter. In their mathematical development, Morari-Zafiriou (1989) used a first order pade approximation for the time delay in process model, by using a non-symmetric second order approximation instead, one can preserve the simple second order form of the controller for their model and not make the structure of the controller complex. In addition significant improvements in model matching and controller tuning can be obtained. Especially for those processes that have significant deadtime