Model-based and PID controllers for disturbance rejection in processes with time delay: a comparison

Abstract

Model-based control systems for processes with a time delay and slow disturbance dynamics are examined and compared. Two of them have a two-degrees-of-freedom Internal Model Control (IMC) structure: the first one (IMC-22) was presented by the authors earlier, and the second one (IMC-GAP) is derived from the Generalized Analytical Predictor (GAP). The nature of the difference between the two is illustrated in a control system with first order process and disturbance transfer function models. The performance of the two is compared for a first and a second order process, the process types for which the GAP was designed. The same type of performance comparison is done for a third controller type, the Model-Dependent Control (MDC), and for the IMC-PID controller derived from an IMC structure. Some modifications of the GAP and MDC controllers are proposed in order to improve the input characteristics as in the IMC-22 controller. The controllers are tuned for equal robust stability in several cases of process parameter uncertainty.