MODEL-BASED AND PID CONTROLLERS FOR DISTURBANCE REJECTION IN PROCESSES WITH TIME-DELAY - A COMPARISON

Model-based control systems for processes with a time delay and slow d isturbance dynamics are examined and compared. Two of them have a two- degrees-of-freedom Internal Model Control (IMC) structure: the first o ne (IMC-22) was presented by the authors earlier, and the second one ( IMC-GAP) is derived from the Generalized Analytical Predictor (GAP), T he nature of the difference between the two is illustrated in a contro l system with first order process and disturbance transfer function mo dels. 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 s ame type of performance comparison is done for a third controller type , the Model-Dependent Control (MDC), and for the IMC-PID controller de rived from an LMC structure. Some modifications of the GAP and MDC con trollers 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. Copyright (C) 1996 Elsevier Science Ltd.