A Comparison of the Smith Predictor and Optimal Design Approaches for Systems with Delay in the Control

The relatively recent application of optimal control theory to the design of control systems for processes with delay has made available an alternative design approach to the classical Smith Predictor approach. Although the designs resulting from the two approaches have many features in common, there are also important differences, and neither the similarities or differences have been examined in any detail in the literature. This paper surveys the work to date in this area, reviews the development of and examines the general characteristics of the control systems resulting from application of the two approaches to a general class of multivariable systems with delay in the control, and presents a detailed comparison of the designs for the case in which the process to be controlled is first order with delay. An important result which emerges is that the design resulting from the optimal approach as developed in the literature to date does not perform as well as the Smith Predictor design in controlling against output disturbances.