Comparison of dead time compensation schemes for discrete implementation of the Q-PID algorithm

A PID type algorithm called Q-PID was developed to improve online quality c ontrol of continuous processes. It has adjustable parameters to improve the controlled variable response or to decrease the manipulated variable movem ents, hence decrease the cost of control, Q-PID has PID type terms, a lead/ lag term and dead time compensation. All previously published work using th is algorithm considered continuous systems. Discrete implementation must be analyzed so that it can be used practically. This paper presents a sound d evelopment and simulation of the three possible dead time implementation sc hemes, Smith predictor, analytical predictor, and generalized analytical pr edictor that could be used for discrete implementation. It was discovered t hat either the Smith predictor or analytical predictor techniques could be used in the Q-PID with satisfactory results. The generalized analytical pre dictor results in drastic cost increases and instability in the presence of modeling error. The Smith predictor is the suggested method as it performs the best in the presence of modeling error and is simple and easy to imple ment. (C) 1999 Elsevier Science Ltd. All rights reserved.