Control Algorithms, Tuning, and Adaptive Gain Tuning in Process Control.

Abstract

Controller tuning relationships based on optimizing the response of a first order lag plus dead time process are developed for proportional-plus-integral (PI) and proportional-plus-integral-plus-derivative (PID) control algorithms. Minimum error integrals were used as criteria of performance for the feedback control loop. The relationships presented are shown to provide excellent response characteristics in particular for processes where little or no overshoot is desired. The effect of applying the proportional action to the feedback variable in a PI control algorithm is analyzed and found to provide a more consistent response to set point changes and load changes than the conventional PI algorithm, tuned for either set point or load changes. A technique of adaptive gain tuning for a PI controller is developed. The method is based on the use of sensitivity coefficient analysis to the identification of model parameters. The model chosen is a second order lag, and the technique is applied to a stirred tank chemical reactor temperature control system. The response of the proposed adaptive gain tuning technique proved to be superior to the response of the unadapted algorithm. Digital computers were used to simulate the control systems studied.