Synthesis of plantwide control systems using PID controllers

Tuning PI controllers as part of a systematic methodology to synthesize plantwide control systems is discussed. In the synthesis methodology the manipulated variables used to control safety variables are first selected using mixed integer linear programming optimization, and the safety variables are assumed to be controlled in a SISO manner with PI controllers. Then, the PI controllers are incorporated into a dynamic process model and the synthesis of product controllers is carried out. To facilitate the synthesis procedure an automatic means of tuning the safety PI controllers is desired. The Tennessee Eastman process is used for illustration and there are 4 safety loops, 3 level loops and a pressure loop. Two approaches to tuning are presented: 1) the averaging level controllers are tuned first using P-only control, and then the tight controllers are tuned using optimization; and 2) PI control is used on the 3 levels, followed by optimization based tuning of the pressure loop. For the Tennessee Eastman process the first approach produces better results