Plantwide control design and analysis of a continuous polymerization process using optimal control methods

Abstract

An optimal control based algorithm, using a linear quadratic state-feedback regulator (LQR) on a linear model, has been developed which identifies viable proportional integral with feedforward (PI/FF) control strategies. In this approach, two matrices, S/sub FB/ and S/sub FF/, are calculated from the linear state space matrices and the optimal control gain. The S/sub FB/ and S/sub FF/ reveal the respective dominant feedback and ratio/feedforward paths of a system. Three screening and four performance heuristics have been developed to interpret these matrices to reveal the dominant control pathways of a system. Information gained from these matrices is used to formulate PI/FF control architecture(s). These architectures are tested on a fixed dynamic simulation to judge their performance. A continuous polymerization process was used as test case to evaluate the results of the optimal control based algorithm and to test the heuristics presented here. The algorithm identified weak manipulated variables and eliminated them from the list of degrees of freedom. It also identified viable potential control architectures that were tested with the fixed dynamic simulations. The algorithm provided information on each candidate architecture's simplicity and degree of decoupled, feedback-path dominance. These results, for each case, were confirmed through simulations.