A Study on the Theory and Practice of Nonlinear Process Control Using Functional Expansion (FEx) Models

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Abstract - Palazoglu - 9800073 Understanding the dynamics of nonlinear systems is important for the design, operation and control of many chemical processes. The lack of information regarding the behavior of nonlinear processes causes the chemical engineer to limit the region of safe operation, to overdesign in an attempt to soften nonlinearities, or to design conservative control systems such that an acceptable operation is maintained. Such engineering solutions may yield suboptimal plant operations, and more economically favorable regimes may be unnecessarily deemed unsafe or unreliable. The goal of this research is to establish a rigorous setting within which nonlinear process control problems can be analyzed, and controllers can be designed and implemented on actual processes. This setting will be built upon a new paradigm that exploits functional expansion (FEx) models to develop novel control system design and analysis tools. Such a setting is not only expected to broaden one's understanding of nonlinear process control problems, but will also promote the application of these new concepts to real process systems. The methods make use of analogous linear analysis and control concepts, thereby providing an intuitive setting for engineers. The work to be done includes: (1) Functional expansions will be used to quantify the "nonlinearity" of a process, and the approximate FEx model structure will be exploited for model identification using process data. (2) The control design effort will be based upon FEx models in the spirit of model predictive control. This will generate new viewpoints about the representation and manipulation of nonlinear discrete-time models for control. (3) A set of criteria will be developed to help assess the stability and robustness of FEx model based control systems. (4) The methods will be tested by real-time applications using a laboratory-scale process as well as pilot-scale processes that are run by commercial Distributed Control Systems(DC S). This last area will take advantage of a long-time collaboration with Prof. Romagnoly of the University of Sydney.