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Nonlinear Model Reduction and Control of Distributed Chemical Processes

Distributed chemical processes are characterized by the coupling of chemical reaction with significant diffusion, convection and phase-dispersion phenomena. Examples include the chemical vapor deposition of thin films and the Czochralski growth of crystals for microelectronics manufacturing, as well as the crystallization of proteins for pharmaceutical applications. Traditional methods for controlling distributed chemical processes are based on the simplifying assumption that the control variables are spatially uniform. Yet, many control problems in distributed chemical processes involve regulation of variables which are distributed in space (e.g., temperature profile across a wafer), and cannot be effectively solved with the existing methods. We have pioneered the development of a general and practical framework for the synthesis of practically implementable nonlinear feedback controllers for distributed chemical processes based on fundamental models that accurately predict their behavior. The philosophy behind this ``model-based'' approach is that the synthesis of efficient control systems should exploit the ability of a fundamental model to predict the behavior of a process and the fundamental knowledge of the underlying physico-chemical phenomena that the model contains.The key difficulty in developing model-based control methods for distributed chemical processes lies in the ``infinite-dimensional'' nature of the distributed process models, which prohibits their direct use for control system synthesis. We have developed nonlinear order reduction techniques for deriving low-dimensional approximations that accurately reproduce the dynamics and solutions of distributed process models. We have used these approximate models for the synthesis of nonlinear feedback controllers via geometric methods and Lyapunov techniques. The controllers can be readily implemented in practice and enforce the desired control objectives in the infinite-dimensional closed-loop system. We will present applications of the theoretical results to: a) a rapid thermal chemical vapor deposition reactor, b) a Czochralski crystal growth process, c) a fluid dynamic system, and d) a continuous crystallizer.

Type of Seminar:
Public Seminar
Ass. Professor Panagiotis D. Christofides
Department of Chemical Engineering University of California at Los Angeles Los Angeles, CA 90095-1592 USA
Aug 03, 2000   10:45

ETH Zentrum, ETL K 25, Physikstr. 3, 8006 Zurich
Contact Person:

Prof. M. Morari
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Biographical Sketch:
Panagiotis D. Christofides was born in Athens, Greece, in 1970. He received the Diploma in Chemical Engineering degree, in 1992, from the University of Patras, Greece, the M.S. degrees in Electrical Engineering and Mathematics, in 1995 and 1996, respectively, and the Ph.D. degree in Chemical Engineering, in 1996, all from the University of Minnesota. Since July 1996 he has been an Assistant Professor in the Department of Chemical Engineering at the University of California, Los Angeles. His theoretical research interests include nonlinear, robust and optimal control, singular perturbations, and model reduction, optimization and control of nonlinear distributed parameter systems, with applications to chemical processes, advanced materials and semiconductor processing, particle technology, biotechnology and fluid flows. He has published over 70 articles and one research monograph. Professor Christofides has received the Teaching Award from the AIChE Student Chapter of UCLA in 1997, a Research Initiation Award from the Petroleum Research Fund in 1998, a CAREER award from the National Science Foundation in 1998, the Ted Peterson Student Paper Award from the Computing and Systems Technology Division of AIChE in 1999, and the O. Hugo Schuck Best Paper Award from the American Automatic Control Council in 2000.