Nonlinear Feedback Control of Hybrid Process Systems

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The objective of this research program is to develop a comprehensive framework for nonlinear model-based feedback control of multivariable hybrid nonlinear processes (i.e., processes with combined continuous dynamics and discrete events). Both lumped and spatially-distributed hybrid systems will be studies. Lyapunov theory will be employed to produce novel analytical nonlinear controller designs that deal explicitly with control actuator constraints and model uncertainty and enforce the desired stability, performance and robustness specifications in the closed-loop system. The motivation for the research is provided by: a) the common coupling of continuous process dynamics with discrete events, b) the abundance of nonlinearities and uncertainties in chemical process models coupled with the common occurrence of hard constraints on the capacity of control actuators, c) the lack of practical nonlinear control methods for hybrid chemical processes that can deal explicitly and simultaneously with nonlinearities, uncertainty and constraints and d) the increasing need to improve chemical process operation to reduce product variability and off-spec production, improve energy efficiency and reduce environmental impact. To realize the desired objective, the research will focus on the following projects: a) nonlinear and robust control of multivariable hybrid nonlinear processes with input constraints, b) output feedback implementation of the nonlinear and robust controllers using nonlinear state estimators, c) nonlinear and robust control of spatially-distributed hybrid processes, d) application of the nonlinear control algorithms to simulated lumped and spatially-distributed hybrid processes with uncertainty and actuator saturation, and e) development and experimental application of a real-time integrated measurement/hybrid feedback control system to a plasma-enhanced chemical vapor deposition (PECVD) reactor. The research will provide fundamental insights into the limitations imposed by the presence of nonlinearities, uncertainty, constraints and discrete events on our ability to modify the dynamics of a chemical process, provide concrete control algorithms that can be readily implemented in practice, illustrate the application of the control methods and derive tuning guidelines for the implementation of the controllers, and produce a research monograph on "nonlinear process control" based on previous and current research of the PI in this area. The new control algorithms are expected to lead to significant improvement in the operation and performance of chemical process systems with combined continuous/discrete dynamics, nonlinearities, uncertainty and constraints. The development of integrated measurement/control systems for PECVD processes is expected to reduce spatial non-uniformity of the deposition, especially as wafer dimensions continue to increase and broaden the use of these processes in semiconductor manufacturing.