Modeling, Identification and Validation of Uncertain Linear and Nonlinear Feedback Systems

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The objective of the proposed work is to develop an integrated suite of tools and approached for the modeling of uncertain systems for feedback control design purposes. Our modeling framework is based upon robust control theory, which is supported by several sophisticated control design methods. These models are in effect set descriptions, where the sets are generated by unknown but bounded dynamic perturbations within the model. The models allow the designer to capture the variety of uncertain behaviors that a physical system will generate. Although this a powerful and flexible modeling framework, the tools available for modeling physical systems are limited.Our prior work on model validation for robust control models from the basis for the work proposed here. This approach has led to tools which allow the designer to experimentally quantify the difference between a physical system and the closest member of a robust control model set. The current work looks at extending these approaches to alternative experimentally scenarios. One direction will be the use of correlated swept-sine experiments; a procedure frequently used in industrial practice. A second direction will be the consideration of noise and perturbations from different signal classes; for example stochastic noise and gain bounded perturbations. Such models agree more closely with typical physical systems, and will make these methods applicable to a wider range of industrial processes. We also propose to develop a robust control modeling framework which will handle certain classes of nonlinear systems. The project will consider two industrially motivated examples from these classes: rotating stall in jet engine compressors; and thermo-acoustic interactions in combustors. The methods will be applied to simplified simulation versions of these problems. The combination of nonlinear behaviors and dynamic perturbations opens up an area of nonlinear robustness analysis which will also be addressed. Three experiments are available and will be used in support of this research: (1) A metalorganic chemical vapor deposition (MOCVD) reactor, used for epitaxial crystal growth of blue LEDs and blue laser diodes. (2) A magnetically levitated bearing system, developed as a prototype for an artificial heart pump (left ventricular assist device). (3) A rapid thermal processing system, which models the dynamics of typical processing steps in the semiconductor and film processing industries. Each of these experiments exhibits common practical difficulties which are not yet well handled by theoretical modeling and identification methods, making them ideal testbeds for the work proposed.