| Scope and method of study. The thesis investigates decentralized control of a class of large-scale nonlinear systems, which contain unmatched, linear and nonlinear inter-connections between constituent subsystems. Adaptive methods and Lyapunov analysis are used to develop stable decentralized control algorithms. Improvements to existing dynamic models of fundamental web handling elements are suggested and discussed. A large experimental platform, which mimics most of the features of an industrial web process line, is used for experimentation with the proposed decentralized controller.; Findings and conclusions. It is shown that decentralized control schemes can be developed for a class of unmatched large-scale systems. Sufficient conditions are developed that will result in closed-loop stability. For linear interconnections, these conditions ensure global stability and for nonlinear interconnections, they ensure semi-global stability. A model reference decentralized adaptive controller is developed for systems with unmatched, linear interconnections. To circumvent the unmatched problem, a new reference model that exchanges reference information between subsystems is proposed. Based on the improved dynamic models for unwind/rewind rolls, accurate inertia compensation terms are computed for on-line compensation. A strategy for obtaining the equilibrium control inputs and reference velocities is given based on the reference tension in each web tension zone and master-speed roller reference velocity. Extensive comparative experiments with the proposed decentralized controllers and an often used industrial decentralized PI controller show substantial reduction in web tension error with the proposed decentralized controllers. |
