On the design of model-based nonlinear control structures: Applications to chemical reactors and general dynamical systems.

摘要

The design of nonlinear control structures for perfectly mixed, continuous chemical reactors is the central objective of this research. Conventional reactor control techniques using linear temperature controllers are sometimes inadequate in highly exothermic, or otherwise nonlinear, reactors for preventing dangerous or costly runaway events which can be explosive.;Two theoretical frameworks are employed in this research. The first is reaction rate control based on extensive variable control concepts in which the deviation of the dominant reaction rate from its steady state value is defined as the controlled variable. The second framework is reference system synthesis which is a model inverse type of control related to the minimal prototype or internal model approaches.;The research techniques used in this study involve both numerical simulation and nonlinear dynamics analysis methods of our own design. Applied to several different reactor models, the reaction rate, reference system, temperature and other control structures are examined comparatively for (i) their setpoint tracking and load disturbance rejection characteristics, and (ii) for their abilities to effectively linearize the closed loop systems.;The major findings are that the reference system controller yields superior servo and regulatory responses relative to both temperature and reaction rate controllers. Reference system synthesis is conceptually straightforward. It relies on well-established mathematics from functional analysis, and is capable of designing feedforward/feedback structures that give excellent control of chemical reactors. The method is also applicable to any class of dynamical systems. Furthermore, the approach provides a systematic way for designing controllers that yield deliberate, advantageous nonlinear closed loop behavior.;Regarding the reaction rate controller, the findings are that it produces superior setpoint tracking compared to a temperature controller in the systems studied. The load disturbance rejection properties are comparable to the temperature controller. The reaction rate controller suffers from a lack of generality and theoretical support that might hinder application to real-world problems.;The significance of this work is in the development of the reference system synthesis algorithm for nonlinear control design. It is not true that the algorithm is completely novel; closely related approaches have been used for linear systems. Applied to nonlinear systems, however, this control design technique yields high quality performance and easy application relative to contemporary nonlinear control design procedures.