Online discrete event control of hybrid systems

Millan, James P. (2006) Online discrete event control of hybrid systems. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The increasing proliferation of automatic control systems in embedded and distributed applications has lead to increasingly complex systems. These systems manifest a mixture of continuous and discrete dynamics due to the interaction of the computer controlled or logical decision-making subsystems interacting with the real world, and are thus referred to as hybrid systems. The inherent complexity of such hybrid systems makes them difficult to model, analyze and design. As such, industrial application of hybrid system theory has yet to gain widespread acceptance. -- This thesis presents an approach to the modeling, synthesis and implementation of automatic controllers for hybrid systems. This work centers on a flexible hybrid system modeling framework that permits automated synthesis of controllers for hybrid systems, based on safety and performance design specifications. This hybrid modeling framework is the switched continuous model (SCM), based on discrete switching between continuous system models (CSM). Discrete abstractions of the CSM dynamics enable the controller actions to be simple discrete decisions at appropriate points in the state space of the controlled system. The SCM communicates with external discrete event systems (DES) through sets of shared discrete events, thus allowing the techniques of DES supervisory control synthesis to be employed. The resulting controllers are model-based, and safe by design, since they encapsulate the continuous and discrete event models that together model the plant and specification dynamics. Due to the inherently uncountable state space of the hybrid system model, the controller computation is performed online, and is limited to a finite time horizon in order to preserve the finite state properties of the discrete abstraction. -- The details of the modeling framework, controller synthesis, and online implementation are developed, including a computational approach, architecture, and algorithms. A software package that implements these control concepts was developed. Two detailed modeling and control synthesis applications are presented: a simple benchmark hybrid control example and a realistic industrial example.

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