State Based Control of Timed Discrete Event Systems using Binary ...

Chapter 1. Introduction 3as means of control and allows modular supervision, possibly under the constraint ofpartial observation.1.3 Objective of the ThesisIn Ramadge-Wonham theory, an automaton (in practice, finite) is used to model both theplant to be controlled and the specification. The RW approach successfully showed theexistence and theoretical synthesis procedure of the nonblocking supervisory controller.Different kinds of synthesis methods are developed and implemented as software CTCT1 for untimed models and TTCT for timed models to compute optimal controllers suchthat the controlled system not only satisfies the specifications but is also as permissive aspossible. However, this implementation of RW theory can only solve problems of smallstate size. This is because an exhaustive list is used to represent the whole model of asystem in TCT. Given that many practical systems have a great number of states, TCThas a very limited use in the synthesis of practical control problems. The inefficiencyof this approach is directly related to the assumption of ignorance of all the structuralinformation in a real world system. TCT uses the easiest way to achieve nonblocking,i.e.exhaustive search of entire reachable state space. This has been considered infeasible inits computational aspect.In [30], the exhaustive search is optimized by using the structural properties for untimedmodels. This optimization was implemented by Integer Decision Diagrams using a softwarecalled STCT. For complex DES systems, STCT offers far better performance thanCTCT.The goal of this thesis is to extend the method in [30] to Timed-DES. We want to showthat the structural information present in the structure of a TDES can be used to op-1 CTCT stands for “C based Toy Control Theory”. Originally there was a TCT written in Pascal,which was given the name “toy” because of its limited ability to deal with large scale systems. Later itwas rewritten in C and thus got the name CTCT.