Research On Fault Diagnosis Of Timed Discrete Event System

Discrete event system is a kind of logic system describing the process of system evolution by state series and event series.A significant feature of such systems is the use of control strategies only allowing occurrences of certain event series compliant with strategies to achieve the demand of engineering.This kind of systems is widely applied in the field of engineering,important communications,transportation and other public service facilities and computer information processing etc.With the development of science and technology,the structure of systems of this type becoming increasingly complex along with frequent faults;fault diagnosis technology in the past is apparently insufficient.The method of diagnosis based on diagnoser of discrete event system proposed by Sampath solves the problem.The fact of this method is that A diagnoser constructed expansively run in parallel with the system,of which status is analyzed to judge whether the system is in failure.Although the fault diagnosis method of discrete event system proposed by Sampath can effectively diagnose system failures,further study on method of safe diagnosability of discrete-event system is conducted by Paoli considering the issues of security of the system during the period of fault diagnosis.This method has been extended to all kinds of systems to solve the problem of system fault diagnosis.The system has been applied to the systems including: discrete event systems,fuzzy discrete event systems,etc..The timed discrete event system is a kind of high efficiency class system.The modeling of the system not only needs to consider the logical behavior of its operation process,but also needs to capture some of the time information.It has a very wide range of applications in the field of computer communications,industrial processing and automation control.Therefore,it is of theoretical significance and practical significance to seek a more secure fault diagnosis method for such systems.Aimed to solve issues of security of fault diagnosis of timed discrete-evnet systems based on automaton,the thesis proposes a safe diagnosis method under the framework of timed discrete-event systems based on the algorithm of safe diagnosis introduced by Paoli.Firstly,the discrete event model is constructed based on the logic information and timeinformation;Then,the security of the timed discrete event system is formally described;And construct a illegal language recognoizer of timed discrete event system to identify forbidden operating sequence of the system,guaranteeing that the identification information is timely feedback to the system once forbidden operation is conducted during the period of fault diagnosis.Furthermore,a safe is constructed on the basis of the already constructed illegal language recognizer,which can be used to diagnose the system online or offline;In the last step,in order to achieve a safe diagnosis,necessary and sufficient conditions for timed discrete event systems are derived through analyzing the status of the safe diagnoser of the system.In this way,it ensures that the fault event can be timely diagnosed and that the system does not perform any unsafe operations during the period of fault disgnosis.Finally,instances are given to verify the efficiencies of the theory of safe diagnosability of timed discrete event system.