Safety Analysis Of Train Control System Based On System-theoretic Process Analysis And Colored Petri Nets

Many technologies are applied to Chinese Train Control System-Level Three(CTCS-3),such as computer,automatic,communication and power supply technologies.The system structure and its functions are complicate.Various kinds of random faults can cause serious consequences leading to train crash.The development of the Chinese high-speed train control system is referring to the ETCS technical standards however considering the characteristics of China's railway.Meanwhile,some technical specifications are still being improved and revised.CTCS-3 has been applied in the field shortly and some potential hazards have not been completely mastered.Traditional safety assurance technologies based on expert experiences and techinical specifications has shown their shortcomings in safety analysis of train control system.Therefore,it is necessary to use formal method to analyze the safety of train control system.In this thesis,CTCS-3 is taken as the research object.In order to analyze the potential hazards in train control systems,a hazard identification method based on System-Theoretic Process Analysis and Colored Petri Nets is proposed.Its major feature is that it can realize the transformation between functional requirements of train control systems,STAMP model and Colored Petri Nets,and guarantee the consistency between these three descriptions.On the basis of this method,the model is verified by model checking and the paths that lead to hazardous states are identified.Finally,unsafe control actions and control flaws of the system are identified.The main contents and achievements of this thesis are as follows:Firstly,the purpose and significance of the safety analysis for train control systems are introduced,and then basic concepts,core ideas of system safety risk theory and popular analysis methods are summarized.Besides,related literature is reviewed to elaborate the current state of domestic and international research.Then,the system theoretical accident model,CPN and model checking are briefly described.Secondly,the hazard identification method based on System-Theoretic Process Analysis and Colored Petri Nets is proposed.In this method,CPN is chosen as the formal specification of hierarchical control structure,which overcomes the shortcomings of STAMP model in describing system hierarchical control structures and control algorithms by natural languages.Not only the ambiguity of nature language is avoided,but also the difficuity of modeling is reduced.Dynamic behavior and state change can also be described.On the basis of that,by analyzing the intermediate product XML document of CPN,the dangerous states and paths that lead to hazardous states are found.The unsafe control actions and control flaws in system are analyzed.This provides guidance for the safe operation of the system.Finally,this method is applied to the safety analysis of a train control system.To some extent,the automatic identification of dangerous states and paths that lead to hazardous states is realized.The analysis process is implemented by software interface,and the development of software tool is completed.It turns out that the method proposed in this thesis is feasible.