Research On Key Technologies Of Fault-Tolerance In Distributed Measurement And Control System

Distributed measurement and control system has been widely applied in many fields with high-reliability requirement, such as the aerospace, military, railway, petroleum, chemical engineering, electric power. With the increase of the distributed processing capacity, the improvement of system security and reliability capacities is also put forward. Currently, it has become a hot topic in both theoretical and applied research about how to improve the fault-tolerant capacity of the distributed measurement and control system.In this dissertation, some key technologies in distributed measurement and control system with high-reliability requirement are investigated to improve the fault-tolerant capacity, which include node fault detection and location in distributed fault-tolerant system; clock synchronization in distributed redundant fault-tolerant system and performance evaluation methods in tolerant system. As is depicted in detail as follows:1 The research on fault detection and location technology in distributed measurement and control system. A top-down fault detection and location technology is proposed for the distributed measurement and control system. The fault is generally detected with prior-knowledge based weighted fuzzy Petri net, and precisely located with hierarchical multi-mode heartbeat detection method, and finally fault-tolerant strategy is designed with threshold-based fault discrimination technology. The details are as follows:1) The coarse location using prior-knowledge based weighted fuzzy Petri net could avoid the aimlessness of fault location, and improve the detection rate as well. Furthermore, in order to improve the weights training rate and prediction accuracy, and reduce the dependence on sample size, a weights optimization algorithm based on Least Square Method is proposed to solve the AND-rule in the fuzzy production rules.2) A hierarchical multi-mode heartbeat detection method is proposed to improve the accuracy and efficiency of node fault detection in distributed measurement and control system, and reduce the communication cost caused by fault detection. The PULL and PUSH combined mode reduces the false detection rate; the method that heartbeat information is integrated into periodic communication data based on hierarchical detection mechanism could reduces the number of communication data packet for fault detection and ensures the real time requirement in measurement and control system.3) Concerning the different effect of transient fault, intermittent fault and permanent fault of the distributed measurement and control system, a distributed fault-tolerant system strategy is proposed according to the threshold-based fault discrimination technology, which could both reduce the malfunction to transient failures, and improve the efficiency and accuracy.2 The research on clock synchronization method in distributed measurement and control system. A hierarchical clock synchronization method is proposed according to the characteristics of distributed measurement and control system. The specific node in each channel is synchronized using convergent functional synchronization strategies, and then the clock synchronization of the remaining nodes within the same channel is achieved using master-slave clock synchronization strategy according to the synchronized node. Because of the low cost communication, the hierarchical clock synchronization method is especially suitable to distributed measurement and control system which is with stringent communication cost requirement and shows large network time delay.3 The research on evaluation method of system reliability. Reliability design and evaluation about distributed measurement and control system are investigated, and the reliability evaluation models based on Markov model and stochastic Petri net model methods are designed according to the characteristics of distributed fault-tolerant system. Furthermore, the advantages and disadvantages, the relationship and application situation about the two methods are analyzed.4 Fault-tolerant design of a steam turbine emergency trip system. To verify the performance of the above research achievements, all the proposed technologies and methods are applied to the steam turbine emergency trip system. The fault-tolerant design of the three-module redundant turbine emergency trip system is achieved with top-down fault detection technology and the hierarchical clock synchronization method which synchronizes the redundant inter-channels and intra-channels respectively. The results show that the proposed methods could meet the requirement of the steam turbine emergency trip system in the fault detection and clock synchronization. Furthermore, the system could work in high reliability situation for a long time under the condition of the specific failure rate of electronic components.