Font Size: a A A

Research On Multi-Module Redundancy And Network Reliability In Control Systems

Posted on:2011-09-24Degree:DoctorType:Dissertation
Country:ChinaCandidate:B H ZhangFull Text:PDF
GTID:1118330332966863Subject:Computer application technology
Abstract/Summary:PDF Full Text Request
There are mainly two kinds of techniques to improve reliability and safety of system——fault-avoidant technology and fault-tolerant technology. The fault-avoidant technology takes the measure of quality control, environmental protection and component integration improvement to avoid faults.into system and then improves reliability and safety. However, even the best fault-avoidant technology can not completely prevent the fault from occurring. By the redundancy of resources, the fault-tolerant technology adopts the method of fault restriction, fault masking or system reconfigurations, which makes the system still produce reliable and safe outputs even in the presence of faults.In computer control systems adopting fault-tolerant technology, dual-modular comparison redundancy (DMCR), dual-modular hot standby redundancy (DMHSR) and triple module voting redundancy (TMVR) are more used. In recent years, a non-voting quadruple modular redundant——double 2-vote-2 redundancy (D2V2R) begins to use in some safety-critical systems. The thesis studies the working principle and control strategy of this redundant structure, and analyzes its performance from the view of reliability, availability and safety. The thesis also proposes a new non-voting quadruple modular redundant——comparison of double dual-module redundancy (C-DDMR), and compares its performance with DMHSP, TMVR and D2V2R.In all computer control systems, except for the direct digital control systems, the processing units are connected through network in other systems, such as decentralized control system, fieldbus control system and network control system. The reliability of those systems is relative with not only the reliability of control unit, but also with the reliability of the link between control units and the network topology structure. This thesis focuses on the computation of reliability and availability in multi-hop control networks and the analyzing method of the component importance.The main contributions of this study are summarized as follows:(1) To the working features of D2V2R, a new control strategy is proposed. The existing control strategies assume when a module in a subsystem faults, the subsystem will stop working. This strategy can ensure that the system have higher safety. If the subsystem doesn't stop work when a detected fault occurs in a module, the system may continue to work as long as one module is normal in any subsystem. Adopting this strategy, the smaller safety can be exchanged for the better reliability in the situation of larger fault detection coverage rate.(2) A new redundancy structure model of C-DDMR is proposed. As the same as D2V2R, C-DDMR also consists of two subsystems. The difference is that subsystem is dual-modular hot standby redundancy structure and the two subsystems are comparison structure. For C-DDMR structure, two control strategies are given, and the performance under the two strategies are studied.(3) With the help of Markov procession, D2V2R structure and C-DDMR structure are comparatively studied and the application scope of those structures is discussed. That is if module has larger fault detection coverage rate and smaller repair rate, C-DDMR structure should be selected. If module has smaller fault detection coverage rate and larger repair rate, D2V2R structure should be selected. In other cases, performance of D2V2R structure is almost as same as that of C-DDMR structure.(4) A method is proposed for computing k-terminal reliability or availability of control network with unreliable nodes at time t. The basic idea of this method is that the edge of graph is defined as link and its terminals of control network first and then the disjoint edge variable k-terminal path sets are obtained by recursive decomposition of the adjacency matrix of the graph. On this basis, k-terminal reliability or availability is solved by computing all the probability of those path sets in the use of conditional probability. The proposed method can be used to analyze not only network with unreliable nodes and links but also network in which there are multiple links between two nodes. In addition, the number of matrix operations can be significantly reduced because transformation object is the matrix elements other than edge of graph when connection matrix is transformed.(5) A method is also proposed for importance analysis of control network components based on complete sets of path sets of graph. Concept of the complete sets is introduced and property and solving method of the complete sets are studied. Steps on calculating structure importance, probability importance and critical importance by the complete sets are also given. The proposed method can simultaneously analysis these three importance metrics quickly.
Keywords/Search Tags:Control system, Multi-module redundancy, Control network, k-terminal reliability, Component importance
PDF Full Text Request
Related items