Fault Detection For Delta Operator Systems With Multi-Packet Transmission

The network control systems uses the network as the transmission medium of information between the system nodes,which greatly improves the system's scalability,compatibility,robustness and effectiveness.In addition,the network control systems are easy to upgrade and maintain,which makes it has great advantages compared to point-to-point control systems.Therefore,the network control systems are rapidly replacing the traditional point-to-point control systems,becoming one of the main control methods in the emerging fields such as automation industry,artificial intelligence,internet of things and so on.However,with the network control systems widely used in production and daily life,a series of shortcomings have gradually exposed.The network control systems use the network for data transmission,so that the disadvantages of the networks are inevitable.Data transmitted in the channel will produce network-induced delay,data packets may be lost in the process of transmission,poor network conditions will lead to communication constraints,insufficient channel bandwidth could cause multi-packet transmission.These disadvantages will greatly affect the performance of the network.Faults sometimes occur while the system is running.The faults could reduce the effectiveness and reliability of the system,and even lead to system collapse,resulting in irreversible consequences.So,in order to ensure the normal operation of the network control systems,it is necessary to detect the faults.Nowadays,most of the networked control systems use digital networks,the research on fault detection of networked control systems is mostly focused on the discrete system model.The traditional discrete method is to use shift operator to discretize the system.However,when the system is in the process of high-speed sampling,the state response model of the shift operator system will deviate from the continuous system model,and the higher the sampling rate is,the more obvious the deviation will be.The problems above can be avoided by using delta operator,when fast sampling,the discrete model is still close to the continuous system model.In this thesis,delta operator method is used to study the fault detection problems of NCSs with multi-packet transmission.The major contributions are as follows:Firstly,for the networked control system with random delay,the multi-packet transmission problem is equivalent to a switching system in the thesis.Firstly,the continuous system model is discretized by shift operator,and the delay,state response and control input are integrated into an augmentation system.Then the augmentation system is transformed into a delta domain augmentation system.Then,a fault detection filter is established and residual signal is generated to show the fault in the system.Through linear matrix inequality(LMI)method and Lyapunov-Krasovskii stability theory,the stability condition of the system is found.Secondly,based on delta operator,the problem of fault detection of multi-packet transmission network control system under the condition of communication constraints is further considered.The multi-packet transmission in the system is modeled as a Markov process,and then a fault detection filter in delta domain is established.The residual error is generated by the residual signal.The residual error is used as the evaluation function of fault detection.By Using LMI method and Lyapunov-Krasovskii stability theory,the sufficient conditions of the system asymptotic stability are obtained,and the effectiveness of the above methods is verified by a MATLAB simulation.Thirdly,the parameter uncertainty in the system is further studied.It is assumed that the communication of the system is limited between the sensor and the controller,and the uncertainties exist inside the system.Based on the system model,a residual system with multiple constraints is established,and the conditions for the system to be asymptotically stable are discussed and the filter parameters are solved by the linear matrix inequality method and Lyapunov-Krasovskii stability theory.Finally,a simulation example is used to show the feasibility of the method,and the advantages of delta operator are illustrated by comparing with the performance of shift operator system.