Research On Multi-objective Fault Detection For Cyber-Physical Systems With High-speed Sampling Under Cyber Attack

With the rapid development of the information age,technology in a single field can no longer meet the needs of people’s daily life.Therefore,the Cyber-physical system integrating communication,control and computer has gradually attracted the attention of all countries.Because of the data transmission through the network,Cyberphysical systems bring great convenience to people.However,with the increase of system scale and the improvement of intelligence,various physical faults are inevitable,resulting in the failure of the normal operation.On the other hand,in recent years,there have been cases of hackers attacking Cyber-physical systems through the network in many countries,causing huge losses to the local economy and property.The above problems may exist at the same time and are easy to affect each other.However,the research on a single problem can not deal with the actual situation well.In the actual process of network data transmission,there may also be problems such as time delay and packet dropout,resulting in abnormal system performance.Therefore,it is particularly important to combine fault with cyber attack and carry out relevant detection research for them in different network environments.The sampling is often needed when the system processes the input and output signals.In order to make the information transmission more complete and reliable,it is necessary to increase the sampling rate.Applying delta operator to the fault detection field of high-speed sampling can not only avoid various ill conditioned problems caused by the traditional discretization method,but also deal with the discretized system and the original continuous time system uniformly.This thesis mainly studies the multi-objective detection of faults and attacks for Cyber-physical systems in different network environments based on delta operator under the condition of highspeed sampling.The main contents and innovations of the thesis are as follows:(1)Aiming at the Cyber-physical system with time-varying delay under highspeed sampling,the problem of fault detection under cyber attack is studied.Based on delta operator,a Cyber-physical system model of coexistence of fault and cyber attack under high-speed sampling is constructed.Consider the cyber attack as a part of random disturbance,then select H∞ performance and H_performance to represent the robustness to random disturbances and the sensitivity to detection targets respectively.Lyapunov stability theory and linear matrix inequalities method are used to analyze the stability and H_/H∞ performance of the system.A simulation example of an unmanned ground vehicle and comparative experiments are used to analyze the effectiveness of this method.(2)Aiming at the Cyber-physical system with random time delay and limited communication under the mixed disturbance,the cooperative detection of fault and cyber attack is studied.Considering the mixed disturbance of the system,the disturbance is divided into known white noise and unknown random disturbance,using H2/H∞ hybrid performance index to characterize the performance of the system under corresponding disturbances.Observers sensitive to the fault and attack are designed to detect and identify them.Lyapunov-Krasovskii functional is constructed to analyze the above system theoretically.The feasibility of this method is verified by the example of angle positioning system and related performance analysis.(3)Aiming at the nonlinear Cyber-physical system in the complex network environment with uncertain time delay,limited communication and two-channel packet dropout,the multi-objective anomaly detection of fault and attack in the case of highspeed sampling is studied.The method of delta operator is used to discretize the system,and the H_/H∞ multi-objective observer is designed to detect abnormal signals including faults and attacks in the system.Through theoretical derivation,the sufficient conditions for the system to have asymptotic stability and corresponding performance indexes are obtained.The feasibility and effectiveness of proposed method are proved by an example of a single link manipulator and comparative analysis.