Research On Security Control Of Cyber-Physical Systems Under Network Quantization Environments

In recent years,the continuous and rapid development of information technology has promoted the further integration of communication and control systems.As a new generation of intelligent systems,cyber-physical systems emerge at the historic moment.Information communication technology introduces new functions to the control systems and raises the security issues of cyber-physical systems.With the increasing openness of the control system,cyber-attacks and quantization error caused by signal quantization processing are brought about,which seriously affect the performance and integrity of the system.In addition,cyber-physical systems are often in a variety of complex environments.Modeling uncertainty and external disturbances often occur during actual operation.In order to solve these problems that exist in the systems,this thesis studies the security control of cyber-physical systems by using adaptive and sliding mode control method.The main contributions can be summarized as follows:(1)A robust adaptive control method is used to study the security control of cyber-physical systems under a frequency-constrained actuator attack and encoder/decoder mismatch.First,by using matrix inequality technology,sufficient conditions for robust H₂performance of cyber-physical systems are derived.Second,based on the upper bound information of the stealthy false attacks and the known upper and lower bounds of codec ratio information,a robust adaptive controller algorithm is proposed to suppress quantization errors,external disturbances,and suppress attacks that cannot be detected by the detector mechanisms.Finally,simulation examples verify the effectiveness of the method.(2)Based on the research of work(1),the problems of non-frequency constrained actuator attack and model uncertainty are introduced.First,by using linear matrix inequality techniques sufficient conditions for robust H₂ performance of cyber-physical systems are derived.Second,based on the projection operator technology and the adaptive estimation method of unknown actuator attack parameters,a new robust control algorithm is designed to ensure the safe and stable operation of the system and achieve the uniform ultimate boundedness.Finally,simulation examples verify the effectiveness of the method.(3)Based on the research of work(2),by analyzing the operation principle of the encoder/decoder,a mismatched relation between the quantization parameters is established by using a time-varying ratio model,where the boundaries of the time-varying ratio can be unknown,and the problem of time-varying encoder/decoder parameter ratio is considered.First,using linear matrix inequality techniques,the prescribed bounded L₂ gain performance condition is obtained for the sliding dynamics.Second,based on the formed boundary unknown time-varying ratio relation,external disturbances and actuator attacks,adaptive integral sliding mode control laws are designed to ensure the reachability of the sliding manifold,then the stability of the closed-loop system is established.Finally,simulation examples verify the effectiveness of the method.