Research On The Control Problems For Cyber Physical System Under Network Attacks

Cyber physical system is a concept put forward in recent years.It refers to the system formed by the close integration of computing,communication and physical processes.Such a system can embed sensing,communication and computing technologies into physical devices,fully realizing distributed sensing,information transmission,intelligent information processing,real-time feedback and control.Hence,cyber physical system has been used in many fields,including chemical industry,grid power,water distribution,automobile and intelligent home.Information transmission is the most basic function in the cyber physical system,and the wired or wireless transmission equipment will be affected by all kinds of attacks from the cyber space,then causing the error or failure of information transmission,even causing the decline of control performance or the unstable operation of the system.Therefore,the security issueof cyber physical system has attracted more and more attention,and related research results have been extended from the initial communication field to the control field.The security issues of cyber physical system mainly fall into two categories:information security and security control theory.The former focuses on encryption and data processing;the latter studies how the network attacks affect the physical dynamics of control systems.The research of information security can't prevent the attacker from affecting the control system,so the research of security control theory is necessary.The security control theory is based on the attack model to carry out the research,how to establish the appropriate attack model is very important.In previous studies,there are two most common types of attacks.The first type is denial of service attack,the other is spoofing attack,of which the false data injection attack is the typical representative.Recently,more and more attention has been paid to the security control problem of cyber physical system under these two types of network attacks,and some progress has been made,but there are still many shortages.For example,the existing researches of resilient control for the cyber physical system under DoS attack have not considering the case that the transition probabilities of cyber layer state are unknown,and the researches on the attack action are also relatively single,that is to say,most of which only consider the control problems for CPS under only one type of attack,furthermore,they are also lack of considering the influence of introducing event trigger and nonlinear sector,etc.Aimed at these shortages,this paper is to research the control system from the aspects of the stable operation,performance optimization and practical application,the concrete contents of which are as follows:1.A control strategy algorithm based on game is proposed for the security problem of CPS under DoS attack.On the one hand,considering the zero sum game of control performance,the hybrid strategy of cyber layer is designed by using physical performance index.On the other hand,considering the zero-sum stochastic game of attack-defense strategy,the controller of physical system is designed by using the optimal cyber hybrid strategy.These two game processes merge with each other to form a research method of security control based on game.2.A resilient control algorithm based on game and reinforcement learning is proposed for the security problem of CPS with unknown cyber state transition matrix under DoS attack.In order to save communication resources,event triggering mechanism is introduced in CPS.Considering the cyber state transition probability is unknown,an on-policy based SARSA method is adopted to update the auxiliary matrix of the cyber layer.Under the above conditions,the relationship between cyber system and physical system is studied,a resilient control algorithm combining game theory,robust control theory,event triggered control method and SARSA learning method is proposed,and a resilient controller and a resilient control strategy are designed to tolerate a series of DoS attack signals with probability characteristics.3.A design algorithm of finite horizon H_?controller is proposed for a class of linear time-varying CPS under hybrid attacks.The above-mentioned hybrid attacks,include the DoS attack on the communication channel between the sensor and controller,and the FDI attack on the sensors and actuators.Considering the hybrid attacks on the physical performance of the CPS may cause more serious harm,the relationship between the injected attack signals and the controlled output is studied,so that the H_?controller gain of the closed-loop system is designed to satisfy the performance condition in a finite horizon.At the same time,in order to reduce the impact of the injected attack signals in the worst case on the linear quadratic Gaussian performance,the sufficient conditions for the existence of the designed controllers are built up by solving two coupled backward recursive Riccati difference equations under certain conditions.4.A security controller design method based on gain scheduling is proposed for the control problem of nonlinear CPS under hybrid attacks.The hybrid attacks here include DoS attacks that block transmission of measurement data or control data,and FDI attacks that destroy sensor data or actuator data.At the same time,a probability-dependent gain scheduling controller is designed by taking into account the randomly occurring nonlinearities in the physical process.Because of the problem that the real-time probability of nonlinear is unknown,the infinite linear matrix inequation conditions are needed to be transformed into the finite linear matrix inequation conditions,and the slack matrix is introduced to solve the problem.Finally,the conclusion of the whole paper is given,and the next research work is put forward.