Research On Attack Detection For Singular Cyber Physical Systems

With the wide spread application of the information science and technology in the modern industrial and society,the Cyber Physical System is presented to define a kind of complicated systems,such as transportation networks,high speed train systems,unmanned grounded vehicles,future power systems and smart grids,that are characterized by tight integration and cooperation between cyber and physical components,like processing units monitor,control physical processes by means of sensors and actuators networks.Essentially,CPSs can be treated as the kind of networked systems with control mechanisms.Thus,it is significant to explore the CPS security with the control theory.On the one hand,it is called for a unify architecture or model to describe the attack,including its knowledge and performance;on the other hand,it is also called for secure control design methods for CPS under different kinds of adversarial attacks,including the conditions and methods of attack detection and secure state estimation.It is noted that,some results are already presented;however,there still exist many drawbacks.For instance,first of all,current researches on attack detection mainly focuses on the linear nonsingular cyber physical systems,but the singularity is ubiquitous in the real system.It is of great practical significance to study the attack detection problem of the singular information physical system.Second,the existing attack detection methods can be classified into two classes.The first is based on a finite time measurement sequences,which ensures the attack detection and secure state estimation to be obtained in a finite time,but its robustness to disturbance and noises needs to be enhanced.The second is based on Luerberger observers,which ensures the attack detection and secure state estimation to be achieved asymptotically or finite but quite a long time,thus novel attack detection and secure state estimation methods whose estimation error can converge to zero more fast or in a given finite time is needed.Utilizing the linear and nonlinear theory,singular system theory and observer design methods,this thesis addresses the attack detection problems for the CPS under attacks,including the model of CPS,the model of attacks,the detectability of attacks,the identifiability of attacks,the solvability of the secure state estimation,and some methods to solve these problems for different kinds CPS under attacks.The methodologies and the contributions are:1 The model of CPS under attack is presented and established,which includes the ability,performance and preferability of the attacks,with that,some existed attacks are also explored,such as their strategies,working modes and damage to the control systems.The fouus of the thesis is also formulated as two problems,the attack detection problem and the secure state estimation problem.2 For a class of linear time-invariant singular cyber physical systems with attacks,a sufficient and necessary condition for the feasibility of attack detection is established.A finite-time state observer with state modification and a detector based on observation error are designed,which can solve the secure state estimation problem in a given finite time.3 Then for a class of nonlinear uncertain interconnected CPS under both state and sensor attacks,a sufficient condition that the attack can be detected and the secure state estimation can be obtained is presented and established,and distributed robust observers are also presented.It is shown that,with the proposed schemes,the state and attack estimation can approach the state and attack simultaneously,and a distributed scheme is also presented which ensures that the robust attack detection can be achieved.