Performance Analysis And Controller Design For Networked Control Systems Under Attacks

Networked Control Systems have many advantages,such as low wiring cost,high reliability and strong extensibility,which have been used more and more widely in daily production and life.However,in addition to traditional network delay,data packet dropout and other problems,NCS has also encountered such a new challenge of security attack.On the one hand,with the formation of business standardization of TCP network protocol,the closure of NCS has been broken,which has virtually increased the chances of NCS being attacked.On the other hand,the abilities of the attacker to discover the vulnerability of the systems and to master the attack technologies are both constantly improving,and the methods of attacking the NCS from outside are also more diversified and complicated.Therefore,the security issue of NCS has gradually become one of the focuses in the field of NCS research.NCS is taken as the research object in this thesis,combined with the traditional network delay problem.DoS attack and replay attack are focused and the switching system analysis method is used to study the performance analysis and controller design of the attacked NCS.The detailed contents are as follows:1)Based on the background and significance of the project,the problems of network delay and security in NCS are analyzed.The principle of DoS attack and deception attack is mainly introduced.At last,the current situation at home and abroad for the NCS security research is summarized.2)The impact of DoS attack on system performance is studied and its stabilizing controller is designed.In the process of DoS attack,the sensor of NCS can't receive the measurement information in time,or the executive can't get the control information in time.The method to deal with DoS attacks is that once the system is subjected to DoS attack and can't update data in real time,the executor keeps the latest data at any time.Firstly,the NCS with DoS attacks is modeled as a closed-loop switched system.Then,with the analysis method of the switched systems,a sufficient condition is derived from the concerned NCS to be exponentially stable,and the corresponding stabilization controller is designed.Furthermore,the upper bound of the probability of occurring DoS attacks is also derived.The concerned NCS is always guaranteed to be exponentially stable,as long as the occurring probability of DoS attacks is no more than the derived upper bound.Finally,a simulation example is given to show the effectiveness of the proposed result.3)The performance analysis of NCS with short network-induced delays DoS attacks is studied,which means that the problems of short network-induced delays and DoS attacks to the NCS are considered together.Firstly,the NCS is modeled as a closed-loop switched system with both stable subsystems and unstable subsystems by redefining the sampling period.The model can handle two types of short network-induced delay and DoS attacks uniformly.And the concerned NCS requires a fact that the actuator period is shorter than the sampling period.Then,with the analysis method of the switched systems,a sufficient condition is derived from the concerned NCS to be exponentially stable.Moreover,an optimal guaranteed cost controller is designed at a given guaranteed cost level.Finally,a simulation example is given to show the effectiveness of the proposed result.4)The impact of replay attack on system performance is studied and its stabilizing controller is designed.First,replay attacks use network monitoring to record system data for a period of time and then put the monitored historical data to the network in a certain period of time,which may cause the system executor to run historical data continuously.Firstly,a strategy that the actuator period is shorter than the sampling period is concerned,and the change of state variables under each actuator period is analyzed.Then,as an upper bound for the maximum duration between the acquisition of the data and the release of the attack data is set,the NCS with replay attacks is modeled as a discrete-time switched system,which contains finite subsystems.Furthermore,with the analysis method of the switched systems,a sufficient condition is derived from the concerned NCS to be exponentially stable,and the corresponding stabilization controller is designed.Finally,a simulation example is given to show the effectiveness of the proposed result.In the end,the thesis is concluded and some future research works are discussed.