| With the deep integration of information and industrialization,the traditional natural gas pipeline system is gradually moving towards the networked cyber-physical system.Due to the openness of network,the pipeline network is vulnerable to cyber attacks,which destroys the system and may cause serious economic and social losses.Among them,the covert attack is considered to be the most destructive cyber attack,because it can evade the detection of monitoring system and steal system information,resulting in system paralysis.The existing covert attack strategies are effective only for systems with all known model parameters.However,the natural gas pipeline system is often affected by a variety of complex factors,so it is difficult to establish an accurate mathematical model,so the existing covert attack strategies are not suitable for natural gas pipeline system.This makes it easy for pipeline network builders to ignore the risk of damage to natural gas pipeline system caused by covert attack.To this end,this thesis carried out the following research.(1)The operation scenario of natural pipeline system is analyzed,and the possible risk of network attack is described.Secondly,according to the uncertain factors existing in the natural gas pipeline system,the uncertain model of the natural gas pipeline system is constructed based on the hydrodynamics principle,pipeline signal measurement mechanism and other information.Based on the constructed system model,the principle of robust covert attack strategy is described,and a new robust covert attack strategy is designed,which does not need to know all the parameters of the system model accurately.It overcomes the limitation that the existing covert attack strategies require the attacker to know all the parameters of the system model.(2)Considering the different kinds of uncertainties in the system,based on the natural gas pipeline system model with matched uncertainty,the design problem of robust covert attack is solved when the system states are known and unknown.Firstly,the auxiliary attack signal is designed according to the attack target,and the output attack signal is designed by using the auxiliary attack signal.Then,the input attack signal is designed to make the system output reach the desired attack target,and the output attack signal is used to compensate the impact of the attack on the system output to achieve the purpose of attack stealthiness.In addition,when the system states are unknown,the model reference observer is introduced to estimate the system states and their derivatives needed to design the input attack signal.Then the stability of the closed-loop system is analyzed,the sufficient conditions for the existence of the model reference observer are obtained,and the effectiveness of the robust covert attack for matched uncertain systems is proved.(3)Based on the natural gas pipeline system model with mismatched uncertainty,the design problem of robust covert attack is studied when the system states are known and unknown respectively.The sliding mode control technology which is insensitive to mismatched uncertainty is used to design the attack signal on the input channel.Subsequently,the idea of time-delayed estimation technology is used to improve the designed attack signal on the input channel,so that the chattering phenomenon caused by sliding mode technology can be reduced.Furthermore,when the system states are unknown,the state and disturbance observer is designed to estimate the system states and lower the requirements on the system uncertainty.Then,through the stability analysis of the closed-loop system,the sufficient conditions for the existence of the state disturbance observer are obtained,and the effectiveness of the robust covert attack for mismatched uncertain systems is proved.(4)Considering a kind of nonlinear factors that exists in practical engineering,a natural gas pipeline system model with both nonlinear and uncertainty is constructed,and the robust covert attack strategy is designed when the system states are unknown.Then,the nonlinearity in the system is approximately represented by the convex polyhedron which can wrap this kind of nonlinearity,and the system model is transformed into a linear model.Thus,the presented method of robust covert attack can be applied to the transformed linear model.The results show that the method of robust covert attack designed in this paper is still applicable to the natural gas pipeline system with both nonlinear and mismatched uncertainty,which provides a new theoretical guidance for the security construction of natural gas pipeline network. |
