| Networked control systems(NCS)have been used widely in many practical fields.The communication connection in NCS allows agents to communicate with each other quickly,which can quickly respond to abrupt changes in the system.Due to the open nature of the network connections between controllers,sensors and actuators,distributed networks in NCS are vulnerable to malicious network attacks.This thesis focuses on the impact of time delayed switching(TDS)attacks and denial of service(DoS)attacks on NCS and the design of security controls to address this situation.Through reviewing relevant literature and research materials,it is found that there are abundant results on the security control of NCS under DOS attacks and some progress in the research results on the security control of network control systems under TDS attacks,but the research results on the detection and estimation of TDS attacks and the security control of time delay NCS are very limited,which also inspires this thesis for such topics,the main research elements are as follows:(1)The problem of security control of NCSs under TDS network attacks is addressed.It is assumed that a hacker injects a TDS attack into the control channel and affects the state of the observer.A Lyapunov theory-based approach is used to design a controller to estimate the delay caused by the delay switching attack and thus mitigate the impact caused by TDS.A new technique for TDS attack detection and observer-based adaptive security control of NCSs under TDS actuator attacks is proposed.The proposed algorithm is able to estimate and compensate for TDS attacks in real time with low computational complexity.Simulation results illustrate the effectiveness of the proposed time-delay switching attack estimator and security control strategy.(2)The problem of security control of time-delayed NCSs under DoS attacks is addressed.An advanced observer-based event-triggered and resilient control co-design scheme is proposed in this thesis.Firstly,the periodic DoS attacks are modeled as a PWM(Pulse-width-Modulated)-type signal.Then,the event-triggered scheme is presented and a controller based on the observer state is designed using the dynamic event-triggered sequence.At the meantime,to ensure the stability of the subsystem during the active DoS attacks,the current last successful trigger state is considered as a control signal for the active attack periods.Through the Lyapunov stability theory and Schur complementary theorem,the system globally exponential stability(GES)criterion can be derived,the co-design scheme of controller,observer and event-triggered parameters is given.The proposed method is proven to be feasible by stability analysis,and the simulation verifies its effectiveness. |
