Research On Resilient Frequency Control And Active Defense Control Of Power System Under Network Attacks

In recent years,network attacks have arisen many power outages worldwidely,which severely affect social production activities even threaten national security.One of the reasons is mainly that the stability of physical power system is influenced by the obstruction of information system caused by network attacks.Especially,when automatic generation system(AGC)is subjected to network attacks,the balance of active power is damaged and even frequency instability is caused.Hence,to sustain frequency stability under network attacks has an important research significance.Frequency control,for example,load frequency control(LFC),plays a very significant role in balancing active power and achieving frequency stability of power system.To keep frequency control performance under network attacks,this dissertation studies secure frequency control of power system.Three problems are mainly investigated.First,attack scenarios are found and attack behaviors are modeled from the viewpoint of cyber-physical security of frequency control system.Second,resilient performance of frequency control system is analyzed and the tolerable attack bound is obtained.Third,active defense control strategy is studied to improve the autonomous security of frequency control system.For the above three problems,the research thought is to establish attack model and frequency control system model under attack,perform system resilient analysis and synthesis,provide active defense control strategy.Based on the research idea,five aspects of results are obtained as follows.1.The resilient analysis and synthesis problem of multi-area LFC system under DoS attack is studied.First,an attack detection mechanism based on input delay is proposed to identify DoS attacks and network-induced delays from time scale.The average dwell time(ADT)and attack duration duty cycle are used to constrain attack frequency and duration.Then,weighted H∞ performance is analyzed by combing piecewise Lyapunov functional method(Piece-wise LKF)and switched system theory.A resilient condition between delay bound,attack parameters and system analysis parameters is established.Finally,the design conditions of resilient LFC is derived from resilient condition on the basis of LMIs and a design algorithm is proposed to obtain control gain.2.The resilient analysis and synthesis problem of double-control-loop LFC system with DoS attack,delay,saturation constraint and parameter uncertainty is studied.First,DoS attacks interrupting the additional control loop is modeled by average dwell time,uniform lower bound of sleep intervals and uniform upper bound of attack intervals.A switched delay system is established for LFC system with double control loops.Then,a resilient condition including delay bound,attack parameters and system analysis parameters is established by using delay system method and switched system theory.Finally,based on LMIs technique and virtual output vector method,a design method of resilient additional control gains is proposed.3.Frequency control problem of power system with high penetration of renewable energy resources(RESs)under DoS attacks is concerned.First,a state space model for frequency system is established on the basis of load frequency control(LFC)and virtual inertia control(VIC).Further,a mode-dependent average dwell time(MDADT)model is proposed for DoS attacks.And dynamic event-triggered mechanism is introduced to lower communication burdens.Second,a switched delay system with event-triggerred condition is established for frequency control system under DoS attacks.The MDADT resilient criterion guaranteeing power system frequency stability is proposed through system analysis.Further,using piece-wise LKF method and LMIs technique,a jointed method to design dynamic triggering mechanism and LFC-VIC is proposed.Finally,a dynamic prediction horizon mechanism is proposed as an active defense control strategy based on MDADT criterion.4.Frequency stabilization problem of multi-area power system with low inertia is considered on the basis of cooperative control of multi-agent system with considering the influence of hybrid attacks.First,a hybrid attack model is proposed,where DoS attacks is represented by a time-varying switching topology modeled by MDADT and false data injection attacks is on the basis of sign function to reflect attack maliciousness.Then,a nonlinear switched system model is established for frequency control system with MAS cooperative control.Further,using switched system theory and nonlinear system method,a resilient condition is established,which quantifies the tolerable ADT lower bounds of residual topologies and the upper bound of false data injection attack.Finally,based on LMIs techniques,a design method of distributed LFC-VIC control gain is proposed.5.An active defense control method is studied for LFC system under DoS attacks.In order to prevent the open-loop instability caused by DoS attacks,a primary-redundancy(PR)control structure based on bandwidth allocation is proposed.Further,a correlated delay model is established to characterize the impact of limited bandwidth resource allocation on the quality of service of PR channel.A design method of switching law between primary channel and redundancy channel is proposed to ensure system autonomous security as well as improve the concealment of redundant channel.Then,a switched system with three modes for LFC system with PR control structure under DoS attacks is established.Finally,a jointed design method is proposed for control gains,trigger parameters and switching law parameters on the basis of piece-wise LKF method and LMIs techniques.