Robust adaptive observer for nonlinear time-delay systems with disturbances and uncertainties

A method of designing robust adaptive observer for nonlinear continuous-time systems with time-delays is presented.It is assumed that the nonlinear functions of the system satisfy Lipschitz condition.The observer is derived considering plant disturbances,structured parameter uncertainties and unknown parameters.Like any other adaptive observer for nonlinear systems with ideal working conditions,it also simultaneously estimates both the states and unknown parameters.This property is very much useful for many applications like fault diagnosis.The convergence of the state errors and estimated unknown parameters are analysed by H_(∞)-control.The sufficient conditions for the existence of the observer are determined and expressed in linear matrix inequality form.With the help of a numerical example,the effectiveness of the proposed observer is demonstrated.

Detection and Estimation of False Data Injection Attacks for Load Frequency Control Systems

False data injection attacks(FDIAs)against the load frequency control(LFC)system can lead to unstable operation of power systems.In this paper,the problems of detecting and estimating the FDIAs for the LFC system in the presence of external disturbances are investigated.First,the LFC system model with FDIAs against frequency and tie-line power measurements is established.Then,a design procedure for the unknown input observer(UIO)is presented and the residual signal is generated to detect the FDIAs.The UIO is designed to decouple the effect of the unknown external disturbance on the residual signal.After that,an attack estimation method based on a robust adaptive observer(RAO)is proposed to estimate the state and the FDIAs simultaneously.In order to improve the performance of attack estimation,the H¥technique is employed to minimize the effect of external disturbance on estimation errors,and the uniform boundedness of the state and attack estimation errors is proven using Lyapunov stability theory.Finally,a two-area interconnected power system is simulated to demonstrate the effectiveness of the proposed attack detection and estimation algorithms.