Research On Stability Margin Of Load Frequency Control System With Time-Varying Delay Based On LMI

Modern power systems are basically interconnected between subsystems,and interconnected power systems rely on wide area measurement technology for information transmission and exchange.As communication networks are widely used to send and receive control signals,time delays have become unavoidable in power systems.Nowadays,the delay of the wide area measurement system(WAMS)brings greater difficulty to the stability of the load frequency of the power system.In the past,most of the references only deal with the case of the stationary delay of the power system.However,for a small amount of time-varying delay research of the power system,the stability margin estimation is often very conservative.Therefore,the research on the control system of load frequency in power systems with time-varying delays is significant and is also necessary.This paper adopts the method based on Linear Matrix Inequalities(LMI)for the stability margin of Load Frequency Control(LFC)system with time delay,this paper does the following research.First of all,based on the improved Jensen inequality,this paper solves the Lyapunov functional derivative based on the time-domain method,and studies the stability margin of single-zone load frequency control system with time-varying delay.This article calculated the maximum delay time that the LFC system allows,for this value is the stability margin.Then based on MATLAB simulation,the validity and superiority of the results are verified.Secondly,the Lyapunov-Krasovskii function(LKF)is established by using the method of flexible integral limit,and the stability margin of multi-area LFC system with time-varying delay is calculated by this method.The main task of this paper is to calculate the upper bound of maximum delay margin and reduce the conservativeness of previous methods.In addition,the superiority of the standards used is also verified by simulation studies.At last,the author summarizes the work done and points out the problems and shortcomings that still exist and the problems that need to be further studied and solved in the future.