Robust Stability Analysis And Load Frequency Control For Uncertain Time-Delay Power Systems

In recent years,with the expansion of interconnected power grid scale and the increase in complexity of operation characteristics,large-scale new energy grid-connection and the construction of uhv transmission projects have become the development trend in the current power grid.However,due to the limitations of existing control measures,it is increasingly difficult to ensure that interconnected power grid operates safely and stably.Modern interconnected power system,which makes use of open communication network to transmit information and exchange data,provides a platform for stability analysis and control of power system from an overall perspective.However,there is a time delay when this network is used to transmit and exchange information.This phenomenon,to a certain extent,will lead to the deterioration of system performance and even make the system unstable.Therefore,the influence of time delay on system performance must be considered in the stability analysis and control of power system.Over the past twenty years,the study of the theory of the time-delay systems has rapidly developed and attracted the extensive attention of scholars.At the same time,a series of related theoretical analysis and design method of time-delay systems also have been proposed,and these methods put forward can contribute to solving practical engineering problems better and perfecting the theory study of time-delay systems.This paper mainly studies the robust stability and load frequency control of uncertain time-delay power systems.In addition to the robust stability analysis of actual power system models,this thesis also improves the theoretical study of time-delay systems.The research results of this paper are summarized as follows:(1)Based on the Lyapunov-Krasovskii functional method,this thesis discusses the delay-dependent robust stability of single-machine infinite systems with uncertain system matrix parameters.By constructing a single machine infinite system model in the link of time-delay,and employing the method of theoretical analysis of the system with time delay,thesis derives a new criterion for robust stability of a power system with time delay.For the single-machine infinite bus system with disturbance in the gain of automatic voltage regulation control,this thesis analyzes the relationship between the disturbance amount of automatic voltage regulation control and the system time delay stability margin by using the derived stability criterion and a numerical examples.(2)The stability problem of a single-area power load frequency control system by considering PID parameters.Firstly,this thesis constructs a mathematical model of power system with communication delay and transforms power system based on PID controller into a closedloop system with feedback control.Secondly,it derives a new criterion for stability with PID parameters in the system matrix by using the theoretical analysis method of time-delay systems.Finally,it verifies the stability criterion derived by numerical examples.The simulation results show that the stability criterion can make the system less conservative.At the same time,it analyzes the relationship between the PI control gain and the stability margin of the system with time delay under three conditions of constant delay(μ=0),time-varying delay(μ=0.5)and stochastic delay(μ= unknown).(3)The problem of power load frequency control system via using sampled-data control.Firstly,this thesis relaxes the positive definition constraint conditions of Lyapunov-Krasovskii functional,and combines with the integral inequality approach to deal with the integral term in the functional derivative so as to reduce system conservatism.At the same time,it versifies the correctness and validity of the proposed criterion by the classical numerical examples,and compares the simulation results with other existing literatures.The results show that the method proposed in this paper has significant advantages.Finally,this thesis also constructs a load frequency control system model based on state feedback controller,and calculates the conditions of augmentation of system under different controllers and the maximum updating period of sampling.