Stability Analysis Of Time-delay Systems And Its Application In Power Systems

With the development of networked control systems and the emergence of large-scale power grids,time-delays become more and more obvious in modern large-scale power systems.In the analysis of power systems,it is necessary to take this factor into consideration.Many published results related to stability analysis of power systems are on the base of frequency method,while the frequency method cannot handle the case of time-varying delays.Therefore,the results of this paper are on the base a time domain approach,Lyapunov method.Firstly,the stability problem of linear time-delay systems is studied.For different cases of time-delay,the free-matrix-based integral inequality method is applied and the corresponding delay-dependent stability conditions are proposed.Secondly,aiming at the stability problem of networked sampling control system,using the input time-delay method,taking full account of the characteristics of sampling process and signal transmission delay,the sampling control system model that considers time-delay in network communication is established.Applying the two-sided closed-loop function proposed recently,some stability criteria are established.Finally,the proposed condition is applied to the small disturbance stability analysis of the power system.This paper focuses on the impact of time delays on the stability of power systems.The contents of the thesis are as follows.(1)The stability of linear time-delay power systems is studied.A new integral inequality method is proposed for the definition of integral terms that are common in time-delay systems.Then,for several different time-delay cases such as constant time delay,time-varying delay and unknown delay,the proposed free matrix integral inequality is used to establish the corresponding stability conditions,and the results are extended to systems with uncertainties.Finally,some numerical examples are provided to illustrate the effectiveness of the proposed method and the superiority of the existing results.(2)The stability of networked sampling control systems is investigated.Firstly,by analyzing the characteristics of sampling and communication time-delay in network control systems,a sampling control system model considering network communication delay is established by employing an input delay method.Then,based on the analysis method proposed for time-delay system in the previous chapter and the recently proposed two-sided closed-loop function method,the stability conditions of the networked control system are obtained.Numerical examples are given to illustrate the effectiveness of the proposed method and the superiority of the existing results.(3)The problem of delay-dependent stability analysis of power system under small disturbance is studied.Firstly,the meanings of system delay stability margin in the cases of constant time delay and time-varying delay are analyzed briefly.Then,based on the proposed delay-dependent stability criterion,a method for delay-dependent stability analysis of power system under small disturbance is proposed.In what following,for the single-machine infinity bus power system equipped with excitation controller,the time-delay stability margin of the system is obtained and the stability domain of the system under small disturbance is calculated via the proposed method.The relationship between the parameters of the excitation controller and the stability domain is analyzed,which provides a guideline for the choice of the design of controller.Finally,the research work of this paper is summarized and some future works on this field are provided.