Research On Theory And Methods Of Online Dynamic Security Assessment Of Large Scale Power System

With the development of power system, the operating conditions have been more andmore complex and changeful. The so called off-line analysis and online matching controlmode can’t ensure secure operation in many cases. The research on the blackouts has alsoshown that the lack of real-time monitoring and control is a main cause of blackout. Andknowing the real-time safety margin and the potential risk of the system is the basis ofreal-time control. All of these create a need for online dynamic security assessment (onlineDSA).In the existing research, there is little work on the weakness identification, onlinedynamic equivalent or the quantitative assessment method of power system security. So thispaper mainly focuses on these above aspects.First, a Thevenin’s equivalent based method for determining the static stability limit ofthe transmission section is proposed. In this method, a two-machine equivalent is used todetermine the static stability limit. Once static stability limit is determined, the staticstability margin can be easily calculated to assess the weakness degree of the transmissionsection in one way.Second, an improved coherency based dynamic equivalent method for onlinemodeling is presented. Slow coherency approach is used to identify the coherent generators;an aggregation method combining both time domain aggregation and weighted averageapproach is used to determine the parameters of the equivalent generator; and an improvedREI method is used to reduce the network. Simulation results show that the equivalentmodel retains the dynamic performance of the original system with good accuracy.Third, some indexes are presented to assess the level of power system security. Basedon these indexes, a weakness identification method is proposed and a quantitativeassessment method for power system security assessment is introduced.