Research On Coordinated Control In Cascading Failure Of Power System Based On Risk

The interconnection of modern power grids increases the operational efficiency of power system and the risk of cascading failures.In recent years,blackouts caused by cascading failures in domestic and overseas power grids frequently occur,resulting in huge economic losses and disastrous consequences.The traditional safety control measures in the prevention and defense of power system cascading failures are still inadequate.In this context,based on the prediction of fault chains and risk assessment methods,a coordinated control model is established considering the safety and economy of power system on the existing defense of large grid,in order to prevent and block the development of chain failures from pre-accident to the process of accident.The main work is summarized as follows.First of all,the background of research is introduced,dozens of blackouts that have occurred worldwide are summarized to illustrate the basic types of blackouts to clarify the research purpose.At the present stage,the research status quo of cascading failures prevention and control model based on "Three Lines of Defense" is introduced.The existing strategies' advantages and disadvantages are analyzed.Secondly,the overload-dominated cascading failure is taken as the research object,according to the existing research results,the initial fault set and the next fault branches are screened by the line failure probability,the initial load rate and so on to form cascading failure simulation model.The generator adjustment due to partial power imbalance,the time characteristic of line backup protection and other factors are considered in the process of fault chains.Aiming at occurred failures in the constructed model,risk assessments are made to judge the safety of power system.Results based on IEEE 39 node system are served as a basis for follow-up control.Thirdly,according to the existing problems cascading overload control strategies,an emergency load shedding strategy based on Prim minimum spanning tree and power flow tracking algorithm is proposed to block the development of the accident chains,aiming at the predicted accidents.Considering the line overload and the voltage over-limit in the development process,the generators and loads control are adjusted according to the source-path relationship.The voltage of the system node is within the normal range,which makes up for the lack of consideration of the voltage factor in cascading overload control.Meanwhile,the implementation of control strategy needs to consider Coordinating the control time with global generator output adjustment time and line backup protection time in order to block the development of the accident chain with less control costs.IEEE-39 system is taken as an example to verify the effectiveness of this method.Finally,based on the analysis of the characteristics and deficiencies of both preventive control and blocking control in power system,a coordinated control model which makes coordination on safety and economy is established.The model is solved by the improved multi-objective optimization algorithm,and coordinated control schemes are evaluated.The multi-objective decision theory considering the preference of dispatchers is used to select the control scheme which accords with the different needs of the power system.The proposed scheme is analyzed compared with the result of the gray relational method and Nash negotiation method.Taking multiple operation scenarios as examples,the validity and rationality of cascading failure coordinated control is verified which includes prevention control and blocking control.And the analysis shows that the model can work out control plan to deal with different load levels and operation modes by choosing reasonable safe and economic preferences.