Research On Risk Assessment And Emergency Control Method Of Power System Cascading Failure

In recent years,large-scale power outages around the world have caused enormous economic losses to human society,which seriously threatening social stability.So how to improve the safety of large power grids become a major task for scholars in the operation and control of power systems.Studies have shown that most of the power outages in the power grid are caused by internal factors such as overload,component failure,control protection and communication system failure,and external factors such as natural disasters,and the critical lines or key nodes in the power grid are out of operation,while the dispatch control center due to a series of reasons,not to accurately evaluate the running system state after the critical line or the critical node exiting,failing to issue emergency control commands actively,or the emergency control measures are not able to eliminate the line overload phenomenon in time,bringing a series of other effects.Eventually,the situation is out of control,causing a cascading failure.Therefore,in the daily operation of the power grid,highlighting the monitoring of the operating status of key components is conducive to improving the safety of the grid operation;after the system status changes,the overall safety status of the system should be accurately evaluated,so that the dispatcher can get an overall recognition of the system status,which is beneficial for dispatchers to make decisions;finally,it is important to formulate an emergency control plan that meets the requirements according to the actual situation,and the trinity can minimize the possibility of a large power outage.The main research contents are as follows:From the perspective of system structure and system status,comprehensively evaluate the importance of the branch to the system.Firstly,it analyzes the emphasis of the existing electrical betweenness and power flow betweenness on the importance of the branch,and then proposes the comprehensive betweenness index to evaluate the importance of the branch in the system topology;then,based on the traditional power flow transfer entropy,the transmission margin of each branch in the system is considered,and the change of the unit entropy average load rate is used to characterize the impact of the operating state of the branch break-off system.Finally,the importance of the branch structure and the importance of the state are combined in the form of weights to more fully measure the importance of the branch in the power grid.Taking into account the different importance of different components to assess the risk of cascading failures of power systems,firstly establish a power system risk assessment model;secondly,consider the different positions of different nodes and lines in the system,the existing accident severity function of the node voltage and the line power are improved.Considering the risk assessment of the importance of different component structures,the power system dispatchers can more clearly understand the changes in various types of risks in the various links of the cascading failure system,and can more accurately control the state trend of the control system,which provide a strong basis for the decision that make emergency control measures.An emergency control method considering the severity of overload of the overload line is proposed.Firstly,the heat generation model of the overload line in the emergency control process is established,and the heat accumulation limit of the overload line is defined to describe the dispatcher's expectation of eliminating the overload degree of the overload line.Secondly,adjusting the output of the generator and cutting load of the cutting machine have different effects on the active power change on the overload line,on the basis of the power sensitivity matrix,the active power circulating on the overload line is adjusted with the output of the generator and the cutting machine is established.Finally,with the objective of minimizing economic compensation,an optimized load shedding model is established to solve the model based on simulated annealing particle swarm optimization algorithm.The obtained emergency control scheme can meet the dispatcher's expectation of eliminating line overload under the full play of the advantages of low generator output cost and short load-cutting measures,the IEEE case proves the method is more practical than existing method.