Forecast And Risk Management Of Overload Leading Cascading Failures

All the domestic and overseas power system accidents indicate that cascading failures of modern power grid are the main cause of blackouts.In particular,heavy-load and near-limit power grid in comparatively developed areas is liable to cause catastrophic accidents.Therefore,in order to make power grid followed the path of consistent growth of economy in our country,it is significant to further study the development mechanism of cascading failures and explore the security and stability control method for cascading failures.This thesis emphases on the following research and its results.(1)The adaptation of steady model and hybrid model in the forecast of cascading failures is compared and analyzed.By comparing the simulation results of DC power flow steady model,AC power flow steady model and transient model,the influence of the bus voltage and generator power angle on the simulation results is analyzed,and the effectiveness of steady model in the slow successive break phase is verified.In order to solve the problems of simulation of fast successive break stage by steady model,the simulation in fast successive break stage of transient model and hybrid model is compared,and the effectiveness of hybrid model is verified.The research results will provide reference frame of the choice of simulation model in different stage of cascading failures,from the aspect of forecast of cascading failures.(2)Aiming at slow successive break stage in cascading failures,using steady model,a cascading failure forecast and risk assessment model based on risk element transfer is established.Based on the application of risk element transfer theory into cascading failure forecast and risk assessment,the risk element transfer model of the outage of the line and the cascading failure prediction and evaluation model are established,and finally the forecast and risk assessment of cascading failures are achieved.This model can assist dispatchers to diagnose the development direction and critical segments in cascading failure paths in current operating conditions and lay the foundation of the research of defence control of cascading failures.(3)As for the propagation stage of cascading failures,using hybrid model,a multi-timescale cascading failure evolution and risk assessment model is established.According to the different time characteristics of the phenomena and the countermeasures in cascading failures,the proposed model has divided the cascadingfailures into short time scale,long time scale and very long time scale respectively.By considering the time relationship of the phenomena and the countermeasures,three time scale process models are established.The three layer calculation structure has been adopted to deal with the relationship between the three processes with different time scales,in order to simulate the evolution process of cascading failures.This model can effectively simulate the evolution process of cascading failures,which demonstrates the influence of the development of cascading failures caused by different time characteristics of the phenomena and the countermeasures.(4)In order to cover the shortage of traditional security and stability control in security analysis and calculation and real-time state perception ability,a model to defend cascading failures in power system based on multistage dynamic games with bounded rationality is established.By applying game theory into the study of preventive control of cascading failures and analyzing the evolution mechanism of cascading failures,the element and hypothesis of the defense of cascading failures based on multistage dynamic games is put forward.Based on risk theory,this model makes the risk of outage and the risk of control cost as the payment function,which can assist dispatchers to master the harmful effect caused by cascading failures and evaluated the effectiveness of control measurements.This model is able to analyze the safety of power grid and provides a visual basis for the development of cascading failure defense strategies.(5)A model of coordinated control of power system cascading failures based on risk assessment is built.On the basis of the prediction and risk assessment of cascading failures,by analyzing the coordination between the preventive control and blocking control of cascading failures,the coordinated control model is expressed as an optimization problem based on risk indexes.By setting the sum of the risk of cascading failures and the cost of coordinated control as an objective function,and considering the position of blocking control,which is confirmed by the risk importance of faults,a model of coordinated control of cascading failures is established.The effect of weather conditions is included in the model,therefore the model is able to trace the system's operating risk under different weather state.A coordinated control scheme for different weather conditions can be obtained by solving the model.