Cascading Failure Analysis And Emergency Control Strategy Considering Distributed Generation

With the continuous development and improvement of new energy power generation technology and the construction of large capacity and long-distance AC/DC hybrid power grid in China,there will be large-scale distributed energy access to the power grid in the future,and the spatiotemporal uncertainty of distributed generation output will further increase the risk of grid interlock failure.According to the spatiotemporal random characteristics of distributed generation output,the probability distribution model of distributed generation output is established,which is conducive to accurately analyze the impact of distributed generation output fluctuation on cascading failure.The power flow distribution is a dynamic process caused by the random fluctuation of distributed generation output and load.In order to improve the reliability of cascading failure analysis,the dynamic regulation effect of power system should be considered.The transmission of cascading failures in power system is directional,which can be effectively suppressed by formulating economic and reasonable control strategies.In view of this,this paper focuses on cascading failure analysis and emergency control.The thesis mainly includes the following:1)Firstly,the probability distribution model of distributed generation output is established according to the output law of single distributed generation at longitudinal instant and the output correlation of multiple distributed generations with similar geographical location.By analyzing the historical statistical data of photovoltaic and wind power,we can see that there are significant differences in the output distribution of single photovoltaic or wind power at different times.Non kernel density estimation method is used to estimate the probability density function of wind power and photovoltaic power output at each moment,and the longitudinal instant distributed generation power output model is established.Copula theory is used to estimate the output correlation of wind power or photovoltaic at different locations at the same time,and the output correlation model of multiple distributed generation is established.The spatiotemporal random characteristics of distributed generation output are described by the longitudinal instant output model and output correlation model.2)Secondly,considering the output characteristics and correlation of distributed generation at longitudinal instant,the cascading failure analysis of power grid is carried out.Based on the output and correlation model of distributed generation,an improved Latin hypercube sampling method is used to generate random variables of distributed generation output.The cascading fault analysis method is based on the mode search theory.The dynamic probabilistic power flow algorithm considering the effect of frequency modulation is used to obtain the power flow probability distribution of the system.The initial fault selection index is established according to the random variable characteristics of line transmission power,and then the lower fault search index is established according to the line outage probability model,the implicit fault of circuit breaker and the random variable characteristics of line power flow.The cascading fault propagation process is simulated by step-by-step interruption,and the influence of longitudinal output characteristics and correlation of distributed generation on cascading fault propagation is analyzed by simulation.3)Finally,the overload control strategy based on bi level optimization programming is proposed.The emergency control problem of power system is regarded as the optimal control problem constrained by objective equation.Firstly,according to the electrical distance,hierarchical clustering algorithm is used to divide the power grid line area to reflect the difference of power regulation effect of different generating units on overload lines.Then,the upper optimization programming model is constructed with the objective of minimizing the total power regulation amount of the system,so as to give priority to the power regulation with shorter electrical distance in order to reduce the number of generators participating in regulation and the situation of long-distance power regulation,the bilevel optimization programming method is used to obtain the control scheme of generator output regulation and load shedding.Finally,the effectiveness of the proposed control strategy is verified by simulation.