Research On Novel Urban Power Grids Failure Analysis Method And Power Supply Restoration Strategy

With the integration of a large number of distributed generation and electrified transportation,as well as the continuous advancement of power electronics in urban power grids,urban power grids have gradually shown new and complex forms,and traditional failure analysis methods and power supply restoration strategies have continuously presented new problems.On the one hand,when a fault occurs,distributed generation output and electric vehicle discharge are random,which makes it difficult to adapt to traditional fault analysis methods based on a certain operating point;on the other hand,after the fault is removed,the increased penetration of distributed generation and electric vehicle also brings new challenges to the restoration of power supply.In this context,this thesis takes the new form of urban power grids as the research object,takes into account the control strategies and random characteristics of distributed generation and electric vehicle,and proposes a fault analysis method.At the same time,based on the soft open point,formulating power supply restoration strategies for power-loss areas to ensure the safe and stable operation of urban power grids has important theoretical significance and application value.The main research contents are as follows:Firstly,a fault calculation model of the urban power grids with the inverter interfaced distributed generation is established.Analyze the control strategy and output characteristics of the inverter interfaced distributed generation,and establish its fault equivalent model based on the characteristics of the nonlinear relationship between the output current and the point of common coupling voltage;By constructing a three-phase short-circuit and two-phase shortcircuit fault equivalent network,the urban power grids fault calculation model is established based on the node voltage equation;A simulation example verifies the accuracy of the proposed model.Secondly,considering the random characteristics of distributed generation output and electric vehicle discharge,a cumulant failure analysis method for urban power grids with the inverter interfaced distributed generation is proposed.This method reflects its randomness by establishing probability models of wind power,photovoltaic power generation and electric vehicle discharge;Then the urban power grids fault calculation model is linearized by Taylor expansion,which includes correction equations,node voltage equations,and branch current equations.The cumulant method is used to calculate the cumulants of the fault voltage and current,and through the Gram-Charlier series to get the probability distribution of the fault voltage and current;The proposed method is analyzed and verified based on the improved IEEE33-node system,which proves the accuracy and effectiveness of the method.Finally,aiming at the problem of power supply restoration after the removal of urban power grids faults,a power supply restoration strategy for urban power grids based on the soft open point is proposed.This strategy establishes its mathematical model by analyzing the control characteristics of the soft open point;Then,on the basis of considering the safety and stability of the system and the supporting role of distributed generation and electric vehicle,a power supply restoration model with the largest load restoration power supply and the smallest network active power loss as the objective function is established,and the control parameters of the soft open point are optimized and solved by the particle swarm algorithm;In order to verify the effectiveness of this method,compare and analyze with other recovery schemes in a variety of scenarios.