Research On Characteristic Analysis And Location Method Of Pole-to-ground Fault In DC Grids Based On VSC

With the energy depletion of fossil energy,China and around the world have taken the development of renewable energy as an important task for the future devlopment.The proportion of the wind power,photovoltaic and other new energy in the power system will be increased gradually.Traditional power grid construction and operation technology has appeared increasingly to be inadequate in facing the stability of renewable energy.While the DC power grid has been paid more and more attention because of its advantages such as power flexibility and controllability,reactive power angle stability and so on.DC grids contain a large number of DC terminals,when the DC line fault occurs,it has more extensive impact on the entire system.In this paper,the transient characteristics of the system are analyzed by using the four terminal DC link network as an example.A fault location method has been proposed based on the analysis of the fault characteristics of the system.This method can effectively eliminate the influence of the fault resistance.The least square method has been used to optimize the location method.The simulation is carried out under Matlab/Simulink amd the simulation results verify the correctness of the fault transient characteristics and the accuracy of the fault location method.The main work has done as follows:1.The analysis of pole-to-ground fault transient characteristics.This paper divides the fault process into three stages which are DC-side capacitor discharge,grid-side current feeding and voltage recovery.According to the transient characteristics of system under different grounding impedance,the capacitor voltage and discharge current expressions of each stage were derived.2.Based on the analysis of fault transient characteristics,a fault location method is proposed.The fault line impedance can be solved with the recorded fault data of capacitor voltage and discharge current.Finally,the fault distance can be obtained by using the impedance of the fault point to the lines,thus the fault location is implemented.3.Optimizing location method with the least square method.The least square method is used to estimate the sample data,and the result of fault line impedance is optimized.The influence of the error of individual sampling points on the location accuracy is eliminated.