Research On Analysis And Treatment Method Of Pole-to-Ground Fault In DC Distribution Network

The DC power distribution technology based on the flexible DC technology has brought a new development direction for urban distribution network.However,due to its own characteristics of the DC distribution network fault,there is still no direct application to urban DC distribution network protection scheme.In this paper,the DC distribution network for urban power supply is viewed as the object.The paper focuses on the fault analysis and modeling methods of DC distribution network,the capability of fault ride-through and the protection method of pole-to-ground fault.Firstly,a simulation model of multiterminal DC distribution network based on VSC is established.The characteristics and advantages of DC distribution network are summarized,and the voltage class,power supply capacity,loss and transmission of DC distribution network are compared with that of AC distribution network.Also,three typical DC distribution network topologies are introduced.Then,the main characteristics of VSC is expounded,and a current limiting method in the process of system startup is designed.Afterwards,the simulation model of DC distribution system is built on the Matlab/Simulink simulation platform,and the simulation results of the system start-up,operation,AC load input etc.are given.Secondly,the fault crossing capability of DC distribution network under transient pole-to-ground fault is studied.When the converter transformer,the DC side capacitor midpoint is being used in different grounding method,DC distribution network operational aspect of the process of phase-to-ground fault as well as the recovery process after fault is analyzed.Based on the requirement of fault crossing capability of the pole-to-ground fault in the DC distribution network,the grounding scheme of neutral point of converter transformer and midpoint of DC side capacitor is proposed,and the rationality of the scheme is verified by simulation.Finally,the protection scheme of permanent pole-to-ground fault for DC distribution network is proposed.According to the fault characteristics of pole-to-ground fault in DC distribution network,the identification criterion of pole-to-ground fault is given to determine whether a pole-to-ground fault occurs or which pole fault occurs.Furthermore,due to the correlation difference analysis of the current between the fault section and the non fault section of the line,the method of locating the fault section of the line is proposed.At last,the effectiveness of the protection scheme based on the above criteria and localization methods is verified by simulation result.