Research On Control And Protection Of DC Distribution Network Based On LLC DC Converter

Electric energy is the foundation of national economic development and social progress,but with the rapid increase in the number and variety of loads,users are increasingly demanding power quality.The traditional AC distribution network faces enormous challenges,so DC power distribution technology has regained the attention of scholars of various countries.The DC distribution network is more likely to accept distributed energy and various DC loads,effectively improve the transmission capacity,power supply efficiency and power quality of the distribution network,and does not need to consider reactive power compensation and power angle stability.The DC distribution network is an ideal grid-connected structure for distributed energy.Firstly,this paper studies the LLC DC converter with energy storage system and designs the resonant network parameters according to the gain characteristics of the converter.According to the equivalent circuit model method,the small-signal modeling of the LLC DC converter is carried out,and the transfer function of the converter control frequency-voltage output is obtained.According to this,the PI controller of the converter is designed to realize the closed-loop control of the LLC DC converter.Secondly,this paper analyzes the equivalent circuit model of each unit of energy storage system in DC distribution network.In order to improve the efficiency of energy storage system,and give full play to the advantages of each energy storage unit,a suitable DC distribution network composed of photovoltaic system,energy storage system and DC load is selected.The coordinated control strategy of each energy storage unit during the operation of the DC distribution network is analyzed to realize the safe and stable operation of the DC distribution network with distributed power access.And the simulation model of DC distribution network was built in Matlab/Simulink.Then,according to the DC distribution network structure used in this paper,the fault characteristics,positioning methods and protection measures of DC line faults are analyzed.A line protection protection method using a sudden change in current across the line is used to protect the line of the DC distribution network.The control and protection of the DC distribution network based on LLC DC converter are modeled and verified in Matlab/Simulink.The experimental platform is used to control the LLC DC converter and verify the operation of the DC distribution network.