Application Of Flexible DC Transmission Technology In Low Voltage Distribution Network

The DC sources such as distributed wind power and solar power with typical DC loads such as electric vehicles are widely accessing the low-voltage distribution network,the simplex AC distribution network can not satisfy the connection of all kinds of distributed new resources and the demand of power for DC loads.This thesis applying back-to-back technology of flexible HVDC on the low-voltage distribution network raises a new AC-DC hybrid distributed power system which can afford the access of DC sources and supply power to AC-DC loads.The system which adapts electrical and electronic technology?energy exchange technology and coordinated control strategy is the smart distributed power hub in the AC-DC hybrid distribution network,realizing the direct access of new resources and DC loads,supplying the sustaining power to the important loads and raising the reliability of power supply.Firstly,this thesis analyses the appliance mode of back-to-back technology of flexible HVDC in low-voltage distribution network and raises a topological structure which divides AC-DC hybrid distributed power system into the grid AC terminal?the load AC terminal and inner DC system.Through the design for interface mode in converters of all the terminals,it realizes the direct access of wind power?solar power?storage equipment and loads.Secondly,based on the former topology structure,this thesis raises the control strategies for DC bus voltage and entire operation,puts forward the operation modes for all the terminals in all kinds of operation conditions and the control strategy for the exchange of them.Using simulation software for the simulation experiment,it verifies the validity of designed topological structure and promoted control strategy.Ultimately,the research of this thesis applies on the demonstration project in Liaoning electric power development stock co.,LTD which establishes a low-voltage AC-DC hybrid distributed power system with 20 k W solar power DC terminal?33k Wh storage DC terminal?30k W electric vehicles load DC terminal?grid AC terminal and load AC terminal by transforming typical DC loads.This quantity of the grid AC terminal is 50 k W and the load AC terminal connects to the important AC loads in the company's vehicle network operation monitoring center.Right now,the project is operating well,the switching process is smooth,the effect of protective power is remarkable,all the thing verifies validity for the design of topology and control strategy.Above all,this thesis can provide a new idea and technology to the operation of the low-voltage distribution network and it also can provide a theoretical and practical basis for the design,control and operation of smart AC-DC hybrid distributed power equipment.The implementation of this thesis which applies in the power grid will change the current situation of disordered access and lack of control of distributed power sources in the existing low-voltage distribution network,further improve the operation level of low-voltage distribution network and the economic efficiency of power network operation.