Research On Coordinated Control Of DC Distribution Network

As people pay more and more attention to environmental issues and future renewable energy issues,distributed new energy power generation methods using clean and renewable energy represented by solar energy and wind energy have been rapidly developed and valued.The DC distribution network technology effectively reduces the AC/ DC link,greatly alleviates the contradiction between the large power grid and the distributed power supply,and becomes an important development direction for the future smart distribution network.Among them,the coordinated control technology of DC distribution network is the main influencing factor to maintain the stability of the system.Based on the above reasons,this paper has carried out the following work on the coordinated control mode of the DC distribution network and its small signal stability:1)The characteristics of the droop control method and the voltage margin control method of the DC distribution network are studied,and the basic principles and advantages and disadvantages of the droop control and voltage margin control are analyzed.In-depth study of the essential relationship between droop control and voltage margin control,a third-order control method suitable for DC distribution network is proposed,and the control effect is verified by Digsilent / PowerFactory simulation software,and the optimization of DC distribution network coordination through combination is discussed The coordination principle of the control mode and the structure of the controller.2)The small signal model of DC distribution network is derived.Through modular modeling,the system is divided into four parts: converter,control system,AC system and DC line.Among them,the control system includes two layers: coordinated control(combined control)between converter stations and station-level control(vector current control)of converter stations.In order to verify the small-signal model,the corresponding small-signal model of the DC distribution network was built using Matlab,and the time-domain model was built using Digsilent / PowerFactory simulation software,and the two models were compared in detail in the time domain.The response waveforms of the two models are almost identical under small disturbances,which proves the correctness of the established small signal model.3)Based on the established small-signal model,conduct small-signal stability analysis on the coordinated control parameters of the DC distribution network.The high-level control of any DC distribution network can be divided into a voltage margincontrol stage and a voltage droop control stage.In the two stages,the station-level control parameters and the droop control coefficient of the converter station are changed,and the root locus is drawn.Based on the theory of eigenvalue analysis of power system small signal stability,the influence of the station-level parameters and droop coefficients of the converter station on the system small signal stability is discussed.It is found that the outer loop active control parameters and inner loop of the converter station The reactive control parameters of the system have little effect on the stability of the small signal of the system.With the increase of the reactive control parameters of the outer loop and the active control parameters of the inner loop,the stability margin of the system increases synchronously.Causes system instability.