Research On Operation Control Strategy Of Flexible Medium And Low Voltage DC Distribution Network

With the rapid development of the global economy and industry,there are imbalances in energy supply and demand and changes in energy structure,which have also led to environmental pollution and energy crises.The development of renewable energy and low-carbon economy have been generally recognized and gradually attracted attention.Electric energy is a core element and an important resource that supports the development of the country,and it is also facing major changes.During the development of electric energy,the disadvantages of traditional power grids have gradually become prominent.It is impacted by the distributed and grid-connected renewable energy.It cannot meet the rapid expansion of the capacity brought about by the increase in industrial scale,and it will cause a conversion process for the increasing number of DC loads.Energy is wasted,so there is an urgent need to develop a DC distribution network.The flexible DC distribution network has the advantages of low line loss,large transmission capacity,high power quality,flexible power supply mode and convenient access to distributed power sources.It has received extensive attention and research and has a huge future development prospect.First,it introduces the background and significance of DC distribution network research,expounds the advantages and characteristics of flexible DC technology,analyzes the topology and voltage level of DC distribution network,and selects the appropriate topology,wiring mode and voltage level.Then,typical components such as voltage source converters,DC transformers,photovoltaic systems,and energy storage systems in the DC distribution network are analyzed,and mathematical models of each module are established.Secondly,in the process of maintaining system voltage stability and power balance through the coordinated operation of multiple converter stations,in view of the shortcomings of the traditional DC voltage control method of the distribution network,an improved compound multi-converter station coordination control strategy is designed.Then the PSCAD simulation model of the three-terminal DC distribution network was built,and four modes of normal operation,load power fluctuation,main converter station withdrawal and slave converter station withdrawal were designed,and the proposed coordinated control strategy was simulated and verified.In order to improve the utilization of new energy and suppress the distributed power supply and load fluctuations in the system,a coordinated control strategy between photovoltaic power generation and energy storage systems in the optical storage DC microgrid is proposed,and the complementary characteristics based on supercapacitors and batteries are used to design;The cascaded topology constitutes a hybrid energy storage system,which further improves the stability of the system.Finally,through the simulation of photovoltaic power output fluctuations and load changes,the effectiveness and feasibility of the coordinated control strategy proposed in the article is verified.