Research On Coordinated Operation Of DC Microgrid Based On Improved Droop Control

As the role of renewable energy in modern power systems becomes more and more important,Microgrid systems can receive great attention by integrating new energy power generation,battery energy storage,and load to achieve "plug and play" functions.In the microgrid system,the DC microgrid has more advantages than the AC microgrid in terms of transmission line losses,system operation stability,and distributed energy efficiency conversion.Of course,the system also has the advantages of independent regulation and easy control.The research object of this paper is DC micro grid.The principle analysis and corresponding modeling of photovoltaic power generation unit,energy storage unit and grid connected converter in the system are carried out.At the same time,the droop control method and system coordinated operation control in DC micro grid are studied carefully.First,the structure of the system is briefly introduced.The principle analysis and modeling of photovoltaic power generation unit are carried out,and the output characteristics were analyzed through the simulation model.Based on this,a maximum power point tracking technology was proposed and its feasibility was verified by MATLAB/Simulink simulation;introducing the general mathematical model of the battery,the working principle of the bidirectional DC/DC converter is analyzed,and the corresponding simulation model is set up to realize the charge and discharge simulation of the energy storage unit;the mathematical model and topology structure of the grid-connected converter are introduced,and the next step The research on its related control principles lays the foundation.Secondly,through the analysis of the principle of traditional DC droop control,the defects of low current sharing accuracy and voltage offset are brought out.Aiming at the defects proposed in this paper,two kinds of improvement methods are proposed,which are droop curveadjustment and droop coefficient adjustment.On this basis,an innovative improvement strategy is proposed,which effectively improves the power distribution accuracy between parallel micro sources in DC micro grid system,and maintain the stability of bus voltage.The reliability of the improved strategy is verified by Matlab/Simulink simulation.Finally,This chapter studies the DC microgrid system' the coordinated operation control.By using the DC bus voltage level as the basis for division,the system operation is divided into four modes,and each unit has a corresponding unit responsible for voltage stabilization.The control strategy and mode switching process of photovoltaic power generation unit,energy storage unit and grid-connected converter are introduced in detail.Finally,simulations are performed to verify the changes in DC bus voltage caused by unstable power output or load changes of the distributed power generation system.The system can change to the corresponding operating mode according to the system voltage level and ensure stable system operation.