Research On Power Allocation Strategy And Smooth Grid Connection Of Distributed Generation With Different Capacity In Microgrid

With the rapid development of society,distributed power has gradually approached people's vision,and microgrids,as a power network capable of coordinating distributed power,have attracted more and more attention from scholars.The droop control in the microgrid control method does not require interconnection,and the characteristics of convenient installation and high reliability have also become hotspots in the research direction of microgrids.Although droop control has many advantages,droop control cannot have a good control effect in low-voltage microgrids with a system impedance of resistive,and power cannot be distributed according to the capacity ratio of distributed power sources.With the change of output power,the frequency and voltage amplitude also deviate from the reference value,resulting in the impact current when the grid is connected,which can not be smoothly connected to the grid.The following researches have been done in this paper.First,the main circuit topology and filter are selected and designed,and then the mathematical model of the inverter from three-phase coordinate system to dq synchronous rotation coordinate system is deduced.The AC quantity is converted into DC quantity,and according to the crossing frequency and Bode diagram designs and analyzes the parameters of the current-voltage dual-loop controller.Secondly,the traditional droop control principle is introduced.Because the impedance of the low-voltage microgrid system is resistive,power cannot be decoupled and power cannot be distributed according to capacity.The traditional virtual impedance is introduced to solve the problem of power decoupling;However,the actual line impedance value cannot be accurately measured,which results in the traditional virtual impedance being inaccurate,which cannot completely solve the problem of power allocation.This article adds an adaptive term based on the traditional virtual impedance,so that the power is based on the distributed power capacity ratio Allocate and establish a small signal model for analysis,and build a simulation model of three DG units connected in parallel in the case of an island.The simulation results verify the feasibility of the proposed control strategy.Finally,in this paper,the microgrid is connected to the grid.It is found that the voltage,phase,and frequency of the micro-grid and the grid will cause a huge impact at the moment of grid connection,which will cause grid failure and damage to the grid.The causes of grid-connected shocks are analyzed,and the phase compensation control of the pre-synchronization control before grid-connection is improved.A phase compensation loop without phase-locked loop is proposed.A microgrid grid-connected simulation model is built.The effectiveness of the improved phase compensation control is verified.