Research On Control Strategy Of Micro-grid Inverter Based On Virtual Synchronous Geneator

With the change of the world energy pattern and the development of economy,the distributed power generation mode with new energy has been paid attention to,and the proportion of power generation is gradually increased,which will become the main force of the future power grid construction.Because of the impact of direct grid connection on traditional power grid,these distributed generation often operate in the form of micro grid.As the key device in the micro network,inverter has an important influence on the stability and safe operation of the micro network.At the same time,the inverter is composed of power electronic components,which has the disadvantages of low damping and low inertia.Direct grid connection operation will affect the power quality and stability of large power grid.Therefore,it is of great significance to optimize the control strategy of inverter.This paper takes the micro grid inverter as the research object,and its main research work is as follows:(1)Aiming at the shortcomings of traditional control strategies in active frequency regulation and voltage regulation and maintaining system stability,the paper studies the virtual synchronous generator(VSG)control strategy inspired by the idea of synchronous generator.Firstly,the physical model of three-phase inverter is established;Secondly,a simplified second-order model is established according to the mathematical principle of synchronous generator;Finally,the relevant mechanism and expression of the virtual synchronous generator are obtained by the mathematical formula and the analogy.(2)In view of the defects of traditional virtual synchronous generator in eliminating harmonic and maintaining system stability,the traditional control algorithm of virtual synchronous generator is improved.Firstly,the principle of virtual excitation,virtual speed regulation and rotor motion equation is analyzed;Secondly,the robust controller is added to the excitation voltage link;Then,the output voltage controlled by the virtual synchronous generator is treated by bypass harmonic,which can achieve better performance in eliminating the harmonic content,improving the stability of the system and reducing the THD(Total Harmonic Distortion)value of the system;Finally,the performance of the proposed control strategy in several different filtering modes is compared.(3)Based on MATLAB/Simulink simulation platform,the system simulation model is built.The simulation results show that the harmonic distortion rate of voltage and current is only 0.97% and 0.67% when the system harmonic processing is carried out by different filtering methods,which proves that the LCL filter has better performance;The performance of the system is studied by LCL filter.The results show that the control strategy is only49.87Hz-50.02 Hz,and the stability is high;Finally,the influence of inertia and damping coefficient on the stability and frequency of the system is analyzed.(4)Based on MATLAB/Simulink simulation platform,the droop control model,traditional virtual synchronous generator control model and other improved virtual synchronous generator control model are built respectively,and the comparison and analysis are made with the improved virtual synchronous generator control model.The simulation results show that the THD value of the proposed control strategy is 1.72% in the system harmonic;The advantages of the proposed control strategy in improving voltage quality are verified;Finally,the frequency change and power quality of the system are analyzed.