Study On Reduced-order Modeling Method And Bifurcation Stability Of DC Microgrid

Microgrid is a kind of distribution system that can integrate distributed energy,energy storage system,power electronic devices and various loads.Microgrid can make full use of distributed,solve the problem of insufficient power supply and environment effectively,and provide a operation mechanism that can make full use of distributed energy generation.Microgrid represents the main trend of future power development.Considering that most of distributed energy sources and loads are DC,and AC distributed generators such as wind turbines and diesel generators need to go through DC link when they are connected to the power grid.Therefore,DC microgrid is more conducive to complementary advantages among various micro-sources,and can better adapt to the future trend of load development.In this paper,a full-order mathematical model of DC microgrid with photovoltaic,wind turbines,energy storage and DC load is established.Then,according to the multitime scale characteristics of DC microgrid model,the full-order model of DC microgrid is simplified by singular perturbation theory.Then the stability of DC microgrid is analyzed by using bifurcation theory,and the stable operation boundary of the system is obtained.Finally,a DC microgrid system is built and tested on the RT-LAB experimental platform.The main contents of this paper are as follows:(1)Establishment of quasi-steady-state model for DC microgrid.Firstly,the topology of DC micro-grid and the control mode of distributed generation are studied.Then,the electromagnetic transient model of islanded DC micro-grid with photovoltaic,fan,battery and DC load is built in MATLAB/Simulink,and the full-order mathematical model of islanded DC micro-grid is established as the research object.(2)By using singular perturbation theory,the eigenvalues and participation factors of DC microgrid system are analyzed in detail.According to the analysis results,the state variables are separated into fast and slow variables.On the premise of guaranteeing the dominant eigenvalues of the system,the singular perturbation theory is used to simplify the full-order model of DC microgrid,and the eigenvalues and characteristics of the reduced-order model and the full-order model are compared.Finally,the analysis results of the bifurcation theory are verified.(3)In view of the non-linear dynamic characteristics of the DC microgrid,the bifurcation theory is used as the research method of stability analysis to analyze the dynamic stability of the DC microgrid model.Firstly,the bifurcation parameters are selected to track the bifurcation points by participating factor analysis.Considering that the islanded DC microgrid with constant power load is more vulnerable to instability,the stability trend of the microgrid is considered and the instability phenomena are predicted when the load increases.Finally,the analysis results of bifurcation theory are verified.(4)By using RT-LAB hardware-in-the-loop simulation platform,a hardware-inthe-loop simulation system for DC micro-grid is built.The experimental results of DC micro-grid under steady and dynamic response are given.The stability analysis results of DC microgrid system are verified by experiments.