Small-signal Modeling And Stability Analysis For Microgrid

In recent years,the microgrid has been widely concerned because of the full use of distributed renewable energy,which has the advantages of flexible installation location,clean,environmental and so on.But,as the power supply unit of microgrid is mainly wind energy,solar energy and other renewable energy,and they all have the characteristics of intermittent and volatility.Thus,it is significant to realize the reliable and stable operation of microgrid through appropriate control method.In this thesis,the modeling of the signal is carried out according to its volatility characteristics,and its stability is analyzed.Firstly,the whole structure of microgrid is introduced in this thesis.Take the photovoltaic(PV)microgrid as an example,the mathematical models of PV array,storage equipment and inverter subsystem are established.Then,the system is analysed focused on the inverter,and its working principle and control method are described.Next,a small-signal modeling method is proposed,and a coordinate transformation method with disturbance is designed.Secondly,This thesis develops the modeling and analysis of autonomous operation of three parallel inverters-based microgrids based on the droop control.The whole model of the system mainly includes two parts,one is the main circuit model and another is the control circuit model.The former mainly contains filter circuit model,distributed power line model and load model;while the latter mainly contains the modelling of three ring droop control method based system for power control loop,voltage control loop and current control loop.Here,The droop control method for power control loop is Q/V and P/f,and the control metheod of voltage loop and current loop is PI control.Turn the small signal perturbation to the deviation angle of the coordinate system conversion and the corresponding state space equations are listed.Thirdly,three inverters are modeled in parallel system according to the proposed three ring droop control method and small-signal modeling method,and take it as the test system in this thesis.Design the system parameters and control gains to obtain the eigenvalues of the whole system.And,according to the sensitivity factor of each eigenvalue,the dominant eigenvalues are selected for analysis.Then,the root locus are also plotted when the system is in the initial state,and when the controller parameters,the droop coefficients and the load vary.The influence of the parameters on the stability of the system is then obtained.In addition,the concept of real stability radius is carried out and the robustness of the proposed control scheme is analyzed.Finally,select the system parameters,and the simulation model is build in MATLAB/SIMULINK.The system simulation of the initial running state and adding disturbance are carried out respectively.And the simulation results are analyzed in detail.The correctness and validity of the proposed method are verified by analyzing the simulation data and waveforms.