Modeling And Stability Analisis Of Microgrid In Islanding Mode

Stability is the key issue in the operation and control of Microgrid.For an inverter-based microgrid,which contains lots of power electronic devices and a small inertia character.It's necessary to conduct a thorough research for the small signal stability of microgrid.This paper mainly focuses on the small signal stability of an inverter-based microgrid,operating in islanding mode.The main contents of this paper are as follows:(1)A detailed overview of research status on several analysis methods of the small signal stability for an inverter-based microgrid is presented.This paper compares respective advantages and disadvantages of each analytical method.For the improvement of the small signal stability,this paper summarizes the research situation in terms of the optimization of controller parameters,the improvement of droop control and the optimized design of hierarchical control strategy.(2)Firstly,the general procedure of the small signal stability is summarized.A complete state-space small-signal model of an inverter is deduced by combining the state-space models of the droop controller,voltage controller,current controller and output LC filter with coupling inductor.Furthermore,the state-space equations of multiple inverter-based microgrid are established in the common DQ reference frame.Finally,the small signal model of a typical microgrid with s inverters,n lines,p RL load and m nodes points is formulated,which provides the basis for the stability analysis and parameters design of the system.(3)The example for a complete state-space small-signal model of the microgrid with two parallel inverters is established.The influence of the variation of load parameters,droop factors,PI controller parameters,LC filter parameters and line parameters on system stability is analyzed through the model.All the eigenvalues and their corresponding damping ratio as well as oscillation frequency are obtained by the state matrix of system.Several oscillation modes of the system are discovered through eigenvalue analysis.The origin of each oscillation mode is revealed through participation factors.Finally,the underdamped oscillation mode is improved by the optimization of system control parameters.Thus,the improvement of the small signal stability is achieved.(4)A simulation model of microgrid with two parallel inverters is built by MATLAB/SIMULINK.The correctness of the established small signal model is verified by the variation of load parameters and droop factors.Then the parameters optimization results of underdamped oscillation mode are verified.