Small-Signal Stability Analysis Of Microgrid With Virtual Synchronous Generator

With the increasingly serious energy crisis and environmental problems,the microgrid has been developed rapidly since it was proposed.It combines renewable energy,control modules and load modules,and forms a system with reliable power supply ability and flexible operation modes.As the interface of new energy generation,the proportion of inverter in power grid is increasing continuously.Unlike the traditional synchronous generator,the power electronic device has fast response speed and low damping,and its large number of connections reduce the total inertia of the system.It is difficult to support the stable operation of the power grid.As a method to simulate the operation characteristics of synchronous generator,virtual synchronous generator control plays an important role in improving the stability of power system.In this paper,a single inverter model with the characteristics of virtual synchronous generator is established in Matlab/Simulink,which proves the effectiveness of the virtual synchronous generator control,and the isolated island and grid-connected model of parallel virtual synchronous generator are built.At the same time,their high-order small-signal models are constructed.Based on the small signal stability of the system,the inertia matching between the virtual synchronous generator and the load or the virtual synchronous generator is analyzed.The selection principle of virtual moment of inertia parameters for flexible control strategy is proposed.When the virtual synchronous generator is connected to the grid,the characteristic root is calculated and its corresponding physical characteristics are analyzed.The main relevant state variables of the characteristic root are obtained from the participation factor.We concern about characteristic roots when the sag coefficient,virtual moment of inertia,line impedance and virtual impedance parameters are changed.And their influence laws are summarized by the eigenvalue analysis method.In order to ensure the good dynamic characteristics and stable operation of the system,it is necessary to take into account the stability of the characteristic root of each frequency band.Finally,the model is simulated in Matlab/Simulink to verify the two machine's inertia matching and the law of the influence of the parameters on the system's characteristic root.This rule can guide the parameter matching and design of multi-inverter parallel system using virtual synchronous generator technology.The established small-signal model is of great significance for parameter setting optimization and system's stability analysis.