Small Signal Stability Analysis Of Microgrid Based On Virtual Synchronous Generator Control

In recent years,the renewable energy such as wind energy and solar energy have been rapidly developed.In order to improve the utilization of energy and stabilize the operation of distributed generation(DGs)system,the control strategy of inverter-interfaced DGs becomes the focus of the research.However,inverter-interfaced DGs with conventional control methods,such as droop control,still cannot provide enough inertia to support the frequency of the microgrid to maintain the stability of grid operation,which has also become a major factor restricting the popularization of microgrid.This paper studies the inverter control strategy of Virtual Synchronous Generator(VSG),which simulates the inertia equation of the conventional synchronous generator rotor.Then,the mathematical modeling and simulation analysis of the VSG control strategy are carried out,and a small signal model of VSG control strategy is built to solve the problem of the microgrid system stable operation.The relationship between operation stability and operation parameters is quantitatively analyzed,which provides basis for improving control strategy and parameter optimization.This dissertation is organized as follows.1.The traditional inverter control strategy is studied,and the application scope and limitations of traditional inverter control strategy are summarized.2.Based on the principle of the traditional synchronous generator and the present VSG control strategy,the mathematical modeling of each control part of the VSG controller includes the LC filter,the active damping controller,the PLL controller,the virtual impedance controller,the virtual governor,the virtual exciter and the voltage and current double loop controller has been built,and the parameters of the VSG has been designed.Through the simulation software,the VSG control model and the single inverter power supply microgrid model are established.Then the simulation examples that the microgrid shifts grid-connected mode to island mode and the load switch under island mode have been designed.Comparing the simulation curves of voltage and frequency of system has VSG control with no VSG control.The simulation results show that the established VSG control model can maintain the frequency and voltage of system when the microgrid is disturbed,and it provides inertial support for the system.3.The complete small signal state space model of island operation microgrid based on VSG strategy is established.The small signal dynamic models contain the grid and line,the inverter power supply,the active damping,the PLL,the virtual governor and exciter,the virtual impedance and voltage current double-control loop.By calculating the characteristic of small signal model of the state matrix,judging the stability of the system.Then the further research,by varying the control parameters of small signal model,the root locus plot can directly reflect the influence of parameters on the stability of the system(if the droop coefficient of active power is too small,it will reduce the stability of the system,and increase the active droop coefficient appropriately,which will improve the stability of the system.),which can be used for control parameters optimization.