| As a new hot research technology in recent years,distributed generation technology can effectively solve many potential problems of traditional large power grid.It is an effective supplement and strong support for the traditional centralized large power grid.Distributed power supply is generally controlled by power electronic inverters,which have the advantages of fast response speed and so on.Virtual synchronous generator(VSG)can effectively simulate the inertia and the stator impedance of synchronous generators,and can effectively control the frequency and amplitude of the output voltage of the inverter.It is a good solution to the power electronic devices to achieve grid stability,damping and inertia etc.Micro-grid combines the energy storage unit,the distributed generation,the control device and the load into an independent controllable system.Due to the reliable power supply and flexible operation mode,micro-grid has become a strong support on reliable and stable power supply.In this paper,several common control strategies of microgrid inverter are studied.Through comparison and analysis,it is considered that VSG control and droop control are better control strategies.Then,the paper analyzes the similarities and differences of the two from principle structure.Through the analysis of the modeling and transfer function of the different parts of the active frequency control link,the equivalence of the two under certain conditions is obtained.At the same time,the correctness of the conclusion is verified by Matlab/Simulink simulation.Secondly,each module of a single VSG controlled inverter is modeled by a small signal,and the eigenvalues of the state matrix are obtained.By changing the droop coefficient,the moment of inertia and the line impedance,the distribution of eigenvalues is analyzed.And the influence of each parameter on the stability of the system is summarized.Finally,a typical model of multi VSG parallel connection is established.On the basis of the single VSG small signal model,the small signal model of the inverter parallel system controlled by multi VSG is established by analyzing the local and global coordinate transformation and the small signal model of the load.The influence of droop coefficient,moment of inertia and load impedance on the stability of the system is analyzed.The step response of the inverter output power is analyzed by Matlab/Simulink simulation under the condition that the line impedance is increased by 20%. |
