Influence Analysis Of Low Frequency Oscillation Of High Penetration Renewable Energy Synchronization Units Under Virtual Synchronous Control

The rapid development of new energy not only solves the future energy dilemma and environmental problems,but also makes the overall electric power system appear a trend of low inertia and weak damping.The new energy grid-connected inverter adopts the virtual synchronous generator control strategy to provide support for the power system.It will also introduce the low frequency oscillation characteristics of traditional synchronous generators.In respect of the issues above,this thesis establishes the overall small-signal model of the inverter grid-connected system based on virtual synchronous control and the parallel operation of large-capacity multi-virtual synchronous control inverters connected to the power system and analyzes it,and then establishes the corresponding simulation model.The conclusions of the small signal stability analysis are verified.Taking the virtual synchronous control inverter connected to the power system as the research object,the influence of the virtual synchronous control strategy on the low frequency oscillation of the system is analyzed.The main research contents are as follows:Firstly,based on the analysis of the control strategy of the virtual synchronous generator,the mathematical models of the power frequency regulator,the simulated rotor motion link and the excitation regulator in the virtual synchronous control link are established.Two control strategies of the current virtual synchronous generator are studied.Simulation analysis of the influence of the voltage-type virtual synchronous generator on the stability of the system.Secondly,the analysis method of low frequency oscillation of small signal model is studied.Based on analyzing the mathematical model of each control link of the virtual synchronous control inverter,the small-signal model of the large-capacity virtual synchronous control inverter grid-connected system is established.The eigenvalue method is used to analyze the influence of different virtual synchronous control parameters on the trajectory of the low-frequency eigenroot.Finally,the influence of parallel operation of multiple virtual synchronous control inverters on the low frequency oscillation mode of the system is further considered,and a multi-machine parallel inertia matching method with consistent frequency response time is proposed,and the additional virtual impedance control method of parallel operation of multiple virtual synchronous generators is studied.By analyzing the overall small-signal model of the large-capacity multi-virtual synchronous control inverter connected to the power system,the result shows that in the multi-machine grid-connected system,the virtual synchronous control parameters and virtual impedance parameters have an impact on the lowfrequency oscillation of the system,the virtual synchronous control parameter is the dominant parameter of the low-frequency oscillation mode of the system.A simulation model corresponding to the small-signal model is established based on MATLAB/Simulink.The simulation analysis verifies the correctness of the small-signal stability analysis.A simulation model corresponding to the small-signal model is established based on MATLAB/Simulink,and the simulation analysis verifies the correctness of the small-signal stability analysis.