Research On Control Technology Of Microgrid Inverter Based On Virtual Synchronous Generator

As the energy crisis and environmental problems become increasingly prominent around the world,traditional fossil energy can no longer meet the requirements of human sustainable development,and the concept of micro-grid(MG)based on renewable energy has attracted widespread attention.Most distributed energy sources in the microgrid use grid-connected inverters as the interface when they are connected to the grid.The shortcomings of inverters such as lack of inertia and damping,poor overload capacity and low output impedance are the stable operation of microgrids and large grids.Bring adverse effects.Drawing on the experience of traditional power system operation,if the grid-connected inverter is controlled to have external characteristics of synchronous generators,it will inevitably be beneficial to the stable operation of distributed power generation systems and microgrids.At the same time,some traditional power system operation control strategies and theoretical analysis can be used.The method is effectively introduced into the microgrid.Based on this idea,scholars at home and abroad have proposed a virtual synchronous generator(Virtual Synchronous Generator,VSG)control technology to provide the necessary inertia and damping for the microgrid,and improve the stability of the microgrid.This paper takes the inverter based on the VSG control in the microgrid as the research object,establishes a synchronous generator(Synchronous Generator,SG)mathematical model,analyzes the equivalent relationship between the VSG and the synchronous generator,and studies the VSG control principle and operating characteristics in detail.Gives the design method of key parameters in VSG and analyzes its influence on the system.Based on the establishment of a single-machine infinite bus system and small signal model,the VSG grid-connected characteristics are studied and the influence of the selection of moment of inertia,damping coefficient and power frequency adjustment coefficient on system stability is analyzed.Through MATLAB/Simulink simulation to verify the correctness of the operating characteristics of a single VSG in off-grid and grid-connected modes.Aiming at the smooth switching of VSG off/on grid,an improved pre-synchronization control strategy is proposed.The traditional pre-synchronization method and the improved pre-synchronization method are compared to show the difference between the two.Simulations verify the effectiveness of the proposed control strategy and its compatibility.The superiority of traditional pre-synchronization methods after comparison.Aiming at the VSG parameter adaptive control strategy,a cooperative adaptive control strategy of moment of inertia and damping coefficient is proposed.The influence of moment of inertia and damping coefficient on the output characteristics of VSG is analyzed by using the typical second-order transfer function of the power frequency regulator in VSG grid-connected mode.Based on the power angle curve and frequency oscillation curve of the synchronous generator,the control principle and realization equation of the proposed control strategy are given,and the parameters are adjusted.The simulation verifies its correctness and the comparison with traditional fixed parameter control and moment of inertia.The superiority of adaptive control after comparison.Finally,build the VSG system experiment platform,design the main circuit parameters of the experiment system,select some components of the control circuit,and verify the correctness of the operating characteristics of the VSG off-grid and grid-connected modes and improve the smoothness of the off-grid and grid-connected through experiments.The effectiveness and superiority of the switching control strategy and the coordinated adaptive control strategy of moment of inertia and damping coefficient.