Research On Virtual Synchronous Generator Control Of Grid-connected Inverter Based On Small-signal Model

In recent years,prompted by multiple measures,including national regulations and the goal of carbon emission peak and carbon neutrality,with solar energy,wind,and other clean,low-carbon renewable energies have been integrated into the power grid,the power systems demonstrated a clear"double high"feature.However,given the erratic and unpredictable of renewable energy output power,and the shortage of inertia and damping that help maintain system stability,it brings great difficulty in efficient and reliable system performance in case of power fluctuation and system malfunction.Reference to the characteristics of traditional synchronous generators’inertia and damping,and the application of the control schemes relevant to synchronous generators to the control of grid-connected inverter,the virtual synchronous generator（VSG）technology is proposed,which improves the output volatility and reliability of renewable energy power system.In this thesis,the grid-connected inverter VSG is studied as follows:Firstly,summarizing the existing inverter control technology to introduce the VSG control of grid-connected inverters.Give the equations of the stator and rotor of traditional synchronous generators.The physical circuit and control part of the VSG system are described,as well as the VSG control algorithm.The power frequency and excitation controllers of VSG are designed by combining the equations and control principle.Then,in order to solve the stable problem of introducing the VSG control technology for grid-connected inverter,the small-signal mathematical modeling method of VSG single machine and multi-VSG parallel systems including all state variables is proposed.The effect law of parameters on the root locus of grid-connected inverter VSG control system is evaluated,when virtual moment of inertia J,virtual damping coefficient D,and line resistance R_c and inductance L_c are altered,and the influence of parameters variation on the system stability is analyzed.The correctness of analysis results is verified through simulation results.Finally,in order to solve the problem of overstrike and oscillation of the system output active power and frequency under power fluctuations,based on the existing VSG control algorithm,studying the power angle and virtual angular frequency curve of the grid-connected inverter to identify the selection rules of control parameters virtual moment of inertia J and virtual damping coefficient D of VSG.The control parameters J and D coordinated adaptive control strategy is proposed based on the selection rules.The simulation results verify the effectiveness of the proposed control strategy.