Research On Transient Stability Of Grid-connected Inverter Based On Droop Control

With the increasing demand for electricity and the shortage of traditional fossil energy,a large number of renewable energy such as photovoltaic and wind power are connected to the grid through power electronic converters,and the power electronic characteristics of the power system have become increasingly prominent.When a large disturbance occurs in the power electronic power system,the grid-connected inverter will lose synchronization with the grid if it cannot operate stably,and may even cause the system to collapse.Therefore,it is of great significance to study the transient stability of power electronic power system.This thesis establishes a large-signal model of the grid-connected droop control inverter to study the transient stability of the grid-connected droop control inverter under power dispatch and grid voltage sag.Firstly,based on the grid-connected operation structure of the droop control inverter,considering the coupling effect between active power loop and reactive power loop,a large-signal model of the grid-connected droop control inverter considering the influence of reactive power loop is established.According to the sinusoidal relationship curve between the output active power and the power angle when the droop control inverter is grid-connected,the transient instability mechanism of inverter is analyzed,and according to the established grid-connected droop control inverter model,an energy function used for transient stability analysis is constructed.Secondly,the energy waveform of the grid-connected droop control inverter under different active power setting value changes and active power droop coefficient is drawn,and the influence of the active power setting value and active power droop coefficient on transient stability is analyzed under power dispatch.The frequency compensation scheme is adopted to reduce the equivalent active power droop coefficient of the grid-connected droop control inverter,reduce the overshoot of the power angle in the transient process,and improve the transient stability of the grid-connected droop control inverter under power dispatch.In addition,the energy waveform of the grid-connected droop control inverter under different grid voltage sag depth is drawn,and the influence of grid voltage sag depth on the transient stability of the grid-connected droop control inverter under fault conditions is analyzed.The voltage compensation scheme is adopted to compensate the voltage drop of the inverter caused by the reactive power loop under faults,expand the maximum grid voltage sag depth that the grid-connected droop control inverter can withstand,and improve the transient stability of the grid-connected droop control inverter when the grid voltage sag.Finally,an inverter platform based on TMS320F28335 was built,the closed-loop performance of the current loop and voltage loop of inverter platform was tested,and the transient stability of the grid-connected droop control inverter under power dispatch and grid voltage sag was experimentally verified.