Research On Resonant Suppression Method Of Grid-connected Inverter Based On Robust H_∞ Control Rejection Control

In recent years,the scale of renewable energy power generation represented by wind energy and solar energy has gradually increased,and the transmission and consumption of electric energy have also increased.As a hub between renewable energy generation and AC grid,grid-connected inverters have become the key to solving grid-connected power quality problems.During the operation of the grid-connected inverter,due to the fluctuation of the impedance of the power grid and the influence of multiple inverter input and cutting out problems,the system may resonate and affect the stability of the grid-connected inverter operation.Therefore,this thesis conducts the following research on the resonance suppression of grid-connected inverters:Firstly,taking the LCL grid-connected inverter as the research object,the transfer function and output impedance expression of the grid-connected inverter are derived on the basis of its topology.According to the grid-connected output power quality standard,the parameters of the LCL filter are designed.At the same time,based on the small signal impedance model of grid-connected inverter,the influence of LCL filter structure,system output impedance and grid impedance fluctuation on the resonance of grid-connected inverter is analyzed,and it is concluded that the main reason for the resonance is the mismatch between the output impedance of the grid-connected inverter and the power grid.Then,for the problem that a single grid-connected inverter is disturbed by grid impedance fluctuations during operation,the analysis of parameter uncertainty range and parameter uncertainty modeling are carried out,and a robust H_∞control method is proposed.In order to solve the problem of inrush current during the operation of the grid-connected inverter,the virtual synchronous machine control and virtual impedance links are added on the basis of the robust H_∞control method.To solve the problem of impedance fluctuation of the power grid,an additive uncertainty model is added to the robust H_∞control method.The simulation model of a single grid-connected inverter is built through the simulation platform,which verifies that the robust H_∞control method can effectively achieve the resonance suppression of the grid-connected inverter under the condition of grid impedance fluctuation.Finally,it is extended on the basis of the control method of a single grid-connected inverter.Taking the impedance fluctuation range of the power grid as the benchmark,the range of multiple grid-connected inverters structure uncertainty is analyzed,and the position relationship between impedance intervals and the Gaussian distribution function are used to describe the multiple grid-connected inverters structure uncertainty.Design a robust H_∞controller to balance the output impedance between the grid-tied inverter and the grid to achieve resonant suppression.The simulation results show that the robust H_∞control method can effectively suppress the grid-connected inverters resonance and improve the output power quality of the grid-connected inverter during the input and cut-out of multiple grid-connected inverters.