Stability analysis and improved control of voltage source converters based on impedance models in weak grids

With the continuous development of renewable energy generation, traditional power grids will gradually transform into weak grids. In recent years, stability analysis methods based on impedance models have gradually been applied to wind and photovoltaic power generation. However, traditional impedance modeling analysis generally only considers the AC side impedance of grid-connected converters, and the established impedance model only includes the AC side impedance information. This article proposes to add DC side impedance information to the impedance modeling process and construct a 3 \(\times \) $\times$ 3 impedance model matrix that includes AC side impedance information, DC side impedance information, and AC/DC side coupling impedance information. By establishing a 3 \(\times \) $\times$ 3 impedance model, the specific operating status of VSC in weak grids can be more accurately predicted. Utilizing virtual impedance control (VIC) to enhance the stability of VSC in weak grids and enhance the networking ability of wind and photovoltaic power generation when facing weak grids. Variable virtual impedance control is a proposed solution for voltage faults in weak grids that aims to suppress both the overcurrent phenomenon that VSC generates during the fault period and the fault-related fluctuation of VSC output frequency. And verify the effectiveness of the proposed modeling method and control scheme through simulation, and analyze the simulation results.