Fundamental-Frequency Bus-Impedance Analysis of Power Grids Dominated by Grid-Forming and Grid-Following Inverters

Due to the low-carbon requirement worldwide, renewable energy resources based on grid-forming (GFM) and grid-following (GFL) inverters are increasingly being integrated into modern power systems, which can be broadly classified as voltage- and current-type apparatuses. However, the impacts of the locations of the GFM and GFL inverters on the grids are still unclear and are not fully understood. One of the most important indices for assessing grid characteristics is the equivalent fundamental-frequency impedance seen at each bus. Therefore, this article investigates how the placement of GFM and GFL inverters influences the equivalent fundamental-frequency impedance at different buses in a large-scale power grid. The study examines impedance variation patterns at each bus when the GFM and GFL inverters are interchanging with each other. Additionally, a placement scheme has been proposed. Numerical calculations and system simulations are performed on 30-bus and 68-bus systems in order to verify the corresponding theoretical analysis.