Reactive Current Profiles of Grid-Forming Converter and Power Plant During Voltage Sags

As an internal voltage source, a grid-forming (GFM) converter is required to deliver a natural response of reactive current to grid voltage variations. However, this behavior differs from the current injection rule in existing grid codes, which were initially defined for grid-following converter. This article first introduces an analytical model quantifying the reactive current profile (RCP) of a GFM converter, defined as the relationship between the reactive current magnitude and voltage deviation. The model highlights the impacts of effective resistance, reactance andQVdroop gain on RCP, offering clear insights into its connection and distinction from thekfactor specified in existing grid codes. Then, an aggregation approach based on Thévenin equivalence is presented to describe the RCP of a GFM power plant consisting of multiple GFM converter strings. The approach provides a simple and efficient tool to evaluate the RCP at the plant level, considering the control effects and disparities within the power plant. The experiments of a downscaled converter and simulations of a nine-converter GFM power plant are presented for validation.