Fault Current Limiting and Grid Code Compliance for Grid-Forming Inverters-Part I: Problem Statement

Grid-forming (GFM) inverters are controlled to directly regulate the voltage. A major challenge stemming from this control model is that sustaining the voltage during faults would require high currents-beyond the levels that an inverter can withstand. Various fault current limiting (FCL) methods have been developed in recent years for GFM inverter-based resources (IBRs). The theoretical analysis supported by detailed simulation studies in Part I of this paper investigates whether existing FCL methods for GFM inverters can be deemed feasible solutions for future IBR-centric power grids. The challenges revealed for the first time in this paper are multifaceted and depend on the type of the FCL method. The focus is not only on a GFM inverter's internal operation, but also on its impact on the grid and the practical requirements for grid integration of an IBR considering most recent grid codes. Part II of this paper will address these challenges.