Impact of Grid Faults on Grid-Following Converter Controller Operation and Phase Instability

Currently, most Inverter-Based Resources (IBRs) connected to power systems use Grid Following Inverter (GFL) models. However, as the penetration of IBRs in power systems increases, concerns about inverter control issues in weak grids are growing. Particularly, when faults occur in weak grids, IBRs produce voltage with uncontrolled phase and magnitude, leading to their disconnection from the grid. This phenomenon is not observed in traditional generator models, highlighting the need for a detailed analysis of the IBRs controller's operation. This paper analysis the relationship between grid strength and inverter controller operation during grid faults. When fault occurs in a weak gird fault current components inject IBRs controller, consequently IBRs output uncontrolled phase voltage. The voltage with uncontrolled phase causes a three-phase imbalance in the output voltage of the inverter. This phenomenon becomes more severe as the system becomes more unstable. As a result, the output of IBRs is stopped, and they are disconnected from the grid. To verify IBRs controller operation during grid faults, PSCAD/EMTDC is used. To this analysis It will help in establishing criteria for the connection of a weak grid.