PQ Capability Analysis of Grid-Forming Inverter in Very Low Grid Strength Condition

As more inverter-based resources (IBR) are connected to the grid, the relative grid impedance seen from the inverter increases. In other words, the grid becomes weaker. To connect such a weak grid, a grid-forming (GFM) inverter has been proposed, which mimics the synchronous generator. However, significant voltage drops can limit the output power when connected to the extremely weak grid. Therefore, this paper analyzes the feasible PQ capability of an inverter considering grid strength and limiting factors. The feasible PQ region is derived output current and voltage limit of an inverter, and the grid impedance. Simulations were performed using MATLAB/SIMULINK and PLECS to validate the feasible PQ region, based on synchronous power control (SPC) GFM inverter.