Influence of a virtual impedance on the dynamic behaviour of the grid-forming control of inverter-based generation plants

The transition to distributed power generation from renewable energy sources introduces challenges in maintaining grid stability when relying on power electronic converters. Grid-forming controls, particularly the droop control, play a crucial role in managing the power system’s voltage and frequency. The integration of a virtual impedance (VI) can influence the dynamic performance of such controls. This study investigates three VI configurations – implemented in the inner, outer, and parallel to the inverter control-analysing their effects on the frequency and voltage dynamics under varying grid strengths and control parameters. In a detailed testbench, the response of each configuration to load changes is evaluated. The results reveal that while inner and outer VIs maintain stable dynamics, the parallel VI introduces additional oscillations and longer settling times. These findings provide critical insights into optimizing VI designs for robust and stable grid-forming inverter systems in diverse operational scenarios.