Controller design-oriented analysis of grid-forming converters for stability robustness enhancement

Grid-forming converters can suffer from control interaction problems in grid connections that can result in small-signal instability. Their inner-loop voltage controller tends to interact with the outer-loop power controller, rendering the controller design more difficult. To conduct a design-oriented analysis, a control-loop decomposition approach for grid-forming converters is proposed. Combined with impedance-based stability analysis, the control-loop decomposition approach can reveal how different control loops affect the converter-grid interaction. This results in a robust controller design enabling grid-forming converters to operate within a wider range of grid short-circuit ratios. Finally, simulation and experimental results, which validate the approach, are presented.