I. Introduction
Grid-forming (GFM) inverters can regulate the grid voltage and frequency more effectively than synchronous machines when operating as voltage-controlled sources due to their fast response and enhanced controllability [1]–[3]. Many advanced control techniques and topologies for GFM inverters have been suggested in recent years. The voltage regulation of a GFM inverter is typically executed using a dual-loop structure formed of linear controllers [4]–[6]. Even though they are simple to understand and simple to use, they operate poorly when the output frequency varies and exhibit unbalancing in transient and steady-state performance. In applications such as hierarchically organized microgrids, a dual-loop structure requires the outer voltage loop to have a significantly lower bandwidth than the inner current loops. As a result, there is a natural limitation on bandwidth that can negatively impact the efficiency of higher regulation layers [7], [8].