System Characteristics of Grid-Forming and Grid-Following Converter Systems

Grid-forming converter controls have been observed to increase voltage stiffness and system strength. This work highlights the reasons for this behaviour, which is inherently fundamentally different from grid-following controls and, thus, why grid-following converters can not participate in the provision of virtual inertia. However, it shows that equipped with additional power-droops these controls can still benefit the grid.Therefore, based on the converter principle and additional support a new terminology that goes beyond the previously used terms "grid-forming" and "grid-following" is proposed. In simple black-box simulations it is proven how the different examples can be distinguished just by investigating their grid-behaviour. In addition to questions that are raised concerning the definition of system strength this work thus yields to a clear definition of grid-forming controls as well.