A fundamental paradigm shift in converter control is currently in progress in order to enable converter-based and climate-neutral electrical power grids in the future. In contrast to grid-following converters, which are dependent on an external grid voltage to inject their current, grid-forming converters, like synchronous generators, are able to generate and maintain this grid voltage autonomously. This paradigm shift in converter control is accompanied by numerous questions. This work focuses on the questions of possible effects on the stability of the interconnected power systems and the necessary minimum share of grid-forming systems.
Dynamic converter models including grid-following and grid-forming converter control serve for the analysis of the systemic effects of high shares of converter-based generation. The transmission grid investigations carried out with these models show that grid-forming converters fundamentally provide the essential characteristics of synchronous generators, i.e. the voltage source behavior combined with inertia provision, since the identified minimum shares of grid forming assets using synchronous generators or grid-forming converters are virtually identical. However, the simulative and system-theoretical comparison of a large number of different grid-forming control concepts shows some significant differences with respect to their impact on frequency stability.