The global shift toward a sustainable energy future has significantly changed the landscape of power generation, replacing a growing number of large, centralized conventional power plants with an increasing amount of smaller, decentralized energy resources. This transformation introduces both opportunities and challenges for maintaining power system stability—particularly in light of the increasing share of converter-based generation. In this evolving context, grid-forming inverters have gained prominence as a core technology to support stable operation in power systems with up to 100% renewable penetration. These inverters not only function as controlled voltage sources, but can also provide synthetic inertia and strengthen the grid.

With the latest development of new regulations and testing guidelines in Germany, the integration of grid-forming inverters becomes more tangible (see “VDE FNN Hinweis – Technische Anforderungen an netzbildende Eigenschaften inclusive der Bereitstellung von Momentanreserve Version 2.0 Mai 2025”). The properties, requirements and behavior of grid-forming systems are now described in more detail in the latest version of the document. In the document, the desired grid services, such as the behavior in the event of defined frequency changes (RoCoF), phase angle jumps or short circuits (FRT) are addressed by corresponding requirements for grid-forming converters.

In particular, the requirements in the RoCoF and phase angle jump case are specified from the perspective of “normal operation” of grid-forming converters. However, grid-forming converters are subject to strict limitations, such as maximum current, and are therefore equipped with current limiting procedures. Depending on the realization of the current limiting procedures, these have a significant influence on the system behavior of the grid-forming converters during current-limiting operation in the highly dynamic and longer-term time range.

The paper examines and discusses the requirements listed in the “VDE FNN Hinweis” for various dynamic events under the influence of the current limiting operation of grid-forming converters. Laboratory tests of a grid-forming converter, which is tested and evaluated by a grid simulator according to the RoCoF, phase angle jump and a fictitious islanding test case, are analyzed. Conclusions are then drawn on the effects of current-limiting operation on the required grid services.