Grid-forming-benchmarking-project – part III: comparative analysis of the properties 'support to power quality, operation during critical grid events and controller interactions'

Grid-forming (GFM) converters are considered a key technology to maintain voltage and frequency stability in future power systems with high shares of converter-based generation. However, differences in the implementation of grid-forming controls across manufacturers require systematic testing and comparative assessment. Within the GFM-Benchmarking-Project, initiated by Fraunhofer ISE in cooperation with the four German transmission system operators 50Hertz, Amprion, TenneT and TransnetBW, a comprehensive testing procedure has been developed to evaluate the dynamic properties of GFM converters in a black-box approach. This paper, as the third part of the project results, focuses on three aspects: the contribution of GFM converters to power quality, their behavior during severe grid events where the grid-forming behavior would exceed the capability limits of a generating unit, and their ability to maintain stable operation in islanded systems. The results confirm that all investigated converters are able to provide fundamental grid-forming functionalities such as harmonic damping, reactive current support during voltage disturbances, and stable islanding operation. At the same time, significant differences in dynamic performance were observed, particularly under deep voltage dips, severe phase angle jumps, and high rates of change of frequency. These findings highlight the need for harmonized performance requirements and standardized testing procedures, ensuring that GFM converters can be reliably integrated into future power systems.