Converters with grid-forming properties will cover a part of the demand for voltage source behavior and thus play an essential role in ensuring power system stability. However, this demand will not be fully met by the transmission system operators' own assets with grid-forming properties, i.e. HVDC converters and STATCOMs. Customer facilities at extra-high, high, and medium voltage levels with grid-forming capabilities will play a key role in meeting the power system’s demand for such properties and significantly shape system dynamics.

The absence of clear guidelines for ‘grid-compatible behavior’ and the resulting interpretive flexibility in the development of grid-forming facilities have led to a wide variety of implementation approaches. While grid-forming converters replicate key characteristics of synchronous generators - particularly voltage source behavior - they do not inherently emulate their dynamic behavior. Unlike synchronous generators, whose dynamics are defined by its physical laws, the behavior of grid-forming converters is mostly defined by its control algorithms. Therefore, it is essential to assess the current state of development across different concepts to accurately reflect their system behavior in future studies and, if necessary, adapt requirements and verification procedures for market-based procurement or grid connection requirements.

In a project of the four German transmission system operators (TransnetBW, 50Hertz, Amprion and Tennet) and Fraunhofer ISE, a verification procedure and a catalog of requirements for grid-forming behavior were developed with the participation of various converter manufacturers. The anonymized comparison and determination of the state of the art of grid-forming converters are the main objectives of this project. Important lessons were learned for future verification procedures and requirements and conclusions were drawn as to where these need to be refined or expanded.

This presentation outlines the project's background and highlights its potential benefits for TSOs, manufacturers, and testing laboratories. It concludes with a summary of the key elements of the developed testing and laboratory procedures.