Researchers at the Fraunhofer Institute for Solar Energy Systems (ISE) have been working on a test procedure for grid-forming inverters.
The GFM Benchmark project has seen Fraunhofer work with four German grid operators – 50Hertz Transmission GmbH, Transnet BW GmbH, Amprion GmbH, and Tennet TSO GmbH – to develop a measurement and evaluation process for the stabilizing properties of inverters.
The work featured a callout to companies interested in having their inverters tested against the evaluation procedure. A total of seven companies from different countries responded to the call. Their devices ranged from a few kW to 5 MW in capacity and were all measured according to the tests. The inverters were at different technology readiness levels, Fraunhofer adds, from pilot to prototype to series production.
The research team used the tests to investigate the differences between the devices in terms of grid formation by exposing them to various operating conditions within the laboratory. Simulated grid situations included rapid frequency changes, short circuits and phase jumps, alongside observations during normal operation.
Roland Singer, project manager from Fraunhofer ISE, said the devices exhibited similar behaviour under clearly defined requirements. “In other cases, however, there were major differences, and we were able to provide the manufacturers with suggestions for optimization for almost every device,” he explained.
The Fraunhofer ISE added that the manufacturers' willingness and commitment towards the development of grid-forming inverters is high, noting that the project has provided both a comprehensive overview of the market readiness of grid-forming inverters and a practical check for new national and European testing standards.
The team has already used the testing results to contribute to the note ‘Grid-forming properties’, created by the Grid Technology/Grid Operation Forum of the German Association for Electrical, Electronic and Information Technologies (VDE FNN). The recently published document describes the requirements and verification procedures for grid-forming units and forms the basis for participation in the future market for instantaneous reserve, set to commence from the beginning of 2026.
The results of Fraunhofer’s tests on the participating grid-forming inverters will be published anonymously and presented to the public on October 8 during the 24th Wind and Solar Integration Workshop, taking place in Berlin.
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