Fraunhofer ISE has developed a standardized test to evaluate grid-forming inverters under European readiness standards
7 manufacturers from various countries participated with storage inverters from small units to 5 MW, tested under simulated grid events
Tests revealed similarities and major differences, with Fraunhofer providing optimization guidance for nearly all devices
Fraunhofer Institute for Solar Energy Systems ISE (Fraunhofer ISE) has developed a standardized test procedure for grid-forming inverters under the GFM Benchmark project. The initiative, commissioned by Germany’s 4 transmission system operators, assesses the technology’s readiness for upcoming national and European testing standards.
The basic difference between a grid-forming inverter and a grid-following inverter is that the former can create and control grid voltage and frequency on its own, while a grid-following inverter needs an existing grid signal to connect and adjust to it. In short, grid-forming leads, grid-following follows.
A grid-forming inverter must contribute to providing a grid voltage with stable amplitude and frequency. Additionally, while grid-forming components planned by transmission operators are important, they will not be sufficient on their own to maintain power system stability, explains the Fraunhofer ISE team. Customer systems will also need to support grid voltage and frequency through grid-forming behavior.
However, Fraunhofer ISE explains that currently, there is no uniform standardization or definition for the grid-forming behavior. To ascertain this, it joined hands with German grid operators, namely 50Hertz Transmission GmbH, Transnet BW GmbH, Amprion GmbH, and Tennet TSO GmbH, and developed a measurement and evaluation procedure. The project aims to evaluate the stabilizing properties of inverters, while incorporating findings from both grid operation and research.
“We wanted to see what manufacturers understand by grid formation and how they implement this in the programming of their devices,” said Fraunhofer ISE Department Head Dr. Sönke Rogalla.
Fraunhofer ISE invited manufacturers to test how their inverters handle grid formation. It received responses from 7 companies from various countries that offered their storage inverters, ranging from small units to 5 MW systems, at different stages of development. Tests simulated various operating conditions, including critical grid events.
“The devices exhibited similar behavior 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,” shared Fraunhofer ISE Project Manager Roland Singer. He added that the willingness and commitment of manufacturers to advance the development of grid-forming inverters is high.
Detailed test results will be published anonymously on October 8, 2025, at the Wind & Solar Integration Workshop in Germany.
TaiyangNews delved into the world of inverter technology at its 1st Virtual Conference on Inverters & Battery Storage in November 2024, where new technologies and processes, including grid-forming inverters, were a subject of discussion (see Discussing Latest Developments of Inverters & Battery Storage, The Brains And Mitochondria Of Today’s Solar Systems).
.png?w=50&fm=png){kind=logo}