Determination of inertia time constant of grid-forming units through load step in islanded operation

Inhalt:
An accurate determination of a grid‐forming unit’s inertia time constant TauA is essential for both system stability and correct remuneration of grid inertia. In this paper, load‐step tests are applied in an islanded test setup to evaluate the unit’s frequency response and to determine the TauA. A simulation study is conducted to establish the ideal system response and based on that a laboratory study is performed to investigate how data-acquisition distorts the determination of frequency and rate of change of frequency (RoCoF). A comprehensive test cycle with variation of applied load steps and parameters of the grid forming (GFM) control indicates that the determined TauA can deviate up to 9 % from the set value in single measurements, but the overall median of the relative error for each specific configuration remains bounded between ± 0.3 %, when employing multiple measurements. To date, no standardized benchmarks, comparative datasets, or defined metrics exist to evaluate these findings. The results demonstrate the critical importance of not only defining a test procedure to determine the TauA but also a standardized evaluation framework to ensure an unambiguous, precise, and reproducible quantification process.