Power grid stability unified: GFM converters and synchronous machines share angle dynamics

A team of researchers from Universidad Pontificia Comillas (Régulo E. Ávila-Martínez, Javier Renedo, Luis Rouco, Aurelio Garcia-Cerrada, Lukas Sigrist) has published a letter on arXiv challenging the conventional classification of power system stability. Their analysis focuses on the phenomenon where generators lose synchronism after small or large disturbances, which has traditionally been split into two separate categories in the IEEE/PES stability classification: rotor-angle stability (for synchronous machines with physical rotors) and slow-interaction converter-driven stability (for power converters like GFM-VSCs).

The authors demonstrate that the underlying physics is identical for both types of generators. The key variable is the angle difference between voltage sources connected to the grid, regardless of whether the source is a rotating synchronous machine or a static power converter. Both exhibit the same slow dynamics that determine whether they remain in synchronism after a disturbance. Based on this, they propose renaming the combined phenomenon simply as 'angle stability' and reserving 'slow-interaction converter-driven stability' for other types of slow interactions involving converters that do not relate to angle differences. The paper is 4 pages and carries report number IIT-25-332WP.