On the definition of angle stability in power systems with grid-forming power converters

R. Ávila-Martínez, J. Renedo, L. Rouco, A. García-Cerrada

Summary:

This letter presents the conclusions of a comprehensive analysis of the stability phenomenon related to the ability of generators to remain in synchronism when subjected to small or large disturbances, in power systems with both synchronous machines and grid-forming voltage source converters (GFM-VSC). This phenomenon is associated with two stability classes in the IEEE/PES classification, namely, rotor-angle stability (when involving synchronous machines) and slow-interaction converter-driven stability (when involving power converters). However, the findings of this work suggest that this phenomenon is fully characterised with the slow dynamics of the angle difference between the voltage sources connected to the power system, regardless of whether those sources are synchronous machines (with rotors) or GFM-VSCs. Therefore, we suggest using the term angle stability to refer to this phenomenon to emphasise that conventional and modern voltage sources must be included, while slow interaction converter-driven stability should only include slow-interactions of different nature involving power converters.

Spanish layman's summary:

El artículo propone redefinir la clasificación de estabilidad de ángulo en sistemas eléctricos, mostrando mediante simulaciones que máquinas síncronas y convertidores grid-forming comparten el mismo fenómeno de pérdida de sincronismo.

English layman's summary:

This letter proposes redefining power system angle stability to unify the behaviour of synchronous machines and grid-forming converters, showing through simulations that both follow the same synchronism stability phenomenon.

Keywords: Voltage source converter, VSC, grid forming, angle stability, transient stability, low-frequency oscillations

Registration date: 22-oct-2025