With the increasing integration of power electronics, accurately representing converter-based resources in power system studies has become essential for analyzing their interactions with the grid. These converters consist of two main subsystems: a power electronic stage based on controllable switches (e.g., IGBTs modules) and a fast-acting control system. Due to their inherently fast dynamics, their transient behavior cannot be properly captured using classical RMS (Root Mean Square)-based phasor models. For this reason, Electromagnetic Transient (EMT) simulations are increasingly used to study converter–grid interactions as well as interactions between converters closely located in the AC grid, as they can represent fast switching and control dynamics with high fidelity. However, applying EMT models to large-scale networks with thousands of nodes is computationally expensive and often impractical for system-level studies.

In this work, a hybrid RMS-EMT based modeling approach is proposed for small-signal stability analysis of converter–grid interactions. The proposed framework extends conventional RMS-based modeling by incorporating selected dynamic effects of converters, enabling a more accurate representation of their interaction with the grid while maintaining computational efficiency suitable for large-scale power system studies. In addition, a more detailed modeling of line dynamics is also implemented, unlike classical RMS approaches, to better capture transient phenomena in the network. In the proposed hybrid RMS-based framework, the conventional phasor representation of transmission lines based on R + jωL is replaced by a dynamic formulation including current differential equations (di/dt), allowing a more accurate representation of transient line behavior.

Our case study focuses on a test system comprising two grid-Following converters connected to an infinite bus. This configuration enables the analysis of interactions between converters under weak grid conditions. Several disturbances are applied in order to evaluate the active and reactive power responses. The set of disturbances are considered:

• phase angle jump at the infinite bus;

• voltage magnitude variation;

• active power reference change;

• reactive power reference change.

The results show strong agreement between the detailed RMS and EMT simulations, confirming the validity of the RMS-based approach. In addition, a stability limit analysis is performed by varying the short-circuit level to create increasingly weak grid conditions and induce oscillatory behavior. The power oscillations are identified and characterized in terms of damping and frequency oscillation, and the critical grid strength at which stability is lost is determined. The results indicate that the hybrid RMS models under estimate slightly the stability limit compared to EMT simulations. Future work will focus on extending this methodology to larger-scale systems, particularly representative portions of the French power system.