Small-signal stability study of grid-connected voltage source converters with grid-forming control

L. Sainz de Ezquerra(1), J. Pedra(1), Ll. Monjo(2), J.J. Mesas(1), O. Cartiel(1), L. Sainz(1) 1. Department of Electrical Engineering (DEE), Escola Tècnica Superior d’Enginyeria Industrial de Barcelona (ETSEIB), Universitat Politècnica de Catalunya – BarcelonaTech (UPC), Barcelona (Spain) 2. Department of Electrical Engineering (DEE), Escola Politècnica Superior d'Enginyeria de Vilanova i la Geltrú (EPSEVG), Universitat Politècnica de Catalunya – BarcelonaTech (UPC), Vilanova i La Geltrú (Spain) 2026-06-27

Abstract

The large-scale integration of renewable energy sources is transforming traditional power grids. Renewable generation is typically connected to distribution networks through voltage source converters (VSCs) operating under grid-following (GFL) control, which has raised technical concerns regarding system stability and security. Grid-forming (GFM) VSCs are emerging as a solution, capable of establishing a grid and operating in parallel with other devices via self-synchronisation mechanisms. However, they introduce new challenges, particularly small-signal stability issues arising from interactions with traditional power-system components. Research on GFM VSC stability is still at an early stages, despite its key role in transmission networks and large-scale renewable plants. Stability studies often rely on time-domain simulations and frequency-domain approaches using white- and black-box admittance models of system components. This paper presents a small-signal stability analysis of grid-connected VSCs under GFM control strategies, including power synchronisation control (PSC) and alternating voltage control (AVC). The analysis is conducted using Simulink-based time-domain simulations and frequency-domain methods based on black-box GFM VSC models.

Key words: Grid-connected voltage source converter, grid-forming control, time-domain simulations, black-box models, stability assessment, small-signal modelling.

References

[1]     P. Kundur, “Power system stability and control,” McGraw-Hill, 1994.

[2]     A. Gomez-Exposito, A. J. Conejo, C. Canizares, “Electric Energy Systems: Analysis and Operation,” CRC Press Taylor & Francis Group, 2nd Edition, Taylor & Francis Group LLC, Boca Raton, 2018.

[3]     International Renewable Energy Agency (2023). Renewable capacity statistics 2023.

[4]     K. Sharifabadi et al., Design, Control and Application of Modular Multilevel Converters for HVDC Transmission Systems. Wiley-IEEE press, 2016.

[5]     A. Albustami and A. F. Taha, “The Iberian Blackout: A Black Swan or a Gray Rhino? A Thorough Power System Analysis,” arXiv preprint, 2025. [Online]. Available: https://arxiv.org/abs/2511.17433.

[6]     M. Chen, et al., "Generalized Multivariable Grid-Forming Control Design for Power Converters," in IEEE Transactions on Smart Grid, vol. 13, no. 4, pp. 2873-2885, July 2022.

[7]     R. Rosso et al., “Grid-Forming Converters: Grid-Synchronization, and Future Trends—A Review,” in IEEE Open J. Ind. Appl. 2021, 2, 93–109.

[8]     L. Zhang, L. Harnefors, and H.-P. Nee, “Power-synchronization control of grid-connected voltage-source converters,” in IEEE Trans. Power Syst., vol. 25, no. 2, pp. 809–820, May 2010.

[9]     L. Harnefors et al., “Robust analytic design of power-synchronization control,” in IEEE Trans. Ind. Electron., vol. 66, no. 8, pp. 5810–5819, Aug. 2019.

[10]   F. Zhao et al., “Robust grid-forming ontrol with active susceptance,” in IEEE Trans. Power Electron., vol. 38, no. 3, pp. 2872–2877, Mar. 2023.

[11]  L. Harnefors et al., “A universal controller for grid-connected voltage-source converters,” in IEEE J. Emerg. Sel. Topics Power Electron., vol. 9, no. 5, pp. 5761–5770, Oct. 2021.

[12]  F. Zhao, X. Wang, and T. Zhu, “Power dynamic decoupling control of grid-forming converter in stiff grid,” in IEEE Trans. Power Electron., vol. 37, no. 8, pp. 9073–9088, Aug. 2022.

[13] F. Zhao et al., "Closed-Form Solutions for Grid-Forming Converters: A Design-Oriented Study," in IEEE Open Journal of Power Electronics, vol. 5, pp. 186-200, 2024, doi: 10.1109/OJPEL.2024.3357128.

[14]  L. Orellana et al., “Stability Assessment for Multi-Infeed Grid-Connected VSCs Modeled in the Admittance Matrix Form,” in IEEE Transactions on Circuits and Systems I: Regular Papers, vol. 68, no. 9, pp. 3758-3771, Sept. 2021.

[15]   O. Cartiel et al., (2026). SARA (Simulation-based Admittance Response Analysis): A MATLAB/Simulink Tool for AC/DC Admittance Measurement. Zenodo, 2026 doi: https://doi.org/10.5281/zenodo.18245306.