Hybrid hydrogen systems for mitigating sub synchronous oscillations in weak power grids

Weak AC grids with high inverter-based renewable penetration are prone to sub-synchronous oscillations (SSOs), especially under low short-circuit ratio (SCR) conditions. This paper proposes a hybrid energy storage system (HESS) combining fast-response electric double-layer capacitors (EDLCs) with slower hydrogen storage to enhance damping across multiple frequency ranges. The methodology integrates detailed dynamic modeling of PEM electrolyzer and fuel-cell behavior, inverter–grid interactions, and a coordinated fast–slow control strategy that allocates rapid transient support to the EDLC and long-term balancing to the hydrogen subsystem. A small-signal linearized model is used to identify the PLL–CCL interaction responsible for SSO formation, and the proposed control design is evaluated in MATLAB/Simulink using a fixed-step solver suitable for high-frequency dynamics. Simulation studies under three disturbance scenarios—solar irradiance steps, transmission-line disconnection (SCR reduction), and sudden load variation—show that the HESS reduces oscillation amplitude by approximately 60–70 % and shortens settling time by more than half compared with the baseline system. The results demonstrate that the proposed hybrid architecture provides robust and practical damping support for weak-grid environments.