The large-scale integration of renewable energy requires upgrades to transmission infrastructure. Grid boosters (GBs) enable increased grid utilization through their curative congestion management capabilities and provide ancillary services. However, their reliance on battery storage makes them a costly solution. This paper investigates hybrid grid boosters (HGBs), which combine, in our case, a battery energy storage system (BESS), a hydrogen electrolyzer (HE), and a gas turbine. The hybrid design reduces BESS capacity, lowers capital costs, and increases operational flexibility.

A detailed and scalable physical dynamic model of the HGB is developed for stability analysis. The EMT model incorporates grid strength, represented through the short-circuit ratio (SCR), and the impact of the interaction between supply and demand on frequency, as well as the coupled electrical–thermal dynamics of the electrolyzer. It employs established representations (e.g., IEEE standard models) for the turbine, governor, and exciter. The dynamic power allocation control strategy is modified and applied to the adopted HGB approach. It enables seamless power sharing between the BESS and turbine, ensuring a reliable response under congestion events. The grid-forming electrolyzer is implemented and evaluated during frequency fluctuations.

Results demonstrate that HGBs can enhance the integration of renewables by providing additional (virtual) transmission capacity and long-term storage, while also supporting voltage and frequency ancillary services during non-congestion periods. The proposed model framework supports the deployment of HGBs to strengthen grid stability and improve the economic viability of future power systems.