Hybridization of pumped-storage hydropower plant with battery energy storage for secondary frequency regulation

Pumped-storage hydropower plants (PSP) play a key role in providing flexibility and secondary frequency regulation in modern power systems. However, continuous operation under frequency regulation requires fast and frequent power adjustments, which translate into intensive guide vane movements and increased mechanical stress on hydraulic and mechanical components. Over time, this operating regime accelerates wear, increases maintenance requirements, and may reduce the lifetime of critical assets. In this context, the hybridization of pumped-storage units with battery energy storage systems (BESS) emerges as an effective solution to support rapid power variations while alleviating mechanical stress on the hydro unit. This work investigates the hybrid operation of a pumped-storage unit assisted by a battery system, with the aim of quantifying the benefits of battery support during secondary frequency regulation. A detailed dynamic model of the hydraulic unit, including the hydraulic circuit, pump-turbine, generator, and control system, is developed using the SIMSEN simulation environment. The model is calibrated and validated using high- resolution operational data from a real plant, ensuring that the non-hybrid behavior is accurately reproduced before introducing battery assistance. The hybrid configuration is implemented by coupling the battery system in parallel with the hydraulic unit, and a parametric analysis is carried out to assess the impact of battery power, ramping capability, and energy capacity. Key performance indicators are defined to evaluate mechanical wear, operational behavior, and dynamic response. The results show that even a relatively small battery, sized at a few percent of the unit rated power, can significantly reduce guide vane activity, mechanical effort, and response time during frequency regulation. These findings demonstrate that battery-assisted hybridization represents an effective strategy to enhance operational flexibility while preserving the mechanical integrity of pumped-storage assets.