The inertia of power systems is a key aspect of frequency dynamics and stability. The increasing penetration of non‐synchronous generation reduces the available inertia and makes it fluctuating during the day depending on the online units. This causes problems for grid operators, particularly in relatively small power systems. The present work examines the impact of decreasing inertia using an aggregate model based on the swing equation, considering future lower inertia scenarios and the implementation of the current protection schemes. The frequency stability of the system is assessed by considering the reference incident, i.e. the loss of the largest operating unit in under‐ and over‐frequency cases. New solutions to balance the grid are addressed and compared, considering the technical impacts of synchronous compensators and battery energy storage systems (BESSs) operated with a new equivalent saturation logic. The model is tested and validated using the real data of a small insular power system (Sardinia Island, Italy), outlining the importance of the high‐voltage direct current and of the BESS control strategies to guarantee the frequency stability of the power system.

This paper explores the potential contributions of modern High-Voltage Direct-Current (HVDC) transmission systems to the Italian National Power System, with a focus on adequacy and security, and providing an overview of their role in system stability. An operational methodology is proposed to assess the impact of planned infrastructure developments, within the context of medium- to long-term forecast scenarios. To this end, starting from a model of the current transmission network, a prospective model of the primary transmission grid for the year 2040 was developed, covering voltage levels of 230 kVAC, 400 kVAC, and 525 kVDC. Load-flow analysis under both N and N-1 conditions was performed, with particular emphasis on the Ionian–Tyrrhenian HVDC backbone “Priolo–Rossano–Latina”.