Assessment of the Impact of HVDC Links on Frequency Containment Capacity in a Portion of the Italian Transmission Network

The progressive replacement of conventional power plants equipped with Synchronous Generators (SGs) by Inverter-based Resources (IBRs), like Photovoltaic (PV), Wind Turbine (WT) and Battery Energy Storage Systems (BESSs) power plants, introduces challenges related to the availability of frequency and voltage regulation resources. To address the primary frequency regulation (PFR) needs, Transmission System Operators (TSOs) have introduced dedicated grid code attachments allowing IBRs to contribute to PFR. Moreover, also the converters connected to High Voltage Direct Current (HVDC) links may participate in PFR. This study, conducted in collaboration with Terna, the Italian TSO, assesses the impact of HVDC converters and IBRs on the PFR capability of the Italian transmission network, with a focus on a potentially critical market zone in the 2030 year. The analysis considers two scenarios: <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$i$</tex>) the participation of SGs, IBRs, and two HVDC links (HVDC2 and HVDC3) in PFR, and ii) an extended scenario including the additional contribution of HVDC-1. The analyzed contingency considers possible failures of conventional or wind turbine Generating Units (Gus), single or coupled AC lines or single HVDC modules. In both scenarios, frequency containment actions successfully limited the steady-state frequency deviation within <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\pm 500[\text{mHz}]$</tex>, with HVDC-1 further improving frequency containment capacity.