In the upcoming years, the operation of Sicily’s power system will be subjected to significant changes, due to the combination of multiple elements, such as: the foreseen massive increase in generation based on Renewable Energy Sources (RES); the further reinforcement of the HVAC (High Voltage Alternating Current) transmission grid; the installation of HVDC (High Voltage Direct Current) terminal stations of links with Sardinia, Campania and Tunisia, by 2030.

In this context, network studies have been carried on, in collaboration with the University of Palermo, with the target to investigate the operational conditions of Sicily’s power system in 2030, 2035, 2040 scenarios, featuring high penetration of generation from RES, considering the HVDC links assumed to be in operation at 2030, equipped with advanced control functions.

The present report describes the analyses and the outcomes of dynamic grid studies of the Sicilian power system in selected operating conditions, consistent with the developed medium-long term scenarios. In particular, several critical cases and different situations of generation, load, outages have been considered and various combinations of different contributions to regulation have been analysed: the goal has been the evaluation of the effectiveness of the possible system support services in terms of primary frequency regulation and synthetic inertia that could be provided by both RES generating units and the Voltage Source Converters (VSC) of the HVDC ties of Tyrrhenian Link (TL) and Tunisia-Italy interconnector (TUNITA/ELMED).

To this scope, control schemes for the operation of Voltage Source Converters of Sicilian HVDC links in Grid-Following (GFL) and Grid-Forming (GFM) modes have been developed, applied and compared. Furthermore, a GFM scheme, able for the operation mode in black-start function, has been developed and implemented.

The results of network analyses firstly highlight the vulnerability of Sicilian grid stability in the situations involving the trip of the link interconnecting Sicily with the Italian continental system, especially in 2035 and 2040 extreme cases featuring a significant decrease of thermoelectric generation. More situations highlight how RES (wind and photovoltaic) generation units actively participate in frequency regulation and may provide advanced support services such as synthetic inertia to guarantee security and stability of Sicily’s system.

Furthermore, it is important to stress the role that VSC-HVDC links may play: in case the operational conditions make it possible, the VSC-HVDC corridors with their flexibility and advanced control functions may contribute to primary frequency regulation, alleviating the loading on the operating thermoelectric and RES units and preventing an extended RES generation curtailment. The analyses prove the effectiveness of the GFM control mode for both the TL and the TUNITA links.

The Report is available on the Italian site