HVDC for frequency stability under RES penetration. The Sardinia island case

High Voltage Direct Current (HVDC) transmission has been increasingly deployed in modern power systems, over long distances in asynchronous interconnections and offshore wind integration, due to lower investment costs, lower losses and higher controllability. Nevertheless, they cannot provide inherently inertia and frequency support, without the adoption of appropriate control strategies. With the increase of renewable generation interfaced by power electronics and the gradual phaseout of conventional power plants, frequency stability management is becoming a great challenge, particularly in small size islanded and asynchronously interconnected power systems. In this paper, we investigate the possibility of controlling a HVDC to support frequency stability providing primary regulation in future scenarios. We present and discuss the opportunities provided by a HVDC, using an aggregate generation-load model, to the frequency regulation of the Sardinia island in Italy also in the light of the trilateral interconnection between Sardinia, Sicily and Italian Peninsula. Simulations show that the HVDC can assure the frequency stability of the Sardinian power system, if primary control strategies are deployed.