The Tyrrhenian Link: A Next-Generation Electrical Infrastructure for the Mediterranean Grid

1. Architecture and Objectives of Strategic HVDC Interconnection

The evolution of transmission systems towards decarbonized and renewable energy-based generation has brought HVDC (High Voltage Direct Current) systems to the attention of stakeholders involved in infrastructure development, planning, and component manufacturing. Compared to HVAC transmission, HVDC, especially in its Voltage Source Converter (VSC) mode, offers direct control of both active and reactive power flows, grid stability support, and the possibility of interconnection between asynchronous systems. These capabilities are required to compensate for the loss of generation programmability and system inertia reduction caused by the increasing penetration of variable renewable energy sources (RESs) [1,2].

Among the new and emerging infrastructures, the Tyrrhenian Link (TL) is one of the most innovative HVDC projects under development in Europe. Designed by Terna, the Italian transmission system operator (TSO), the TL is made up of two ±500 kV bipolar submarine interconnections: the East Link, connecting Sicily with Campania (mainland Italy), and the West Link, connecting Sicily with Sardinia. Every line will carry a maximum of 1000 MW, with complete bi-directional capability and four converter stations employing modular multilevel VSCs [3]. This is the longest undersea cable connection in Terna’s history, and the first national installation in a VSC configuration.

The technological rationale for applying VSC-based HVDC has been discussed in the literature. Black-start capability, short-circuit contribution to weak areas, reversible power flow at high speed, and real-time frequency and voltage support are benefits offered by VSC connections that are not provided by LCC (Line-Commutated Converter) schemes, and are particularly critical for isolated or weakly intermeshed networks such as those of Sardinia and Sicily. As stated in [3] and further investigated in [4], the locations for converter station installation were chosen to better exploit system support operations, with points of access at Montecorvino (Campania), Caracoli (Sicily), and Selargius (Sardinia). The system is designed to continue operating even under monopole failure conditions, with seawater electrodes employed to enable current return (Figure 1).

Beyond the technical project, the TL forms part of Italy’s long-term grid vision. It is one of five “backbones” of the Hypergrid strategy, as stated by [5], which has the objective of enhancing the Net Transfer Capacity between RES-abundant southern regions and high-load northern regions. The system will also help to reduce contingency risks and the cost of redispatching, and enhance market coupling between Italian bidding zones. Moreover, the cable infrastructure, among the most advanced ever implemented in Italy, is currently undergoing the first phase of undersea positioning in its western part. Its technical maturity, combined with its modular structure and innovative applications, positions the TL as not only a national asset but also a European benchmark in HVDC deployment.

2. Systemic Impacts on the Italian Power Grid

There is an extensive body of literature that explores grid impact through dynamic simulations, economic dispatch models, and multi-scenario power-flow studies. From both power-flow and contingency perspectives, TL is characterized as a key asset in defining grid stress management in Sicily. Advanced scenario analyses of the island’s future grid indicate that HVDC interconnection significantly reduces transformer loading and high RES injection, especially with 2030 projections having strong solar and wind development [6]. In [7], the authors compare scenario-based 2030 power-flow simulations of the Sicilian network, and conclude that higher renewable penetration leads to frequent congestion and overload, emphasizing the significant contribution of the TL to counteracting these issues and increasing interconnection capacity. Similar analyses have also validated the strategic value of the TL. For instance [8] evaluates the technical and economic benefits of converting a Sicilian HVAC line to HVDC under 2030 conditions, while [9] suggests a three-phase power-flow algorithm for AC/DC networks, enhancing unbalanced load analysis in HVDC-interconnected networks.

In the frequency domain, several studies have highlighted the role of TL in dynamic system stability. VSC-based HVDC links like the TL can offer grid-forming capability and, hence, facilitate frequency regulation even in low-inertia conditions [10,11]. One of the most recent studies shows that the converter station would be capable of suppressing frequency deviations and reducing the RoCoF (Rate of Change of Frequency) even after massive imbalances [12]. Another study simulated the impact of the TL on the probabilistic power flow of the national network; the results show that it could enhance resilience by smoothing oscillations caused by non-dispatchable generation [13]. Directly linked with the dynamic behavior of the system is the issue of minimizing inertia, an important topic for grids experiencing the transition from synchronous generation to RESs. A detailed market simulation analysis applied frequency-security constraints, namely minimum kinetic energy and maximum non-synchronous penetration, to a case in Sardinia [14]. It was found that the TL, when combined with these constraints, allows the system to be frequency-stable while optimized unit commitment is achieved. In cases when inertia is limited, the injection of synthetic inertia from the converter could limit the frequency nadir as well as the RoCoF following disturbances.

Additional economic and dispatching-related analyses show that the TL can reduce redispatching costs and reliance on out-of-merit generation. By acting as a controllable bridge between regions with variable generation profiles and consumption patterns, the TL enables more efficient power balancing and price convergence [15,16,17]. In a comparative study using real market data, dispatch strategies with the TL in operation resulted in lower operational costs, reduced CO2 emissions, and fewer hours of wind curtailment. This economic flexibility is reinforced by [18], which proposes rethinking national transmission planning based on the increased operability and transfer capabilities introduced by HVDC corridors.

The technical modeling efforts that support these results are remarkable. Some of the studies applied multi-period AC/DC power-flow models to simulate system behavior with the Link in service, confirming improvements in loads and voltage profiles in weakly meshed areas. The models also confirmed the ability of the TL to relieve critical load conditions without the need for extensive reinforcements of the installed HVAC network, which facilitates the amortization of expenses considering the potential expenses avoided. In addition to direct operational benefits, the infrastructure influences long-term grid development and regulatory planning. It supports the national shift from regional planning to scenario-based forecasting, in which interconnection projects are valued not only for their capacity but also their systemic resilience and multi-service potential. This perspective aligns with the European strategy of moving toward a unique continental hybrid grid.

3. Scientific, Technological, and Industrial Engagement

The technological research supporting the TL has been largely industry-driven by companies such as Siemens Energy and Prysmian, alongside TSOs like Terna, the owner and developer of the project. These entities have produced a robust dataset of applied research aimed at assessing central HVDC gear, particularly cables, converters, electrodes, and protection schemes. A primary focus lies in the ±500 kV submarine cables, whose integrity is critical to the system’s reliability. Qualification and sea-trial testing campaigns, as described in [19], partially authored by Terna and Prysmian, demonstrate the mechanical and electrical strength of the cables in high-pressure and deep-sea environments. Moreover, in [20] the authors performed simulations of accelerated aging methods for calculating the life expectancy of MIND-type insulated HVDC cables to yield data required for long-term reliability predictions. The converter–cable interface is the most significant aspect of the infrastructure, a technically demanding topic requiring the precise modeling of inductive coupling and transient responses. Siemens Energy addresses this in [21], presenting two methods for cable and converter model harmonization (one using frequency-dependent tabulated data, the second geometric) and simulations considering materials in a software environment (PSCAD). Both were found to be accurate in time-domain studies, a necessary step for insulation coordination and overvoltage mitigation. Operationally, Terna’s field experience is evident in [22], where they report empirical evidence of commutation failure immunity strategies applied in Italian HVDC schemes. The work highlights the importance of converter designs that guarantee control and power transfer under AC-side faults. The reliability of return current systems, particularly that of sea electrodes, is another important research area. In [23], the authors recommend the systematic selection of electrode positions based on marine geology, thermal dissipation, and corrosion risk, critical parameters in subsea corridors like those of the TL. Regarding interactions with RESs, ref. [24] illustrates how wind turbines can be controlled to provide frequency-sensitive operation through droop control, which, in combination with the speed-responsiveness of VSC converters, allows the HVDC link to be an active player in frequency regulation. Network optimization studies related to this topic are also covered in the literature. For instance, ref. [25] discusses the system benefits of retrofitting existing HVAC corridors to HVDC, which include increased transfer capacity and operating flexibility, and reduced energy loss. Such advantages are further enhanced when HVDC lines are complemented by strategically placed energy storage systems. Similarly, ref. [26] formulates an optimization strategy for storage allocation along transmission corridors in Sicily in order to demonstrate how the proper siting of batteries can locally enhance HVDC capability, nodal price stabilization, and the provision of balancing services. In addition, ref. [27] proposes planning methodologies such as dynamic thermal rating that consider such integrated solutions in encouraging holistically examining the value proposition of transmission investment, while ref. [28] positions the TL within the context of larger-scale submarine HVDC facilities, pointing to their scalability, smaller land use footprint, and synergy with EU decarbonization policies.

4. Conclusions and Outlook

The TL is currently under construction, but interest in this infrastructure and its strategic potential has been present for several years. This is evidenced not only by numerous publications in academia, but also by studies conducted by TSOs, research centers, and manufacturing companies. In the coming years, this new project will drive the development of the electrical system and stimulate related industries, from renewable energy investors and operators to component manufacturers. Expectations for the TL are high, as is confidence in its success. It is therefore expected that there will be growth in the scientific literature on this topic in the coming years, in terms of both the first tests after its full implementation and actual trials of innovative services that, at present, have only been theorized and demonstrated in simulated environments.