The global commitment to reduce carbon emissions and build a more sustainable society relies on the transition towards highly interconnected power grids which connect a wide variety of renewable sources, storage facilities and consumers via innovative converter-based energy links. Concerning ac distribution, medium voltage static frequency converters (SFC) assure a seamless connection between sources/utilities, while optimizing the transmission frequency and voltage levels as well as providing primary/ancillary services that enhance grid resilience and system stability. Therefore, such grid intertie achieved through SFCs is a technology enabler to establish an efficient and flexible electrical infrastructure. For instance, connecting offshore equipment with a landfall point through sub-sea cables significantly increase the attractiveness of those remote areas where large offshore wind farms might be built. A loss-optimized energy link with shore serves as a collector for multiple interconnected units, opening-up to several climate response initiatives and enhanced economical assets for the site owner(s). Interestingly, most of the European offshore wind parks (in operation or committed) are in the 100–300 km distance range with power ratings of 40–200 MW(*). For these installations within a mid-to-long distance range, a grid intertie based on a low frequency high voltage alternate current (LF-HVAC) transmission framework represents a cost-effective solution compared to other alternatives. A transmission frequency below 20Hz reduces both the charging current and the reactive power on the cable, thereby requiring smaller size reactive power compensators, i.e., lowering the installation cost. Due to the different frequency range that offshore wind parks could exhibit compared to the one characterizing the onshore grid, the LF-HVAC transmission is established with a dual SFC configuration. The onshore SFC station—primary interface to the main grid—is operated such that the power exchange along the ac cable is realized at, e.g., 16.7Hz, while the offshore SFC station—main connection point to the generation site—converts it back to the required ones. The fluctuations of the generation units may lead to experience low short-circuit ratio at the SFC terminals, particularly critical during contingency events. Moreover, in case of an onshore grid showcasing lack of inertia, the entire system is prone to instability. Nevertheless, both aspects can be mitigated by the enhanced controllability given by the proposed grid intertie scheme, further extending its installation benefits. Motivated by the above, this paper will describe such dual SFC configuration currently offered by Hitachi Energy, targeting the above-mentioned application. To demonstrate the advantages of the proposed solutions, comprehensive simulations at steady-state and during transient operations are presented, along with the ability to ride through the most relevant fault scenarios.

(*) Due to experience matured from previous/existing projects, similar circumstances are observed in East Asia and North America too.