Converter Station Configurations for GW-scale MVDC Systems using Superconducting Cables

High-temperature superconducting (HTS) cable technology is appearing as a promising candidate for implementing bulk power Medium Voltage Direct Current (MVDC) corridors with reduced footprint and considerably lower losses. HTS demonstrators have achieved currents of 5-10 kA, raising a challenge for substation ratings, limited to 3 kA for Modular Multilevel Converter (MMC) and 6 kA for Line Commutated Converter (LCC) topologies. This paper studies topologies for implementing 10 kA/100 kV substations suited for HTS-based GW-scale MVDC links. The study addresses challenges and possible benefits of four high-current MMC-based substation designs in terms of hardware/control requirements, fault handling considerations and substation overall design (Valve Hall size modifications, AC/DC yards requirements). The first configuration presents challenges related to the increased energy per submodule, raising concerns regarding internal converter fault scenarios. The rest of the topologies use a standard submodule voltage and current rating matching those used in existing HVDC MMC designs. A 3D modelling approach is used to estimate valve hall size for each case and a reference 500 kV MMC hall of the same rating, with results showing potential for a 60% volume reduction. This size reduction is especially relevant in offshore applications, where size of platforms is a large cost driver.