Assessment of interconnection options for 1GW remote offshore wind farm utilising superconducting HVDC cable without offshore platform

This paper analyses feasibility and benefits of using superconducting DC cables for interconnecting large and remote offshore wind farms. The study has shortlisted 4 feasible offshore topologies for energy conversion assuming 1GW wind farm, using 100kV superconducting cable. The study presumes that offshore platforms will not be needed with any of the topologies and considers conventional, 15MW, type 4 generators where possible. Topologies 1 and 2 consider parallel connection of wind generators, and the initial design study shows excellent efficiency and operating flexibility. Topology 1 employs only one converter bridge, but gearbox is needed for the generator and transformer will be much larger. It is concluded that the converter in topology 1 requires large number of IGBT modules (600 approximately), and this has consequences for the costs and poses challenges with the converter size. Topology 2 employs AC/DC bridge and another DC/DC converter, all located in the generator tower, and simulation demonstrates good performance and efficiency. Topologies 3 and 4 utilise 10 arrays with 7 generators series connected in each array. The
study shows that only 42 IGBTs and 42 diodes are needed for the main bridge, and it is proposed to use platforms to enable transmission-level insulation. The operation at variable power is simulated and it is confirmed that reverse power flow on individual machines is also possible. The topologies with series-parallel offshore connection have disadvantage in operating flexibility and may result in lower efficiency or, power curtailment or require some overdesign. The study concludes that superconducting DC cable technology brings benefits in lowering
transmission voltage, which simplifies and reduces costs of the collection systems for large offshore wind farms.