A Novel Multiterminal VSC-HVdc Transmission Topology for Offshore Wind Farms

Multiterminal voltage source converter (VSC) topologies of high voltage direct current (HVdc) transmission systems (M-HVdc) for the integrating large offshore wind farms are scrutinized. A novel two wind farm with one onshore substation (2WF-1SS) topology is proposed. M-HVdc system standards are defined along with control schemes. HVdc switch gear and HVdc-link topologies are reviewed, considering the need of HVdc circuit breakers, dc cables, and extra offshore substations. Numerous M-HVdc-link topologies are analyzed and compared based on certain techno-economic criteria: length, number and ratings of HVdc circuits, cost, flexibility, stability, number of HVdc circuit breakers, and offshore substations. Operation of various topologies with respect to the designed control system is analyzed and compared through PSCAD/EMTDC simulations considering two different tests: permanent VSC disconnection and a dc line-to-line fault. Results show that 2WF-1SS is a promising topology for future multiterminal HVdc grids.