TenneT 2GW Bipole Offshore HVDC Transmission Schemes – Key Advanced Control Features

Sea wind power: 150–300 km links delivering 2000 MW at ±525 kVdc between offshore terminals and onshore stations near Maasvlakte (NL) and Unterweser (DE). Engineered for future multi-terminal expansion and representing the most powerful, highest-voltage, and longest radial HVDC links deployed in offshore wind to date, the schemes centre on SGFM control, whereby converters act as controllable voltage sources behind an impedance during normal and disturbed conditions. SGFM delivers fast dynamic voltage control for weak grids, inertial support to limit rate of change of frequency (RoCoF), active-power response to phaseangle steps, and natural exchange of positive- and negative-sequence currents that mitigates asymmetrical voltages and transient swings while remaining within converter limits. The paper also demonstrates the extraction of instantaneous reserves from offshore wind (notably in

German projects), pole power balancing with reduced common-conductor current in dedicated metallic return (DMR)-less operation, and robust islanded operation, including HVDC energization and wind-farm startup from very weak onshore systems, followed by seamless resynchronization to strong AC networks via DC-voltage modulation and power-angle control.

The described mechanisms comply with Dutch and German grid codes and advance the state of the art in offshore wind transmission.