Control concept including validation strategy for an AC/DC hybrid link (»Ultranet«)

Two main aspects demand for high-voltage long distance energy transfer from the north of Germany to the south: Increasing power generated by wind farms in the north and the need for secure and stable grid conditions in the south also after the nuclear phase out. Against this background Amprion and TransnetBW, two of the four Transmission System Operators in Germany, are planning the HVDC connection Ultranet on existing towers, i.e. an AC/DC hybrid link. Multi-terminal capability, mastering DC faults and AC/DC inter-system faults are essential requirements for the Ultranet. The required dynamic performance can be achieved with MMC converter applying a two-level multi-state control. A laboratory test bench representing the Ultranet and the adjacent AC system at appropriate scale is employed to validate simulation results.