High power HVDC-DC converters for the interconnection of HVDC lines with different line topologies

The structural change in energy generation and distribution will demand that large amounts of power are transported over long onshore distances. High Voltage Direct Current (HVDC) power transmission is most suitable for that task since, compared to High Voltage Alternating Current (HVAC) power transmission, there are no stability issues and the transmission losses are much lower. However the junction points of a segmented HVDC transmission corridor still have to be realized as AC nodes, since missing components, like DC breakers and or efficient HVDC-DC converters prevent the direct interconnection of transmission segments to a radial or even meshed DC grid. With the new HVDC auto transformer topology the direct interconnection of HVDC lines with different voltage levels becomes feasible. In this paper the ability of this new HVDC-DC converter topology to connect different DC line topologies and to preserve the transmission redundancy in case of a DC pole malfunction is investigated.