COBRAcable link is a sub-sea high voltage direct current (HVDC) power link connecting Eemshaven in the Netherlands and Endrup in Denmark which is expected to be in operation by 2019. The converter stations in Eemshaven and Endrup will be built based on voltage source converter (VSC) technology. At a later stage, COBRAcable link will be expanded into multi terminal HVDC (MTDC) transmission system by connecting another onshore and/or offshore converter stations (e.g.: wind farms, oil/gas platforms) to the cable. One of the possible MTDC configuration can be illustrated in the following figure:

In order to ensure a secure operation, different converters within the MTDC need to be coordinated. Since VSC technology is still advancing and different vendors have their own vision on the development, it may happens that the future expansion of COBRAcable will use different technology as compared to the one already been used. Moreover, the lack of operational experiences of VSC-based MTDC transmission system and the intellectual property rights (IPR) issues have restrain the vendors to come into agreement. Therefore, this research project will tackle aforementioned challenges to allow a smooth transition from point-to-point connection into MTDC operation.

This research project will mainly focus on the DC-side impact of COBRAcable link expansion, while its influence to the existing AC networks will be studied by a PhD student at Delft University of Technology (TUD). This research project includes the review of the state of the art, VSC-HVDC model development, development of converters coordination method and DC fault studies. A collaboration work with TUD will be established during development of the VSC-HVDC model and study cases for testing the methods developed in this project. Industry collaboration with Energinet.dk and TenneT will also be considered and transfer of knowledge among academias and industries by the means of papers, workshops or patents is expected throughout the project period. In the end, this research project will provide guidelines for future connections of converter to COBRAcable towards efficient, highly reliable, secure, and flexible MTDC transmission system.

COBRAcable research project methodology is depicted in the following diagram: 

The upper-part of the diagram contains methods that will be developed by a team from Delft University of Tecnology (TUD), while the lower-part of the diagram shows methods for Aalborg University's (AAU's) team. The middle-part of the diagram represents the common tasks for both AAU and TUD research teams.