Expansion of offshore HVDC grids: An overview of contributions, status, challenges and perspectives

The goal of this paper is to review, systematize and critically discuss the approaches that have been proposed so far for grid transmission expansion in HVDC systems. In particular, the paper will focus on the special planning requirements of offshore HVDC grids, which have been seldom addressed by available literature. This contribution will first highlight how traditional expansion planning approaches commonly applied to AC systems need to be modified to properly include the HVDC technology; then it will outline how strategies and tools should be adapted when dealing with large offshore HVDC systems, such as the forthcoming North Sea Offshore Grid. On this respect, an updated overview of existing and planned HVDC links in the North Sea will be provided. Finally, a discussion of the specific challenges that need to be properly addressed by the expansion problem of offshore HVDC networks will be presented, with particular emphasis on renewable energy integration and control issues.