Review and outlook of HVDC grids as backbone of transmission system

HVDC technology has undergone many major de­velopments in the past decades, resulting in higher power ratings, increased efficiency, and the availability of effective means for HVDC grid protection. These developments have made overlay HVDC grids a viable option to shift towards a carbon-free power system, by enabling optimal use of renewable resources. In particular, overlay HVDC grids greatly increase the prospect of building (trans-) continental supergrids to facilitate global economic development. However, overlay HVDC grids still encounter challenges due to the distance and amount of power involved. This paper focuses on analyzing the readiness of the current technologies and the challenges associated with overlay HVDC grids. An in-depth analysis is carried out to evaluate the applicability of current technologies for overlay HVDC grids. Based on the review of recent research and development efforts, the gaps and challenges towards the realization of a global HVDC grid are summarized.