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

Abstract

Abstract-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.

Dynamic Analysis of MMC-Based MTDC Grids: Use of MMC Energy to Improve Voltage Behavior

“…The DC grid is composed by four cables with equal length (70 km), namely "C1", "C2", "C3" and "C4", with detailed Wide Band cable models whose parameters are given in [27]. The chosen cable length is in accordance with real HVDC offshore projects [28]. The model of the Wind Farm (WF) is much simplified and assumed to be a simple power injector (P wf ) as depicted in Fig.…”

“…The expressions for the modulated voltages v ∆ mdq and v Σ mdqz are shown in (25) (at the bottom of the page). In (26), (27) and (28), the dynamic equations for…”

Integration of Distributed Energy Resources into Offshore and Subsea Grids

“…Furthermore, the interconnection of otherwise-isolated offshore electric distribution systems to offshore HVDC and HVAC grids will push the innovation from component-level to system-level. Considering the increasing number of offshore HVDC deployments [145], Medium Voltage DC grids, already emerging in the maritime sector [146], could be extended to some offshore and subsea systems [147], [148].…”

Optimizing HVDC Grid Expansion and Control for Enhancing DC Stability

“…Considering the technical and financial implications of deploying highly-interconnected offshore grids, the expansion planning stage is of paramount importance. However, many commonly adopted expansion planning approaches are based on techno-economical optimization and do not take stability and performance of the grid dynamics into sufficient consideration [3]. HVDC links however contribute significantly to the latter aspects and are often used to solve grid problems such as congestions and mitigation of power imbalances [4].…”