The introduction of modular multilevel converters (MMCs) created a new momentum in the field of high voltage direct current (HVDC). HVDC is not anymore used only in point-to-point links embedded in ac systems or between asynchronous areas. It is now also used to transport power from offshore wind farms (OWF) far from shore to land and multi-terminal direct current (MTDC) systems are becoming a reality. With the expected massive development of renewable energy sources and the limited rights-of-way to create new overhead lines in many countries, the power system must evolve and HVDC technologies will have a major role to play. This presentation will remind the motivations for dc and MTDC solutions and give a brief state-of-the-art of HVDC converters. Some examples of MTDC will be presented. An insight on the stepwise development of MTDC will highlight new functionalneeds which can be provided thanks to devices involving power electronics: DC current breakers, DC/DC converters, power flow controllers (or current flow controllers), integration of energy storage elements… For these needs, some technologies and their status of development will be reviewed.
Keynote presented at EPE’21 ECCE Europe