Overview of DC-DC Converters dedicated to HVDC Grids

HVDC grids are a promising alternative for the expansion of the existing AC grid. They are interesting for the integration of large-scale renewable energy sources, connecting high power offshore windfarms, interconnecting new market areas, including asynchronous AC grids and off-grid communities, and they can even provide ancillary services to the AC system. It is expected to create a more reliable and flexible transmission grid using HVDC grids. However, their development will require, among other technologies, DC-DC conversion systems. Although the DC-DC conversion techniques are well understood in low and medium voltage, a specific review on the approaches for high voltage is needed. This paper presents an overview of the DC-DC power converters dedicated to HVDC proposing a classification based on their structure. Two large families are established: those which provide galvanic isolation, and those which do not. Several sub-families are also proposed. An overview of the main HVDC applications that can be targeted with each family is also presented, highlighting the main converter requirements for each application case.