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 subfamilies 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.