Scaling Laws for the Magnetic Components in Galvanically Isolated Single-Stage Multi-Level Converter Systems

Abstract

In order to reduce the volume of the filter components at the input or at the output of non-isolated DC/DC converter stages, so-called multi-level (ML) converter topologies are used more and more often, which, by connecting several identical converter cells in series, reduce e.g. the voltage-time areas across inductors, whereby they have to store less energy and can therefore also be built smaller in volume. The advantages of this ML approach have often been proven by means of realized hardware demonstrators with remarkable power densities, but only for systems without galvanic isolation. In order to show why the ML approach is so rarely seen in galvanically isolated systems, and why it is not reasonable to be used in such systems even from a conceptional point of view, scaling laws for the magnetic components in galvanically isolated ML converter systems are derived in this paper, which are then used to investigate how the volumes of the different magnetic components change with increasing number of series-connected converter cells. Finally, the scaling laws of the individual magnetic components are combined, which allows to make a final statement about how the total volume of the galvanically isolated ML converter changes with the number of cells. Even though the scaling laws are derived based on a simple galvanically isolated buck/boost converter topology, the general scaling trends found are not limited to this specific topology, but rather apply to any galvanically isolated ML converter structure.