Addressing Cross-Coupling Issues in Magnetically Integrated Three-Port DC-DC Converters

DC grid-forming converters are used to provide dc power distribution inside buildings. Often, such converters are based on dual-active bridge (DAB) technology to provide high-frequency isolation. Certain developing standards related to dc installations specify different isolation classes and protection zones. This is a critical requirement for power converter design, especially for building applications where end-users are close to the loads, and it is necessary to provide extra safety. To comply with these requirements, isolation is needed between the primary DC buses (700 V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dc</inf>), dc power distribution buses (320-380 V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dc</inf>), and extra-low voltage levels (24-60 V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dc</inf>), where loads are connected. Three-port converters are a potential solution for this application to reduce the number of power processing stages. However, when working under droop control at the output, magnetic cross-coupling issues must be addressed. In this paper, a three-port isolated dc-dc converter is described and analyzed, verifying the influence of magnetic cross-coupling on the extra-low voltage port, which is usually not regulated. To experimentally verify this proposal, a 5.3 kW prototype was built, and laboratory tested, comparing different transformer designs.