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 Vdc), dc power distribution buses (320-380 Vdc), and extra-low voltage levels (24-60 Vdc), 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.