Unregulated series resonant converter for interlinking DC nanogrids

DC nanogrids have become a subject of interest in recent years due to the increase of renewable energy sources with energy storage systems. Hybrid AC/DC systems with different DC buses are an interesting solution to efficiently supply different AC and DC loads. In this paper, a high efficiency bidirectional converter to interlink a 400 V DC bus with a 48 V DC bus is presented. The proposed converter is based on a LLC resonant converter operating as a DC transformer at a fixed frequency and duty cycle without any complex control strategy. A clear and simplified design procedure for high efficiency operation and optimal self-load regulation is presented. To verify the converter operation, a 1 kW prototype has been implemented, featuring on maximum efficiency of 96.7 % and a self-regulated output voltage with 3 % of maximum offset from the nominal voltage.