This paper presents the analysis and experimental verification of an LLC resonant converter based on the three-level (3L) series half-bridge (HB) converter intended for a modular DC/DC stage of a two-stage solid-state transformer (SST) system. In general, efficiency and cost are key performance metrics for the SST design and implementation. Therefore, the paper focuses on the design of the modular multilevel DC/DC stage, aiming at the optimization of its efficiency and cost. An additional contribution of the paper is a comparison study considering Si IGBT and SiC MOSFET semiconductor technologies. A down-scale laboratory prototype rated at 750 V / 5 kW has shown a peak efficiency of 98.6%.
