This paper analyzes and compares 2-level and multilevel topologies for an LLC resonant converter intended for a modular DC/DC stage of a solid-state transformer (SST) in a green hydrogen system. To leverage the benefits of multilevel topologies, a design methodology is developed to evaluate the topologies concerning efficiency, power density, number of devices, and cost. A general scaling law is derived to determine the minimum number of power modules in the modular DC/DC stage. An optimization algorithm is developed to identify which number of levels achieves the best trade-off among the key performance metrics. Experimental results of an 1 kV / 5 kW three-level LLC resonant converter demonstrate an efficiency of 98.6%.
