Topology Evaluation and Comparison for Isolated Multilevel DC/DC Converter for Power Cell in Solid State Transformer

In this paper, the primary side phase leg topology for a multilevel DC/DC converter is explored for a power cell in solid state transformer (SST) that converts medium-voltage (MV) AC input to low-voltage (LV) or medium voltage DC output. To take the high voltage DC bus provided by the multilevel AC/DC front end, two different topologies for the isolated DC/DC stage are thoroughly investigated based on the LLC resonant circuit operation. The key performance such as soft switching conditions and requirements for the two topologies with different modulation schemes are analytically compared. The design procedure for the selected topology is presented and experimental performance evaluation was done on a 15-kW isolated DC/DC converter at various operating conditions.