This paper analyzes the effectiveness of the integration of the series inductor into the medium frequency transformer used for series resonant or dual active bridge converters - galvanically isolated DC-DC converters for high-power medium-voltage (solid state transformer) applications. The design of the two different DC-DC converter topologies is provided, considering high power ratings, with the emphasis on the required reference electrical parameters of the medium frequency transformer, especially the leakage inductance. An internally developed design optimization tool is used to analyze the influence of these reference parameters on the medium frequency transformer efficiency and power density, thus providing valuable insights and design guidelines.