A novel power electronic transformer (PET) topology with multiport bidirectional resonant DC-DC converters is proposed where several medium-frequency multi-winding transformers is applied to realize the isolation. The topology is with high power density as well as high efficiency, which is a appropriate solution for electric tracton application like locomotives and high speed EMU trains. The power balancing could be realized by common flux linkage of the transformer, so that the load of the PET ports can be different from each other. Three control strategies of the multi port bidirectional LLC resonant DC-DC converters are proposed for either independent and paralleled secondary DC links with small LC parameter difference. Simulation and experimental results are given to validate the proposed topology and control strategies.