Bidirectional　DC-DC　converter　plays　an　important　role　in　distributed　power　generation　system　due　to　it　is　necessary　to　control　the　power　flow　between　energy　storage　devices　and　DC　bus.　The　conventional　phase-shifted　dual-active-bridge　(PS-DAB)　converter　inherits　simple　control,　symmetrical　stricture,　and　zero　voltage　switching　(ZVS).　However,　large　dv/dt　will　be　created　when　applied　in　a　high　voltage　range.　Modular　multi-level　DC　transformer　(MMDC)　originates　in　the　modular　multi-level　converter　(MMC)　and　dual　active　bridge　(DAB).　The　MMDC　topology　can　be　obtained　via　displacing　the　power　devices　in　the　primary　side　of　DAB　with　series-connected　submodules.　A　vital　issue　to　ensure　MMDC　is　operating　in　a　stable　state　is　balancing　the　capacitor　voltage　of　each　submodule　in　the　arm.　A　capacitor　voltage　balance　method　is　proposed　in　this　paper.　The　operating　principle　is　reassigning　the　gate　signals　of　higher　capacitor　voltage　submodules　(SMs)　to　lower　capacitor　voltage　SMs.　According　to　the　simulation　results,　the　capacitor　voltage　has　different　outputs.　The　N}+1　level　change　of　each　N-SMs-arm　balanced　when　the　MMDC　starts,　which　means　that　EMI　and　dv/dt　are　reduced　in　the　transformer　pressure.　©　2021　IEEE.