For the input-series-output-parallel (ISOP) DC transformer (DCT), the input voltage sharing (IVS) control is an essential but complex design process. This paper proposes an improved ISOPDCT based on dual-active-bridge modules. By integrating the switched resonant branches in the input bridges of the modules, this topology not only succeeds in the self-voltage balancing without any IVS control but also has few impacts on the dual-active-bridge modules operation. This paper builds a full-order continuous-time small-signal model of the proposed DCT and the closed-loop input impedance for the future unified controller design of the proposed topology. The experimental results and simulation have verified the functions and impedance modeling of the proposed self-voltage balancing DC transformer.

ISOP DC transformer; input-side self-voltage balancing; small-signal modeling; input impedance