Voltage Balance Scheme for Input-Series Output-Series DAB DC–DC Converter With Bidirectional Power Flow

The dual-active-bridge (DAB) dc–dc converter with the input-series output-series (ISOS) structure is applicable for flexible interconnection of a power grid, where both the input and output sides are high voltage. However, the bidirectional series structure and bidirectional power flow pose significant challenges to voltage balance between modules. To address the issue, this letter proposes a voltage balance scheme, in which the LC resonant branch is integrated into the ISOS DAB dc–dc converter to balance the voltage of the input side, while the control strategy eliminates the unbalanced voltage of the output side by phase-shift ratio regulation. Hardware-in-the-loop test results indicate that the proposed scheme simultaneously realizes voltage balance on both the input and output sides of the ISOS DAB dc–dc converter.