A Two-Stage Four-Switch Buck-Boost Integrated Dual-Active-Bridge Converter with Wide Range Soft-Switching and Minimized Backflow Power

Dual-active-bridges (DABs) inherently lack the ability to ensure zero-voltage switching (ZVS) during light load operation. To achieve soft-switching across the entire load range and enhance system efficiency, DABs are recommended to operate in the DC transformer (DCX) mode, which enables unity output voltage gain. Therefore, to widen the voltage gain range, this paper proposes a two-stage four-switch Buck-Boost (FSBB) integrated DAB (FI-DAB) with high control flexibility. The hybrid structure allows the sharing of a bridge arm between FSBB and DAB, significantly reducing the number of utilized switches and system conduction loss. To further reduce the system loss caused by the backflow power of DAB, an optimized dual-phase-shift with bidirectional inner phase shifts (ODPS-BIPS) modulation method is applied to the DAB. Additionally, based on the DCX concept, to match the system output voltage, the output voltage of FSBB is regulated by adjusting its duty cycle with a PI compensator plus input voltage feedforward. A fast-dynamic response control method is simultaneously introduced to alter the phase shift of DAB, aiming to improve the system's transient response performance during load variations. Furthermore, the FI-DAB employs an additional phase shift, providing extra control freedom to further boost the system's overall efficiency. Consequently, implementing the proposed structure enables full-range ZVS and ultra-fast output transient response, and simulations and experiments are conducted to validate the effectiveness of the proposed configuration and control method.