Fully Soft-Switched Dual-Active-Bridge Series-Resonant Converter with Switched-Impedance-Based Power Control

Both conduction loss and switching loss can contribute significantly to the overall power loss of an isolated bidirectional dual-active-bridge series-resonant dc-dc converter (DABSRC) operating at high frequency. To achieve soft switching and minimum-tank-current operation under wide-range variations in output voltage and current, a switched-impedance-based DABSRC is proposed. Minimum-tank-current operation aims to reduce conduction loss arising from circulating current at the low voltage, high-current side of DABSRC. Full-range soft switching is achieved in all switches, thus, switching loss is significantly reduced. With this new topology, power control is achieved by controlling a switch-controlled capacitor in the series resonant tank while ensuring minimum-tank-current operation and soft switching in all switches. The proposed topology and modulation scheme are validated by means of a 1-kW experimental prototype of DABSRC operating at 100 kHz designed to interface a 250-V dc bus to a supercapacitor with a rated output voltage of 48 V. The effectiveness of the proposed topology for charging/discharging a supercapacitor at a maximum rated power of 1 kW is verified by simulations and experimental results with a maximum efficiency of 97.5%.