A Method to Enlarge the Soft-switching Range for the Dual Active Bridge Series Resonant Converter

The dual-active-bridge series-resonant-converter (DAB-SRC) has been widely used due to its ability to achieve natural synchronous rectification. At light load conditions, the small turn-off current leads to long charging and discharging times of the switching junction capacitor, making it difficult to achieve soft switching. In order to extend the range of soft switching for light load conditions, a very high switching frequency can be used to increase the harmonic component. This approach often results in an extremely wide switching frequency range. In order to extend the soft-switching region for very light loads and reduce the range of switching frequency without increasing the number of devices, the effects of magnetizing inductance and transformer turns ratio on the soft-switching region are considered, and a hybrid control strategy are proposed. In this paper, variable frequency phase shift (VFPS) control strategy is adopted at 20%~100% load and constant frequency phase shift (CFPS) is adopted at 5%~20% load. The feasibility and correctness of the proposed control strategy are verified by a 1.2kW experimental prototype.