An Approach to Reconfiguring Transformer Turn Ratio Using Multibridge-Legs for Wide-Voltage-Gain DAB and LLC Converters

To improve the efficiency of isolated bidirectional dc–dc converters for off-board dc charging over a wide voltage gain, such as dual active bridge (DAB) and inductor-inductor-capacitor (LLC) resonant converters, this article proposes an approach to reconfiguring transformer turn ratio using multibridge-legs (RTTMBL). The proposed RTTMBL approach reconfigures a large number of turn-ratio combinations by adding a few auxiliary components. The different combinations of turn ratio are selected for different operating conditions to match the primary and secondary voltages of the converter, obtaining a lower inductor rms current and a wider zero-voltage switching (ZVS) range, thus reducing conduction and switching loss. This article first analyzes the principle of the proposed approach and describes the application of RTTMBL on DAB (DAB-RTTMBL) converter. Second, the DAB-RTTMBL is compared with the existing solutions regarding inductor rms current and ZVS range. Finally, a DAB-RTTMBL converter prototype with a power of 1kW and a voltage gain varying from 0.4 to 2.5 is built to verify the effectiveness of RTTMBL, which has six turn-ratio combinations. The results demonstrate the great potential of the proposed RTTMBL for wide-voltage-gain applications.