An Efficient Dual-Active-Bridge Converter for Wide Voltage Range by Switching Operating Modes With Different Transformer Equivalent Turns Ratios

This article proposes a variable transformer equivalent turns ratio dual-active-bridge (VTDAB) dc-dc converter, which aims to increase the efficiency of the conventional dual-active-bridge (CDAB) dc-dc converter over a wide voltage range. By changing the driving logic of the secondary-side three bridge legs, the VTDAB controls the voltages across the dual transformers with two different turns ratios, resulting in three operating modes with different equivalent turns ratios that do not require any extra components. First, the principle, mathematical model, and zero-voltage switching (ZVS) conditions of VTDAB are introduced. Second, the turns ratios of the dual transformers are designed, the boundaries between the different operating modes are determined, and a complete control strategy is proposed with the aim of lowering the inductor root mean square (rms) current. Finally, a 1-kW prototype with a voltage gain range of 0.4-2.5 is built. Comparisons are made between the maximum attainable transmitted power, the inductor rms current, and the ZVS range of VTDAB and CDAB. According to the experimental results, the VTDAB maintains an efficiency of 92%-98.3% across the whole operating range while having a lower inductor rms current and higher efficiency over a wide voltage range.