A Soft-Switching Bidirectional DC-DC Converter With High Voltage-Gain and Low Voltage Stress for Energy Storage Systems

In this paper, an interleaved soft-switching bidirectional dc-dc converter (BDC) with high voltage conversion ratio (VCR) and low voltage stress is proposed for battery charging/discharging applications. A built-in transformer (BT) is integrated into conventional half-bridge BDC and three-level structure to achieve high VCR and reduced voltage stresses simultaneously. The feature of BT is that the balanced magnetic flux exists in the magnetic core, which allows for a small size of magnetic core. The current ripple in the battery side is reduced by adopting the interleaved structure. Moreover, the voltage-matching on both sides of the BT is realized by the adjustment of the duty cycle. As a result, the BT always operates under the highest-efficiency condition. Besides, by employing phase-shift control, power flow can be regulated monotonously. Soft-switching of all the switches within a wide range of battery voltage is obtained by employing the optimal design. The operational principles, characteristics and design considerations are analyzed in detail. Experimental results from the BT-BDC prototype of 1-kW, 40—60 V to 400 V verify the effectiveness.