High-Conversion-Ratio Isolated Bidirectional DC–DC Converter for Distributed Energy Storage Systems

In this paper, a novel high-conversion-ratio isolated bidirectional dc-dc converter for distributed energy storage systems is proposed. In the buck mode, the proposed converter is equivalent to that of a cascade consisting of an isolated buck-boost converter and a buck converter, thus achieving a high step-down ratio. Likewise, in the boost mode, the converter is equivalent to the cascaded structure consisting of a boost converter and an isolated buck-boost converter, and then, a high step-up ratio is achieved. Therefore, the proposed topology exhibits a high conversion ratio with low transformer turns ratio, improving the efficiency of high-frequency transformers and the integration and reliability of the control system. In addition, voltage spikes caused by the leakage inductance can be avoided as the leakage inductance energy is released to capacitors in a high-voltage side or a low-voltage side. Moreover, a zero-voltage-switching (ZVS) operation reduces switching losses and improves the conversion efficiency. The operating principles and theoretical derivations of the proposed converter along with ZVS implementations are discussed in detail in this paper. Furthermore, the validity and performance of the proposed converter are verified using a prototype with 600-V high voltage, 48-V low voltage, and 2-kW output power.