Cascaded High Voltage Conversion Ratio Bidirectional Nonisolated DC–DC Converter With Variable Switching Frequency

In this paper, a multistage nonisolated high voltage conversion ratio (VCR) bidirectional dc-dc converter is proposed. The VCR is n times of the conventional buck/boost converter using only n+ 2 switches. All the switches can achieve full-range zero voltage switching (ZVS) despite the power flow direction. The operating principle, ZVS condition, and design considerations of a four-stage topology are analyzed in detail. In addition, an improved dynamic switching frequency modulation is proposed to reduce the power loss. Analyses and comparisons between the conventional constant frequency and variable frequency control are made to show the effectiveness. A 500-W experimental prototype interfacing 20-30 V with 270 V is fabricated to verify the performance of the proposed converter and control strategy.