A High-Boost Ratio Isolated Current-Fed DC/DC Converter Based on Constant Off Time Control

In solar-charged electric vehicles, an isolated dc/dc converter is required to link the low-voltage roof photovoltaic (PV) panel to the high-voltage battery pack. It needs to maintain a high step-up ratio and a low ripple input current. This brings significant challenges to the optimal design of this dc/dc converter. To address those challenges, an interleaved isolated current-fed converter with constant off time (COT) control is proposed in this paper. It has a low components count with a single stage structure. The interleaved current-fed structure facilitates an enhanced boost ratio and ensures continuous output current from the PV panel. COT control utilizes the resonance between the transformer leakage inductor and the resonant capacitor across the switches. This enables zero voltage switching on the primary side MOSFETs and zero current switching on the secondary side diodes. A 200-W prototype is built to validate the analysis and design methodology. The converter is tested under various load conditions at 15 V input and 400V output. A 93.95% peak efficiency is recorded.