A Quasi-Two-Stage Boost Full-Bridge <i>LLC</i> Converter With Partial Power Transmission

This paper presents a quasi-two-stage boost full-bridge LLC (QBT-FLLC) converter aimed at improving the efficiency of traditional two-stage resonant converters while reducing the zero-voltage switching (ZVS) burden on the first stage. In the QBT-FLLC converter, a direct power transfer loop is formed by decoupling the resonant converter stage from the traditional two-stage architecture and directly paralleling the bridge arms with the input power source. Thus, compared to conventional two-stage resonant converters, the proposed QBT-FLLC reduces power transfer in the front-end stage, alleviates the ZVS burden on the front-end switches, and enhances the efficiency of the front-end stage. In the QBT-FLLC, the voltage is regulated through the front stage of the duty cycle at a fixed switching frequency, with voltage gain remaining independent of the load. The QBT-FLLC is particularly suitable for transportation electrification applications, such as electric vehicles (EV) and railway traction systems, where high efficiency and reduced switching losses are critical. Besides, a comprehensive analysis of the operation principles, gain, ZVS analysis, parameter design, and efficiency of the QBT-FLLC converter is presented. The experimental results confirm the effectiveness of the proposed QBT-FLLC converter, demonstrating its feasibility and performance.