High efficiency control strategy for isolated full-bridge-boost converter suitable for wide input voltage range

A family of isolated Buck-Boost converters is proposed to be suitable for the application, where the input voltage range is wide and galvanic isolation is required in this paper. Full-Bridge (FB)-Boost converter is analyzed as one of the typical topologies. Considering the duty cycle loss, an improved two-edge modulation strategy based on phase-shift control is proposed to minimize the inductor current ripple over the input voltage range. In order to achieve the reliability and efficiency of this converter, a 3-mode dual-frequency control scheme is proposed. Under the 3-mode dual-frequency control scheme, the input voltage is divided into three regions, i.e. the low, medium and high voltage rang, and corresponding operating modes are Boost, FB-Boost and FB modes respectively. As the inductor current ripple in FB-Boost mode is much smaller, the switching frequency of the boost cell in this mode can be lowered to reduce the switching loss and further improve the efficiency. To verify the effectiveness of the design and control, a 250~500 V input, 360 V output and 6 kW rated power prototype is fabricated. High efficiency can be achieved all over the input voltage range, and the highest efficiency is 97.2%.