Isolated Buck-Boost DC/DC converter for PV grid-connected system

A family isolated Buck-Boost converter is proposed in this paper, and FB-Boost converter is analyzed as one of the typical topologies. An improved two-edge modulation strategy is proposed to minimize the inductor current ripple over the input voltage range. In order to improve the efficiency and reliability of FB-Boost converter, three-mode control scheme is proposed in this paper, according to the different region of input voltage, FB-Boost converter can operate at Boost, FB-Boost and FB modes respectively. As the input voltage in FB-Boost mode is close to the output voltage, the inductor current ripple in this mode is smaller than the other modes, so the switching frequency in this mode can be lowered to reduce the switching loss. To verify the effectiveness of the design and control, a 250 V ~ 500 V input, 360 V output and 6 kW rated power prototype is fabricated, the average efficiency over the input voltage range is 95.6%, and the highest efficiency can achieve 96.7%.