Research Of A Buck-Boost And Dual Active Bridge Integrated Three-port DC-DC Converter

Among various three-port DC-DC converters, partial isolated three-port DC-DC converters integrated with dual-active-bridge(DAB) have the merits of simple topology, reduced devices, easy to achieve ZVS(zero-current-switching, ZVS) and bidirectional power flow, etc. Therefore, they are suitable for renewable energy generation systems.Since the structure of Boost or Buck integrated with DAB can only realize voltage stepping up or stepping down, they can not realize voltage matching all the time when input voltage varies in a wide range. To solve this problem, a three-port DC-DC converter integrated of bidirectional Buck-Boost and DAB is studied in this dissertation, two input ports of which are connected in series. With the flexible voltage stepping up and down ability, voltage of the two input ports can be well matched in real time, which overcomes the input voltage level limits.System energy management, basic operation principle and characteristics of the converter under PWM plus dual phase shift control are detailed in this dissertation. Equivalent circuit, voltage and current equations in each sub period are derived. Based on this, output power formulas in different voltage patterns are calculated. The ZVS characteristics of both the primary and secondary MOSFETs are analyzed. The backflow power characteristic of the converter is also considered. The minimum backflow power scheme in different voltage patterns is clarified. Together with the ZVS characteristic, an optimal control scheme is deduced to make sure that the backflow power under the same output power is minimized and that the ZVS range is extended.Finally, the hardware design of the topology is performed according to experiment requirement. A 350 W prototype is built to validate the correctness of theoretical analysis. Basic operation principle, ZVS and backflow power characteristics of the converter are all verified with experiments under different operation conditions. The efficiency curves of the converter are given. The feasibility of the topology and effectiveness of the optimal control scheme are demonstrated by the experimental results.