中文摘要：

Buck-LLC两级DC／DC变换器同时具有源级变换（Buck变换器）宽电压调节范围和负载级变换器（LLC谐振变换器）软开关的优点。当LLC谐振变换器工作于谐振频率点时，LLC变换器效率的提升可补偿前级Buck变换器带来的效率下降，从而使变换器的总体效率得到提升。针对Buck-LLC两级DC／DC变换器，分析了Buck变换器和LLC变换器的工作原理，研究了Buck变换器电感电流和LLC变换器输出电压反馈的双环定频控制策略。最后，搭建了一台样机进行了实验验证。

英文摘要：

Advantages of the Buck-LLC two-stage DC/DC converter include the wide voltage regulation range of source converter（Buck converter） and soft switching of load converter（LLC resonant converter）.When the LLC resonant co- nverter works at the resonant frequency point, the efficiency of LLC resonant converter can be compensated for the decline in the efficiency of the former stage Buck converter.Therefore, the overall efficiency of the converter is imp- roved.Aimed at Buck-LLC two-stage DC/DC converter,the operation principle of Buck converter is analysed as well as LLC converter and dual loop constant frequency control strategy for Buck converter inductor current and LLC con- verter output voltage feedback is investigated.A prototype is built to verify the validity of the proposed strategy.