Abstract: On the basis of LLC，considering from the perspectives of soft-switching technology，DC/DC

cascade converter technology and three-level technology，a new DC/DC composite cascade structure topology on

the basis of Buck-LLC structure was proposed. A 980 W prototype was designed and built for verification，which

prove that the proposed composite Buck-LLC cascade structure can effectively reduce the processing power of the

previous Buck circuit，and reduce the Buck inductor volume，and increase power density while maintaining the

efficiency of the traditional Buck-LLC cascade structure. It can also effectively reduce the withstand voltage value

of the bus capacitor and maintain the advantages of PWM closed-loop modulation，and can output a stable voltage.In addition，the design of the working parameters of the subsequent LLC fixed frequency is more convenient.

      Key words: soft-switching；composite Buck-LLC；cascade structure；three-leve（l TL）