A Combined PWM and Phase-Shift Control Method With Adaptive ZVS Boundary Regulation for Bridge-Arm Reused FSBB-LLC Converter

The four-switch buck-boost converter (FSBB) cascaded with LLC resonant converter can achieve zero-voltage switching (ZVS) of power switches and wide-range voltage regulation. To improve the power density and reduce costs, the bridge arms in the two converters can be reused, thereby forming the bridgearm reused FSBB-LLC converter. However, the reuse of bridge arms reduces the degrees of control freedom, which is detrimental to the realization of ZVS. In this paper, a combined PWM and phase-shift control method with adaptive ZVS boundary regulation for FSBB-LLC converter is proposed, which realizes ZVS of power switches while maximize the reduction on inductor current ripple in the full range (full voltage and load range). Firstly, the ZVS conditions of power switches along with the selection principle of the inductor are revealed. Then, the basic idea of the adaptive ZVS boundary regulation and its design method are proposed. Based on that, a combined PWM and phase-shift control method and its implementation for the FSBB-LLC converter are proposed, which not only realizes fullrange ZVS but also maximize the reduction on inductor current ripple. Finally, a prototype of a 500-W FSBB-LLC converter is built and tested in the lab. The experimental results are provided to verify the effectiveness of the proposed control method.