Single-stage LLC AC/DC converter with wide input range and low bus voltage

The traditional single-stage boost LLC resonant AC/DC converter has been widely studied due to advantages such as few power stages, high power factor, and soft switching. However, it also has several disadvantages, such as a low and narrow input voltage, a DC bus voltage that is much higher than the input voltage, and high stress of the switching devices. Therefore, it is generally used in power grids under 110 V. In order to overcome the above problems, this paper proposed a buck-boost LLC resonant AC/DC converter for both 110 V and 220 V power grids. In addition to its traditional structure, the proposed converter has the advantages of a wide input voltage range and a low bus voltage. The proposed converter adopts the PFM–PWM hybrid control strategy. In this paper, the working principle of the proposed converter is analyzed in detail, the realization of the power factor correction mechanism and the soft switching are described, and the design methods of the key parameters are given. Finally, an experimental prototype with a 110 V-250 V input and a 48 V/100 W output is built. Experimental results verify the correctness of the theoretical analysis of the converter and its applicability to power grids.