Design Methodology of LLC Resonant Converters for Single-stage Power Factor Correction Application

This paper proposes a new design methodology for LLC resonant converter with single-stage power factor correction (PFC) function. By designing the achievable gain of resonant tank at a certain point of the AC voltage higher than the required gain, its gain will satisfy the requirement of the whole AC line voltage cycle and lead to a good single-stage PFC design. By adjusting switching frequency and changing voltage gain along with the AC voltage, the converter can realize PFC with high efficiency. The proposed converter inherits the advantages of the traditional LLC resonant converter, including soft switching of power switches across the whole load range, buck-boost power conversion ability which benefits the optimization of the down-stream DC-DC converter. Gain characteristic and design consideration for PFC purpose are analyzed in detail. Experimental results are presented to show its validity and feasibility.