Soft-switching Characteristics Analysis Based on LLC Resonant Converter

In fundamental harmonic approximation (FHA) method, it is assumed that converter operates at resonant frequency. When converter is operating below the resonant frequency, traditional FHA method is not accurate to obtain an adequate inductor to let system operate in zero-voltage-switching (ZVS) mode. This paper proposes a novel method to analyze the value of magnetic current from the perspective of energy conversion. Compared with FHA method, the novel analysis method is practical to get an adequate value of magnetic inductor. It reduces reactive power loss and turn-off loss of LLC resonant converter. The method ensures that converter can get soft-switching characteristics at full range of load and the efficiency of converter is improved at the same time. Finally, a 300W 500kHz 400V/24V half-bridge LLC resonant converter is built to verify the validity of method.