An Accurate Time Domain Analysis Based ZVS Evaluation Tool for LLC Resonant Converters

LLC converters are popular in numerous industrial applications owning to their high efficiency and soft switching characteristics. Conventionally, the first harmonic approximation (FHA) analysis method is used to perform the zero-voltage switching (ZVS) analysis for LLC resonant converter. However, the FHA method assumes that the LLC resonant converter is always operating at resonant frequency point so that the primary switch turn-off current is a constant value during the whole operation range. When the LLC resonant converter operating point is away from the resonant frequency, considerable errors would exist, which will lead to unoptimized deadtime design or ZVS failure. Therefore, in this article, a ZVS evaluation tool is developed based on the time domain analysis, the analysis results have much higher accuracy when compared with the traditional FHA method, which can be used to guide the analysis and design of the converter. Experimental validations are presented.