Design Considerations for LLC Series-Resonant Converter in Two-Resonant Regions

A current waveform modeling for describing the dynamic behavior of a half-bridge LLC series-resonant converter (LLC-SRC) working in two resonant regions is proposed. The resonant inductor current i_L is modeled approximately as a linear combination of the magnetizing current i_m and the primary current i_p, where both two currents are orthogonal. The key parameter estimations, including K factor, resonant L_r. and C_r, quality factors Q_K and Q_r are clearly derived and described for design considerations. Two 240 W LLC-SRC converters are designed and examined for performance evaluation. Both two efficiencies are as high as 91%-95% in the two regions. Simulation and experiment is close to the estimation works.