Analysis of Multiple Phase-shift Control for Full-bridge CLLC Resonant Converter Based on Improved Fundamental Harmonic Approximation Method

To solve the light-load problem of CLLC resonant converters, this paper proposes a comprehensive analysis of multiple phase-shift control based on improved fundamental harmonic approximation (FHA) method. A precise multi-harmonic approximated AC impedance model is firstly built to derive the analytical relations between the output voltage gain and rms values of resonant currents of CLLC converters and three phase-shifts. Then, the influences of different phase-shifts on voltage gain and rms values of resonant currents are investigated with simulation verifications. Finally, an optimal dual phase-shift control achieving both effective voltage regulation and satisfying power efficiency is concluded and verified on a 18~25V/400V, 200W GaN based CLLC resonant converter prototype.