Triple Phase Shift Modulation for Optimizing Phase Shift Angle of CLLLC Resonant Converters

CLLLC resonant converters are extensively applied in the field of power electronics. However, their current modulation methods exhibit notable limitations. Variable frequency modulation demonstrates a restricted voltage gain range, particularly under low-voltage conditions, while phase-shifted modulation struggles to achieve wide-range zero-voltage soft-switching. To address these challenges, a triple phase-shift modulation strategy designed to optimize the phase-shift angle is introduced. By appropriately selecting three distinct phase-shift angles, the proposed method effectively extends the voltage gain range of CLLLC resonant converters under low-voltage operation and significantly improves overall conversion efficiency. First, the impact of the three phase-shift angles on both voltage gain and the root mean square(RMS) value of the resonant current is systematically analyzed, leading to the establishment of optimization criteria for selecting the phase-shift angles. Subsequently, a multiple harmonic impedance model is developed for the CLLLC resonant converter employing the proposed modulation strategy, and the corresponding voltage gain expression is derived. Finally, the validity and performance advantages of the proposed triple phase-shift modulation approach are confirmed through the implementation of a 1 kW experimental prototype, achieving a peak efficiency of 96.1%.