Refined Zero‐Voltage Switching Boundary Analysis and Parameter Design for Bidirectional DCX‐LLC Converters Considering Dead‐Time High‐Frequency Resonance

Benefiting from full load range zero‐voltage switching (ZVS), open‐loop LLC converters operating near the resonant frequency have been widely adopted in isolated dc transformer (DCX) applications. In conventional ZVS criteria, the magnetizing inductor during the dead time is typically approximated as a constant current source to drive the commutation of the bridge‐arm midpoint voltages on both sides. However, the high‐frequency resonant interaction between the semiconductor output capacitances and the resonant network during the dead time can distort the voltage and current waveforms, potentially leading to inaccurate ZVS boundary prediction and even ZVS failure. To address this issue, the commutation process involving the output capacitances and the associated resonant mechanism during the dead time are investigated in detail for a full‐bridge DCX‐LLC converter, based on which a refined magnetizing inductance boundary is derived. The proposed boundary explicitly reveals the effects of load conditions and resonant parameters on ZVS, thus providing a clearer theoretical basis for DCX‐LLC parameter design. Furthermore, a systematic design procedure is established and validated using a 160‐W, 95‐kHz prototype.