Modeling and ZVS Constraints of the Hybrid-bridge LLC Resonant Converter for MHz Level Operation

This paper presents a model of the hybrid-bridge LLC converter, emphasizing on deadtime interval dynamics that become too impactful to ignore for preserving model accuracy at MHz-level operation. The time-domain modeling approach is adopted and a new parameter $k_{\mathrm{C}}$, defined as the capacitance ratio between the resonant capacitance $C_{\mathrm{r}}$ and switch output capacitance $C_{\mathrm{oss}}$, is introduced to model the state variables during the transition intervals. The proposed model, validated by PSIM circuit simulation, is used to derive ZVS constraints of the topology, especially for the less frequently addressed upper deadtime limit to prevent an eventual $C_{\text{oss}}$ recharge, due to an early resonant current reversal. The ZVS limits proposed are validated on a $\mathbf{5 0 0}\mathbf{W},\mathbf{4 0 0}\mathbf{V}/\mathbf{1 8 - 3 6}\mathbf{~}$ GaN-based experimental prototype at $\mathbf{5 0 0 \mathrm { kHz }}$.