Analytical Determination of the ZVS Boundaries for Resonant Dual Active Bridge Converters

Recently, a variation of the conventional single-phase dual active bridge (DAB) topology has been proposed, where an inductor-capacitor-inductor (LCL) resonant network tuned to the converter switching frequency is used as the AC coupling network. The approach reduces the reactive current component that circulates between the converter bridges and thus reduces their VA rating. However it does not achieve zero voltage switching (ZVS) conditions at lower levels of power transfer. To address this question this paper uses frequency domain analysis to accurately predict the individual half-bridge ZVS boundaries for DAB converters with a resonant coupling inductance. The outcome is then used to modify the converter modulation strategy to extend the ZVS operating regions, allowing ZVS to be maintained at lower power transfer conditions and for off-nominal primary-to-secondary de-link voltage ratios. The theoretical ZVS boundary predictions are in precise agreement with results from switched simulations.