Precise Identification of the Zero Voltage Switching Boundaries of CLC-Resonant Dual Active Bridge Converters

One of the primary requirements of dual active bridge (DAB) dc-dc converters is to operate under zero voltage switching (ZVS), to reduce switching losses and increase operating efficiency. The known limited ZVS capability of CLC-resonant single-phase DAB converters can be extended using a frequency domain model accounting for all relevant harmonics that takes into consideration the complex non-ideal coupling impedance as well as non-ideal switching effects and practical ac port impedances. This paper presents detailed analytical expressions for the ZVS operating boundaries of a CLC-resonant DAB, capable of precisely predicting the converter's ZVS capability while accounting for all these practical complexities. This mathematical model is then used to define the converter modulation strategy to extend the ZVS operating regions, allowing for ZVS to be maintained at lower power transfer conditions. The precise ZVS boundary predictions are validated with extensive experimental results.