Efficiency Comparison of DAB Module for LVDC-Connected EV Fast Charging Systems

Addressing key challenges in the roadmap toward transportation electrification requires more grid flexibility and highly efficient modular fast charging systems capable of wide voltage operation in line with evolving EV battery voltage levels. This paper investigates optimal system configurations for Dual Active Bridge (DAB) modules connected to a bipolar LVDC grid (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$+/-350 \mathrm{V}$</tex>), targeting 400 V and 800 V battery systems. DAB module designs are based on real-world charging voltage and power profiles. Using detailed PLECS-based simulations incorporating SiC MOSFET and high-frequency transformer models, the switching and conduction losses are analyzed across varying operating conditions. Results show that ultra-high efficiencies (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$&gt;99 {\%}$</tex>) are achievable at higher voltage levels (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$700-800 \mathrm{V}$</tex>), although switching losses increase at lower charging power. At lower voltage operation (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$350-400 \mathrm{V}$</tex>), a narrower efficiency range <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(92 \%-98 \%)$</tex> is observed across the full power range. Therefore, from the DAB module perspective, this configuration can be optimal to maintain higher efficiency over a wide charging power range, particularly when battery and LVDC grid voltages are closely matched. For a 150 kW IPOP modular fast charger, high voltage operation (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$700-800 \mathrm{V}$</tex>) results in lower total losses (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1.5-3 \text{kW}$</tex>), making it the preferred configuration for typical fast-charging profiles.