Closed-Form ZVS Boundaries for Three-Phase M-Level-to-N-Level DAB Converters With Different Winding Configurations

One of the essential characteristics of a three-phase dual-active-bridge (DAB) dc–dc converter is its inherent zero-voltage switching (ZVS) capability during the turn-
on
of the switches. This article provides closed-form equations that identify the ZVS boundaries for an M-level-to-N-level DAB converter, where M and N can be any natural numbers. It is shown that the derived ZVS boundaries can be used for different converter topologies, including but not limited to: two-level full-bridge converter, three-level neutral-point-clamped converter, T-type converter, transition arm converter, modular multilevel converter, and controlled-transition-bridge converter. The effect of different winding configurations of the medium frequency transformer—YY, Y
$\Delta$
, and
$\Delta \Delta$
—is also considered in the study. In addition, easy-to-implement simplified ZVS boundaries are provided, and the effects of the different number of levels, transition times, and dead times on the ZVS operation are quantified. An important result shown is that the converters with the YY and the
$\Delta \Delta$
windings lose ZVS at partial loads as soon as the transition time increases from zero, whereas the ones with the Y
$\Delta$
configuration retain ZVS at partial loads and dc ratios close to unity, without any advanced modulation techniques. The derived analytical models are validated with MATLAB simulations and experiments.