A Three-Level Current-Fed Dual-Active Bridge DC–DC Converter Under Dual-Phase-Shift Control

Current-fed isolated DC-DC converters are widely studied and adopted in low-voltage high-current applications, such as photovoltaic (PV) systems, fuel cells, and energy storage systems. This is due to the advantages they provide, including low input current ripple and high step-up ratio. In high-voltage DC-DC applications or thin-film PV modules with higher maximum power point (MPP) voltage ranges, high-voltage switches are required as switches in conventional two-level dual active bridge (DAB) DC-DC converters must withstand the whole port voltage. In this paper, a three-level current-fed neutral-point-clamped (3L-CF NPC) DC-DC converter is designed and implemented, utilizing low-voltage rating MOSFETs and offering high control flexibility and low electromagnetic interference (EMI) due to the limited dv/dt. First, the operation principle, power characteristics, and current characteristics in different modes under the dual-phase shift (DPS) modulation scheme are discussed. It has been discovered that certain operating regions impose voltage stress on the primary switches under this modulation strategy. A detailed circuit analysis is presented to identify the coordinates of the safe operation region with reduced voltage stress, demonstrating the expansion of the safe operation region for 3L-CF NPC compared to 3L-voltage-fed (VF) NPC. An extensive analysis of zero-voltage switching (ZVS) conditions is performed for both primary and secondary switches to determine the soft-switching areas under various operating and design conditions. Moreover, the trajectories of control parameters, aimed at optimizing the turn-off current and RMS values of switches under different source and load conditions, are identified for the purposes of efficiency improvement. Finally, the performance of the proposed converter is verified with experimental results from a laboratory prototype, exhibiting high efficiency, voltage balancing, no voltage stress, and ZVS across various load conditions.