H5-CFDAB: A Current-Fed Dual-Active-Bridge Converter for Application in Modular DC Solid-State Transformer

Isolated dc-dc converters in dc solid-state transformers (DCSSTs) must conform to stringent requirements such as high voltage conversion ratio, high efficiency, and reliable operation with grid fault handling capabilities. This article proposes a novel current-fed dual-active-bridge (CFDAB) converter, named H5-CFDAB, for modular DCSST application. Compared to the existing topologies, the proposed converter provides a single-stage power conversion with reduced component count and semiconductor volt-ampere rating. The proposed modulation scheme makes the pulsewidths of the transformer winding voltages independent of the duty ratio. This allows further optimization of the high-frequency-link (HFL) characteristics like minimized HFL conduction losses and full range zero-voltage-switching (ZVS) at turn on for the switches, further increasing the converter efficiency. Several modules of the proposed H5-CFDAB converter connected in input-series-output-parallel configuration makes the system suitable for medium-voltage high-power applications. The operation of the proposed converter is analyzed in detail, including the HFL characteristics and derivation of the ZVS conditions for the switches. In addition, a closed-loop control scheme is proposed for achieving tight regulation of the converter outputs during transients. A 1.2-kW laboratory prototype is built to verify the effectiveness of the proposed converter, along with the control scheme.