Asymmetrical-Bidirectional ISOP Modular DC–DC Converter in DC Distribution Grids with Renewables

Interlinking dc-dc converters are essential in urban-area dc distribution grids to interconnect the medium-voltage (MV) and low-voltage (LV) buses. The increasing installation of renewable energy sources at the LV side will result in backward power flow through these converters, which is usually less than the forward power. This article presents an asymmetrical-bidirectional input-series output-parallel (AB-ISOP) dc-dc converter with a partial-scale backward power rating to satisfy the above realistic requirement. Single-active bridge (SAB) and dual-active bridge (DAB) converter modules are combined in the proposed structure: the unidirectional SABs process most of the forward power, while the bidirectional DABs provide passage for the backward power flow. A string of embedded nonisolated resonant dual active bridge (NRDAB) converters is constructed at the input stage to realize natural power coupling and voltage sharing. Compared with the all-DAB ISOP scheme, the proposed one requires fewer devices and presents higher conversion efficiency as active switches are omitted at the secondary side of SABs. Experiments conducted on the downscale prototype verify the operating principles and performance of the proposed converter.