A Modular Multiport DC-DC Converter With MVDC Integration for Multiple DC Units

This paper deals with a modular input-independent output-series (IIOS) multiport dc power electronic transformer (DCPET), which can interface with multiple dc units (such as PV array, storage devices and dc loads) to the medium-voltage dc (MVdc) bus directly without extra low-voltage dc (LVdc) converters. Therefore, the number of converters and the system expend are greatly reduced and saved when compared with the conventional dc distributed network. Due to the input power of these dc units are different and the multiple modules are in serial connection on MVdc side, which will lead to the output voltage imbalance between submodules (SMs). By inserting a single LC branch between adjacent SMs to transfer the differential power in the proposed topology, SM output voltage mismatched problem can be solved. Moreover, all SM power switches can realize zero voltage switching (ZVS), which further ameliorates the system efficiency. Finally, the above theoretical analysis is verified by simulation and experimental results, and the proposed multiport PET can operate stably in different working states.