A Modular Multiport DC Power Electronic Transformer Based on Triple-Active-Bridge for Multiple Distributed DC Units

This article deals with a modular input-independent output-series (IIOS) multiport dc power electronic transformer (MDCPET). The IIOS structure allows for the connection of multiple dc units, such as photovoltaic (PV) arrays, storage devices, and dc loads, directly to the medium-voltage dc (MVdc) bus. This topology offers splendid galvanic isolation and less power conversion stages between dc units and the MVdc grid. Therefore, it has lower cost, and requires fewer number of low-voltage dc-dc converters and switches compared to the traditional dc distribution networks. The main challenge lies in the submodule output voltage imbalance problem of the IIOS architecture, which is caused by the varying input power of multiple dc units. To address this problem and achieve submodule output voltage equilibrium, an isolated series resonant converter is developed without the need for additional switches. In addition, the zero-voltage switching of all active switches can be achieved to improve the system efficiency. And the proposed MDCPET can operate stably in both on-grid and off-grid conditions. Finally, the six-submodule MDCPET simulations and down-scale experimental platform are carried out to verify the above theoretical analysis.