A Multiport Power Electronic Transformer With MVDC Integration Interface for Multiple DC Units

This article proposes a modular input-independent output-series (IIOS) multiport dc power electronic transformer (MDCPET), which can interface with multiple dc units, such as photovoltaics (PV) array, storage devices, and dc loads, directly to the medium-voltage dc (MVDC) bus. Meanwhile, the IIOS structure can provide good galvanic isolation and one-stage power conversion between dc units and the MVDC grid, which indicates that the proposed topology has lower cost and less number of converters when compared with the traditional dc distribution network. The main challenge is the submodule (SM) output voltage imbalance problem of the IIOS architecture due to the different input power of different dc units. To realize SM output voltage equilibrium, an isolated series resonant dual active half-bridge converter based on multiwinding coupled-inductor is developed. The first SM is retained and it is connected to the low-voltage direct current (LVDC) bus to ensure the MVDC bus voltage remains constant when MDCPET is disconnected from the MVDC grid. In addition, the zero-voltage switching of all active switches can be achieved to improve the system transmission efficiency. The proposed MDCPET can operate stably in both the on-grid and off-grid conditions. Finally, the four-SM MDCPET simulation and downscale experimental platform are carried out to verify the above theoretical analysis.