An Improved DC Power Electronic Transformer Based on Voltage Balancing Converter for Bipolar Distribution System

This article proposes a bipolar dc power electronic transformer (DCPET) with monopole fault operation capability for medium-voltage/low-voltage dc (LVdc) distributions. Compared with the conventional bipolar LVdc topology, the proposed DCPET considers the reduced number of switching devices and the normal operation under monopole faults, which improves power supply reliability. The dc fault ride-through (FRT) strategy is further proposed in this article to increase the power supply reliability under LVdc short-circuit faults. To reduce the short-circuit current and maintain the LVdc voltage, the switching device reversely series with the capacitor is blocked after the fault. Thus, the fault current is restricted, and power supply recovery time after fault clearance is reduced. Moreover, the LLC resonant converter adopting phase-shift control outputs stable fault criterion current to assist the protection system in locating the fault location and fault removal. Finally, a downscaled prototype is built to verify the proposed topology and FRT strategy through experiments.