Fault Ride-through of Bipolar Short-circuit Fault on Output Side of DC Transformer

DC transformers are widely used in DC distribution networks, and the dual active bridge (DAB), as its core component, may cause overcurrent blocking of the internal switching tubes of the DAB when a short-circuit fault occurs on the output DC side. Such blocking reduces the fault ride-through capability of the system and adversely affects the fault recovery of the system. In this paper, we propose a fault ride-through method for the dual active bridge without latching after a bipolar short circuit on the low voltage side to improve the transient controllability of the system. By connecting inductors in series on the secondary side of the high-frequency transformer inside the dual active bridge, the shift compared to the fault period is regulated, increasing the controllability of the system during the fault. The current stress of the switching tubes is reduced, and the output-side fault current is limited. The above method enables the DAB to provide stable electrical quantity characteristics during faults, which facilitates the fault identification and fault recovery in the DC distribution networks. Simulations based on the PSCAD/EMTDC software are performed for a 20 kV/750 V DC transformer, and the simulation results verify the correctness of the proposed method. © 2022 Power System Technology Press. All rights reserved.