Topology of a Hybrid DC Circuit Breaker with Coupled Inductor-assisted Current Limiting

[Objective] With the increase in transmission capacity of DC grids， issues such as rapid rise of fault current， high amplitude， difficulty in breaking， and high cost arise in hybrid DC circuit breakers based on fully controlled power electronic devices. To address these issues， this paper proposes a hybrid DC circuit breaker topology with coupled inductors for current limiting. [Methods] In the proposed topology， the primary side of the coupled inductors in the main branch limits the fault current for the first time， and the current-limiting branch limits the fault current for the second time， thereby effectively reducing the fault current rise rate. The secondary side of the coupled inductors in the main branch pre-charges the self-charging capacitor； this remarkably reduces the equipment complexity. Traditional IGBTs and parallel capacitors are replaced by thyristors to switch surge arresters， improving the economy. [Results] The working principle and parameters of each main circuit in the proposed topology were analyzed. On this basis， a four-terminal DC transmission grid system model was established in PSCAD/EMTDC. The proposed topology was then compared with existing topologies via simulations. When a short-circuit fault occurs， the proposed topology further reduces the peak value of the fault-current limit， shortens the breaking time， reduces the energy absorption of the surge arrester， and provides economic benefits. [Conclusions] The analysis shows that the proposed topology affords good breaking performance and certain economic benefits. These findings can provide a theoretical basis for the future application of high-voltage DC circuit breakers in DC transmission grid systems.