A Thyristor-Based Multiline Hybrid DCCB in Protection Coordination With MMC in Multiterminal DC Grids

Protection against dc short circuits is a crucial challenge in multiterminal direct current (MTDC) grids due to the low-impedance characteristic of the dc grids. One of the promising solutions is using the multiline hybrid dc circuit breakers (MLH-DCCB), which recently acquired more attention owing to decreased power electronic devices, coordination capability, and selective fault isolation. This article presents a protection strategy employing a Thyristor-based MLH DCCB in coordination with the half-bridge modular multilevel converter (HB-MMC). The main merits of the proposed method are 1) limiting the fault current using the coordination technique between MMC and the proposed MLH DCCB; 2) employing a smaller size of current-limiting reactors and lower DCCB short circuit interruption requirement; 3) presenting the cost-effective and reliable protection system; and 4) providing the fast fault-clearing period and grid restoration procedure. The performance of the proposed coordinated dc fault protection strategy is validated in a four-terminal HVDC grid by the Typhoon HIL-404 real-time digital simulator. Also, the scaled-down dc grid prototype is implemented in the laboratory, and the experimental results are presented to confirm the theoretical analysis. A comprehensive comparison with the other protection approaches proves its superiority and effectiveness in terms of economy and fault-clearing performance.