Study of Superconducting Fault Current Limiters for MMC-MTDC with HVDC CBs

To minimize the impact of dc faults in modular multilevel converter based multi-terminal high voltage transmission system (MMC-MT-HVDC, MMC-MTDC), HVDC circuit breakers (HVDC CBs) combined with superconducting fault current limiters (SFCLs) was a preferred choice. For MMC-MTDC with HVDC CBs and SFCLs, this paper firstly analyzed the dc fault characteristics based on the equivalent electrical circuit for different operation stages. Then, this paper introduced the basic principle of resistive SFCLs and inductive SFCLs, and their effect in limiting the dc fault current. Based on the main purposes for installing SFCLs, this paper proposed a dc side main circuit parameters selection method for determining the parameters of the smoothing reactor and the SFCLs. The case studies are performed on a ±500 kV 3-ternimal MMC-MTDC system. The time-domain simulation results showed that both the resistive SFCLs and the inductive SFCLs could limit the dc fault current to a reasonable extend by selecting the proper parameters of the smoothing reactor and the SFCLs, and the energy stress on the voltage limiting element of the HVDC CBs is more severe when using the inductive SFCLs.