Optimized design and electromagnetic analysis of a hybrid type DC SFCL in MMC system

Abstract With the increase of DC transmission voltage and capacity, large dc fault current becomes an important issue due to the bottleneck of the capacity of the DC breaker. In order to solve the problem, we have proposed a novel hybrid type DC superconducting fault current limiter (DC SFCL) in our previous papers. Based on a series of previous researches, some improvements are made to design the hybrid type DC SFCL for application in a MMC system in this paper. The target is to limit short circuit current and avoid converter valves blocked when the DC short circuit occurs. In consideration of cost and stability, combined with the transient characteristics and parameter matching of the DC SFCL, an effective optimization design method consisting of electromagnetic theory and intelligent algorithm is proposed, which can obviously promote the utilization efficiency and stability of YBCO coated conductors. According to the optimization design method, a design scheme of the DC SFCL is put forward. Combined with three operation states of the DC SFCL (normal state, current limiting state I and current limiting state II), a corresponding finite element model is established to simulate and evaluate the performance of superconducting coil in the DC SFCL, which further reveal the AC loss characteristics of superconducting coil during current limiting process.