Single-Line-to-Ground Fault Section Location for Multi-Terminal DC Distribution Networks

Accurate and reliable identification of single-line-to-ground (SLG) faults is critical to ensuring the safe and stable operation of multi-terminal DC (MTDC) distribution networks. This paper proposes a novel MMC-based control strategy for SLG fault isolation and fault section location, which identifies the fault section while limiting the fault current. First, an improved configuration of the modular multilevel converter’s (MMC’s) converter transformer is proposed to provide a grounded neutral point for the MMC. Second, a zero-sequence current isolation strategy is designed to limit the fault current during SLG faults. Further, a non-power-frequency zerosequence current injection strategy is proposed. After a fault occurs, the MMCs at each terminal inject detection signals with orthogonal frequencies into the network to locate the fault section. A three-terminal DC distribution network model is built in PSCAD/EMTDC, and the proposed control strategy and fault identification scheme are added to the model. Simulation results proved that during an SLG fault, the fault current is limited to below 10 A, and the faulted section can be accurately located even with a fault transition resistance as high as $500 \Omega$.