A Hierarchical Identification Method of Commutation Failure Risk Areas in Multi-Infeed LCC-HVDC Systems

In the multi-infeed LCC-HVDC system, the concurrent commutation failure (CCF) caused by the AC fault of the receiving-end system may lead to the blocking of multiple converter stations, which challenges power grid security and stability. This paper proposes a novel method to quickly and accurately identify the CF risk areas, considering the CF probability (CFP) during the single-line-to-ground (SLG) fault. First, an AC-DC voltage asymmetry factor (ADVAF) and its theoretical derivation are proposed to quantify the influence of the fault position on the CF. Second, the critical ADVAF (CADVAF) is derived based on the equivalent method. By comparing ADVAF and CADVAF, the CF risk areas can be quickly divided into non-, possible- and inevitable-concurrent CF risk areas. Third, the relationship between local CFP (LCFP) and fault position is established, and the concurrent CFP (CCFP) is calculated. The proposed method has improved the accuracy and computational efficiency of theoretical analysis than earlier methods. Finally, the validity and accuracy of the proposed method are verified in dual-infeed and five-infeed LCC-HVDC systems built based on the IEEE 39-bus and IEEE 118-bus models, respectively.