Evaluation of commutation failure risk in single- or multi-infeed LCC-HVDC systems based on equivalent-fault method

In single- or multi-infeed line-commutated converter-based high-voltage direct current (LCC-HVDC) systems, commutation failure (CF) induced by alternating current (AC) faults may lead to serious consequences. Considering the randomness of fault occurrences, an accurate evaluation of the CF risk (CFR) from the system point of view becomes necessary in power system planning and operation. This paper first provides a definition of the CF severity (CFS) index corresponding to an AC fault. Then, on the basis of electromagnetic transient (EMT) simulation, an approach to calculate the CFS index considering the randomness of fault-occurrence time is presented. A novel equivalent-fault method is further put forward to make the EMT simulation scalable to calculate the CFS index in terms of a fault occurring in a large-scale receiving-end grid. Thereafter, the CFR index is introduced, which is defined as the sum of the products of the CFS index of each AC fault and the corresponding fault rate. Finally, the proposed method is verified on the modified IEEE 9-bus and modified IEEE 39-bus systems using PSCAD/EMTDC.