Subsequent commutation failure suppression control for LCC-HVDC system based on fuzzy clustering

Line-commutated converter based high voltage direct current (LCC-HVDC) may experience subsequent commutation failure (SCF), following the first commutation failure (CF). The SCF could create a series of serious disturbances to the AC grid and DC system, which may lead to large power reduction or even system instability issues. To prevent its occurrence, a SCF suppression control strategy based on fuzzy clustering and identification approach is proposed in this paper. First of all, the similar dynamic behavior, of DC side electrical quantities, in different types of AC fault at the inverter side are revealed and validated by theoretical analysis and simulation. Then, the transient responses information of the selected DC side electrical quantities at the rectifier side are collected in an offline preset specific AC fault. To identify the inverter transient stage, a mapping relationship between the selected DC side electric quantities, during the transient stages of the preset fault conditions, is established by fuzzy c-means (FCM) clustering algorithm. Finally, an approach to inhibit SCF by directly adjusting the firing angle at the rectifier side is proposed based on the mapping relationship. Simulation results show that the proposed control method, which is realized by detecting the local DC-side electrical quantities at the rectifier side and quickly identifying the transient stage of the inverter, can effectively inhibit SCF by directly regulating the rectifier firing angle.