Evaluation of Dynamic Influence of Harmonics of AC System on HVDC Commutation Failure

Currently, most of the works done on the popular problem of commutation failure (CF) in HVDC systems are based on analyzing the fundamental voltage and lack the consideration of the influence of harmonics. This paper uses the method called commutation voltage-time area to analyze the mechanism of the commutation process. We concluded that the commutation area is mainly affected by the harmonic voltage amplitude. Based on the qualitative research of harmonic-related parameters affecting CF, this paper proposes evaluation indexes of CFI through theoretical derivation, and we concluded that the real-time variation of hth-degrees harmonics ratio (HRU
_h
) and CFI can be used to dynamically evaluate the influence of harmonics on CF. By PSCAD/EMTDC simulation analysis and index calculation, we identified voltage distortion caused by harmonic as an important cause for the CF of single-phase asymmetric fault and the subsequent CF of three-phase symmetric fault, and the 3rd, 2nd non-characteristic harmonics produced by the corresponding faults have the greatest influence on CF. Because of CFI has the same variation trend with the total harmonic distortion (THD
_u
), THDu can be used for risk estimation of the CF by AC system faults. Moreover, we found that the harmonics generated by asymmetry fault are more likely to cause CF, and the voltage distortion during the fault recovery is an important cause of the power fluctuation during the recovery of the CF. These research results have important theoretical guiding significance for taking corresponding protection and control measures in engineering and reducing the probability of CF.