Investigation on different negative sequence current control options for MMC-HVDC during single line to ground AC faults

This paper presents the effect of the negative sequence current control strategy of an MMC-HVDC system on the single-line-to-ground (SLG) fault response of the high AC transmission lines. Four different methods reported in the literature are compared. The paper shows that the negative sequence current suppression by the MMC-HVDC station demonstrates increased double-frequency power oscillations in the DC link and high over-voltages in the AC terminals during single line to ground faults. On the other side, the adequate control of the negative sequence current during unbalanced faults in the grid improves the observed DC link voltage and power ripples. Furthermore, the negative sequence current injection, increases the zero sequence current amplitude measured at the PCC of the MMC-HVDC station. The later, enhances the fault detection capability of protection schemes in the AC transmission during SLG to ground faults in the vicinity of the MMC substation.