Multiple commutation failure suppression method of LCC-HVDC transmission system based on fault timing sequence characteristics

Aiming at the problem of commutation failure and the poor transient response of line commutated converterbased high-voltage direct-current (LCC-HVDC) transmission systems, this paper starts from the harmonic components of an AC system fault on the inverter side. The quantitative relationship between the harmonic wave and the trigger angle of the inverter side is derived in detail, and the effect of the trigger on the commutation of the LCC-HVDC transmission system is qualitatively analyzed with a phase-locked trigger. On this basis, an improvement scheme for an anti-harmonic control system is proposed. First, a virtual separated phase-locked control method is used to determine the fault occurrence time. Additionally, the characteristics of the trigger angle of the rectifier side and extinction angle of the inverter side after the fault are used to determine the fault position and generate the corresponding fault timing sequence. Then, the generated fault timing sequence is used to control the notch filter and modify the input voltage of the voltage-dependent current order limiter to improve the robustness of the control system in terms of the harmonics. Finally, based on CIGRE benchmark LCC-HVDC transmission system model, the advantages of the improved method are verified. The results can provide a reference for actual projects.