Line commutated converter based high voltage direct current (LCC-HVDC) links are widely employed for long distance bulk power transmission and asynchronous alternating current (AC) grid connections. However

LCC-HVDC systems often suffer from commutation failures when AC voltage is distorted

oscillating or reduced by AC faults

which leads to overheating of converter valves and interruptions in transmitted power. All of which can have an adverse impact on the safety and stability of the entire power system. This paper proposes a supplementary control for mitigation of successive commutation failures on the basis of analyzing the influence of phase-locked loop (PLL) dynamics on the commutation process. By analyzing the impact of PLL dynamics on the actual leading angle

it is found that changes in the AC voltage phase remarkably influence commutation. Accordingly

the error between the AC voltage phase and PLL's output angle is added to the output of the extinction angle or DC voltage control to mitigate the successive commutation failures of LCC-HVDC stations. Simulations conducted on the CIGRE benchmark model in PSCAD/EMTDC validate the performance of the supplementary control

which effectively mitigates successive commutation failures.