Series Voltage Conditioner (SeVC) to Mitigate Commutation Failure in HVDC-LCC Systems

Long-distance HVDC-LCC (High Voltage DC - Line Commutated Converter) transmission utilizes thyristor-based converters and offers advantages such as high efficiency and low cost compared to AC transmission. However, it also suffers from drawbacks such as thyristor commutation failure (CF), a critical issue leading to power interruptions. The concern of CF intensifies when multiple HVDC-LCC inverters are electrically close, causing multi-infeed interaction. To address this problem, this paper proposes the series voltage conditioner (SeVC) to mitigate CF. The SeVC employs six single-phase Modular Multilevel Converters (MMC) based on full-bridge submodules for a 12-pulse LCC. This paper aims to propose the SeVC to provide a feasible solution for real-world applications by achieving high performance in mitigating CF while operating with reduced rated power well below that of the LCC. Additionally, the proposed control method ensures a reduction of submodule capacitance. Simulation results are presented, comparing the SeVC approach with other methods. The results also include the outstanding performance of the SeVC in mitigating CF within the Brazilian power system with its six HVDC-LCC bipoles.