This paper proposes a modified threshold virtual impedance (MTVI) control to ensure an AC fault ride-through (FRT) for modular multilevel converters (MMCs). The proposal limits the AC current of the MMC by virtually increasing its output impedance. It prevents to trigger its protection systems when a fault occurs. Compared with conventional TVI control, the proposed method avoids not only MMC blocking but also increases its power quality by providing undistorted voltage and current waveforms in the case of asymmetrical faults. Simulations in MATLAB/Simulink are carried out to validate the effectiveness of the proposed MTVI control, which is compared with the conventional TVI control. The results show the ability of the MTVI control to limit voltage and current perturbations in the MMC and to provide better voltage and current profiles compared to the classical TVI during unbalanced faults.

Sidlawendé OUOBA & Florent Morel

Presented at EPE 2025

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