Open-Circuit Faults Localization With Error Elimination for Modular Multilevel Converters Under Various Control Modes

The modular multilevel converter (MMC) is an attractive option for high-voltage and high-power applications. Fault localization (FL) is one of the most challenging tasks for the MMC consisting of a large number of power electronic switches. Existing literatures have not provided a complete FL strategy for MMC submodule (SM) capacitor voltage tangency under different voltage balancing strategies as well as modulation methods. This article proposes an FL strategy for the MMC under open-circuit fault, which is suitable for the MMC controlled by both pulse wide modulation (PWM) and nearest-level modulation (NLM). This article also considers the error during computing process based on fault characteristic, which eliminates error between adjacent calculation steps, and the faulty SM can be effectively located by the proposed strategy without the effect of computing error. The proposed strategy is implemented by simulation with MATLAB/Simulink and by an experiment with a downscale MMC prototype. The experimental results confirm the effectiveness of the proposed strategy.