Switch Open-Circuit Fault Detection and Localization for Modular Multilevel Converters Based on Signal Synthesis

The open-circuit fault detection and localization (FDL) scheme plays a significant role in improving the reliability of modular multilevel converters (MMCs). This article presents a simplified signal synthesis-based FDL scheme with good generality and robustness. The proposed FDL scheme exploits the characteristics that the capacitor voltages of faulty submodules (SMs) have different patterns and higher values than those of healthy ones. Based on this knowledge, certain signature voltage signals are selected, and waveforms consisting of such signatures are reconstructed by the signal synthesis technique to detect and localize the fault. The proposed scheme is suitable for both low- and high-voltage MMCs since the computational complexity does not change with the number of SMs. The scheme does not rely on system parameters, which makes it immune to parameter uncertainties, and there is no need for any additional sensors. Both single and simultaneous multiple faults can be handled with the proposed scheme. Simulation and experimental results validate that the proposed approach based on the signal synthesis method can effectively detect and localize the fault accurately under different loading conditions and has robustness against load change and circuit parameter uncertainties.