Submodule Voltage Similarity-Based Open-Circuit Fault Diagnosis for Modular Multilevel Converters

Fault diagnosis is indispensable for the reliable operation of modular multilevel converters (MMCs). This paper presents a submodule voltage similarity-based, real-time, and fast open-circuit fault diagnosis method for MMCs. The proposed fault detection and location (FDL) method is derived based on the similarity analysis of capacitor voltages under both normal and fault conditions. Due to the absence of the discharging current path caused by the open-circuit fault, capacitor voltage of the submodule with the faulty switch will differ from those with healthy switches. This characteristic can be extracted by designing the correlation coefficients of the capacitor voltages at the same arm. With the help of correlation coefficients, the open-circuit fault can be located at the early stage before the capacitor voltage is charged very high. All the data required for the proposed FDL method can be obtained by the available sampled data for the control scheme of MMCs. No extra measurement or hardware is required. Experimental results validate that the proposed FDL method can detect and locate the open-circuit fault rapidly and accurately within one fundamental period.