A Novel Sensor-Reduction Condition Monitoring Approach for MMC Submodule IGBTs Based on Statistics of Inferred On-State Voltage

Condition monitoring (CM) of modular multilevel converters (MMCs) submodule insulated gate bipolar transistors (IGBTs) is of significance to ensure reliable operation. The ON-state voltage of IGBT is a promising indicator to perform CM while its application in MMC is tricky due to high blocking voltage and numerous submodules. In this article, a novel sensor-reduction approach is presented to infer the ON-state voltages of MMC submodule IGBTs. Such an estimation method of the ON-state voltages is based ON Kirchhoffs voltage law (KVL) applied to an MMC arm. This method focuses on a statistical analysis of capacitor voltages and arm voltages. The switching-state combinations are specifically selected for the purpose. A case study is conducted on a single-phase seven-level MMC test bench to verify the proposed ON-state voltage estimation method, which only shows an error of less than 3%. Furthermore, continuous ON-state voltage estimations are made with this MMC test bench under steady-state operations and carry out statistical analysis of the inferred ON-state voltage at various deterioration levels. Finally, a confusion matrix is proposed, whose maximum accuracy reaches 92.4% for the early-deterioration condition.