Fault Diagnosis and Localization of MMC-Type High-Frequency, High Turns Ratio DC Transformer Submodules

Abstract

Due to the increasingly widespread use of modular multilevel converter (MMC) topology, the fault problem of its bridge arm submodules has become a key issue that cannot be ignored. In the topology structure of the MMC-H type high-frequency high ratio transformer analyzed in this article, due to its high-frequency characteristics and full bridge topology, the sampling accuracy of traditional voltage sensors cannot be met when submodules fail, and general detection criteria can also produce misjudgment results. Therefore, this article analyzes and sorts out the fault characteristics of the submodules after an IGBT open circuit fault based on the new submodule topology structure and the high-frequency characteristics of the system. It judges the variation law of the capacitance voltage of the submodules within a single bridge arm after the fault, and proposes the Grubbs test method based on this. This method can be summarized and organized according to the different increase in capacitance voltage of the submodules on the bridge arm after the occurrence of an IGBT open circuit fault, Then locate the faulty submodule and its specific faulty IGBT through the table lookup method. Finally, the MMC-H DC transformer simulation platform was built through PLECS, and the proposed fault detection method was verified through the simulation platform to locate the fault submodule and detect the faulty IGBT.