A Diagnosis Strategy for Multiple IGBT Open-Circuit Faults of Modular Multilevel Converters

Multiple insulated gate bipolar transistor (IGBT) open-circuit faults severely affect the reliable operation of modular multilevel converters (MMCs). The existing literatures have not provided an effective diagnosis algorithm for MMCs when multiple IGBT open-circuit faults simultaneously appear in one arm. This article presents a diagnosis strategy to handle that condition. Fault detection and estimation of the faulty submodule (SM) number is implemented by checking the value of the arm voltage error. The faulty SMs are located by observing when the transition of their switching functions leads to an obvious change of the arm voltage error. Meanwhile, the errors between the measured and predicted capacitor voltages are utilized to accelerate the localization. All of the faulty SMs can be quickly located one by one within several control cycles by using the proposed localization method. Simulation and experimental results demonstrate the validity of the proposed diagnosis strategy.