Monitoring and Confirmation Method for Submodule IGBT Open-Circuit Faults in MMCs Under Different Modes

The flexible transmission system for the renewable energy contains multiple modular multilevel converters (MMCs) working in different modes. The reliable operations of MMCs are vital to the premium operation of the transmission system. The fault detection scheme is an available method to guarantee the reliable nature of MMCs. This paper presents a fault detection scheme for the insulated gate bipolar transistor (IGBT) open-circuit failure inside the submodule (SM). The proposed detection consists of fault monitoring and fault confirmation. The first part is based on the feature that abnormal extra components emerge in the circulating current under IGBT faults. To precisely capture this characteristic, the voltage reconstruction and discrete Fourier transformation based on the sliding windows are adopted. The general characteristics of IGBT faults in the two operation modes are analysed and the pulse signal of the specific SM is used in the fault confirmation part. The two functional parts can significantly relieve the calculation burden by shrinking the fault scope and precisely detect the faulty arm without being influenced by the operation disturbance and fault scenarios. Besides, this detection is efficient in both inverter and rectifier MMCs. The effectiveness of the detection scheme is demonstrated by the studies in Matlab/Simulink.