Open-Circuit Fault Diagnosis for MMC Based on Event-Triggered and Capacitor Current State Observation

The module multilevel converter (MMC) is composed of dozens of the insulated gate bipolar transistors (IGBT) and its reliability should be seriously considered. This brief presents a fault diagnosis and localization (FDI) method for open-circuit fault of the IGBT in an MMC, which combines event-based capacitor voltage with capacitor current state observation. Under the event-triggered mechanism, the fault diagnosis program is activated only when the capacitor voltage of submodules (SMs) violated the designed event-triggering condition, which can effectively reduce the computational burden for the controller. The current direction of the capacitor will change when the submodule has an open-circuit gault. This characteristic is extracted and used for diagnose and locate the fault IGBT by comparing the observed value with the theoretical value of capacitor current. The proposed FDL method can effectively reduce the computation intensity of the controller and do not require extra hardware. Simulation results show that the proposed FDL can diagnose and locate the open-circuit fault of IGBT accurately within two fundamental periods.