An IGBT Open-Circuit Fault Diagnosis Method for Grid-Tied T-Type Three-Level Inverters

This paper presents a novel method to diagnose IGBT Open-circuit (OC) faults in grid-tied T-type three-level (T3L) inverters. The average values of the inverter-side line voltage deviations during a switching period are compared with thresholds to diagnose the faults. In the T3L inverter, OC faults in the leg IGBT and the middle IGBT may show the same faulty characteristics. To identify the exact faulty IGBT accurately and quickly, the diagnosis process is divided into two steps. Step one, detect the fault in normal three-level operation; Step two, identify the fault in fault-tolerance operation where the faulty leg works in two-level mode. With the average model, this method requires only signals available in the controller. Therefore, no extra sampling or diagnosing circuits are needed. In addition, error-adaptive thresholds are adopted to make the method robust. Hardware-In-Loop (HIL) experimental results are used to verify the effectiveness.