A Real-Time Diagnosis Method of Open-Circuit Faults in Cascaded H-Bridge Rectifiers Based on Voltage Threshold and Current Coefficient of Variation

To effectively diagnose open-circuit (OC) faults in the insulated gate bipolar transistor (IGBT) of a cascaded H-bridge rectifier (CHBR) in real-time, this paper uses a single-phase three-cell CHBR as an example. Through mechanism analysis, the variation patterns of the capacitor voltage and grid current due to OC faults are defined. Based on this, the DC capacitor voltage threshold (VT) and the grid current coefficient of variation (CCV) are introduced as fault diagnosis indices, and a real-time OC fault diagnosis method for CHBR is established. The robustness, accuracy, timeliness, and universality of the proposed method are validated through simulations. The results show that the proposed method exhibits strong robustness when the grid voltage fluctuates, either dropping from 3 kV to 2.85 kV or rising from 3 kV to 3.15 kV. Compared to existing diagnostic methods, the proposed approach requires less diagnostic time, with the faulty IGBT being identified in as little as 3.09 ms under optimal conditions. Additionally, the diagnostic performance remains unaffected by changes in control strategies, making it universally applicable for OC fault diagnosis in CHBR under various control strategies (such as dq current decoupling control, PR current control, and transient current control), with comparable diagnosis results and speeds.