A Current Residual-Based Open-Circuit Fault Diagnosis Method for Cascaded H-Bridge Multilevel Converters

The increasing importance of cascaded H-bridge multilevel converters (CHBMC) in supplying electrical energy to loads or grids places a higher priority to detect and protect against fault conditions. This paper proposes a simple open-circuit fault diagnosis method for CHBMC by analyzing the current residuals in the output side. Comparing the estimated output current with the calculated current, the change features of current residuals are extracted to detect and isolate single or multiple faulty switches. Compared to the existing approaches, the proposed method can detect and identify multiple faulty switches in the different faulty cells. The fault feature extraction of different cells is independent, which ensures that the fault diagnosis between cells is not affected each other. Furthermore, all of specified parameters can be obtained directly. And the diagnosis time is within three control periods under the appearance of fault features. Finally, simulation and experiment results have verified the applicability and effectiveness of the proposed method.