OC Switch Fault Diagnosis, Pre- and Postfault DC Voltage Balancing Control for a CHBMC Using SVM Concept

The voltage imbalance and the open-circuit (OC) switch fault present significant issues for a single-phase cascaded H-bridge multilevel converter, leading to negative effects such as unbalanced dc voltages, overshoot current, and high current harmonics. To address these challenges, this article presents a novel technique for OC switch fault diagnosis and dc voltage balancing control using the space vector modulation (SVM) concept. Initially, this article provides an analysis of the SVM technique, which efficiently controls the dwelling time of the vector to generate driving signals. Leveraging the advantages of SVM, a voltage residual is employed as a detection variable. Subsequently, an active vector transition scheme is devised to identify the OC switch in a power cell-by-power cell manner. Furthermore, a prefault selection principle for redundant vectors is implemented to achieve power cell voltage balancing, considering voltage differences, and ensuring smooth voltage level transitions to minimize switching losses and voltage stress. In addition, by optimizing the vector arrangement based on the reduced vector range in the postfault condition, the proposed technique optimizes current harmonics and maximizes voltage output capability while maintaining smooth switching transitions. Finally, the effectiveness of the proposed technique is verified through the simulation and experimental results.