Simple Vector Calculation and Constraint-Based Fault-Tolerant Control for a Single-Phase CHBMC

The single-phase cascaded H-bridge multilevel converter (CHBMC) stands out as a prominent topology in medium- and high-voltage applications due to its scalability and modularity. However, the CHBMC may encounter multiple open-circuit (OC) switch faults, leading to significant degradation in both dc voltages and grid current. To facilitate fault-tolerant operation postidentification of multiple OC switches, conventional approaches typically involve adjusting phase angles in the pulsewidth modulation. This, however, results in complex control loops for dc voltage balancing and lacks flexibility. This article proposes a simple fault-tolerant control (FTC) technique based on online vector calculation and a constraint mechanism to simultaneously address multiple objectives, including dc voltage balancing, reduction of grid current total harmonic distortion, and even power distribution following OC switch faults in the CHBMC. Depending on the specific OC switches involved, the voltage levels of healthy or faulty power cells are automatically calculated and adjusted using vector constraints to maintain balanced dc voltages and mitigate current harmonics. Subsequently, the resulting vectors are flexibly determined to meet the requirements of reduced voltage stress and even power distribution. This technique is independent of voltage levels and easily extended to the single-phase CHBMC with more faulty power cells. Experimental results validate the effectiveness of the proposed FTC technique.