A Counter-Based Open-Circuit Switch Fault Diagnostic Method for a Single-Phase Cascaded H-Bridge Multilevel Converter

A cascaded H-bridge multilevel converter (CHBMC), which is composed of power cells, is an attractive ac–dc converter for medium- and high-voltage applications in terms of its modularity, improved harmonic performance, and higher rated voltage withstand capability. Nevertheless, the overall operation and stability of the CHBMC can be affected by inevitable issues, such as the open-circuit (OC) switch fault. This issue causes adverse effects. Hence, it is vital to develop an effective but straightforward method to identify the OC switches. This article proposes an OC switch fault diagnostic method, which is based on counters. These counters are defined to have a one-to-one correspondence with the CHBMC switches. First, a fault feature variable is obtained based on a current residual generated from the estimated current model and the OC switch fault output voltage conditions. Subsequently, based on a postfault logic judgment process, the output voltage levels, the driving signal combinations, and the current polarity, the counters indicate the OC switch fault and its position. The proposed method is simple and voltage level-independent, making it ideal for diagnosing multiple OC switch faults for the CHBMC in a power cell and different cells. The effectiveness of the proposed method is verified by simulation and experimental results.