A Fast Diagnosis Scheme for Multiple Switch Faults in Cascaded H-Bridge Multilevel Converters

The increasing importance of cascaded H-bridge multilevel converters (CHBMCs) in high-power applications requires a higher priority to detect and protect against fault conditions. In this article, a current residual-based diagnosis scheme is proposed for the CHBMCs without additional sensors. On the premise of filtering the sampled dc voltages, comparing the calculated actual values of output current with the expected values in the control system, normalized diagnostic variables are established to localize single or multiple open-circuit switches. Benefit from the diagnostic variables corresponding directly to the switches of each H-bridge, this method can be easily extended to the CHBMCs with arbitrary submodules. Furthermore, the parameter estimation and enhanced detection algorithm are introduced to ensure the immunity of the diagnostic method to the large parameter changes and measurement noises. The faulty component can be accurately diagnosed within one line cycle regardless of the faulty modules and operating conditions. The effectiveness of the proposed method is substantiated using experimental results from the hardware platform of the CHBMCs.