Open Circuit Switch Fault Detection in Flying Capacitor and Cascaded H-Bridge Multilevel Converters

This article proposes a simple and fast active power device open circuit fault detection and localization technique. The proposed technique applies to the family of flying capacitor multilevel converters (FCMCs), including dc/dc FCMCs, single or multi-phase H-bridge FCMCs, and cascaded H-bridge multilevel converters. The localization technique needs to sense the voltage and direction of current at the output terminals of converters to detect and localize the fault. A circuit with multiple window detectors is utilized to track the output voltage level and current direction with high bandwidth. The algorithm compares the measured and expected terminal voltage, considering the commanded switch states and the terminal current direction. Once potential fault locations are identified, healthy switches are filtered out from the set of potential faulty switches over successive switching transitions. The proposed technique is experimentally validated on a single phase H-bridge FCMC. The switch state commands and pulsewidth modulation (PWM) is handled by a DSP while the fault detection and localization algorithm is implemented on a separate field programmable gate array (FPGA). The asynchronous operation of the DSP and FPGA is discussed.