Fast online diagnosis of open-circuit switching faults in flying capacitor multilevel inverters

Abstract

Flying capacitor multilevel (FCML) inverter is an attractive power converter topology which provides high-quality staircase output voltage waveforms by cascading flying capacitor cells. However, the large number of semiconductor devices utilized in the FCML inverters degrades the hardware reliability, which may constrain such converters from being applied in safety-critical applications. Targeting at open-circuit switching faults, a fast online fault diagnostic method for FCML inverters is presented. Conventional phase-shifted PWM (PSPWM), which can naturally balance the voltage across flying capacitors, is used as the modulation method in this work. Hence, to retain the simplicity feature of the PSPWM, the proposed diagnostic method is developed so that it does not require any voltage measurements of flying capacitors. Only the output AC voltage and current data along with the switching PWM signals from the microcontroller are needed to detect an open-circuit switching fault, and all such sensory data is typically available in the inverter, requiring no additional sensors or hardware for the implementation of this diagnostic method. The detection process takes 5% of the fundamental period of the inverter output signals to diagnose the faulty switch. Simulation and experimental results are presented to verify the effectiveness of the proposed diagnostic method.