To diagnose single- and double-switch open-circuit faults in cascaded H-bridge (CHB) photovoltaic (PV) grid-connected inverters

an open-circuit fault diagnosis method based on an adaptive sliding mode observer is proposed. First

an adaptive sliding mode observer is designed using the mixed logic dynamic (MLD) model of the CHB PV inverter

and fault detection variables are constructed based on actual and estimated currents. Second

voltage thresholds derived from the DC-side capacitor voltage are used for fault module localization. Then

fault localization variables are constructed from current residuals

and the variations of current residuals of the adaptive sliding mode observer under fault conditions are compared to distinguish diagonal switch faults. Finally

double-switch open-circuit fault diagnosis is realized by designing an adaptive sliding mode observer based on the previous fault state. Experiment results show that the proposed method can accurately identify single- and double-switch faults at any position within one fundamental cycle

with fast diagnosis speed and strong robustness.