A New Model-Based Fault Detection and Localization Scheme for Cascaded H-bridge Multilevel Converter

In this paper, a new model-based fault detection and localization algorithm is proposed for cascaded H-bridge (CHB) multilevel converter to localize the open-circuit faults without the use of any additional sensors. Using DC bus voltages, switching states and grid voltage, grid current is estimated and compared with the measured grid current. Any significant deviations in the estimated and actual grid current of the CHB trigger an open circuit (OC) fault. Upon open circuit fault detection, the modulation scheme is altered from phase-shifted unipolar SPWM to phase-shifted bipolar SPWM for fault localization. At selected time instants, the change in measured grid current for a period of 5T s (T s being the step time of controller) is calculated and compared with the estimated change in grid current from the system model. The above-mentioned comparisons are used to localize the open-circuit faults in the CHB. The proposed method is verified on a scale-down CHB prototype and experimental results are presented to demonstrate the effectiveness of the proposed method.