Transistor Open-Circuit Fault Diagnosis for Three-Phase DAB Converters Using a Reduced Number of Sensors

This work presents a diagnosis strategy of transistor open-circuit faults for three-phase dual-active bridge DC-DC converters. The diagnostic approach evaluates the DC components of the phase currents established due to a fault condition. In addition, as these symptoms are reflected in the DC-side current waveform of the active bridges, this paper proposes a fault diagnosis scheme by measuring only the current from one source side, significantly reducing the number of sensors compared to previous proposals. It is demonstrated that the faulty transistor can be identified within a time interval of less than two switching periods, enabling the implementation of a protection scheme that modifies the modulation strategy to prevent saturation of the transformer's core by the presence of the DC components. In order to verify the practical feasibility of the proposal, the whole transition is evaluated from the moment a fault condition occurs, the proposed diagnostic strategy identifies the failed device, and finally the converter is reconfigured to begin operating in a fault-tolerant mode, operating in its single-phase mode, continuing with the power transfer to the load. The new operating limits are established, corresponding to maximum transferable power and soft-switching operating conditions. Experimental results obtained with a 1.5 kW laboratory prototype under various operating conditions are presented.