Mode Analysis and Identification Scheme of Open-Circuit Fault in a Three-phase DAB Converter

The three-phase Dual Active Bridge (3$-\Phi$ DAB) is a popular DC-DC converter topology for high power applications; it provides high efficiency, bidirectional power transfer capability with galvanic isolation between the input/output terminals. With the wide-scale adoption of such power electronic converters, their reliability becomes increasingly important. A prominent failure mode in the high power converters is the open-circuit fault that occurs due to failure in a semiconductor device or its gate drive circuit. In this study, detailed waveform analyses are presented for the normal and the fault mode operation of the $3-\Phi$ DAB. Main symptoms of the converter during normal and fault conditions have been identified, and a unique pattern in the DC bias of phase currents under fault mode is noted. A logic-based fault diagnosis scheme is proposed to detect the fault and identify the faulty transistor. The scheme requires sensing of currents on only one side of the transformer to detect faults on either side. Therefore, lower-rated current sensors may be placed on the low current side of the high-gain converters, thereby reducing the cost. Moreover, the detection scheme relies only on the DC bias value of the phase currents, implying that low-bandwidth current sensors can be used. Experimental results at 5.5 kW rated power have been provided to verify the analyses and the proposed identification scheme. The study also reveals a new potential benefit of the 3$-\Phi$ DAB converter over the 1$-\Phi$ DAB; i.e., even in the presence of a secondary-side open-circuit fault, the 3$-\Phi$ converter may continue to operate normally. The analyses and the open-circuit fault diagnosis scheme proposed for the 3$-\Phi$ DAB converter will improve the system’s reliability.