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Dual-active-bridge (DAB) converters have been widely recognized as one promising topology for high-frequency-link power conversion applications. However, one critical issue concerning DAB converters is the transient dc-bias current due to the voltage-second imbalance, which may occur frequently in typical dynamic operations of DAB converters such as the start-up, sudden load or output voltage change, and power flow direction change. Due to the high-frequency operation, the dc-bias current of DAB converters will impose more harm to magnetic components because of the limited range of operating flux density and possible magnetic saturation compared with the counterpart low-frequency dc-bias current. Over the past several years, extensive researches have been conducted to address the high-frequency transient dc-bias current of DAB converters under different phase-shift modulation strategies such as single phase shift, extended phase shift, and triple phase shift. In this article, a comparative review of typical dc-bias current mitigation strategies under typical phase-shift strategies for DAB converters is presented. An experimental evaluation of selected strategies under various scenarios is conducted in terms of the settling time, inductor current stress, efficiency, switching number, and implementation complexity. This article ends up with an overview of high-frequency dc-bias mitigation strategies and a discussion for the further optimization. [ABSTRACT FROM AUTHOR]

The dc power transmission system has been obviously attracting more research interests in recent years. In order to satisfy the high-reliability requirement of the dc power transmission system, the power converter should be able to keep uninterrupted operation after multiple unexpected faults. However, high fault-tolerant capability usually leads to the bulky redundant circuit, which increases the cost, volume, and complexity of the power converter. Thus, a fault-tolerant dual active bridge (DAB) converter is proposed to maintain the power transferring ability under multiple unexpected open-circuit faults (OCFs) conditions, which can significantly enhance the reliability of the dc power transmission system. By reconfiguring the central-tapped transformer and two symmetrical auxiliary inductors, the half-bridge conduction branch is built to maintain uninterrupted operation when a single or dual OCF has occurred. The proposed fault-tolerant strategy only requires four extra voltage sensors to detect and locate OCFs for the reconfiguration process. Thus, it significantly improves the system reliability with a low additional cost. Besides, the inductor current, transmission power, and the small-signal models of the proposed fault-tolerant converter have been presented. It proves the proposed fault-tolerant topology can smoothly switch between normal and postfault operation due to the constituency of the inductor current. Finally, the 250-W prototype is designed to verify the advantage of the proposed fault-tolerant DAB converter. [ABSTRACT FROM AUTHOR]