Enhanced Dual-Active-Bridge DC–DC Converter for Balancing Bipolar Voltage Level of DC Distribution System

Conventional dual-active-bridge (DAB) dc-dc converters have a limited structure to balance the bipolar voltage level of the bipolar dc distribution system. Therefore, to regulate the bipolar voltage level, additional voltage balancers are needed for the DAB converters, which eventually requires more devices resulting in low power conversion efficiency and low power density. This article proposes an enhanced DAB dc-dc converter that can balance the bipolar voltage level without the additional voltage balancers. The bipolar voltage level can be tightly regulated under entire unbalanced load condition and even when there is no-load at one side of the dc poles. Besides, its zero-voltage-switching capability can be extended to cover the entire load range, including the no-load condition. Furthermore, the proposed converter can be operated by using a simple single phase-shift modulation. Therefore, its control algorithm can be easily implemented in digital controllers. Finally, the theoretical analysis and the effectiveness of the proposed DAB converter are validated by a 3-kW prototype converter.