Voltage Balancing for Triple-Active-Bridge Converter Using Integrated Transformer

The bipolar dc grid has many advantages compared with the unipolar dc grid. The triple-active-bridge (TAB) converter is a popular topology to implement the bipolar dc grid due to its dual-output structure. However, the voltage imbalance caused by the asymmetric load condition is a major issue. This study proposes an integrated transformer to achieve voltage balancing in the TAB converter without the need for any additional balancer circuits or dedicated control schemes. In this study, the high-frequency transformer and two external inductors in the conventional TAB converter are integrated into a single magnetic structure. As a result, the desired voltage balancing is automatically achieved, and the total magnetic volume in the converter is reduced. The balancing performance of the proposed integrated transformer was experimentally confirmed using a 4 kW prototype under severe unbalanced load conditions, and the results were compared with those of the conventional TAB converter.