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

The bipolar dc distribution has many advantages compared with the unipolar type. The triple-active-bridge (TAB) converter is a popular topology for the implementation of bipolar dc distribution due to its dual-output structure. However, the unbalanced output voltages caused by the asymmetric load condition is a big issue. This article proposes a voltage balancing integrated transformer to achieve the output voltage balancing in the TAB converter without requiring any additional balancer circuits or dedicated control schemes. In this article, the high-frequency transformer and two external inductors in the conventional TAB converter are merged into a single magnetic structure. As a result, the desired voltage balancing is automatically achieved and the power density of magnetic components in the converter can be increased. The voltage balancing performance of the proposed integrated transformer was tested with a 4-kW experimental prototype under severely unbalanced load conditions, and the imbalance of the output voltages is reduced to less than 1.6% where the conventional TAB converter shows 80% unbalanced results. In addition, the power density of magnetic components increased by 35% (7.9–10.7 kW/L) and the total loss of magnetic components is reduced by 19%.