Triple-Active-Bridge Converter With Automatic Voltage Balancing for Bipolar DC Distribution

The bipolar dc grid outperforms the conventional unipolar dc distribution in terms of quality, flexibility, efficiency, reliability, transmission capacity, and safety. Despite many advantages, it has a voltage imbalance problem. Unbalanced and asymmetrical load conditions are the major contributors to this imbalance. This article proposes the triple-active-bridge converter with an automatic voltage balancing capability for bipolar dc distribution that eliminates the need for a dedicated voltage balancing controller and any additional active/passive components. Furthermore, along with the bidirectional power flow feature of a converter, the proposed method utilizes the magnetic integration of a converter's existing inductors. This voltage balancing coupled inductor offers the required inductance for power transfer and zero-voltage-switching, over and above provides effective voltage balancing without increasing the magnetic volume of a converter. The proposed method does not require an individual output voltage sensing and moreover; it decreases the complexity by reducing the system from two control variables to one. A 5-kW prototype is tested under an extreme-unbalanced load condition during the steady-state and as well as during transients. The analysis and experimental results are presented to validate the performance.