Triple-Active-Bridge converter Coupling Power control method for Voltage Balancing in Bipolar DC Distribution

In composing the dc grid, bipolar dc distribution is preferred over unipolar for reasons of efficiency, quality, reliability, stability, and safety. Despite the above advantages, the bipolar system has a voltage imbalance problem due to the difference in the amount of power between the two voltage buses. Therefore, this paper presents the voltage balancing strategy based on a triple-active-bridge (TAB) converter. While previous studies focus on decoupling methods due to the problem of unintentional power coupling in the TAB converter, this paper proposes a strategy to utilize coupling power for voltage balancing of bipolar dc distribution. The control variable of the TAB converter is changed by analyzing each H-bridge power through the Fourier formula and phasor diagram. The proposed method does not require an additional active or passive component, and voltage balancing operation is achieved in both grid-connected mode and islanding mode of dc distribution. The feasibility of the proposed strategy has been verified through PLECS simulation.