DC-Bias Extraction and Elimination of Three-Phase Dual-Active Bridge via Intelligent DC-Link Sensing

This letter proposes a novel DC-bias flux extraction and elimination method to prevent transformer core saturation in three-phase dual-active bridge converters with a minimum count of sensors. Distinguished from the state-of-the-art DC-bias detection method that measures the three-phase currents or flux, the proposed method monitors the DC-link current and recon- structs the three-phase currents by analyzing a few selective sampling points within a single switching period. Thus, DC bias can be conveniently and accurately extracted through dedicated yet simple calculations. A closed-loop control is employed to independently adjust the duty cycles of the primary and secondary phase legs, effectively nullifying the DC magnetic flux bias of three phases. The proposed control is simple, easy to implement, and adaptive to bidirectional power transmission. It avoids the need of bulky DC-blocking capacitors and excessive current or flux sensing circuits, thereby reducing the hardware complexity and cost. Finally, simulation and experimental results validate the effectiveness of the proposed approach.