Universal Flux Balancing Control to Suppress Transient DC-Bias of Phase-Shift Modulated Multi-Active-Bridge Converters

As a multiport version of the bidirectional isolated dual-active bridge converter, multi-active bridge (MAB) has promising applications in energy routers for dc microgrids and more electric aircraft. The power flow control can be primarily realized by applying phase shifts between AC voltages of different ports, whereas the duty cycles of the voltages are additional degree of freedom to optimize the power loss. However, in the transient conditions, the varied phase shifts and duty cycles result in transient dc-bias in the transformer winding currents and the magnetizing flux linkage, which not only imposes significant current stress on the semiconductor devices but also may saturate the high-frequency transformer. To address this issue, this paper develops a generic model of the MAB converter using the superposition theorem, and proposes a universal dynamic phase-shift control for the MAB converter to suppress the transient dc-bias. The highlights of the proposed method are 1) applicability in different modulation schemes and various transient conditions, 2) extendability to arbitrary number of ports for the MAB, and 3) simplicity with a unified analytical solution that can be implemented in an open-loop control. The effectiveness of the proposed control method is validated by simulation results of triple-active bridge and penta-active bridge converters.