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Transient DC Bias and Universal Dynamic Modulation of Multiactive Bridge Converters

Multiactive bridge (MAB) converters are attracting increasing attention due to their advantages of mutual electrical isolation and bidirectional power flow capability among different ports. However, the presence of transient dc bias in MAB can increase the current stress and lead to transformer saturation, thus affecting the system reliability. This letter establishes a quantitative and general description of the transient dc bias based on the instantaneous middle current of the high-frequency transformer and proposes a general dynamic modulation method to eliminate the bias, which is robust irrespective of the phase-shift modulation methods and the power flow directions. Also, it works at both the normal and startup modes. More importantly, the proposed method can ensure that the high-frequency transformer current reaches to new steady state without transient dc bias within one half cycle. Finally, the MAB experimental prototypes, including a triple active bridge and a modular MAB with a high-frequency ac bus, are built to verify the superior performance of the proposed method.