Transient DC Bias Current Reducing for Bidirectional Dual-Active-Bridge DC–DC Converter by Modifying Modulation

Transient dc bias current will appear in dual-active-bridge (DAB) dc-dc converter when power changes, resulting in transformer core saturation. Traditionally, a transitional period with extra calculation is added in the transient process to keep the voltage-second balance and eliminate the dc bias current for the DAB converter. In this article, the modulation process rather than the phase-shift control is concerned, and the transient dc bias current can be reduced or even eliminated by staggering the load time of the primary bridge and secondary bridge compare values. The modulation scheme with this modification does not need any transitional period or extra calculation, and the time delay in the closed-loop control is constant and smaller than the previous schemes. Besides, as only the load time is modified, the modulation scheme can be implemented in all the phase-shift control methods and the whole operation range. The experimental results verify the theoretical analysis and show the practical feasibility of the modified modulation schemes.