Universal Transient DC-Bias Current Suppression Strategy in Dual-Active-Bridge Converters for Energy Storage Systems

The dc-bias current may result in the magnetic flux saturation and endanger the safe operation of switching devices. By regulating the inductor current slope during the transient, this article proposes a novel transient phase shift control (TPSC) to suppress the dc-bias current in dual-active-bridge (DAB) converters, which is universal for different phase shift control strategies. First, the dc-bias current models under different transient scenarios are built. Then, the optimal switching transient is determined so that the proposed TPSC is able to achieve the possible maximum inductor current slope and the shortest settling time. Furthermore, the settling time is independent of the specific circuit parameters, such as inductance, which improves the universality of the proposed TPSC algorithm. With the TPSC, the inductor current slope, which depends on the appropriate combination of bridge voltages in DAB converters, becomes the sole variable in the practical algorithm implementation. Moreover, the inductor current can be changed linearly rather than in a piecewise linear way. Thus, the implementation of the TPSC becomes straightforward and the complicated calculations in conventional methods are avoided. The proposed TPSC was compared with other advanced dc-bias eliminating strategies experimentally under different transient scenarios. The results show that the TPSC can successfully eliminate the dc-bias current, and the transient process can be accelerated within 12% of a switching cycle.