Unified state-space modeling method for dual-active-bridge converters considering bidirectional phase shift

In this paper, unified modeling method for dual-active-bridge (DAB) bidirectional converters (BDCs) considering bidirectional phase shift is proposed. There is only one model, and it is shared by both positive and negative phase shift. DAB and its extended converters are widely used in energy storage systems. These converters are regulated by duty cycle plus phase shift. The existing modeling methods model these converters in positive and negative phase shift directions respectively. Though the two models are built in similar ways, they are not the same. Hence they are hard to be utilized in applications where phase shift direction changes. Therefore, a modeling method to build only one model for both phase shift directions is desired. In this paper, a conjugate shifted phase based superposition technique is proposed to facilitate the proposed bidirectional unified modeling method. By this technique, voltage on the shifted side of the transformer is expressed in a superposition form, which represents both situations of positive and negative phase shift simultaneously. This superposition form will collapse to actual form, once the shift direction is given. Hence situations in both directions are unified. Besides, a newly proposed current division technique is integrated into this method for high model accuracy. A buck-boost coupled dual-active-half-bridge (DAHB) converter is selected to describe the method. The only one large-signal model for both phase shift directions is established, so as a small-signal model. Simulations and experiments have validated the proposed modeling method and its high accuracy.