Stable and Passive High-Power Dual Active Bridge Converters Interfacing MVDC Grids

Dual active bridge (DAB) is a topology that is receiving more and more attention as a potential solution to interface dc grids of different voltage levels. From a system level, the implications of DABs on the stability of complex power systems are addressed in this paper. Dynamics modeling and stability assessment for a DAB implementation aimed to interface low-voltage energy resources with medium-voltage dc (MVdc) collection and distribution grids are presented. The DAB admittance is analytically derived and assessed in order to describe its dynamics and anticipate its behavior when integrated in a complex MVdc grid. The model considers the low-frequency range, mostly dominated by the controller action, and the high-frequency range, described by a nonlinear operation. The theoretical analysis is verified by hardware-in-the-loop emulation, with the controller running on a digital signal processor. The proposed implementation is proved to achieve passivity in the whole spectrum, which undoubtedly is a desired feature for massive power electronics integration in the future MVdc grids.