I. Introduction
A dual active bridge (DAB) converter is an isolated bidirectional dc-dc converter. Its advantages include flexible power flow control, zero voltage-switching, high efficiency, and modular structure, which make it useful for a wide variety of modern power-distribution systems. In particular, DAB converters play an important role in many multi-converter systems, such as dc micro grids [1], automotive power systems [2], electric ships [3], and electric aircrafts [4].