I. Introduction
The dual active bridge (DAB) converter is widely used in new energy applications for its high power density and high efficiency [1]–[5]. For power electronic transformer (PET), DAB converter has significant features comparing with the traditional power frequency transformer: on the one hand, high-frequency transformer makes the system obtain higher efficiency and controllability, and the power switch device of primary and secondary H bridge can realize soft switch control and reduce switching loss [6]; on the other hand, it could improve the power density of system with the smaller size and lighter weight.