In this paper, the multi-frequency modeling technique is adopted to derive a general small-signal model for various DAB resonant converters, based on which, the explicit expressions of the associated transfer functions as well as the general control block diagram of DAB resonant converters are obtained. At last, a simulation circuit of a DAB series resonant converter is built, and the phase-shift-angle-to-output-voltage transfer function is measured to validate the proposed model.