Transient system-level simulations of future DC grids require modeling the behavior at the terminals of the power system's components, and thus also of power converters. The internal electrical variables of the power electronic devices are not relevant in such simulations. Based on this, this paper presents an approach for eliminating all the internal electrical nodes of a single-phase Dual-Active Bridge DC-DC converter for EMTP-type simulations. Nonetheless, the switching dynamics at the terminals of the converter are maintained, while the dynamic effects of the converter-internal circuitry like transformer and capacitors are accounted for. By reducing all internal nodes of the converter model, the computational burden is reduced, which is especially important for system-level simulations of large grids. The approach presented here is a first step towards a similar implementation for the three-phase Dual-Active Bridge DC-DC converter topology, a promising converter topology for future DC grids.