Modeling improvements are proposed for systems containing dual active bridge (DAB) converters. First, a systematic approach to constructing models of multi-converter systems is described. The method generates continuous-time large-signal average models that are suitable for system-level analysis and efficient time-domain simulation. Although the base DAB models are derived using generalized average modeling (GAM), the system-level construction does not require the specification of a base period. Secondly, a method of reconstructing currents in the high-frequency DAB transformer is proposed. This method significantly improves accuracy in modeling transformer current, which is a critical weakness of DAB models derived using GAM. Furthermore, the method is applied offline as needed, so it does not affect the computational complexity of time-domain simulation. Both the system-level model construction procedure and harmonic reconstruction method are validated in switching simulations and hardware experiments.