Simulation and Analysis of Multilevel DC Transformer Using Different Dual-Active-Bridge DC- DC Converter Models

The DC transformer is an interface device between AC and DC distribution networks. In order to simulate multiscale transients, the DC transformer models are developed using different Dual-Active-Bridge (DAB) DC-DC converter models, and different voltage source converter (VSC) models. Three different models of the converters are considered: detailed model, switching function model, averaged model. Furthermore, a multilevel DC transformer model is developed based on cascading DAB modules. The proposed models are implemented in PSCAD/EMTDC. The simulation results show that the detailed and switching function models of DC transformer produce accurate results, while the averaged model provides an efficient simulation with large time-step sizes.