Modeling of a Hybrid Distribution Transformer Without Series Coupling Transformers

Distribution grids require new solutions to cope with the negative consequences of the new kinds of loads that are supplied. In this scenario, effects such as high-amplitude grid voltage variations are expected due to the highly variable penetration of renewable energy systems, as well as voltage and current harmonics due to the nonlinear loads. The Hybrid Distribution Transformer (HDT) has been proposed as a solution to solve future grid problems, combining a conventional transformer with a power converter stage. Typically, the series converter is integrated into the medium or low-voltage grid through coupling transformers or by an additional winding of the main transformer, increasing the weight and volume of the solution. Therefore, this work proposed an HDT in which the series converter is directly connected to the medium voltage windings of the distribution transformer, operating at low current levels. The galvanic isolation is delivered by an intermediate isolated DC/DC stage based on Dual-Active Bridge (DAB) converters. The model and control of the proposed HDT are presented and confirmed by simulation results.