Simplified dynamic models and harmonics relationships of hybrid distribution transformer

Hybrid distribution transformer (HDT) represents the next generation of transformers for advanced distribution networks, which are characterized by high controllability. This article employs switching function relationships to derive two simplified dynamic models of HDT: the switching function model and the duty cycle averaged model. Compared with simulation models based on existing MATLAB/Simulink modules, the proposed simplified models built with basic modules demonstrate faster simulation speeds. The instantaneous power balance equation of HDT is derived, revealing how the positive/negative sequence harmonics in grid-side voltage and load current affect the DC-link voltage harmonics of HDT. Both simulations and experiments validate the correctness of the simplified models and harmonic characteristics analyses. The results indicate that the simplified models are close to the simulation models in the low-frequency domain, while their simulation time is dramatically reduced.