Hybrid modular smart transformer for asymmetrically bidirectional power flow operation

The presence of renewable energy resources in LV distribution networks may lead to distribution transformers, also a Smart Transformer (ST), experiencing the bidirectional power flow. Therefore, the ST must have the capability to operate in both directions. However, the reverse power is less as compared to the forward power, thus the design of ST with the same capacity in both directions increases the hardware cost and decreases the system efficiency. This paper proposes a Hybrid-modular-ST (H-ST), composing by a mixed use of single active bridge-based series resonant converter and dual active bridge instead of complete use of uni- or bi-directional converter adopted in the conventional solid-state-transformer. Based on the proposed H-ST, the impacts of power imbalance among cascaded modules in reverse operation mode are analyzed and then an effective solution based on reactive power compensation combining with the characteristics of the proposed architecture is adopted. The simulation and experimental results both clearly validate the effectiveness and feasibility of the theoretical analyses.