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Adding capacity to an existing electric power distribution network using a solid state transformer system

In this paper, an approach to add capacity to an existing line-frequency transformer (LFT) in distribution networks using solid state transformers (SSTs) is proposed. This new concept facilitates capacity addition without significant increase in footprint and complexity. A closed loop control is proposed to regulate power sharing. The proportion of power handled by the SST and LFT is decided based on load conditions. Further, an AC-AC multi-level buck converter can be incorporated in the concept to adapt to different distribution voltage levels. This paper discusses the operation, modeling and design of the proposed topology for a target load of 100 kVA and 0.9 power factor. Simulation results demonstrate that the topology can control the amount of power handled by the SST. A scaled-down laboratory prototype was designed and experimental results prove the main functionality of the topology.