University of Wisconsin-Milwaukee University of Wisconsin-Milwaukee
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In this paper, the design of a compact high frequency four-port transformer for a Solid-State Transformer (SST) is presented. Unlike other SSTs, the four-port system integrates three active sources and a load port with galvanic isolation via a single transformer core. In addition to this feature, one of the three source ports is designed to operate at medium voltage (MV) 7.2kV, for direct connection to 4.16kV AC grid. The nominal voltage for other ports is 400V. The transformer is designed to operate at 50kHz and to supply 25kW/port. Thus, the proposed system connects the MV grid, energy storage system (ESS), PV and DC load to each other on a single common transformer core. This work focuses mainly on the high frequency transformer design. An extensive study is carried out to obtain the optimal, compact, cost effective, and high efficiency model. In addition, a decoupled control strategy is introduced to control the power flow and load voltage. Modeling, mathematical, and simulation results are derived and presented to demonstrate the viability of the design.