Design considerations of high voltage and high frequency transformer for solid state transformer application

This paper presents overall design considerations of the high-voltage and high-frequency (HV-HF) transformer in dc/dc converter stages of solid state transformer (SST). SST is a new concept of an interface for direct connection between the distribution line and local customers which can be considered as another generation source as well from the local smart-grid point of view. Therefore, the size and weight reduction are the main objectives of this system. Therefore, increasing operating frequency to minimize the bulky magnetic elements and solid insulation become necessary. Especially, the inductance of transformer plays a crucial role in Dual-Active Bridge (DAB) converter to determine the power transfer, therefore, the inductance optimization depending on winding structures is investigated and a high voltage insulation is carefully designed to support 15kV in this paper. A comprehensive electromagnetic analysis is conducted to validate the proposed design by finite element analysis (FEA) and experimental result with 2kVA scale-down transformer is analyzed first and, finally, 3 versions of 7kVA HV-HF transformer are built and tested for SST application.