High frequency transformer design for modular power conversion from medium voltage AC to 400V DC

The paper presents a high frequency modular medium voltage AC (4160 VAC and 13.8 VAC) to low voltage DC (400 VDC) power conditioning system block (PCSB) that are scalable so that they can be used for micro grids of different scale (several-hundred kW to multi-MW). The modular approach is intended to result in higher-volume, lower-cost, less-loss power electronics building blocks that service many applications, such as DC data center and electric vehicle charge station. In this paper, a 225kW, 500 kHz PCSB is demonstrated to direct converter 4160 VAC to 400V DC for a DC date center. WBG power devices and CLLC resonant converter are used to minimize switching related loss at high frequency. The high frequency transformer of CLLC resonant converter is one of the key elements for the proposed modular approach. This paper will focus on high frequency transformer design to realize high-voltage-isolation, high-efficiency and high-density at the same time. Based on a split winding transformer structure, transformer insulation material and dimension parameters are determined referring to insulation standard. Transformer magnetic loss model is reviewed based on which loss design trade-off is carefully analyzed. Finally a 500 kHz transformer prototype has been developed and demonstrated with 30kV isolation capability, whole CLLC resonant converter holds 98% peak efficiency and 48 W/in3 power density.