99 % Efficient 10 kV SiC-Based 7 kV/400 V DC-Transformer for Future Data Centers

摘要： The power supply chain of data centers from the medium voltage (MV) utility grid down to the chip level voltage consists of many series connected power conversion stages and accordingly shows a relatively low ef?ciency. Solid-State Transformers (SSTs) could improve the ef?ciency by substantially reducing the number of power conversion stages and/or directly interfacing the MV AC grid to a 400 V DC bus, from where tens of server racks with a power consumption of several kilowatts could be supplied by individual SSTs. The recent development of SiC MOSFETs with a blocking voltage of 10 kV enables the realization of a simple and hence highly reliable two-stage SST topology, consisting of an AC/DC PFC recti?er and a subsequent isolated DC/DC converter. In this context, an isolated 25 kW, 48 kHz, 7 kV to 400 V series resonant DC/DC converter based on 10 kV SiC MOSFETs is realized and tested in this paper. To achieve zero voltage switching (ZVS) of all MOSFETs, a special modulation scheme to actively control the amount of the switched magnetizing current on the MV and LV side is implemented. Furthermore, the design of all main components and especially the electrical insulation of the employed medium frequency (MF) transformer is discussed in detail. Calorimetric ef?ciency measurements show that a full-load ef?ciency of 99.0 % is achieved, while the power density reaches 3.8 kW/L (63 W/in3).