High-Efficiency and High-Power-Density DC/DC Converters for Data Center Application

The rapid growth of the information and communications technology industry, including streaming services, cloud computing, artificial intelligence, and the Internet of Things, has introduced significant challenges for effective power management in data centers. Developing high-performance DC/DC converters for power supplies in data centers is particularly challenging, as it requires expertise in various areas, such as circuit topology, parameter design, magnetic design, component selection, PCB layout, and even electromagnetic compatibility. A successful design demands careful and thorough consideration of all these factors.
Firstly, a comprehensive literature review on high-performance DC/DC power converters for data center applications is presented. The various categories of DC/DC power converters are depicted, and existing power solutions from both academia and industry are explored. Moreover, key design considerations for achieving high-power-density and high-efficiency DC/DC converters are summarized and provided.
Secondly, a design methodology for compact and efficient converters has been developed, including aspects such as power conversion structure selection, circuit parameters design, magnetic integration, and vertical power delivery. Several innovative ideas are proposed and experimentally verified.

• Power conversion structures: To determine the optimal power conversion structure, a methodology for comparing different power conversion architectures is established. Based on the given specification with a wide input voltage range of 38-72 V and a fixed output voltage of 53.5 V, six different structures are analyzed and compared in terms of power density and efficiency. As a result, the two-stage Boost + LLC configuration is selected for implementation.

• Magnetic integration: To shrink the magnetic size, a matrix core is proposed to integrate two Boost inductors and one LLC transformer for the selected power structure. Compared to the traditional magnetic design using two E-I cores, the footprint of the proposed core is reduced by approximately 30%. A 1 kW prototype is implemented, which demonstrates a peak efficiency of 95.6% and a power density of 126 W/inch³.

• Vertical power delivery: To achieve both high efficiency and power density, a vertical transformer cell is proposed to facilitate vertical power delivery. Utilizing these vertical transformer cells, three 40-to-5 LLC-DCX converters are developed and implemented as unregulated intermediate bus converters with two different winding configurations, including diagonal operation mode and same-side operation mode (SOM). The 550 kHz vertical LLC converter with DOM configuration achieves a maximum output power of 606 W and the corresponding power density of 725 W/inch³. And the peak efficiency is 96.3%. Furthermore, the 48-to-1 vertical LLC-DCX converter achieves a peak efficiency of 91.3% at 190 A output current and a full load efficiency of 88.6% at 488 A output current, corresponding to the current density of 0.24 A/mm².

Besides, other research topics related to the modeling and mitigation of electromagnetic interference (EMI) noise are presented.

• DM noise modeling and analysis in a USB-C charger: Based on common-mode and differential-mode (DM) electrical behaviors, the DM noise model is presented considering both intrinsic DM noise and mixed-mode noise. Besides, the impedance mismatch in EMI filter design is studied and discussed.

• Parasitic inductance elimination for EMI filter capacitors: A general model using mutual coupling is proposed to eliminate parasitic inductance for EMI filter capacitors. In the case studied, the equivalent series inductance of the X-capacitor has been effectively eliminated up to 40 MHz. Consequently, the DM noise of the active clamping flyback converter exhibits a significant reduction from approximately 3.5 MHz to 30 MHz