本論文提出應用於資料中心的隔離式直流-直流轉換器。在1 MHz的開關切換頻率下，採用能夠全負載範圍達到一次側開關零電壓切換與二次側開關零電流切換的LLC串聯諧振式轉換器，並採用寬能隙元件氮化鎵取代傳統的矽元件降低功率開關的截止損耗。針對變壓器一、二次側皆為低電壓大電流的電路規格下，本論文採用四分之一圈平板變壓器結構，在一樣維持8：1電壓轉換比下，一、二次側的繞組的圈數更少，具有更低的直流銅線損耗的優勢。並且針對變壓器繞組的並聯模式和繞組排列進行探討及優化，最終選擇交流損耗最小的情況做為變壓器繞組設計。同時將變壓器的尺寸大小利用參數化設計，在有限的電路面積下選擇最佳的鐵芯損耗與銅線損耗的平衡點。並且在電路佈局的功率級走線與導通孔擺設採用交錯式排列，有效降低電流不均所造成的電路損耗以及熱點分布。利用ANSYS的磁性模擬軟體Maxwell驗證四分之一圈平板變壓器的電壓轉換比是否正確與電路佈局優化是否符合設計理論，最終實現切換頻率操作於1 MHz、輸入電壓48 V、輸出電壓6 V、輸出功率為1100 W且功率密度為70 W/cm3，最高效率可以達到98.2%的LLC串聯諧振式轉換器。

For data centers, this study proposed an isolated DC-DC converter with MHz-level switching frequency that can achieve zero voltage switching and zero current switching in the full load range. In the proposed LLC resonant converter, conventional silicon devices are replaced with wide band-gap gallium nitride devices to reduce switching losses in the power device. This work adopted a quarter turn transformer structure for low voltage and high current applications to reduce the dc resistance and copper loss. The turns ratio of quarter turn transformer remains 8:1, but the path of the primary and secondary winding is equivalent to a quarter turn. The current sharing between parallel layers and winding arrangement of the transformer was analyzed to choose the lowest ac copper loss as design. Within a limited circuit layout area, optimal points for the efficiency of core loss and copper loss were calculated. This study adopted interleaved PCB traces and vias to reduce loss and heat distribution. The magnetic simulation software ANSYS Maxwell was employed to verify whether the voltage ratio and PCB layout optimization of this planar transformer conformed to the design theory. Finally, a resonant converter was achieved with a switching frequency operating at 1 MHz, an input voltage of 48 V, an output voltage of 6 V, an output power of 1.1 kW, the power density of 70 W/cm3, and maximum efficiency of 98.2%.

[1] United States Department of Energy, “Energy 101: Energy Efficient Data Centers.” [Online]. Available：https://www.energy.gov/eere/videos/energy-101-energy-efficient-data-centers
[2] E. Orlando, Lawrence Berkeley National Laboratory, “United States data center energy usage report,” Jun. 2016.
[3] Efficiency in Data Centers. [Online]. Available：
https://www.comsoc.org/publications/tcn/2019-nov/energy-efficiency-data-centers
[4] E. R. Masanet et al., Global Data Center Energy Use: Distribution, Compo- sition, and Near-Term Outlook, Evanston, IL, 2018.：
[5] IEA (2019), Tracking Buildings, IEA, Paris https://www.iea.org/reports/tracking-buildings [Online]. Available：https://www.iea.org/reports/tracking-buildings/data-centres-and-data-transmission-networks
[6] IEEE.tv, “KeyTalk with Xin Li and Shuai Jiang: Google 48V Power Architecture – APEC 2017.” [Online]. Available：https://ieeetv.ieee.org/ieeetv-specials/keytalk-xin-li-and-shuai-jiang-google-48v-power-architecture-apec-2017?rf=events|114&

[7] Y. Ren, M. Xu, K. Yao and F. C. Lee, "Two-stage 48 V power pod exploration for 64-bit microprocessor," Eighteenth Annual IEEE Applied Power Electronics Conference and Exposition, 2003. APEC '03., Miami Beach, FL, USA, 2003, pp. 426-431 vol.1, doi: 10.1109/APEC.2003.1179248.
[8] M. Ahmed, C. Fei, F. C. Lee and Q. Li, "High efficiency two-stage 48V VRM with PCB winding matrix transformer," 2016 IEEE Energy Conversion Congress and Exposition (ECCE), Milwaukee, WI, 2016, pp. 1-8, doi: 10.1109/ECCE.2016.7855150.
[9] T. Liu, X. Wu and S. Yang, "1 MHz 48V-12V Regulated DCX with Single Transformer," in IEEE Journal of Emerging and Selected Topics in Power Electronics, doi: 10.1109/JESTPE.2019.2955607.
[10] M. H. Ahmed, A. Nabih, F. C. Lee and Q. Li, "High-efficiency, High-density Isolated/Regulated 48V Bus Converter with a Novel Planar Magnetic Structure," 2019 IEEE Applied Power Electronics Conference and Exposition (APEC), Anaheim, CA, USA, 2019, pp. 468-475, doi: 10.1109/APEC.2019.8722216.
[11] M. H. Ahmed, F. C. Lee and Q. Li, "Two-Stage 48V VRM With Intermediate Bus Voltage Optimization For Data Centers," in IEEE Journal of Emerging and Selected Topics in Power Electronics, doi: 10.1109/JESTPE.2020.2976107.

[12] S. Jiang, C. Nan, X. Li, C. Chung and M. Yazdani, "Switched tank converters," 2018 IEEE Applied Power Electronics Conference and Exposition (APEC), San Antonio, TX, 2018, pp. 81-90, doi: 10.1109/APEC.2018.8340992.
[13] Y. Li, X. Lyu, D. Cao, S. Jiang and C. Nan, "A 98.55% Efficiency Switched-Tank Converter for Data Center Application," in IEEE Transactions on Industry Applications, vol. 54, no. 6, pp. 6205-6222, Nov.-Dec. 2018, doi: 10.1109/TIA.2018.2858741.
[14] M. Wei, Y. Li, Z. Ni, C. Liu and D. Cao, "Zero Voltage Switching Switched-Tank Modular Converter for Data Center Application," 2019 IEEE 7th Workshop on Wide Bandgap Power Devices and Applications (WiPDA), Raleigh, NC, USA, 2019, pp. 245-250, doi: 10.1109/WiPDA46397.2019.8998894.
[15] Vicor Inc., “Vicor 48V products from source to point-of-load_BCM Bus Converter Module.” [Online]. Available：http://www.vicorpower.com/products?productType=cfg&productKey=BCM6123T60E10A5T01
[16] Z. Ye, R. A. Abramson and R. C.N. Pilawa-Podgurski, " A 48-to-6 V Multi-Resonant-Doubler Switched-Capacitor Converter for Data Center Applications," 2020 Applied Power Electronics Conference and Exposition (APEC)

[17] ANALOG DEVICES Inc., “Data Center Solution for Higher Efficiency, Density, and Reliability.” [Online]. Available：https://www.analog.com/en/applications/markets/data-center.html
[18] EPC Inc., “Boosting Power Density in 48 V to 5 V DC-DC Converter Using EPC2053, with up to 25 A Output (How2AppNote009).” [Online]. Available：
https://epc-co.com/epc/Portals/0/epc/documents/application-notes/How2AppNote009%20-Boosting%20Power%20Density%20in%2048%20V%20to%205-12%20V%20DC%20to%20DC.pdf
[19] M. Ilic and D. Maksimovic, "Interleaved Zero-Current-Transition Buck Converter," in IEEE Transactions on Industry Applications, vol. 43, no. 6, pp. 1619-1627, Nov.-dec. 2007, doi: 10.1109/TIA.2007.908175.
[20] E. Adib and H. Farzanehfard, "Zero-Voltage-Transition PWM Converters With Synchronous Rectifier," in IEEE Transactions on Power Electronics, vol. 25, no. 1, pp. 105-110, Jan. 2010, doi: 10.1109/TPEL.2009.2024153.
[21] R. Priewasser, M. Agostinelli, C. Unterrieder, S. Marsili and M. Huemer, "Modeling, Control, and Implementation of DC–DC Converters for Variable Frequency Operation," in IEEE Transactions on Power Electronics, vol. 29, no. 1, pp. 287-301, Jan. 2014, doi: 10.1109/TPEL.2013.2248751.

[22] B. Yang, F. C. Lee, A. J. Zhang and G. S. Huang, "LLC resonant converter for front end DC/DC conversion," APEC. Seventeenth Annual IEEE Applied Power Electronics Conference and Exposition (Cat. No.02CH37335), Dallas, TX, USA, 2002, pp. 1108-1112 vol.2.
[23] B. Yang, “Topology Investigation of Front End DC/DC Power Conversion for Distributed Power System,” PhD Dissertation, 2003.
[24] J. Millán, P. Godignon, X. Perpiñà, A. Pérez-Tomás and J. Rebollo, "A Survey of Wide Bandgap Power Semiconductor Devices," in IEEE Transactions on Power Electronics, vol. 29, no. 5, pp. 2155-2163, May 2014, doi: 10.1109/TPEL.2013.2268900.
[25] U. K. Mishra, P. Parikh and Yi-Feng Wu, "AlGaN/GaN HEMTs-an overview of device operation and applications," in Proceedings of the IEEE, vol. 90, no. 6, pp. 1022-1031, June 2002, doi: 10.1109/JPROC.2002.1021567.
[26] Y. C. Liu, C Chen, K. D. Chen, Y. L. Syu, M. C. Tsai, “High-Frequency LLC Resonant Converter with GaN Devices and Integrated Magnetics,” Energies 2019, 12, 1781.
[27] C. Fei, F. C. Lee and Q. Li, "High-Efficiency High-Power-Density LLC Converter With an Integrated Planar Matrix Transformer for High-Output Current Applications," in IEEE Transactions on Industrial Electronics, vol. 64, no. 11, pp. 9072-9082, Nov. 2017, doi: 10.1109/TIE.2017.2674599.

[28] D. Huang, S. Ji and F. C. Lee, "LLC Resonant Converter With Matrix Transformer," in IEEE Transactions on Power Electronics, vol. 29, no. 8, pp. 4339-4347, Aug. 2014, doi: 10.1109/TPEL.2013.2292676.
[29] S. Li, E. Rong, Q. Min and S. Lu, "A Half-Turn Transformer With Symmetry Magnetic Flux for High-Frequency-Isolated DC/DC Converters," in IEEE Transactions on Power Electronics, vol. 33, no. 8, pp. 6467-6470, Aug. 2018, doi: 10.1109/TPEL.2018.2789939.
[30] E. Rong, S. Li, R. Zhang, X. Du, Q. Min and S. Lu, "A magnetic integration half-turn planar transformer for LLC resonant DC-DC converters," 2018 IEEE Applied Power Electronics Conference and Exposition (APEC), San Antonio, TX, 2018, pp. 484-488, doi: 10.1109/APEC.2018.8341055.
[31] Y. Liu et al., "Quarter-Turn Transformer Design and Optimization for High Power Density 1-MHz LLC Resonant Converter," in IEEE Transactions on Industrial Electronics, vol. 67, no. 2, pp. 1580-1591, Feb. 2020, doi: 10.1109/TIE.2019.2902821.
[32] Infineon Inc., “Resonant LLC Converter: Operation and Design 250W 33Vin 400Vout Design Example.” [Online]. Available：https://www.infineon.com/dgdl/Infineon-MOSFET_OptiMOS_resonant_LLC_converter_operation_and_design-AN-v01_00-EN.pdf?fileId=db3a30433acf32c9013ad11cddde01b6

[33] MPS Inc., “Application Note for an LLC Resonant Converter Using Resonant Controller HR1000A.” [Online]. Available：https://www.monolithicpower.cn/cn/documentview/productdocument/index/version/2/document_type/Application%20Note/lang/en/sku/HR1000A/document_id/5926/
[34] C. Fei, M. H. Ahmed, F. C. Lee and Q. Li, "Two-Stage 48 V-12 V/6 V-1.8 V Voltage Regulator Module With Dynamic Bus Voltage Control for Light-Load Efficiency Improvement," in IEEE Transactions on Power Electronics, vol. 32, no. 7, pp. 5628-5636, July 2017, doi: 10.1109/TPEL.2016.2605579.
[35] H. Cui and K. D. T. Ngo, "Transient Core-Loss Simulation for Ferrites With Nonuniform Field in SPICE," in IEEE Transactions on Power Electronics, vol. 34, no. 1, pp. 659-667, Jan. 2019, doi: 10.1109/TPEL.2018.2812856.
[36] Liu, Y.-C. & Chen, C. & Chen, K.-D. & Syu, Y.-L. & Tsai, M.-C. (2019). High-Frequency LLC Resonant Converter with GaN Devices and Integrated Magnetics. Energies. 12. 1781. 10.3390/en12091781.
[37] Y. Cai, M. H. Ahmed, Q. Li and F. C. Lee, "Optimal Design of Megahertz $LLC$ Converter for 48-V Bus Converter Application," in IEEE Journal of Emerging and Selected Topics in Power Electronics, vol. 8, no. 1, pp. 495-505, March 2020, doi: 10.1109/JESTPE.2019.2939469.
[38] P. L. Dowell, "Effects of eddy currents in transformer windings," in Proceedings of the Institution of Electrical Engineers, vol. 113, no. 8, pp. 1387-1394, August 1966, doi: 10.1049/piee.1966.0236.

[39] Z. Ouyang, O. C. Thomsen and M. A. E. Andersen, "The analysis and comparison of leakage inductance in different winding arrangements for planar transformer," 2009 International Conference on Power Electronics and Drive Systems (PEDS), Taipei, 2009, pp. 1143-1148, doi: 10.1109/PEDS.2009.5385844.
[40] J. Schäfer, D. Bortis and J. W. Kolar, "Novel Highly Efficient/Compact Automotive PCB Winding Inductors Based on the Compensating Air-Gap Fringing Field Concept," in IEEE Transactions on Power Electronics, vol. 35, no. 9, pp. 9617-9631, Sept. 2020, doi: 10.1109/TPEL.2020.2969295.