本論文提出應用於雲端伺服器的隔離式直流-直流轉換器，在MHz等級的切換頻率下，選擇能夠全負載範圍達成零電壓切換的LLC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元件的截止損耗。本論文提出一個新型半圈式變壓器的結構，採用磁通抵銷降低鐵心損耗的同時，二次側的繞組依然能夠繞製半圈達到分數圈的效果，同時又能夠維持繞線圈數比為16:1，解決先前文獻中分數圈變壓器體積倍數增加的問題，此新型半圈式變壓器可以同時達到減少鐵心鐵損以及體積與提升功率密度目標。並且利用參數化的形式，在有限的電路佈局的面積中，計算鐵心損耗以及銅線損耗達到效率的最佳點。隨後同時又能夠維持繞線圈數比為16:1利用ANSYS的磁性模擬軟體Maxwell驗證此平板變壓器的實際電路行為是否符合先前的設計理論，最終實現切換頻率操作於1 MHz、輸入電壓380 V、輸出電壓12 V、輸出功率為800 W且功率密度為55 W/cm3，最高效率可以達到95.21%的諧振式轉換器。

This paper proposes an isolated DC-DC converter for cloud servers. With a switching frequency in the range of MHz, an LLC resonant converter is selected that can achieve zero voltage switching over the full load range. It replaces the traditional switch components with wide bandgap devices, like GaN, to reduce the turn-off loss of the power components. This paper proposes a new half-turn transformer structure, which uses magnetic flux cancellation to reduce the core loss. The secondary winding is a half-turn to achieve a fractional winding that maintains a winding ratio of 16:1. Solving the problem of increasing the volume of the fractional-circle transformer in previous research, the new half-turn transformer can simultaneously achieve the goal of reducing core loss and volume while increasing power density. Parametric form is used to calculate the core loss and copper loss to achieve an optimized design in the limited circuit layout area. The magnetic simulation software Maxwell of ANSYS is used to verify the circuit behavior with a planner transformer, which conforms to the previous design theory. Finally, the implemented 800-W LLC resonant converter with the proposed design switches at 1 MHz, has an input voltage of 380 V and an output voltage of 12 V, achieves a maximum efficiency of 95.21%, and has a power density of 55 W/cm3.

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