本論文提出應用於資料中心48 V電壓調節模組的48 V-12 V隔離式直流-直流轉換器。考量到在1 MHz的開關切換頻率下，開關切換損耗大幅上升，因此選擇具有一次側開關零電壓切換與二次側開關零電流切換特性的LLC諧振式轉換器做為電路架構，以及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。本論文針對先前文獻中提出的數種鐵心損耗模型進行探討和分析，並利用ANSYS Maxwell模擬驗證鐵心模型在損耗計算上的差異，接著針對變壓器繞組高頻阻抗損耗模型進行推導和分析。本論文採用新型平板變壓器結構並提出新型鐵心結構，同時分析如何利用新型整合式變壓器達到兩相LLC諧振式轉換器並聯和提升效率的目的。根據鐵心磁通分布優化鐵心結構，分析繞組堆疊排列的方式降低磁動勢進而降低交流阻抗損耗和繞組並聯均流分布。並且將鐵心尺寸以參數化的形式，在數種不同的電路面積下得到最佳的變壓器損耗設計點。最後結合ANSYS Maxwell和參數化形式優化邊緣磁通對於變壓器繞組損耗影響。最終實現輸入電壓48 V、輸出電壓12 V、切換頻率操作於1 MHz、輸出功率為850 W、效率96.7%和功率密度為56 W/cm3的LLC串聯諧振式轉換器，達到兩相之間均留、高功率密度和高轉換效率的目標。

This dissertation proposed an isolated 48 V-12 V DC–DC converter used in data centers. Considering the switching loss will increase substantially under switching frequency operated at 1 MHz. LLC resonant converter capable of zero-voltage switching at the primary-side switch and zero-current switching at the secondary-side switch was adopted. Furthermore, a wide bandgap component, namely gallium nitride, replaced the conventional silicon component to reduce the cutoff loss of the power switch. This dissertation also discussed and analyzed the core loss model and ac resistance model which was provided by several research paper and identify these loss model by ANSYS Maxwell. This dissertation proposed novel core structure to solve the issue of current sharing. Moreover, according to the flux distribution in the core and the arrangement of the transformer winding were optimized to achieve the lowest core loss and ac copper loss, respectively. The transformer size was subjected to design parameterization, and the optimal balance point between iron core loss and copper wire loss was selected under the condition of a limited circuit area. Using design parameterization and ANSYS Maxwell to optimize the copper loss increasing caused by fringing flux. The final LLC series resonant converter had a switching frequency of 1 MHz, input voltage of 48 V, output voltage of 12 V, output power of 850 W, efficiency of 96.7 %, power density of 56 W/cm3.

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