本論文提出應用於資料中心48 V電壓調節模組的48 V降 6 V隔離式直流直流轉換器。本電路架構採用能夠在全附載範圍達到一次側開關零電壓切換、二次側開關零電流切換的全橋LLC串聯諧振轉換器，將開關的操作頻率固定在諧振點做為直流變壓器使用。在切換頻率為1 MHz時，功率開關的切換損耗會大幅上升，因此採用寬能隙元件氮化鎵取代傳統矽元件，以降低功率開關的損耗。針對變壓器二次側為低電壓大電流的規格，本文利用分數圈平板變壓器，於二次側多組中心抽頭的結構下，降低二次側迴路功率元件的電流應力，並且維持8：1圈比的電壓轉換比下，一、二次側繞組的圈數將比傳統變壓器更少，具有更低直流銅線損耗的優勢。本文於多組二次側架構下分析各迴路雜散元件對電路之影響，並針對變壓器板層繞組的排列進行探討及優化，最終選擇銅線損耗最佳的排列進行變壓器繞組設計。同時將變壓器的尺寸大小利用參數化設計，在合理的損耗範圍內選擇最佳功率密度之設計點。最終實現切換頻率為1 MHz、輸入電壓48 V、輸出電壓6 V、輸出功率為600 W且功率密度為54.987 W/cm3，最高效率可以達到97.107 %的LLC串聯諧振式轉換器。

This thesis proposes a 48 V-6 V isolated DC-DC converter for 48 V voltage regulation modules in data centers. This architecture uses a full-bridge LLC series resonant converter that can achieve ZVS on the primary side and ZCS on the secondary side in the range for full load conditions. The switching frequency of the power devices is selected at the resonance point and use it as a DC transformer. Under 1 mega switching frequency, the switching loss increases significantly when op-erating, the MOSFET device is replaced by GaN device to reduce the losses of the power devices. For the specification of low-voltage and high-current on the secondary side of the transformer, this paper adopts a fractional-turn planar transformer to reduce the current stress of the power components of the secondary side loop under the structure of multiple sets of center taps on the secondary side, and maintaining the voltage conversion ratio of 8:1, the number of turns of the primary and secondary side windings will be less than that of traditional transformers, which has the advantage of lower DC copper loss. Under the transformer with multiple secondary winding, this paper research the impact of secondary side parasitic parameters. The winding arrangement of the transformer are discussed, and the size of the transformer is designed by parameterization, to find the design point of the best power density within a reasonable loss range. Finally, an LLC series resonant converter with a switching fre-quency of 1 MHz, an input voltage of 48 V, an output voltage of 6 V, an output power of 600 W, the power density of 54.987 W/cm3 and a maximum efficiency of 97.107 % is realized.

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