本論文旨在研製一數位控制高功率三相隔離型直流-直流降壓轉換器，適用於高壓輸入、低壓輸出之應用場合。電路架構為高壓側三個半橋所組成的三臂切換開關、三個隔離變壓器、低壓側的三相整流二極體與輸出電感電容所組成的濾波電路，三個變壓器的一、二次側分別是以Y-Δ的方式連接，此架構能有較高的降壓比，且在二次側有較好的分流效果。
實作電路上完成一組最大輸出功率9 kW的轉換器，輸入電壓範圍為380 V到420 V，輸出穩壓45 V，最大輸出電流為200 A。驅動信號與電路控制等是使用數位信號處理器TMS320F28335來達成，其中包括電路啟動、保護偵測等。回授控制是採用平均電流控制法，此控制法可以使電路在輸出負載變化時，電感電流與輸出電壓之超越量較低。在20 %到100 %負載條件下，轉換效率皆在86 %以上，最高可達90.72 %。

This thesis presents the design and implementation of a high-power three-phase isolated DC-DC step-down converter, which is suitable for high voltage-input and low voltage-output applications. The power circuit consists of three half-bridge switch legs at high voltage-side, three isolated transformers, a three-phase diode rectifier at low-voltage side and an output LC filter. The primary and secondary windings of three transformers are connected in Y-Δ configurations. The benefits are high voltage-transfer-ratio and good current sharing performance for secondary side.
A laboratory prototype converter with 9 kW rated output power has been built and tested. The input voltage is from 380 V to 420 V, the regulated output voltage is 45 V, and the maximum output current is 200 A. The driver signals and controller are implemented by a DSP, TMS320F28335. The control procedures include start up and protection functions. Average current mode control is adopted to reduce the overshoot of inductor current and output voltage during load change. The converter efficiency is above 86% from 20% to 100% load condition. The peak efficiency is 90.72%.

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