本論文所提雙模式三相Y-Δ主動雙橋串聯諧振直流-直流轉換器可以工作於相移模式或變頻模式。於變頻模式操作時，一次側Y接開關具有零電壓切換，二次側接有較低的切換損失，因此能減少切換損失並提升轉換效率。於相移模式操作時，定頻工作在電感性，改善諧振電路輸出空載失真問題。本論文詳細分析與敘述此兩種模式之電路理論與設計方法，且透過模擬與實作結果，驗證所提直流-直流轉換器之可行性。最後實作出一台輸出功率為2.2kW的實體電路，比較兩模式輕載前效率改善，整體效率可在90 ％以上。

The operations of the proposed three-phase wye-delta connected dual-active-bridge Series Resonant DC-DC Converter can be under either phase-shift (PS) mode or variable-frequency (VF) mode. For VF mode operation, The primary side Y-connected switch has zero voltage switching (ZVS), and the secondary side is -connected with a low switching loss, thus reducing switching losses and improving conversion efficiency. On the other hand, the PS mode operation with fixed switching frequency in inductive. Improve the problem of no-load distortion of the output voltage of the resonant circuit. Circuit principles and design procedures are presented and verified by the simulations and experimental results. Finally, a laboratory prototype with 2.2 kW rated power output is built and tested. Compare the efficiency of the two modes before light load, The measured efficiency is above 90 .

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