雙主動橋式轉換器因其兼具雙向功率傳輸與併網能力且架構簡單，在電動車的充電應用中被廣泛運用，然而在轉換器工作於電壓轉換比小於1且輕載時，傳統單相移之雙主動橋式轉換器會失去零電壓切換，效率顯著下降。為此本文提出一種結合切換式電容於半橋雙主動橋式直流轉換器。在低輸出電壓且輕載時將電壓幅值降至一半，使主功率級在不同的輸出電壓條件下仍能工作於電壓轉換比等於1，保持高效率。當負載進入重載區域時，將切換式電容轉換器旁通，系統恢復至原始模式，保持高效能。本文先透過向量圖分析切換式電容-半橋雙主動橋式轉換器在不同負載下的工作機制，以實驗驗證該架構在輸入電壓400 V轉換至輸出電壓22V、切換頻率100kHz隔離降壓應用中的性能。結果顯示，切換式電容-半橋雙主動橋式直流轉換器在輕載（10 %額定功率）時的效率較傳統半橋雙主動橋式轉換器提升約10%，具有顯著優勢。

The dual-active-bridge (DAB) converter is widely used in electric vehicle charging systems due to its bidirectional power flow capability, grid-friendly interface, and structural simplicity. However, when operating at a conversion ratio M<1 under light-load conditions, the conventional single-phase-shift DAB can lose its zero-voltage-switching (ZVS) capability, leading to reduced efficiency. This thesis proposes a Switched-Capacitor Assisted Half-Bridge Dual-Active-Bridge DC-DC converter to improve efficiency under light-load conditions. The converter integrates a Switched-Capacitor Converter (SCC) into HB-DAB to dynamically adjust the primary-side voltage. Under light load condition, SCC reduces the voltage amplitude by half, allowing the main power stage operate in M=1 condition to improving efficiency. When the load enters the full-load region, SCC is bypassed, allowing the system returns to pure HB-DAB operation for maintaining high efficiency.
This thesis analyzes the operational mechanism of SC-HB-DAB under different loads using vector diagrams, and verifies the performance of the isolated buck architecture in voltage conversion from 400 V to 22 V . Results show that SC-HB-DAB improves efficiency by up to 10 percent compared to the traditional half-bridge DAB under light load (under 10% of the rated power), which confirms the advantages of this design.

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