本論文以應用於直流微電網系統之高電壓隔離電能轉換器作為研究目標，研製一台雙向三相三階式串聯-串聯諧振直流轉換器，本轉換器具有輸入/輸出電容以及功率開關電壓應力減半的特色，可減緩元件耐壓的限制，且保有開關柔性切換特性，有助於提高轉換器的電壓應用範圍。三相變壓器採用Y-Y連接型式，可降低變壓器繞組圈數，進而降低線圈損耗，適合高壓應用場合。除此之外，本文提出兩種電路操作模式，分別為變頻模式以及相移模式，可改善僅有變頻模式之調壓範圍不足的情形，以因應可能之寬範圍調壓需求。
本論文詳細分析兩種操作模式之電路理論以及輸入/輸出串聯電容均壓控制方法，並且使用650 V規格之碳化矽功率開關，實際完成一台輸出功率約7 k-W、輸入電壓800 V及輸出電壓800 V的高壓雙向隔離型轉換器，在雙向功率傳遞下，轉換器滿載效率皆可達到97 %以上。

This dissertation studies and implements a Three-Phase Three-Level Bi-Directional Series-Series resonant DC-DC converter for DC-Micro grid application, which is used as an isolated DC transformer in the DC-Micro grid system. The voltage stress of input/output capacitors and power switches is halved on the proposed converter, meanwhile, the power switches still have zero voltage switching capability. The three isolated transformers are configured in Y-Y connection, which has lower winding loss due to fewer transformer turns. It is an attractive candidate for high voltage conversion. Besides, two operation modes are proposed in this converter, which are variable-frequency mode and phase-shift mode. Due to the voltage gain are wider comparing to only variable-frequency operation mode. The converter specification of wide voltage regulation requirement can be easier to accomplish.
In this dissertation, the circuit operation principles in both operation modes are analyzed, the voltage balancing of input/output capacitors are explained. A laboratory prototype using 650 V SiC-MOSFET with 800 Vin/ 800 Vout and 7 k-W rated power has been built and tested. Under bi-directional power transfer condition, the measured efficiencies are above 97% at full load condition.

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