本論文主旨為研製一雙向三相三階諧振式直流-直流轉換器，此電路架構功率開關元件電壓應力為輸入電壓的三分之一，輸出同步整流開關也為輸出電壓的三分之一，故適用於高壓高功率，應用在直流微電網中做電器隔離。電路架構為輸入側三臂半橋(六個開關)、一次側二次側各三組諧振槽、三個隔離變壓器以Y-Y接法構成、二次側採用與一次側對稱之同步整流開關所組成。開關控制部分採用每一臂控制信號相位相差120度，一次側與二次側開關可達到零電壓切換，減少導通損失。
本文探討雙向三相三階直流-直流轉換器，分析其各個階段的動作原理與推導諧振槽之轉移函數，並利用數學軟體MathCad繪製出曲線。最後實作出一臺輸出功率3 kW的實體電路，在不同負載下，順向模式轉換效率最高可達97.69 %，逆向模式轉換效率最高可達97.28 %。

The thesis presents the study and implementation of a bidirectional three-phase three-level DC / DC resonant converter. The topology of this thesis mean to make the input side and the output side are symmetrical and evaluate its performance. It is satisfied with the high voltage and high power application. Hence, it is applied in isolation of DC micro-grid systems. The voltage stress of switches on the primary side are 1/3 input voltage. The voltage stress of Synchronous rectifier switches on the secondary side are 1/3 output voltage. The topology consists of three half-bridge switch legs, six switches, at input, three resonant tanks on both primary and secondary side, three isolated transformers with Y-Y connection and three synchronous rectifier switches which is symmetrical to primary side at output. The zero-voltage-switching could be achieved at the input and output.
This thesis will discuss the three level and three phase DC-DC converter. The operation principles are analyzed including the transfer function of resonant tank. By using a mathematical software, Mathcad, plot the curves of voltage gain. Eventually, a laboratory prototype with 3 kW rated power was been built and tested. The measured highest efficiencies is 97.69% under different load conditions at forward operating and measured highest efficiencies is 97.28% under different load conditions at reverse operating.

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