本論文主旨為研製一台三階三相諧振式直流-直流轉換器，並刻意將輸入輸出端以對稱型的方式呈現，評估其可行性。本架構適用於高壓高功率，應用在直流微電網中做電氣隔離。輸入端開關的電壓應力皆為1/3之輸入電壓。輸出端整流二極體的電壓應力皆為1/3之輸出電壓。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接與輸出端與一次側對稱之二極體所組成。開關控制部分採用每一臂控制信號相位相差120°，輸入側的開關可達到零電壓切換。
本文將探討三階三相直流-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 繪製出增益曲線。最後實作出一台輸出功率3 kW 的實體電路，在不同負載下整體轉換效率最高在96.19%。

The thesis presents the study and implementation of an isolated three-phase and three-level resonant DC to DC 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 diodes 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 rectified diodes which is symmetrical to primary side at output. Control signals have a phase-shift of 120° between each leg. The zero-voltage-switching could be achieved at the input.
This thesis will discuss the three level and three phase DC-DC converter. The operation principles are analyzed including the transfer function of the resonant tank. By using a mathematical software, Mathcad, plot the curves of voltage gain. Eventually, a laboratory prototype with 3kW rated power was been built and tested. The measured highest efficiencies is 96.19% under different load conditions.

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