近年來由於全球能源短缺與溫室效應的影響，世界各國積極推動分散式潔淨能源的開發，例如：光伏系統與燃料電池。但光伏系統及燃料電池輸出電壓準位相當低，需要依靠高升壓比之電源轉換器，將其提升至較高電壓以便於後端應用。本論文之主要目的在於研發一新型高升壓比直流轉換器，以作為此二類新能源系統之介面，俾使整體系統能夠得到更好的轉換效率。

本論文之主要貢獻如下：首先，提出一新型高效率高升壓比之直流轉換器。經由新的電路拓樸，此轉換器之主動開關與輸出二極體跨壓可大大的降低，故可選用導通電阻更小的主動開關與降低二極體逆向回復造成的影響。再者，配合四相交錯式切換，不僅輸入電流漣波得以下降，並可分散輸入電流至各個開關減少導通損失，以提高轉換效率。第二點貢獻則是針對本論文所提出之新型轉換器，分析其操作狀態與工作原理，以及進一步推導出直流與小信號數學模型，以作為閉迴路控制之參考，此外並提供一些設計準則以方便實體製作。第三點貢獻則是依據理論分析的結果實際製作一輸入電壓 20V、輸出電壓400V 以及輸出功率額定300W 之雛型系統，以驗證新型轉換器的可行性。經由實測結果顯示，主動開關與二極體跨壓分別為輸出電壓的八分之一與二分之一，其電源轉換效率於60W 至260W 的負載情況下均在90％ 以上，且最高可達94％。電路模擬與實測結果確實印證了本文所提轉換器確實可以達到預期目標。

Recently, due to the global energy shortage and global warming effects,many countries are actively promoting the developing clean distributed energy sources such as fuel cells and photovoltaic systems. However, the output voltage
of solar cells and fuel cells is rather low and a high step-up dc converter is normally required as an interface for back-end applications. Therefore, the objective of this thesis is focused on developing a high efficiency high step-up dc converter for these two new energy systems.

Basically, the major contributions of this thesis can be summerized as follows.First, a novel high efficiency and high step-up dc converter is proposed. Through the new topology, the voltage stress of both active switches and diodes are greatly reduced so that lower on-resistance switches can be adopted and less reverse recovery effect of diodes will be induced. Also, the interleaved configuration
will not only reduce the input current ripple but also further increase the system efficiency. Second, both DC and small signal models of the proposed converter are derived for better closed loop control. In addition, some design
guidelines are given for convenient implemention. Finally, a 20V input 400V output prototype with 300W rating is also constructed. It is seen that the voltage stress of the active switches and the diodes are equal to one eighth and half of the output voltage respectively and the resulting system efficiency can be maintained above 90% as the load is varied from 60W to 260W. In fact, the highest efficiency
is 94%. Both simulation and experimental results indeed verify the effectiveness of the proposed converter.

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