摘要

近幾年，基於有限的石化燃料和環境影響，世界各國無不著手研究及開發各種的替代能源。其中，擁有高效率和低維修需求的燃料電池被視為最具發展空間的替代能源之一。因為燃料電池的低輸出電壓和緩慢的暫態響應，通常需要一個直流轉換器將其電壓提昇至更高等級。然而，基於切換式電源供應器的固有特性，高頻漣波電流是無法避免的，而此一高頻漣波電流會對燃料電池的工作效率和使用壽命造成影響。
基於上述的問題，本碩論提出一應用於燃料電池系統具漣波鏡電路之高效率升壓型轉換器。本碩論的貢獻點可以被概述如下。第一，所提漣波鏡電路用於升壓型轉換器可以達到零輸入電流漣波和增加燃料電池的工作效率及使用壽命。而與兩相交錯式的升壓型轉換器相比，所提的漣波鏡電路技術也展現了較好的設計彈性，可以藉由設計來調整零漣波的工作點。由於燃料電池系統中直流轉換器的工作點大多遠大於0.5，所以比起兩相交錯式控制，此特性更加適合應用於燃料電池系統。此外，由於漣波電流之消滅，使得轉換器可以使用更小的升壓電感進一步減少導通損失。第二，為了提高轉換器的效率，控制方式採用臨界模式控制可以同時達到柔性切換及固定工作週期控制。第三，推導及分析本文所提轉換器之直流模型和小訊號模型，以方便簡化所提轉換器之設計。最後，藉由設計並完成一200瓦48伏輸入及200伏輸出的雛型電路，以驗證本論文所提出之漣波鏡電路技術的性能及可行性。在相同的輸出條件和臨界模式控制下，升壓型轉換器使用所提漣波鏡達到的峰對峰電流漣波小於6.67%，而使用兩相交錯式控制則是69.88%。所提轉換器的滿載效率約為93.90%，其中，漣波鏡電路只造成0.04%的整體效率損失，此點顯示漣波鏡電路僅對漣波能量進行補償，而模擬及實驗結果皆驗證了本文所提漣波鏡電路之有效性。

Abstract

Due to consideration of the limited fossil fuel and impact of the environment, various alternative energy sources have now been explored and developed. Among them, fuel cell is considered as one of the most promising energy vector because of its high efficiency and low maintenance requirement. Because the low output voltage of fuel cell and its slow dynamic response, usually a DC converter is required for boosting the fuel cell voltage to a higher value. However, due to the inherent characteristic of switching-mode power supplies, high frequency ripple current cannot be avoided. In fact, it is well known that the magnitude of the high frequency ripple current have rather significant impact to the operating efficiency and the life time of the fuel cell.
In view of the above problems, a high efficiency step-up converter with a ripple mirror (RM) circuit is proposed in this thesis for fuel cell systems. Basically, the contributions of this thesis can be summarized as follows. First, a RM circuit is proposed for the step-up converter to achieve zero ripple condition and enhance the operating efficiency and life time of the fuel cell. The proposed RM circuit technique provides much better flexibility than the two-phase interleaved boost converter for locating the zero ripple operating point in the design stage. This characteristic is especially suitable for applying to fuel cell systems where the duty ratio of the step-up converter is usually much larger than fifty percents. Moreover, smaller boost inductor can be adopted to reduce the conduction loss. Second, a boundary mode control is adopted to achieve both soft-switching and constant duty ratio control for the converter to further increase the efficiency. Third, both DC and small signal models are derived and analyzed for simplifying the design of the proposed converter. Finally, a 200 watts 48 volts input 200 volts output prototype is constructed. It is seen that the resulting peak to peak input current ripple is less than 6.67 percents as compared with the 69.88 percents ripple of the two-phase interleaved boost converter with the same boundary mode control and power capacity. The full load efficiency of the proposed converter is about 93.90 percents and the added RM circuit for processing the ripple power only consumes 0.04 percent of the total losses. Both simulation and experimental results indeed verify the effectiveness of the proposed converter.

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