三相昇壓型交/直流轉換器，由於其輸入功率因數可調整為單位功因及輸出直流無兩倍輸入電源頻率之交流漣波電壓等特點，近幾年已逐漸取代傳統利用相位控制之閘流體交/直流轉換器，成為高功率交/直流轉換器之主流;但當其操作於三相電壓不平衡狀況時，傳統的脈波調變控制法卻無法維持輸入單位功因及輸出無二次交流漣波之特性，因此國際上有許多文獻針對此問題提出解決之策略，不過這些文獻在研究解決此問題，大都只著重在如何維持輸入端瞬時功率在負載固定下為定值，但維持輸入瞬時功率為固定值只能達到三相輸入功率因數為單位功因，並無法達成輸出交流漣波電壓最小之控制目標;有鑑於此，本論文主要目的即為針對三相昇壓型交/直流轉換器操作於輸入電壓不平衡狀況下，如何降低輸出漣波電壓做一有系統之研究。
本論文主要貢獻有四點，第一點，推導出三相昇壓型交/直流轉換器在三相輸入電壓不平衡下之封閉式數學解析公式，俾便後續嚴謹地分析研究。第二點，推導出三相昇壓型交/直流轉換器在三相輸入電壓為不平衡情況下輸入功率因數為單位功因之充分條件。第三點，在輸入電壓不平衡條件下，推導出兩種計算三相昇壓型交/直流轉換器之輸出電壓漣波峯值解析公式。第四點，提出一新式三相昇壓型交/直流轉換器控制器，可控制轉換器使其在輸入電壓不平衡下其輸入功率因數仍能維持單位功因，並且可以達到輸出漣波電壓降低的效果。

Theoretically, a three-phase boost rectifier can be controlled to achieve unity power factor as well as clean sinusoidal current at the input and zero voltage ripple at the output. Hence, it is now gradually replacing the traditional thyristor rectifiers to avoid power pollution problems. However, the ideal characteristic of the boost rectifier will be lost when the boost rectifier is operated under unbalanced three-phase voltage source. Hence, many control methods were proposed to solve this problem in the existing literature. Nevertheless, these methods, although can be used to achieve unity power factor, do not consider the minimization of the output voltage ripples. In view of this drawback, it is the major motivation of this thesis to solve this dilemma.

Basically, the contributions of this thesis may be summarized as follows.
First, general closed form analytic duty ratio control expressions of the three-phase boost rectifier are derived under unbalanced three-phase input voltage condition for further theoretical analysis. Second, based on the derived mathematic expressions, the corresponding necessary condition for the converter to achieve unity power factor is obtained. Third , two closed form output voltage-ripple expressions are derived under unbalanced three-phase input voltage condition . One is derived under the condition of allowing the existence of both positive and negative sequence currents. The other is derived by assuming having only positive sequence current. Fourth, based on the consideration of achieving better efficiency, a minimum output voltage ripple control strategy is proposed. In addition, a prototype is also constructed to
verify the effectiveness of the proposed control.

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