電力公司為維護市電良好之電力品質，要求用戶端之電力轉換器須具備高功因校正能力，但具功因校正能力之電力轉換器，其電力轉換效率不高。因此，本論文中，吾人將應用柔切技術以提高電力轉換器之效率，達到節約能源的目標。
本論文係以[LCY05]所提出之單級隔離式高功因電力轉換器為基本架構，結合柔性切換技術，改善切換損失，提高效率，而設計出新型之零電壓轉移單級高功因返馳式電力轉換器。
當此新型電力轉換器之輸入電感電流及磁化電感電流皆操作於DCM時，不但天生具有優異的功因校正能力，而且可使儲能電容電壓不受負載變動的影響，避免產生高電壓應力。為了改善切換損失，吾人於電力轉換器中，加入輔助開關、共振電感及箝位二極體。利用輔助開關以控制共振時間，使主開關切換為on時，可達到ZVS；且輔助開關切換為off時，亦可達到ZCS，有效地提升轉換器之效率。
論文中，針對提出的零電壓轉移單級高功因返馳式電力轉換器，分析其動作原理，並以平均化法，推導在半線電壓週期 下，電力轉換器之數學模式。由於此數學模式為非線性微分方程式且含有難以積分之柔切項，因此，吾人先忽略柔切項，以求得直流工作點之聯立方程式。然後依據轉換器之操作條件，可求得直流工作點 ，並將 與 代入直流工作點之聯立方程式後，可設計出電力轉換器之元件值，再應用疊代法驗證忽略柔切項並作穩態直流分析係合理的。
接著，將上述之非線性微分方程式於直流工作點作線性化，以推導小信號數學模式，然而柔切項含有相當複雜之積分式，故無法直接求出各項偏導數。因此，吾人利用指導教授Lin提出的圖解法，可輕易求出各偏導數之值，順利推導出小信號數學模式。再以頻譜分析儀，量測實作電路之波德圖，以驗證小信號數學模式推導之正確性。
最後，利用電路模擬軟體IsSpice模擬與電路實作，驗證理論推導之正確性。由實作結果顯示：當輸出功率 時，未具有ZVT柔性切換技術之電力轉換器，其功因 及效率 。而具有ZVT柔性切換技術的電力轉換器，其功因 及效率 。驗證所提出的零電壓轉移單級高功因電力轉換器仍具有高功因，且可改善5.5%的效率。
為了達到輸出穩壓的目的，吾人依據數學模式，設計控制器。經由實作結果可知：在線電壓或負載變動下，所設計之控制器具有良好的穩壓效果。

For improving the electricity quality, the power company requires customers to have the high power factor of their power converters. However, the efficiency of these power converters is not high. Therefore, for the purpose of energy saving, soft-switching technique will be applied to increase the power efficiency of power converters with high power factor correction.
Based on the single-stage isolated high power factor correction converter proposed in [LCY05], a novel zero-voltage-transition single-stage high power factor correction flyback ac/dc converter is proposed by adopting soft switching technique. It is applicable to improve the switching losses, and thus increase the power efficiency of the proposed converter.
When input inductor and magnetizing inductor currents are operating in DCM, the proposed converter not only exhibits an inherent gift of high power factor but also avoids the bulk capacitor to suffer from high voltage stress under load variations. Moreover, to reduce switching losses, an auxiliary switch, a resonant inductor, and a clamped diode are added to the single-stage power converter in [LCY05]. Thus the main switch achieves ZVS at turn on, and the auxiliary switch achieves ZCS at turn off. As a result, the efficiency of the converter can be increased effectively.
In this thesis, the operating principle of the proposed zero-voltage-transition single-stage high power factor correction flyback ac/dc converter is presented. Moreover, the mathematical model of the power converter over one half line period is derived by averaging method. Since the mathematical model are nonlinear differential equations, which contain complicated soft-switching terms, so that these terms are neglected to determine the operating point of the converter. Then, according to the operating conditions, the operating point of the bulk capacitor voltage is then obtained. By substituting dc voltages and into the equations of operating point, the component values can thus be obtained. Finally, the iterating method is used to verify that the DC steady-state analysis, which neglects the terms of soft-switching, is reasonable.
To proceed, the non-linear differential equations are linearized around the operating point to derive the small-signal model. However, the soft-switching terms include complicated integrals, so that the partial derivatives around the operating point are quite difficult to be obtained. Therefore the graphical method, presented by Professor Lin, is adopted to easily derive the partial derivatives, and the small-signal model is thereby easily determined. Then the experimental results, measured by FFT servo analyzer R9211, verify the accuracy of the derived small-signal model by the Bode plots.
Finally, IsSpice simulations and experimental results are used to validate that the theoretical analysis. The experimental results reveal that when the output power is , the power factor and power efficiency of single-stage high power factor correction converter without ZVT soft-switching technique, are and . But for power converter with ZVT soft-switching technique, they are and . It is verified that the proposed ZVT single-stage high power factor correction converter still maintains the high power factor and improves the power efficiency of 5.5%.
According to the small-signal mathematical model, a controller is designed to achieve output voltage regulation. The experimental responses show that the controller has a good regulation capacity under the variations of line voltage and load.

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