本論文係整合降升壓式(功因級)與返馳式(穩壓級)電力轉換器，並應用輔助變壓器法，而提出一個新型的低電壓應力之單級高功因AC/DC電力轉換器，以達到高功因、輸出穩壓及低電壓應力的拓樸要求。
一般而言，為了提高輸出功率，單級式高功因AC/DC電力轉換器之穩壓級，必須操作於CCM，但儲能電容卻產生高電壓應力問題。文獻中，改善高電壓應力常用之方法為磁性負回授法，其概念係利用儲能電容之回授電壓，以調節輸入電流之大小，而降低高電壓應力。但此法卻使輸入電流波形產生電流死帶(dead band)，而降低功率因數。為克服此缺點，本文所提出之新型低電壓應力之單級高功因AC/DC電力轉換器，係採用輔助變壓器法。
輔助變壓器法之設計理念為：利用輔助變壓器，將部分之輸入能量直接傳送至負載，而不經由儲能電容，故傳送至儲能電容之能量減少，故降低儲能電容的高電壓應力，且不會使輸入電流波形產生電流死帶，因此，電力轉換器仍然保持良好之功因校正能力。
論文中詳細說明新型低電壓應力之單級高功因AC/DC電力轉換器之設計理念，並分析轉換器之電路動作原理，再以平均化法及電流注入法推導轉換器之數學模式，此模式為非線性之微分方程式。然後，由轉換器之數學模式可求出直流工作點，再依據轉換器操作於DCM+DCM+CCM及電容電壓漣波百分比，設計元件規格。並依該元件規格，以IsSpice軟體模擬新型低電壓應力之單級高功因AC/DC電力轉換器，以確認數學模式推導及元件設計之正確性。此外，吾人在直流工作點作小信號擾動，即可推導出轉換器之小信號模式。
最後，吾人完成一組輸出電壓 及輸出功率 之AC/DC電力轉換器，且根據古典控制理論設計PI電壓回授控制器，使輸出電壓達到穩壓，不受線電壓及負載變動之影響，並以實作結果驗證理論分析之正確性及轉換器之性能。

By integrating a power factor correction bulk-boost cell with a voltage regulation flyback cell, a novel single-stage HPFC ac/dc converter with low voltage stress is proposed by using an auxiliary transformer. This topology exhibits the capabilities of high power factor, output voltage regulation and low voltage stress across the bulk capacitor.
In general, the dc/dc cell of a single-stage HPFC ac/dc converter is operating in CCM for high power applications. However, the single-stage converter will thus suffer from the high voltage stress across the bulk capacitor. In the literature, a negative magnetic feedback technique is generally used to solve this problem. A tertiary winding of the transformer is added to generate a feedback voltage, which is proportional to the bulk capacitor voltage. Due to this feedback voltage, the current of the input inductor is decreased. The high voltage stress across the bulk capacitor is thus reduced. However, it causes the deadband of the input current, which degrades the power factor. To overcome this drawback, an auxiliary transformer technique is adopted in the proposed converter in this thesis.
The auxiliary transformer technique is used to deliver some portion of the input energy directly to the load. Hence, the energy stored in the bulk capacitor is decreased, and voltage stress across the bulk capacitor is thereby reduced. Furthermore, there exists no deadband in the input current and the power factor is not degraded.
In this thesis, the design procedure and operating principle of the proposed novel single-stage HPFC ac/dc converter with low voltage stress are presented. The current injection and averaging methods are both used to derive the mathematical model of the converter, which is described by nonlinear differential equations. Moreover, the components of the proposed converter are also well designed according to the operating mode of DCM+DCM+CCM and the specified voltage ripple percentages of the capacitors. Based on the design specifications and component values, the theoretical analysis and derived model are validated by IsSpice simulations. In addition, the small-signal model is derived by perturbation around the operating point of the proposed converter.
Finally, for input and output, a prototype of the proposed single-stage HPFC ac/dc converter with low voltage stress is established. Then based on the classical control theory, a PI voltage feedback controller is designed to regulate the output voltage in the presence of the variations of line voltage and load resistance. The theoretical analysis and performances of the proposed converter with a PI controller are thereby validated by the experimental results.

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