使用二極體作橋式整流的方式早已不符合單位功因，降低電流諧波的要求，因此發展出 “昇壓型交流對直流轉換器” 做為交流對直流電力轉換系統。其控制理論，一般最常使用的是遲滯電流控制法。它的設計簡單，且容易實現，可使實際電流追隨電流命令，並保持在磁滯誤差區間內，得到單位功因的輸出。對負載的變動亦有相當好的響應。然而，使用遲滯電流控制法最大的問題是隨負載電流的增加，切換頻率有明顯提高的現象，而切換頻率的不固定將造成濾波器設計的困難，且過高的切換頻率會對元件造成過高的熱應力及較大的切換損失。
在本論文提出三相昇壓型交流對直流轉換之固定切換頻率切換演算法。利用此切換演算法，可使線電流和電壓波形同相位，達到單位功因，降低電流諧波的目的，且保有良好的負載變動之電流響應。並使濾波器設計的更為簡單。另外，本論文之切換演算原則是在一固定切換週期內，使用單一的電壓向量切換模式。因此將更明顯地減少電晶體的切換次數，大幅降低電晶體的熱應力及切換損失。
同時，本論文對切換演算法之電流誤差容許值ε、切換頻率 和昇壓電感L三者之間的關係，亦做一深入的探討。證明使用適當的切換頻率 及昇壓電感L，能正確的限制電流誤差在合理的範圍內。
在控制器的實現上選擇以高速、具浮點運算能力的數位訊號處理器(Digital Signal Processor, DSP)，配合類比對數位(A/D)與數位對類比(D/A)轉換介面來實現。模擬與實作的結果驗證了本論文的可行性。

Because of the need for a unity power factor and reducing the line current harmonics, the traditional diode rectifier is ineffective at the higher standard. The boost AC to DC converter has therefore been developed. The common control theorem method is hysteresis current control (HCC). This method has the advantages of simple implementation and design. The input current is kept within a hysteresis band about the reference current wave to reach the unity power factor. The HCC dynamic response to load variations is fast. However, the major problem in HCC control is that the switching frequency varies with the DC load current. At heavy loads the frequency increases substantially. The switching frequency is uneven and random, causing excessive stress and switching losses on the devices. The input filter is also difficult to design.
In this thesis, a switching algorithm that uses a fixed switching frequency for a three-phase boost AC-DC converter is proposed. Using this switching algorithm the input current waveform can be controlled close to a sinusoidal template that is derived from the input voltage waveform. This converter has the advantages of a unity power factor, the current response is kept fast and the filter is easier to design. The switching algorithm uses the principle of one voltage vector used in one switching period. The switching count for this device is therefore greatly reduced. The stress and losses in the switching devices are substantially reduced.
A relationship between the current error, switching frequency and boost inductor was developed in this thesis. The current error can be restricted within a definite range using an appropriate switching frequency and boost inductor.
The proposed scheme was implemented using a 32-bit digital signal processor TMS320C32, analog to digital converter and digital to analog converter. The simulations and experimental results demonstrate the feasibility of this control system.

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