本研究採用控制方法結合正弦脈波寬度調變(SPWM)與分切合整數位控制(D-Σ Digital Control)，以實現半橋三相四線式換流器模組並聯系統。相較於傳統類比控制，數位控制在系統功能的實現相對容易，能減少硬體電路的使用並且降低電路的複雜性，其中分切合整數位控制透過控制器的設計，抵消系統變化參數如直流鏈電壓、切換週期以及電感值變化等對受控體的影響，最後得到開關責任比率控制法則。本論文首先推導分切合整數位控制法，並且說明電路動作原理，最後將所得開關責任比率以通式表示，使其在軟體上容易實現。在電路實作方面，本研究利用數位控制的優勢，預先將電感值所對應電流變化儲存於微控制器內部，以利微控制器每週期調整迴路增益。
本研究主要貢獻為採用分切合整數位控制法，免除傳統abc–dq座標軸轉換，避免繁複的運算量與冗長的計算時間。此外，將直流鏈電壓變動量與電感值變化納入控制法則，可允許寬廣的電感值變化，有效縮小電感鐵芯尺寸與降低鐵芯損失。在均流控制方面，換流器模組採用負載阻抗估測法，藉由電壓與電流回授訊號，直接計算所需輸出電感電流變化量，並且平均分配至運轉中模組以達到均流目的，因此不需要外部中央控制器調節穩壓與均流。最後，本研究中並聯系統由三部三相四線式換流器模組所組成，經由模擬與實測結果驗證本論文所使用控制方法，可達到穩定輸出三相弦波電壓與平均分配電流。

This thesis presents an SPWM-based division-summation (D-Σ) digital control for a three-phase parallel-connection uninterruptible power supply (UPS) system. Compared to analog control, it is easier to implement digital control to achieve system functions, which can minimize circuit complexity and reduce the volume of hardware circuits at the same time. A controller with the D-Σ digital control is designed to cancel the variation effects of dc-bus voltage, switching period and inductance. This study will derive D-Σ digital control laws first and express them in general forms for readily software programming. In the circuit implementation, the inductances corresponding to various inductor currents were measured at the start-up and stored in the controller for scheduling loop gain cycle by cycle.
This research adopts D-Σ digital control avoiding conventional abc to dq frame transformation so that the calculation process can be significantly simplified. In the meantime, the variation of dc-bus voltage and inductance are taken into account in the control-law derivation, which allows wide inductance variation and reduces the core size accordingly. From the perspective of current sharing, the paralleled inverters control the variation of inductor currents based on voltage and current feedback signals directly and the inverters operating in parallel share them equally. Thus, there is no need to have an external controller to achieve output voltage regulation and equal current distribution. Finally, the paralleled system consisting of three three-phase inverters has been simulated and implemented to verify the feasibility of the proposed control scheme.

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