近年來電壓驟降在工業界已成為非常重要的電力品質議題。由於電力電子技術的發展與數位控制的進步，使得工業應用上所使用的電機設備，對於電力品質的要求愈來愈嚴格。在配電系統中任何的電壓驟降事故，都可能使得敏感性負載因欠電壓而停機導致生產製程中斷，造成嚴重的損失。因此，眾多的解決方法因應而生，其中以建立於電壓源反流器的串聯式耦合變壓器之電壓驟降補償器，是所有解決方案中最符合經濟效益的。
大多數的電壓驟降補償器使用開迴路控制的控制策略以增加電壓補償之響應速度，但裝置於反流器輸出端的電感-電容濾波器於補償器起動瞬間會引入電壓諧振，且在負載變動的情形下，可能會造成負載電壓擾動。另外，為了簡化控制器運算所使用的同步框轉換也會造成於同步框下因產生d-q軸互相耦合的成分，使得在控制上產生補償誤差，亦影響電壓驟降補償的品質。本文提出使用閉迴路控制方法以達成系統之主動減振，避免加入阻尼電阻而造成線路上的能量損失，而所有的控制器運算都在同步框之下操作，並確認所產生的d-q軸互相耦合成分以進行解耦合之控制。本文將詳細說明串聯式電壓驟降補償器之閉迴路控制方法，並進一步以模擬及實驗結果，來驗證所提之串聯式電壓驟降補償器之效能。

Voltage sags have become a major power quality issue encountered by industries in recent years. Industrial manufacturing equipments are very sensitive to the power quality issues. Any voltage sag event in the power distribution system could cause under-voltage fault in sensitive loads and inflict significant losses with production process interruption. The voltage sag compensator, based on the transformer-coupled series-connected voltage source inverter, is among the most cost-effective solution to protect sensitive loads.
Many voltage sag compensators adopt open-loop control strategies to increase the response speed for the sag compensation. But the L-C filter installed at the output of the voltage source inverter could introduce oscillations in transient, and the voltage disturbance could appear due to varied load conditions. In addition, the coupling components could appear due to coordinate transform for simplified operation process. It is unclear how errors can affect the performance of the voltage sag compensation. A close-loop control scheme is designed in this thesis to accomplish active damping without using any damping resistors. The entire controller is implemented in the synchronous reference frame, and all the cross-coupling terms under the synchronous reference frame are identified and de-coupled in the controller. Detailed explanations of the proposed close-loop control scheme are presented, and the effectiveness of the proposed scheme is verified by simulation and laboratory test results.

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