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。對可調速驅動系統(Adjustable-speed drive, ASD)而言，當供電端發生電壓驟降時，直流鏈電容儲能不足以提供負載所需之功率使得直流鏈電壓下降。當直流鏈電壓過低驅動器將啟動欠電壓保護而停機，導致生產製程中斷。為了解決此一問題，利用主動前端轉換器(Active front-end converter, AFE)具有雙向電力潮流、可控式直流電壓以及交流端弦波輸入電流等特性，可用來幫助渡過電壓驟降對直流鏈電壓的影響。
本文所提之輔助式前端轉換器，對馬達驅動系統而言，正常操作下提供主動濾波、馬達煞車能量回升的功能。驟降發生時，利用輔助式前端轉換器來維持直流鏈電壓，利用正同步框轉換及負同步框轉換的技巧，可將輸入電壓的正序成份和負序成份分離，利用分離的正負序電壓量可計算出正序的電流命令以及負序的電流命令，並在靜止框下完成電流控制。如此不僅可以消除不平衡輸入電壓對直流鏈所產生的120Hz電壓擾動量，並且可維持直流鏈電壓的準位。最後將以模擬結果與實驗結果來驗證所提之系統架構與控制方法的可行性。

Voltage sags have become a major issue of power quality for industries in recently years. For the adjustable-speed drive systems, the energy charged in the dc bus capacitor is not enough for the load and cause the dc bus voltage to be drop down when voltage sag. If the dc bus voltage low enough could cause under-voltage fault and inflict significant losses with production process interruption. Therefore, in order to solve this problem, we can use the properties of active front-end converter that has bidirectional power flow, full control of dc bus voltage, and makes the ac side current nearly sinusoidal waves. It helps to provide ride-through capability for the voltage sag.
This thesis proposes an auxiliary front-end converter for the adjustable-speed drive systems. At the normal operation, it provides active filter for the harmonic current and energy regeneration capability for the motor load. Upon detection of a voltage sag, the auxiliary front-end converter operates to maintain a regulated dc-link voltage. Using positive and negative synchronous reference frame transformation, the input voltage will be separated with positive- and negative-sequence magnitude that be used to calculate the positive- and negative-sequence current command, and then transfer to stationary frame to accomplish current control. This controller can not only eliminate the 120Hz voltage ripple in the dc-link under unbalance voltage sag but also maintain a regulated dc bus voltage. Finally, the effectiveness of the proposed scheme and control method is verified by simulation and laboratory test results.

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