本文主旨在建構一於不理想電源下具有改善電流不平衡功能之三相三階交流直流轉換器，文中建構電路數學模型，推導直流側平均電流，證實輸入電流不平衡使直流輸出電壓漣波振幅擾動愈加嚴重。為有效改善此情形，進而提出一調變控制策略，本文分析各種三相不理想電源交錯點寬度，並依據寬度差異於控制迴路中加入一補償迴授變數，修正三相輸入電流命令，以補償不平衡電壓的影響，產生高電力品質之輸入電流，達成三相輸入電流不平衡度修正、直流側輸出電壓調控、單位功率因數以及中性點電位補償。
控制系統使用MATLAB/SIMULINK模擬軟體進行模擬，並實作一直流輸出電壓750伏特、輸出功率2千瓦三相三階交直流轉換器供系統驗證使用，控制核心採用德州儀器公司所生產數位訊號處理器TMS320F28069作數位控制器進行實驗。模擬與實測結果證實本論文正確及可行性，其改善效果以功率因數、三相電流不平衡度表示。

關鍵字：電網電壓不平衡、三相交流電壓交錯點寬度、三相三階二極體箝位整流器、單位功因控制器

This thesis proposed a method for improving the current unbalance of a three-level AC/DC converter under unbalanced ac source. A mathematical model of the average current at the DC side is build. It is known that the unbalanced ac current will impose more interference to DC output voltage ripples. To address this problem, this study proposed a modulation control strategy to analyze the widths among the intersection points of the unbalanced ac source voltage. According to the discrepancy of the widths, a compensating variable was added into the control circuit to generate suitable three-phase input current commands. The proposed method is able to compensate the unbalance three-phase ac currents, regulate the output DC voltage, obtain unit power factor, and balance the neutral point potential.
The control scheme of this thesis is verified by using MATLAB/SIMULINK simulation software. A 750VDC/2kW three-phase three-level AC-DC converter was established for testing. The results obtained by simulation and practical testing demonstrate the correction and validity of the proposed method.

Keyword：Unbalanced Grid Source, Width of The point of Intersection in Three-phase Nonideal Power Grids, Three-phase Three-level Neutral Point Clamped rectifier, Unity Supply Power Factor

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