本論文提出一個應用於電壓源不平衡之十八脈波交流/直流二極體轉換器的直流側電流注入法，以改善不同電壓不平衡度情形下電源端的總電流諧波失真，並降低電流不平衡度。系統中以Delta/delta/double polygon移相變壓器提供三組相位移各為正二十度、零度與負二十度的三相電壓源至三組二極體轉換器，並以相間變壓器並聯，構成十八脈波交流/直流轉換器系統。本系統以數位訊號處理器(TMS320F2812)做為系統控制核心，用以回授系統參數、計算補償命令及控制三相變流器開關之觸發信號，產生補償電流，再將補償電流直接注入於相間變壓器前級的直流端，改善電源端的電流品質。此直流側電流注入法使用之三相變流器除了具有低容量之優點[2.409%Po(pu)]，並與原十八脈波轉換器系統並聯操作，故當變流器發生故障無法注入電流時，系統仍可以傳統十八脈波轉換器型式操作，適合加裝至固有十八脈波轉換器系統以使用至更低電流諧波要求與需降低電源電流不平衡度之場合。本論文建立一3kW系統，並透過模擬與實作結果驗證其可行性。

In this thesis, a dc side current injection method is proposed for an 18-pulse AC/DC diode converter system with unbalanced voltage source to improve current total harmonic distortion of the power source and reduce the current unbalanced factor. In the proposed scheme, the Delta/delta/double polygon phase-shifting transformer is deployed to offer three three-phase voltage sources with +20°, 0° and -20° phase-shift to the three diode rectifiers and their outputs are parallel to the inter-phase transformer for generating the 18-pulse ac/dc converter system. This thesis applied the digital signal processor (TMS320F2812) as the core of control for feedback the parameters in system, calculating the compensation commands, and generating the trigger signals for control three phase inverter to generate the compensation current, then the compensation currents are injected to the dc side in front of the inter-phase transformer directly to improve the quality of the power supply side current. The three-phase converter used in this DC current injection method in addition to the advantages of low capacity [2.409% Po (pu)], and parallel operation with the original 18-pulse converter system, so when the converter malfunctions and cannot be injected current, the system can still work as traditional eighteen-pulse converter. It is suitable for preexisting 18-pulse converter systems to operate on the occasions demanding lower harmonics or need to reduce current unbalance factor. A 3kW prototype is built for test. Both simulation and experimental results demonstrate the validity of the proposed scheme.

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