為因應再生能源發電佔比的提升，本文主要針對獨立運行的交流孤島微電網架構，側重研究於如何抑制責任分界點端的電壓諧波的成分。現今之儀器設備所屬的類別大多屬於非線性負載，當微電網架構運行於孤島模式中，系統引入非線性負載時，甚至連接至微電網的距離增加等情況下，將會造成責任分界點端的電壓失真，此時使用者端所接受到的電壓信號品質將產生大幅降低。 為了減少微電網輸出電壓諧波成分，本文基於垂降控制架構提出了一種應用於三相諧波抑制的垂降控制策略。當分散式再生能源電能轉換器輸出功率時，於初級控制下估算轉換器與責任分界點之間的線路阻抗，並設計負虛擬阻抗的方式以消除線路阻抗對電壓諧波分量產生的影響，使得微電網於孤島模式引入非線性負載的情形下能具備減少微電網電壓諧波輸出的效果。隨後，透過加入諧波垂降控制法則於本地控制器中，將進一步抑制垂降控制所輸出的電壓諧波分量，此時於孤島模式運行下的微電網所產生的責任分界點電壓可維持輸出穩定供給，並減少責任分界點的電壓總諧波失真量，以提高整體孤島微電網的可靠性。 本文所提的線路阻抗估算策略主要適用於以下類別：於強電網、弱電網、弱電網加入非線性負載以及孤島下加入非線性負載造成電壓電流失真的情形。然而，一般於弱電網和孤島下加入非線性負載的情境下將添增計算難度，這將使得阻抗估算性能受到影響。於此本文的估算策略使用了一種基於二階廣義積分正交信號產生器的帶通濾波器，利用基本波實現線路阻抗估算的策略，使得轉換器將不受限於嚴峻的環境中影響其估算阻抗的能力。 ;Due to the increasing of the renewable energy power generation, this thesis is mainly focuses on the standalone operating architecture of the AC microgrids, which focuses on how to reduce the output voltage harmonics of the point of common coupling (PCC). Most of today′s instruments and equipments are belong to the category of nonlinear loads, when the microgrid system is operating in the standalone mode which including the nonlinear loads, or even when the distance between the converter and PCC of the microgrid increases, the output voltage of the PCC will result in large distortion, at this time the quality of the voltage received by the user will be significantly increased. In order to reduce the microgrid voltage harmonics of PCC, this thesis proposes a harmonic suppression control strategy based on the fundamental droop controller architecture. When the Distributed Energy Resources (DER) converter outputs power under grid-connected mode, the line impedance between the converter and the PCC can be estimated under primary control. Futhermore, the negative virtual impedance method is used to eliminate the influence of the line impedance on the output voltage harmonics. This method enables the microgrid to reduce the output voltage harmonics within the nonlinear loads. Subsequently, by adding the harmonic droop control to the converter local controller, the voltage harmonic of the PCC is further suppressed. At this time, the voltage quality generated by the microgrid in the standalone mode can be improved. It is worth mentioning that the strategy of line impedance estimation applied in the thesis is mainly suitable for the following cases: the strong power grids, weak power grids, weak power grids that introduced the nonlinear loads and the case of standalone mode under the introduce of nonlinear loads. However, generally the cases of adding nonlinear loads in weak grids or standalone mode will decrease the estimation accuracy. This thesis applied a robust estimation strategy based on a second order generalized integrator (SOGI) bandpass filter, which extracts the fundamental voltage and current to estimate line impedance, so that the estimation accuracy will not be affeced in some severe load condictions.
