併市電型太陽能光伏系統中之脈寬調變換流器電壓諧波抑制之研究

Abstract

隨著近年來再生能源的發展，太陽能發電漸漸受到了各國的重視。對應用於市電連結型太陽光伏系統中的單相式脈波調變型換流器而言，其經過濾波後流入市電的系統輸出電流在理想上應該為一擁有特定大小和市電頻率之弦波，然而換流器輸出端存在之電壓諧波往往被視為是干擾的一種形式，儘管其中較高頻的諧波成分可以透過濾波器將其濾除，但由市電基頻所引起之低頻諧波卻難以透過濾波器濾除，進而造成流入市電之系統輸出電流扭曲、失真；此外，考慮真實情況的系統參數變化也往往是影響換流器性能的問題之一。 針對上述問題，本論文提出了一個有效的解決方法，乃是將實驗室發展之雙互質干擾觀測器(DCFDOB)架構應用於併市電的換流器中。此種雙互質干擾觀測器架構可以在免去複雜計算或外加電路的前提下提供系統對抗不同形式干擾的能力；另一方面，透過在設計觀測器參數的過程中加入了迴路整形法的觀念，藉此滿足系統穩健性與響應規格。本論文後段將會提供一系列的模擬來驗證雙互質干擾觀測器應用在併市電換流器上的可行性，結果顯示此觀測器架構不只改善了系統輸出電流的總諧波失真(THD)，亦可以降低真實情況之系統參數擾動造成的影響。

Nowadays, the solar energy has gained importance in recent years with the development of the renewable energy sources. For a single-phase dc-ac pulse-width modulated (PWM) inverter in grid-connected photovoltaic (PV) system, the system output current, which is injected into the utility grid, is expected to be a sinusoidal waveform of desired fundamental frequency and magnitude after filtering. However, the harmonics in the PWM inverter output voltage are often generated as a result of voltage source disturbances. The high-frequency harmonics are relatively easier to filter out; nevertheless, the low-frequency voltage harmonics induced by the fundamental component can cause the ac current, which is injected into the utility grid, to be distorted. In addition, the variation of system parameters is also a major problem that can affect the inverter performance. In this thesis, a Doubly Coprime Factorization Disturbance Observer (DCFDOB) structure is applied in order to solve the problems mentioned above effectively. This structure provides a sufficient flexibility to reject different types of disturbances without complicated calculations or adding extra circuit components. In addition, its design procedure contains the H∞-loop shaping method to guarantee the robust stability and robust performance. Some simulations are given to illustrate the effectiveness of the DCFDOB. The results reveal that with the application of the proposed DCFDOB scheme, the total harmonic distortion (THD) of the system output current in both nominal and practical cases are improved and the effects of system parameter variations in practical cases are reduced.