【摘要】：分布式光伏集群并網(wǎng)系統(tǒng)是大量光伏逆變器在并網(wǎng)點處集群并網(wǎng)的復(fù)雜高階系統(tǒng)。分布式光伏發(fā)電通過光伏逆變器集群并入配電網(wǎng),會導(dǎo)致電網(wǎng)發(fā)生多重電能質(zhì)量問題,包括電壓突升、電壓暫降、電壓波動與閃變、電壓短時中斷、電壓與電流諧波、電壓與電流不平衡分量、諧振等等。這嚴重影響了電網(wǎng)的電能質(zhì)量,因此對分布式光伏集群并網(wǎng)系統(tǒng)中的諧振問題進行有效抑制勢在必行,而準確有效的諧振擾動量檢測是對其進行治理的重要前提。本文首先結(jié)合分布式光伏集群并網(wǎng)系統(tǒng)的典型結(jié)構(gòu),建立分布式光伏集群并網(wǎng)諧振的數(shù)學(xué)模型。結(jié)合串并聯(lián)諧振原理,分析分布式光伏集群并網(wǎng)諧振產(chǎn)生的原因。分布式光伏集群中大量逆變器的引入,使得配電網(wǎng)成為含有諸多固有諧振點的復(fù)雜高階電氣網(wǎng)絡(luò)。此外,電網(wǎng)中含有各種頻譜豐富的擾動量,當(dāng)這些擾動量的頻率與系統(tǒng)固有諧振頻率相匹配時,系統(tǒng)將發(fā)生諧振現(xiàn)象。其次,分析分布式光伏集群并網(wǎng)諧振頻率分布的影響因素。從LC參數(shù)、逆變器并聯(lián)臺數(shù)、系統(tǒng)控制參數(shù)、系統(tǒng)網(wǎng)架結(jié)構(gòu)變化以及光伏功率波動幾方面分析分布式光伏集群諧振頻率的影響因素。然后分別分析小波變換(Wavelet Transform,WT)和希爾伯特-黃變換(Hilbert-Huang Transform,HHT)的諧振檢測原理。諧振表現(xiàn)為波形的幅值逐漸增大,甚至因過壓、過流保護動作導(dǎo)致逆變器停機。在此基礎(chǔ)上,本文提出一種考慮奇異性的分布式光伏集群諧振的檢測方法。該方法通過WT分析分布式光伏集群并網(wǎng)諧振電壓或電流,得到奇異性明顯的頻帶范圍。然后利用HHT分析上述頻帶。為了提高檢測的速度,只關(guān)心包含突變點頻帶范圍內(nèi)的諧波,得到該頻帶內(nèi)各次諧波的頻率和幅值。最后觀測HHT的分析結(jié)果。查看上述頻帶內(nèi)哪一次諧波的幅值呈正增長,則該諧波信號的頻率即諧振頻率。仿真和實驗結(jié)果表明該方法能夠準確有效地檢測分布式光伏集群并網(wǎng)系統(tǒng)的諧振擾動量。
[Abstract]:Distributed photovoltaic cluster grid-connected system is a complex high-order system in which a large number of photovoltaic inverters are connected to the grid at parallel points. The integration of distributed photovoltaic power generation into distribution network through photovoltaic inverter cluster will lead to multiple power quality problems, including voltage surge, voltage sag, voltage fluctuation and flicker, short-term voltage interruption, voltage and current harmonics. Unbalanced components of voltage and current, resonance, etc. This seriously affects the power quality of the power grid, so it is imperative to effectively suppress the resonance problem in the distributed photovoltaic cluster grid-connected system, and accurate and effective resonance disturbance detection is an important prerequisite for its treatment. In this paper, based on the typical structure of distributed photovoltaic cluster grid-connected system, the mathematical model of grid-connected resonance of distributed photovoltaic cluster is established. Based on the principle of series-parallel resonance, the causes of grid-connected resonance in distributed photovoltaic clusters are analyzed. With the introduction of a large number of inverters in distributed photovoltaic clusters, distribution network has become a complex high-order electrical network with many inherent resonance points. In addition, there are a variety of spectrum rich disturbances in the power grid, when the frequency of these disturbances matches the natural resonance frequency of the system, the resonance phenomenon will occur in the system. Secondly, the influencing factors of grid-connected resonant frequency distribution of distributed photovoltaic clusters are analyzed. The influencing factors of resonant frequency of distributed photovoltaic cluster are analyzed from the aspects of LC parameters, number of parallel inverters, system control parameters, system grid structure change and photovoltaic power fluctuation. Then the resonance detection principles of wavelet transform (Wavelet Transform,WT) and Hilbert-Huang transform (Hilbert-Huang Transform,HHT) are analyzed respectively. The resonance shows that the amplitude of the waveform increases gradually, and even the inverter is shut down because of overvoltage and overcurrent protection. On this basis, a distributed photovoltaic cluster resonance detection method considering singularity is proposed in this paper. In this method, the resonant voltage or current of distributed photovoltaic cluster is analyzed by WT, and the band range of singularity is obtained. Then the above frequency band is analyzed by HHT. In order to improve the detection speed, only the harmonics in the band range containing mutation points are concerned, and the frequency and amplitude of each harmonic in the frequency band are obtained. Finally, the analysis results of HHT were observed. If the amplitude of which harmonic in the above frequency band increases positively, the frequency of the harmonic signal is the resonant frequency. The simulation and experimental results show that the method can detect the resonance disturbance of distributed photovoltaic cluster grid-connected system accurately and effectively.
【學(xué)位授予單位】：華北電力大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TM615

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