分布式光伏集群并网谐振问题分析及其检测方法

发布时间：2019-06-04 08:43

【摘要】：分布式光伏集群并网系统是大量光伏逆变器在并网点处集群并网的复杂高阶系统。分布式光伏发电通过光伏逆变器集群并入配电网,会导致电网发生多重电能质量问题,包括电压突升、电压暂降、电压波动与闪变、电压短时中断、电压与电流谐波、电压与电流不平衡分量、谐振等等。这严重影响了电网的电能质量,因此对分布式光伏集群并网系统中的谐振问题进行有效抑制势在必行,而准确有效的谐振扰动量检测是对其进行治理的重要前提。本文首先结合分布式光伏集群并网系统的典型结构,建立分布式光伏集群并网谐振的数学模型。结合串并联谐振原理,分析分布式光伏集群并网谐振产生的原因。分布式光伏集群中大量逆变器的引入,使得配电网成为含有诸多固有谐振点的复杂高阶电气网络。此外,电网中含有各种频谱丰富的扰动量,当这些扰动量的频率与系统固有谐振频率相匹配时,系统将发生谐振现象。其次,分析分布式光伏集群并网谐振频率分布的影响因素。从LC参数、逆变器并联台数、系统控制参数、系统网架结构变化以及光伏功率波动几方面分析分布式光伏集群谐振频率的影响因素。然后分别分析小波变换(Wavelet Transform,WT)和希尔伯特-黄变换(Hilbert-Huang Transform,HHT)的谐振检测原理。谐振表现为波形的幅值逐渐增大,甚至因过压、过流保护动作导致逆变器停机。在此基础上,本文提出一种考虑奇异性的分布式光伏集群谐振的检测方法。该方法通过WT分析分布式光伏集群并网谐振电压或电流,得到奇异性明显的频带范围。然后利用HHT分析上述频带。为了提高检测的速度,只关心包含突变点频带范围内的谐波,得到该频带内各次谐波的频率和幅值。最后观测HHT的分析结果。查看上述频带内哪一次谐波的幅值呈正增长,则该谐波信号的频率即谐振频率。仿真和实验结果表明该方法能够准确有效地检测分布式光伏集群并网系统的谐振扰动量。
[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.
【学位授予单位】：华北电力大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM615

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