适用于光伏并网系统的传输电缆线性化模型研究

在包含长距离传输电缆的分布式发电并网系统中,电缆的阻抗模型表达式是一个超越函数。所以在对此类系统进行分析时难以直接绘制传输电缆阻抗幅频特性曲线,同时传输电缆引入的超越项对系统的多谐振及稳定性分析等问题造成困难。为了方便解决此类问题,在分析传输电缆实际阻抗模型特征的基础上提出Pade线性化拟合方法。在对不同长度电缆的拟合阶数进行分析后,得出长距离电缆使用高阶拟合模型,短距离电缆使用低阶拟合模型的结论。并且,为了让Pade拟合后的模型更加接近实际,进一步考虑电缆的集肤效应,然后通过引入去峰因子消除了拟合模型高频段不准确的谐振峰,从而使模型更加可靠和准确。最后对拟合得到的电缆模型进行验证,并利用拟合后的传输电缆模型对光伏并网系统的稳定性进行分析。仿真和实验均可验证拟合模型在光伏并网系统分析中的准确性。

LINEARIZATION MODELING OF TRANSMISSION CABLE FOR ANALYSIS OF PV GRID TIED INVERSION SYSTEM

In a distributed generation grid-connected system with long transmission lines,the transmission cable impedance model expression is a transcendental function. It is difficult to directly plot the transmission cable impedance curve when analyzing such systems,and the transduction term introduced by the transmission cable makes it difficult for the system to multi-resonance and stability analysis. To simplify the analysis of such problems,based on the transmission cable model,a Padé linearization fitting method is presented after analyzing of the characteristics of the actual impedance model of the transmission cable. The conclusion is drawn that the long transmission cable uses the high-order fitting model and the short transmission cable uses the low-order fitting model through the analysis of the fitting order of the transmission cables of different lengths. In addition,in order to bring the fitting model closer to the actual situation,the skin effect of the long transmission cable is considered. The introduction of the peak factor eliminates the inaccurate resonance peaks of the high frequency band of the Padé fitting model,which makes the fitting model more reliable. Finally,the cable model obtained by fitting is verified,and the stability of photovoltaic grid connected system is analyzed by using the fitted transmission cable model. Simulation and experiment verify the accuracy of the fitting model in the analysis of photovoltaic grid connected system.