并网逆变器小信号建模方法对比及其适用性分析

Comparison and Applicability Analysis of Small-signal Modeling Methods for Grid-connected Inverter

小信号建模是当前微电网稳定性分析和逆变器控制器设计的重要手段。依据是否考虑滤波器和线路的动态特性,小信号模型可以分为高阶模型和降阶模型,因此产生两种模型的对比问题。文中在考虑功率环、LC滤波器与线路阻抗等各环节小信号建模的基础上,针对单逆变器并网系统建立了高阶小信号模型。进而采用稳态方程描述滤波器和线路的动态特性,得到系统的降阶模型与误差表达式。然后针对单逆变器并网工况,利用MATLAB/Simulink软件,仿真验证了两种模型的正确性。随后,通过对特征根、主要相关状态变量与误差表达式进行分析,均表明降阶模型能够高精度地获取低频特征根。此外,通过对两种小信号模型获取的参数灵敏度和根轨迹进行分析,发现降阶模型应用到低频振荡、阻尼分析和控制器设计等场合的效果与高阶模型一致。但因无法获得中高频特征根,在低阻抗比或感性网络中存在稳定性判断错误的可能性。最后,通过根轨迹及功率响应波形,验证了这些结论的正确性。

Small-signal modeling method is one of the main methods to analyze microgrid stability and design inverter controller.According to whether the dynamic characteristics of filters and lines to be considered or not,the smali-signal models can be divided into the high-order model and the reduced-order model,thus the research takes the comparison of these two models into consideration.Considering the small-signal modeling of power loop,LC filter and line impedance,a high-order small-signal model for a single-inverter grid-connected system is built.Furthermore,the steady-state equation is used to describe the dynamic characteristics of the filter and the line,and the reduced-order model and error expressions of the system are obtained.After that,for the single-inverter grid-connected system,the correctness of the two smalI-signaI models is verified by the simulation on the MATLAB/Simulink software.Then,the analysis of the eigenvalues,the main related status variables and error expressions demonstrates that the low frequency eigenvalues could be acquired accurately by the reduced- order model.In addition,by analyzing the parameter sensitivity values and root locus obtained by the two small-signal models, it is found that the effect of the reduced-order model in some occasions,such as low frequency oscillation analysis,damping anaIysis and controller design,is consistent with that of high-order model.But as the reduced-order model cannot obtain high and middle frequency eigenvalues,the stability analysis in low impedance ratio value network or inductive network may reach wrong conclusions.Finally,the correctness of these conclusions is verified by the root locus and power response waveforms.