并网逆变器降阶模型及其构建方法的分析与对比

并网逆变器的小信号模型是判断系统稳定性和参数设计的重要工具。并网逆变器的完整状态方程描述会附带较多冗余信息,采用适当的降阶模型能够方便系统参数整定与调试。然而现有的一些典型降阶模型适用面较窄,在特定工况下精度较低或随着参数的变化而失去通用性。首先,通过等效惯性常数与等效阻尼系数的概念建立了通用的功率环模型;通过单边傅里叶分析指出传统的三阶模型仅适用于分析大惯性、高阻尼系统;通过输出阻抗分析指出电磁五阶模型精度对于控制参数较为敏感。为了解决降阶模型精度的问题,利用逆变器时间尺度自然分离的特性,提出了一种基于时间常数的模型降阶方法,所提方法简单、有效,并导出了可靠、简洁的高带宽降阶模型,所得模型精度高、适用面广。最后,通过对比实验验证了理论分析的正确性和所提降阶方法与降阶模型的有效性。

Analysis and Comparison of Reduced-order Model and Modeling Method for Grid-connected Inverter

The small-signal model of grid-connected inverter is an important tool for judging system stability and parameter design. The complete state equation of the grid-connected inverter will be accompanied by more redundant information. It is convenient to tune and debug system parameters by adopting appropriate reduced-order model. However, some of the existing typical reduced-order models have narrow applicability, low accuracy under specific conditions or loss of generality with the change of parameters. Firstly, this paper develops a general power-loop model based on the concepts of equivalent inertia constant and equivalent damping coefficient. Through single-side Fourier analysis, it is pointed out that the traditional third-order model is only suitable for the analysis of the systems with large inertia and high damping. Through the analysis of output impedance of grid-connected inverter, it is pointed out that the accuracy of the electromagnetic fifth-order model is sensitive to the control parameters. In order to solve the accuracy problem of reduced-order model, a model order-reduction method based on time constant is proposed by using the characteristics of natural separation of the time scale of inverters. The proposed method is simple and effective. And a simple reduced-order model of the inverter is derived. The obtained model has high accuracy and wide application. Finally, the correctness of the theoretical analysis and the effectiveness of the order-reduction method and the reduced-order model are verified by comparative experiments.