弱电网条件下考虑频率耦合的三相并网逆变器简化阻抗建模及宽频带振荡分析

并网逆变器作为新能源并网时的关键接口，其输出阻抗和电网阻抗的交互，可能会引起10-2kHz宽频带振荡问题，通过分析锁相环、电流环及延时环节对阻抗特性的影响，发现锁相环和电流环是引起系统中低频振荡的主要原因，延时是引起系统高频振荡的主要原因。在考虑频率耦合的情况下建立了并网逆变器单输入单输出(SISO)序阻抗模型，并根据不同控制环主导影响不同频段的动态，建立了中低频段（10-800Hz）和高频段（＞800Hz）简化模型。针对不同控制器对系统阻抗影响界限模糊的问题，通过对系统阻抗曲线的分频段分析，明确了不同控制器对于系统稳定性的影响界限，通过阻抗匹配和奈奎斯特判据对逆变器并网系统的稳定性进行了研究，最后，仿真和实验结果验证了本文的分析。

Simplified Impedance Modeling and Broadband Oscillation Analysis for Three-phase Grid-connected Inverter Considering Frequency Coupling under Weak Grid Conditions

Grid-connected inverter is the key interface of new energy grid-connected, the interaction between its output impedance and the grid impedance, it may cause 10-2kHz broadband oscillation problems. By analyzing the influence of phase lock loop, current loop and delay on impedance characteristic, it is found that phase lock loop and current loop are the main causes of low frequency oscillation in the system, while delay is the main cause of high frequency oscillation in the system. The single input single output (SISO) sequence im-pedance model of grid-connected inverter is established considering frequency coupling, and the simplified models of middle and low frequency (10-800hz) and high frequency (> 800Hz) are established according to the different control loops dominating and influencing the dynamics of different frequency bands. Aiming at the problem of fuzzy boundary of influence of different controllers on system impedance, Through the subband analysis of the system impedance curve, made clear the region of influence of the controller for system stability, through the impedance matching and Nyquist stability criterion, the stability of the grid-connected inverter system is studied, and finally, the simulation and experimental results verify the analysis in this paper.