This paper considers the three-phase grid-connected inverter (GCI) as a MIMO system, and presents some new perspectives on the stability of GCI. It is found that with traditional Nyquist criterion (NC)-based method which ignores the off-diagonal components of impedance or admittance matrix, the stability results of impedance and admittance models are different. To make up this disadvantage, a simple stability analysis method based on system feedback ratio matrix (SFRM) is proposed. Instead of ignoring the couplings of impedance or admittance, the SFRM in the proposed method can be equivalent to diagonal matrix by adding a perturbation matrix into the system model, so identical results of stability analysis under impedance and admittance models are attained. Furthermore, to ensure the correctness of stability result, the boundary conditions of the proposed method are also provided. Theoretical analysis, simulation and experimental results show that compared with the state of art methods, the proposed SFRM-based method is of low computational complexity and high accuracy, and is more suitable for engineering application.

中文翻译：

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考虑系统耦合的三相并网逆变器稳定性分析新视角

本文将三相并网逆变器 (GCI) 视为一个 MIMO 系统，并对 GCI 的稳定性提出了一些新的观点。发现与传统的基于奈奎斯特准则(NC)的方法忽略阻抗或导纳矩阵的非对角分量，阻抗和导纳模型的稳定性结果不同。为了弥补这一不足，提出了一种基于系统反馈比矩阵（SFRM）的简单稳定性分析方法。该方法中的SFRM不是忽略阻抗或导纳的耦合，而是通过在系统模型中加入扰动矩阵等价于对角矩阵，从而得到阻抗模型和导纳模型下稳定性分析的相同结果。此外，为了确保稳定性结果的正确性，还提供了所提出方法的边界条件。理论分析、仿真和实验结果表明，与现有方法相比，所提出的基于SFRM的方法计算复杂度低，精度高，更适合工程应用。