【摘要】 高比例新能源经大量电力电子变换器并网容易诱发系统不稳定,近年来针对多变流器并网系统的小干扰稳定性分析已成为研究热点。为简化分析过程,该文将构网型与跟网型逆变器统一表示为诺顿等效电路,在此基础上推导了含构网型与跟网型逆变器的多机系统小干扰稳定性判据,该判据适用于任意网络结构,且考虑了变流器序阻抗的频率耦合效应,具有很好的普适性。依据所提出的稳定性判据,给出系统稳定性分析步骤,该方法简单易行且有助于分析各变流器对系统小干扰稳定性的影响;同时,通过详细分析虚拟同步发电机(VSG)输出序阻抗矩阵行列式在50 Hz频点处的频率特性,提出其Nyquist曲线在50 Hz处的补线原则,实现了VSG输出序导纳矩阵行列式右半平面极点数量的准确获取;最后,结合算例对多变流器系统进行了小干扰稳定性分析,并将临界稳定下系统的时域仿真结果、硬件在环实验结果和理论分析结果进行对比,定量验证了所提出的稳定性分析方法的准确性。更多还原

【Abstract】 In recent years, small-signal stability analysis of multi-converter grid-tied systems has gained significant research attention. Existing methods in the literature often overlook three critical aspects:(1) calculating the number of right-half-plane(RHP) poles in the closed-loop transfer function,(2) addressing the singularities of the converter admittance matrix at 50 Hz, and(3) evaluating the impact of individual converters on system stability. To address these gaps, this study investigates small-signal stability analysis methods for multi-converter systems comprising grid-forming(GFM) and grid-following(GFL) inverters, with a focus on determining the number of RHP poles in the sequence admittance of GFM inverters. First, a Norton-form mathematical model of the multi-converter system is established based on sequence admittance modeling. On the basis, the small signal stability analysis method of the multi-converter system is derived, and the step-by-step stability assessment procedures are presented. Secondly, due to the possibility of RHP poles in the sequence admittance matrix of the GFM converters, the frequency characteristic of the output sequence impedance matrix of the grid-forming converter, virtual synchronous generator(VSG), at 50 Hz is analyzed. A principled approach is proposed to construct the Nyquist curve at 50 Hz, enabling accurate calculation of the RHP poles in the VSG admittance matrix. Third, two case studies of multi-converter systems are analyzed to demonstrate how individual converters influence system stability. Finally, time-domain simulations and hardware-in-the-loop experiments validate the proposed method by comparing critical stability conditions with theoretical predictions. Key findings include:(1) The proposed Norton-form model accommodates arbitrary network topologies and any number of GFM/GFL converters, enabling holistic stability analysis while quantifying the impact of individual converters. Stability margins are computed using Nyquist curves, with mirror-frequency effects accounted for to prevent misjudgment.(2) Analysis of VSG admittance RHP poles reveals that ignoring impedance matrix behavior at 50 Hz and ∞Hz leads to erroneous pole counts and stability assessments. Three conclusions are drawn:(1) The recursive formulation of the proposed method supports systems with arbitrary converter counts, while the use of open-circuit impedance matrices generalizes the approach to any grid structure.(2) The method circumvents high-dimensional eigenvalue analysis of closed-loop transfer functions, relying instead on analytical eigenvalue formulas without numerical approximations.(3) By resolving the 50 Hz singularity in GFM admittance matrices, the correct count of RHP poles in the return ratio matrix is ensured, eliminating stability misclassification.更多还原