同步机和非同步机电源接入强弱网系统小扰动稳定特性比较与统一分析

doi:10.19595/j.cnki.1000-6753.tces.242348

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摘要

同步发电机和跟网型变流器并网系统在弱网下会存在稳定性问题,而构网型变流器并网系统在强网下会存在稳定性问题,但这三种电源接入电网后强弱网失稳的特性缺少统一认识。为此,本文对同步机和非同步机电源并网系统的强弱网小扰动失稳机理进行比较分析。首先,用特征值分析法对三种电源并网系统的同步环二阶模型和考虑外环（即分别对应励磁调节和暂态电势、直流电压控制、端电压控制）的四阶模型的小扰动稳定性进行比较,确定了三种电源并网系统强弱网失稳现象均与外环控制有关。然后,分别构建三种电源并网系统的类Heffron-Phillips模型,通过同步环为主导环路,外环控制为附加支路的统一视角进行分析。基于反馈支路传递函数分解法,将三种电源并网系统不同结构的反馈传递函数G(s)分解为统一结构的二阶振荡环节H₁(s)和剩余环节H₂(s),统一分析系统强弱网失稳的附加负阻尼转矩机理。上述理论分析结果均通过了MATLAB/Simulink仿真和硬件在环实验验证。论文最后对同步机和非同步机电源接入强弱网系统小扰动稳定的更加一般化统一认识加以讨论。

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关键词 ：同步发电机, 构网型变流器, 跟网型变流器, 类Heffron-Phillips模型, 反馈支路传递函数分解法

Abstract：

The grid-connected systems of synchronous generators (SG) and grid-following converters may experience stability issues under weak grid conditions, while the grid-forming converter systems may face stability issues under stiff grid conditions. Nevertheless, a unified understanding of the instability characteristics of these three types of power sources under varying grid strengths is still lacking. To address this, this paper conducts a comparative analysis of the instability mechanisms under stiff or weak grid conditions for the SG and converter-interfaced generations. Firstly, the small-signal stability of the second-order synchronization loop model and the fourth-order model considering the outer loop for the three types of grid-connected systems was compared using eigenvalue analysis. It is determined that the instability issues under stiff or weak grid conditions for all three power source grid-connected systems are produced by the outer loop control. Next, the Heffron-Phillips-like models were constructed. Analysis is conducted from a unified perspective where the synchronization loop is the dominant loop and the outer loop control is treated as an additional branch. Based on the feedback branch transfer function decomposition method, the feedback transfer functions G(s) with different structures were decomposed into a unified second-order oscillation component H₁(s) and a left component H₂(s). A unified analysis of the instability mechanisms under stiff or weak grid conditions is conducted. The conclusions of this paper are as follows:
1) A unified Heffron-Philips-like model was developed for three types of power source grid-connected systems. The study reveals that the different instability phenomena in the weak or stiff grids are due to the involvement of outer loop control. Although the SG and grid-forming converter systems have the same synchronization loop, they exhibit significantly large negative damping coefficients under weak and stiff grid conditions, respectively, due to their differences in the outer loop control structure. This ultimately leads to instability under different grid strengths.
2) A feedback branch transfer function decomposition method was proposed for the analysis of instability mechanisms. Based on this method, the structural differences in the transfer functions used for stability analysis in different grid-connected systems can be eliminated, enhancing the uniformity of stability comparisons and analyses.
3) Since the phase of H₁(jω_n) at the natural oscillation frequency f_n is -90°, the differences in the coefficients of H₁(s) among the three types of power sources lead to different trends in the relative distance between the system oscillation frequency f_s and f_n. Consequently, the grid strengths at the instability also differ. It can be deduced that: in weak grids, the f_n of the SG is close to f_s, leading to instability; in strong grids, the f_n of the GFM-VSC is close to f_s, resulting in instability; and in weak grids, the f_n of the GFL-VSC is far from f_s, with the additional influence of the phase from the additional transfer function causing instability.

Key words： Synchronous generator GFM-VSC GFL-VSC heffron-phillips-like model feedback branch transfer function decomposition method

收稿日期: 2024-12-26

PACS:

TM712

基金资助:

国家自然科学基金资助项目（U22B6008）

通讯作者: 占萌男,1974年生,教授,博士生导师,研究方向为电力电子化电力系统动态、新能源并网稳定。E-mail：zhanmeng@hust.edu.cn

作者简介: 刘琦女,2001年生,硕士研究生,研究方向构网型变流器并网系统稳定性。E-mail：liuqi67@hust.edu.cn

引用本文:

刘琦, 占萌, 李威, 朱玲. 同步机和非同步机电源接入强弱网系统小扰动稳定特性比较与统一分析[J]. 电工技术学报, 0, (): 258103-258103. Liu Qi, Zhan Meng, Li Wei, Zhu Ling. Characteristics Comparison and Unified Analysis of Stiff or Weak Grid-Tied Small Disturbance Stability of Synchronous Generator and Converter-Interfaced Generations. Transactions of China Electrotechnical Society, 0, (): 258103-258103.

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