异构变流器混合并网系统的暂态同步稳定性分析及可行域刻画

doi:10.19595/j.cnki.1000-6753.tces.251973

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摘要

随着新型电力系统发展,跟网型与构网型变流器并存成为趋势,两者通过线路阻抗相互耦合显著增加了系统暂态同步稳定性的复杂性。现有方法单独分析各变流器的功角特性,无法阐明异构变流器混合并网系统整体的暂态稳定性情况。为此,该文提出一种完整的暂态稳定性分析方法,阐明了稳定平衡点（Stable Equilibrium Point, SEP）存在的主导因素,并推导了参数变化下SEP存在的条件,明确了其存在的电网阻抗范围。进而,基于环路特性与主导动力学环节,将系统降阶为二阶模型,大幅简化分析难度,系统性的揭示了影响暂态稳定性的关键因素。最后,通过实验验证了理论分析结果的正确性。

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	常锦波

关键词 ：并网变流器, 多机并联, 电网阻抗, 鞍同宿分岔, 流形理论

Abstract：

With the large-scale integration of renewable-energy grid-connection equipment, power systems are increasingly characterized by weak grid strength, low inertia, and poor damping, leading to elevated stability risks. Since grid-forming converter (GFMC) can provide voltage and frequency support and have been gradually deployed in practice, they are expected to coexist with grid-following converter (GFLC) over the long term. However, the two types of converters are coupled through transmission lines and grid impedance, and transient synchronizing instability can occur under large disturbances; hence, single-converter power-angle analysis is inadequate to characterize the overall stability boundary. To address this issue, this paper establishes a transient model that accounts for impedance and control-loop coupling, and proposes a complete transient stability analysis method focusing on the existence of a stable equilibrium point (SEP) and whether guaranteed stability recovery (GSR) can be achieved after fault clearing.
First, based on the power-synchronization mechanisms of the GFLC and the GFMC, the key nullclines of the system are derived. By leveraging the intersection relationships among zero potential surfaces, it is shown that the GFMC is the dominant component determining the existence of the SEP, and an SEP existence criterion is further obtained. With this criterion and system parameters, the grid operating-condition region in which the SEP exists is characterized. The results clarify how heterogeneous coupling compresses the feasible region for SEP existence and indicate that power allocation has a significant impact on the SEP existence range.
Second, considering that the time scale of the phase-locked loop in the GFLC is faster than that of the power-synchronization dynamics in the GFMC, and that during fault-induced oscillations the GFLC phase-angle trajectory often stays close to the corresponding zero potential surface, the GFLC is not the dominant factor leading to oscillatory instability. On this basis, a model reduction approach that preserves the dominant dynamics is adopted: the original high-order model is first reduced to a third-order model via an implicit-function constraint, and is then further reduced to a second-order model using an approximation based on the average voltage magnitude over multiple equilibrium points. Comparisons of phase-plane trajectories show that the reduced model can accurately describe the oscillatory trajectories, providing a computationally tractable low-dimensional framework for global stability analysis.
Building on the second-order model, the saddle point and its stable/unstable manifolds are used to reveal the possible existence of stable limit cycles. Moreover, a saddle homoclinic bifurcation is identified as the boundary between global stability and oscillatory instability. A GSR assessment and solution procedure is then developed to jointly characterize the SEP existence region and the GSR region. The results show that these two regions generally do not coincide: even if an SEP exists, the system may still fail to return to stable operation due to a limit cycle. In addition, the proposed method indicates that the grid voltage and power allocation parameters simultaneously affect both the SEP and GSR ranges, while heterogeneous coupling further reduces the GSR region. On the other hand, although the active-power droop coefficient and the bandwidth of the active-power loop filter do not affect the SEP existence range, they have a pronounced influence on the size of the GSR region. With proper parameter tuning, the two regions can overlap, enabling an engineering criterion under certain conditions whereby “the existence of an SEP guarantees stability recovery.”
Finally, an RT-Lab hardware-in-the-loop experimental platform is established to validate the SEP boundary, the GSR boundary, and the impacts of key parameters. The experimental results are consistent with the theoretical analysis, further demonstrating the effectiveness and practical applicability of the proposed method.

Key words： Grid-connected converter multi-converter parallel grid impedance saddle-homoclinic bifurcation manifold theory

收稿日期: 2025-11-18

PACS:

TM464

基金资助:

国家自然科学基金资助项目（52167021）

通讯作者: 陆益民女,1970年生,教授,博士生导师,研究方向为电力电子系统建模、分析与控制E-mail：gxulym@163.com

作者简介: 李玉龙男,1999年生,博士研究生,研究方向为新能源并网系统的建模、分析与控制E-mail：liyulong@st.gxu.edu.cn

引用本文:

李玉龙, 陆益民, 董洛铭, 吴盛源, 常锦波. 异构变流器混合并网系统的暂态同步稳定性分析及可行域刻画[J]. 电工技术学报, 0, (): 36-. Yulong Li, Yimin Lu, Luoming Dong, Shengyuan Wu, Jinbo Chang. Transient Stability Analysis and Feasibility Region Characterization of Hybrid Grid-Connected Systems with Heterogeneous Converters. Transactions of China Electrotechnical Society, 0, (): 36-.

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