Recently, subsynchronous oscillation (SSO) has been captured in direct-drive permanent magnetic synchronous generator (PMSG) based wind farms in many areas without series compensation in nearby power grids. However, there are fewer reports related to this new type of SSO. In addition, an analysis of the new SSO based on existing methods is computationally cumbersome, and the control effect of the converter was generally simplified in previous studies, which lead to serious errors. This paper proposes a method for analyzing the resonance characteristics of wind farms based on impedance measurement to simplify calculations and improve accuracy. The correctness and effectiveness of the proposed method are validated through the IEEE first benchmark model. A time-domain simulation model of a direct-drive PMSG is established and analyzed by harmonic impedance measurement. The results show that SSO exists when direct-drive PMSGs are connected to a weak AC system. The converter of the direct-drive PMSG exhibits a small negative value at the oscillation mode frequency. This means that the converter behaves like a capacitor with negative impedance. The capacitive impedance of the converter forms a resonant loop with the inductance of the AC grid and causes unstable SSO.

中文翻译：

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基于谐波阻抗测量法的风电场谐振特性分析

最近，在许多地区，在没有串联补偿的直接驱动永磁同步发电机（PMSG）的风电场中，已经捕获了亚同步振荡（SSO）。但是，与这种新型SSO相关的报告较少。此外，基于现有方法对新SSO的分析在计算上很麻烦，并且在以前的研究中通常简化了转换器的控制效果，这导致了严重的错误。本文提出了一种基于阻抗测量的风电场谐振特性分析方法，以简化计算并提高精度。该方法的正确性和有效性通过IEEE第一基准模型进行了验证。建立了直驱式永磁同步电动机的时域仿真模型，并通过谐波阻抗测量对其进行了分析。结果表明，当直接驱动PMSG连接到弱交流系统时，SSO存在。直接驱动PMSG的转换器在振荡模式频率下呈现较小的负值。这意味着转换器的行为类似于具有负阻抗的电容器。转换器的电容性阻抗与AC电网的电感形成谐振环路，并导致SSO不稳定。