Growing concerns with the harmonic oscillation phenomenon of multiterminal DC (MTDC) systems calls for appropriate harmonic stability analysis methods. However, the conventional ac or dc admittance-based stability assessment methods cannot effectively protect trade secret and user privacy, distinguish different system instability root causes, and put forward corresponding instability mitigation methods. To address the aforementioned issues, this article first establishes a hybrid ac/dc admittance-based stability assessment model for a MTDC system. Then, by introducing the determinant-based General Nyquist Criterion (GNC), the system stability is assessed and three types of instability root causes, including the ac side, the dc side, and the coupling interaction between the ac and dc sides are identified. Regarding the instability caused by the ac side, the dominant interlinking converter is directly identified, in which the instability can be mitigated by reshaping its q-axis admittance. In contrast, for the instability caused by the latter two root causes, the most influential interlinking converter is recognized by an additional sensitivity analysis. The instability is then mitigated by reshaping the dc-side equivalent admittance of the most influential interlinking converter. Compared with the conventional methods, the proposed method offers advantages as follows: 1) trade secret and user privacy is effectively protected, 2) different system instability root causes can be effectively distinguished, and 3) instabilities caused by diverse root causes can be mitigated by corresponding methods. Finally, the proposed method is verified by simulations in the MATLAB/Simulink environment.

中文翻译：

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基于混合交直流导纳模型和行列式 GNC 的多端直流 (MTDC) 系统谐波稳定性评估


人们对多端直流 (MTDC) 系统谐波振荡现象的日益关注需要适当的谐波稳定性分析方法。然而，传统的基于交流或直流导纳的稳定性评估方法无法有效保护商业秘密和用户隐私，区分不同的系统不稳定根源，并提出相应的不稳定缓解方法。针对上述问题，本文首先建立了一种基于混合交直流导纳的MTDC系统稳定性评估模型。然后，通过引入基于行列式的通用奈奎斯特准则（GNC），对系统稳定性进行了评估，并识别了三种类型的不稳定根源，包括交流侧、直流侧以及交流侧和直流侧之间的耦合相互作用。对于交流侧引起的不稳定性，直接识别出占主导地位的互连变换器，其中可以通过重塑其q轴导纳来减轻不稳定性。相比之下，对于后两个根本原因引起的不稳定，通过额外的敏感性分析来识别最有影响力的互连转换器。然后通过重塑最有影响力的互连转换器的直流侧等效导纳来减轻不稳定性。与传统方法相比，该方法具有以下优点：1）有效保护商业秘密和用户隐私；2）可以有效区分不同的系统不稳定根源；3）可以通过以下方法缓解不同根源造成的不稳定。相应的方法。最后，在MATLAB/Simulink环境下通过仿真验证了所提出的方法。