Assessing the capability and limitations of small signal simplified grid following models for the identification of sub-synchronous oscillations

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Coffey, Sophie and Harrison, Sam and Egea-Àlvarez, Agustí and Xu, Lie (2025) Assessing the capability and limitations of small signal simplified grid following models for the identification of sub-synchronous oscillations. IEEE Access, 13. pp. 116025-116036. ISSN 2169-3536 (https://doi.org/10.1109/ACCESS.2025.3586197)

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Abstract

Electricity grids are seeing dramatic changes due to increased power converter penetration, causing variations in grid strength, X/R ratio, and new dynamic bandwidths, which present stability challenges that need to be captured in models. The use of appropriate modelling techniques is critical to achieve an accurate stability assessment; however, it is also important to balance this accuracy with computational burden. This paper compares three key small signal models of a grid following converter; a full detail small signal model, a model order reduction (MOR) method, and a simplified phasor model. They are compared for their ability to represent transient accuracy, eigenvalue stability and ability to identify the presence of key modes that could cause sub-synchronous oscillations. Furthermore, the bandwidth and accuracy of these different modelling approaches across a range of parameters, especially as extreme conditions, needs to be defined. Therefore, this paper addresses the need for parametric sensitivity studies, and presents a methodology of evaluation of lower detail models, for highlighting instability, and the sub-synchronous, oscillatory modes that low detail models fail to capture, even when they are expected to. Results show that the MOR performs slightly better than the simplified phasor model, however, both fail to capture critical dynamic information regarding oscillatory modes at sub-synchronous frequencies in certain parameter conditions. Additionally, they both have reduced accuracy in representing system instability, especially at low short circuit ratios, when the full detail model should be used.

ORCID iDs

Coffey, Sophie ORCID logoORCID: https://orcid.org/0000-0001-6619-0669, Harrison, Sam ORCID logoORCID: https://orcid.org/0000-0002-2898-4537, Egea-Àlvarez, Agustí ORCID logoORCID: https://orcid.org/0000-0003-1286-6699 and Xu, Lie ORCID logoORCID: https://orcid.org/0000-0001-5633-7866;
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