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Di Wu, Associate Professor, NDSU

Wednesday, July 24, 2024

IEEE PES GM, Seattle, Washington

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Oscillation Analysis for Power Systems Dominated by Grid-Forming Converters

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Reported SSO events 2007-2023

  1. Y. Cheng, IEEE PES IBR SSO Task Force, “Real-World Subsynchronous Oscillation Events in Power Grids With High Penetrations of Inverter-Based Resources,” IEEE Transactions on Power Systems, Vol. 38, no. 1, pp. 316 – 330, 2023
  2. Rob O Keefe, “January 24 & March 10, 2023 SSO Events in AEP,” EPRI SSO Workshop, Charlotte, April20, 2023.

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Low-Frequency Oscillation Arising From GFM Converters

  1. J. Tan, S. Dong, and A. Hoke, "Lessons Learned from Real-world Oscillation Events," IEEE PES General Meeting, Orlando, FL, USA, 16-20 Jul. 2023.

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Oscillation Analysis

Weak grid condition

Stiff grid condition

Remark: Low-frequency oscillation issues occur in power systems dominated by GFM converters under stiff grids rather than weak grids.

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Mode Shape and Participation Analysis

Stiff grid condition

Remarks:

1) Two GFM converters may oscillate against each other;

2) the oscillation stability is mainly related to converters’ simulative swing equations and voltage controls

Mode Shape Analysis

Participation Analysis

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Modal Analysis under Unsymmetrical Network Topology

System Decoupling

Remarks:

  1. All dominant modes are sensitive to external grid dynamics and all line impedances;
  2. The system oscillation stability depends on external grid dynamics and all line impedances.

Impact of Network Parameters on System Modes

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Modal Analysis under Symmetrical Network Topology

System Decoupling

Remark:

The system stability is more sensitive to line impedances between converter PCCs and PM, but no or less sensitive to grid impedance Zg and external grid dynamics.

Impact of Network Parameters on System Modes

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Conclusions

  • Low-frequency oscillation may arise due to the control interaction of GFM converters

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  • The oscillation may occur in stiff grids rather than weak grids

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  • Under stiff grids, oscillation characteristics depend on network topologies

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    • Under unsymmetrical network topology, the oscillation stability is sensitive to all network line impedances and external grid dynamics

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    • Under symmetrical network topology, the oscillation stability is sensitive to line impedances between converters and points of measurement but is less or not sensitive to grid impedances and external grid dynamics

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Thank you!