underfrequency load shedding protection

System frequency response model with underfrequency load shedding protection

Use case purpose and context

4 simple test cases have been developed in the context of XX by University of Ljubljana.

Network description

All 4 cases are based on the Underfrequency load shedding protection scheme and SSystem frequency response model as described here

Case studies

Input data

In the presented four case studies we considered a rated frequency of 50 Hz and the following SFRM parameters: H = 4, D = 1, FH = 0.3, R = 0.05, KM = 0.95 and TR = 8.

A 10-second-long time domain simulation was carried out with a time step of 1 microsecond. ΔP was modeled as a step change of ΔP = -0.7 occurring at time t = 1 second. A frequency limit value fLIM for the calculation of M via equation (3) is fLIM = 47.5 Hz.

Case study #1: Simulation without UFLS.

Case study #2: Simulation with conventional UFLS with the following settings:

  • number of stages n = 6,
  • stage frequency thresholds 49.00 Hz, 48.80 Hz, 48.60 Hz, 48.40 Hz, 48.20 Hz, 48.00 Hz,
  • stage amounts 0.10/stage.

Case study #3: Simulation with innovative UFLS with the following settings:

  • number of stages n = 6,
  • stage frequency thresholds 49.00 Hz, 48.80 Hz, 48.60 Hz, 48.40 Hz, 48.20 Hz, 48.00 Hz,
  • stage M thresholds 2.0, 1.80, 1.60, 1.40, 1.20, 1.00 seconds,
  • L-shaped fthr(M) threshold function
  • stage amounts 0.10/stage.

Case study #4: Simulation with innovative UFLS with the following settings:

  • number of stages n = 6,
  • stage frequency thresholds 49.0, 48.95, 48.90, 48.85, 48.80, 48.75 Hz,
  • stage M thresholds 2.0, 1.80, 1.60, 1.40, 1.20, 1.00 seconds,
  • ellipse-shaped fthr(M) threshold function
  • stage amounts 0.10/stage.

Case study results

The results, provided in the continuation, can be obtained by running any of the three models provided (numerical integration with Matlab, Simulink simulation, Numerical integration with Python).

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Fig.1. Case study #1: electric power system frequency response, obtained with SFRM without UFLS

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Fig.2. Case study #2: electric power system frequency response, obtained with SFRM with conventional UFLS

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Fig.3. Case study #3: electric power system frequency response, obtained with SFRM and UL (L-shaped threshold function)

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Fig.4. Case study #4: electric power system frequency response, obtained with SFRM and UL UFLS (ellipse-shaped threshold function)

Implementations

Software URL Created
Python Link 03/06/2024
Matlab/Simulink Link 03/06/2024

References

[1] P. M. Anderson and M. Mirheydar, ‘A low-order system frequency response model’, IEEE Trans. Power Syst., vol. 5, no. 3, pp. 720–729, Aug. 1990, doi: 10.1109/59.65898.

[2] T. Skrjanc, R. Mihalic, and U. Rudez, ‘A systematic literature review on under-frequency load shedding protection using clustering methods’, Renew. Sustain. Energy Rev., vol. 180, p. 113294, Jul. 2023, doi: 10.1016/j.rser.2023.113294.

[3] U. Rudež, ‘Method and device for improved under-frequency load shedding in electrical power systems: US 11 349 309 B2 - 2022-05-31’, 2022 [Online]. Available: https://si.espacenet.com/publicationDetails/originalDocument?FT=D&date=20220531&DB=&locale=si_SI&CC=US&NR=11349309B2&KC=B2&ND=4

[4] U. Rudez, D. Sodin, and R. Mihalic, ‘Estimating frequency stability margin for flexible under-frequency relay operation’, Electr. Power Syst. Res., vol. 194, p. 107116, May 2021, doi: 10.1016/j.epsr.2021.107116.

[5] U. Rudez and R. Mihalic, ‘RoCoF-based Improvement of Conventional Under-Frequency Load Shedding’, in 2019 IEEE Milan PowerTech, Jun. 2019, pp. 1–5. doi: 10.1109/PTC.2019.8810438.

[6] M. Vadillo, L. Sigrist, and U. Rudez, ‘Design and comparison of UFLS schemes of isolated power systems based on frequency stability margin’, in 2023 IEEE Belgrade PowerTech, Belgrade, Serbia: IEEE, Jun. 2023, pp. 1–6. doi: 10.1109/PowerTech55446.2023.10202842.

[7] U. Rudež, T. Dimitrovska, and R. Mihalič, ‘A RoCoF-based supplement to conventional under-frequency load shedding protection characteristic’, presented at the Pacworld 2019, Glasgow, Scotland: s. n.], p. Str. 1-12.

[8] D. Sodin, R. Ilievska, A. Čampa, M. Smolnikar, and U. Rudez, ‘Proving a Concept of Flexible Under-Frequency Load Shedding with Hardware-in-the-Loop Testing’, Energies, vol. 13, no. 14, Art. no. 14, Jan. 2020, doi: 10.3390/en13143607.

[9] A. Bonetti, J. Zakonjsek, and U. Rudez, ‘Bringing ROCOF into spotlight in Smart Grids: new standardization and UFLS method’, in 2020 2nd Global Power, Energy and Communication Conference (GPECOM), Oct. 2020, pp. 238–244. doi: 10.1109/GPECOM49333.2020.9248722.

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