Document Type : Original Research Paper


1 Niroo Research Institute (NRI), Tehran, Iran

2 Department of Electrical Engineering, Amirkabir University of Technology, Tehran, Iran


Background and Objectives: Uncertainty and variability are two main specifications of wind generation and the ability of the power system to overcome these challenges is called flexibility. The flexibility index is a measure to evaluate the flexibility level of the power system mainly to achieve the best level system flexibility.
Methods: Flexibility index should show a good view of the ability of the power system and also be easily converted to an equivalent cost to be combined with the operation cost function. So, in this paper by using economic dispatch simulation for the economic trade-off between the generation cost and the cost of flexibility, the best level of system flexibility in the presence of wind farms considering unit constraints and system loss is achieved. Where the difference between flexibility index in the no wind base case and the flexibility index in each time zone with wind incorporation is defined as the flexibility penalty by the suitable penalty factor. The combination of generation cost and flexibility cost makes the main part of objective function.
Results: The results on the test system verify the proposed method where by increasing penalty factor, improvement in flexibility index is achieved but the generation cost will be increased. So, it shows a good economic trade-off between generation cost and flexibility value. Also the desired flexibility level can be obtained by changing the penalty factor in each wind power penetration. So, the result of the sensitivity analysis shows the best level of flexibility regarding operation cost.
Conclusion: In this paper a new flexibility index is introduced especially for wind power incorporation and for real time operation purpose. This index can be combined by economic dispatch objective function as the penalty (cost) for economic trade-off analysis and to show the best flexibility level of generation system in each operation point.

©2019 The author(s). This is an open access article distributed under the terms of the Creative Commons Attribution (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, as long as the original authors and source are cited. No permission is required from the authors or the publishers.


Main Subjects

[1] Danish Energy Agency, Flexibility in the Power System, 2015.

[2] E. Lannoye, D. Flynn, M. O'Malley, “Evaluation of power system flexibility,” IEEE Transactions on Power Systems, 27(2): 922-931, 2012.

[3] M. Poncela, A. Purvins, S. Chondrogiannis, “Pan-european analysis on power system flexibility,” Energies, 11(7): 1-19, 2018.

[4] A. Akrami, M. Doostizadeh, F. Aminifar, “Power system flexibility: an overview of emergence to evolution,” Journal of Modern Power Systems and Clean Energy, 7(5): 987-1007, 2019.

[5] J. Zhao, T. Zheng, E. Litvinov, “A unified framework for defining and measuring flexibility in power system,” IEEE Transactions on Power Systems, 31(1): 339-347, 2016.

[6] G. Papaefthymiou, E. Haesen, T. Sach, “Power system flexibility tracker: Indicators to track flexibility progress towards high-res systems,” Renewable Energy, 127: 1026-1035, 2018.

[7] J. Kiviluoma, E. Rinne, N. Helistö, “Comparison of flexibility options to improve the value of variable power generation,” International Journal of Sustainable Energy, 37(8): 761-781, 2018.

[8] V. Oree, S. Z. S. Hassen, “A composite metric for assessing flexibility available in conventional generators of power systems,” Appl. Energy, 177: 683–691, 2016.

[9] B. Mohandes, M. S. E. Moursi, N. Hatziargyriou, S. E. Khatib, “A review of power system flexibility with high penetration of renewables,” IEEE Transactions on Power Systems, 34(4): 3140-3155, 2019.

[10] T. Guo, Y. Gao, X. Zhou, Y. Li, J. Liu, “Optimal scheduling of power system incorporating the flexibility of thermal units,” Energies, 11(9): 2195, 2018.

[11] J. Cochran, M. Miller, O. Zinaman, M. Milligan, D. Arent, B. Palmintier, M. O’Malley, S. Mueller, E. Lannoye, A. Tuohy, B. Kujala, M. Sommer, H. Holttinen, J. Kiviluoma, S. K. Soonee, “Flexibility in 21st Century Power Systems,” 21st  Century Power Partnership,.

[12] M. Juan, S. Vera, B. Régine, S. Kirschen Daniel, F. Ochoa Luis, “Exploring the use of flexibility indices in low carbon power systems,” presented at the 2012 3rd IEEE PES Innovative Smart Grid Technologies Europe (ISGT Europe), Berlin, 2012.

[13] H. Berahmandpour, S. Monraser Kuhsari, H. Rastegar, “A new power system operational planning flexibility index development,” The 33rd Power System Conference, Tehran, Iran, 2018.(in persian)

[14] A. A. S. Shetava, R. El-Azab, A. Amin, O. h. Abdolla, “Flexibility measurement of power system generation for real-time applications using analytical hierarchy process,” presented at the IEEE Green Technologies Conference (GreenTech), Austin, TX, USA, 2018.

[15] A. A. Thatte, L. Xie, “A metric and market construct of inter-temporal flexibility in time-coupled economic dispatch”, IEEE Transactions on Power Systems,  31(5): 3437-3446, 2016.

[16] C. G Min, M. K. Kim, “Flexibility-based evaluation of variable generation acceptability in Korean power system,” Energies, 10(6): 825, 2017.

[17] C. G. Min, J. K. Park, D. Hur, M. K. Kim, “A risk evaluation method for ramping capability shortage in power systems,” Energy, 113: 1316–1324, 2016.

[18] C.-G. Min, “Analyzing the impact of variability and uncertainty on power system flexibility,” Appl. Sci. 9(3): 1-13, 2019.

[19] A. Ulbig, “Operational flexibility in electric power systems,” A thesis submitted to the degree of Doctor of Science of ETH Zurich, 2014.

[20] T. L. Baldwin, E. B. Makram, “Economic dispatch of electric power systems with line losses,” IEEE, Presented at the Twenty-First Southeastern Symposium on System Theory, Tallahassee, FL, USA, 1989.

[21] J. Hetzer, D. C. Yu, K. Bhattarai, “An economic dispatch model incorporating wind power,” IEEE Transaction on Energy Conversion, 23(2): 603-611, 2008.

[22] A. J. Wood, B. F. Wollenberg, B. S. Gerald, “Power generation, operation and control,” Third Edition, John Wiley and Sons, 2014.


Journal of Electrical and Computer Engineering Innovations (JECEI) welcomes letters to the editor for the post-publication discussions and corrections which allows debate post publication on its site, through the Letters to Editor. Letters pertaining to manuscript published in JECEI should be sent to the editorial office of JECEI within three months of either online publication or before printed publication, except for critiques of original research. Following points are to be considering before sending the letters (comments) to the editor.

[1] Letters that include statements of statistics, facts, research, or theories should include appropriate references, although more than three are discouraged.

[2] Letters that are personal attacks on an author rather than thoughtful criticism of the author’s ideas will not be considered for publication.

[3] Letters can be no more than 300 words in length.

[4] Letter writers should include a statement at the beginning of the letter stating that it is being submitted either for publication or not.

[5] Anonymous letters will not be considered.

[6] Letter writers must include their city and state of residence or work.

[7] Letters will be edited for clarity and length.