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Controllability of Magnetic Flux Linkages in Variable-Speed Electrically-Excited Synchronous Generators

B. Polajžer(1), A. Muetze(2), S. A. Seyed-Bouzari(2), J. Ritonja(1)

1. Faculty of Electrical Engineering and Computer Science
University of Maribor, Maribor, Slovenia.

2. Electric Drives and Power Electronic Systems Institute
Graz University of Technology, Graz, Austria

2026-06-27

Synchronous generators (SGs) are the primary technology for large-scale electricity generation, with stator windings connected directly to the grid. This setup limits controllability, as control action is exerted only through rotor voltage. Variable-speed SGs, which integrate a power electronic converter between the stator and grid, enhance controllability. This paper analyzes the controllability of an electrically excited SG using a d-q-axis model of the electromagnetic subsystem, assuming that both the rotor and stator voltages are controlled. The analysis shows that the model parameters significantly affect controllability. Therefore, SG controllability can be enhanced as early as the electromagnetic design phase.

Key words: Controllability, electrically-excited SG, electromagnetic design, variable-speed system.

[1] M. Valavi, A. Nysveen, “Variable-Speed Operation of Hydropower Plants: A Look at the Past, Present, and Future”, IEEE Industry Applications Magazine (2018), vol. 24, no. 5, pp. 18–27.

[2] H. Chen, et al., “Modern electric machines and drives for wind power generation: A review of opportunities and challenges”, IET Renewable Power Generation (2021), vol. 15, pp. 1864–1887.

[3] T. Holzer, et al., “Generator Design Possibilities for Full-Size Converter Operation of Large Pumped Storage Power Plants,” IEEE Transactions on Industry Applications (2020), vol. 56, no.4, pp. 3644–3655.

[4] C.-T. Chen, Linear System Theory and Design, 3rd ed. Oxford: Oxford University Press, New York (1999).

[5] T. H. Summers, F. L. Cortesi and J. Lygeros, “On submodularity and controllability in complex dynamical networks,” IEEE Transactions on Control of Network Systems (2016), vol. 3, no. 1, pp. 91–101.

[6] J. H. Stavnesli and J. K. Nøland, “Stator Flux-Regulatory Excitation Control in Converter-Fed Synchronous Machines for Pumped-Storage Variable-Speed Hydropower,” IEEE Open Access Journal of Power and Energy (2022), vol. 9, pp. 340–350.