Analysis and Enhancement of HQT and ENTSO-E Synthetic Inertia Criteria Using the Unison U151 Wind Turbine

Yong Cheol Kang, Kicheol Kang, Youngsun Lee and Kyu-Ho Kim ()
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Yong Cheol Kang: Department of Electrical Engineering, Kwangwoon University, Seoul 01897, Republic of Korea
Kicheol Kang: Korea Renewable Energy Institute, Kunsan 54002, Republic of Korea
Youngsun Lee: Korea Renewable Energy Institute, Kunsan 54002, Republic of Korea
Kyu-Ho Kim: Department of Electrical Engineering, Hankyong National University, Anseong 17579, Republic of Korea

Energies, 2025, vol. 18, issue 20, 1-20

Abstract: Synthetic inertia (SI) enables wind turbine generators (WTGs) to support frequency stability by releasing stored kinetic energy during disturbances. Existing grid-code requirements, such as those of Hydro-Québec TransÉnergie (HQT) and ENTSO-E/Nord Pool, improve the first frequency nadir but often aggravate a second frequency dip (SFD) or risk rotor over-deceleration (OD) when the boost magnitude is large. This paper proposes an enhanced SI requirement that retains the stepwise boost-and-hold structure but replaces the time-based ramp-down with a rotor-speed-dependent recovery, followed by a smooth transition back to maximum power point tracking (MPPT). The proposed scheme was validated using an electromagnetic transient model of the Unison U151 wind turbine (4.569 MW, inertia constant 9.68 s), designed for Korea’s low-wind conditions. Five case studies at wind speeds of 5 and 7 m/s with varying boost levels confirmed that all methods yield identical first nadirs for a given boost, but only the proposed approach consistently maintained a higher second nadir, stabilized rotor dynamics, and prevented repeated dips. These results demonstrate that rotor-speed-dependent SI requirements, when combined with high-inertia turbines, can enhance frequency stability while protecting turbine operation, offering practical guidance for future grid-code revisions.

Keywords: frequency stability; grid code requirements (HQT; ENTSO-E); second frequency dip (SFD) and over-deceleration (OD); synthetic inertia (SI); Unison U151 (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2025
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