Study on Variable Speed Wind Turbines’ Capabilities for Frequency Response

1. Study on Variable Speed Wind Turbines’ Capabilities for Frequency Response Germán Claudio Tarnowski - Technical University of Denmark & Vestas Wind Systems A/S Jacob Østergaard - Technical University of Denmark Poul E. Sørensen - Risø National Laboratory, Denmark Philip C. Kjær - Vestas Wind Systems A/S, Denmark

2. Outline • Introduction: variable speed wind turbine frequency response for grid frequency stability. • Simulation set-up • Small/low inertia power system with wind power • Models • Simulation cases: generation trip • Conventional generation only (Base Case) • Wind power Without inertia response • Wind power + Inertia response • Wind power + Inertia response + Primary frequency control • Conclusions & remarks

3. Introduction • Grid frequency variations  Imbalance between generation and consumption • Wind Turbine Frequency Response: Change in the wind turbine active power output as response to a change in the grid frequency • Inertia response (power from rotating kinetic energy) • Primary frequency control (power from wind reserve) • Study on capabilities of WT-DFIG for providing controlled frequency response during frequency drop in a small/low inertia power system, combining inertia response and primary frequency control

4.  = 0 CP (,)  = 10 Simulation set-up: WT-DFIG model Drive train 3rd order DFIG Converter control: active and reactive power. Aerodynamics Pitch control: rotational speed

5. f (-) PDROOP(+) Power Change Wind turbine frequency response • Inertia response (inertia emulation) • Primary frequency control (Droop) • Plant power reserve (reserve factor) WT control block

6. Simulation set-up: Power system Conventional generators 50 MW Generation Loss (20%) Wind Farm replacing ST1 30% Wind Power Penetration

7. Simulation set-up: Conventional generatorsmodel Model for Steam Power Plant and Hydro Power Plant

8. Simulation cases: Inertia response from wind turbine Grid with conventional generators Grid without inertia response from WT Grid with inertia response from WT 50 MW Generation Loss (20%)

9. Results: Grid frequency Grid Frequency [Hz] Conventional generators case WT without inertia response case WT with inertia response case Frequency gradient

10. Results: Power plants electric power output Power [MW] Steam turbine ST2 Conventional generators Wind power without inertia response Inertia response from wind power Steam turbine ST1 Wind turbine Hydro turbine

11. WT inertia response Powers [pu] Torques [pu] Rotational speed [pu] Pitch angle [deg]

12. Simulation cases: inertia response + primary frequency control Droop 16% + Inertia response Droop 10% + Inertia response Droop 9% + Inertia response (Instability) 50 MW Generation Loss (20%)

13. Results: Grid frequency Grid Frequency [Hz] Conventional generators WT Droop 16% + Inertia response WT Droop 10% + Inertia response Frequency gradient

14. Results: Power plants electric power output Power [MW] Steam turbine ST2 Conventional generators Droop 16% + Inertia response Droop 10% + Inertia response Steam turbine ST1 Wind turbine Hydro turbine

15. Turbine droop 10% + inertia response Powers [pu] Torques [pu] Rotational speed [pu] Pitch angle [deg]

16. Turbine droop 9% + inertia response. Instability. Powers [pu] Torques [pu] Rotational speed [pu] Grid Frequency [Hz]

17. Conclusions & remarks • Variable speed WTs’ capabilities for inertia response and primary frequency control was studied • Suitable control systems for variable speed WTs need to be developed for integrating high amounts of wind power in the grid • Grid frequency stability can be improved combining WT inertia response and primary frequency control • Instability in wind turbines with bad settings of primary control and inertia response: Capability depends on the combination of droop value, power reserve and inertia emulation.

18. Thank you for your attentionGermán C. TARNOWSKIgct@elektro.dtu.dk