Temporary Rotor Inertial Control of Wind Turbine to Support the Grid Frequency Regulation

Temporary Rotor Inertial Control of Wind Turbine to Support the Grid Frequency Regulation Bing Liu, Kjetil Uhlen, Tore Undeland Department of Electric Power Engineering, NTNU The 9th Deep Sea Offshore Wind R&D Seminar 19 20 January 2012, Trondheim, NORWAY

This study focuses on variable speed wind turbine s capability of providing inertia response to support the grid frequency regulation, especially for short term frequency drop in low inertia grid.

What is inertia? Inertia is the resistance of physical object to a change in its state of motion. * Rotating objective inertia: J= m r 2 Typical 2.0 MW wind turbine has: J wind turbine = 40k * (37.5/3) 2 = 6.25 * 10 6 Kg.m 2 Energy stored in rotor mass: E = 0.5 J ω m 2 Inertia Constant is defined as the kinetic energy stored in the rotor at rated speed divided by the VA base. H = E/S= 0.5 J ω m 2 /S E wind turbine = 0.5 J ω m 2 = 0.5 *J * 1.75 2 = 9.57 * 10 6 J = H = E/S= 4.79 s Similar as conventional power generation 20 ton @ 80km/h * From Wikipedia

Why power system needs inertial control? Frequency control by keeping balance between generation and consumption. Long term balance : by power reservation Short term balance : by rotating kinetic energy

Frequency control requirements to wind turbines Nordic Grid Code 2007: Hydro Québec requires wind farm to be able to contribute to reduce large ( 0.5 Hz), short term ( 10 s) frequency deviation.* * Technical Requirements for the Connection of Generation Facilities to the Hydro Québec Transmission System: Supplementary Requirements for Wind Generation, Hydro Québec, Tech. Rep., May 2003, revised 2005.

Inertial Control is similar as Liquid Level System wind V w Pitch control E = 0.5 J ωm 2 (output power) Kinetic Energy (Energy storage) Generator electrical torque P Grid PCC

Wind turbine modeling for inertial control Extra power command Speed- Power Relationship Nominal rotor speed Rotor speed + - - Pitch Controller + + Generator power Reference power + - Converter representation Drive train representation Torque controller Aerodynamic representation

Vector Controller for generator side converter Torque Control executed in q axis. Faster than load angle control strategy*. Extra power command Reference power Speed- Power Relationship Generator power Nominal rotor speed Rotor speed - - + Pitch Controller Converter representation Drive train representation Torque controller Aerodynamic representation * P109, Wind Energy Generation: Model and Control, Olimpo A. et al.

Simulation: Wind turbine parameters when Power reference=110%, starts at 10s. y 15.0 14.0 13.0 12.0 11.0 10.0 9.0 8.0 7.0 0.50 wind speed Cp Power=10%, 70% rated rotor speed, deltap starts at 10s, 1112 P2 Wind speed (m/s) 0.40 y 0.30 0.20 0.10 Power co efficiency 0.00-0.30 Ta y (MW) -0.40 Air dynamic torque (PU) y y (pu) y (MW) y -0.50 0.100 0.075 0.050 0.025 0.000-0.025-0.050-0.075-0.100 0.00-0.20-0.40-0.60-0.80-1.00 1.000 0.950 0.900 0.850 0.800 0.750 0.700 0.650-0.50-0.60-0.70-0.80-0.90-1.00 Beta TM Wr Pm 0 10 20 30 40 50 60 TE Pitch angle Generator mechanic torque (PU) Power output (MW) Rotor speed (PU) 0 s Time (s) 60 s

How is the inertial control ability? Y: Time before reach minimal 70% rotor speed (s) X: extra power reference in PU 60 50 40 Ws=8.0m/s Pm=0,33PU 55 43 Ws=10.6m/s Pm=0,70PU 30 20 10 23 18 14 10 0 0,1 0,2 0,3 WTG Rating Control Rotor Diameter Hub Height Rated Tip speed 5 MW Variable Speed, collective Pitch 126 m 90 m 80 m/s

Power reservation by pitching for long term frequency response 1 0.8 0.6 0.4 0.2 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4

Frequency response with pitch control and inertial response control combined method implemented HZ [pu] Rotation Speed[pu] Power[pu] Torque[pu] (a) Frequency 1.01 1 0.99 1 1.5 2 2.5 (b) Rotation Speed 3 3.5 4 0.95 0.9 0.85 1 1.5 2 2.5 3 (c) Power Generation - Wind 3.5 4 0.8 0.7 0.6 1 1.5 2 2.5 3 3.5 4 1 0.5 (d) Torque 1 1.5 2 2.5 3 3.5 4 time [s] Rated (base) apparent power 400 MVA 1.0 pu Rated (base) voltage, offshore AC 115 kv 1.0 pu Rated (base) voltage, HVDC link 120 kv 1.0 pu System Frequency f ref 50 HZ 1.0 pu 150 km dc transmission line Resistance per km 0.0217 Inductance per km 0.792mH

How to make wind parks grid frequency friendly? Wind parks need react to changes in grid frequency Short term inertial response capability is limited Need to combine with long term pitch control.

Thanks! 感謝!