Control of Wind Turbines: Past, Present and Future

1. Control of Wind Turbines: Past, Present and Future Jason Laks,Lucy Pao Alan Wright

2. OUTLINE • HAWT TURBINE OVERVIEW • BASIC TURBINE CONTROL • TORQUE AND PITCH CONTROL LOOPS • BASIC TURBINE MODEL • PITCH ORIENTATION • POWER COEFFICIENT • REGIONS OF OPERATION • BASIC TORQUE/ PITCH CONTROLLER SIMULATION • DESIGN TOOLS • ADVANCED CONTROL

3. TURBINE OVERVIEW Upwind HAWT CART3 [figure courtesy of US Dept. of Energy]

4. BASIC TURBINE CONTROL Wind w ta Ka Pitch Motor Pitch Angle b tb we wd Pitch Controller Kb Load Torque tc Torque Controller Power Converter Speed Sensor Rotor Speed

5. BASIC TURBINE CONTROL Wind w ta Ka OPERATIONAL CONTROLLER Pitch Angle b tb we wd Pitch Controller Kb Load Torque tc Torque Controller Rotor Speed

6. BASIC TURBINE CONTROL Pitch Angle b Blade Direction Tower Nacelle Wind Direction Rotor Blade

7. BASIC TURBINE CONTROL Blade Velocity: Blade Direction b Relative Velocity Wind Direction Wind Velocity: w

8. BASIC TURBINE CONTROL Blade Direction b (torque) “Thrust” Lift Wind Direction Tip Speed Ratio: Relative Velocity

9. Normalized Torque Versus Tip Speed Ratio 0.1 0.09 0.08 0.07 0.06 Normalized Torque 0.05 0.04 0.03 0.02 0.01 0 1 2 3 4 5 6 7 8 9 10 l BASIC TURBINE CONTROL • Available Wind Power • Power Harvested • Region 2:

10. BASIC TURBINE CONTROL • Region 2: torque control at optimal (tc=ta*) • Region 3: regulate speed/power • Region 4: shut down (“cut out”) (Rated Power) w

11. BASIC TURBINE CONTROL • Regions 1 & 2: Generator speed <1800 rpm • Pitch Held constant at b* • Torque adjusted according to sqare law once generator speed is > 200 rpm • Region 3: Generator speed > 1800 rpm • Torque is held constant at rated (~3500 KN-m) • Pitch is adjusted based on speed error using a PID controller . • w • Cut-Out: Once wind speed > 28m/sec • Pitch is ramped up to near perpendicular • Torque is held constant until generator speed is < 200 rpm and then regulated with a 2nd PID (no brake!)

12. BASIC TURBINE CONTROL • PID Pitch Loop Response • (HSSV = gen. speed)

13. BASIC TURBINE CONTROL

14. DESIGN TOOLS Wind Modeling System Simulation • FAST • Structural and aeroelastic simulation of two and three bladed wind turbines • Dynamically linked with simulink • TURBSIM • Generation of model-based wind fields for input to simulation • Simulink • MathWorks integration engine FAST/SIMULINK SIMULATION

15. ADVANCED TURBINE CONTROL Blade Flexible Modes (Flap & Edge) Drive Train Torsional Compliance Tower Flexible Modes (Fore-Aft, Side-Side)

16. ADVANCED TURBINE CONTROL • Numerically Linearized Model

17. ADVANCED TURBINE CONTROL • ADD FEEDBACK FROM INDIVIDUAL BLADES • INSTRUMENT TOWER TO DETECT SWAY • USE MIMO DESIGN TECHNIQUES • INDIVIDUAL BLADE PITCH • INCORPORATE WIND DISTURBANCE MODELS Torque Command MIMO CONTROL TURBINE TORQUE CONTROL Generator Speed TORQUE CONTROL Blade Measurements Individual Pitch TORQUE CONTROL Tower Measurements

18. ADVANCED TURBINE CONTROL • LIDAR BASED FEEDFORWARD • MEASURE WIND UPSTREAM FROM TURBINE • REAL TIME WIND SPEED • PRE-VIEW OF WIND SPEED CHANGES DELAY TURBINE S DIST

19. ADVANCED TURBINE CONTROL Low Speed Shaft Response 46 PID 45 FB FBFFprev 44 42.5 Speed [rpm] 42 43 41.5 38 39 40 41 42 43 44 45 42 41 30 40 50 60 70 80 90 100 Blade Flap Bending Moment Response 400 100 300 0 200 -100 38 39 40 41 42 43 44 45 100 Rm [kN-m] 0 -100 -200 -300 30 40 50 60 70 80 90 100 Time [sec]

20. SUMMARY • Operational controllers can be constructed using basic parallel torque and collective pitch controllers. • There are public domain tools and modelling codes available so that you can get started relatively quickly. • MIMO Control approaches can improve load mitigation with additional instrumentation on the turbine. • Advanced wind measurement technologies hold the promise of great improvements in performance.

21. Control of Wind Turbines: Past, Present and Future THANK YOU Jason Laks,Lucy Pao • Alan Wright