Control of Wind Turbines: Past, Present and Future

11 June 2009American Control Conference St. Louis, MO

Control of Wind Turbines: Past, Present and Future

Alan WrightJason Laks, Lucy Pao

http://www.colorado.edu/


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


American Control Conference, 11 June 2009Laks , Pao & Wright 3

TURBINE OVERVIEWUpwind HAWT Horizontal Axis Turbine Types

Fixed Speed Variable Speed

FIXED PITCH Low Power

VARIABLE PITCH

Utility Scale Turbines

½ MW and Larger

CART3

[figure courtesy of US Dept. of Energy]



BASIC TURBINE CONTROL

Wind

w

wd

Speed Sensor

Pitch Motor

Rotor Speed

Pitch Angle

b

Load Torque

tc

we

Torque Controller

Pitch Controller

tbKb

Ka

ta

caeroJtttw b

1

Power Converter



OPERATIONAL CONTROLLER

Wind

w

wd

Rotor Speed

Pitch Angle

b

Load Torque

tc

we

Torque Controller

Pitch Controller

tbKb

Kata




TowerNacelle

Blade

Pitch Angle

b

RotorWind Direction

Blade

Direction




b

Wind Velocity: w

Relative Velocity


Wind Direction

Blade

Direction

Blade Velocity:



b“Thrust”

Relative Velocity

Lift

(torque)


Wind Direction

Blade

Direction

Tip Speed Ratio:



Pitch [deg]

TPS

,

CART3 Cp Level Curves

-4 -2 0 2 4 6 8

1

2

3

4

5

6

7

8

9

10

0

0.05

0.1

0.15

0.2

0.25

0.3

• Available Wind Power

• Power Harvested

• Region 2:


1 2 3 4 5 6 7 8 9 100

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1Normalized Torque Versus Tip Speed Ratio

Nor

mal

ized

Tor

que



• Region 2: torque control at optimal (tc=ta*)• Region 3: regulate speed/power• Region 4: shut down (“cut out”)


w(Rated Power)




• 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!)

• Regions 1 & 2: Generator speed < 1800 rpm– Pitch Held constant at b*

– Torque adjusted according to sqare law once generator speed is > 200 rpm

w

• 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 .



• PID Pitch Loop Response


(HSSV = gen. speed)



Wind Modeling System Simulation

PITCHff

PITCHlimit

PITCHsim

HSSVEsim

LSSVsim

WINDsim

OutData

extract wf(u)

Yaw Controller

Out1

TransportDelay

To Workspace

TIMEsim

GENTQsim

SelectShaftMeasures

measurementsHSSVE

LSSV

Scope 2

Scope 1

Scope

PitchControl

CTRLsim

PitchActuator

actmodPitchSet*pi/180

WindSet

Pitch Limits

FeedForward

FFsim

FAST Nonlinear Wind Turbine

Gen. Torque (Nm ) and Power (W)

Yaw Position (rad) and Rate (rad/s)

Blade Pitch Angles (rad)

OutData

q_out

qdot_out

Electrical Power667e3

Clock

TorqueController

LSSV Tq

w

Tg

PITCH_op (rad)

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/SIMULINKSIMULATION

DESIGN TOOLS



Blade-2 Lag

Tower Side-Side

Rotor Rotation

(b) Frontview

Blade-1 Lag

Blade-1 Flap

Tower Fore-Aft

Rotor Teeter

(a) Sideview

Blade-2 Flap

Generator RotationDrive-train

Torsion

ADVANCED TURBINE CONTROL

Tower Flexible Modes(Fore-Aft, Side-Side)

Blade Flexible Modes(Flap & Edge)

Drive Train TorsionalCompliance



Numerically Linearized Model





• ADD FEEDBACK FROM INDIVIDUAL BLADES

• INSTRUMENT TOWER TO DETECT SWAY

• USE MIMO DESIGN TECHNIQUES– INDIVIDUAL BLADE PITCH– INCORPORATE WIND DISTURBANCE

MODELS

TORQUECONTROL

TORQUECONTROL

TORQUECONTROLMIMO

CONTROL TURBINEIndividual

Pitch

TorqueCommand

BladeMeasurements

GeneratorSpeed

TowerMeasurements



TURBINE

DIST

DELAY

S

• LIDAR BASED FEEDFORWARD

– MEASURE WIND UPSTREAM

FROM TURBINE

– REAL TIME WIND SPEED

– PRE-VIEW OF WIND SPEED

CHANGES





30 40 50 60 70 80 90 10041

42

43

44

45

46Low Speed Shaft Response

Spee

d [r

pm]

PID

FB

FBFFprev

30 40 50 60 70 80 90 100-300

-200

-100

0

100

200

300

400Blade Flap Bending Moment Response

Rm [

kN-m

]

Time [sec]

38 39 40 41 42 43 44 4541.542

42.5

38 39 40 41 42 43 44 45-100

0100



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.



THANK YOU

Control of Wind Turbines: Past, Present and Future

Jason Laks, Lucy Pao Alan Wright


Control of Wind Turbines: Past, Present and Future

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