Power Management

ofWind

Turbines

presented by:

Barry RawnMASc CandidateUniversity of Toronto

Wind Power Generation Symposium- February 20th, 2004 SF1105 1-5pm

motivation

modelling

control

potential

Power Management

ofWind

Turbines

motivation

motivation

Improving the flexibility and power quality provided by wind generation can enable the spread of wind power.

motivation

what are the main differences between conventional generatorsand wind turbines?

motivation

The power available in the wind varies on several time-scales. This could impact:

-power planning-power quality

I.

motivation

Wind turbines are systems having nonlinear dynamics and oscillatory modes.

This can affect considerations of grid stability where controlled wind turbines are present.

II.

motivation

Modern turbines run at variable speeds and interface to the grid through power electronic converters.

An exploration can be made of the extent to which a controlled turbine can act as a more stable-looking generator.

modelling

modelling

0.8

0.4

λ

The blades of a turbinetransfer momentum from the wind like the wings of an aircraft.

The character of the flow depends on an effective angle of attack

-blades

modelling

Aerodynamic stall has two important effects:

-dictates an optimal power extraction

-defines a division between two dynamical regimes

STABLEUNSTABLE

SLOWFAST

hub speed

torq

ue

pow

er

-blades

modelling

irregular wind field forces system both periodically and randomly

disturbance at the blade passing frequency mayoccur due to:

●tower shadow●wind shear●rotational sampling

-spinning blades

modelling

blade passing frequency present in spectrum of blade forces, but not in spectrum of wind

averaging force signals associated with rotor angle reveals periodiccomponents

less significant for variable speed systems

100

101

100

102

win

d

Spectra of Measured Wind and Torque Signals

100

101

torq

ue

Frequency (Hz)

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-0.5

-0.4

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Torque associated with angle, 10 minute average

Hub Angle (degrees)

To

rqu

e (

kN

m)

-spinning blades

modelling

flexible structure has many mechanical modes of oscillation

these must be considered in structural designs

-mechanical modes

modelling

for control and power system studies, capturing the two main inertias and their flexible coupling is sufficient

-mechanical modes

modelling

control

control

●several degrees of freedom available to control energy flow within the system ●power in must balance power out

control

●different strategies exist

control

Tony Turbine Greg Grid

control

Tony Turbine

uses control freedom to:- optimize power extraction- minimize torsional oscillations

control

Greg GridLeft with responsibility to balance power

Can partially influence how power is delivered to the grid

control

Tony Turbine feeds Greg Grid a power that's best for the wind turbine, and Greg accommodates.

control

●control tasks are decoupled in some sense

●influence on grid is a shared responsibility between both Tony Turbine and Greg Grid

control

let's consider a different division of tasks: one based on energy management

control

Fast Freida Cool Clara

control

Fast Freida

maintains power balance and minimizes torsional oscillations using energy from the turbine

control

Cool Clara

sets a smooth power extraction, and reacts to grid changes appropriately using full freedom

control

Cool Clara requests a power that is least harmful to the grid. Fast Freida conveys it and attempts to contain wind disturbances.

control

The success of such a control scheme places trust in two main assumptions.

control

95 100 105 110 115

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Time (s)

Ta

ero

, Tg

en

0 50 1000

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wh

ub

, wg

en

Time (s)

Fast Freida has to trust that Cool Clara will always demand a power that is achievable.

control

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wh

ub

, wg

en

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Vc

ap

(V)

Time (s)

Cool Clara has to trust that Fast Freida will manage the capacitor voltage within tolerances, and limit mechanical resonance

control

34 36 38 40 42 44595

600

605

Vc

ap (

V)

Time(s)

100 105 110 115 120 125 130

2

4

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x 104

Pm

ech,

Pele

c

Time (s)

Stall Recovery

appropriate control design makes both assumptions valid

control

0 100 200 300 400 500 600

5

10

15

win

dsp

eed

(m

/s)

Extraction of Optimal Power

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wh

ub,

wg

en

(rad

/s)

0 100 200 300 400 500 6000

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4x 10

5

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ec

h,

Pe

lec

(W)

Time (s)

control

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win

dsp

eed

(m

/s)

Extraction of Averaged Optimal Power

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x 104

Pm

ec

h,

Pe

lec

Time (s)

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wh

ub,

wg

en

(rad

/s)

control

0 50 100 150 200 250 3000

10

20

win

dsp

eed

(m

/s) Constant Power Extraction Based on Hub Speed Variation

0 50 100 150 200 250 3000

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wh

ub,

wg

en (

rad

/s)

0 50 100 150 200 250 300-2

0

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4x 10

5

Pm

ec

h,

Pe

lec

Time (s)

potential

potential

Assuming such control could be practically realized, thismethodology:

●further reduces potentially troublesome influence of wind variation

●frees the converter interface to make the system appear more robust over short time scales

●allows the possibility of shifting between optimal and conservative power extraction, based on grid conditions

potential

Future investigation would further characterize the properties of such a controlled system. Examples include:

●controls based on inference of hub energy could eliminate need for accurate wind speed measurement and reduce stall recovery incidents

●some potential may exist for a kind of dispatchability of energy on short time scales between turbines in a wind farm

thanks!

presented by:

Barry RawnMASc CandidateUniversity of Toronto

Power Managementof

Wind Turbines