power management of wind turbines
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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)
0 50 100 150 200 250 300 350
-0.5
-0.4
-0.3
-0.2
-0.1
0
0.1
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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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3500
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
1 2 3 4 5 6 7 8 9 10
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wh
ub
, wg
en
1 2 3 4 5 6 7 8 9 10
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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
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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
0 100 200 300 400 500 600150
200
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wh
ub,
wg
en
(rad
/s)
0 100 200 300 400 500 6000
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4x 10
5
Pm
ec
h,
Pe
lec
(W)
Time (s)
control
0 50 100 150 200 250 300 3500
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win
dsp
eed
(m
/s)
Extraction of Averaged Optimal Power
0 50 100 150 200 250 300 3500
5
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15
x 104
Pm
ec
h,
Pe
lec
Time (s)
0 50 100 150 200 250 300 350
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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
2
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
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