Transcript Document

Power
Management
of
Wind
Turbines
presented by:
Barry Rawn
MASc Candidate
University of Toronto
Wind Power Generation Symposium- February 20th, 2004 SF1105 1-5pm
Power
Management
of
Wind
Turbines
motivation
modelling
control
potential
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 generators
and wind turbines?
motivation
I.
The power available in the
wind varies on several timescales. This could impact:
-power planning
-power quality
motivation
II.
Wind turbines are systems
having nonlinear dynamics
and oscillatory modes.
This can affect considerations
of grid stability where
controlled wind turbines are
present.
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
-blades
0.8
0.4
The blades of a turbine
transfer momentum
from the wind like the
wings of an aircraft.
The character of the
flow depends on an
effective angle of
attack
λ
modelling
-blades
UNSTABLE
SLOW
power
torque
FAST
Aerodynamic stall has
two important effects:
STABLE
-dictates an optimal
power extraction
-defines a division
between two dynamical
regimes
hub speed
modelling
-spinning blades
irregular wind field forces system both
periodically and randomly
disturbance at the blade passing
frequency may
occur due to:
tower shadow
●wind shear
●rotational sampling
●
Spectra of Measured Wind and Torque Signals
2
wind
10
0
10
0
modelling
1
10
10
torque
-spinning blades
0
blade passing frequency
present in spectrum of blade
forces, but not in spectrum
of wind
1
10
Frequency (Hz)
10
Torque associated with angle, 10 minute average
0.5
averaging force signals
associated with rotor angle
reveals periodic
components
0.4
Torque (kNm)
0.3
0.2
0.1
0
-0.1
-0.2
-0.3
-0.4
-0.5
0
50
100
150
200
Hub Angle (degrees)
250
300
350
less significant for variable
speed systems
modelling
-mechanical modes
flexible structure has
many mechanical
modes of oscillation
these must be
considered in
structural designs
modelling
-mechanical modes
for control and power
system studies,
capturing the two
main inertias and their
flexible coupling is
sufficient
modelling
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
Left with responsibility to balance
power
Can partially influence how power
is delivered to the grid
control
Greg Grid
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
400
350
3000
300
2500
250
Taero, Tgen
w hub, w gen
Fast Freida has to trust
that Cool Clara will
always demand a power
that is achievable.
3500
200
150
2000
1500
100
1000
50
500
0
0
control
50
Time (s)
100
95
100
105 110
Time (s)
115
w hub, w gen
300
200
100
1
2
1
2
3
4
5
6
7
8
9
10
V cap (V)
800
700
600
3
4
5
6
Time (s)
7
8
9
10
control
Cool Clara has to trust that
Fast Freida will manage the
capacitor voltage within
tolerances, and limit
mechanical resonance
4
Stall Recovery
x 10
605
14
12
Pmech, Pelec
Vcap (V)
10
8
600
6
4
2
100
105
110
115
Time (s)
120
125
130
595
34
36
38
40
Time(s)
appropriate control design makes both assumptions valid
control
42
44
windspeed
(m/s)
Extraction of Optimal Power
15
10
5
0
100
200
300
400
500
600
0
5
x 10
100
200
300
400
500
600
0
100
200
300
400
500
600
250
(rad/s)
w hub, w gen
300
200
150
2
(W)
Pmech, Pelec
4
0
Time (s)
control
10
0
0
50
100
150
200
250
300
350
50
100
150
200
250
300
350
50
100
150
200
Time (s)
250
300
350
300
(rad/s)
w hub, w gen
windspeed (m/s)
Extraction of Averaged Optimal Power
20
200
100
Pmech, Pelec
0
4
x 10
15
10
5
0
0
control
10
0
w hub, w gen (rad/s)
windspeed (m/s)
Constant Power Extraction Based on Hub Speed Variation
20
0
50
100
150
200
250
300
0
5
x 10
50
100
150
200
250
300
0
50
100
150
Time (s)
200
250
300
600
400
200
0
Pmech, Pelec
4
2
0
-2
control
potential
Assuming such control could be practically realized, this
methodology:
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
●
potential
Power Management
of
Wind
Turbines
presented by:
Barry Rawn
MASc Candidate
University of Toronto
thanks!