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GE Energy
Voltage And Reactive Power Control
Nicholas W. Miller
August 23, 2011BPA Voltage Control Technical Conference
2 /
GE WTG Dynamic Models
Two classes of models: DFG and FC
3
GE Energy
WTG Reactive Power Capability
• Full leading and lagging range over full power range
• Faster reactive response than synch. generator
• Capability of reactive compensation with no wind
• Behavior like a FACTS devices
4
GE Energy
Voltage at POI
Wind Plant Power Output
Voltage & Reactive Power ControlsActual measurements from a
162MW wind plant
Wind Plant Voltage
• Regulates Grid Voltage at Point of Interconnection
• Minimizes Grid Voltage Fluctuations Even Under Varying Wind Conditions
• Regulates Total Wind Plant Reactive Power through Control of Individual Turbines
Average Wind Speed
Voltage and Reactive Power RegulationLike A Conventional Power Plant…with FACTS speed
5
GE Energy
Tu
rbin
e k
VA
R
75
Time (seconds)
15000
1500
Tu
rbin
e k
VA
R
75
Time (seconds)
15000
1500
WindFREE Reactive Power
• Wind Turbine converter can deliver reactive power (kVAR) without wind (kW)
• Benefits weak grids and systems with high wind penetration
• Voltage support continues without active power generation…even following trips
Active
Power
(zero)
Reactive
Power
Field Test Results (2.5 unit)
Reactive Power - even without wind:A valuable option – An unreasonable requirement
6
GE Energy
The following 11 figures are from IEEE panel session paper:
“Validation of GE Wind Plant Models for System Planning
Simulations
Electric Machinery Committee
IEEE Power & Energy Society General Meeting
Jason MacDowell
Kara Clark
Nick Miller
Juan Sanchez-Gasca
July 25, 2011, IEEE General Power Meeting Detroit
7 /
High Side Bus (collector, e.g. 34.5kV) Terminal Bus
P gen
Q gen
Vreg bus Vterm
Project Substation
Unit Transformer
Point of Interconnection
(POI) Bus
Substation Transformer
CollectorEquivalentImpedance
GE 1.5 MW machines offered in a range of steady-state reactive power capabilities at their terminals. A common range:
• 0.90 pf overexcited (delivering 730 kVARs to the system)• 0.90 pf underexcited (drawing 730 kVARs from system)
Frequently provides +/- 0.95 pf at POI
The supervisory control will instruct individual machines to adjust their reactive power output in order to regulate system voltage; normally at the point-of-interconnection
Volt/Var Control for Application Studies
8 /
Vreg
Kiv
s+
Vref reg
1
1+ sTc
11+ sTr
Qord
-Kpv
1+ sTv
+
+
ΠΠΠΠVref qd
-
11+ sTlpqd
Kqd
QPOI
+
+
Qgen
Vref term
Vterm
KVi
s
XIQmax
Eq"cmd
XIQmin
KQi
s
-
-
+
Test
Signal
Slow Plant Level
Voltage Regulator
(WindCONTROL Emulation)
Fast Turbine Level
Voltage Regulator
Intermediate Turbine Level
Reactive Power Regulator
Verror
Vterm
IQcmd
Ipmx IPcmd
-Iqmn
Iqmx
to generator /
converter model
Converter
Current LimitP,Q priority flag
+
Doubly Fed
Full
Converter
to generator /
converter model
+
KVi
s
TestSignal
Vref qd
Pord
Vterm
Ipmx*
IPcmd
PelecPdbr
from wind
turbine model
from generator /
converter model
Dynamic Braking
Resistor to wind
turbine model
to generator /
converter model
Doubly
Fed
Full
Converter
* Ipmx is fixed for the doubly fed model, or calculated by the converter current limit
function for the full converter model.
Plant and WTG Electrical Control
9 /
Vreg
Kiv
s+
Vref reg
1
1+ sTc
11+ sTr
Qord
-Kpv
1+ sTv
+
+
ΠΠΠΠVref qd
-
11+ sTlpqd
Kqd
QPOI
+
+
Qgen
Vref term
Vterm
KVi
s
XIQmax
Eq"cmd
XIQmin
KQi
s
-
-
+
Test
Signal
Slow Plant Level
Voltage Regulator
(WindCONTROL Emulation)
Fast Turbine Level
Voltage Regulator
Intermediate Turbine Level
Reactive Power Regulator
Verror
Vterm
IQcmd
Ipmx IPcmd
-Iqmn
Iqmx
to generator /
converter model
Converter
Current LimitP,Q priority flag
+
Doubly Fed
Full
Converter
to generator /
converter model
+
KVi
s
TestSignal
Vref qd
Pord
Vterm
Ipmx*
IPcmd
PelecPdbr
from wind
turbine model
from generator /
converter model
Dynamic Braking
Resistor to wind
turbine model
to generator /
converter model
Doubly
Fed
Full
Converter
* Ipmx is fixed for the doubly fed model, or calculated by the converter current limit
function for the full converter model.
Plant and WTG Electrical Control
10 /
Model Validation – Field Test Results
11 /
Volt/Var Control
Vreg
WindCONTROL Emulator
Kiv/s+
Vrfq
(vref)
1
1+ sTc
1
1+ sTr
Qmax
Qmin
1/fN Qord
s5
s4
s3
-Kpv
1+ sTv
s2
Qwv
+
+
Vqd
-
Vermx
Vermn
< Vfrz?
If yes, freeze
2 integrators
From Q Droop
Function
Slower Plant-Level Control
++
Qcmd
Qgen
Vref
Vmax
Vterm
KVi / s
XIQmax
Vmin
Eq"cmd
To Generator
Model
s0
s1
XIQmin
KQi / s
(efd)
--
+
( model[@index].sigval[0] )
Auxiliary Test Signal
Slower WTG Q Control Fast WTG V Control
12 /
Individual WTG Test
• Test fast response of individual turbine
• 3% positive step, slow reset
++
Qcmd
Qgen
Vref
Vmax
Vterm
KVi / s
XIQmax
Vmin
Eq"cmd
To Generator
Model
s0
s1
XIQmin
KQi / s
(efd)
--
+
( model[@index].sigval[0] )
Auxiliary Test Signal
Voltage Step Stimulus
13 /
Unit Internal Voltage Reference Step Test
0
400
800
1200
1600
0 10 20 30 40 50 60 70 80 90 100
Seconds (50ms sample)
kV
APwr
QPwrGrid
Q PSLF
WTG Reactive Power ResponseP
Q
Q - Model
Unit Internal Voltage Reference Step Test
Model replicates equipment response
Full response in ~200 ms
14 /
Unit Internal Voltage Reference Step Test
0
300
600
900
1200
1500
25 26 27 28 29 30 31 32 33 34 35
Seconds (50ms sample)
kV
A
Pwr
QPwrGrid
Q PSLF
Detail - WTG Reactive Power Response
P
Q
Q - Model
Full response in ~200 ms
Unit Internal Voltage Reference Step Test
10x expanded time scale
15 /
Plant Level Volt/Var Test
VPOI WindCONTROL
Qwtg
nQcmd
Vmeas
Imeas
VTerm
Shunt Bank(s):
Manually switched
for test stimulus
Pwtg
P PLANT
Q PLANT
Qcmd i
Switch Off 10 MVAr Shunt Capacitor
16 /
Model closely replicates field response
Field Test vs. Simulation – Reactive Power and Voltage
24650
24900
25150
25400
0 10 20 30 40
kV
Seconds
V POI - MODEL
V POI - TEST
V REFERENCE
-1000
1000
3000
5000
7000
9000
11000
0 10 20 30 40
kVAR
Seconds
Q_ACTUAL - TEST
Q POI- MODEL
Q_CMD - TESTQ ord - MODEL
Q_TURBINES - TEST
Q gen - MODELCap Bank
Switched Offline
17 /
Cap Switching Test vs. Model – (100 MW Plant)
0 1 2 3 4 5 6 7 8 9 10 Seconds
0.985
0.99
0.995
1
1.005
Vpoi (p
u)
W42: V POI (Blue = Measured Green = Simulated) [(W10)|overplot(W45)]
0 1 2 3 4 5 6 7 8 9 10 Seconds
-20
-10
0
10
Qcm
d (
MV
Ar)
W44: Qcmd POI (Blue = Measured Green = Simulated) [(W19)|overplot(W47*90.18)]
0 1 2 3 4 5 6 7 8 9 10 Seconds
-6
-3
0
3
6
9
Qpoi (M
VA
r)
W43: Q POI (Blue = Measured Green = Simulated) [(W14)|overplot(W46)]
POI Voltage Response
POI Q Response
Plant Qcmd
BLUE = MEASURED GREEN = SIMULATED
Very fast, if necessary
18 /
ConclusionVoltage and Reactive Control of GE Wind Plants:
• In many respects are more flexible and faster than conventional plants
• Flexibility means attention to basic planning and operation engineering needs to be applied
• Blind application of default control settings without consideration of local requirements has, upon occasion, caused problems
• Field tuning of plant supervisory control to be relatively slow (~30 seconds) has generally resulted in good grid performance; faster is possible, if necessary
• We have NEVER encountered a voltage/reactive issue than can’t be corrected
19 /
ConclusionThe GE wind models presented here are based on:
• Currently available design and test data
• Extensive engineering judgment
• The models represent actual equipment/plant behavior appropriate for bulk planning studies and have been validated via type and field tests.
These models are:
• Evolutionary and continuously updated as experience and test data are obtained
• Open and publicly available
• Able to be shared and distributed as required
Active Power Control
Nicholas W. Miller
August 23, 2011BPA Voltage Control Technical Conference
21
GE Energy
0
5000
10000
15000
20000
25000
30000
35000
4:30:00
AM
4:38:00
AM
4:46:00
AM
4:54:00
AM
5:02:00
AM
5:10:00
AM
5:18:00
AM
5:26:00
AM
5:34:00
AM
5:42:00
AM
5:50:00
AM
5:58:00
AM
6:06:00
AM
6:14:00
AM
6:22:00
AM
6:30:00
AM
Time
Pow
er
kW
0
5
10
15
20
Actual power
Wind speed
Curtailment and Ramp Rate Limits(Example 30 MW Plant)
Ramp rate limit enforced
when curtailment is
released
Curtailed to 10
MW: regulation is
very tight
22
GE Energy
Over-Frequency Droop Response
2% Frequency Increase
50% Power Reduction
Po
we
r (k
W)
Fre
qu
en
cy (
Hz)
Function is Grid Friendly with Little Opportunity Cost: A Reasonable Request
Initial Steady-State Conditions:
• 25% power reduction for 1% frequency increase
Test:
• 2% frequency ramp-up @ 0.125 Hz/sec
• 50% reduction in plant watts with 2% over-frequency
Equivalent Under-frequency Function has High Opportunity Cost: To Be Used Sparingly
23
GE Energy
Why Inertial Response: System Needs
• Increasing Dependence on Wind Power
– Large Grids with Significant Penetration of Wind Power
• Modern variable speed wind turbine-generators do not contribute to system inertia
• System inertia declines as wind generation displaces synchronous generators (which are de-committed)
• Result is deeper frequency excursions for system disturbances
• Increased risk of
– Under-frequency load shedding (UFLS)
– Cascading outages
Inertial response enabled by power electronics enables CONTROLLED performance
(not just Park’s equations!)
24
GE Energy
How does it work? Electrical Torque, Te
Mechanical Torque, Tm
• In steady-state, torques must be balanced
• When electrical torque is greater than mechanical torque, the rotation slows extracting stored inertial energy from the rotating mass
WindINERTIAtm uses controls to increase electric power during the initial stages of a significant downward frequency
event
Electrical power delivered to gridis completely controlled by power electronics
P statorF stator
P convF network
25
GE Energy
Objectives and Constraints on Inertial Controls
• Target incremental energy similar to that provided by a synchronous turbine-generator with inertia (H constant) of 3.5 pu-sec.
• Focus on functional behavior and grid response
– do not try to exactly replicate synchronous machine behavior
• Not possible to increase wind speed
• Slowing wind turbine reduces aerodynamic lift
– must avoid stall
• Must respect WTG component ratings
– mechanical loading
– converter and generator electrical ratings
• Must respect other controls
– turbulence management
– drive-train and tower loads management
26
GE Energy
Field Tests Results:
Test count:
8 m/s - 19 tests
10 m/s – 19 tests
14 m/s – 52 tests
0
300
600
900
1200
1500
1800
0 10 20 30 40 50 60 70 80
Time (Seconds)
Po
wer
(kW
)
8 m/s Avg Meas 10 m/s Avg Meas 14 m/s Avg Meas
27
GE Energy
59.4
59.5
59.6
59.7
59.8
59.9
60
60.1
0 5 10 15 20 25 30 35 40
Time (seconds)
Fre
qu
en
cy
(H
z)
No Wind
20% Wind
20% Wind with WindINERTIA
28,000
29,000
30,000
31,000
32,000
33,000
0 5 10 15 20 25 30 35 40
Time (seconds)
Po
we
r (M
W)
20% Wind
20% Wind with WindINERTIA
Inertial response reduces
and delays minimum
frequency
Margin above UFLS
increases by about
40mHz
Response in this case is
overly aggressive:
Inertia is now another
control variable that
can be tuned.
Inertial Response from Wind Generation
Minimum frequency ~12% better
Governor response
better (more headroom)
Controlled inertial power
Inertial energy
recovery
The following 4 figures are fully discussed in
IEEE paper: “Frequency Responsive Wind Plant
Controls: Impacts on Grid Performance
N.W. Miller, K. Clark, M. Shao, GE Energy, IEEE
General Power Meeting 2011, Detroit
28
GE Energy
59.4
59.5
59.6
59.7
59.8
59.9
60
60.1
0 5 10 15 20 25 30 35 40
Time (seconds)
Fre
qu
en
cy (
Hz)
20% Wind with WindINERTIA
20% Wind with Tuned WindINERTIA
28,000
29,000
30,000
31,000
32,000
33,000
0 5 10 15 20 25 30 35 40
Time (seconds)
Po
we
r (M
W)
20% Wind with WindINERTIA
20% Wind with Tuned WindINERTIA
Tuning inertial response
further improves
frequency nadir and
reduces impact of
recovery energy
Margin above UFLS
increases by about
80mHz
(i.e. case without wind is
about 20% worse than
with wind)
Tuning Inertial Response from Wind
Minimum frequency ~20% better
Tuned inertial response
Inertial energy recovery
moderated
29
GE Energy
28,000
29,000
30,000
31,000
32,000
33,000
0 5 10 15 20 25 30 35 40
Time (seconds)
Pow
er
(MW
)
20% Wind
20% Wind with Tuned WindINERTIA
20% Wind with WindINERTIA, Different Operating Point
59.4
59.5
59.6
59.7
59.8
59.9
60
60.1
0 5 10 15 20 25 30 35 40
Time (seconds)
Fre
quency (
Hz)
No Wind
20% Wind
20% Wind with Tuned WindINERTIA
20% Wind with WindINERTIA, Different Operating Point
Same initial loadflow
condition: fewer WTGs
producing the same MW
at higher wind speed
When wind speed is high,
system response is
superior throughout
Frequency Nadir/Margin to
UFLS improved by
~80mHz
Impact of Operating Point on Inertial Response
No energy recovery when wind speed greater than rated
30
GE Energy
Frequency Response Curve
0
0.2
0.4
0.6
0.8
1
1.2
0.95 0.96 0.97 0.98 0.99 1 1.01 1.02 1.03 1.04 1.05 1.06 1.07
Frequency (pu)
Active
Po
we
r O
utp
ut
(pu
)
Point
A
(Fa,Pa)
Point B
(Fb,Pbc) Point C
(Fc,Pbc)
Point D
(Fd,Pd)
From PSLF manual
WTGs reduce power very effectively.
Symmetric droops aren’t required.
Genesis of present defaults is for systems with deeper frequency nadirs… may not
be adequate for North American grids.
36mHz DB and 5% droop is present NERC guideline.
All parameters can be set/customized. Is easy
to selectively enable/disable all
frequency sensitive controls. 2 sets of
parameters allowed: SOP in Ireland.
31 /
Turbine and Turbine Control
PitchCompensation
Power Response
Rate Limit
Torque
ControlPitch
Actuator
Pitch
Control
Wind
Power
Model
Pmech ωωωωWind
Speed
θθθθ
ωωωωrotor
+
+
+
+
ωωωω
Pelec
Rotor
Model
Pdbr
from electrical
control model
+ +
TerminalBus
Frequency
Pset
Pord
Speed Reference
Function
ωωωωref
Power
Control
Active Power
Control (optional)
from generator /
converter model
to electrical
control model
1.
WindINERTIA
Control
(optional)
+
+
Doubly
Fed
FullConverter
0
-
ωωωωerr
θθθθcmdx
-
default
APC on
0.
default
WI on
GE Energy
Thanks
GE Energy
For more information or to contact us please visitwww.ge-energy.com/ease
Nicholas W. Miller
For more information or to contact us please visitwww.ge-energy.com/ease
Nicholas W. Miller
