Wind Turbine Modeling - PowerWorld

Transient Stability Analysis
with PowerWorld Simulator
T12: Wind Turbine Modeling
2001 South First Street
Champaign, Illinois 61820
+1 (217) 384.6330
support@powerworld.com
http://www.powerworld.com

Need for Wind Turbine Models
• Over the last decade
wind turbine capacity
has grown to the point
where they need to be
explicitly considered in
system-wide transient
stability studies
Growth in US Wind Capacity
http://www.awea.org/publications/reports/AWEA-Annual-Wind-Report-2009.pdf
T12: Wind Turbine
© 2012 PowerWorld Corporation
2

Wind Turbine Modeling
• A wind farm usually consists of many small turbines in a
collector system
• Each turbine’s voltage is usually less than 1 kV (usually 600
V) with a step-up transformer (usually to 34.5 kV)
• Usually, the wind farm is modeled in aggregate, but how
accurate such aggregate models are is an open question
• PowerWorld Simulator provides support of each of the four
major types of wind turbine models used in transient
stability studies
– Type 1: Induction generator with fixed rotor resistance
– Type 2: Induction generators with variable rotor resistance
– Type 3: Doubly-fed induction generators
– Type 4: Full converter generators
• New wind turbines are either Type 3 or Type 4
T12: Wind Turbine
© 2012 PowerWorld Corporation
3

Wind Turbine Modeling:
Power Flow Solution
• Wind turbines are represented as generators in
the power flow
– Type 1 and 2 units operate at fixed real/reactive
power with the unit supplying real power and
consuming reactive power; usually there are
compensating capacitors
– Type 3 and 4 are treated as regular PV buses
T12: Wind Turbine
© 2012 PowerWorld Corporation
4

Wind Generator Models
• Wind Turbines do not have an “exciter”, “governor”, or
“stabilizer”
• However, modeling is very analogous
– Wind Machine Model = Machine Model
– Wind Electrical Model = Exciter
– Wind Mechanical Model = Governor
– Wind Pitch Control = Stabilizer
– Wind Aerodynamic Model = Stabilizer
• Simulator will show wind models listed as though they
are Exciters, Governors, and Stabilizers
– Obviously you should not use a synchronous machine
exciter in combination with a wind machine model and wind
governor!
T12: Wind Turbine
© 2012 PowerWorld Corporation
5

Generic Wind Turbine Models
Type 1 Type 2 Type 3 Type 4
GE DYD PSS/E DYR GE DYD PSS/E DYR GE DYD PSS/E DYR GE DYD PSS/E DYR
Machine WT1G WT1G1 WT2G WT2G1 WT3G WT3G1,
WT3G2
• Old Type 1 models as induction machine
– MOTOR1, GENIND
– CIMTR1, CIMTR2, CIMTR3, CIMTR4
• GE-specific Type 2 wind turbine model
– GENWRI, EXWTG1, WNDTRB
• GE-specific Type 3 wind turbine model
– GEWTG, EXWTGE, WNDTGE
– Detailed model for GE 1.5, 1.6 and 3.5 MW turbines
WT4G
WT4G1
“Exciter” WT2E WT2E1 WT3E WT3E1 WT4E WT4E1
“Governor” WT1T WT12T1 WT1T WT12T1 WT3T WT3T1 WT4T
“Stabilizer” WT1P W12A1 WT1P WT12A1 WT3P WT3P1
T12: Wind Turbine
© 2012 PowerWorld Corporation
6

Wind Turbine Voltage Control
• Voltage control of wind turbines depends on the type
• Type 1 squirrel cage induction machines- no direct
voltage control
• Type 2- wound rotor induction machines with variable
external resistance, no direct voltage control, but
external resistance system usually modeled as an exciter
• Type 3 and Type 4- have the ability to perform voltage
or reactive power control, similar to synchronous
machines. Common control modes are constant power
factor control, coordinated control across a wind farm to
maintain a constant interconnection point voltage, and
constant reactive power control
T12: Wind Turbine
Glover, Sarma, Overbye, Power System Analysis and Design
© 2012 PowerWorld Corporation
7

Wind Turbine Modeling
• Types 1 and 2- Induction machine models, stator windings are
connected to the rest of the network, rotor currents are
induced by the relative motion between the rotating magnetic
field due to the stator currents and the rotor
• Slip is the difference between the synchronous speed and the
rotor speed, defined using motor convention as
S
=
n
s
− n
n
• Synchronous speed is n s an rotor speed is n r , per unit
s
r
+
V t
-
R a
I
jX a
jX m
jX 1
R 1 /S
Equivalent
circuit for a
single cage
induction
machine
T12: Wind Turbine
Glover, Sarma, Overbye, Power System Analysis and Design
© 2012 PowerWorld Corporation
8

Type 1 Wind Model- WT1G Power
Speed Curve
Real Power
Type 1 generators usually operate with a small negative slip since the
wind turbine causes the machine to spin slightly faster than
synchronous speed
T12: Wind Turbine
2.8
2.6
2.4
2.2
2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1
-1.2
-1.4
-1.6
-1.8
-2
-2.2
-2.4
-2.6
-2.8
Real Power
-0.95-0.9-0.85-0.8-0.75-0.7-0.65-0.6-0.55-0.5-0.45-0.4-0.35-0.3-0.25-0.2-0.15-0.1-0.05 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95
Slip
Real Pow er
© 2012 PowerWorld Corporation
1
Values are
calculated
between
a Slip of -1 and 1
9

Type 2 Wind Models
Real Power
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1
-1.2
-1.4
• Type 2 models augment Type 1 by allowing for variable rotor
resistance control in the wound rotor induction generator
• By using turbine speed and electrical power output as inputs to the
control system, the wind turbine can provide a more steady power
output during wind variation
Real Power
external
resistance = 0.05
-1.6
-0.95 -0.9 -0.85 -0.8 -0.75 -0.7 -0.65 -0.6 -0.55 -0.5 -0.45 -0.4 -0.35 -0.3 -0.25 -0.2 -0.15 -0.1 -0.0500.050.10.150.20.250.30.350.40.450.50.550.60.650.70.750.80.850.90.951
Slip
Real Pow er
Real Power
Real Power
0.9
0.8
0.7
0.6
0.5
0.4
external resistance
0.3
0.2
= 0.99 pu
0.1
0
-0.1
-0.2
-0.3
-0.4
-0.5
-0.6
-0.7
-0.8
-0.9
-0.95 -0.9 -0.85 -0.8 -0.75 -0.7 -0.65 -0.6 -0.55 -0.5 -0.45 -0.4 -0.35 -0.3 -0.25 -0.2 -0.15 -0.1 -0.0500.050.10.150.20.250.30.350.40.450.50.550.60.650.70.750.80.850.90.951
Slip
Real Pow er
T12: Wind Turbine
© 2012 PowerWorld Corporation
10

Type 3 Wind Models
• Models Doubly-Fed Asynchronous Generators (DFAGs) or
Doubly-Fed Induction Generators (DFIGs)
• In addition to the stator windings, rotor windings are connected
to the AC network through a converter
• Allows separate control of both real and reactive power
• Allows a much wider speed range
• No electrical coupling with the turbine dynamics
• The DFAG dynamics are well approximated as a voltage-source
converter (VSC)
Output from
reactive power
control system
E q
−1
X eq
I q
I p
High/Low
Voltage
Management
I sorc
V∠θ
jX eq
I
Network
Type 3 DFAG Model, Voltage Source Converter (VSC)
Glover, Sarma, Overbye, Power System Analysis and Design
T12: Wind Turbine
© 2012 PowerWorld Corporation
11

Type 3 Wind Models
• Physically, these models usually consist of a wound rotor
induction machine coupled with a voltage-source converter
AC excitation system
• Electrical performance is dominated by the converter which
acts on a much faster time scale than transient stability level
dynamics
– Machine model consists of a synthesized voltage behind a
reactance
– Rotor dynamics are not important electrically
• Modeling
– Represents the generator by a machine model
– Reactive power control by an exciter model
– Mechanical control by a governor model
– Blade pitch control by a stabilizer model
T12: Wind Turbine
© 2012 PowerWorld Corporation
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Type 3 Wind Model Example
• Generator 3 will be modeled using a GEWTG
machine, which models a 85 MW aggregation
of GE 1.5 MW DFIGs
• Exciter model EXWTGE will be used to model
the reactive power control of the wind turbine
• Governor model WNTDGE will be used to
model the inertia of the wind turbine and its
pitch control
• Generators 1 and 2 remain unchanged
• Open the case which has these settings,
wscc_9bus_Type3WTG.pwb
T12: Wind Turbine
© 2012 PowerWorld Corporation
wscc_9bus_Type3WTG
13

Type 3 Wind Model Example
• Set up Plot Definitions as desired
• Click “Run transient Stability”
90
85
80
75
70
65
60
1.05
1
0.95
0.9
0.85
0.8
0.75
0.7
0.65
0.6
0.55
0.5
0.45
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
0
1
2
3
4
5
6
7
8
Voltage recovery
9
10
V (pu)_Bus Bus1 V (pu)_Bus Bus 2 V (pu)_Bus Bus 3
V (pu)_Bus Bus 4 V (pu)_Bus Bus 5 V (pu)_Bus Bus 6
V (pu)_Bus Bus 7 V (pu)_Bus Bus 8 V (pu)_Bus Bus 9
11
12
13
14
15
16
17
18
19
20
2.5
2.4
2.3
2.2
2.1
2
1.9
1.8
1.7
1.6
1.5
55
50
45
40
35
30
25
20
15
10
5
0
0
1
2
3
4
5
Wind turbine MW
Mechanical input and
terminal output
6
7
8
9
10
Mech Input_Gen Bus1 #1 MW Terminal_Gen Bus1 #1 Mech Input_Gen Bus 3 #1
MW Terminal_Gen Bus 3 #1 Mech Input_Gen Bus 2 #1 MW Terminal_Gen Bus 2 #1
Generator 3
EXWTGE states
11
12
13
14
15
16
17
18
19
20
1.4
1.3
1.2
1.1
1
0.9
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
T12: Wind Turbine
States of Exciter\EField_Gen Bus1 #1 States of Exciter\Sensed Vt_Gen Bus1 #1
States of Exciter\VR_Gen Bus1 #1 States of Exciter\VF_Gen Bus1 #1
© 2012 PowerWorld Corporation
wscc_9bus_Type3WTG
14

Type 3 Wind Model Example
• During the fault the wind turbine terminal bus voltage will be quite
low. This will cause the turbine’s Low Voltage Power Logic (LVPL) to
reduce the real power current to zero.
• This will cause the wind turbine pitch
control system to begin to pitch the blades
to reduce the mechanical power into the
rotor. This pitch control occurs slowly.
0.158
0.156
0.154
0.152
0.15
0.148
0.146
0.144
0.142
0.14
0.138
0.136
0.134
0.132
0.13
0.128
0.126
0.124
0.122
0.12
0
T12: Wind Turbine
1
2
3
4
5
6
7
Generator 1
Turbine Power
8
9
10
11
12
13
14
15
States of Governor\Turbine Pow er, Gen '1' '1'
16
17
18
19
20
© 2012 PowerWorld Corporation
3
2.8
2.6
2.4
2.2
2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
0
1
2
3
4
5
6
7
Pitch
8
9
10
11
12
13
States of Governor\Pitch_Gen '3' '1'
14
States of Governor\Pitch Control_Gen '3' '1'
States of Governor\Pitch Compensation_Gen '3' '1'
States of Governor\Mech Speed_Gen '3' '1'
• Once the fault is cleared, this current
is ramped back up, subject to a rate
limit.
wscc_9bus_Type3WTG
15
16
17
18
19
20
15

Example: Impact of a Complex Load
• The way load dynamics are modeled often has a significant impact
on the results of transient stability studies
• So far, we have mostly been looking at generator models, but many
load models are also available in Simulator
• The default (global) models are specified on the Options, Power
System Model page as constant impedance loads
– Used when no other model is specified
– Discussed in the Transient Stability Basics section
• Simulator makes it very easy to add complex load models
• More detailed models are added by selecting “Stability Case Info”
from the ribbon, then Case Information, Load Characteristics Models.
• Models can be specified for the entire case (system), or individual
areas, zones, owners, buses or loads.
• To insert a load model, right-click and select “Insert”
to display the Load Characteristic Information dialog.
T12: Wind Turbine
© 2012 PowerWorld Corporation
16

Complex Load Example
• Add a CLOD model to the system
– Go to the Load Characteristic page
in Model Explorer
– Right-click and choose “insert” to
open the Load Characteristic
information dialog
• In the dialog, click “System” in the
Element Type box to apply the
load model to all buses in the
system
• Click “Insert” to select the model
type. Use CLOD (see [1]), which
models the load as a combination of
large and small induction motors,
constant power and discharge
lighting loads
Applies at the system level
Insert a CLOD model
[1] J.A. Diaz de Leon II, B. Kehrli, “The Modeling Requirements for Short-Term Voltage Stability Studies,” Power Systems
Conference and Exposition (PSCE), Atlanta, GA, October, 2006, pp. 582-588.
T12: Wind Turbine
© 2012 PowerWorld Corporation
17

Complex Load Example
0.151
0.151
0.15
0.15
0.149
0.149
0.148
0.148
0.147
0.147
0.146
0.146
0.145
0.145
0.144
0.144
0.143
0.143
0.142
0.142
0.141
0.141
0.14
0.14
0.139
• The case with these settings is wscc_9bus_Type3WTG_CLOD
• Run the simulation
• Compare the plots obtained with and without the CLOD load
model
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
States of Governor\Turbine Pow er_Gen '1' '1'
Plots after inserting system-level CLOD model
16
17
18
19
20
1.05
1
0.95
0.9
0.85
0.8
0.75
0.7
0.65
0.6
0.55
0.5
0.45
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
0
1
2
3
4
5
6
V (pu)_Bus '1'
V (pu)_Bus '5'
V (pu)_Bus '9'
7
8
9
10
V (pu)_Bus '2'
V (pu)_Bus '6'
11
12
13
14
V (pu)_Bus '3'
V (pu)_Bus '7'
15
16
17
V (pu)_Bus '4'
V (pu)_Bus '8'
18
19
20
T12: Wind Turbine
© 2012 PowerWorld Corporation
wscc_9bus_Type3WTG_CLOD
18

Complex Load Example
• On the Simulation page, increase the time
for when the line is opened from 1.12
seconds to 1.155 seconds
• Open the Events tab on the Results page
• The Transient Contingency events are
there, but there are also under voltage
load trip events present
1.1
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
1
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
V (pu)_Bus Bus1 V (pu)_Bus Bus 2 V (pu)_Bus Bus 3
V (pu)_Bus Bus 4 V (pu)_Bus Bus 5 V (pu)_Bus Bus 6
V (pu)_Bus Bus 7 V (pu)_Bus Bus 8 V (pu)_Bus Bus 9
19
20
T12: Wind Turbine
© 2012 PowerWorld Corporation
wscc_9bus_Type3WTG_CLOD
19

Complex Load Example
• In the PowerWorld CLOD model, under-voltage motor tripping may be
set by the following parameters
– Vi = voltage at which trip will occur (default = 0.75 pu)
– Ti (cycles) = length of time voltage needs to be below Vi before trip will occur
• In the example, under voltage trips occurred at bus 5 and bus 8 when
the fault clearing time was increased to 1.155
• Verify that increasing the clearing time further to 1.2 causes additional
under-voltage trips of loads at buses 6, and an over-frequency trip of
Generator 2
Mechanical Power (MW)
160
150
140
130
120
110
100
90
80
70
60
50
40
30
20
0
1
2
3
cleared at 1.155 seconds
4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Time (Seconds)
Generator
Pmech
Mechanical Power (MW)
160
140
120
100
80
60
40
20
0
0
1
2
3
4
cleared at 1.2 seconds
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
Time (Seconds)
20
Mech Input_Gen Bus 2 #1 Mech Input_Gen Bus 3 #1 Mech Input_Gen Bus1 #1
Mech Input_Gen Bus 2 #1 Mech Input_Gen Bus 3 #1 Mech Input_Gen Bus1 #1
T12: Wind Turbine
© 2012 PowerWorld Corporation
wscc_9bus_Type3WTG_CLOD
20

Complex Load Example
3
2.8
2.6
2.4
2.2
2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
-0.2
Plots when fault is cleared at 1.2
seconds
0
1
2
3
4
5
6
7
8
Generator
exciter states
9
States of Exciter\EField_Gen Bus1 #1 States of Exciter\Sensed Vt_Gen Bus1 #1
States of Exciter\VR_Gen Bus1 #1 States of Exciter\VF_Gen Bus1 #1
10
11
12
13
14
15
16
17
18
19
20
Large and Small Induction Motor Loads
experience under voltage trips at buses 5,6,
and 8 at about 2 seconds after the line opens
Generator 2 opens due to over
frequency at 4.2 seconds after the line
recloses
1.2
1.1
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
1
2
3
4
5
6
Voltages
7
8
9
10
11
12
13
14
15
16
17
18
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20
V (pu)_Bus Bus1 V (pu)_Bus Bus 2 V (pu)_Bus Bus 3
V (pu)_Bus Bus 4 V (pu)_Bus Bus 5 V (pu)_Bus Bus 6
V (pu)_Bus Bus 7 V (pu)_Bus Bus 8 V (pu)_Bus Bus 9
T12: Wind Turbine
© 2012 PowerWorld Corporation
wscc_9bus_Type3WTG_CLOD
21

Complex Load Example
1.1
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
• CLOD model under-voltage tripping can be turned off by setting its
parameter Vi to zero
• Re-open the CLOD dialog, and set Vi to zero
• Run the simulation, clearing
the fault at 1.2 seconds
• Compare the plots
1
2
3
V (pu)_Bus Bus1 V (pu)_Bus Bus 2 V (pu)_Bus Bus 3
V (pu)_Bus Bus 4 V (pu)_Bus Bus 5 V (pu)_Bus Bus 6
V (pu)_Bus Bus 7 V (pu)_Bus Bus 8 V (pu)_Bus Bus 9
Voltages with undervoltage
tripping turned
OFF
T12: Wind Turbine
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
1.2
1.1
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
160
150
140
130
120
110
100
90
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 80
70
V (pu)_Bus Bus1 V (pu)_Bus Bus 2 V (pu)_Bus Bus 3
60
50
V (pu)_Bus Bus 4 V (pu)_Bus Bus 5 V (pu)_Bus Bus 6
40
V (pu)_Bus Bus 7 V (pu)_Bus Bus 8 V (pu)_Bus Bus 9
30
20
10
0
-10
0 1
Voltages with undervoltage
tripping turned
ON (default)
© 2012 PowerWorld Corporation
Mechanical Power (MW)
Set to zero to turn off
under-voltage tripping
Time (Seconds)
Mech Input_Gen Bus 2 #1 Mech Input_Gen Bus 3 #1
Mech Input_Gen Bus1 #1
wscc_9bus_Type3WTG_CLOD
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20
22

Type 4 Wind Models
• Completely asynchronous by design, called a “full converter
model”
• The wind turbine’s output is completely decoupled from the
network using an AC-DC-AC converter
• This decoupling allows considerable freedom in selecting
what type of electric machine is used
– Machine could be a conventional synchronous generator,
permanent magnet synchronous generator, or squirrel cage
induction machine
– No electrical coupling with the turbine dynamics
• Represented as a VSC, like Type 3, but with I p and I q as direct
control variables and without effective reactance
• Modeled
– Machine/Exciter combination WT4G1/WT4E1 (PSSE)
T12: Wind Turbine
– Machine/Exciter/Governor WT4G, WT4E, and WT4T (PSLF)
© 2012 PowerWorld Corporation
23