wind turbine modeling

[email protected] http://www.powerworld.com

2001 South First Street Champaign, Illinois 61820 +1 (217) 384.6330

2001 South First Street Champaign, Illinois 61820 +1 (217) 384.6330

Transient Stability Analysis with PowerWorld Simulator

T12: Wind Turbine Modeling

2 © 2012 PowerWorld Corporation T12: Wind Turbine

• 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

Need for Wind Turbine Models

http://www.awea.org/publications/reports/AWEA-Annual-Wind-Report-2009.pdf

Growth in US Wind Capacity


• 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

Wind Turbine Modeling


• 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

Wind Turbine Modeling: Power Flow Solution


• 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!

Wind Generator Models


• 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

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

WT4G WT4G1

“Exciter” WT2E WT2E1 WT3E WT3E1 WT4E WT4E1

“Governor” WT1T WT12T1 WT1T WT12T1 WT3T WT3T1 WT4T

“Stabilizer” WT1P W12A1 WT1P WT12A1 WT3P WT3P1


• 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

Wind Turbine Voltage Control

Glover, Sarma, Overbye, Power System Analysis and Design


• 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

Wind Turbine Modeling

s r

s

n nSn−

=

• Synchronous speed is ns an rotor speed is nr, per unit Ra jXa

+

-

Vt

I jXm

jX1

R1/S

Equivalent circuit for a single cage induction machine



Type 1 Wind Model- WT1G Power Speed Curve

Type 1 generators usually operate with a small negative slip since the wind turbine causes the machine to spin slightly faster than synchronous speed

Real Power

Real Pow er

Slip10.950.90.850.80.750.70.650.60.550.50.450.40.350.30.250.20.150.10.050-0.05-0.1-0.15-0.2-0.25-0.3-0.35-0.4-0.45-0.5-0.55-0.6-0.65-0.7-0.75-0.8-0.85-0.9-0.95

Rea

l Pow

er

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

Values are calculated between a Slip of -1 and 1


• 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

Type 2 Wind Models

Real Power

Real Pow er

Slip10.950.90.850.80.750.70.650.60.550.50.450.40.350.30.250.20.150.10.050-0.05-0.1-0.15-0.2-0.25-0.3-0.35-0.4-0.45-0.5-0.55-0.6-0.65-0.7-0.75-0.8-0.85-0.9-0.95

Rea

l Pow

er

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

Real Power

Real Pow er

Slip10.950.90.850.80.750.70.650.60.550.50.450.40.350.30.250.20.150.10.050-0.05-0.1-0.15-0.2-0.25-0.3-0.35-0.4-0.45-0.5-0.55-0.6-0.65-0.7-0.75-0.8-0.85-0.9-0.95

Rea

l Pow

er

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

-0.1

-0.2

-0.3

-0.4

-0.5

-0.6

-0.7

-0.8

-0.9

external resistance = 0.05

external resistance = 0.99 pu


• 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)

Type 3 Wind Models

V θ∠

jXeq

High/Low Voltage Management

1

eqX−

Isorc

Iq

Ip

Eq

I

Type 3 DFAG Model, Voltage Source Converter (VSC)

Output from reactive power control system

Network



• 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

Type 3 Wind Models


• 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

Type 3 Wind Model Example

wscc_9bus_Type3WTG


States of Exciter\EField_Gen Bus1 #1 States of Exciter\Sensed Vt_Gen Bus1 #1States of Exciter\VR_Gen Bus1 #1 States of Exciter\VF_Gen Bus1 #1

20191817161514131211109876543210

2.5

2.4

2.3

2.2

2.1

2

1.9

1.8

1.7

1.6

1.5

1.4

1.3

1.2

1.1

1

0.9

Mech Input_Gen Bus1 #1 MW Terminal_Gen Bus1 #1 Mech Input_Gen Bus 3 #1MW Terminal_Gen Bus 3 #1 Mech Input_Gen Bus 2 #1 MW Terminal_Gen Bus 2 #1

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90

85

80

75

70

65

60

55

50

45

40

35

30

25

20

15

10

5

0

V (pu)_Bus Bus1 V (pu)_Bus Bus 2 V (pu)_Bus Bus 3V (pu)_Bus Bus 4 V (pu)_Bus Bus 5 V (pu)_Bus Bus 6V (pu)_Bus Bus 7 V (pu)_Bus Bus 8 V (pu)_Bus Bus 9

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1.051

0.950.9

0.850.8

0.750.7

0.650.6

0.550.5

0.450.4

0.350.3

0.250.2

0.150.1

0.050

• Set up Plot Definitions as desired • Click “Run transient Stability”


Wind turbine MW Mechanical input and terminal output Voltage recovery

Generator 3 EXWTGE states

wscc_9bus_Type3WTG


States of Governor\Pitch_Gen '3' '1'States of Governor\Pitch Control_Gen '3' '1'States of Governor\Pitch Compensation_Gen '3' '1'States of Governor\Mech Speed_Gen '3' '1'

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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

• 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.

States of Governor\Turbine Pow er, Gen '1' '1'

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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

• Once the fault is cleared, this current is ramped back up, subject to a rate limit.

Generator 1 Turbine Power

Pitch

wscc_9bus_Type3WTG


• 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.

Example: Impact of a Complex Load


• 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

Complex Load Example

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.


• The case with these settings is wscc_9bus_Type3WTG_CLOD • Run the simulation • Compare the plots obtained with and without the CLOD load

model


States of Governor\Turbine Pow er_Gen '1' '1'

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0.1510.151

0.150.15

0.1490.1490.1480.1480.1470.1470.1460.1460.1450.1450.1440.1440.1430.1430.1420.1420.1410.141

0.140.14

0.139

V (pu)_Bus '1' V (pu)_Bus '2' V (pu)_Bus '3' V (pu)_Bus '4'V (pu)_Bus '5' V (pu)_Bus '6' V (pu)_Bus '7' V (pu)_Bus '8'V (pu)_Bus '9'

20191817161514131211109876543210

1.051

0.950.9

0.850.8

0.750.7

0.650.6

0.550.5

0.450.4

0.350.3

0.250.2

0.150.1

0.050

Plots after inserting system-level CLOD model

wscc_9bus_Type3WTG_CLOD



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1.1

1

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

• 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




Mech Input_Gen Bus 2 #1 Mech Input_Gen Bus 3 #1 Mech Input_Gen Bus1 #1

Time (Seconds)20191817161514131211109876543210

Mec

hani

cal P

ower

(MW

)

160

140

120

100

80

60

40

20

0

Mech Input_Gen Bus 2 #1 Mech Input_Gen Bus 3 #1 Mech Input_Gen Bus1 #1

Time (Seconds)20191817161514131211109876543210

Mec

hani

cal P

ower

(MW

)

1601501401301201101009080706050403020

• 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


cleared at 1.2 seconds Generator Pmech

cleared at 1.155 seconds



States of Exciter\EField_Gen Bus1 #1 States of Exciter\Sensed Vt_Gen Bus1 #1States of Exciter\VR_Gen Bus1 #1 States of Exciter\VF_Gen Bus1 #1

20191817161514131211109876543210

32.82.62.42.2

21.81.61.41.2

10.80.60.40.2

0-0.2


20191817161514131211109876543210

1.2

1.1

1

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0


Voltages

Generator exciter states

Plots when fault is cleared at 1.2 seconds

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



• 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

Voltages with under-voltage tripping turned OFF

Voltages with under-voltage tripping turned ON (default)



20191817161514131211109876543210

1.1

1

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0


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1.2

1.1

1

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

Set to zero to turn off under-voltage tripping

Mech Input_Gen Bus 2 #1 Mech Input_Gen Bus 3 #1Mech Input_Gen Bus1 #1

Time (Seconds)20191817161514131211109876543210

Mec

hani

cal P

ower

(MW

)

1601501401301201101009080706050403020100

-10


• 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 Ip and Iq as direct

control variables and without effective reactance • Modeled

– Machine/Exciter combination WT4G1/WT4E1 (PSSE) – Machine/Exciter/Governor WT4G, WT4E, and WT4T (PSLF)

Type 4 Wind Models

wind turbine modeling

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