Doubly Fed Induction Generator models in PSS/E

1

2004-29-01 Workshop - Nordic TSOs

SINTEF Energiforskning AS

Doubly Fed Induction Generator models in PSS/E

Ian Norheim

SINTEF Energy Research

January 2004

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DFIG system

AC

DCAC

DC

us=usq+jusd

isq+jisd

irq+jird

ucq+jucd urq+jurd

icq+jicd

xt

m α urq urd

Pd,loss Pr,loss

IvId

C

Ud

DFIGPgen

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Some benefits of Doubly Fed InductionGenerators for Wind Turbines

1. Torque pulsations are reduced

2. The system efficiency is improved (?)

3. The acoustic noise at low power operation is lowered

4. Possible reactive compensation

5. Reduced requirements to the pitch controller

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Implemented PSS/E model of DFIG

Programmed in FortranThird order model, i.e the stator transients due to the stator flux are neglectedInteracts with turbine models via the mechanical power and the speedThe transients due to the DC-link are neglected The active power flowing into the rotor circuit equals the active power drawn from the grid by the net side converterAn initialisation routine for the model has been implemented

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Implemented PSS/E model of DFIG cont.

qrr

mNsqNrsqs

r

m

s

dsd v

xx

vixxv

Tv ωωωωω

ωω

+−++−

/=

•'

2'

'0

' )()(

drr

mNsdNrsds

r

m

s

qsq v

xx

vixxv

Tv ωωωωω

ωω

−−−+/

−=•

'2'

'0

' )()(

)(21

aggenr TTH

−=•

ω

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The reactive power flowing through the net side converter depends on the terminal voltage of the DFIG

Vref

Cc

+

-

Qnet

G1+Ts

+

-

|vs|

PI Qconv

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The structure of the torque controller

ωt

PIvdr

Tsp(ω)

+

-

Tsp

G1+T s

Tag

*ωs

ωr iqr

+

-

xrr –(xm )2

xss

G1+Ts

*

|vs |

xm

xr

+

-

+

+

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The control of reactive power delivered to the external grid via the stator

G1+Ts

PI+Qset

-Qs

+

*

-

ωs

ωr idr

vqr

+

-

xrr –(xm)2

xss

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Simulation CASE 1In this case the DFIG model was used to represent the Havøygavlen wind farmA model of the Havøygavlen wind farm was placed into a detailed PSS/E model of the Nordic system The chosen load flow in the simulated case was built on measurements performed by Statnett/SINTEF in October 2003Disturbances in the grid were used to trigger the dynamic responses of the DFIGThe simulated dynamic responses of the wind farm are analysed and compared with the measured dynamic resposeThe turbine torque is assumed to be constant during the simulation. The shaft is modeled with a stiffness and a damping

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CASE 1 cont.

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CASE 1 cont.

Initial load flow, measurements:Produced power from the wind farm: 18 MW / -2 MvarSmørfjord – Lakselv/Skaidi: 8 MW / ? MvarSkaidi – Hammerfest: 22 MW / ? MvarInitial load flow, simulation:Produced power from the wind farm: 18 MW / -2 MvarSkaidi – Smørfjord: 5.0 MW / -2.2 MvarLakselv – Smørfjord: 3.2 MW / -1.1 MvarSkaidi – Hammerfest: 21.9 MW / -1.9 Mvar

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CASE 1 cont.

After 8 seconds of the simulation time the line Skaidi-Smørfjord was disconnected and after 22 seconds this line was reconnected. The wind farm’s active power, reactive power production, and terminal voltages were monitored in both the simulation and in the measurements

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CASE 1 cont.

0 5 10 15 20 25-5

0

5

10

15

20

Tid (sekunder)

MW

/ M

var

Aktiv effekt

Reaktiv effekt

0 5 10 15 20 25-5

0

5

10

15

20

25

Time (sec)

MW

/ M

var

Active power

Reactive power

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CASE 1 cont.

5 10 15 20 25

-3

-2.5

-2

-1.5

-1

-0.5

0

Tid (sekunder)

Rea

ktiv

effe

kt (M

var)

Utkobling av Skaidi-Smørfjord

Innkobling av Skaidi-Smørfjord

0 5 10 15 20 25-3

-2.5

-2

-1.5

-1

-0.5

0

Time (sec)

Mva

r

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CASE 1 cont.

0 5 10 15 20 2566

66.5

67

67.5

68

68.5

69

69.5

70

Tid (sekunder)

Linj

espe

nnin

ger (

kV)

0 5 10 15 20 2566

66.5

67

67.5

68

68.5

69

69.5

70

Time (sec)

Line

vol

tage

(kV

)

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CASE 1 cont.

The uncertainty due to the distibution of active power flow on the lines Smørfjord-Skaidi and Smørfjord-Lakselv may explain some of the large difference in the transient response in active powerAnother factor in this may be the difference in control strategyThe difference in the response of the line voltages are due to different load flow in the simulation and the measurementsThe chosen control strategy for the DFIG in the simulated case does work satisfactory

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CASE 2Single 2.5 MW wind turbine delivering power to a grid via a line and a transformerSimulation of the response in speed, power, and voltage from a 600 s wind series with average speed 7.9 m/s. 3P pulsations are taken into consideration through a wind field modelA two mass model representation of the drive trainCp(λ,β) calculation based on turbine speed, wind speed, and pitch angle

f n

Gear - box

v w

β

AG

ω f n - f r f r

f n

Gear - box Gear - box

v w

β

v w

β

AG

ω f n - f r ω f n - f r f rf r

Powergrid

Zline

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CASE 2 cont.

100 200 300 400 500 6000

1

2

3

4

5

6

7

8

9

10

m/s

seconds

Weighted average wind speed on the rotor blades

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CASE 2 cont.

100 200 300 400 500 6000.5

0.55

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1Generator speed

pu

seconds

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CASE 2 cont.

100 200 300 400 500 6000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Active power delivered to the grid

MW

seconds

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CASE 2 cont.

100 200 300 400 500 600-0.1

-0.08

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0.08

Reactive power flowing from the stator to the grid

Mvar

seconds

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CASE 2 cont.

100 200 300 400 500 6000.9

0.92

0.94

0.96

0.98

1

1.02

1.04

1.06

1.08

1.1

Terminal voltage

pu

seconds

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Further work

Make the DFIG model more user friendly (put in warning messages etc.)Improve the documentation on how to use the modelPerform thorough test simulations with the DFIG model (Faults, 3P fluctuations, system damping)

Documents

Doubly Fed Induction Generator models in PSS/E