Presented at 2012 3rd IEEE PES ISGT Europe, Berlin, Germany

Voltage and Reactive Power

Control by Wind Turbines

Jens Fortmann, REpower Systems SE

Berlin, October 16th 2012

2Jens Fortmann, IEEE ISGT, 16.10.2012, © REpower Systems SE

Voltage and Reactive Power Control by Wind Turbines

Starting point is the behavior of a synchronous generators

Questions for the turbine reactive power control design:

How should we operate a wind turbine

to offer the best grid support possible

How should wind turbines behave to replace conventional power stations

with no need for further grid reinforcement or grid equipment

Can we do even better

(than conventional power stations)

How do conventional power stations contribute to grid stability

?

?

1

2

3 ?

?

Presented at 2012 3rd IEEE PES ISGT Europe, Berlin, Germany, October 14 -17, 2012



Why consider dynamic requirements?

Static requirements: reactive current during normal operation

Dynamic requirements: reactive current if voltage changes

Initially (before E.ON 2003): no dynamic requirement

=> all conventional power stations must stay in operation

Future (starting already…): fully replace conventional power stations

=> conventional power stations may shut down

Now: (SDLWindV): some dynamic requirements

=> most conventional power stations must stay in operation

1

2

3


Agenda

1. Basis: Behaviour of synchronous generators

2. Wind plant implementation

3. Simulations

4. Conclusion



Agenda



3. Simulations

4. Conclusion



Starting of E.ON Netz in 2003

Analysis of E.ON Netz from 2003:

Response of a synchronous generator of a conventional power station

Source: Kühn, Radtke, “Der Einfluss von

Windenergie auf das Verbundnetz”, E.ON Netz

2003



pv

d dj jx x

d dj jx x

qv

sv

qv

djx

d0v

q qj jx x

q qj jx x

dv

dv

qjx

sr Tr

z

HVv

Trv

ev

Setpoints field voltage /excitation controller

reactive currentgeneration (genertor)

high voltage transformer

refv HV

i

AV

R



Starting point – diagram of a synchronous generator of a conventional power station



Change of reactive current and reactive current gain

of a synchronous generators during grid faults, high voltage terminals

Static calculation – behavior of a synchronous generator during grid faults, HV-level

Reactive current change of a synchronous generator during grid faults as function of voltage change at HV-level.

Reactive current gain iQHV/ uHV of a synchronous generators during grid faults as function of voltage change on HV-level.

1 0.8 0.6 0.4 0.2 00

1

2

3

4

5

i QH

V/v

HV /

p.u

.

vHV

/ p.u.

stationary

transient

subtransient

1 0.8 0.6 0.4 0.2 00

1

2

3

4

vHV

/ p.u.

i Q,H

V /

p.u

.

stationary

transient

subtransient




Synchronous generator model used for dynamic simulation

Dynamic simulation – 7th order SG model and fault model

10 kV 110 kV

xk = 10 %

rk = 1.0 %

Fault impedance

SN = 55 MVA

PN = 50MW

cos = 0.9

7th order dynamic model

xd = xq = 2 p.u.

xd’ = xq’ = 0.4 p.u.

xd’’= xq’’= 0.25 p.u.

td’ = 1 s, td’’ = 0.05 s

Hg = 5 s

vfd

ve

SN = 55 MVA

xk = 12 %

rk = 0.3 %

Grid

IEEE Type 1

excitation system

Grid fault model

Grid model

HV transformer



Reactive current of a synchronous generators during grid faults

Dynamic simulation – reactive current of a SG during grid faults, HV-level

Voltage and reactive current of a synchronous generators during grid faults at HV-levelParameter: field control on/off

0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.90

0.25

0.5

0.75

1

1.25

vH

V /

p.u

.

0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

I QH

V /

/ p

.u.

t / s

AVR on

vf=const

IQ

<2.5%

simple model is good enough

Current decreases as expected




Reactive current gain of asynchronous generators during grid faults

Dynamic simulation - gain QHV/ HV of a synchronous generator during grid faults

Reactive current gain QHV/ HV over time of a synchronous generators during grid faults at the high voltage terminals. Parameter: (electrically) distant fault / close fault

0.5 0.55 0.6 0.650

0.5

1

1.5

2

2.5

3

3.5

4

i Q,H

V/v

HV /

p.u

.

t / s

distant fault

close fault

average distant fault

average close fault

xd

' with t

d

' =

0.5 0.55 0.6 0.650

0.5

1

1.5

2

2.5

3

3.5

4

i Q,H

V/v

HV /

p.u

.

t / s

distant fault

close fault

average distant fault

average close fault

xd

' with t

d

' =

Constant gain as average over the

fault duration:Basis for WT

controller design!

Grid fault of 150 ms






3. Simulations

4. Conclusion




Comparison of different reactive current control concepts during grid faults

Development of reactive current control during grid faults

Qref iQ ref,WT WTi k v v

3. Control withoutdead-band

2. Modified control approach with dead-band

1. First control approachwith dead-band

„historic“ approach based on concept of loads:

- cos(- Voltage control during fault

E.ON 2003, E.ON 2006,

Analogous to synchronous

generator, but with adjustable gain

SDLWindV, Tennet,…

-Avoid discontinuity- dead-band adjustable,

- gain adjustableSDLWindV

Qi

WTv

refref

Q,ref iQ 0 Q0

iQ 0 Q0

sin( ) or for 0.9 1.1

for 0.9

for 1.1

qpv

v v

i k v v v i v

k v v v i v

ref

Q,ref

0

sin( ) for 0.9 1.1

2 for 0.9 and 1.1

pv

vi

v v v v

Qi

WTv

iQk

v

Q0i



Wind plant reactive power control

Reactive power control of wind plant during normal operation

Transformer

LV/MV

PMU

Grid

Impedance

HV Grid

Transformer

MV/HV

Turbine Control / WT 1

Cable

Impedance

PCC

measurement

TSO

Control Centre

control signals

GB

Converter control / WT1

Transformer

LV/MV

GB

WEAn

Turbine Control / WT 2

Converter control / WT 2

Q, U, cosVref,WT

vref,WT

• Normal operation: Plant controller (PMU) modifies voltage reference to achieve given reactive power Q

• speed of response can be set between 1s up to very slow

ref,WT

K

PCCrefq

PCCq

maxq

minqmaxv

minv

q

vPCCv




3. Simulations



3. Simulations

4. Conclusion



Wind plant model used for dynamic simulation

Dynamic simulation – model of wind plant used for simulation

Wind plant with 50 MW

20 kV 110 kV

Fault impedance

Wind Plant 50 MW / 55 MVA

Grid

xk = 10 %

rk = 1.0 %

SN = 55 MVA

xk = 12 %

rk = 0.3 %

Grid fault model

Grid model

HV transformer




Response to voltage drop of 5% (= switching operation in the grid)

Voltage drop by 5% in the high voltage grid: Wind Plant and Synchronous Generator

Reactive current of synchronous generator (green) and wind plant (blue) at voltage drop of 5% in the HV grid.

Effective gain iQ/ v at HV-level at voltage drop by 5% for synchronous generator (green), wind plant as proposed (blue).

0.3 0.4 0.5 0.6 0.7 0.80.94

0.96

0.98

1

1.02

1.04

vH

V /

p.u

.

0.3 0.4 0.5 0.6 0.7 0.8-0.2

-0.15

-0.1

-0.05

0

0.05

QH

V /P

n /

p.u

.

t / s

WP

SG

0.5 0.55 0.6 0.65-1

0

1

2

3

4

5

6

7

8

i QH

V /v

HV /

p.u

.

t / s

WP

SG

Same voltage stabilizing effect

by Wind Plant

Same behaviour at HV terminals


0.5 0.55 0.6 0.65-1

0

1

2

3

4

5

6

7

8

i QH

V/v

HV /

p.u

.

t / s

WP

SG

Voltage drop by 5% in the high voltage grid:

Synchronous Generator, Wind Pant, Wind Plant with deadband

Reactive current of synchronous generator (green) and wind plant (blue) at voltage drop of 5% in the HV grid. Comparison to wind plant with dead-band (red)

Effective gain iQ/ v at HV-level at voltage drop by 5% for synchronous generator (green), wind plant as proposed (blue) and wind plant using dead-band (red).


Response to voltage drop of 5% (= switching operation in the grid)

0.3 0.4 0.5 0.6 0.7 0.80.94

0.96

0.98

1

1.02

1.04

vH

V /

p.u

.

0.3 0.4 0.5 0.6 0.7 0.8-0.2

-0.15

-0.1

-0.05

0

0.05

QH

V /P

n /

p.u

.

t / s

WP

SG

WP w. deadband

0.5 0.55 0.6 0.65-1

0

1

2

3

4

5

6

7

8

i QH

V/v

HV /

p.u

.

t / s

WP

SG

WP w. deadband

Without deadband wind turbines can

stabilize voltage like conventional power

stations

Wind Plant with

dead-band control

Voltage drops lower



Conclusion



3. Simulations

4. Conclusion



Conclusion: WEC reactive power control without deadband

Reactive current control equivalent to synchronous generators

Technical issues

• Reactive current control equivalent to synchronous generators

• fast response to voltage changes, slow response to setpoint changes

• reactive current proportional to voltage change

• damping of voltage changes in the grid

• no deadband

Key points

• Use of deadband risks voltage stability at very high wind penetration

• fast voltage control equivalent to synchronous generators stabilizes grid voltage

• Technology available for different wind turbine control implementations

=> Technology ready for the grids of the future



© REpower Systems SE

All rights reserved. No part of this document may be reproduced or transmitted in any form or by any means, electronic or mechanical,

including photography, recording, or any information storage and retrieval system, without permission from REpower Systems AG.



Response to voltage dip by 15% (= distant fault)

Voltage dip of 15% in the high voltage grid : SyncGen, WP, WP with deadband

Reactive current of synchronous generator (green) and wind plant (blue) at voltage dip of 15% in the HV grid. Comparison to wind plant with dead-band (red)

Effective gain iQ/ v at HV-level at voltage dip of 15% for synchronous generator (green), wind plant as proposed (blue) and wind plant using dead-band (red).

0.4 0.6 0.8 1 1.2 1.40.8

0.85

0.9

0.95

1

1.05

1.1

vH

V /

p.u

.

0.4 0.6 0.8 1 1.2 1.4-0.5

-0.25

0

0.25

0.5

QH

V /P

n /

p.u

.

t / s

WP

SG

WP w. deadband

0.5 0.55 0.6 0.65-1

0

1

2

3

4

5

6

7

8

i QH

V /v

HV /

p.u

.

t / s

WP

SG

WP w. deadband

Almost no support by Wind Plantwith dead-band control




Comparison of synchronous generator and wind plant using proposed control

Voltage in the high voltage grid: Synchronous Generator and Wind Plant

Voltage dip by 80% Voltage dip by 15%

0 1 2 3 40

0.250.5

0.751

1.25

v /

p.u

.

0 1 2 3 4-0.5

00.5

11.5

2

P/P

n /

p.u

.

0 1 2 3 4-1

-0.5

0

0.5

1

Q/P

n /

p.u

.

t / s

WP,HV

SG,HV

0 1 2 3 40.8

0.9

1

1.1

v /

p.u

.

0 1 2 3 40.5

0.75

1

1.25

P/P

n /

p.u

.

0 1 2 3 4-0.5

-0.25

0

0.25

0.5

Q/P

n /

p.u

.

t / s

WP,HV

SG,HV

Severe oscillations of Sync. Generator

Almost no oscillations by Wind Plant



Comparison of synchronous generator and wind plant using proposed control

Voltage dip by 80% in the high voltage grid: Synchronous Generator and Wind Plant

Voltage and Currents at HV side Voltage and Currents at MV side

0.4 0.6 0.8 10

0.25

0.5

0.75

1

1.25

vH

V /

p.u

.

0.4 0.6 0.8 1-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

I QH

V /I P

n /

p.u

.

t / s

WP

SG

v > 10%

v < 2%

IQ > 50%

0.4 0.6 0.8 10

0.25

0.5

0.75

1

1.25

vM

V /

p.u

.

0.4 0.6 0.8 1-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

I QM

V /I P

n /

p.u

.

t / s

WP

SGHigher currents by

Sync. Generator

BUT

Almost no impact

on voltage

SG: Poor response following dip



pv

d dj jx x

d dj jx x

qv

sv

qv

djx

d0v

q qj jx x

q qj jx x

dv

dv

qjx

sr Tr

z

HVv

Trv

ev




refv HV

i

AV

R




„subtransient“

qv

djx

d dj jx x q HV

Q

d TR

reactive short circuit current

j

:

v vi im

zx


pv

d dj jx x

d dj jx x

qv

sv

qv

djx

d0v

q qj jx x

q qj jx x

dv

dv

qjx

sr Tr

z

HVv

Trv

ev




refv HV

i

AV

R

„subtransient“

qv

djx

„transient“

djx

qv

d dj < jx x




q HV

Q

d TR

reactive short circuit current

j

:

v vi im

zx



pv

d dj jx x

d dj jx x

qv

sv

qv

djx

d0v

q qj jx x

q qj jx x

dv

dv

qjx

sr Tr

z

HVv

Trv

ev




refv HV

i

AV

R

„subtransient“

qv

djx

„transient“

djx

qv

d dj < jx x

„stationary“

pv

djx




d

q HV

Q

TR

stationary reactive current

j

:

v vi im

zx


Documents

Presented at 2012 3rd IEEE PES ISGT Europe, Berlin, Germany