AC/DC System Dynamics Under AC Power System Faulted Conditions · 2015-09-21 · AC/DC System Dynamics Under AC Power System Faulted Conditions A sensitivity on DC Voltage Control

AC/DC System Dynamics Under AC Power System Faulted

Conditions

A sensitivity on DC Voltage Control parameters

1

Mario Ndreko Delft University of Technology, Faculty of EEMCS,

Intelligent Electrical Power Grids, Delft, the Netherlands

[email protected]

• Background

• Model of the VSC-Based MTDC grid

• Control of the DC voltage in the MTDC grid

• Test system and results

• Conclusions

2

Contents

3

Problem Background

• What is the combined AC-DC

system dynamic response under

AC power system faulted

conditions?

• How does DC voltage control parameters

influence the AC-DC system dynamics?

• What is the influence of the DC grid

topology on these interactions between the AC and the DC system?

topology

2

1

9

acdc

acdc

301

Multi-terminal DC grid

ACPower System

acdc

acdc

AC Power System

meshed Radial

VSC-HVDC System

4

=

~

PWM pulses

VSC

abci,c abcu

DC Chopper

chR

,s abcu

LR

3

ωL

ωL

𝑘𝑝 +𝐾𝑖

𝑠 𝑘𝑝 +

𝐾𝑖

𝑠

𝑘𝑝 +𝐾𝑖

𝑠 Σ

Σ

+

+

+

+

-

-

-

-

Inner

Controller

qidi

ref

diref

qi

,

d

c refu,

q

c refu

abcdq

modulator

,c abcu

abcdq

di qi

PLL

s

dcU

+

-

dcC

Outer

Controllers

ref

dcU

sUref

sU

• Outer Controllers

• Inner Controllers

• PWM

• Switching modules

• Detailed switch model includes small time constants which involves high computational costs

• Simplifications are necessary when modeling AC and DC systems for stability studies

• The models should be simple enough for system stability studies but should not neglect the DC circuit dynamics

5

Model of the MTDC Grid

Model of the MTDC Grid

6

DC cable modelVSC

sdc

dc

PI

U

dcC dcUprjX

ssource pr

pr

UI I

jX

sU

sPQ

ref

sU

refQ,s refP

ref

dcU

dcU

CurrentLimiter

ref

qi

diqi

xydq

prI

+

-

prIsourceI

ref

di CurrentLimiter

diqi

xydq

Inner Controllerand phase

Reactor model

ref

diref

qi

Case where inner controller and phase reactor are included

*

qi*

di

d

su

q

su

xiyi

pr x yI i ji

OuterControllers

j

sU e

cos sin

sin cos

x d

y q

i i

i i

prI

Simplified model of the converter: Quasi steady state model

• Assuming an infinite band width

of the inner controller we

neglect the inner controller dynamics

• The active and re-reactive current

references as given by the outer

controller are directly used in the

dqxy transformation

• The output current is also limited

by means of control

• AC and DC side are coupled by the

relation of the power balance

Model of the MTDC Grid

7

Newton Raphson DC grid system power flow

for initialization of state space model

(Loss-less converter)

+

1 2 1 2

1 ( )

Tn m

dc dc dc br br br x m nx U U U I I I

1 2T

n

dc dc dcu I I I

(1)

dcU

(2)

dcU

(3)

dcU

( )n

dcU (1)

dcI

(2)

dcI

(3)

dcI

( )n

dcI

dxAx Bu

dt

Model of the DC cables

Control of the DC voltage

8

• In a MTDC grid it is crucial to control the DC voltage at controllable levels both during normal operation and faulted conditions

Power In the

DC grid

Power Out of

the DC Grid

Cdc

Multi-terminal DC grid

Control of the DC voltage

9

• The most common method of DC voltage control in a MTDC is the power based droop control

Power based DC voltage droop control

+0dcU

-

dcU

max

diDC Voltage Droop Controller

ref

dimin

di

pk

Active current component of the VSC-HVDC

-

+

+,0sP

-

sP

_

_

i P

p P

kk

s

_dc droopP

ac

AP acP

B

dcU

A

B

0dcU

0

InverterRectifier

ac

BP

Test System: Results

10

30

2

1

39

9

8

7

6

5

4

3

10

32

11

12

1331

14

15

16

1718

27

19

20

34

33

21

40

22

35

23

36

24

26

28

29

3825

4137

acdc

302

acdc

301

400 MW

400 MW

convenional generation = 5202.4 MW

onshore wind generation = 1600 MW

offshore wind generation = 800 MW

Total load = 7467.2 MW

Multi-terminal DC grid

• IEEE 39-bus test

system in PSS/E

• Quasi-steady state

model of the

converter

• Standard type 4

model of wind

turbines

• Standard 6th order

generator model

with control

Test System: Results

11

Radial connection

30

ac

dc

acdc

dcac

1

2

3

4

5

1001 1008

1002

1003 1004

1007

1005

1006

acdc

L13, L15, L25, L24, L34=100km

Meshed DC grid

ac

dc

NE system

2

1

39

9

8

301

302303

6

Radial DC grid

L16, L26 =20km

L56, L46, L63 =100km

201

202

1 1.05 1.1 1.15 1.20

2

4

6

Converter Active Power

p.u

time[s]

1 1.05 1.1 1.15 1.20

0.5

1

AC Terminal Voltage

p.u

time[s]

1 1.05 1.1 1.15 1.20.95

1

1.05

1.1

1.15

DC Terminal Voltagep.u

time[s]

DC terminal 302

DC terminal 303

DC terminal 301

VSC 301

VSC 302

Bus 301

Bus 302

1 1.05 1.1 1.15 1.20

50

100

150

200Onshore Converters DC Chopper

Pch

[M

W]

time[s]

VSC 301

VSC 302

Test System: Results

12

Effect of the fault in the MTDC connected remote AC system

30

ac

dc

acdc

dcac

1

2

3

4

5

1001 1008

1002

1003 1004

1007

1005

1006

acdc

L13, L15, L25, L24, L34=100km

Meshed DC grid

ac

dc

NE system

2

1

39

9

8

301

302303

6

Radial DC grid

L16, L26 =20km

L56, L46, L63 =100km

201

202

1 1.05 1.1 1.15 1.20

2

4

6

Converter Active Power

p.u

time[s]

1 1.05 1.1 1.15 1.20.95

1

1.05

1.1

1.15

DC Terminal Voltage

p.u

time[s]

DC terminal 303

VSC 303

1 1.05 1.1 1.15 1.20

50

100

150Onshore Converters DC Chopper

Pch

[M

W]

time[s]

VSC 303

0 2 4 6 8 10 12 1415

-1

0

1

2

De

gre

es

time[s]

G1002- Rotor angle deviation

13

Test System : Results

1 1.05 1.1 1.15 1.20

2

4

6Converter Active Power VSC 301

p.u

time[s]

1 1.05 1.1 1.15 1.23

4

5

6Converter Active Power VSC 302

p.u

time[s]

1 1.05 1.1 1.15 1.23

4

5

6Converter Active Power VSC303

p.u

time[s]

1 1.05 1.1 1.15 1.2

0

0.5

1

1.5Dissipated Power chopper 302

P (

p.u

)

time[s]

1 1.05 1.1 1.15 1.2

0

0.5

1

Dissipated Power chopper 303

P (

p.u

)

time[s]

0 5 10 15

-1

0

1

2Deviation from st.st valie of rotor angle for G1002

De

gre

es

time[s]

Kp=15

Kp=5

1 1.05 1.1 1.15 1.20

1

2

Dissipated Power chopper 301

P (

p.u

)

time[s]

1.0 p.u

Sensitivity of the DC voltage droop control parameters (radial connection)

1

p

slopek

dcU

AP P

B

dcU

A

B

0dcU

0

Inverter

BP

dcU

AP P

B

dcU

A

B

0dcU

0

Inverter

BP

14

Test System: Results

0.95 1 1.05 1.1 1.150

1

2

3

4

5 Active Power - VSC 301

p.u

time[s]

0.95 1 1.05 1.1 1.153

3.5

4

4.5

5Active Power - VSC 302

p.u

time[s]

0.95 1 1.05 1.1 1.153.5

4

4.5

5

5.5

6Active Power - VSC 303

p.u

time[s]

Radial MTDC

Meshed MTDC

0.95 1 1.05 1.1 1.150

0.5

1

AC Terminal Voltage - VSC 301

p.u

time[s]

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

-1

0

1

2

Angle deviation from steady state of generators in Seven Generator System

De

gre

es

time[s]

G1002- Meshed MTDC

G1002 - Radial MTDC

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

-1

0

1

2

Angle deviation from steady state of generators in Seven Generator System

De

gre

es

time[s]

G1001- Meshed MTDC

G1001 - Radial MTDC

Sensitivity of the DC grid topology (meshed and radial MTDC)

Summary

15

• Under AC side disturbances it is more the DC voltage droop

control parameters which influence the AC/DC system interactions and less the topology of the MTDC grid itself

• The higher is the proportional gain of the DC voltage droop controller, the larger is the active power overshoot that appears and the disturbance added to the asynchronously HVDC connected power system

• There is a trade-off between the choice of the DC voltage droop controller and the Chopper in terms of power dissipated

• In the case of ancillary services provided by the MTDC grid, the interactions between the DC voltage droop controller and the dedicated control loops should be extensively studied

Thank you!!

16

References

17

[1] M.Ndreko, A. A. van der Meer, M. Gibescu and M.A.M.M van deer Meijden, «Impact of DC Voltage

Control Parameters on AC/DC System Dynamics Under Faulted Conditions,» σε IEEE Power Energy

Society GM , 2014.

[2] M.Ndreko, A.van der Meer, M. Gibescu, B. Rawn and M.A.M.M van der Meijden, «Damping Power

System Oscillations by VSC-Based HVDC Networks: A North Sea Grid Case Study,» Wind Energy

Integration in Large Power Systems workshop, London, Oct. 2013, 2013.

[3] M. Ndreko, A. A. van der Meer, J. Bos, M. Gibescu, K. Jansen and M.A.A.M van der Meijden, “Transient

Stability Analysis of an Onshore Power System With Multi-Terminal Offshore VSC-HVDC: A Case study

for The Netherlands”.IEEE PES General Meeting, July 2013, Vancouver BC.