ac/dc system dynamics under ac power system faulted conditions · 2015-09-21 · ac/dc system...
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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
m.ndreko@tudelft.nl
• 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.
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