Hybrid Time Domain Simulation:
Application to Fault Induced Delayed
Voltage Recovery (FIDVR)
Vijay Vittal
Arizona State University
PSERC Webinar
Jan. 20, 2015
Presentation background
• The work presented in this webinar is a
part of the work being done in PSERC
project S-58 at ASU
• The PIs on this project are V. Vittal and S.
Meliopoulos
• The graduate student at ASU is Qiuhua
Huang and the collaborator is Dr. John
Undrill
2
Outline
1. Introduction
2. Part -1: OpenHybridSim: A new hybrid
simulation platform
3. Part -2: Application to FIDVR study
4. Conclusions
3
Introduction: Background
 An increasing demand for simulating a portion of a
system in detail with a very small time step and capturing
point on wave detail while preserving the effects on the
rest of the system
• Power electronic converter based renewable energy integration
• HV AC/DC systems
• Residential air conditioners, variable frequency drive(VFD) and
other power electronics based loads
• Representing other needed detail at the distribution level
PV Farm
VSC-HVDC
air conditioner
4
Introduction: Hybrid simulation
Involves electromagnetic transient (EMT)- electro-mechanical
transient stability(TS) hybrid simulation
Remainder of the system
• Sequence,
phasor model
• TS simulator
Region of interest
• Instantaneous
variable model
• EMT simulator
Boundary
Boundary bus i
Iiabc
Zik
……
Composite
Load
Model
Detailed
System
modeled in
3-phase
PV
Converter
Vi0abc
Zi
+ -
Thévenin
equivalent
Vk0abc
Vkabc
Boundary bus k
Zk
Boundary bus i
Ii120
Current
injections
External
network
Ik120
+ -
Detailed system modeled in an EMT Simulator
Boundary bus k
External system modeled
in a TS Simulator
5
Introduction: Hybrid simulation
 Key requirements for a successful hybrid simulation
platform
•
•
•
•
Architecture : embedded/decoupled
Interaction: communication + protocol
Equivalent models of both detailed and external system
Preparation and initialization of both detailed and external
system
 Synopsis of literature review of EMT-TS hybrid
simulation
• Lab research or proof-of-concept type
• The architecture design is not flexible and the simulators are
limited to run on one computer
• Targeted mainly for three-phase balanced applications
• No publically available tool for hybrid simulation
6
Time scale of transient phenomena
7
OpenHybridSim:
A new hybrid simulation tool
 Overall design
•
•
•
•
Loosely decoupled architecture
Socket communication
InterPSS, an open source power system simulator
A generic interface to an EMT simulator, e.g.,
PSCAD, Maltab/SimPowerSystems
EMT
Simulator
Socket
Communication
Socket
Component
I120
EMT (t )
V abc
T (t )
InterPSS Core Engine
Network
Equivalent Helper
Socket
Server
HybridSim
Manager
8
Socket based communication framework
 TCP/IP socket based communication framework
• Enables decoupling of the EMT and TS simulators
• Supports application environment
- Single computer
- Local area network(LAN)
- Internet
• Socket components in PSCAD and Matlab/SimPowerSystems
are developed for interfacing
Socket component in PSCAD
9
External system equivalent
for EMT simulation
 Supports both 1-phase and 3-phase equivalents
• 1-phase: mainly for three-phase balanced applications
• 3-phase: any type of fault within the detailed system
• Facilitates simulation of unsymmetrical faults
 3-phase Thévenin equivalent of external system based
on a 3-sequence network model
• The given base case is modeled using 3-sequences
• Details are provided on the next slide
10
Three-phase Thévenin equivalents
of the external system
• Step 1: Calculate 3-sequence
Norton equivalents
ziab
• Step 2: 3-sequence to 3-phase
transformation for each boundary bus
abc
120 −1
y
=
Sy
S
I Niabc = SI 120
i
i
Ni
• Step 3: 1-phase Norton to
Thévenin for each boundary bus
VTip = I Nip / yip
zikabc
zkac
bus k
zip = 1 / yip
where p stands for one of the three phases
……
Detailed
system
Single-phase line
+_
VTia
zib
+
_
VTib
zic
+
_
VTic
zka
+
_
VTka
zkb
+_
VTkb
zkc
+_
VTkc
ziac
zibc
……
where S is the transformation matrix,
is the bus primitive admittance
bus i
zia
zkab
zkbc
Three-phase line
11
Detailed system represented by sequence
current sources in TS simulation
 Need to extract three-sequence, fundamental frequency
currents from instantaneous, waveform values
 Use well-established FFT algorithm
• PSCAD provides an FFT component
 Directly used in the network solution (I=YV) in TS
simulation
FFT Component in PSCAD
12
Three-sequence based TS simulation for
simulating unsymmetrical faults
I
(1)
EMT ( t )
Positive-sequence network
solution and integration step
x (t ) = f ( x(t ), y )
x(t + ∆T ) = x(t ) + x (t ) ∆T
(1)
(t )
(1)
TS ( t +∆T )
V
(1)
0 g1 ( x(t + ∆T ), y((1)t + ∆T ) , I EMT
=
(t ) )
I
I
(2)
EMT ( t )
(0)
EMT ( t )
Negative- and zerosequence network solver
(2)
0 = g 2 ( y((2)
,
I
t + ∆T )
EMT ( t ) )
(0)
0 = g 0 ( y((0)
,
I
t + ∆T )
EMT ( t ) )
VTS(2)(t +∆T )
VTS(0)(t +∆T )
13
The interaction protocols
between two simulators
2
(a) series
3
1
TS
…
…
EMT
5
4
..
.
..
.
..
.
T
T+ΔT
T+3ΔT
T+2ΔT
TS
…
…
EMT
(b) parallel
...
...
(c) combined
T
T+2ΔT
T+ΔT
Parallel Protocol
...
T+3ΔT
Series Protocol
Parallel Protocol
…
…
…
…
...
...
T
Fault on
T+ΔT
T+2ΔT
...
...
...
T+3ΔT
T+4ΔT
...
T+5ΔT
TS
EMT
T+6ΔT
Fault cleared
14
Implementation with the series type protocol
 The series protocol
• Use the updated equivalent data for simulation with each simulator
• Performance issue: One simulator has to remain idle when the other
is running the simulation
I
x(t )
I
I
x (t ) = f ( x(t ), y((1)t ) )
x(t + ∆T ) = x(t ) + x (t ) ∆T
Negative- and zerosequence network solver
(2)
EMT ( t )
0 = g2 ( y
(0)
I EMT
(t )
120
EMT ( t )
Step (1)
0 = g0 ( y
Step (2)
(2)
( t + ∆T )
(0)
( t + ∆T )
,I
(2)
EMT ( t )
)
,I
(0)
EMT ( t )
)
InterPSS
(1)
VTS ( t +∆T )
V 120
TS (t + ∆T )
(1)
=
0 g1 ( x(t + ∆T ), y((1)t + ∆T ) , I EMT
(t ) )
socket
server
VTS120(t )
Positive-sequence network
solution and integration step
(1)
EMT ( t )
VTS(2)(t +∆T )
120
I EMT
(t )
VTS(0)(t +∆T )
Calculate 3-phase
Thévenin
V abc
equivalent
T (t + ∆T )
x(t + ∆T )
socket
server
VTS120(t +∆T )
Step (3)
V abc
T (t + ∆T )
Three-sequence TS simulation
Step (4)
I
120
EMT ( t )
120
I EMT
( t +∆T )
socket
client
t
EMT
step
1
EMT
step
2
EMT
step
3
Step (5)
……………………………………..
EMT
EMT
step
N-1
EMT
step
N
t + ∆T
15
Implementation with the parallel type protocol
 The parallel interaction protocol
• Steps (d) and (e) run simultaneously
• May cause significant interfacing errors under fast transient
conditions, as the Thévenin equivalent data is one-step delayed
x(t + ∆T )
VTS120(t )
Calculate
three-phase
socket
120
Thévenin
server
I EMT
( t ) equivalent
x(t )
VTS120(t )
120
I EMT
(t )
I
Step (b)
Step (a)
socket
server
Threesequence TS
simulation
Step (d)
Step (c)
V abc
T (t )
120
I EMT
( t +∆T )
Step (e)
120
EMT ( t )
socket
client
t
EMT
step
1
EMT
step
2
...
VTS120(t +∆T )
EMT
step
N-1
EMT
step
N
t + ∆T
16
Automatic protocol switching algorithm
 Automatically switch interaction protocol based on the
system conditions, reflected by the maximum rate of
change of sequence current injections
I
RI
I
120
EMT ( t )
120
EMT ( t )
I 120
EMT (t −∆T )
max(
max
i
p ∈ (1, 2, 0)
Maximum
rate of
change
120
RI EMT
(
Y
EMT ( i , t )
I
−I
( p)
EMT ( i , t − ∆T )
)) / ∆T
(1)
EMT ( i , t − ∆T )
1
series
120
RI EMT
>ε?
N
time step
( p)
N
last step
used series?
Y
Delay
0
parallel
∆T
Logic of the protocol switching algorithm
17
Automatic creation and initialization
of the external network
Boundary
bus i
Base case
Ii120
Boundary
Configuration
bus i
bus m
Ii120
……
The remainder
of the external
system
bus k
bus n
Ik120
Vk120
The remainder
of the external
system
Detailed
System
1) Set buses and
branches within the
detailed system out of
service
2) initialize the external
system
……
Depth first
search(DFS)
to identify
detailed
system
bus m
bus n
Ik120
Vk120
bus k
Boundary
Power flow
18
Testing of the developed platform
 Test system
Bus2
18 kV
Bus 8
230 kV
100+j35MVA Bus 9 Bus 3
230 kV 13.8 kV
Bus 7
230 kV
0.0085+j0.072
(case 1)
0.0119+j0.1008
G2
G3
0.017+j0.092
125+j50MVA
0.01+j0.085
Bus 5
230 kV
0.039+j0.17
0.032+j0.161
192MVA T2
XT=0.0625
T3 128MVA
XT=0.0586
Bus 6
230 kV
90+j30MVA
Bus 4
230 kV
T1
XT=0.0576
Bus 3
16.5 kV
G1
247.5MVA
The IEEE 9 Bus system
Modeling of Bus 5 and the external network
Thévenin equivalents in PSCAD
19
Case 1: The interaction protocols
 Case 1 setting:
12
PSCAD
- EMT time step = 50 us
-TS time step = 5 ms
-Threshold ε = 0.004
- Delay = 2 cycles
 A three-phase fault at 0.1 s
and lasts for 4 cycles
 Plots
(Top) Positive-sequence
current injection at bus 5
into the external network
(Bottom) Protocol switching
signal
current (kA)
 Protocol control setting:
EMT-TS(series)
EMT-TS(parallel)
10
EMT-TS(combined)
8
6
4
2
0
0.05
0.1
2
1
0
0.15
(a)
0.2
0.25
0.2
0.25
-5
120
log(RIEMT(t))
-10
0.05
log(0.004)
protocol signal
0.1
0.15
Time (s)
(b)
20
Case 2: Performance of the developed
platform under unsymmetrical faults
 Internal network: Bus 5 and branch Bus5-Bus7
 Two-port three-phase Thévenin equivalent
 Detailed modeling of bus 5 using the WECC composite load model,
with the 1-p air conditioner compressor motor represented by a EMTP
type model developed by Yuan Liu, et al [1]
Bus2
18 kV
Bus 8
230 kV
100+j35MVA Bus 9 Bus 3
230 kV 13.8 kV
Bus 7
230 kV
0.0085+j0.072
0.0119+j0.1008
G2
G3
0.039+j0.17
0.017+j0.092
125+j50MVA
0.01+j0.085
Bus 5
230 kV
0.032+j0.161
192MVA T2
XT=0.0625
T1
XT=0.0576
T3 128MVA
XT=0.0586
•
Single line to
ground fault
• starting at 2.0 s
• 4 cycles
230 kV/69kV
150 MVA
10%
69kV
69/12.47 kV
50 MVA
8%
Bus 6
230 kV
90+j30MVA
12.47 kV
Bus 4
230 kV
Equivalent
feeder
Bus 3
16.5 kV
G1
Bus 5
230 kV
Composite
Load
Model
12.47 kV
Composite
Load
Model
69/12.47 kV
50 MVA
8%
12.47 kV
Composite
Load
Model
247.5MVA
Detailed modeling of Bus 5
[1] Y. Liu, V. Vittal, J. Undrill, and J. H. Eto, "Transient Model of Air-Conditioner Compressor Single Phase Induction Motor," IEEE
Transactions on Power Systems, vol. 28, pp. 4528-4536, 2013.
21
Case 2: Performance of the developed
platform under unsymmetrical faults
EMT-TS(parallel)
PSCAD
EMT-TS(combined)
protocol signal
2
Voltage (kV)
200
PSCAD
EMT-TS(parallel)
EMT-TS(combined)
protocol signal
100
1.5
0
-100
1
-200
Phase A
-300
1.95
2
2.05
2.1
2.15
Current (kA)
200
Voltage (kV)
0.5
2.2
100
0
0
-0.5
0.7
-100
-1
-200
0.6
Phase B
-300
1.95
2
2.05
2.1
2.15
2.2
-1.5
0.5
Voltage (kV)
200
0.4
-2
100
2.014
0
-2.5
1.95
-100
2
2.05
2.1
2.016
2.018
2.15
2.2
Time (s)
-200
Phase C
-300
1.95
2
2.05
2.1
2.15
Time (s)
Three-phase voltage of Bus 5
2.2
The phase A current injection at
Bus 5 into the external network
22
Takeaways of part-1
1. The combination of the decoupled architecture and
socket-based communication facilitates both simulators
to be run on either one computer or several computers
to achieve more flexibility and a better performance
2. The proposed combined interaction protocol with the
auto-switching feature helps improve the hybrid
simulation efficiency while a good accuracy is
guaranteed
3. Application of the multi-port three-phase Thévenin
equivalent enables simulating unbalanced faults within
the detailed system, without the constraint of phase
balance at the boundary buses
23
Fault induced delayed voltage recovery (FIDVR)
 Fault
• distribution, subtransmission and
transmission
systems
 Delayed voltage
recovery
• several to tens of
seconds
 Root cause of
FIDVR
• air conditioner
(A/C) compressor
motor stalling and
prolonged tripping
Voltage profile during a typical FIDVR event [2]
[2] D. N. Kosterev, A. Meklin, J. Undrill, B. Lesieutre, W. Price, D. Chassin, et al., "Load modeling
in power system studies: WECC progress update," in 2008 IEEE Power and Energy Society General
Meeting - Conversion and Delivery of Electrical Energy in the 21st Century, 2008, pp. 1-8.
24
Fault induced delayed voltage recovery (FIDVR)
 Accurate FIDVR studies require
• Detailed A/C modeling
• Detailed network model down to distribution feeder level
 Limitations of the conventional positive-sequence TS
simulator
• Distribution system configurations
• Response of single-phase devices when subjected to
unsymmetrical faults
 FIDVR events are generally localized
• Detailed modeling can be limited to a small portion of a large
power system
FIDVR
Area
A large
power system
25
Determination of the boundary
of detailed system
 Use a simple yet generic test case to quantify the voltage dip
threshold at a transmission bus causing A/C motor stalling
 Criterion: A bus is included in the internal system if a singlephase or three-phase fault at that bus causes a phase-to-neutral
voltage at buses with a large percentage of A/C motor loads to
drop below 0.75 pu.
x = 0.025
T
x = 0.05
x = 0.1
T
T
X=
2.5 − 20%
T
Bus 3
0.03 + j 0.04
Composite
Load model
s
Voltage dip magnitude (pu)
115 kV
1.04 pu 0.005 + j 0.05
Voltage dip magnitude (pu)
Equivalent
Step-down
feeder
transformer Bus 2
Bus 1
impedance
T
x = 0.2
T
0.5
0.5
Equivalent
source
impedance
x = 0.15
0.45
0.4
0.35
0.3
0.45
0.4
0.35
0.3
115/12.47 kV
0.25
0.6
0.9
0.7
0.8
A/C load percentage
(a)
1
0.25
0.6
0.7
0.8
0.9
A/C load percentage
(b)
1
Voltage dip magnitude w.r.t. the A/C load
percentage and the transformer impedance: (a)
A/C power = 4.9 kW (b) A/C power = 6.0 kW
26
Applied the boundary selection criterion
to the WECC system
The WECC system
Transmission
Buses
lines
Generators
15750
13715
24156 26105
24097
3074
24042
NORTH
14005
Buses with a large percentage
of 1-Ф A/C motor load
Loads
• Bus 24151
7787
STATISTICS OF THE DETAILED SYSTEM MODEL
15061
Total number
of buses
24086
15021
sub
sub
15090
24092
24236
EAST
24801
24138
sub
28040
15093
sub
sub
24151
115 kV
M M M
Load
Load
• Bus 24138
Number of
buses of
different
voltage levels
500 kV
sub
sub
Sub-system below 500 kV
Total Load
238
500 kV
7
230 kV
37
161 kV
3
115 kV
68
92 kV
18
<= 66kV
105
11.9 GW
One-line diagram of the study region
27
Initialization of the detailed system with a
large percentage of load as induction motors
 The built-in initialization function of PSCAD fails to
initialize the detailed system
 A two-step initialization approach
Bus
(1) The switch K is turned to the position 0,
and the distribution systems and the CLMs
are energized by the fixed voltage sources
and initialized independently.
(2) After the CLMs are successfully
initialized, the switch K is turned to the
position 1 such that distribution systems are
connected to the transmission system.
NOTE: The magnitude and phase angle of
the fixed voltage source, S, are set based on
the power flow solution of the given base
case
HV
LV
1
s
0
K
Static
equivalent
load
Distribution network
CLM
CLM
CLM
CLM: composite
load model
28
Benchmarking hybrid simulation against
conventional transient stability
1.1
1
EMT-TS
InterPSS
0.95
0.85
0
1.05
0.1
0.2
0.3
0.4
0.5
Time (s)
1
EMT-TS
InterPSS
0.95
0.9
0.85
0.8
0.75
0.1
0.2
0.3
Time (s)
0.4
0.5
Machine reactive power (pu)
Voltage magnitude(pu)
Bus 24801 positive sequence voltage
0.9
Bus 24151 positive sequence voltage
0.7
0
1.05
Voltage magnitude(pu)
 Both use constant impedance load
 A single line to ground (SLG) fault
is applied on the phase A of bus
24151 at t = 0.2 s
0.25
Bus14931 machine #1 reactive power
0.23
EMT-TS
InterPSS
0.21
0.19
0.17
0.15
0
0.1
0.3
0.2
Time(s)
0.4
0.5
29
FIDVR event triggered by a SLG fault
 Detailed modeling of the region served by Bus 24151
Bus 24151
500 kV
415 +j*75 MVA
415 +j*75 MVA
0.2536 pu
560 MVA
531.615/120 kV
403 +j*96 MVA
403 +j*96 MVA
0.2536 pu
560 MVA
531.615/120 kV
0.2536 pu
560 MVA
531.615/120 kV
0.2536/0.40/0.512 pu
560 MVA
Bus 24229 115 kV
Bus 24160 115 kV
22 + j*1.1
MVA
46.8 MVAr
Bus 25423
115 kV
M
0.12 pu
250 MVA
115 /12.47 kV
0.12 pu
250 MVA
115 /12.47 kV
M
M
f-2
Equivalent Feeder f-1
Equivalent
feeder
Model
202+j*(-8) MVA
 Feeder
modeled in
two sections
f-3
Equivalent
feeder
Model
Equivalent
feeder
Model
202+j*(-8) MVA
1
Z
4 feeder
A
B
f-4
Equivalent
feeder
Model
202+j*(-8) MVA 202+j*(-8) MVA
f-5
Equivalent
feeder
Model
202+j*(-8) MVA
f-6
Equivalent
feeder
Model
202+j*(-8) MVA
f-7
Equivalent
feeder
Model
f-8
Equivalent
feeder
Model
202+j*(-8) MVA 202+j*(-8) MVA
3
Z
4 feeder
C
M
M
A/C
30
FIDVR event triggered by a SLG fault (cont’)
Terminal voltage of the A/C motors at the 1/4 length point
• 70% 1-Ф A/C motor,
15% 3-Ф induction
motor, 15% constant
impedance
• Phase A and C were
directly affected by the
SLG fault at Bus 24151
• A/C motor stalling
propagated to nonaffected phases (phase
B in this case)
• Voltages of all three
phases were depressed
after 0.95 s
1
phase A
phase B
phase C
0.5
0
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
Speeds of the A/C motors at the 1/4 length point
1
0
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
Speeds of the A/C motors at the end of the feeder
1
0
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
Sequence voltages of the 115 kV bus# 24160
1
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
Sequence voltages of the 500 kV bus# 24151
1
1.4
1.5
1.4
1.5
Positive
Negative
Zero
0.5
0
0.5
1.5
Positive
Negative
Zero
0.5
0
0.5
1.4
phase A
phase B
phase C
0.5
0.5
1.5
phase A
phase B
phase C
0.5
0.5
1.4
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5
31
Effects of load composition on FIDVR
4
5
•
•
Propagation of A/C motor stalling to
unfaulted phase is consistent across
a substantial range of load
compositions
The impacts of SLG faults close to
certain regions of the system with
high A/C penetration could be more
severe than perceived
Speed (pu)
Speed (pu)
75% 1-Ф A/C motor,
25% constant impedance
75% 1-Ф A/C motor,
10% 3-Φ NEMA type B induction
motor, 15% constant impedance
70% 1-Ф A/C motor,
15% 3-Ф NEMA type B induction
motor, 15% constant impedance
60% 1-Ф A/C motor,
15% 3-Ф NEMA type B induction
motor, 25% constant impedance
50% 1-Ф A/C motor,
25% 3-Ф NEMA type B induction
motor, 25% constant impedance
B
Casephase
1
phase C
1.5
Speed (pu)
3
Load composition
Speed (pu)
2
phase A
Speed (pu)
Case
#
1
1
0.5
Case 1
0
0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9
1.5
1
0.5
Case 2
0
0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9
1.5
1
0.5
0.5
0.5
2
Case 4
0
0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9
1.5
1
2
Case 3
0
0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9
1.5
1
2
2
Case 5
0
0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9
Time (s)
2
32
Effects of point-on-wave (POW) on FIDVR
(a1)
0.5
1
(b1)
0.5
0
0.5
1.5
1
2
bus 24151
bus 24160
1
(c1)
0.8
0.6
0.5
1.5
1
2
Phase C
1
(a2)
0.5
0
0.5
2
Voltage(pu)
1.5
1
Speed(pu)
1
0
0.5
Voltage(pu)
Phase B
Positive Seq.Voltage(pu)
Speed(pu)
Phase A
Positive Seq.Voltage(pu)
• POW effects on the
occurrence and
evolution of FIDVR
are apparent,
based on the
differences in the
response of the
A/C motors of bus
24160
• The POW when the
fault occurred
should be
considered for
detailed FIDVR
study
1.5
1
2
1
(b2)
0.5
0
0.5
1.5
1
2
bus 24151
bus 24160
1
(c2)
0.8
0.6
0.5
1.5
1
t(s)
t(s)
Case 5A, POW = 45 deg
Case 5, POW = 0 deg
2
33
Takeaways of part-2
1. The study shows that a normally cleared,
single line to ground fault at a 500 kV bus
close to the A/C loads can lead to a FIDVR
event. The event begins with A/Cs stalling on
two directly-impacted phases, followed by A/C
stalling propagating to the unimpacted phase.
2. Further, five study cases with quite different
load compositions show similar A/C motor
stalling results.
3. The POW when the fault occurs could have a
significant impact on the response of the A/C
compressor motors.
34
Conclusions
1. A new EMT-TS hybrid simulation tool is developed,
which features 1) decoupling architecture, 2) generic
interfacing with an EMT simulator, 3) flexible switching
of interaction protocol and 4) support of three-phase
equivalent of external system.
2. The hybrid simulation tool has been applied to study
the FIDVR phenomenon within a region of WECC
system, certain aspects of the evolution of the
phenomenon were uncovered for the first time.
3. The developed tool is not limited to FIDVR study, but
also applicable to studies that require detailed models
and simulation of a part of a large power system, while
preserving the slow dynamics of the rest of the system
35
Thank you!
36