Post on 14-Jun-2018
MVDC FAULT PROTECTION FOR
SHIPBOARD POWER SYSTEMS Presenter: Xianyong Feng, PhD
Contributors: Dr. Angelo Gattozzi, Doug Wardell, Dr. Bob Hebner
Center for Electromechanics
The University of Texas at Austin
March 23, 2018 – ONR Control Workshop
Key Points
• Proposed a hybrid prot. method and an extra-fast fault
localization method for dc distribution systems
• Proposed a dc series fault detection/localization method
• Validated the approach in simulation and experiment
2
Outline
1. Overview
2. Methodology • Pole-to-pole dc short circuit fault
• Series dc arc fault
3. Simulation Study
4. Experimental Results
5. Conclusion
3
4
Motivation
• Power Equipment Damage and Human Safety
• Fire Hazards
5
Power System Fault Management
Detection
• Real-time monitoring
• Detect electrical abnormality
Localization
• Quickly and accurately localize fault
• Minimize system impact
Isolation
• Open protective devices
• Minimize load interruption
Restoration
• Quick recovery
• Restore interrupted loads to normal
6
DC System Protection Challenges
7
AC fault current
DC fault current
1. No fault current zero-crossing
2. Lower line impedances
3. High di/dt
4. Power electronic devices can not tolerate high fault current
5. Fast capacitor discharge
Overcurrent Protection
Advantage Disadvantage
1. Algorithm is simple
2. Need less sensors
1. Prot. coordination is difficult
8
Protection
unit
Protection
unit
Protection
unit
i1
i3
i2
...
...
Legend
Protective device
Current sensor
Current
measurement signal
Control command
Over-current protection
strategy
IF i1<ith, no downstream fault
IF i1>ith, downstream fault
A tripping command is generated
after a certain time delay
ith : preconfigured current threshold
Zone 1
Zone 2
Zone 3
Differential Protection
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Differential
Protection Zone
Legend
Protective device
Current sensor
Protection
unit
i1
i2
i3
i4
i5
Current
measurement signal
Control command
Differential Protection
Strategy
IF i1+i2+i3+i4+i5<ith, no fault in zone
IF i1+i2+i3+i4+i5>ith, fault in zone
ith : preconfigured current threshold
Advantage Disadvantage
1. Reliable fault detection
2. Algorithm is simple
1. Need signal synchronization
2. May need comm. for long lines
Impedance Protection
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Protection
unit
Protection
unit
Protection
unit
i1
i3
i2
...
...
Legend
Protective device
Current sensor
measurement signal
Control command
Impdeance Protection Strategy
Use current to detect downstream fault. If
a fault is detected, estimate impedance
IF Lestimated<Lth, fault in zone (internal fault)
IF Lestimated>Lth, downstream fault (external
fault)
Lestimated : estimated fault inductance
Lth : preconfigured inductance threshold
Zone 1
Zone 2
Zone 3
v3
v2
v1
Voltage sensor
Advantage Disadvantage
1. Good fault localization accuracy
2. Extra-fast fault localization
1. Need high sampling rate for voltage and current
2. Need fast controller
Converter Fault Current Limiting
1. Buck converter
2. Full-bridge MMC
3. Thyristor-based rectifier
11
Phase A
Cell1T1
T2
D1
D2uC1
Cell1
CellN
iSA
CellN
D3
D4
T3
T4
Full-bridge MMC
iSA
iSCiSB
S1
S2
S3
S4
S5
S6
Thyristor-based rectifier
=
Level 3 Level 4
Level 5
=~ =
DC UPS
...
...
Buck converter
12
Simplified MVDC Shipboard Power System
13
FCL
FCL
DP
DP
DPDPDPDP
OPOP
OPDP
OP
DP
OPOPDP
DP
DP
DP
DP
DPDP
OP
OP
OP
DP
DPDP
FCL
FCL
FCL
FCLFCL
FCL
Ref: N. Doerry and J. Amy, “The Road to MVDC,” Proc. of ASNE Intelligent Ships Symposium, Philadelphia PA, May 2015.
Short-Circuit Fault Detection and Localization
14
Differential
Protection Zone 1
Legend
Normally close device
Current sensorProtection
unit
i1
i2
i3
Current
measurement signal
Control command
Differential protection
strategy
IF i1+i2+i3<ith, no fault in zone
IF i1+i2+i3>ith, fault in zone
ith : preconfigured current threshold
...
Differential
Protection Zone 2Protection
unit
i4
Load
center
Normally open device
Protection
unit
Overcurrent
Protection Zone 3
Over-current protection
strategy
IF i4<ith, no downstream fault
IF i4>ith, downstream fault
A tripping command is generated
after a certain time delay
ith : preconfigured current threshold
Zone 1Zone 2
Zone 3
FCL
• Conceptual section of dc distribution system with a hybrid
protection system
Fast DC Fault Localization Algorithm
Inductance-based dc fault localization*
1. Estimate fault inductance with locally
measured v(t) and i(t)
2. Use estimated L to locate fault
=
L L L
Zone 1
(20 m)Zone 2
(65 m)Zone 4
(1.5 m)
=
~ =
Converter
with FCL
...
...
Fault 1 Fault 2
Fault 3...
L L L...
Zone 3 (10.2 m)...
...
Equivalent
inductance
Distance
level 1 level 2 level 3
L1
L2
L3
Line inductance distribution
RF
LRi
v
+
-
Equivalent fault circuit
* X. Feng, L. Qi, J. Pan, “A novel fault location method for dc distribution protection,” IEEE Trans. Industrial Applications, vol. 53, no. 3, 2017.
15
Fast DC Fault Localization Algorithm
16
Protection strategy design 1. Online moving-window least square method
2. Algorithm on micro-controllers Start
Go to next time
intervalFault detected? No
Read in (M+1) data points
v and i
)(/)(
)2(/)2(
)1(/)1(
MidtMdi
idtdi
idtdi
A
)(
)2(
)1(
Mv
v
v
B
BAAARR
L TT
F
1
Use estimated L to calculate the distance
from measurement point to fault
End
di/dt estimation
Flowchart of inductance-based fault
localization
Series Arc Fault Detection and Localization
• DC series arc faults
17
Series arc fault protection apparatus1,2
Flowchart of series arc fault detection
and localization1
1. X. Feng, et. al., “Converter-based dc distribution system protection,” IEEE IAS Annual Meeting, 2018, in review
2. Q. Xiong, et. al., “Arc fault detection and localization in photovoltaic systems using feature distribution maps of parallel capacitor currents,”
IEEE Journal of Photovoltaics, 2018, accepted
Arc inception
Series Arc Fault Detection and Localization
• More experimental test data are still required 1. Electrode distance
2. Separation speed
3. Separation acceleration
4. Electrode orientation
Vertical
Horizontal
5. Electrode material
Copper
Aluminum, etc.
6. Ambient conditions
Humidity
Pressure, etc.
18
Fabian M. Uriarte, et. al., “A dc arc model for series faults in low voltage microgrids,”
in IEEE Trans. Smart Grid, vol. 3, no. 4, pp. 2063-2070, Dec. 2012.
19
Simplified System Description
20
1. Two PGMs
‒ FCL in the converters
2. One propulsion load
‒ VFD + motor
3. One pulse load
‒ High di/dt
4. DC isolation devices
‒ Isolate faulted zone
5. Protection strategy1,2
‒ FCL + hybrid prot.
1. S. Strank, et. al., “Experimental test bed to de-risk the navy advanced development model,” Proc. of Electric Ship
Technology Symposium, Arlington, VA, Aug. 2017, pp. 352-358.
2. X. Feng, et. al., “Converter-based dc distribution system protection,” IEEE IAS Annual Meeting, 2018, in review
NC = Normally closed
FCL = Fault Current Limit
1 = Capacitor
2 = Mechanical Circuit Breakers
3 = Contactors
4 = Line Reactor
850 V, 1.2 MW
60 Hz, 3-phase
Lab Power
M
1.1 kV
2 MW
200 Hz
MISSION
LOAD
PMM
PGM
PGM
PCM
1.15 kV main dc bus
Equivalent
DC zonal
Load
PFN
Railgun
PROPULSON
LOAD=
=
==
850 V, 0.8 MW
60 Hz, 3-phase
Lab Power
2 2
3 3 333
1 & 4
1 & 4
Toshiba
NC NCNCNC
FCL
NCNC
NC
FCL
NC
3
NC
3
DP DP
DP
DP
DP
OP OP
OP
Circuit and Parameters
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• Impact of fault resistance
on system behavior
• Differential prot. method
study
• Fault at the midpoint of
the main dc bus
1. Case 1: Rf = 20mΩ
2. Case 2 : Rf = 500mΩ
Rf – fault resistance
==
==
Reactor 1
Reactor 2PGM 2
PGM 1
Load 1
Load 2
0.6 MW
1 MW
0.39 mH0.39 mH
0.39 mH0.39 mH
5 mF
5 mF 0.5 mF
0.5 mF
9 mΩ
9 mΩ
80 µH
80 µH
Main
dc bus
950 V 60 Hz
3-Ph ac
950 V 60 Hz
3-Ph ac
1150 V dc
10 µH 2 mΩ
10 µH 2 mΩ
OP
OP
DP
DP + IP
DP
20 µH
20 µH
2 mΩ
2 mΩ
DP
DP
FCL
FCL
Reactor 1
0.39 mH0.39 mH
0.5 mF
9 mΩ80 µHPGM 1
Reactor 2
0.39 mH0.39 mH
0.5 mF
9 mΩ80 µHPGM 2 10 µH 2 mΩ
10 µH 2 mΩ
Equivalent Circuit during Fault
System Single Line Diagram
High Fault Resistance leads to faster settling time
22
Rf = 20 mΩ Rf = 500 mΩ
PGM current
PGM voltage
Current differential
Sensitivity Analysis
• Impact of fault resistance
• Criteria for current
differential threshold:
23
9.9 10 10.1 10.2 10.3 10.4 10.50
100
200
300
400
time (ms)
Cu
rre
nt (A
)
delta t = 2 us
delta t = 5 us
delta t = 10 us
delta t = 20 us
delta t = 50 us
Ithreshold > max(di/dt)·max(ΔT)
Current differential of the main dc bus zone
PGM fault currents with different Rf
ΔT - measurement time difference
of zonal boundary currents
Inductance-based Fault Localization HIL Test
Control-HIL test
1. Opal-RT simulator
‒ Simulate a dc system
‒ Convert v(t), i(t) to analog
‒ Read in switch status
2. Microcontroller
‒ Read in v(t), i(t) signals
‒ Execute prot. algorithm
‒ Send trip signal for fault
isolation
24
PXIe Real-Time/FPGA
HIL System Opal-RT Simulator
High speed
communication link
DC microgrid circuit in Opal-RTSimulated switching devices in NI PXI simulator
Control, Protection and Monitoring Hardwares
Digita
l/ana
log
I/O in
terfa
ce
Control Room
Time Sensitive Network
NI / TI controllers
Central series arc
fault localization
...
Local fault detection
and localization
Other functions
...
Central
controller
Inductance-based Fault Localization HIL Test
Control-HIL test results1
1. L estimation error < 9%
2. Fault detection/location time < 0.7 ms tripping signal
current signal
current signal
voltage signal
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Estimation accuracy
1. X. Feng, et. al., “Fault inductance based protection for DC distribution systems,” Proc. of
IET Conference on Development of Power System Protection, March 2016, pp. 1-6.
26
LVDC Test Circuit (up to 250 V dc)
LVDC fault test circuit
DC power supply
30-kW converter with FCL
Downstream circuit
NI sbRio control board
=
Line impedance 1
Load Source 2Source 1
Line impedance 2
Current and
voltage sensors
Controller
=
7.7 mF 1.2 mF
27
Control Platform
• NI sbRIO-9606 (top-layer)
1. Processor speed: 400 MHz
2. Memory: 256 MB
3. FPGA: Xilinux Spartan-6 LX45
4. Comm. rate: 10-100 Mbps
• NI GPIC (middle-layer)
1. Digital/analog I/Os
2. FPGA and processor expansion I/Os
3. Half-bridge digital output Custom interface board
GPIC NI sbRIO-9606
28
Typical DC Fault Waveform
Switching spikes
Relay chattering
29
Single Source Fault Localization
*: measured inductance value
: estimated inductance value
Case # RF (mΩ) L (µH)
1 33 12.5
2 33 24
3 33 42
4 50 12.5
5 50 24
6 50 42
7 100 12.5
8 100 24
9 100 42
Case Definition*
*5 tests in each case
Test Circuit 1. Fault is on the load side
2. Sampling rate: 20 kHz
3. Data sample number: 5
30
Inductance estimation error
High sampling rate improves the accuracy
-30
-25
-20
-15
-10
-5
0
5
10
Test1 Test2 Test3 Test4 Test5
31 E
rror
[%]
Sampling rate: 20 kHz Sampling rate: 50 kHz
Two-Source Fault Test
Test Circuit 1. Two dc sources
2. Fault is on the load side
3. Sampling rate: 50 kHz
4. Data sample number: 5
In-zone fault Protection procedure: 1. Differential prot. accurately
detects in-zone fault
2. Activate fault localization
program
32
Current differential
Fault current
Two-Source Fault Localization
Test Scenario 1. Fault resistance: 50 mΩ
2. Source 1 fault inductance: 42 µH
3. Source 2 fault inductance: 24 µH
Test
#
Source 1 Source 2
Estimated L (µH) Error (%) Estimated L (µH) Error (%)
1 45.3 7.9% 21.5 -10.4%
2 41.6 -1.0% 25.3 5.4%
3 43.0 2.4% 22.3 -7.1%
4 45.3 7.9% 22.4 -6.7%
33
Summary
1. The inductance prot. uses local measurements only
‒ Fault detection and localization time < 0.7 ms
‒ L estimation error in control-HIL test < 9%
‒ L estimation error in hardware test < 12%
2. Differential protection can accurately detect in-zone
faults
3. Converter FCL effectively limits fault current
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Ongoing Work: MW Fault Protection Test
Main elements
1. 3-ph 480-V ac
power source
2. Transformer
3. Controlled rectifier
4. Line reactor
5. Semikron power
converter modules
6. Cables
7. Fault resistor
8. Fault path switch
35
Controlled rectifier Line reactor
1.67-MVA 3-ph
converter module Cable
Fault
resistor
Fault path
switch
Transformer
Conclusion
1. Fault management is critical for power system safety
and reliability
2. The proposed dc prot. approach reduces fault clearing
time and system recovery time
3. The fast prot. method improves dc power system
resilience
36
Research Papers
1. S. Strank, et. al., “Experimental test bed to de-risk the navy advanced development
model,” Proc. of Electric Ship Technology Symposium, Arlington, VA, Aug. 2017, pp.
352-358.
2. X. Feng, et.al., “A novel fault location method for dc distribution protection,” IEEE
Trans. Industrial Applications, vol. 53, no. 3, May-June, 2017.
3. X. Feng, et. al., “Converter-based dc distribution system protection,” IEEE IAS Annual
Meeting, 2018, in review.
4. Q. Xiong, et. al., “Arc fault detection and localization in Photovoltaic systems using
feature distribution maps of parallel capacitor currents,” IEEE Journal of Photovoltaics,
2018, accepted
5. Q. Xiong, et. al., “Detecting and locating series arc fault in Photovoltaic system based
on time and frequency characteristics of capacitor current,” Solar Energy, 2018, in
review.
37
Thanks for your attention
Contact information: Xianyong Feng
Center for Electromechanics
The University of Texas at Austin
Email: x.feng@cem.utexas.edu
Phone: 512-232-1623
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