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A Front-to-Front (FTF) System Consisting ofTwo Modular Multilevel Cascade Converters
Based on Double-Star Chopper-Cells
Firman Sasongko, Makoto Hagiwara, and Hirofumi Akagi
Tokyo Institute of Technology
1
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Outline
Research Background
Key Technologies for HVDC Network
FTF System Based on MMCC-DSCC
Simulation Results
Summary
2
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Research Background
Key Technologies for HVDC Network
FTF System Based on MMCC-DSCC
Simulation Results
Summary
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Introduction
4
0
1
2
3
4
5
Annually added
Advantages
Higher wind speed
Less turbulence
Large areas availability
Less constructional and
operational restrictions
Challenges
Harsh environment
Remote
Limited accessibility
Installed offshore wind farm in Europe (GW)
Source: EWEA
0
1
2
3
New 2012
Source: GWEC
Offshore Wind Farm
Global offshore wind farm installed capacity in 2012 (GW)
1993 2002 2012
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Offshore Wind Farm Trend
further
fromshore
Monopile
0 ~ 30 m, 1 ~ 2 MW
Jacket/Tripod
25 ~ 50 m, 2 ~ 5 MW
Floating Structures
>50 m, 5 ~ 10 MW
Floating Structures
>120 m, 5 ~ 10 MW
Source: Principle Power
Challenges
deeper water (>50m)
more difficult bottom
conditions
higher waves
more robust wind
turbines necessity
power collection and
grid in terconnection
Reduce visual impacts ???
Increase the size ???
5
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Offshore Wind Farm Interconnection
AC/AC layout
AC/DC layout
DC/DC layout
Cable charging current
Limited voltage
regulation
Limited phase angle
difference
up to 155 kV, 100 km
AC voltage level
constraints
Higher flexibility and
reliability
DC Power Collection
6
100 ~ 1000 MW
[1] I. Erlich, F. Shewarega, C. Feltes, F. W. Koch, and J. Fortmann, Offshore wind power generation
technologies, Proceedings of the IEEE, vol. 101, no. 4, pp. 891905, Apr. 2013.
[6] S. Lundberg, Evaluation of wind farm layouts,EPE Journal, vol. 16, pp. 1421, 2006.
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High-Power Long-Distance Offshore Transmission
0
100
200
300
400
500
600
0 50 100 1 50 2 00 2 50 3 00 3 50 4 00
Cost
DistanceAC terminal
cost
AC line cost
DC terminal
cost
DC line cost
DC losses
AC losses
Total
AC
Cost
Total
DCCost
Power [MW]
Distance [km]
LCC-HVDC
VSC or LCC-HVDC
AC
Estimated Optimal Solution
for Offshore Transmission
7
AC vs. DC Transmission Cost
[i] M. Okba, M. Saied, M. Mostafa, et. al., High Voltage Direct Current Transmission A Review,
Part I,IEEE Energytech, pp. 17, May. 2012.
[2] N. M. Kirby, L. Xu, M. Luckett , and W. Siepmann, HVDC transmission for large offshore wind
farms,Power Engineering Journal, vol. 16, no. 3, pp. 135141, Jun. 2002.
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Research Background
Key Technologies for HVDC Network
FTF System Based on MMCC-DSCC
Simulation Results
Summary
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Multi-Terminal HVDC Networks
9
Offshore Onshore
Stability Issue:
Fast fault interruption required
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DC Circuit Breakers
10
Mechanical
Switches Slow
Power
ElectronicsInefficient
ABBsbreakthrough: up to one gigawatt
with the interrupt time of 5 ms and
power loss less than 0.01%.
Hybrid
SystemFast and Efficient ?
Cost???
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Key Technologies for HVDC Networks
DC/DC Transformer
DC
DC Technicallyfeasible
Economicallyfeasible?
DC Circuit Breaker
Technicallyfeasible? Economicallyfeasible???
11
Medium
FrequencyTransformerFault-ProtectiveDC/DC Converter ?
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Research Background
Key Technologies for HVDC Network
FTF System Based on MMCC-DSCC
Simulation Results
Summary
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MMCC-DSCC Basic Principles
leg
arm
=
+
=
=
+
=
n+1 level
13
[13] R. Marquardt, A. Lesnicar, and J. Hildinger, Modulares stromrichterkonzept fur
netzkupplungsanwendung bei hohen spannungen, ETG-Conference, 2002.
[14] H. Akagi, Classification , terminology , and application of the modular multilevel cascade
converter (MMCC),IEEE tran. on power elect., vol. 26, no. 11, pp. 31193130, Apr. 2011.
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BTB and FTF System Applications
Aims
HVDC transmission
Frequency changer
Asynchronous power
flow controller
Aims
DC-to-DC systems
Galvanically
isolated systems
Voltage changer
Back-to-Back System
Front-to-Front System
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Front-to-Front (FTF) System Based on DSCC
Modular Structure & Redundant
Operation Bi-directional Power Flow
Inherent Faults Handling
Passive Components Reduction
DC AC DC
Multilevel Signal
Waveforms
Chopper Cell
n-CellsMedium FrequencyTransformer
Less Space
Less Weight
Lower Cost15
150 ~ 500 Hz
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Faults on an FTF System
16
ifault
Fault Protection: Handled by
circuit operation
Very fast
interruption
OFF OFF OFF
OFF OFF OFF
OFF OFF OFF
OFF OFF OFF
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Power Collection Based on FTF System
17
Collecting SideConverters
Transmission Side
Converter
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Research Background
Key Technologies for HVDC Network
FTF System Based on MMCC-DSCC
Simulation Results
Summary
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Circuit Configuration for Simulation
6.6 kV 150 Hz
LAC: 0.37 mH (8%)LC: 1.1 mH (23.8%)
n: 16
DC Capacitors1.65 kV/3 mF
Switching MethodPhase-Shifted PWM
fc = 1350 Hz
Dead-time = 4 s
Vref
1:1
13.2 kV
P* :
10 MW
Power Control
- Decoupled Current
Control
Capacitor Control
- Leg Balancing
- Arm Balancing
- Individual Balancing
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-10
0
10
20 ms0
1.65
-10
0
10
-1.25
0
1.25
-0.75
0
0.75
-10
0
10
20 ms0
1.65
-10
0
10
-1.25
0
1.25
-0.75
0
0.75
Simulation Results
DSCC-1 DSCC-2Power
[MW]
Line
Voltages
[kV]
LineCurrents
[kA]
Leg
Capacitor
Voltages
[kV]
DC
Currents
[kA]
iZuiDC
vC1u vC9u
20
C ll i Si l i l
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-10
0
10
20 ms0
1.65
-1.25
0
1.25
0
1.65
0
1.65
Power Collection Simulation Results
Power
[MW]
Line
Currents
[kA]
DSCC-1
CapacitorVoltages
[kV]
DSCC-2
Capacitor
Voltages
[kV]
DSCC-3
Capacitor
Voltages
[kV]
P2* :8 MW
P3* :2 MW
vC1u1 vC9u1
vC1u2 vC9u2
vC1u3 vC9u3
p1p2 p3
iu1 iu2 iu3
6.6 kV 150 Hz
21
VDC: 13.2 kV
S
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Summary
HVDC transmission is likely to be preferred option for future
offshore wind farms.
Dc/dc transformers and dc breakers are the key components
to multi-terminal dc grid.
A front-to-front (FTF) system is a dc/dc transformer that is
capable of handling faults inherently.
The proposed FTF system based on MMCC-DSCC is
applicable for dc power collection.
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Thank you
23
R f
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References
[1] I. Erlich, F. Shewarega, C. Feltes, F. W. Koch, and J. Fortmann, Offshore wind power generation
technologies,Proceedings of the IEEE, vol. 101, no. 4, pp. 891905, Apr. 2013.
[2] N. M. Kirby, L. Xu, M. Luckett, and W. Siepmann, HVDC transmission for large offshore wind farms,Power Engineering Journal, vol. 16, no. 3, pp. 135141, Jun. 2002.
[3] V. G. Agelidis, G. D. Demetriades, and N. Flourentzou, Recent advances in high-voltage direct-current
power transmission systems,IEEE International Conference on Industrial Technology, 2006. ICIT 2006.,
pp. 206213, Dec. 2006.
[4] A. M. Abbas and P. W. Lehn, PWM based VSC-HVDC systems - a review,PES 09. IEEE Power &
Energy Society General Meeting, 2009., pp. 19, Jul. 2009.
[5] J. Glasdam, J. Hjerrild, L. H. Kocewiak, and C. L. Bak, Review on multi-level voltage source converter
based HVDC technologies for grid connection of large offshore wind farms,IEEE International
Conference on Power System Technology (POWERCON) 2012, pp. 16, Oct. 2012.
[6] S. Lundberg, Evaluation of wind farm layouts,EPE Journal, vol. 16, pp. 1421, 2006.
[7] W. Lu and B.-T. Ooi, Premium quality power park based on multiterminal HVDC,IEEE Transactions on
Power Delivery, vol. 20, no. 2, pp. 978983, Apr. 2005.
[8] L. Xu, B. W. Williams, and L. Yao, Multi-terminal dc transmission systems for connecting large offshorewind farms, 2008 IEEE Power and Energy Society General Meeting - Conversion and Delivery of
Electrical Energy in the 21st Century, pp. 17, Jul. 2008.
24
R f ( td)
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References (contd)
[9] J. Zhu and C. Booth, Future multi-terminal HVDC transmission systems using voltage source converters,
45th International Universities Power Engineering Conference (UPEC) 2010 , pp. 16, Aug. 2010.
[10] R. Marquardt, Modular multilevel converter topologies with dc-short circuit current limitation, 8thInternational Conference on Power Electronics ECCE Asia, pp. 14251431, Jun. 2011.
[11] S. Kenzelmann, A. Rufer, M. Vasiladiotis, D. Dujic, F. Canales, and Y. de Novaes, A versatile dc-dc
converter for energy collection and distribution using the modular multilevel converter,Proceedings of the
2011-14th European Conference on Power Electronics and Applications (EPE 2011), pp. 110, Aug. 2011.
[12] S. Kenzelmann, D. Dujic, F. Canales, Y. de Novaes, and A. Rufer, Modular dc/dc converter: comparison
of modulation methods, 15thInternational Power Electronics and Motion Control Conference
(EPE/PEMC) 2012, pp. LS2a.11LS2a.17, Sep. 2012.
[13] R. Marquardt, A. Lesnicar, and J. Hildinger, Modulares stromrichterkonzept fur netzkupplungsanwendung
bei hohen spannungen,ETG-Conference, 2002.
[14] H. Akagi, Classification , terminology , and application of the modular multilevel cascade converter
(MMCC),IEEE Transactions on Power Electronics, vol. 26, no. 11, pp. 31193130, Apr. 2011.
[15] H. Fujita, M. Hagiwara, and H. Akagi, Power flow analysis and dc capacitor voltage regulation for the
MMCC-DSCC,IEEJ Transactions on Industry Applications, vol. 132, no. 6, pp. 659665, Dec. 2012.[i] M. Okba, M. Saied, M. Mostafa, et. al., High Voltage Direct Current Transmission A Review, Part I,
IEEE Energytech, pp. 17, May. 2012.
25
E Wi d F
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European Wind Farms
MMCC F il M b
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MMCC Family Members
Medium-Voltage High Power Converter
Voltage Source
Multilevel
Modular MultilevelCascade Converter
Double Arm
Star Connection
Chopper-Cells
Bridge-Cells
Single Arm
Star Connection
Bridge-Cells
Delta Connection
Bridge-Cells
CascadedH-Bridge
Diode-Clamped
FlyingCapacitor
Two-Level
Current Source
LoadCommutated
PWM
27
A. Lesnicar, R.Marquardt, An Innovative Modular Multilevel Converter Topology Suitable for a Wide Power Range, IEEE PowerTech conf.,
2003.
Hirofumi Akagi, Classification, Terminology, and Application of the Modular Multilevel Cascade Converter (MMCC),IEEE trans. power
elect., vol.26, no. 11, 2011.
Modular Multilevel
Cascade Converter
Double-Star Chopper-Cells
(MMCC-DSCC)
Li i f AC C bl T i i C i
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Limits of AC Cables Transmission Capacity
28
for three voltage levels, 132 KV, 220 KV and 400 KV
T. Ackermann, N. Barberis Negra, J. Todorovic, L. Lazaridis, Evaluation of Electrical Transmission Concepts for
Large Offshore Wind Farms, presented at the Copenhagen Offshore Wind -Int. Conf. Exhib., Copenhagen, Denmark,
Oct. 2005.
Chopper Cell Basic Operation
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Chopper Cell Basic Operation
S1 S2 iP vpi Capacitor C
ON OFF + vci charging
OFF ON + 0 -
ON OFF - vci discharging
OFF ON - 0 -
Cell Voltage
Command
AC Voltage
Command
Maintain AC
Side Voltage
DC Voltage
Command
Maintain DC
Side Voltage
Capacitor
Voltage
Command
Maintain
Capacitor
Voltage
output side
input side
29
MMCC DSCC Control Method
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MMCC-DSCC Control Method
Controlling Output Power
DecoupledCurrent Control
Controlling Capacitor Voltage
Leg BalancingControl
Arm Balancing
Control
IndividualBalancing Control
iP,iN
VPi ,
VNi Cap. C
+ vci charging
- vci discharging
30
Front to Front for DC/DC Application
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Front-to-Front for DC/DC Application
* S. Kenzelmann, D. Dujic, F. Canales, Y. de Novaes, and A. Rufer, Modular DC/DC converter:
Comparison of modulation methods, 15th International Power Electronics and Motion Control
Conference (EPE/PEMC) 2012, pp. LS2a.11LS2a.17, Sep. 2012.
Previous Research*
Single-Phase Configuration
Two-level & Square-wave
modulation
Our ResearchThree-Phase Configuration
Coupled Inductor
Sinusoidal Phase Shift Pulse Width
Modulation
Simulated and Experimental
Verification
31
Fault on a Multilevel Converter
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AC
Fault on a Multilevel Converter
32
AC
Solutions:
1. DC Breakers2. Full-Bridge Cells
3. Parallel Thyristors
Circuit Configuration
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Circuit Configuration
33
1:1
6.6 kV 150 Hz
LAC: 0.37 mH (8%)LC: 1.1 mH (23.8%)
n: 16
DC Capacitor1.65 kV/3 mF
Switching MethodPhase-Shifted PWM
fc = 1350 HzDead-time = 4 s
13.2 kV
P* :10 MW
Simulation Results
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-10
0
10
10 ms
0
1.65
-10
0
10
-1.25
0
1.25
-3
-2
-1
0
1
2
3
Simulation Results
34
DSCC-1 DSCC-2
Power[MW]
Line
Voltages
[kV]
Line
Currents
[kA]
Leg
Capacitor
Voltages
[kV]
DC
Currents
[kA]
iDCiZu
vC1u vC9u
-10
0
10
10 ms
0
1.65
-10
0
10
-1.25
0
1.25
-3
-2
-1
0
1
2
3
Short Circuit
Event
Experimental Setup 400 V 10 kW FTF System
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U-phase
Module Structure:
16 cells/leg
Chopper Cell:
150-V 70-A MOSFET42
50-V 6600-mF Capacitor
Experimental Setup 400 V 10 kW FTF System
Controller System:
- A DSP board
- Two FPGA boards
AC Voltage:
200 V 50 Hz
35
Medium Frequency Transformer
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Medium Frequency Transformer
3 4
Volume and Frequency Relation:
U.Drofenik, A 150kW Medium Frequency Transformer Optimized for Maximum Power Density,7th
International Conference on Integrated Power Electronics Systems (CIPS12), 2012.
1 +
12 +
1
Winding Core Dielectric
Transformer Losses
36