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The Roles of Power Electronics in
Renewable Energy Deployment
Eduard Muljadi National Renewable
Energy Laboratory
Panel Presentation
IEEE-PES-ISGT 2014
Washington, DC
February 19-22, 2013
Credit: NREL – pix library
Outline
• Introduction
• Renewable energy resources
• Grid integration
• Power electronics control
• Environment
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Introduction
• Applications mW or MW level Isolated or grid connected
• Variability of the source Temporal (seconds, hour, day, week, season) Spatial (continental, local, plant)
• Large area coverage – Diversity (resource and electrical characteristics)
• Operation Normal/abnormal Balanced/unbalanced
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4
PV Plant (5~50 MW)
Rooftop PV
(1~30 kW)
Mobile 9-kW PV System
Bechler Meadows Ranger Station
Yellowstone National Park
Introduction
Cre
dit S
un P
ow
er
Corp
. /
23816
Credit: Dennis Schroeder / NREL / 22192.JPG
Credit DOE / FEMP /27638
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California Region
Spring Peaking Summer Peaking
Pea
k
S
hif
t 24-Hour Wind Resource
24-Hour Solar Resource
Wind Resource – Midwest Wind Resource – West Coast
Low Output
8 a.m. – 14 p.m.
High Output
8 a.m. – 12 p.m.
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Offshore Wind Resource
U.S. Wind Resource
Solar Resource
Resources
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Synchronous Generator (left) vs.
Wound Rotor Induction Generator (right)
What will happen if there is a sudden
disturbance in the transmission
network? To power AC-DC-AC power
converter to operate WTG in
variable speed
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Generator Sgen 4,000-W (Siemens)
1,300 to 2,235 MVA
Wind Turbine
Generator
1-6 MW
Conventional Power Plant vs. Renewable Energy Power Plant
Plant Diversity
Cre
dit:
David
Hic
ks / N
RE
L
/ 18454
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era
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Cre
dit: W
ikip
edia
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Type 1 Wind Turbine Generator (1% Slip)
Type 3 Wind Turbine Generator ( + 30% Slip) Type 4 Wind Turbine Generator (Full Conversion)
(100% Slip)
Type 2 Wind Turbine Generator (10% Slip)
Examples of Renewable Energy Resources
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Cre
dit:
NR
EL –
Dav
id H
icks
/ N
REL
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88
1
Credit: David Hicks / NREL / 18557
Credit: Bill Timmerman/ 08989
Cre
dit G
reg G
latz
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r /
NR
EL /
19807
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Credit: Dennis Schroeder / NREL / 27806
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Reference: Li, Y.; Yu, Y. H. (2012).
Synthesis of Numerical Methods for
Modeling Wave Energy Converter-Point
Absorbers: Preprint. 36 pp.; NREL Report
No. JA-5000-52115.
Grid Integration
• Interconnection
• Operation
• Standards – Grid codes
• Ancillary services (inertial response, frequency and governor response, reserves)
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Transmission to
other utilities
115kV and higher
Power plantUtility Scale Wind Farms (above 10 MW)
Small Wind Farm (less
than 10 MW)
26-115 kV
Single Large Wind
Turbine
Small Wind Turbine
Subtransmission
CustomersDistribution
Customers
Distribution Customers
4-35 kV 120-480 V
Step-up
transformer
Step-up
transformerStep-down
transformer
Step-down
transformer
Step-down
transformer
Distributed Interconnections per
IEEE-1547 Wind Farm Interconnections
Interconnection
Credit: NREL’s TGIG presentation archive.
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Base
Generators Adjustable
Generators
(Conventional
Gen., RE)
Variable
Generators
(RE)
Reserves
Storage
Base
Loads
Adjustable
Loads Variable
Loads Power Losses
Real Power
Freq UP
Freq Down
Line
Capacitance Switched
Capacitors Synchronous
Generators/
Condensers
Static
Compensation
Line
Inductance
Inductive
Load
Induction
Motors/Generators
Reactive Power
Voltage UP
Voltage Down
Real and Reactive Power Balance (To Keep Frequency and Voltage Constant)
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Voltage Ride Through
0
0.2
0.4
0.6
0.8
1
1.2
1.4
-1 0 1 2 3 4
Time (sec)
Vo
lta
ge
(p
.u.)
661
661A
LVRT-WECC Prop.
HVRT-WECC Prop.
Fault Ride-Through Capability
• Wind power plants should be able to stay on-
line under transient faults/disturbances.
• The voltage should tolerate 0 p.u. for 15 ms
(9 cycles).
• Wind power plants should be able to regulate
the power factor between 0.95 leading/lagging.
• Wind power plants should have a SCADA
system to allow remote access and monitoring.
Voltage vs. Maximum Clearing
Time as Described in IEEE 1547
Adaptable to
Regional Code
Power Electronics Control
• Generator level
• Plant level
• Transmission level
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Ma
xim
ize
En
erg
y C
ap
ture
Load Control
Gearbox Preservation
Po
wer
Qu
ality
Re
al a
nd
Re
ac
tive
Po
wer
Co
ntr
ol
Short/Long-Term DC
Distributed Storage
Provide Active Damping to
Power System Network
At the
Generator Level
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Ma
xim
ize
En
erg
y C
ap
ture
Po
wer
Qu
ality
Re
al a
nd
Re
ac
tive
Po
wer
Co
ntr
ol
Short/Long-Term DC
Distributed Storage
Provide Active Damping to
Power System Network
At the
Generator Level
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•Many (hundreds) of wind turbines (1 MW to 5 MW each)
•Prime mover: Wind (wind turbine) – Renewable (free, natural, pollution free)
•Controllability: Curtailment
•Predictability: Wind variability based on wind forecasting, influenced more by nature (wind) than humans, based on maximizing energy production (unscheduled operation).
•Located at wind resource; may be far from the load center.
•Generator: Four different types (fixed speed, variable slip, variable speed, full converter) – Non-synchronous generation
•Types 3 and 4: Variable speed with flux-oriented controller (FOC) via power converter. Rotor does not have to rotate synchronously.
At the Plant Level
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A
B
C+
RPMARPMC
A
B
C+
RPMARPMC
5 10 15 20 250
1 106
2 106
Max Cp
8 m/s
9.2 m/s
10.8 m/s
12 m/s pitch=0 deg
12 m/s pitch=4.75 deg
Power vs RPM for different wind speeds
RPM (low speed shaft)
Pow
er
(W) 1 .5 10
6
11 21
A
B
C
D
D’
P
5 10 15 20 250
1 106
2 106
Max Cp
8 m/s
9.2 m/s
10.8 m/s
12 m/s pitch=0 deg
12 m/s pitch=4.75 deg
Power vs RPM for different wind speeds
RPM (low speed shaft)
Pow
er
(W) 1 .5 10
6
11 21
A
B
C
D
D’
P
Trated limit
Type 1 & 2
Type 3 & 4
At the Plant Level
Inertial Response from a Wind Turbine
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(Load
Center)
Wind Power
Generator
Other
Generators
VAR
Compensation
to Help
Regulate
Voltage
Storage
VR d, V
P, Q
d, V
Wind
At the
Transmission Level
Variability
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Thermal Limit
(Thin Wire)
Stability Limit
(High Impedance,
Long Distance,
Weak Grid)
Wind Power
Generator
Wind Power
Generator
Storage
Storage (Load Center)
FACTS
At the
Transmission Level
Transmission Constraints
Environment
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26 G
oo
gle
Ma
p o
f a
win
d p
ow
er
pla
nt,
Te
ha
ch
ap
i, C
A
Credit: Stephen Drouilhet / 05626
Reference: McNiff, B. (2002). Wind Turbine Lightning Protection Project:
1999-2001. 100 pp.; NREL Report No. SR-500-31115.
Reference: NREL Software Aids Offshore Wind Turbine Designs (Fact
Sheet). Innovation Impact: Wind, NREL (National Renewable Energy
Laboratory). (2013). 1 pg.; NREL Report No. FS-6A42-60377.
Conclusions
• Cost reduction in the past 20 years • Many and diverse opportunities for Power Electronics
Generation, transmission, and distribution
• Know the limitations Thermal, magnetic, electric (voltage, current) etc.
• Know the applications Environment: Ocean, land-based, isolated, clusters Opportunities to work in parallel (PV – Wind – CSP)
• Leverage existing and future technologies Other industries (drives, transportation, ship building) Modern technologies (smart control, wireless, condition monitoring,
cyber physical and security, synchrophasor, market driven)
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The information contained in this presentation is subject to a government license.