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Challenges in Integrating Renewable Sources into the Electric Power Grid:
A Power Electronics Perspective
Bingsen [email protected]
Assistant Professor, Electrical EngineeringArizona State University
April 7, 2009
1
Topics
• Overview of renewable energy• Motivation of grid integration• Functional role of power electronics• The challenges• Summary
4/7/2009 2
Renewable vs. Sustainable Energy
• Renewable energy – is regenerative or virtually inexhaustible.
Focused on supply side.• Sustainable energy
– can be replenished at a rate higher than consumption and the waste stream can be naturally absorbed at a rate higher than injection. Focused on supply and use sides.
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Renewable Energy Sources
• Renewable energy sources include– Solar– Wind– Biomass– Hydro– Geothermal– Tidal
• Wind and solar enjoy very fast growth rate
4/7/2009 4
Renewable Portfolio Standards
Source: K.S. Cory and B.G. Swezey, “Renewable Portfolio Standards in the States: Balancing Goals and Implementation Strategies,” NREL/TP-670-41409, 2007.
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World PV Installation
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• Accumulated PV installed capacity reached 10.5 GW by the end of 2007.
Source: Renewables 2007 Global Status Report, www.ren21.net.
Data from “World Wind Energy Report 2008”
Wind Installations Worldwide
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7.5 9.713.7
18.024.3
31.239.3
47.7
59.0
74.2
93.8
121.2
29%
42%
32%
35%
28%26%
21%
24%26%
27%
29%
0%
10%
20%
30%
40%
0
20
40
60
80
100
120
140
Ann
ual G
row
th
Capa
city
(GW
)
Year
Wind Power Capacity in U.S.
• Installed wind capacity in U.S. reached 25 GW by the end of 2008.
Source: American Wind Energy Association
4/7/2009 8
Renewable Energy Conversion
• Converted to electricity – and delivered using the power system
infrastructure– or consumed locally
• Converted to fuel – and delivered through conventional
infrastructure
4/7/2009 9
Why Grid Integration
• Necessity– Geographic locations of sources may not
match the locations of load centers (particularly true for wind resources)
• For performance / economics– Integration provides ways to manage
resource output variability– Economically advantageous– Regulation
4/7/2009 10
Integration Involves
• Technical aspects– Physical layer– Information layer
• Market and economics• Policy and regulation• ...
4/7/2009 11
Power Electronics for Electric Power Applications
4/7/2009 12
Interconnection Levels
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Power Electronics
Power Electronics
• Electronics for processing power rather than just for processing signal information.
• Power flows and signal flows co-exist in a power electronics system.
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Power Processor
Signal Processor
Application of Power Electronics is Evolving
• Power devices drive the power flow path
• Signal processors drive the information flow path
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Mercury Arc Valve
Press pack IGBT
IGCT
State of the Art in High Power Conversion
• In electric drives, power throughput of matured single power converter has reached 10 MW.
• These high power converters switch at approximate frequency of 1 kHz.
• They operate at medium voltage 3.3 – 6.9 kV.• Modular scaling up to 30-100 MW which covers
majority of renewable interface.
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Role of Power Electronics in Integrating Renewable Energy Sources
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Functional Role Change
• Power electronics has been traditionally used to interface the power system with loads (such as motors).
• Power electronics will be broadly used to interface sources and with the power system.
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Source LoadPEPE
Higher PE Penetration
• Higher penetration of power electronics can be expected as use of renewables grows. Power electronics will be used for:– Grid interface– Energy storage– Power flow management
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Power Electronics
Wind Generation System - Yesterday
• In “Danish concept” wind generation systems, no power electronics is utilized.
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Gear Box
Squirrel Cage Induction Generator
Reactive Power Compensation
Wind Generation System - Today
• In wind generation systems equipped with DFIG, power converter handles about 30% power flow.
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Gear Box
Wound Rotor Induction Generator
Power Converter of 30% Rated Power
Wind Generation System - Tomorrow
• In the expected large wind generation systems (> 5 MW) that utilize PM generators, power converter handles full power.
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Permanent Magnet Synchronous Generator
Power Converter of 100% Rated Power
Energy Storage
• Energy storage is one of the options to deal with variability of renewable sources.– Pumped hydro– Compressed air– Supercapacitor– Flywheel– PHEV
• Majority of the energy storage technologies involve power electronics
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FACTS Devices and Integration
• FACTS devices will become more important at transmission level because of increased power flow traffic resulting from variability of renewable sources.
• Even at distribution levels, power flow control will become necessary as the radial distribution system is shifted to a meshed system.
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Series FACTS Device
• Power flow controller
4/7/2009 25
VinjV1 V2
X1+-
Vinj
V1
+V2
+
X2
Shunt FACTS Device
• Reactive power compensation
4/7/2009 26
V1 V2
X1
IinjV1
+V2
+
X2
Series and Shunt FACTS Device
• Unified power flow controller
4/7/2009 27
V1
X1
IinjV1
+V2
+
X2+-
Vinj
Adding Value with Power Electronics
• Voltage support by reactive power generated by power electronics
• Ramp up and down quickly• Improve power quality• Control of a large number of sources
centrally• Low voltage ride-through
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Evolution of Standards
• Larger grid support requirement is expected from renewable sources as reach higher penetration levels.
• One of the evolution examples is the low voltage ride through for wind power generation systems.
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Low Voltage Ride Through
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0.9
0.15
0.625 3.0
Wind Plant Required to Remain On-line
Wind Plant Not Required to Remain On-line
0
Vol
tage
at P
CC
(pu)
Time (sec)
Communications and Control
• Power electronics needs augmented communication capability to use smart grid features.
• Control in microgrids will rely heavily on power electronics.
4/7/2009 31
Technical Challenges
• New design perspective from downstream to upstream in power flow chain
• Interactions among much larger number of distributed resources with power electronic converters
• Integrated design in high power areas• Standardized design to improve inter-
operability
4/7/2009 32
Non-Technical Challenges
• Assessing the economic value of power electronics solutions– Cost reduction challenging today due to non-
standardized designs– Inclusion of lifecycle operating costs– Quantification of indirect benefits such as
GHG reduction• Less operational experience as compared
to conventional power generation sources4/7/2009 33
Myths That Need to be Dispelled!
• System “polluter” – harmonics?
• Complex failure modes?
4/7/2009 34
Summary
• Integration challenges must be addressed given anticipated growth penetration of renewable sources.
• Renewable energy integration will be enabled by power electronics.
• The new operating regime and design space present challenges for the needed use of power electronics.
4/7/2009 35