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© University of Wisconsin November 2010
1
Distributed Generation and Storage:Exploring the Microgrid
3rd Energy Storage SummitNovember 15-17, 2010, Chicago, IL
Bob LasseterUniversity of Wisconsin - Madison
16 November 2010
© University of Wisconsin April 2010
2
Electrical Power System
Customers
Power Plants(200-1000 MW)
Transmission networkLines (~100 mi)
DistributionSubstation
DistributionTransformer
DistributionLine (~10 mi)
High Voltage Transmission Network Issues
– Generation/transmission efficiency (~25%)
– Peaking generation capacity (~20%)
– Cascading blackout 2003
– Penetration of intermittent sources
– Building new generation and transmission
+ Smart controls & ~ 99.9% reliable
+ Evolutionary changes (most technology is proven)
Power Distribution System Issues
–~100 year old technology
– Poor reliability
– Basically uncontrolled radial feeders
– Most problems are reported by customers
+ Prime for Smart grid concepts
© University of Wisconsin November 2010
3
Power System Reliability
Stand-aloneSteam Generation
1900 1950 2000
Year
Electricity Reliability(in “9”s)
10 9 8 7 6 5 4 3 2 1 0
(3 ms/yr)
(30 ms/yr)
(0.3 sec/yr)
(3 sec/yr)
(30 sec/yr)
(5 min/yr)
(1 hr/yr)
(9 hr/yr)
(3-4 day/yr)
(1 mo/yr)
Interconnected CentralStation Generation
DER-basedDistributionSystem
RobustG&T
Local Reliability
Higher efficiency
Renewables
Smarter components
*EPRI
Greater need forsophisticatedenergy services
© University of Wisconsin April 2010
4
Electrical Power System
Customers
Conventional UtilityPower Plant(~1000 MW)
Transmission Line (~100 mi)
DistributionSubstation
DistributionTransformer
DistributionLine (~10 mi)
DER-based DistributionPower Plant(~1000 MW)
Transmission Line (~100 mi)
Robustgeneration &transmission
DER-baseddistribution
© University of Wisconsin April 2010
5
DER TechnologiesDispatchable Sources (10kW ~ 3 MW)• Internal combustion-engine generator• Small gas turbines generators• Microturbines• Fuel cellsIntermittent Sources•Wind turbines•PhotovoltaicStorage•Batteries•Ultra-capacitors•Fly-wheels
Electrical vehicles?
© University of Wisconsin November 2010
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Smart Distribution“When it comes to a utility figuring out howto manage this wide, dynamic set of resourcesand control points, the only way they can dothat efficiently is to break their networksdown into small nodes i.e. microgrids– andthen add a level of control on top of it.”
Dave Pacyna, senior vice president of Siemens Energy’s North American
© University of Wisconsin November 2010
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Microgrids
A microgrid is an integrated energy systemconsisting of interconnected loads anddistributed energy resources which as anintegrated system can operate in parallel withthe grid or in an intentional island mode.
© University of Wisconsin November 2010
Microgrid: Fast Controls and Communications
Utility SystemPrimary Connection
(13.2 kV)
Utility SystemInterface Control(Synchronization, faultprotection, islanding
detection, etc.)
Isolating Device(opens during micro-
grid mode)
Heat Distribution
1.2 MVA
0.8 MVA
1.4 MVA
GeneratorStep Up
Transformer
GenGenGen
GeneratorProtection
andControl
Paralleling Bus (4.8 kV)
1.75MVA
1.75MVA
1.75MVA
Heat Recoveredfrom ICE Units
Loadcontrol
Communication & ControlSignal Path
Issues:• Loss of control &communication
• Extensive siteengineering
• Costly heatdistribution system.
• Complex voltage &power balancingsystem
• Speed of response
EPRI: Campus Microgrid System: CEC Workshop
© University of Wisconsin November 2010
CERTS Microgrid: Local Control
Utility SystemPrimary Connection
(13.2 kV)
Smart Switch Heat Distribution
1.2 MVA 0.8 MVA
1.4 MVAParalleling Bus (4.8 kV)
CERTSGen
CERTSGen
CERTSGen
• Local Control (nomaster control)
• Plug & Play Model(avoids extensive siteengineering, designerrors & allowsplacement nearheat/cooling loads)
• Units control power &voltage using localinformation only
CERTSStorage
© University of Wisconsin November 2010
Multi-CERTS Microgrids
Microgrid + CHP
• Mixed building based microgrid• Enhances use of waist heat• Peer-to-Peer and Plug & Play Model• Each DER unit has embedded
CERTS controls
Microgrid with localCombined Heat & Power Microgrid + CHP
13.2 kV
120 kV
Smart Switch Other loads
Lc L
c Lc
LLCHP
PV
Storage
PV
Controller
CHP
© University of Wisconsin November 2010
Current CERTS Microgrid Field Demonstration Projects• DOE Phase III: CERTS/AEP Test Site (PV and ac storage)
• CEC/SMUD: Microgrid Demonstration (3-100 kW, CHP, UPS, PV &
export)
• DOE/Chevron Energy Solutions: Distribution Microgrid (12 kV, static
switch, storage, diesel generation, fuel cell and PV).
• CERL/Odyssian Technology: Scalable & Deployable Microgrids
(research on microgrid controller)
• Air Force/Sandia: Maxwell Air force base (100kw NG and 2 existing
diesels)• CERL/Ft. Sill Army: (2-190kW NG generators, 400KW ZBB Battery, 30 kW PV)
© University of Wisconsin April 2010
12
Microgrids and storageSystem approach (Currently one DER unit, IEEE 1547)
Support high penetration of DER (Ca. expects 100s of thousands of DER units)
Support use of waste heat (efficiency ~ 80%)
Reduces transmission losses
Support intermittent sources
Enhance robustness and reliability
Promote self healing
Eliminate need for fast central controls
© University of Wisconsin November 2010
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CERTS Microgrid Control Concept*
• Voltage Control (V vs. Q droop)• Each unit has an overload capacity• The islanded system operates over a
well defined frequency range (±0.5Hz).This frequency is key for:• Transfer load among units• Intelligent load and source
shedding.• Automatic re-synchronizing to the
network.
*Research History CERTS MicrogridDOE– 1999-‐2002(Development of original concepts bench-‐scaletesFng )
CEC PIER – 2001-‐2006(ConstrucFon & compleFon of proof-‐of-‐concept onAEP CERTS Microgrid test bed)
DOE RDSI– 2006-‐2009(Value and technology assessment to enhance thebusiness case)
DOE Smart Grid – 2009-‐present(IntegraFon of variable renewablegeneraFon/storage)
© University of Wisconsin November 2010
Load Transfer
.
Assume two DER sources
P01 & P02 are dispatchedpowers while grid connected
For a step load (islanding orwhile islanded) The increasedload is ~ equally sharedbetween both sources
Transient Overload• Storage most robust• Syn machine and InVerde
could stall• PV has minimum overload
capabilities without dc storage.
∆P ∆P
© University of Wisconsin November 2010
Load Transfer & Stalling Issues
2-100kW CERTS sourcesA1: 90 kWA2 : 10 kWImport 90 kW
Opening Smart Switch loose 90 kWsA1: 90 + 47.5 =137.5 kWOverload 37.5 kWWill Stall if overload too long
Voltage sourcesCB31
CB41
P1=10 kW P2=90 kW
Load 190 kW
A1 A2
90 kW
© University of Wisconsin November 2010
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Lc
Lc
LcL
LCHP
PV
Storage
PV
CHP
Controller
Basic Building Block: Microgrid
Microgrid as a Grid Resource:• Provides a standard building block for “Smart
Distribution”.• Dispatchable bi-directional real & reactive power.• Multiple points of electrical coupling.• Islands & re-synchronizes autonomously• Controller interfaces with system controllers and
locally optimizes the microgrid operation.
Can have different features: CHP/UPS Microgrid, MixedMicrogrid & PV Microgrid.
© University of Wisconsin November 2010
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Basic Types of Microgrid
High Power Quality Microgrid with CCHP• UPS functions & effective use of waste heat• DER units must follow a peer-to-peer and plug-and-play concept
Mixed Microgrid• Higher voltages and power levels change the DER mix.• Synchronous generators and ac storage (different response times)• Plug-and-play
PV Microgrid• High export of PV• Reduce intermittent power fluctuations (storage and/or CHP units).• Need to back off PV output during islanding
© University of Wisconsin November 2010
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High Power Quality Microgrid with CCHPUPS functions & effective use of waste heatEach DER units must follow a peer-to-peer and plug-and-play concept
•Need fast response with overload capacity (i.e. InVerde, storage) or•DC storage as part of the source (i.e microturbines, fuel cells…)•No standalone ac storage
Examples• DOE: CERTS/AEP Test Site
• CEC/SMUD: Sacramento Municipal Utility District, Microgrid
Demonstration (3-100 kW, CCHP, UPS & export)
© University of Wisconsin November 2010
High Power Quality Microgrid with CCHP
Loads
60 kWSources
StaticSwitch
3-New 100 kW InVerde for SMUD Microgrid(InVerde is a CERTS compatible source)
CERTS/AEP Microgrid Test Bed
© University of Wisconsin November 2010
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Microgrids with slower DER units
Higher voltages and power levels change the DER mix.Synchronous generators and ac storage.Storage provides:
• Enhance reliability with Intentional islanding (smallest energy sizing)
• Arbitrage of energy price differentials (largest energy levels)
• Firm intermittent resources( DG and storage)(Loss of ac storage reduces microgrid flexibility).
ExampleDOE/Chevron Energy Solutions: (12 kV, 12 MW hour storage, diesel
generation, fuel cell and PV).CERL/Ft. Sill Army: (2-190kW NG generators, 400KW ZBB Battery, 30 kW
PV)
© University of Wisconsin November 2010
DOE/Chevron: Microgrid
© University of Wisconsin November 2010
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PV Microgrid: High export of PV
High levels of energy from PV in a CERTS microgrid•PV overload (i.e. islanding) requires dc storage
•Reduce intermittent power fluctuations (storage and/or CHP units).
•Need to back off PV output during islanding also requires ac or dcstorage
Active Research:UW test facility & CERTS/AEP test bed (100kW PV)
© University of Wisconsin November 2010
Storage in Microgrids
Peer-to-Peer Microgrids•DC storage needed for most sources including PV
•No AC storage
Mixed Microgrids (AC storage)•Needed for Islanding
•Arbitrage of energy price differentials
•Firm intermittent resources (also can use other sources & dc storage)
© University of Wisconsin November 2010
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Lc
Lc
LcL
LCHP
PV
Storage
PV
CHP
Controller
Microgrid is a basic building block
Microgrid :• Provides a standard building block for “Smart
Distribution”.• Dispatchable bi-directional real & reactive power.• Components include dispatchable generation,
renewable sources, storage, loads and a smart switch• Provides a system approach
© University of Wisconsin November 2010
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Smart Distribution: Coupled Microgrids
LcLc
LcL
LCHP
PV
Storage
PV
CHP
Controller
LcLc
LcL
LCHP
PV
Storage
PV
CHP
Controller
LcLc
LcL
LCHP
PV
Storage
PV
CHP
Controller
LcLc
LcL
LCHP
PV
Storage
PV
CHP
Controller
LcLc
LcL
LCHP
PV
Storage
PV
CHP
Controller
Distribution coordinator
SmartSwitch
High Voltage Network
© University of Wisconsin November 2010
27
Load
MWs fromgrid
Power from ICE generator
Power from storage
Loss of grid
Islanding on Loss of grid
Energy level
Combined Storage/Genset
Charging Discharging
• Constant Power from grid 24/7.• Storage is charged during low load periods.• Generation is run at optimum level during
high loads.• Storage follows load and provides fast power
balance during islanding.• Storage sizing
Islanding onlyArbitrage
sources