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1IEEE USA 5-4-2012
Smart Grid and Renewable
Energy Grid IntegrationJian Sun, Professor and Director
Department of ECSE & Center for FutureEnergy Systems
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2IEEE USA 5-4-2012
How Smart Can WeMake This Grid?
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3IEEE USA 5-4-2012
Smart Grid Drivers Need to Use Renewable Energy
Peak Oil; Energy Security GHG Emission; Climate Change
Electrification of Transportation Sector
Energy Storage
Demand Response; Efficient Utilization
Stronger Transmission Network Intelligent, Bidirectional Distribution System
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4IEEE USA 5-4-2012
Energy is a National Priority
1
2
3
Energy
Security
Climate
Change
Green
Economy
Nuclear
Energy
R
enewable
Energy
Energy
Efficiency
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5IEEE USA 5-4-2012
Role of Power Electronics
Smart Grid
Renewable
Generation
Renewable
Generation
Energy
Storage
Energy
Storage
Load
Manag.
Load
Manag.
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6IEEE USA 5-4-2012
With Electric Machines With Power Electronics
t
Production of AC
B()
v(t)
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7IEEE USA 5-4-2012
Traditional vs. Wind Generators
0.01 0.1 1 10 100 1000 10000Frequency (Hertz)
Prime Mover
Control
Prime Mover
Control
Excitation
Control
Excitation
ControlTraditional
Generator
SemiconductorSwitching
SemiconductorSwitchingCurrentControlCurrentControl
DC-Link
Control
DC-Link
Control
Turbine SpeedControl
Turbine SpeedControl Grid Q & VControlGrid Q & VControlLa
rgeWind
G
enerator Grid
Synchronization
Grid
Synchronization
Limited Controllability at Low
Frequencies
Complex Control & Dynamics
at High Frequencies
Limited Controllability at Low
Frequencies
Complex Control & Dynamics
at High Frequencies
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8IEEE USA 5-4-2012
0.1 1 10 100 1000 10000 100000.
Grid Operation & Control
102
103
109
102 0.1 1 10 102 103 104 Hz
105
106
107
108
104
Central Control
Manual Dispatch
Control Frequency (F)
Numbe
rofUnits(N)
102
103
109
105
106
107
108
104
Fast, Autonomous Control
of Many Units
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9IEEE USA 5-4-2012
Impedance is a Key Parameter
c
1
PhaseMargin
Gain
Margin
Im
Re
Partition System into a Source and a Load Subsystem
Determine Source Subsystem Output Impedance (Zs) and LoadSubsystem Input Impedance (Zl)
System is Stability ifZs/Zl Meets Nyquist Stability Criterion
+
Zs
ZlVs Vl
+
Source Load
)(
)(1
1)()(
)()()(
sZ
sZsZsZsZ
sVsV
l
ssl
l
s
l
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10IEEE USA 5-4-2012
Grid-Parallel Inverter Stability
Grid-Connected Inverters are Controlled as Current Sources
Different System Model and Stability Requirement
Ratio of Grid Impedance to Inverter Output Impedance MustMeet Nyquist Stability Criterion
Voltage-Source System Current-Source System
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11IEEE USA 5-4-2012
An Example Solar Inverter
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12IEEE USA 5-4-2012
Grid Impedance Line + Transformer + Generator Impedance
Typically Inductive at Fundamental Frequency Focus of Traditional Power System Theory
Weak Grid
Resonance at Harmonic Frequencies
Effects of Loads; Variability with Time
Effects of Neighboring Renewable Sources Active Control; Different from Passive Impedance
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13IEEE USA 5-4-2012
Inverter Output Impedance Depends on Physical Design and Control
Filter Inductors and Capacitors (L, LC, LCL) Current & Voltage Control, Grid Synchronization
Inverter Impedance Modeling
Native Circuit & Control Models are Nonlinear
Small-Signal Impedance has to be Used
Time-Varying Operation; No DC Operation Point
Traditional Linearization Methods cannot be Applied
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14IEEE USA 5-4-2012
Small-Signal Modeling Phasor-Based Methods
Not Compatible with Impedance-Based Analysis Limited to Line Fundamental Frequency
DQ-Transformation Method
Impedance in DQ-Coordinate System is Difficultto Measure and Interpret
Coupling between DQ Axes Requires Generalized
Nyquist Criterion
Direct Harmonic Linearization
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15IEEE USA 5-4-2012
Three-Phase Converter Modeling Decomposition Using Symmetric Components
Positive-Sequence Impedance
Negative-Sequence Impedance
Zero-Sequence Impedance Usually Open-Circuit
Single-Phase Model for Each Sequence Component
No Crossing Coupling between Positive and NegativeSequence Subsystems
va
vb
vc
ia
ib
ic
ip in+
vp
+
vp
Positive Sequence Negative Sequence
+
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16IEEE USA 5-4-2012
Smart Grid System Test-Bed Need a Controllable Grid to
Emulate Different Grid Conditions
Test Analysis Method and System Theory
Demonstrate System Control Techniques
A System Test-Bed has been Developed
Grid Simulator
Programmable Voltage, Frequency, Harmonic Contents,
and Impedance
Single or Three-Phase Operation, 75 kW Power
Standalone, Grid Parallel Mode, Micro Grid
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17IEEE USA 5-4-2012
Simulate
dGridwithProgrammable
SimulatedGridwithProgrammable
Volt/Freq/Impedance
Volt/Freq/Impedance
PV SimulatorsPV Simulators
CentralCentral
Inverters (3)Inverters (3)
Inverters(20)
Inverters(20
)
=~
44thth Gen Wind Turbine SimulatorGen Wind Turbine Simulator
ElectronicElectronic
LoadsLoads
~= MMMGGG
= ~
=~
=~
UtilityUtilityGridGrid
=~
Grid SimulatorGrid Simulator
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18IEEE USA 5-4-2012
Single-Phase Solar InverterGrid Voltage (500V/div)
Grid Current (10A/div)
Lp = 0 mH
Grid Voltage (500V/div)
Grid Current (10A/div)
Lp = 12.8 mH
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19IEEE USA 5-4-2012
Harmonic Resonance
0
1
2
3
4
5
2 7 12 17 22 27 32 37
Lp = 0 mH
Lp = 12.8 mH
Ih/I1 (%)
h
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20IEEE USA 5-4-2012
Three-Phase Wind Inverter
rd
ib (5 A/div.)ia (5 A/div.) ic (5 A/div.)
Sequence Gain Margin Phase Margin
Positive 1.04 dB 5
Negative 15 dB 42
Sequence Gain Margin Phase Margin
Positive >15 dB 25
Negative >15 dB 55
PLL Bandwidth 100 Hz PLL Bandwidth 10 Hz
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21IEEE USA 5-4-2012
Nature of Harmonic Resonance
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22IEEE USA 5-4-2012
Inverter Impedance Shaping Grid Synchronization Methods
Current Control Loop Active Damping
Online Grid Impedance Identification
Adaptive Control
Inverter Interactions in Wind Farms
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23IEEE USA 5-4-2012
HVDC for Offshore Wind Farms
Speed
Source
1600 rpm
mech
690 V
7 km
PM
Speed
Source
1600 rpm
mech
690 V
7 km
PM
SpeedSource
1600 rpm
mech
690 V
7 km
PM
Speed
Source
1600 rpm
mech
690 V
7 km
PM
Speed
Source
1600 rpm
mech
690 V
7 km
PM
400*2.5MW Turbines
33kV AC
Bus
7km Cable
Direct-Drive Technology HVDC Rectifier
(VSC or LCC)
HVDC
300 MVA
STATCOM
300 MVA
STATCOM
ACBus
Filters
ACBus
Filters
Stability & Control of AC Collection Bus
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24IEEE USA 5-4-2012
Multi-Terminal HVDC
DC Output from Individual Turbines
Series and Parallel Connections
Modular Voltage-Source Converter Design
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25IEEE USA 5-4-2012
=~
=~
=~
=~
=
~
=~
~=
Utility GridUtility Grid
RealReal--TimeTime
SimulatorSimulator
AC DGAC DG
TestTest--BedBedMTHVDC
MTHVDC
Hybrid AC-DC System Test-Bed
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26IEEE USA 5-4-2012
Summary Renewable Energy and Electric Transportation Will
Drive Smart Grid Development
Energy Storage and Demand Management Required
Ubiquitous Use of Power Electronics
New Stability Problems at High Frequencies
New Modeling and Analysis Tools Needed
Fast, Autonomous Control are Essential
New Impedance-Based System Analysis Methods
Hardware-in-the-Loop System Test-Bed for
Validation and Demonstration
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