Power Converters and Control of Renewable Energy Systems
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Transcript of Power Converters and Control of Renewable Energy Systems
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Power Converters and Controlof Renewable Energy Systems
by
Professor Frede BlaabjergAalborg University
Institute of Energy [email protected]
http://www.iet.aau.dk
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Outline
1. Short introduction to Aalborg University2. Development in Energy Technology3. Distributed power sources4. Single-phase PV-inverters5. Control of single-phase PV6. Control of three-phase inverters7. Converter topologies for wind turbines8. Control of wind turbines9. Summary
Power Converters and Controlof Renewable Energy Systems
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13000 students 150mill € 2500 employed 1600 VIP 900 TAP
Aalborg University
Faculty of Engineering and ScienceFinn Kjaersdam
20 Faculty Members10 Research Assistants10 Guest Researchers15 Ph.D. students 2 External professors12 TAP
Institute of Energy TechnologyJohn K. Pedersen
4000 Students 800 VIP 340 TAP
Institute of Electronic SystemsFlemming B. Frederiksen
PowerSystems
PowerElectronicSystems
ElectricalMachines
FluidPower
Systems
FluidMechanics
andCombustion
ThermalEnergy
Systems
Aalborg Universityand
Institute of Energy Technology
• Founded 1974
• Project-oriented and problem-based
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Energy Technology
POWER STATION
SOLAR CELLS
WIND TURBINE
MOTOR
PUMP
ROBOTICS
REFRIGERATOR
TELEVISION
LIGHT
TRANSFORMER
TRANSFORMER
INDUSTRY
=
POWER SUPPLYac dc
TRANSFORMER
COMPEN-SATOR
FACTS
FUELCELLS
FUEL
COMMUNICATION
COMBUSTIONENGINE
SOLARENERGY
TRANSPORT
3 3 3 1-3
3
DCAC
~
Energy System
POWER STATION
SOLAR CELLS
WIND TURBINE
MOTOR
PUMP
ROBOTICS
REFRIGERATOR
TELEVISION
LIGHT
TRANSFORMER
TRANSFORMER
INDUSTRY
=
POWER SUPPLYac dc
TRANSFORMER
COMPEN-SATOR
FACTS
FUELCELLS
FUEL
COMMUNICATION
COMBUSTIONENGINE
SOLARENERGY
TRANSPORT
3 3 3 1-3
3
DCAC
~
DCAC
DCAC
• Only full Energy Institute in Denmark
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Organisation
Strateticcooperation:• EMSD• EDS• CEES• NEED• FACE• WEST• DFV
Lab. Facilities:• Power electronics Systems• Drive Systems Tests• Hydraulic• Power systems• High Voltage• DSpace• Laser Systems• Fuel Cell Systems• Proto Type FacilitiesF
uel
cell
s
Inte
gra
ted
en
erg
y s
yst
em
s
Th
erm
al d
esi
gn
of
ele
c.
de
vic
e
Ind
ust
rial
dri
ve s
yst
em
s
Tra
ctio
n a
nd
au
tom
oti
ve
Po
wer
con
vert
ers
Ad
van
ced
Co
mb
ust
ion
an
d
Mu
ltip
hase
Pro
cess
es
Act
uato
rs a
nd
Mo
tio
n
Co
ntr
ol
••
20 VIP
15 PhD
10 Guest Researchers
10 Research Assistansts
12 TAPInstitute of Energy Technology
Power Systems
Thermal Energysystems
ElectricalMachines
Fluid PowerSystems
PowerElectronicSystems
Fluid Mechanics and
Combustion
Research Programme
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Key Competence
Power Electronic Systems
• Power Electronic Components
• AC/DC – DC/AC Converters
Topologies
• DC/DC Converter Topologies
• AC/AC Converter Topologies
• PFC and Active Filters
• PWM and Resonans Control
• Random Modulation
• Modelling and simulation
• Optimized Design
• FACTS – Converters for Power Systems
• Electrical Drive Systems
• DSP /:-controllers
• Test of Components and Systems
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Collaboration Partners - Industry
Danfoss Drives A/SDanfoss A/S
Grundfos A/S
Axel Åkerman A/S
Elfor
Nesa A/S
VestasWind Systems A/S
Logimatic A/S
Mita-Teknik a/s
Cooper Bussmann
DEFU
B&O
APC
ABB Motors
Migatronic
ThrigeElectric
Electrolux
Sauer Danfoss
Eltra
Nordex
Bonus Energy
PowerLynx
E2
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Basic Structure
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8
7
6
5
4
3
2
1
Master Specialisation
Fundamental
Education
Basic Year
B.Sc.Thesis
Intro semester
The study each semester is based on a combination of courses and team based problem-oriented project work
Problem-based and project-oriented learning
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Implementation of problem-oriented andproject-organised education
Problem-based and project-oriented learning
Project solving
Literature Lectures Groupstudies
Experiments/Fieldwork/Tutorials
Problemanalysis
Problemsolving Report
PrototypingSimulation
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Distribution between courses and project work (one semester, 30 ETCS)
INT
RO
DU
CT
ION
solvingAnalysis Report
100%
75%
50%
25%
0%5 weeks 10 15 weeks
1. period 2. period 3. period 4. periodStart End
COURSES
Problem
EVALUATION(project/courses)
100%
75%
50%
25%
0%5 10 weeks
1. 2. 3. 4. Start
1 day
20 weeks
• 50% project work
• 25% project-oriented courses
• 25% basic courses
• Full week time table
Problem-based and project-oriented learning
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• Project proposal
• Group room
• Computer / Internet
• Laboratory
• Supervisor
What do the students need
Problem-based and project-oriented learning
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• Project themes during a complete study in power electronics anddrives
• Every semester one report
Design Oriented Analysis ofElectrical Machines andPower Electronic Systems
M.Sc. Project
Dynamics in electricalMachines and Power Systems
Dynamics
Controlin PowerElectronic Systems
ControlElectroni Systems
Design of ElectronicSystemsSystems
DesignSystem Design
Micro computersMicro-
Analogue andDigital Electronics
Analogue
Models RealityModels Reality
Reality and ModelsReality and Models
Power Control inElectrical Systems
B.Sc. Project
1. semester
2. semester
3. semester
4. semester
5. semester
6. semester
7. semester
8. semester
9. semester
10. semester
Power
Curriculum at Aalborg University
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Curriculum at Aalborg University
Offered courses and project time in the main areasof the power electronics and drives curriculum
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2. Development in Energy Technology
• Early developers shift around $15,000 per capita ($1997 PPP) as less energy-intensive services dominate economic growth
• Signs of saturation beyond $25,000
• Later developers require less energy
Per capita primary energy consumption grows with income in a similar pattern across countries and time
Source: Energy Needs, Choices and Possibilities – Scenarios to 2050 (Shell International 2001)
PPP = Purchasing Power Parity
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1970 1980 1990 2000 2010 20200
1,000
2,000
3,000
4,000
5,000
Commercial
Residential
Industrial
History Projections
Annual Electricity Sales by Sector, 1970-2020 (billion kWh)
WorldWide 13.000 22.500
US ~27% ~22%
2. Development in Energy Technology
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2. Development in Energy Technology
- Energy comsumption increases· More people (born, longer life-time etc.)· More equipment· Higher living standard· More production
- Global Energy Market becomes deregulated(electrical power, natural gas, etc.)
- Oil Prize rises
- New power sources interesting- More efficient use of the existing sources
· From production to end user· Power balance extremely important· New energy storage devices
Therefore
⇒ Power Electronics Technology one important enabling technology
General Trends
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2. Development in Energy Technology
POWER STATIONMOTOR
PUMP
ROBOTICS
REFRIGERATOR
TELEVISION
LIGHT
TRANSFORMER
INDUSTRY
=
POWER SUPPLYac dc
TRANSFORMER
3 3 3 1-3
~
Classical Power System
POWER STATIONMOTOR
PUMP
ROBOTICS
REFRIGERATOR
TELEVISION
LIGHT
TRANSFORMER
INDUSTRY
=
POWER SUPPLYac dc
TRANSFORMER
THERMALHEAT 3 3 3 1-3
~
POWER STATIONPOWER STATION
POWER STATIONPOWER STATION
3
3
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2. Development in Energy Technology
POWER STATION
SOLAR CELLS
WIND TURBINE
MOTOR
PUMP
ROBOTICS
REFRIGERATOR
TELEVISION
LIGHT
TRANSFORMER
TRANSFORMER
INDUSTRY
=
POWER SUPPLYac dc
TRANSFORMER
COMPEN-SATOR
FACTS
FUELCELLS
FUEL
COMBUSTIONENGINE
SOLARENERGY
3 3 3 1- 3
3
DCAC
~
Future Power System
POWER STATION
SOLAR CELLS
WIND TURBINE
MOTOR
PUMP
ROBOTICS
REFRIGERATOR
TELEVISION
LIGHT
TRANSFORMER
TRANSFORMER
INDUSTRY
=
POWER SUPPLYac dc
TRANSFORMER
COMPEN-SATOR
FACTS
FUELCELLS
FUEL
COMBUSTIONENGINE
SOLARENERGY
3 3 3 1- 3
3
DCAC
~
DCAC
DCAC
WIND TURBINEWIND TURBINE
TRANSFORMER
33Demands• Stability• Frequency control• Voltage control• Optimized control• ProtectionFocus in this
presentation
Focus in thispresentation
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2. Development in Energy TechnologyDevice development
Silicon carbide FETs
MOSFETs
Insulated-gatebipolar transistors
MOS-gated thyristors
Silicon
Bipolar transistors
1950 r6 0 r70 r80 r90 2000 2004 2010Year
Trench
Coolmos
IGCT
Diode
GTO
• Power devices are still being improved
• Both low-power and high-power devices
(S. Bernet, Berlin)
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2. Development in Energy Technology
0
50
100
150
200
1968
1983
1988
1993
1998
Year
Rel
ativ
e un
it
Components
Functions
0
20
40
60
80
100
120
1968
1988
1998
Year
%
Size (volume)
Weight
System level development
Adjustable Speed Drives (industrial )
• More integration• Lower volume• Higher power density• Lower cost
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Wind:
Problems to be solved
p(t) variable p(t) fixedp(t) variable
Energy storage?
Short-term solution - Long-term solution
Power Station
3. Distributed Power Sources
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3. Distributed Power Sources
Wind
Angle of attack:
Trailing edge
wind
Leading edge
Lift force
Drag force
Pitching moment
αα
β
β
φ
Pitch angle:
pCvRP 322
1ρπ=
v
R Ω⋅=λ
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3. Distributed Power Sources
Wind power conversion:
Power conversion &power control
Wind powerPower converter
(optional)
Power conversion &power control
Power conversionPower transmission Power transmission
Supply grid
Consumer
Rotor Gearbox (optional) Generator
Electrical Power
Key technology
Wind:
• Electromechanical Energy Conversion• Many configurations exist
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0
250000
500000
750000
1000000
1250000
2000 2005 2010 2015 2020 2025 2030
Year
MW
WF 10, 1999
BTM, 1999
EWEA, rev, 2000
EU, WP, 1997
IEA, 1998
Installed capacity: 2002 32 GW
Windforce 10: 2010 180 GW2020 1200 GW
2
2,5
3
3,5
4
4,5
5
2000 2005 2010 2015 2020Year
USD cent/kWh
Prediction of wind energy (associations)
3. Distributed Power Sources
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22
19891985 1992 1993 1996
∅ 15 m
∅ 30 m
∅ 46 m
∅ 37 m 600 kW
500 kW
300 kW
50 kW
∅ 46 m
∅ 112 m
4.500 kW
1.500 kW
∅ 70 m
200x
Growth of WTG‘s
Track recordin Denmark Development
3. Distributed Power Sources
Bigger and more efficient !
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3. Distributed Power Sources
Photo-voltaic
iSC
iPV
id uPV
IPV
PPV
pMPP
UPVuO C
iSC
(uMPP, iMPP)
Efficiencymaximum 20 %
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3. Distributed Power Sources
PV – Installed capacity
Japan and German leading countries(Source: www.iea-pvps.org)
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3. Distributed Power Sources
PV – Price development
• Price is decreasing
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3. Distributed Power Sources
Fuel-cell
• PEM• Solid Oxide• Molten Carbonate• Phosphoric Acid
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3. Distributed Power Sources
Fuel-cell
Characteristic (ideally and non-ideally)Steady progress but no long track-recordMany potential applications (micro-power to power-station)
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4. Single-phase PV-inverters
PVArray
PV Inverter& Filter Grid
Controlreference
Basic control
• Maximize power from the PV array/Sun• Interconnect to the grid
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4. Single-phase PV-inverters
Central inverter String inverter Module integratedinverter
PV - configurations
• Power level dependent• Prize dependent
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4. Single-phase PV-inverters
PVInverters
with DC-DCconverter
without DC-DCconverter
with isolation
without isolation
on the LF side
on the HF side
with isolation
without isolation
Characteristics of topologies
• Galvanic isolation necessary some places• LF/HF transformer (cost-volume issue)• Without boost / with boost of voltage
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4. Single-phase PV-inverters
DC
ACGridPV
Array
DC
DC
DC
ACGridPV
Array
DC
AC
AC
DC
PV inverter with HF transformer in the dc -dc converter
• Isolated push-pull boost converter
• PWM VSI
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4. Single-phase PV-inverters
DC
DC
DC
ACGridPV
Array
• Boost converter
• Full-bridge inverter (PWM VSI)
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4. Single-phase PV-inverters
DC
ACGridPV
Array
• Full -bridge inverter (PWM VSI)• Grid-side transformer• Volume high
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4. Single-phase PV-inverters
DC
ACGrid
PVArray
• PWM IGBT inverters (VSI) • Multilevel inverter
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5. Control of single-phase PV
ug
SYSTEM CONTROL
Qref P ref
Structure
• Maximum Power Point Tracking (MPPT)• Anti – Islanding detection• Low current THD• Active part in grid control
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5. Control of single-phase PV
Duty-cycle control
•Simpel (no current sensor)
•Difficult to protect converter
Compensator Pulse-widthmodulator
Converter
Sensor gain
vref
vFC(t)
iload
(t)
d(t)+
-
vDC
(t)Errorsignal
Controlsignal
Referenceinput
CompensatorComparator and
controller
Converter
Sensor gain
vref
vFC
(t)
iload
(t)
d(t)+
-
v DC(t)
Errorsignal
Controlsignal
Referenceinput
iswitch (t)
iswitch (t)iswitch_ref(t)
Current control
•Extra current sensor
•Better dynamics and protection
DC-DC converter
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5. Control of single-phase PV
The current loop with PR controller and HC
ii*
ii
GPI(s)
Gd(s)
Gf(s) ii ui
*
ug
ii*
ii
Gc(s)
Gh(s)
Gd(s)
Gf(s) ii ui
*
The current loop with PI controller
( ) IPI P
KG s Ks
= + 2 2( )c P Io
sG s K Ks ω
= ++
( )223,5,7
( )h Ihh o
sG s Ks hω=
=+
∑
• Proportional Resonant (PR) controller uses GI for integration• No grid voltage feed-forward is required when using PR• Additional GIs used for selective harmonic compensation (HC)
Dc-ac converter – current-controlled H-bridge with LCL filter
( )( )
2 2
2 2
( ) 1( )
( )L Ci
fi i res
s zi sG s
u s L s s ω
+= =
+
12LC g fz L C
− =
( ) 22 i g L C
resi
L L z
Lω
+ ⋅=
21
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5. Control of single-phase PV
2 2( )GI I
o
sG s K
s ω=
+
• Double integrator • Infinite gain at resonance frequency ωo
• High attenuation outside ωo
• Notch filter à selective harmonic compensation• Zero stationary error• High disturbance rejection
0
5 0
1 0 0
1 5 0
2 0 0
2 5 0
3 0 0
Mag
nitu
de (
dB)
102
103
-90
-45
0
4 5
9 0
Pha
se (d
eg)
Ki=10Ki=1Ki=100
Ki=10Ki=1Ki=100
Bode Diagram
Frequency ( rad/sec)
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
time [sec]
GI response
inout
Generalized integrators (GI)
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5. Control of single-phase PV
Disturbance rejection (current error ratio disturbance) of the P R+HC, PR and P
-150
-100
-50
0
-540
-450
-360
-270
PR+HCPIP
( )* 0
( )( )( ) 1 ( ) ( ) ( ) ( )
i
f
g c c d fi
G ssu s G s G s G s G sε
=
=+ + ⋅ ⋅
• PR exhibit higher attenuation (125 dB) than PI (8 dB)• PI rejection capability at 5th and 7th harmonic is comparable with
that one of a simple proportional controller, the integral action being irrelevant.
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5. Control of single-phase PV
Grid voltage and current with PI controller.
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04-25
-20
-15
-10
-5
0
5
10
15
20
25
time[sec]
Ig (exp) [5A/div]Ug (exp) [100/div]
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04-25
-20
-15
-10
-5
0
5
10
15
20
25
time[sec]
Ig (exp) [5A/div]Ug (exp) [100/div]
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04-25
-20
-15
-10
-5
0
5
10
15
20
25
time[sec]
Ig (exp) [5A/div]Ug (exp) [100/div]
Grid voltage and current with PR controller.
Grid voltage and current with PR + HC controller.
THD = 12% THD=8% THD=5%
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5. Control of single-phase PV
The measured grid current harmonic spectrum for PI, PR and PR+HC control strategies and the limits for IEEE 929
5 0 1 5 0 2 5 0 350 4 5 0 5 5 0 6500
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
Cur
rent
har
mon
ic [A
]
F r equency [Hz ]
P I - [% ]THD=12 .665P + R E S - [ % ] T H D = 8 . 1 6 5 5P + R E S + H C - [ % ] T H D = 5 . 4 0 2 8I E E E 9 2 9 - [ % ] T H D = 5
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5. Control of single-phase PV
Grid impedance measurement embedded on the inverter control using harmonic injection
Anti-islanding – Grid impedance measurement
Grid impedance measurement using external device
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5. Control of single-phase PV
Goals
-Developing a measurement technique for estimating the grid impedance value.
-Embedding the technique into an existing single-phase Photo-Voltaic inverter.
-Testing the method against the ENS requirements.
ENS Requirements (Mains monitoring unit with allocated Switching Devices)
-Detection of the grid impedance change of more then 0.5 Ω.
-Isolation of the PV-inverter from the grid within 5 s .
-Existence of two independent monitoring-units for redundancy.
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5. Control of single-phase PV
Gri
d co
nnec
tion
Control
75 Hz injection
PWM
Impedance estimation
Inverter DC-DC converter dc-link
Software development and download
PV cells
DSP board
Trip
ping
&
Pr
otec
tions
Voltage
Current
LCD Display
System diagram of the PV-inverter with implementation of the grid impedance estimation.
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5. Control of single-phase PV
Principle of Operation-The PV-inverter injects a harmonic disturbance
-The duration of the disturbance is limited to several fundamental periods
-The grid response is recorded by the same sensors used for the c ontrol
loop
-By knowing the voltage and the current, the grid impedance value is
derived as:
where: Rg and Lg denote the resistive and inductive part of the grid,
ω h and ϕh represent the frequency and the phase angle of the injected harmonic,
N is the number of samples per fundamental period,
v(n) is the input signal (voltage or current) at the n sample,
Λh is the complex vector of the hth harmonic, having the real and the imaginary parts λhrand λh i
)()()(
hIhVhZ =
ghg LjRhZ ⋅⋅+= ω)( hihrh
N
n
N
n
h
j
Nnh
nvjN
nhnv
λλ
ππ
⋅+=Λ
⋅⋅
⋅⋅−
⋅⋅
⋅=Λ ∑∑−
=
−
=
1
0
1
0
2sin)(
2cos)(
25
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HarmonicInjection
Grid
Anti-aliasing Sample&Hold A / D Windowing Pre-processing DFT
Post-processing
Anti-aliasing Sample&Hold A / D Windowing Pre-processing DFT
Voltage Signal
Current Signal
U Z = —
I
ImpedanceTripping
&Display
Internal Logic
Harmonic Current
Harmonic Voltage
Principle of harmonic detection and calculation of the grid impedance .
5. Control of single-phase PV
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Non-continuous injection of the harmonic into the grid.
Final settings used in the PV implementation.
5. Control of single-phase PV
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Measured response detecting a 0.5 Ω resistive increase of impedance.
Experimental setup for testinga grid impedance change.
Oscilloscope Synchronization
5. Control of single-phase PV
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6. Control of three-phase inverters
- More high distributed power applications
- Common issues as an active filter inverter· grid interaction· need to minimise switching ripple impact
⇒ The control of a distributed inverter has an advantage compared to an active filter (easier dc-link control) but has also to deal with grid interaction which may be more complex comparedto motor interaction
- Common issues with ASD· Less responsibility on the dc-voltage control· Manage the parallel connection of several units
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6. Control of three-phase invertersL-filter grid connection LCL-filter grid connection
( ) ( ) ( ) ( ) ( ) ( )
( ) ( ) ( ) ( ) ( ) ( )
1 12
1 12
dq d d d o
qd q q q o
di ti t Ri t e t p t v t
dt Ldi t
i t Ri t e t p t v tdt L
ω
ω
− = − − +
+ = − − +
1
1 1
11 11 1
1 1
2 2
22 2
2 2
2
2 2
10 0 0
10 0 0
1 10 0 0
1 10 0 0
10 0 0
10 0 0
f f
f f
d d
q q
C d C df f
C q C q
f fd d
q q
RL L
Ri iL Li i
v vC Cdv vdt
C Ci iRi i
L LR
L L
ω
ω
ω
ω
ω
ω
− −
− − − − = − − − − − −
1
1
2
2
1 0 000 0
1 0 000 0
0 0 10
0 00 0 1
00 0
d d
q q
L
e vLe v
L
L
− − + +
In a dq-frame rotating at the line frequency
F r e q u e n c y ( H z )
1 0 2 1 0 3 1 0 4- 1 0 0
- 8 0
- 6 0
- 4 0
- 2 0
0
2 0F r o m : I n p u t P o i n t T o : O u t p u t P o i n t
F r e q u e n c y ( H z )
Mag
nitu
de (
dB)
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6. Control of three-phase inverters
Cascade control
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6. Control of three-phase inverters
Current control in a rotating frame
The current control can be performed
on the grid current or on the
converter current
The voltage used for the dq-frame orientation could be measured after a dominant reactance
d
q
β
α
)(te
)(ti
qi di
ω
0( )
0
ip
PI dqi
p
KKsD s
KKs
+ =
+
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6. Control of three-phase inverters
Grid voltage Harmonic compensators
( )223,5,7 0
( )R ihh
sG s k
s hαβ
ω=
=+ ⋅
∑
2 20
2 20
0
( )0
ip
PRi
p
K sK
sD s
K sK
s
αβω
ω
+ + = +
+
Current control in a stationary frame
the harmonics to be compensated should be within the bandwidth of the current controller otherwise stability problems may arise
In both the cases (stationary and rotating) the stability using an LCL-filter should be verified
( )( )
2 2
2 22
( ) 1( )
( )LC
res
s zi sG s
v s L s s ω
+= =
+
29
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6. Control of three-phase inverters
To stabilize the current loop against LCL-filter resonance:
- passive damping (resistor -> losses)
- active damping:
- multi-loop (use of more sensors)
- notch filter in cascade to the main controller
2 2
2 2( ) oAD
o
z zG z
z p −
= −
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6. Control of three-phase inverters
Direct power control
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6. Control of three-phase inverters
Results (grid voltage background distortion)
Effect of the grid voltage background distortion on the currents
Use of harmonic compensators
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6. Control of three-phase inverters
Results (LCL-filter resonance)
Use of active
damping
No active
damping
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6. Control of three-phase inverters
Other issues:
- reduction of the number of sensors:
- voltage sensorless (DPC, VOC with PLL as an observer)
- current sensorless (overcurrent protection ?)
- non-ideal conditions:
- measurement of the grid voltage after a dominant reactance
- grid unbalance
- EMC issues:
- differential mode: IEC limitation only for < 2 kHz > 150 kHz
- common mode: use of extra filter or modify LCL-filter
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7. Converter topologies for wind turbines
Basic topology for wind turbine
• Fixed speed with capacitor bank
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7. Converter topologies for wind turbines
Mechan ica l Ene rgy Sou rceVar iab le Speed
D i r e c t G e a r b o x
Mult ipolar Synch ronous& Nove l Mach ines
Conven t iona lSynchronous Mach ines
Induct ion Mach ines
Wound Ro to r( f ie ld contro l )
L a r g e P Econver te r
Pe rmanen tM a g n e t
L a r g e P Econver te r
C a g eR o t o r M / C
L a r g e P Econver te r
W o u n d R o t o r o rBrushless DF
Wound
Electr ical Energy SourceF ixed Frequency o r DC
R o t o r
Stator
Machinet ype
Transmiss ion
Wound Wound W o u n d
G r i dconnect ion
O u t p u t
S m a l l P Econver te r
Input
P o w e rconvers ion
Heat lossdump load
Variable speed
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7. Converter topologies for wind turbines
ØLimited speed range (-20% to +20%, typically)ØSmall -scale power converter (Less power losses, price )ØComplete control of active Pref and reactive power Q ref
ØNeed for slip-ringsØNeed for gear
Gear
Doubly-fedinduction generator
Pitch
Grid
V
DC
AC
AC
DC
PrefQref
Doubly-fed induction generator - wounded rotor
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7. Converter topologies for wind turbines
ØFull speed rangeØNo brushes on the generatorØComplete control of active og reactive powerØProven technologyØFull-scale power converterØNeed for a gear
Gear
Inductiongenerator
Pitch
GridDC
AC
AC
DC
Pref Qref
VI
Induction generator - Squirrel cage rotor
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7. Converter topologies for wind turbines
ØFull speed rangeØPossible to avoid gear (multi -pole generator)ØComplete control of active and reactive powerØBrushless (reduced maintenance )ØNo power converter for field (higher efficiency)ØFull scale power converterØMulti -pole generator big and heavyØPermanent magnets needed
Synchronous generator - Permanent magnets
PM-synchronousGeneratorMulti-pole
Pitch
GridDC
AC
AC
DC
Pref Qref
IX
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7. Converter topologies for wind turbines
• Doubly-fed induction generator system• Horns Reef, Denmark
160 MW Windfarm (in operation)
Group 1 out of 5
Grid
Group 5 out of 5
....................
Power station
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7. Converter topologies for wind turbines
Why offshore?
Advantages:· Better wind resources· Low roughness· Many unexploited sites· No people around to be bothered· Possibility for large projects near
loadcenters· No physical limits for size and
weight = great future!
Disadvantages:· Installation and maintenance are
more complicated and expensive· More safety measures to be taken
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7. Converter topologies for wind turbines
Why offshore?
Horns Reef: 80 turbines, V80-2.0 MW, 160 MW installed in total.Water depth: 7-13 m, waves 8 m, 560 x 560m btw. turbines, 20 sq km 600 GWh (expected) ~ 2% of Denmark’s annual electricity consumption
Distance to Blåvandshuk = 14 km
Distance to Esbjerg harbour = 40 km
Horns Reef
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7. Converter topologies for wind turbines
• Two-speed windturbine system• Nysted, Denmark
160 MW Windfarm (in operation)
G r o u p 1
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Group4
G r o u p 5
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G r o u p 8
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Power station
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8. Control of wind turbines
Doubly-fed generator system
DFIG control
Power controller Speed controller Wind turbine control
Rotor side converter controller Grid side
converter controller
Measurement grid point M
θ
AC DC AC DC
meas gen ω
PWM PWM
N T
ref conv grid P ,
ref conv grid Q ,
meas d c U
meas grid P
meas grid P
meas grid Q
meas a c I
ref dc U
ref rated grid P ,
cross - coupling Grid
operators control system
meas rotor I
DFIG control
Power controller Power controller Speed controller Speed controller Wind turbine control
Rotor side converter controller Rotor side converter controller Grid side
converter controller
Measurement grid point M
θ
AC DC AC DC
meas gen ω
PWM
N T
ref conv grid P ,
ref conv grid Q ,
meas d c U
meas grid P
meas grid P
meas grid Q m
a c I
ref dc U
ref rated grid P ,
cross - coupling Grid
operators control system
mea s rotor I
72
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8. Control of wind turbines
Multi-pole generator system
vDC
vDC
Generatorrectifier
Gridinverter Inductance
Gridcontrol
Powercontrol
PMG
Grid
refQrefP
vga, gb, gc
iga, gb, gc
v vi i
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9. Summary
• Renewable energy is on its move• Power electronics important enabling technology• Basic power conversion• Advanced control enters into the systems• Both internal and external control (system)• New control methods appear to improve performance• New methods are still necessary• Monitoring and advanced diagnosis will also be integrated