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Wind Power -A Technology enabled by power electronics
Center of Reliable Power Electronics
Center of Reliable Power Electronics
Frede Blaabjerg
Professor, IEEE Fellow
Aalborg UniversityDepartment of Energy Technology
Aalborg, Denmark
CORPE
www.corpe.et.aau.dk
Outline
2Center of Reliable Power Electronics
Aalborg University and Department of Energy Technology
Power Electronics for Wind Turbines
Reliability Challenges of Power Electronics
LVRT and Resonance Issues in DFIG Wind Turbines
Conclusions
Wind Power -
A Technology enabled by power electronics
3Center of Reliable Power Electronics
Aalborg University and
Department of Energy Technology,
Denmark
Aalborg University - Denmark
4Center of Reliable Power Electronics
PBL-Aalborg Model
(Problem-based learning)
Inaugurated in 1974
22,000 students
2,300 faculty
Aalborg
Esbjerg Copenhagen
Adapted from Wikimedia Commons: https://upload.wikimedia.org/wikipedia/commons/c/c1/Denmark_regions.svg
Aalborg University - Campus
5Center of Reliable Power Electronics
Department of Energy Technology
6Center of Reliable Power Electronics
Energy Production | Distribution | Consumption | Control
Department of Energy Technology
7Center of Reliable Power Electronics
E.T. Facts
40+ Faculty members
100+ Ph.D. students
30+ RA and post-docs
30+ Visiting scholars and
students
30+ Technical and
administrative staff
2 In-house company
divisions
60%+ of the above manpower
are in power electronics
and its applications
2 in-house company
divisions heavily involve
in power electronics
8Center of Reliable Power Electronics
Power Electronics for Wind Turbines
9Center of Reliable Power Electronics
Renewable Electricity in Denmark
Proportion of renewable electricity in Denmark (*target value)
Key figures 2011 2015 2025 2035
Wind share of net generation in year 29.4% 51.0% 58%*
Wind share of consumption in year 28.3% 42.0% 60%*
RE share of net generation in year 41.1% 66.9% 82%* 100%*
RE share of net consumption in year 39.5% 55.2%
2015 RE Electricity Gener. in DK
2015 RE-Share
67%
Energinet.dk, Electricity Generation, http://www.energinet.dk/EN/KLIMA-OG-MILJOE/Miljoerapportering/Elproduktion-i-Danmark/Sider/Elproduktion-
i-Danmark.aspx
10Center of Reliable Power Electronics
Energy and Power Challenge in DK
Very High Coverage of Distributed Generation
Energinet.dk, Electricity Generation, http://www.energinet.dk/EN/KLIMA-OG-MILJOE/Miljoerapportering/Elproduktion-i-Danmark/Sider/Elproduktion-
i-Danmark.aspx
11Center of Reliable Power Electronics
Energy and Power Challenge in DK
Very High Coverage of Distributed Generation
Energinet.dk, Electricity Generation, http://www.energinet.dk/EN/KLIMA-OG-MILJOE/Miljoerapportering/Elproduktion-i-Danmark/Sider/Elproduktion-
i-Danmark.aspx
Development of Electric Power System in Denmark
12Center of Reliable Power Electronics
From Central to De-central Power Generation
Danish Energy Agency, “Overview map of the Danish power infrastructure in 1985 and 2015” https://ens.dk/sites/ens.dk/files/Statistik/foer_efter_uk.pdf, last accessed Mar. 6, 2017.
13
Source: http://electrical-engineering-portal.com
Source: www.offshorewind.biz
Source:
http://media.treehugger.com
from Central to De-central Power Generation
(Source: Danish Energy Agency)
(Source: Danish Energy Agency)
from large synchronous generators to
more power electronic converters
Development of Electric Power System in Denmark
14Center of Reliable Power Electronics
State-of-Art Development – Wind Power
Larger individual size (average 1.8 MW, up to 6-8 MW).
More power electronics involved (up to 100 % rating coverage).
Global installed wind capacity (until 2015): 433 GW, 2015: 63.5 GW
1980 1985 1990 1995 2000 2005 2011
50 kW
D 15 m
100 kW
D 20 m
500 kW
D 40 m
600 kW
D 50 m
2 MW
D 80 m
5 MW
D 124 m
7~8 MW
D 164 m
0% 10% 30% 100%Rating:Power
Electronics
2018 (E)
10 MW
D 190 m
Global Wind Energy Council, http://www.gwec.net/wp-content/uploads/vip/GWEC-Global-Wind-2015-Report_April-2016_22_04.pdf
15Center of Reliable Power Electronics
Top 5 Wind Turbine Manufacturers & Technologies
DFIG: Doubly-fed induction generator
PMSG: Permanent magnet synchronous generator
IG: Induction generator
SG: Synchronous generator
Manufacturer Concept Rotor Diameter Power Range
Goldwind (China)PMSG
IG
70 – 109 m
110 m
1.5 – 2.5 MW
3 MW
Vestas (Denmark)DFIG
PMSG
80 –110 m
105 – 164 m
1.8 – 2 MW
3.3 – 8 MW
GE Energy (USA)DFIG
PMSG
77 – 120 m
113 m
1.5 – 2.75 MW
4.1 MW
Siemens (Germany)IG
PMSG
82 – 120 m
101 – 154 m
2.3 – 3.6 MW
3 – 6 MW
Gamesa (Spain)DFIG
PMSG
52 –114 m
128 m
0.85 – 2 MW
4.5 MW
16Center of Reliable Power Electronics
Important issues for converters in renewables:
Reliability/security of supply
Efficiency, cost, volume, protection
Control active and reactive power
Ride-through operation and monitoring
Power electronics enabling technology
…
Load/
Generator
Power
Electronics
Intelligent
ControlReferences
(Local/Centralized)Communication
Bi-directional Power Flow
2/3 2/3
Renewable
Energies Power
Grid
(PV, Wind Turbines, etc.)
16
Power Electronics based Renewable Energy Systems
17Center of Reliable Power Electronics
Requirements for Wind Turbine Systems
Wind Power
Conversion
System
1. Controllable I
2. Variable freq & U
P
Q
P
Q
1. Energy balance/storage
2. High power density
3. Strong cooling
4. Reliable
1. Fast/long P response
2. Controllable/large Q
3. Freq & U stabilization
4. Low Voltage Ride Through
Generator side Grid side
General Requirements & Specific Requirements
18Center of Reliable Power Electronics
Wind Turbine Concept and Configurations
Variable pitch – variable speed
Doubly Fed Induction Generator
Gear box and slip rings
±30% slip variation around
synchronous speed
Power converter (back to back/
direct AC/AC) in rotor circuit
State-of-the-art solutions
Variable pitch – variable speed
Generator
Synchronous generator
Permanent magnet generator
Squirrel-cage induction generator
With/without gearbox
Power converter
Diode rectifier + boost DC/DC + inverter
Back-to-back converter
Direct AC/AC (e.g. matrix,
cycloconverters)
State-of-the-art and future solutions
Partial scale converter with DFIG
Full scale converter with SG/IG
Asynchronous/
Synchronous
generator
AC
DC
DC
AC
Grid
Filter FilterGear
Transformer
Full scale power converter
Double-fed
induction generator
AC
DC
DC
AC
Grid
Filter
Gear
Transformer
1/3 scale power converter
19Center of Reliable Power Electronics
Converter Topologies under Low Voltage (<690V)
Back-to-back two-level VSC
Proven technology
Standard power devices (integrated)
Decoupling between grid and generator
(compensation for non-symmetry and other
power quality issues)
High dv/dt and bulky filter
Need for major energy-storage in DC-link
High power losses at high power (switching
and conduction losses) low efficiency
Diode rectifier + boost DC/DC + 2L-VSC
Suitable for PMSG or SG
Lower cost
Low THD on generator, low
frequency torque pulsations in
drive train
Challenge to design boost
converter at MW
Transformer
2L-VSC
Filter Filter
2L-VSC
Generator Transformer
Filter Filter
Boost
2L-VSCDiode rectifier
Generator
20Center of Reliable Power Electronics
Solution to Extend Power Capacity
(b) with normal winding generator(a) with multi-winding generator.
Parallel converter to extend the power capacity
State-of-the-art solution in industry (> 3 MW)
Standard and proven converter cells (2L VSC)
Redundant and modular characteristics.
Circulating current under common DC link with extra filter or special PWM
21Center of Reliable Power Electronics
Multi-Level Converter Topology – 3L-NPC
Three-level NPC (3L-NPC)
Most commerciallized multi-level topology
More output voltage levels Smaller filter
Higher voltage, and larger output power with the same device rating
Possible to be configured in parallel to extend power capacity
Unequal losses on the inner and outer power devices derated
converter power capacity
Mid-point balance of DC link – under various operating conditions
Transformer
3L-NPC
Filter Filter
3L-NPC
22Center of Reliable Power Electronics
Multi-Level Converter Topology – H-Bridge BTB
More equal loss distribution higher output power
More output voltage levels compared to 2L VSC
Redundancy if 1 or 2 phases failed.
Higher controllability coming from zero sequence.
Open windings for generator and transformer – higher cost
Hard to be configured in parallel to extend power capacity.
Transformer
open windings
Filter Filter
3L-HB 3L-HB
Generator
open windings
5L-HB
Transformer
open windings
5L-HB
Filter Filter
Generator
open windings
H-Bridge Back to Back (HB-BTB)
23Center of Reliable Power Electronics
Multi-Cells Converter Topologies (Future Solution)
...
Cell 1
Cell N
...
AC
DC
DC
AC
AC
DC
DC
AC
...
AC
DC
DC
AC
AC
DC
DC
AC
MFT
MFT
GridGenerator
...
AC
DC
DC
AC...
AC
DC
DC
AC
DC
AC...
DC
AC
...
AC
DC
AC
DC
GridGenerator
Cascaded HB with medium frequency transformer Modular multi level converter (MMC)
Reduced transformer size for CHB-MFT
Easily scalable power and voltage level.
High redundancy and modularity.
Filter-less design, direct connection to distribution grid.
Significantly increased components counts
Still very high cost-of-energy.
24Center of Reliable Power Electronics
HVAC power transmission
HVAC grid
AC
DC
DC
AC
AC
DC
DC
AC
MVAC grid
…
AC
DC
DC
AC
AC
DC
DC
AC
HVAC grid
MVAC grid
HVDC grid
…
AC
DC
DC
AC
AC
DC
DC
AC
+-
AC
DC
MVAC gridAC
DC
AC
DC
DC
AC
HVDC grid
+-
AC
DC
Solid state transformer
or DC/DC transformer
MVDC grid
HVDC power transmission
DFIG system Full-scale converter system
DC transmission grid DC distribution & transmission grid
Wind Farm with AC and DC Power Transmission
25Center of Reliable Power Electronics
Active/Reactive Power Regulation in Wind Farm
MVAC
Grid
AC
DC
DC
AC
DC
DC
AC
DC
DC
AC
DC
DC
Distributed energy storage system
Centralized energy storage system
Distributed energy storage system
DC
AC
HVAC
grid
AC
DC
DC
AC
AC
DC
DC
AC
MVAC grid
DC
AC
DC
AC
Reactive power compensator
connected to MVAC grid
Reactive power compensator
connected to HVAC grid
Advanced grid support feature achieved by power converters and controls
Local/Central storage system by batteries/supercapacitors
Q compensators
STATCOMs/SVCs
Medium-voltage distribution grid/High-voltage transmission grid
Control Structure for a Wind Turbine System
26Center of Reliable Power Electronics
Gear-box
LCLLow pass
filter
Vgenerator
Igenerator
Grid fault ride through
and grid support
Igrid
Vgrid
Vdc
Power Maximization
and Limitation
Inertia
Emulation
Power
Quality
Extra functions
WT specific functions
Basic functions (grid conencted converter)
Current/Voltage
Control
Vdc
Control
Energy
Storage
Grid
Synchronization
AC
DC
DC
AC
Xfilter
Pitch actuator
Wind speed
Superviosry commmand from TSO
wgenerator
SG
IG
DFIGlocal
load
utility
micro-
grid
Braking
Chopper
Pulse Width Modulation
Power has to be controlled by means of the aerodynamic system and has to
react based on a set-point given by a dispatched center or locally with the goal to
maximize the power production based on the available wind power.
Current Development Example
27Center of Reliable Power Electronics
Vestas V164 offshore turbine
Rated power: 8,000 kW even higher
Rotor diameter: 164 m
Hub height: min. 105 m
Turbine concept: medium-speed gearbox,
variable speed, variable pitch, full-scale
power converter
Generator: permanent magnet
Vestas Wind Systems A/S Denmark
Target market: Big offshore farms
Vestas V80–2.0 MW
Horns Reef I 160 MW, Horns Reef II 209.3 MW• 80 x 2MW (Vestas V80, in
operation Dec 11, 2002)
• 91 x 2.3MW (Siemens SWT-2.3-93, in operation Sep 17, 2009)
Rotor Diameter 80 mHub Height 60-100 mWeight 227-303 tonsMin/Max rotation speed 9/19 rounds/minuteMin/Nom/Max Wind 4/16/25 m/sGear box Yes (1:100.5)Generator DFIG (4 pole – slip rings)
Development Example – Wind Farm
Center of Reliable Power Electronics 28
29Center of Reliable Power Electronics
Power Level for Renewable Applications
IT & Consume
Automotive
Industry
<500W 1-5kW 30-350kW 5-50kW 5-100kW 100kW-1MW >1MW
Photo Courtesy:
IEEE Madison Section - 2007
Drive
UPS
Power Distribution
Wind Turbines
PV Plants
Transportation
Residential PV
Appliances
30Center of Reliable Power Electronics
Power Device Applications
High-End Solutions
Middle-End Solutions
Low-End Solutions
GaN
GaN Super Junction MOSFET
200 V 600 V + 1200 V
Silicon IGBT Super Junction
MOSFET
Silicon IGBT
Silicon IGBT Super Junction
MOSFET
Super Junction MOSFET SiC
SiC
Yole Development. Status of the power electronics industry. 2012
31Center of Reliable Power Electronics
Wide Bandgap (WBG) Devices
Benefits of WBG devices in power electronic applications:
Si technology is approaching its material limits.
Campactness due to low losses, high operaion temperature and high bearkdown voltage.
High Power Density owing to high breakdown voltage.
High Efficiency because of high operation temperature and low losses.
Less Passive Components thanks to low losses.
Simple thermal management due to high breakdown voltage.
High Reliability because of high breakdown voltage.
Fast Switching Speed due to high drift velocity.
WBG devices (discrete or module) are available for purchase at:
…
M. Chinthavali, “WBG Technology for Transportation Applications”, WiPDA, 2013.
32Center of Reliable Power Electronics
Advancement of Wide BandGap Devices
2000 2005 2010 2015
First SiC
Schottky
diode
launched
First SiC
JFET
launched
First hybrid
SiC power
module
launched
First full
SiC power
module
launched
6-inch
SiC
wafer
appears
4-inch
SiC
wafer
appears
ROHM/
Cree SiC
MOSFET
launched
Infineon
CoolSiC
JFET
launched
2011 2013 2015
IR launched
first GaN
power device
8-inch
GaN-on-Si
Epi wafer
appears
6-inch
GaN-on-Si
Epi wafer
appears
2010 2012 2014
MicroGaN
launched
600V GaN
HEMT
Transphorm
launched 600V
GaN-on-SiC
transistor
Fujitsu
launched 600V
GaN-on-Si
transistor
Transphorm
launched 600V
GaN transistor
and Schottky
diode
Milestones in SiC power electronics development
Milestones in GaN power electronics development
Eden, R. The World Market for Silicon Carbide & Gallium Nitride Power Semiconductors – 2013, HIS, Wellingborough, 2013.
33Center of Reliable Power Electronics
Potential Power Devices for Wind Power
IGBT Module IGBT Press-PackIGCT Press-
Pack
SiC-MOSFET
Module
Power Density Low High High Low
Reliability Moderate High High Unknown
Cost High High High
Failure mode Open circuit Short circuit Short circuit Open circuit
Easy maintenance + - - +
Insulation of heat sink + - - +
Snubber requirement - - + -
Thermal resistance Large Small Small Moderate
Switching loss Low Moderate Moderate Low
Conduction loss Moderate Moderate Moderate Large
Gate driver Moderate Moderate Large Small
Major manufacturersInfineon, Semikron,
Mitsubishi, ABBWestcode, ABB ABB
Cree, Rohm,
Mitsubishi
Voltage ratings 1.7 kV-6.5 kV 2.5 kV / 4.5 kV 4.5 kV / 6.5 kV 1.2 kV / 10 kV
Max. current ratings 1.5 kV - 750 A 2.3 kA / 2.4 kA 3.6 kA / 3.8 kA 180 A / 120 A
34Center of Reliable Power Electronics
Reliability Challenge of Power Electronics
35Center of Reliable Power Electronics
Cost of EnergyT
yp
ica
l L
CO
E r
an
ge
s U
SD
/ k
Wh
Cost of fossil fuel
generation
&Cap O M
Annual
C CCOE
E
CCap – Capital cost
CO&M– Operation and main. cost
EAnnual – Annual energy production
Determining factors for renewables
- Capacity growth
- Technology development
36Center of Reliable Power Electronics
Approaches to Reduce Cost of Energy
&Cap O M
Annual
C CCOE
E
CCap – Capital cost
CO&M– Operation and main. cost
EAnnual – Annual energy production
Approaches Important and Related Factors Potential
Lower CCap Production / Policy +
Lower CO&M Reliability / Design / Labor ++
Higher Eannual Reliability / Capacity / Efficiency / Location +++
Reliability is an Efficient Way to Reduce COE
– Lower CO&M & Higher EAnnual
37Center of Reliable Power Electronics
Typical Lifetime Target in PE Applications
Applications Typical design target of Lifetime
Aircraft 24 years (100,000 hours flight operation)
Automotive 15 years (10,000 operating hours, 300,000 km)
Industry motor drives 5-20 years (40,000 hours in at full load)
Railway 20-30 years (10 hours operation per day)
Wind turbines 20 years (18-24 hours operation per day)
Photovoltaic plants 20-30 years (12 hours per day)
Different O&M program
38Center of Reliable Power Electronics
Failure in Wind Applications
13,0%
21,3%
5,1%
11,3%
49,3%
18,4%
23,3%
4,7%
7,3%
46,3%
0% 10% 20% 30% 40% 50% 60%
Power Converters
Pitch System
Gear Box
Yaw System
Others
Contributions of Subsystems and Assemblies to the Overall FAILURE RATE of Wind Turbines
Contributions of Subsystems and Assemblies to the Overall DOWNTIME of Wind Turbines
Reliawind, Report on Wind Turbine Reliability Profiles – Field Data Reliability Analysis, 2011.
39Center of Reliable Power Electronics
Shift of Reliability Challenges in Industry
Customer expectations
Replace if failure
Years of warranty
Low risk of failure
Request for maintenance
Peace of mind
Predictive maintenance
Reliability target Affordable return rates Low return rates Controllable return rates
R&D approach Reliability test
Avoid catastrophes
Robustness tests
Improve weakest components
Design for reliability
Lifetime estimation
Stress/strength balance
R&D key tools Product feedback data Testing at the limits
Understanding failure
mechanisms, loading,
component strength, …
Multi-domain analysis
Yesterday Today Tomorrow
40Center of Reliable Power Electronics
Shift of Reliability Analysis Approach for PE
In the future
Root cause based
Failure mechanism modeling
More designable and controllable
More considerations of Mission Profile
In the past
Observations and statistics based
Handbook/guideline calculation
Hard to design and control
Less dependent on mission profile
2L converter
690 Vrms
Filter
2L converter
Grid
1.1 kVDC
IGBT
Wind turbine
Generator
Hand book/
Guidance
Application & converter
Mean time between failure (MTBF)
Stress Analysis Strength Models
Cyc
les
to fa
ilure
?Tj (K)10 100
Mission profile to component stress.
Time to a certain probability of failures
Lifetime model
41Center of Reliable Power Electronics
Mission Profile Based Reliability Analysis
Key features:
• Mission-profile and physics-of-failure based
• Generate reliability metrics of converter (Reliability vs. time, lifetime,
robustness, margin, weakness…)
2L converter
690 Vrms
Filter
2L converter
Grid
1.1 kVDC
IGBT
Wind turbine
Generator
Converter
Designs
Reliability
Metrics
Mission
Profiles
Reliability
Evaluation Tools
42Center of Reliable Power Electronics
Flow in Reliability Analysis for Power Electronics
Identification
Stress Analysis
· Mission profile translation
· Multi-physics stress
· Multi-time scales stress
Strength Modeling
Reliability Mapping
· Critical components
· Failure mehanisms
· Major stress & strength
· Component-based
· Accelerated/Limit test
· Degradation model
· Stress organization
· Variation & statistics
· Multi-components system
Reliability Metrics
· Thermal loading
· Voltage/current stress
· Stress margin
Direct
· Bx lifetime
· Robustness
· Reliability/unreliability
Indirect
Key features:
• Physics-of-failure based
• Mission-profile oriented
• Multi-physics
• Multi-timescales
• Reliability engineering-included
43Center of Reliable Power Electronics
Identification: Critical Components in WTS
ElectricalGeneratorGearboxTurbines
1/4
1/2
2
4
An
nu
al
failu
re r
ate
Do
wn
tim
e
(da
ys)
Control
Hydraulic Blades
6
Source: B. Hahn, M. Durstewitz, K. Rohrig “Reliability of wind
turbines – Experience of 15 years with 1500 WTs” Kassel, Germany.
Failure distribution of power electronics.
(Source: ZVEL, 2008)
Semiconductor 21%
Capacitor30%
PCB26%
Converter has high failures in wind turbine system
Capacitor, PCB and power semiconductor are reliability critical components.
44Center of Reliable Power Electronics
Identification: Failure Mechanism for IGBT Module
Chip Chip
Substrate
Base plate
Heat sink
Chip
Solder
Base solder
Thermal
grease
bond wire
…
IGBT module
Cooling system
Copper
Break down of a typical IGBT module.
Mechanism: Coefficient of Thermal Expansion (CTE) mismatch
Symptom: Dislocations of at material boundary
Stress: Thermal cycling
Strength: Number of cycles to failure
Bond wire lift-off
Soldering cracks
Mauro Ciappa ”Selected failure mechanisms of modern power modules,” Microelectronics Reliability 42, pages 653–667, 2002
45Center of Reliable Power Electronics
Mission Profiles of Wind Power ConverterW
ind
sp
ee
d (
m/s
)A
mb
ien
t T
em
p. (º
C)
Time (hour)
Vw
Ta
Harsh environment
Variable wind and temp.
Grid faults
Q support
All have impacts to thermal
cycling and reliability !
0
25
75
90
100
150 500 750 1000 1500
Voltage(%)
Time (ms)
DenmarkSpain
Germany
US
Keep connected
above the curves
P/Prated (p.u.)
Q/Prated (p.u.)
0.2
0.4
0.6
0.8
1.0
0.4OverexcitedUnderexcited
-0.3
Underexcited
Boundary
Overexcited
Boundary
Limited space
Wind Power
Conversion
System
P
Q
P
Q
Generator side Grid side
46Center of Reliable Power Electronics
Stress Organization by Rainflow Counting Method
Thermal stress vs. t imeRainf low counting Cycle number vs. ΔT and Tm
ΔT and Tm at each cycleTypical l ifetime model
Or
47Center of Reliable Power Electronics
General Flow to Assess Reliability in WTS
Loss profile
analysis
· Generator model
· Loss model
Thermal profile
analysis
· Thermal model
Power cycling
analysis
· Coffin-Manson
· On-state time effect
Power profile
analysis
· Wind speed
· Turbine model
Ps (vw) PT (vw)
PD (vw)
Tjm (vw)
dTj (vw)
Nf (Vw)Bx
lifetime
Mission profile
analysis
· Speed distribution
· Wind class
Vw at 3 m/sPG_3
Loss calculationPT_3
Thermal calculation
Tjm_3
dTj_3Power cycles
ton_3
Nf_3 Consumed lifetime
per year
fe_3
CL3
Vw at 25 m/sPG_25
Loss calculationPT_25
Thermal calculation
Wind speed increment: 1 m/s
dTj_25Power cycles
ton_25
Nf_25 Consumed lifetime
per year
fe_25
CL25
CLm
Total consumed
lifetime
Tjm_25
Weighting factor: D
Annual wind distribution
Wind speed
decomposition
48Center of Reliable Power Electronics
Configuration Effect on Lifetime
Reliability
Cost-of-energy
Hardware design
· Configuration
· Passive component
· Power module
Mission profile
· Grid codes
· Wind class
· Ambient temperature
Control scheme
· Reactive power
· Fault ride-through
· PMW modulation
Significantly unbalanced lifetime of the back-to-back power converters
49Center of Reliable Power Electronics
Grid Codes Effect on Lifetime
DFIG: OE Q injection significantly increases the consumed lifetime
PMSG: Both the OE and UE Q injection increase the consumed lifetime
-40%30%
20%
40%
60%
80%
100%
Over-excited
(OE)Under-excited
(UE)
Q (in % of PN)
P
(in % of PN)
Reliability
Cost-of-energy
Hardware design
· Configuration
· Passive component
· Power module
Mission profile
· Grid codes
· Wind class
· Ambient temperature
Control scheme
· Reactive power
· Fault ride-through
· PMW modulation
50Center of Reliable Power Electronics
Wind Class Effect on Lifetime
0 5 10 15 20 25 300
0.04
0.08
0.12
Wind speed (m/s)
Pro
bil
ity d
istr
ibu
tion
Cut-in Rated Cut-out
I II III IV
Class I
Class II
Class III
Reliability
Hardware design
· Configuration
· Passive component
· Power module
Mission profile
· Grid codes
· Wind class
· Ambient temperature
Control scheme
· Reactive power
· Fault ride-through
· PMW modulation
Consumed lifetime increases with higher wind class for both DFIG and PMSG
51Center of Reliable Power Electronics
Combined Q Control Effect on Lifetime
DFIG
Rotor-side
Converter
Filter
Transformer
Grid-side
Converter
C
Qs
T1 D1
T2 D2
T1 D1
T2 D2
Combined Q compensation from both RSC and GSC
Enhanced lifespan of the power converters by 1.4 times
Same tendency at various wind classes
Reliability
Cost-of-energy
Hardware design
· Configuration
· Passive component
· Power module
Mission profile
· Grid codes
· Wind class
· Ambient temperature
Control scheme
· Reactive power
· Fault ride-through
· PMW modulation
RSC (pu) GSC (pu) Udc (V)
Case I 0 -0.4 1500
Case II -0.1 -0.3 1350
Case III -0.2 -0.2 1200
Case IV -0.3 -0.1 1100
Case V -0.4 0 1050
Class I
Class II
Class III
GSC
RSC
Optimized point
52Center of Reliable Power Electronics
Wake Effect in Wind Farm
Reduced wind speed of downstream WT due to wake effect
Speed deficit is affected by wind farm layout, inlet angle of wind speed
Power loss: 5-10% in onshore wind farm; 15% in offshore wind farm
Wake effect on reliability consideration of wind farm
k1D AolAR
φ
u
α=270°+φ
XDcos(φ)
XDWT1 WT2
v2v1
αNorth
uDefinition of the
wind direction
53Center of Reliable Power Electronics
LVRT and Resonance Issues in DFIG Wind Turbines
54Center of Reliable Power Electronics
External Challenges for DFIG during Grid Fault
1.50.15 150.1
20
40
60
80
100
Time (s)
Ug (%)
≈
120
Fault occurs
Low voltage
ride-through
High voltage
ride-through
0
Ug (pu)
100
10
0.5 1.20.95
50
Deadband
Iq / IN (%)
-40
1.05
Stay connected for a certain period at different fault levels
Reactive current to support grid voltage recovery
55Center of Reliable Power Electronics
Demagnetizing Control
DFIG
To GSC
RSCSVMurαβ
*
0( ) rje
urdq
*
PI+
-
0( ) rje
irαβirdq
Power
control irdq*
Ps*
Qs*
-kψsndq
irdq*
abc
αβ
abc
αβ
irabc
usabc
isabc
usαβ
isαβ
PLL
0 je
usdq
isdq
θ0
ω0
θr
d
dtωr
Flux
observer
usαβ
isαβ
irαβ
ψsdqFilter
ψsndq
Grid
MPPT or reactive support
After fault or fault
clearance
Flux observer
Switched control objectives
Rotor current is controlled in the opposite direction with natural flux
Nature flux can be extracted from stator flux using band-passing filter
Demagnetizing coefficient is the control freedom
56Center of Reliable Power Electronics
Safety Operation Area (SOA) of RSC
p=0.8
p=0.6p=0.4
p=0.2
0 1 2 3 4 50
1
2
3
4
5
ir (pu)
ur
(pu
) 2
2.5
2.0
1050 rpm
SOA
SOA
0 1 2 3 4 50
1
2
3
4
5
ir (pu)
ur
(pu
)
2
2.5
2.0
1800 rpm
p=0.8
p=0.6
p=0.4p=0.2
sLr Rr+Rs
RSCEMF
DFIG
irnr
urnr
ernr=-jωmψsn
r
Equivalent DFIG model in viewpoint of the
rotor side Demagnetizing current effects on rotor terminal voltage at various dip levels
Higher demagnetizing current causes lower rotor voltage
SOA restricted by power module rating
• Rotor current up to 2.0 pu
• Rotor voltage up to 2.5 pu
57Center of Reliable Power Electronics
External Challenge – Reactive Current Injection
0 0.2 0.4 0.6 0.8 10
0.5
1
1.5
p
Sta
tor
an
d r
oto
r cu
rren
t (p
u)
1.05
0.7
is_Q
ir_Q
If dip level is higher than 0.5, the reactive current remains 1.0 pu
In the case of 0.7 pu voltage dip, the reactive current component from rotor is 1.05 pu
Response time: 150 ms
Ug (pu)
100
10
0.5 1.20.95
50
Deadband
Iq / IN (%)
-40
1.05
58Center of Reliable Power Electronics
Simulation Validation
Simulation conditions: 1800 rpm; 0.6 pu dip (500 ms); DC chopper limits: Lower-1100 V, Upper-1300 V
Traditional vector control Optimized demagnetizing control
us (pu)
ird (pu)
irq (pu)
ψs (pu)
ir (pu)
Tj (ºC)
ird*
ird
irq*
irq
ψsd
ψsq
IGBTDiode
127.2 ºC99.3 ºC
3.0 pu
4.8 pu
IGBTDiode
100.1 ºC
us (pu)
ird (pu)
irq (pu)
ψs (pu)
ir (pu)
Tj (ºC)
ird*
ird
irq*
irq
ψsd
ψsq
98.8 ºC
2.7 pu
2.8 pu
59Center of Reliable Power Electronics
Resonance Issues in DFIG based Wind Farm
Basic Principle of Resonance
Equivalent Impedance Circuit
i
u
0
1
LC
0
0 0
0 0
1 1C L s j
Z Z j L j Lj C C
LZ sL
Inductor impedance Capacitor impedance1
CZsC
Total impedance
Total impedance is equal to zero when
Triggering Resonance Resonance Frequency
00
1 1
2 2f
LC
u / i waveforms
60Center of Reliable Power Electronics
Resonance Issues in DFIG based Wind Farm
Different Connections of the DFIG based Wind Farm
DFIG
Rotor Side Converter (RSC)
Grid Side Converter (GSC)
Vdc
GSC Control
Lf Lg
CfLNET
CNET
Series RL+ Shunt C weak network
~RNET
Three-terminalStep-up
Transformer
RSC Control
LNET
Series RL weak network
~RNET
LNET~
RNET
CNETSeries RLC
weak network
PCC
ZSR_PCC
ZGLCL_PCC
ZSYS_GL
ZNETN
Lf
or
1) Non-Compensated Network
2) Series Compensated Network
3) Parallel Compensated Network
VPCC
VSR
VG
VHV
TransmissionTransformer
ZGL
ZSR
ZGLCL
ZGL_PCC
ZSYS_GLCL
ZNETS
ZNETP
ZNETN
ZNETS
ZNETP
61Center of Reliable Power Electronics
Resonance Issues in DFIG based Wind Farm
Impedance Modeling of the Cable
LNET
CNET
Series RL+ Shunt C weak network
~RNETLNET
~RNET
CNETSeries RLC
weak network
Series Compensated Network ZNETS Parallel Compensated Network ZNETP
2 2
3 3 2
3
1/ /NETS NETS NETS
NETS
Z sL K R KsK C
2 2
3 3 2
3
2 2
3 3 2
3
1/ /
1/ /
NETP NETP
NETPNETP
NETP NETP
NETP
sL K R KsK C
Z
sL K R KsK C
62Center of Reliable Power Electronics
Resonance Issues in DFIG based Wind Farm
Bode diagram based Analysis of SSR and HFR
Frequency(Hz)
Mag
nit
ude(
dB
)P
has
e(deg
ree)
90
0
10 5020 30 40 60 70 80-90
0
-20
20
-40
-60Large scale DFIG system
with L/LCL filter
40
180
SSR in 2.0 MW large scale DFIG system with L/LCL filter
Phase difference > 180°, causing SSR at 5.8 Hz
ZNETS
SSR between large scale DFIG system and series compensated
weak network.
Frequency(Hz)
Mag
nit
ud
e(d
B)
Ph
ase(
deg
ree)
90
0
200 1000400 600 800 1200
HFR in 2.0 MW large scale DFIG system with L/LCL filter
1400 1600-90
0
20
with L filter
1800 2000
180
10
Phase difference > 180°,
causing HFR at 1385 Hz
270
-10
-20
-30 with LCL filter
① Phase difference ≈ 0° at 530 Hz and 570 Hz, no HFR② Phase difference < 180° at 980 Hz and 1020 Hz, no HFR③ Phase difference ≈ 60° at 1350 Hz, no HFR
①
②
③
ZNETP
HFR between large scale DFIG system and parallel compensated
weak network.
63Center of Reliable Power Electronics
Resonance Issues in DFIG based Wind Farm
Simulations
Simulation of SSR = 7.5 Hz in the 2 MW DFIG system
us (p
.u.)
-2.0
0
2.0
i s (
p.u
.)
-2.0
0
2.0
time (s)
i r (p.u
.)
-2.0
0
0
2.0
i g (
p.u
.)
-1.0
01.0
0.020.01
PsQ
s (p
.u.)
Te
(p.u
.)
0
2.0
-2.0
-4.0
-1.0-1.4-1.8
Simulation of HFR = 1520 Hz in the 2 MW DFIG system
us (p
.u.)
-2.0
0
2.0
i s (
p.u
.)
-4.0
0
4.0
time (s)
i r (p.u
.)
0
0
i g (
p.u
.)
0
0.40.2
PsQ
s (p
.u.)
0
Te
(p.u
.)
0
-12
-4.0
4.0
4.0
-4.0
10
-10
-4
-8
64Center of Reliable Power Electronics
Resonance Issues in DFIG based Wind Farm
Active damping for HFR
PCC
Lσr
ir
Rr/slip Lσs Rs
Lm
is
ir
*
0 0( ) ( )r c di G s j G s j slip
0
0
/( )
* ( )/
RSC
c
d
Z slipG s j
G s jslip
RSC current closed-loop control
DFIG machine
0( )vZ s j
Virtual Impedance
VPCC
Impedance modeling of the RSC and DFIG machine with the
virtual impedance in the stator part.
Frequency(Hz)
40
Mag
nit
ud
e(d
B)
Ph
ase(
deg
ree)
90
0
20
-90600 800 1000 1200
45
-45
ZNETP
1400400
60
0ZSYSTEM
1600 1800 2000
135
Original phase difference of 180°, causing HFR
Reshaped phase difference of 150°, active damping
ZSYSTEM_Sv
The 7.5 kW small scale DFIG system impedance with virtual impedance Zv in the stator part
Bode diagram of the small scale DFIG system impedance
with the virtual impedance in the stator part, Rv = 120 Ω,
fcut = 1400 Hz, Td = 150 μs.
_SR Sv
Lm s L s v Lm s L s v
Lm
Z
Z H R Z Z H Z R Z Z
Z H
s s
Virtual impedance for active damping:
65Center of Reliable Power Electronics
Resonance Issues in DFIG based Wind Farm
Experimental Validation of Active Damping Strategy for HFR
us
(500 V/div)
is
(10 A/div)
ir
(10 A/div)
ug
(500 V/div)
ig
(5 A/div)
us
(500 V/div)
is
(10 A/div)
ir
(10 A/div)
Enabled active damping
ug
(500 V/div)
ig
(5 A/div)
Enabled active damping
Experimental result of the HFR in the 7.5 kW small scale DFIG system when the active damping strategy is enabled
Experimental result of the HFR damping transient response in the 7.5 kW small scale DFIG system when the active
damping strategy is enabled
Summary
66Center of Reliable Power Electronics
A solution for the long term future in society
Coordinated control of production and consumption – grid stability
Systems should be able to run in on-grid and off-grid modes – grid codes
Wind turbines have been the fastest growing but PV will come…
Wind turbine technology – better performance
- Full-scale power electronics
- New generator concepts (e.g. PM, gearless)
- Larger size – lower cost per kWh
- Reliability – a key to lower cost of Energy
- Will be organized in power stations
- Methods to do large scale power transmission
- Stability issues should be adressed
Power Electronics for Wind Power – The enabler..
Power Electronic Based Power System
Electricity
generation
Electricity
transmission,
distribution,
consumption
Towards 100% Power
Electronics Interfaced
Integration to electric grid
Power transmission
Power distribution
Power conversion
Power control
Power Electronics enable efficient conversion
and flexible control of electrical energy
67
Modern
Power Systems
(source: ABB) (source: Google)
(source: ABB) (source: EPRI)
Towards 100%
Renewables
Converter
level
System
level
Power Electronic Based Power System - Future
68
Hybrid alternating/direct current transmission/distribution grids
69Center of Reliable Power Electronics
A solution for the long term future in society
Smart grid pushed by renewable
Increased power production close to the consumption place
Coordinated control of production and consumption
Future grid configurations may be different – but intelligent
Systems should be able to run in on-grid and off-grid modes
PV-plants will get same specifications as wind turbines
Wind turbines have been the fastest growing but PV will come
Wind turbine technology – better performance
- Full scale power electronics
- New generator concepts (e.g. PM, gearless)
- Larger size – lower cost per kWh
A university-industry collaborated center has been established to advance
the research progress in reliability of power electronic, especially for the
applications in renewable energy systems.
Power Electronics
Enabling wind power into an intelligent grid
Relevant links
70Center of Reliable Power Electronics
www.corpe.et.aau.dk (Presentation can be downloaded)
www.harmony.et.aau.dk
www.et.aau.dk
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Books in power electronics
74
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