Wind Power - A Technology enabled by power electronicswesc2017.org/onewebmedia/Blaabjerg -Wind Power...

Wind Power -A Technology enabled by power electronics

Center of Reliable Power Electronics

Center of Reliable Power Electronics

Frede Blaabjerg

Professor, IEEE Fellow

[email protected]

Aalborg UniversityDepartment of Energy Technology

Aalborg, Denmark

CORPE

www.corpe.et.aau.dk

http://www.corpe.et.aau.dk/

mailto:[email protected]

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


Aalborg University and

Department of Energy Technology,

Denmark

Aalborg University - Denmark


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


Department of Energy Technology


Energy Production | Distribution | Consumption | Control

Department of Energy Technology


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


Power Electronics for Wind Turbines


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


Energy and Power Challenge in DK

Very High Coverage of Distributed Generation


i-Danmark.aspx


Energy and Power Challenge in DK

Very High Coverage of Distributed Generation


i-Danmark.aspx

Development of Electric Power System in Denmark


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


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


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


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


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


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


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


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


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


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)


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.


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


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


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


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


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


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


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.


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.


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


Reliability Challenge of 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


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


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


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.


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


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


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


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


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.


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


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


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


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


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


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


· Power module

Mission profile

· Grid codes

· Wind class


Control scheme

· Reactive power


· PMW modulation


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


· Power module

Mission profile

· Grid codes

· Wind class


Control scheme

· Reactive power


· PMW modulation

Consumed lifetime increases with higher wind class for both DFIG and PMSG


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


· Power module

Mission profile

· Grid codes

· Wind class


Control scheme

· Reactive power


· 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


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


LVRT and Resonance Issues in DFIG Wind Turbines


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


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


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


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


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


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



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



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



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.



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



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:



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


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


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


www.corpe.et.aau.dk (Presentation can be downloaded)

www.harmony.et.aau.dk

www.et.aau.dk

http://www.corpe.et.aau.dk/

http://www.harmony.et.aau.dk/

References

71

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Power Electronics, vol.24, No.8, pp.1859-1875, Aug 2009.

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Journal of Wind Engineering, Vol. 28, No. 3, pp. 247-263, 2004.

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Trans. on Ind. Appl., vol. 49, no. 2, pp. 922-930, Mar./Apr. 2013.

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Trans. on Power Electronics, vol. 28, no. 1, pp. 325-335, Jan. 2013.

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References

http://dx.doi.org/10.1109/TPEL.2014.2382565



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