Atti della Conferenza GENERAZIONE EOLICA “PULITA”: aspetti meccatronici/azionamentistici e trends

“Clean“ wind power generation

Electric/mechatronic aspects and trends

Luca Peretti - ABB Corporate Research, 2012-04-04

Presentations

The wind energy sector – a bird’s eye view

What is ”clean” wind energy?

Mechatronic aspects of wind turbines

Control aspects of wind turbines

Reflections

Soft conclusion

Overview

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April 4th, 2012 | Slide 2

Presentations

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Some about myself….

Born in Udine, Italy, in 1980

M.Sc. In Electronic Engineering, University of Udine (Italy), 2005

Ph.D. in Mechatronics and Industrial Systems, University of Padova in

Vicenza (Italy), 2009

Post-doc, University of Padova in Vicenza (Italy), 2009-2010

Scientist, ABB Corporate Research, Västerås (Sweden), 2010-today

Member of the technical steering committee in the SWPTC

Member of reference group for Vindforsk projects

Member of the IET

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ABB – a multinational corporation Power and automation technologies

~133,600 employees in about 100 countries

2011 revenue: $ 38 billion

Formed in 1988, merger of Swiss and Swedish engineering companies

Predecessors founded in 1883 (ASEA) and 1891 (Brown Boveri)

Publicly owned company with head office in Switzerland


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$9.9 billion

$7.6 billion

$8.0 billion

$7.6 billion

Based on 2011 revenues

$4.9 billion

Power Products Power Systems Discrete

Automation and Motion

Process Automation

Low Voltage Products

ultrahigh, high and

medium voltage

products (switchgear,

capacitors, …);

distribution

automation;

transformers

electricals,

automation and

control for power

generation

transmission

systems and

substations

network

management

control systems

and application-

specific

automation

solutions for

process

industries

• machines

• motors

• drives

• robotics

contactors

instrumentation

panels

softstarters

ABB offers Divisional structure and portfolio


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Innovation: key to ABB’s competitiveness Consistent R&D investment

More than $1 billion invested annually in R&D*

Approx. 6,000 scientists and engineers

Collaboration with approx. 70 universities

MIT (US), Tsinghua (China), KTH Royal Institute of Technology (Sweden), Indian

Institute of Science (Bangalore), ETH (Switzerland), Karlsruhe (Germany), …

* Comprises non-order related R&D and order-related development


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ABB Corporate R&D – globally distributed

Power Technologies Automation Technologies

SECRC - Västerås (Oslo)

CHCRC - Baden-Dättwil

DECRC - Ladenburg

PLCRC - Krakow

USCRC - Raleigh

INCRC - Bangalore

CNCRC - Beijing and Shanghai


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Approx. 260 Employees

240 Scientists and engineers

135 Ph.D.

Power Technologies labs

High Voltage

High Power

Motor/machines test benches

Power electronics test benches

Insulation systems and materials

Automation Technologies labs

Mechatronics

Communications

Technology Support labs

Chemistry

Mechanics

c

ABB Corporate Research, Västerås Resources: brains and muscles


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Wind energy sector

A bird’s eye view on the market and (ABB’s) technologies


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Wind energy sector Growing… ?

China number 1, and growing

Very politically-driven market (financial crisis has a big impact)

Germany’s very ambitious plans are interesting… (but already behind schedule) (http://www.thenational.ae/thenationalconversation/industry-insights/energy/german-wind-energy-plans-in-the-doldrums)

From: http://www.wwindea.org/home/index.php?option=com_content&task=view&id=345&Itemid=43


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http://www.thenational.ae/thenationalconversation/industry-insights/energy/german-wind-energy-plans-in-the-doldrums















Offshore wind Mainly a European challenge so far

From [1]


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Offshore wind in Europe

Lot of plans, few installations done

Offshore is still a small percentage

Technological reasons behind it?

From [1]

From [1]


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ABB contribution to renewable energy Component supplier for wind power

Offering to wind turbine

manufacturers:

Generators and motors

LV and MV converters

LV and MV switchgears

Transformers

Control and protections

Low voltage products

Full life cycle management

to all products delivered

Sales to wind farm owners,

operators or developers:

Sub-stations

Transformers

Grid connections

AC and HVDC underground

and sea

Cables

System studies

Full life cycle management

to all products delivered


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Squirrel-cage induction machine (0-100% speed) Doubly-fed induction machine (±30% speed)

Permanent magnet DD machine (0-100% speed) Permanent magnet machine (0-100% speed)

Generators for different drive train concepts A complete coverage


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From [6]

Induction generators

Fixed-speed generators

Doubly-fed generators

Full-speed generators

Generator directly coupled to the grid

From single- to two-speed, air- and water-cooling, cast iron and welded housings

Typical rated speed 1000 – 1500 rpm, 4 – 6 poles

Normally powers from 1 MW to 2 MW

Direct on-line stator and a wound rotor connected to the grid using a frequency

converter, torque and speed ranges limited by the converter power rating

Typical rated speed 1000 – 1500 rpm, 4 – 6 poles

Normally powers from 1,5 MW to 5 MW

Welded modular construction

Fully controlled with variable speed, reactive power supply

High power quality and efficiency for the end user

Typical rated speed 1000 – 1500 rpm, 4 - 6 poles



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From [7]

Synchronous (PM) generators

Integration of turbine and generator.

Simple and robust low speed rotor design with no separate excitation or cooling system

High efficiency, simple and robust, lowest maintenance demand, maximum reliability

Typical rated speed 14 – 30 rpm, multi-pole

Normally powers from 1,5 MW to 3 MW

Slow speed system, single-stage gearbox.

Same simple and robust low speed rotor design with no separate excitation or cooling system

High power with small space requirement

High efficiency, simple and robust, low maintenance demand

Typical rated speed 120 – 450 rpm, multi-pole


Mechanically similar to the doubly-fed type with smaller space requirements

Highest power density with well-proven, high speed gear solution

High efficiency, no slip rings, low maintenance demand

Typical rated speed 1000 – 2000 rpm, 4 to 8 poles


Low-speed generators

Medium-speed generators

High-speed generators


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From [7]

Low-voltage (<1 kV) drives: ABB ACS800 family

ACS800-77LC - 0,6 to 3,3 MW

Robust grid code compliance

Nacelle or tower installation

Redundant configuration

available at higher ratings

ACS800-87LC - 1, 5 to 6 MW

Robust grid code compliance

Compact size, back-to-back configuration

Optimized for tower base installation

ACS800-67LC - 1,7 to 3,8 MW

Small and light weight

Lowest harmonics and highest

efficiency at rated point


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From [6]

Medium voltage (~3 kV) drives: ABB PCS6000 family

2011-08-23: first order from Global Tech I project (400 MW offshore wind farm, 110km

north-west of Cuxhaven, Germany)

80 wind turbines (Multibrid) of 5 MW each - provided by AREVA

$ 30 millions from AREVA Wind to provide 5MW-MV drives


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From [6,8]

What is “clean” wind

energy?

...or the “behind the scene” aspect


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“Clean” energy Is it this...?

From: http://www.greenpeace.org/eu-unit/Global/eu-

unit/image/2011%20pix/December%202011/turbine%20on%20the%20beach.jpg

From: http://www.cbc.ca/news/pointofview/WindTurbine.jpg

From: http://www.bettergeneration.co.uk/images/stories/blog/wind-eolic-turbine-in-hands.jpg


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“Clean” energy ...or this?

From: http://www.cbc.ca/gfx/images/news/photos/2011/07/07/li-rare-earth-mine-620rtxu1.jpg

From: http://graphics8.nytimes.com/images/2010/11/08/opinion/08rfd-image1/08rfd-

image1-custom2.jpg

From: http://andysrant.typepad.com/.a/6a01538f1adeb1970b0154361c515e970c-500wi


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Mechatronics aspects ...or wind turbines from the view of a power electronics engineer

(no grid aspects included)


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Wind turbines structures How did we get here

Picture from [2]


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Growing and growing… Foreseen problems?

Picture from [2]


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Inside a wind turbine The real mechatronic application

Picture from [2]

The turbine rotor rotates at low speed – approx. 5 rpm nominal

Depending on the drive train concept, the generator rotates either at low (15 rpm), medium-(300-

400 rpm) or high (1000-1800 rpm) speed


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A true mechatronic vision is needed

Design of

larger

generators

Maximum

efficiency

control

Mechanical

vibration

damping

Foundations

for offshore

Electrics Electronics Mechanics Civil Material

science

Vibration

damping

algorithms

Grid-fault

compensation

control

Flexible

blades design

Light-weight

materials

New

generator

concepts

Reliable

electrical

contacts

Results in each field stimulate

and benefit all other fields

Interdisciplinary exchange

and circulation of ideas is

essential


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Let’s start: cost breakdown of a wind turbine

Picture from [2]

Generator and power converter do not account for much of the cost… (so far)

The gearbox is indeed quite a big part of it


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The gearbox One of the most unknown things ever (for electrical guys)

From: http://www.designnews.com/document.asp?doc_id=230485

Mature product trying to enter a new market

One or more stages between the turbine rotor and the electric generator (epicyclical or

parallel axis type)

Mechanical multi-body simulations are performed by suppliers (but not available)

Source of noise (and failures)

Today, closer interaction with turbine manufacturers

From: http://eetweb.com/wind/gearbox-failure-fig1.jpg


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Noise from the gearbox

From: S. Li, D. Jiang, M. Zhao, "Experimental investigation and analysis for gearbox fault", Proc. of the World

Non-Grid-Connected Wind Power and Energy Conference (WNWEC), Nanjing, China, Nov. 5th-7th, 2010.

There might be some vibrations (mesh frequency and maybe others)

What happens during normal operation? And during a fault?


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The mechanical drive train

𝑑𝜔𝑟𝑜𝑡

𝑑𝑡=

1

𝐽𝑟𝑜𝑡 𝜏𝑟𝑜𝑡 − 𝜙𝐾𝑠𝑕𝑎𝑓𝑡 −

𝑑𝜙

𝑑𝑡𝐵𝑠𝑕𝑎𝑓𝑡

𝑑𝜔𝑔𝑒𝑛

𝑑𝑡=

1

𝐽𝑔𝑒𝑛 −𝜏𝑔𝑒𝑛 +

1

𝑁 𝜙𝐾𝑠𝑕𝑎𝑓𝑡 +

𝑑𝜙

𝑑𝑡𝐵𝑠𝑕𝑎𝑓𝑡

𝑑𝜙

𝑑𝑡= 𝜔𝑟𝑜𝑡 −

1

𝑁𝜔𝑔𝑒𝑛

A classic mechanical engineering work

Quite different structures for different concepts (direct-drive, gearbox-based)

Surprisingly (or not?), few information available for high-frequency behaviour (above 100 Hz)

There might be some resonances... what happens when they are hit?

From: J. Sopanen, V. Ruuskanen, J. Nerg, J.

Pyrhönen, "Dynamic torque analysis of a wind

turbine drive train including a direct-driven

permanent magnet generator", IEEE Trans. Ind.

El., vol. 58, no. 9, Sept. 2011.

From: J. D. Grunnet, M. Soltani, T. Knudsen, M.

Kragelund, T. Bak, “Aeolus toolbox for dynamic wind

farm model, simulation and control”, Proceedings of

the European Wind Energy Conference and

Exhibition (EWEC) 2010, 20th-23rd April 2010,

Warsaw, Poland.


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The (twisting) tower…

Fore-aft oscillations:

𝜏𝑟𝑜𝑡 =1

2

𝑣𝑟𝑜𝑡3

𝜔𝑟𝑜𝑡

𝜌𝐴𝑟𝑜𝑡𝐶𝑝 𝜆,𝛽

From: T. Thiringer, J.-Å. Dahlberg, "Periodic pulsations from a three-bladed wind turbine", IEEE Trans. En. Conv., vol. 16, no. 2,

Jun. 2001

Side-to-side and fore-aft oscillations: impact on power generation

Side-to-side oscillations:

The sideways oscillation of the tower causes an

oscillating angular deflection of the nacelle and

thereby superimposes an apparent oscillation in the

rotating magnetic flux. This leads to a corresponding

power fluctuation.

Change of the equivalent wind speed over the rotor: change of torque

contribution from the wind source.

Torque produced on the shaft:


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The nature adds some wind effects

Wind shear and tower shadow effects

From: D. S. L. Dolan, P. W. Lehn, “Simulation Model of wind turbine 3p torque oscillations due to wind shear and tower

shadow”, IEEE Trans. En. Conv., vol. 21, no. 3, Sept. 2006

Variation of the wind field with the height Disturbance related to tower presence

http://www.geograph.

org.uk/photo/754033

Pitch systems

That’s what individual pitch control is used for!


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Designing the best generator…the PMSG case

𝑁𝑝 =2𝑝

𝐻𝐶𝐹 𝑄, 2𝑝

𝜏𝑐𝑜𝑔 𝜗𝑚 = 𝑇𝑘

+∞

𝑘=1

sin 𝑘𝑁𝑝𝑄𝜗𝑚 + 𝜑𝑘𝑁𝑝

From: N. Bianchi, S. Bolognani, “Design Techniques for Reducing the Cogging Torque in Surface-Mounted PM Motors”, IEEE Trans. Ind. Appl.,

vol. 38, no. 5, Sept./Oct. 2002, pp. 1259-1265.

Let’s not consider issues like size or weight or mounting procedures

Cogging torque (for synchronous generators) could be an issue

Q: number of slots

p: pole pairs


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Designing the best generator…the PM case

From: J. Sopanen, V. Ruuskanen, J. Nerg, J. Pyrhönen, "Dynamic torque analysis of a wind turbine drive train including a

direct-driven permanent magnet generator", IEEE Trans. Ind. El., vol. 58, no. 9, Sept. 2011.

Best design for cogging torque reduction,

but not elimination


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The grid…why should it be perfect?

± 2% voltage unbalance

± 8,7% stator current unbalance

±7,8% stator active power unbalance

± 10,1% torque unbalance

± 0,5% DC-bus voltage unbalance

From: L. Xu, Y. Wang, "Dynamic modeling and control of DFIG-based wind turbines under unbalanced network

conditions", IEEE Trans. Pow. Syst., vol. 22, no. 1, Feb. 2007

Weak grids could introduce voltage asymmetries

Issue for doubly-fed generators (a superimposed 2nd-harmonic torque is generated)


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Put it all together An engineering miracle that it actually works

…but how do the components affect the turbine reliability?

ReliaWind Project: http://www.reliawind.eu/

EU funding within the frame of the European Union’s Seventh Framework Programme

for RTD (FP7)

450 wind-farm months’ worth of data

350 onshore wind turbines operating for varying lengths of time

35,000 downtime events

”old type” turbines (probably no direct-drive concepts)


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http://www.reliawind.eu/

Reliability & maintenance aspects

ReliaWind project – turbine failure rate

From: http://www.reliawind.eu/files/file-inline/110502_Reliawind_Deliverable_D.1.3ReliabilityProfilesResults.pdf


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Reliability & maintenance aspects Reliawind project - downtime



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Reliability & maintenance aspects Previous studies



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Interpreting the reliability figures...

Converters’ reliability should be improved

Pitch control is also very sensitive

Gearbox impact: to be further analysed (lot of effort from manufacturers

reported)

We should also don’t forget the scheduled maintenance (i.e. change of the oil

in the gearbox)

Do we gain something by changing the drive train concept?

High-speed, medium-speed or low-speed generators?

With or without gearbox?


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Drive train concepts The different approaches

Traditional concept: high-speed generator with gearbox

Direct-drive concept: low-speed generator, no gearbox

Medium-speed concept: medium-speed generator, reduced-stage gearbox

low raw material and investment costs

high full-load efficiency of the drive train

higher failure rate for high-speed components

(e.g. high-speed shaft and generator bearing)

no fast rotating parts, maybe higher reliability

higher partial load efficiency

more raw materials

Tries to combine the two above ?


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Magnets’ price variability Up and downs – direct impact on generators’ price

Picture from: http://aussiemagnets.com.au/pages/Rare-Earth-Magnet-Price-Increases.html Picture from: http://www.metal-pages.com/metalprices/neodymium/

Rare-earth materials’ price is going up and down

China dominates the market

Future?


© ABB Group

Control aspects Mainly converter ones, not pitch control ones


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The general picture Pitch control and generator control

Picture from [2]

Pitch control and torque control;

Pitch control: PLC level (turbine

manufacturer);

Torque control: frequency converter

(supplier)

Power references are accepted as

well for the torque control;

Speed-power-torque relationships

based on turbine and generator

characteristics;

There is one drawback from the

electric drive point of view. Where?


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The two cases: DFIG and PMSG

DFIG: converter connected to the rotor

windings, slip rings

Stator connected to the grid

Smaller converter size (roughly 30% of

the rated power)

PMSG: grid/generator interaction

only through the converter

Bigger size of the converter (rated

power)

Picture from [2]

Picture from [2]


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A conventional speed-power curve

Picture from [2]


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The importance of the limitations The PMSG case

Picture from [3]


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The importance of the limitations The DFIG case

Picture from [4]


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Grid-codes compliance

• Static and dynamic requirements to be fulfilled by a wind power installation

• Static requirements: voltage and power control, power quality (THD, flicker)

• Dynamic requirements: dynamic behavior under grid disturbance (fault ride-

through, FRT)

Picture from [3]


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Fault ride-through capabilities

Picture from [3]

Turbine connected during temporary faults. Requirements:

voltage dip length

behaviour with a balanced (symmetrical) dip

behaviour with an unbalanced (unsymmetrical) dip.

Depending on the country, the wind turbine:

has to stay connected to the power system for a certain time

may not take power from the power system

must produce capacitive reactive current as much as required.


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Reflections (Technical) tendencies and expectations on the turbine side


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Challenge 1 – The scaling of generators

Coping with: increased weight? Increased disturbances and vibrations? PM availability?

It is not only a raw material problem; it is also a production capacity issue.

Concept comparisons (3MW reference)


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Drive train

concept

Low Speed Full

Converter (LSFC) -Direct drive

Medium Speed Full

Converter (MSFC)

High Speed Full

Converter (HSFC)

Typical size70 tons 20 tons 8 tons

Relative

Production capacity

need

Per unit

4,5

(450%)

1,5

(150%)

1

(100%)

Efficiency

at nominal load

95,1% 98,2% 97,7%

Relative

Magnet weight 10 2,5 1

Drive train

concept

Low Speed Full

Converter (LSFC) -Direct drive

Medium Speed Full

Converter (MSFC)

High Speed Full

Converter (HSFC)

Typical size70 tons 20 tons 8 tons

Relative

Production capacity

need

Per unit

4,5

(450%)

1,5

(150%)

1

(100%)

Efficiency

at nominal load

95,1% 98,2% 97,7%

Relative

Magnet weight 10 2,5 1

Challenge 2: the offshore

From: J. Sheng, S. Chen, "Fatigue Load Simulation for Foundation Design of Offshore Wind Turbines Due to Combined

Wind and Wave Loading“, Proc. of the Non-Grid-Connected Wind Power and energy Conference (WNWEC), Nanjing,

China, Nov. 5th-7th,2010.

• Harsher conditions in offshore

• Wind AND waves effects!

• Water depth, soil stiffness: significant effect on

the fatigue load/bending

• Indirect effects on the drive train (vibrations)

• Control may have a bigger role


© ABB Group

Challenge 3: maintenance

http://www.rope-access-photos.com/picture/number395.asp

http://www.flightglobal.com/blogs/aircraft-pictures/assets_c/2009/01/Eurocopter-EC135.html http://images.pennnet.com/articles/pe/cap/cap_0705pe-dsc06925.jpg

Do we design with maintenance in mind?

What does the offshore challenge require?

How a different drive train topology affect

maintenance?


© ABB Group

Challenge 4 – Cold climate

Research to enhance power production in cold regions

Blades do play a big role

New materials, new concepts needed

Condition monitoring (not only for blades...)

Converters, generators could be affected by altitude

From: Ø. Byrkjedal - Kjeller Vindteknikk, “Detailed national mapping of icing”, Seminar on wind energy aerodynamics - icing

and de-icing of WT blades, KTH, Sept. 5, 2011 - Chalmers, Sept. 6, 2011,

https://document.chalmers.se/workspaces/chalmers/energi-och-miljo/vindkraftstekniskt/icing-de-icing/oyvind_byrkjedal


© ABB Group

Do not limit the fantasy Airborne turbines?

http://en.wikipedia.org/wiki/Airborne_wind_turbine

Twind Savonius style

Aerogenerator X KiteGen

http://www.windpower.ltd.uk/index.html http://kitegen.com/press/kiwicarusel_hd_logo.jpg April 4th, 2012 | Slide 57

© ABB Group

Soft conclusion To ease the listeners before the discussion


© ABB Group

From: http://www.chalmers.se/ee/swptc-en

ABB support to academia

The right time for knowledge


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SWPTC partners

Universities

Chalmers University of Technology

Industries

ABB

DIAB

GE Wind

Göteborgs Energi

Marström Composite

SKF Sweden

Triventus Energiteknik

WindVector

Municipal/Regional/Government

Region Västra Götaland

Swedish Energy Agency


© ABB Group

SWPTC’s direct-drive wind turbine in Göteborg Main technical data

From: http://www.goteborgenergi.se/Foretag/Projekt_och_etableringar/Fornyelsebar_energi/Vindkraft/I_drift/Goteborg_Wind_Lab

Picture from Göteborg’s harbour


© ABB Group

Time-lapse video

http://www.youtube.com/watch?v=jHn1n2tdnRc


© ABB Group

Thank you!

Picture from: http://blog.luciolepress.com/2010/08/05/funny-photo-a-sheep-a-wind-turbine-and-a-rainbow-in-germany.aspx


© ABB Group

References

1. “Wind in our Sails - The coming of Europe's offshore wind energy industry”, EWEA report, November 2011,

http://www.ewea.org/fileadmin/ewea_documents/documents/publications/reports/Offshore_report_web_01.pdf

2. ABB Technical application papers no. 13, ”Wind power plants”, ABB document 1SDC007112G0201 - 10/2011 - 4.000.

3. "ABB wind turbine converters - System description and start-up guide, ACS800-77LC wind turbine converters (840 to 3180

kW)", ABB document 3AFE68802237 Rev B EN 2010-10-25.

4. ABB wind turbine converters- System description and start-up guide, ACS800-67LC wind turbine converters, ABB document

3AUA0000059432 Rev A (EN) 2011-01-14

5. "ABB wind turbine converters - Firmware manual - Grid-side control program for ACS800 wind turbine converters", ABB

document 3AUA0000075077 Rev B EN 2011-05-26

6. “Products and services for wind turbines - Electrical drivetrain solutions and products for turbine subsystems”, ABB document

3AUA0000080942 REV A 18.5.2010 #14995

7. “Wind turbine generators - Reliable technology for all turbine applications”, ABB brochure 9AKK104735 EN 04-2009

Piirtek#14426

8. “Medium voltage for wind power PCS 6000 - full-scale converters up to 9 MVA”, ABB document 3BHS275725 E01


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Atti della Conferenza GENERAZIONE EOLICA “PULITA”: aspetti meccatronici/azionamentistici e trends