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Structural Design of W
ave Energy Devices –
www.sdw
ed.civil.aau.dk
WP 3 – PTO‐Systems
Generator systems for WED Jochen Bard, Peter Kracht; Fraunhofer IWES
02‐05‐2012
Structural Design of W
ave Energy Devices –
www.sdw
ed.civil.aau.dk
02‐05‐2012
Overview
•
Design of rotating generator system
•
Use case ¼‐OWC
•
Simulation technologies
•
Ongoing Research on linear generators
Structural Design of W
ave Energy Devices –
www.sdw
ed.civil.aau.dk
02‐05‐2012
Generator system design
Horn’s ref
Key part / Impact on:
•
Reliability,
•
Efficieny,
•
O&M costs etc.
=> Project success depends on good generator design!
Research aims at:•
Knowledge base on requirements
and characteristics
•
Improved design process
•
Simulation technologies etc
Windpark Horns Rev (source: Wikipedia)
Structural Design of W
ave Energy Devices –
www.sdw
ed.civil.aau.dk
02‐05‐2012
Generator system design
control
Generator system
Requirements on generator system
Grid connection
Hull
…. Mooring
Turbine
Control
Maintenance
Marine Environment
Structural Design of W
ave Energy Devices –
www.sdw
ed.civil.aau.dk
02‐05‐2012
Generator system design
Design process
Tools:
•
Knowledge base,
•
Simulation software,
•
HIL‐tests etc.
Structural Design of W
ave Energy Devices –
www.sdw
ed.civil.aau.dk
02‐05‐2012
Generator system design
Generic requirements:
‐
Variable speed operation
‐
Low operational speeds
‐
Possibly no gear box
‐
High part load efficiency
‐
High overload capacity
‐
High mechanical reliability
‐
...
Similar requirements for other frequently
used turbine types
Impulse‐Turbine
‐ Low operational speed,‐ High starting torque,‐ High efficiency over wide flow range‐
Expectable power range 0.5 – 1 MW‐
…
Turbine characteristics
Characteristics of an example air‐turbine
Structural integration
Structural Design of W
ave Energy Devices –
www.sdw
ed.civil.aau.dk
02‐05‐2012
Generator system design
Candidate systems
‐
Doubly fed induction generator (DFIG)
‐
Asynchronous generators (ASG)
‐
Permanent magnet synchronous generators (PMG)
‐
Separate excited synchronous generators (SG)
frequency converter‐
generator system
G
Control
Structural Design of W
ave Energy Devices –
www.sdw
ed.civil.aau.dk
02‐05‐2012
Generator system design
Efficiency ~ 90‐95% (full load)
Overload
Capacity
Torque_max/…rated~ 2‐4
Control time
constants
2..20ms
Power factor 0…1Independently
controllable
Fault‐ride‐
through
Good performance
Transient
short circuit
torques
Up to 15 times the
rated torque
… …
Torque vs speed curve (source: DiracDelta)
Performance of FC‐generator systems
Structural Design of W
ave Energy Devices –
www.sdw
ed.civil.aau.dk
02‐05‐2012
DFIG ASG PMG SG
Efficiency (full‐load) +++ ‐ ++ ++
Efficiency (part‐load) ‐ ‐ ++ ++
Maintenance ‐‐‐
(slip ring) + + +
Investment costs + + ( magnets?) +
Reliability ‐‐‐
(slip ring) ++ ++ + (?)
Range of rated speeds ‐ ‐ +++ ++
Availability ‐ + ‐ ‐
… … … … …
DFIG
no option due to slip‐ring wear out
ASG
transitional technology, demonstration projects
SG &
PMG
most promising for future full‐scale WECs
Benchmarking of generator systems
Comparison of generator systems at 1MW rated power
Generator system design
Structural Design of W
ave Energy Devices –
www.sdw
ed.civil.aau.dk
02‐05‐2012
Use case ¼‐scale OWC
CORES – EU / FP7 ‐
Project (source: HMRC)
Structural Design of W
ave Energy Devices –
www.sdw
ed.civil.aau.dk
02‐05‐2012
Use case ¼‐scale OWC
(oebuoy)
Device characteristics Requirements from dynamic simulations Generator specifications
‐
OWC‐
Floating structure‐
Backward Bent Duct‐
¼‐scale‐ Impulse‐Turbine‐
…
‐
Rated power: 11kW‐
Rated speed: 785 RPM‐
Operating speed: 300 – 1300‐
Run‐away speed: 1600 RPM‐ Overload capacity: 20%‐
…
‐ 8‐pole Asynchronous generator‐ Rated power 11kW‐ Overload capacity 300%‐ Rated speed: 769RPM ‐ Operating speed: 0 –
3000 RPM‐Marine version (certified by DNV, GL)‐ Standard frequency converter (IP21)‐
…
PMG turned down mainly due to delivery time and costs!
(source: OceanEnergy Ltd.)
Structural Design of W
ave Energy Devices –
www.sdw
ed.civil.aau.dk
02‐05‐2012
OEBuoy in storm event (source: OceanEnergy LTD.)
Results
of 3‐month sea
trial
period Lessons
learned
‐
No mechanical
or
electrical
faults
in fc‐generator
system
‐ 100% availability‐
Peak power up to 25kW delivered
to the
onboard
grid
‐
…
‐ Starting
torque
underestimated‐
Hardware‐in‐the‐Loop
test significantly
reduced
comissioning
time ‐
…
Drehzahl drehmoment verlauf
Design process
would
significantly
benefit
from
further
simulation!
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1 113 225 337 449 561 673 785 897 1009 1121 1233 1345 1457 1569 1681 1793 1905 2017 2129 2241 2353 2465 2577 2689 2801 2913
FC_SPEED [RPM]
FC_TORQUE [Nm]
Measured data from OEBuoy in operation May 17th, 2011
Use case ¼‐scale
OWC
Structural Design of W
ave Energy Devices –
www.sdw
ed.civil.aau.dk Simulation technologies
Modelling by set of characteristic curves, limits
G
‐ Torque limit‐Max speed‐ Control response time‐
….
Suitable for investigations on:
• Control schemes
• Annual yield
• PTO‐hull interaction
• Generator system specifications
• ….
Sufficient model grade for most use cases
Structural Design of W
ave Energy Devices –
www.sdw
ed.civil.aau.dk Simulation technologies
Integration in Wave to Wire model
Generatorsystem
Hull
Turbine
Control
Physical connection
Signal path
GridConnection
Tools:
• Adams
• Matlab/Simulink
• Modelica
• ….
Structural Design of W
ave Energy Devices –
www.sdw
ed.civil.aau.dk
02‐05‐2012
Ongoing research
•
Matlab/Simulink model of PTO and hydrodynamics
•
Aiming at investigations on PTO‐system layout and control schemes
Wavestar(SDWED)
Structural Design of W
ave Energy Devices –
www.sdw
ed.civil.aau.dk
02‐05‐2012
Ongoing research
NEMOS WEC (source: Nemos)
Linear generator
technologies
Funded by
The International Research Alliance
02‐05‐2012