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Novel PM generators for large
wind turbines
by Alexey Matveev
Wind Power R&D seminar - Deep sea offshore wind power, 20-21 January 2011, Trondheim, Norway
18.01.2011 2
Contents
• Drive train configurations
• State-of-the-art PMG-based solutions
• Integration: the path to win for direct drive
• SmartMotor in wind
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The general drive train scheme
G
Nacelle and tower
Grid
C TP
BGB
GB – gearboxB – brakeG – generatorC – converterT – transformerP - protection
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Basic drive train solutions
Configuration 1: gear + double-fed IG
Configuration 2: gear + IG
Configuration 4: gear + PMSG
Configuration 3: direct SG with wound rotor
Configuration 5: DD PMSG
Efficiency of different drive trains
• Components included: gearbox, generator, converter, transformer– Direct driven PM generator solution gives the best efficiency at speeds below rated
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Analysis performed in cooperation with Zhaoqiang Zhang, NTNU (supervisor Prof. Robert Nilssen)
LS – low speedMS – medium speedHS – high speed
PMSG – permanent magnet synchronous generatorDFIG – doubly-fed induction generatorEESG – electrically excited synchronous generatorSCIG – squirel-cage induction generator
60,00 %
65,00 %
70,00 %
75,00 %
80,00 %
85,00 %
90,00 %
95,00 %
100,00 %
3 5 7 9 11 13 15
MS_PMSG HS_PMSG
HS_DFIG MS_EESG
HS_SCIG HS_EESG
LS_PMSG LS_EESG
Wind Speed (rpm)
Eff
icie
ncy
• Direct drive is larger and heavier, but
• it doesn’t suffer gearbox-related problems
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Direct drive vs geared solution
Source: NTNU
turbine
gear
generator
• High-torque generator for direct drive is large. This is basically the only drawback of direct drive solution
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High-torque generator for direct drive
PM generator from Siemens. 3 MW, 17 rpm
• Drive trains with PM generators have the best efficiency– Especially without gear (direct drive) and 1-stage gear
• However, there are other characteristics to take into account:– Weight– Cost– Power factor– Lifetime– Reliability– Manufacturability– ...
• Design means finding a trade-off between various criteria
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Some conclusions
Efficiency
cos_fi
P/kg
T/kg
1/Length
Tan. tensionDesign 1
Design 2
Design 3
Design 4
Design 5
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...next part
• Drive train configurations
• State-of-the-art PMG-based solutions
• Integration: the path to win for direct drive
• SmartMotor in wind
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Available solutions with PMG
Low-speed PMG (DD) Medium-speed PMG (1-s.g.)
High-speed PMG (3-s.g.)
• Low-speed, medium-speed and high-speed generators
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Products of ABB and TheSwitch
<3.3 MW <300 rpm
<4.25 MW <20 rpm
<1 MW <2000 rpm
• Examples of medium-voltage (ABB) and low-voltage (TheSwitch) converters
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Commercial power electronics
ABB TheSwitch
Is it end of the story?
• Big companies have products and even complete packages up to approximately 5-7 MW. Is it end of the development?
NO!!!
• New concepts under investigation, for example:– Magnetic gears and Pseudo-direct drive
– Superconducting machines
• There are problems when going to powers higher then 5-7 MW. These are to be solved!
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• Magnetic gears, pseudo-direct drive (PDD), superconducting machines
• The concepts have not been proven yet for high-power WEC
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Examples of new concepts
Magnomatics Converteam/Zenergy
PDDMagnetic gears Direct drive using HTS superconductors
Technology frontier for PM generators
• State-of-the-art in generator weight (expressed via power and torque densities, each point corresponds to one generator design)
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0,00
50,00
100,00
150,00
200,00
250,00
300,00
350,00
400,00
450,00
1,00 10,00 100,00
<1.5 MW
1.5-2 MW
2-3 MW
3-4 MW
>4 MW
Superconducting
Some new designs
Po
wer
Den
sity
(W
/kg)
Torque Density (Nm/kg)
Area of state-of-the-art designs
TheSwitch 4,25 MW DDSiemens 3,6 MW DD
TheSwitch 3,3 MW geared
ABB 2 MW 3-stage gear
Analysis performed in cooperation with Zhaoqiang Zhang, NTNU (supervisor Prof. Robert Nilssen)
• Active parts make 30-40% of total weight
• Cooling system defines size of active parts, it may take considerable space
• Carrying structure is usually massive
16 16
~60
00
~1000-1500
<30000 kg
Active parts, cooling and carrying structure
TheSwitch
When going for higher powers...
• Weight of carrying structure grows disproportionally!
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Source: TU Delft
Enercon
• Drive train configurations
• State of the art PMG-based solutions
• Integration: the path to win for direct drive
• SmartMotor in wind
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...next part
Integration strategies
• For drive trains with gearboxes: integrate generator with gearbox (see examples below)
• For direct drive: integrate generator with the turbine! (examples will follow)
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TheSwitch ABB Magnomatics
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Direct-driven generator in the nacelle
• Just a few of numerous patented designs
• Popular concept: generator between blades and tower
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Direct-driven generator in the nacelle
MTorres
Northwind Mervento
Vensys
• Integration variants
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Direct-driven generator in the nacelle
Source: NREL
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Direct-driven generator outside the nacelle
Bearing
Outer rotor
Inner stator
Emergia
• No shaft• Single bearing common for generator and blades
• Different approaches to weight reduction
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Direct-driven generator outside the nacelle
Concept: light carrying structure of the generator
Concept: integration of generator with blades
Key to success for generator supplier
• Work in close contact with the turbine designers
• Provide best active parts– Lightest
– Most compact
– Giving high efficient energy conversion
– Segmented
– Easy to integrate
– Cheap in production
– With low cogging
– Medium- and low-voltage
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...next part
• Drive train configurations
• State of the art PMG-based solutions
• Integration: the path to win for direct drive
• SmartMotor in wind
18.01.2011 27
What is SmartMotor
• Established in 1996 in Trondheim, Norway
• One of the largest R&D groups in the world with focus on PM technology
Reference projects offshore
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• Low-voltage and medium-voltage machines of MW-class
1.1 MW tidal turbine of Atlantis Resource Corporation (delivered)
0.8 MW propulsion system for Rolls-Royce Marine (in operation)
10 MW offshore wind turbine of SWAY (under construction)
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The technologies we believe in
• PM machines with concentrated winding and ironless machines
• Ideal for high-torque applications like wind turbines with direct drive
NTNU
Our technologies
• Concentrated winding technology is advantageous compared to distributed winding in high-torque applications due to– higher slot fill factor and consequently better cooling of the copper
Pre-shaping of the coil No insulation is needed between different phases
– segmentation with distributed winding leads to half-empty slots (10% loss in total slot filling), while with concentrated winding all slots are filled
– low cogging Competitors achieve this by shaping magnets SmartMotor apply patented slot/pole combinations
• Ironless technology is advantageous for machines with large diameter– There is no attracting force between rotors and stator– The structure is not sensitive to relative displacement of rotors and stator
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Our R&D directions
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• Shift PMG technology frontier by introducing new concepts
• Find new integration solutions together with wind turbine manufacturers
0
100
200
0 30 60
Pow
er p
er w
eigh
t [W
/kg]
Torque per weight [Nm/kg]
Enercon 4.5 MW
Siemens 3.6 MW
TheSwitch 4.2 MW
Siemens 3.0 MW
Vensys 1.5 MW
0
32
1
0
1
2
3
State-of-the-art
New active parts (NAP)
NAP+mech. integration
MAG-concept
Our R&D directions
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• Novel transformer-less concepts• ABB have developed concepts with direct high-voltage DC outputs based
on use of machines with high-voltage insulation• SmartMotor have developed similar concept where machine with low-
voltage insulation can be used (which means considerably more compact and cheap machine)
ABB concepts
