Dr Longya Xu The Ohio State University April 2010 Contents Introduction Major Wind Power System Configurations Challenges to Remain in Power Grid Why PM DirectDriven WTG Getting Popular ID: 404856
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Slide1
2MW PM Machine Design for Direct–Driven Wind Turbine Generator Application
Dr.
Longya
Xu
The Ohio State University
April, 2010Slide2
Contents
Introduction
Major Wind Power System Configurations
Challenges to Remain in Power Grid
Why PM Direct-Driven WTG Getting Popular
Initial Design and Performance Analysis
Specifications and Sizing
Stator and Rotor Design
Performance Evaluation
ConclusionsSlide3
1.2 Major Wind Power Generation System ConfigurationsSlide4Slide5
Example: Windformer (ABB)Slide6
Capacity Trajectory of Single UnitSlide7
Off-Shore Wind Farm Based on HVDCSlide8
Multi Units connected in series and power transmitted through HVDC Slide9
Specifications and Sizing
V
Rated(V,
rms
)
690
Frequency
5~11Hz
I
Rated(A,
rms
)
1700
Speed
10~22
rpm
KW Rated2,000Torque (peak)850kNm
The reason for low speed at:10~22 rpm
Tip Speed of Wind Blades: vtip = 115 meters/sec.
The reason for low Frequency at:5~11 hzSlide10
Sizing Equations
Consider the electrical and magnetic loadings are relatively constant, we have a traditional sizing equation:
where subscript “r” indicates rotor related variables.
(
1
)
In (1) the electrical loading refers the current along the air-gap in the unit of
Ampere per Meter (A/M)
.
The magnetic loading refers the magnetic flux density passing through air-gap in the unit of
Tesla
. Slide11
Sizing Equation Alternative
where subscript “o” indicates the stator related variables and a coefficient proportion to the current density and magnetic flux density.
Here current density is in the unit of
Ampere per Square Meter
and magnetic flux density in
Tesla.
(
2
)
is also closely Do/Dr related and at certain value of Do/Dr,
is maximized, or minimized.Slide12
Combining (1) and (2), we have two new sizing equations, one in terms of stator OD
(
3
)
(
4
)
another in terms of rotor OD
In sizing an electric machine, the
new equations take many variables
into consideration: electrical loading, magnetic loading,
D
o
/D
r
ratio, and slot current density.Slide13
Stator OD
3820mm
Pole #
60
Stator ID
3500mm
Slot #
288
Stack L
1300mm
Air-gap
6mm
Sizing ResultsSlide14
Stator Slot Shape and Dimensions
Stator current density at 2 MW
0.77(A/mm
2
)Slide15
Considerations on Slot Numbers
360 Slots: Integer
Number/Pole/Phase
288 Slots: Fractional Number/Pole/Phase
Pros: reduced
slot harmonics and
cogging torque
Cons: reduced
fundamentals and less effective in EM conversion
Pros: increased
fundamentals and more effective EM energy conversion
Cons: more slot harmonics and increased cogging
torque possibilitySlide16
Considerations on Inner or Outer Rotor
Inner
Rotor
Outer
Rotor
Pros:
traditional
mechanical structure to design and manufacture
Cons:
extra
effort to install permanent magnets
Pros:
easy installation of permanent magnets
and better utilization of space
Cons:
non-traditional mechanical structure and extra effort
for bearing installationSlide17
Estimation of Losses
and
Efficiency
Estimated Copper Losses
P
cu
= 3I
2
R = 2.7~3
kw
Assume equal amount of iron and other losses
Effi
. = 97%
Expected energy efficiency
P
Fe+other
= ~3
kwSlide18
FEM Comparison Results
(1)
Outer Rotor with 360 Stator
Slots
Slide19
In order to keep copper losses the same in comparison, some changes are made as follows:
Cross-section of stator slot for conductor:
1400mm
2
(288 slots)
vs.
1120mm
2
1400*288/360 (360 slots)
Current (peak)
flow in each conductor:
1300A(288 slots)
vs.
1040A (360 slots)1300*8/10FEM Comparison ResultsSlide20
Torque Production
Winding Flux Linkage
(1)
Outer Rotor with 360 Stator
SlotsSlide21
(2)
Outer Rotor with 288 Stator
Slots
FEM Comparison ResultsSlide22
Winding Flux Linkage
Torque Production
(2)
Outer Rotor with 288 Stator
SlotsSlide23
(3)
Inner Rotor with 360 Stator
Slots
FEM Comparison ResultsSlide24
Winding Flux Linkage
Torque Production
(3)
Inner Rotor with 360 Stator
SlotsSlide25
(4)
Inner Rotor with 288 Stator
Slots
FEM Comparison ResultsSlide26
Winding Flux Linkage
Torque Production
(4)
Inner Rotor with 288 Stator
SlotsSlide27
3. Conclusions
PM machine
plays a
critical role in WTG
systems
Direct-driven
WTG requires a large size machine and heavy use of permanent magnet
Optimal sizing of PM machine is significant
Two rotor structures are possible
S
lot/phase/pole
fractional
or
integer
makes differences
FEM comparison results are presented
Design of PM machine satisfying specifications is achieved.Slide28
Thanks!
Q & A