Constant Voltage Permanent Magnet
Wind Generator
Andrew Hirzel
LE Incorporated
October 14, 2003
[e-mail]
Material
Slide 1
Patent Pending
Overview
" Problem Description (3)
" Geometry Construction (8)
" Propose Solution (9)
" Review Solution
" Power, Voltage, Efficiency (6)
" BEMF waveform (2)
" Cogging (6)
" Rotor Losses (3)
" Axial Force (1)
Material
Slide 2
Patent Pending
Project Definition
" Speed range: 1000  2000 rpm
" Voltage range: 410  480 Vrms (line)
" Machine Efficiency:
" 90% min at lightest load
" 95% min at maximum power
" Passive Rectification to DC
" Power Output Proportional to Rotor-Speed3
" Power Output 100 kW at 2000 rpm
Material
Slide 3
Patent Pending
Wind Generator Goal
Power Output and Terminal Voltage
Output Voltage, max
Output Voltage, nom
Output Voltage, min
" Power ~ rotor-speed3
Target Power ~ Rotor Speed Cubed
500 120
" Voltage > 410 Vrms
100
450
" Voltage < 480 Vrms
80
400
60
350
40
300
20
250 0
900 1400 1900 2400
Speed, RPM
Material
Slide 4
Patent Pending
Voltage
kW Power
Wind Generator Goal
Power Output and Machine Efficiency
120
99%
100
97%
95% 80
Target Efficiency
93%
60
Target Power
91%
40
89%
20
87%
85% 0
900 1400 1900 2400
Speed, RPM
Material
Slide 5
Patent Pending
Percent
kW Power
Axial Airgap Stator:
Example with 12 slots
" One stator shown
" Single wound
amorphous metal
ribbon, followed by
slot cutting
Material Maxwell 3D Magnetostatic
Slide 6
Patent Pending
Stator shown with Phase Coils
" 0.5 slots/phase/pole
C
" Discrete coils
B
A
" Wired A-B-C-A-B-C
B A
C
Material Maxwell 3D Magnetostatic
Slide 7
Patent Pending
Axial-Gap Rotor and Shaft: 8 Poles
" Surface magnets
(thru rotor)
" North red
" South blue
" Shaft and rotor
shown for clarity
Material Maxwell 3D Magnetostatic
Slide 8
Patent Pending
Complete Axial-Gap Machine: 12 Slots
" One rotor assembly
" Two stator assemblies
" Housing not shown
Maxwell 3D Magnetostatic
Material
Slide 9
Patent Pending
Minimum Machine for EM Analysis
" Shaft and disk not
needed for analysis
C
" Actual airgap 2.5 mm
B
A
Maxwell 3D Magnetostatic
Material
Slide 10
Patent Pending
Boundary and Planar Entities: 12 Slots
" Master-slave boundaries
" Current sources (not
shown)
" Analysis surfaces;
orthogonal grid
" Tangent/normal
boundaries
Maxwell 3D Magnetostatic
Material
Slide 11
Patent Pending
Actual Sized Machine to meet
Project Specifications
" 466 cm diameter
" 13 cm axial length
" 72 Slots
" 24 Pole Pairs
Maxwell 3D Magnetostatic
Material
Slide 12
Patent Pending
Maxwell 3D Macro
" 1200 lines main code; 400 lines post processor code
" Performs following:
" Allows direct change to all parameters
" Draws geometry
" Assigns materials
" Assigns boundaries
" Defines solver options
" Runs solver
" Runs post processor macro
" Writes inputs/outputs and writes to a .txt file
" Iterates all of the above, on any variable
Material  Homegrown Optimetrics
Slide 13
Patent Pending
Variation in Flux Density Inside Coils
1
Analysis for 1/6
0.8
of synchronous
0.6
cycle, i.e. 1/6 of
0.4
pole-pair angle.
0.2
A phase
0
B phase
1 2 3 4 5 6 7 8 C phase
Observation of
-0.2
symmetry
-0.4
concludes that -0.6
-0.8
this is all the
-1
analysis needed.
Rotor Position
Material
Slide 14
Patent Pending
Tesla
 Assembled Variation in Flux Density
1
0.8
" Assembly of
0.6
synchronous
0.4
cycle from 1/6
0.2
A phase
analysis
0
B phase
C phase
-0.2
" Makes macro
-0.4
code much
-0.6
faster and much
-0.8
easier to write -1
Rotor Position
Material
Slide 15
Patent Pending
Tesla
1
7
13
19
25
31
37
43
49
55
Results from Macro
" Cogging
" Ripple
" Flux in core and backiron
" Flux variation in magnet  demagnetization potential
" Axial Forces
" Limited by your code
Material
Slide 16
Patent Pending
On to the Solution
" Need&
" Constant Voltage plus
" Increasing Speed plus
" Increasing Power plus
" Permanent magnet equals
" & .
" Not possible (?)
Material
Slide 17
Patent Pending
Stators In-line
Standard stator
arrangement: Both
stators are
physically in-line,
causing series
connected voltage
to add to 2X single-
side voltage.
Maxwell 3D Magnetostatic
Material
Slide 18
Patent Pending
Stator Shifting: Method of EMF Control by
Relative Rotation about Z-axis
Upper stator section is kept
fixed relative to the rotation
about z-axis of the lower
section.
Previously in-phase coils
are taken out of phase.
Series connection causes
additive resulting sine-
wave voltage.
Maxwell 3D Magnetostatic
Material
Slide 19
Patent Pending
Stator Movement: Method of EMF Control by
Relative Rotation
Amount of relative
rotation &
never greater than &
1 pole pitch; in this
example 1 pole pitch
~30 mm.
Maxwell 3D Magnetostatic
Material
Slide 20
Patent Pending
How much movement?
" 1 Pole Pitch = 7.5 degrees
" 1 Pole Pitch ~ 30mm circumferentially
" 1 Slot Pitch = 2/3 Pole Pitch
Material
Slide 21
Patent Pending
Stators Shifted by 25% Pole Pitch with Serial
Addition of Waveforms
2
1.5
1
" No load Stator fixed
0.5
Stator shift 25%
0
Series stators
" THD=2%
-0.5
Best Fit Series
-1
-1.5
-2
Rotor Position
Material
Slide 22
Patent Pending
Tesla
Stators Shifted by 25% Pole Pitch with Serial
Addition of Waveforms
2
1.5
1
Stator fixed
" Rated load
0.5
Stator shift 25%
0
Series stators
" THD=4%
-0.5
Best Fit Series
-1
-1.5
-2
Rotor Position
Material
Slide 23
Patent Pending
Tesla
Stators Shifted by 66% Pole Pitch with Serial
Addition of Waveforms
2
1.5
1
Stator fixed
" No load
0.5
Stator shift 66%
0
Series stators
" THD=7%
-0.5
Best Fit Series
-1
-1.5
-2
Rotor Position
Material
Slide 24
Patent Pending
Tesla
Stators Shifted by 66% Pole Pitch with Serial
Addition of Waveforms
2
1.5
1
Stator fixed
" Rated load
0.5
Stator shift 66%
0
Series stators
" THD=20%
-0.5
Best Fit Series
-1
-1.5
-2
Rotor Position
Material
Slide 25
Patent Pending
Tesla
Stators Shifted by 66% Pole Pitch with Serial
Line-Line Waveform
2
1.5
1
" Rated load Phase A
0.5
Phase B
0
Line A-B
" THD=6%
-0.5
Best Fit
-1
-1.5
-2
Rotor Position
Material
Slide 26
Patent Pending
Tesla
How is this all useful?
" Find a machine solution, passive rectification using
basic phasor diagrams and algebra
" Solve at lowest speed, 0% shift
" Solve at increasing speed, while increasing the stator
shift to keep terminal voltage near constant
" Solution: 73% pole pitch shift needed = 22 mm
movement circumferentially
Material
Slide 27
Patent Pending
Results Voltage vs. Target Voltage
600
550
500
V @ max power
450 V @ min power
target V nominal
400
350
300
900 1400 1900 2400
Speed, RPM
Material
Slide 28
Patent Pending
Voltage
Results Power vs. Target Power
Voltage would be exceeded
So power cannot be maintained
600 120
550 100
target V nominal
500 80
Target Power
450 60
max power
400 40
min power
350 20
300 0
900 1400 1900 2400
Speed, RPM
Material
Slide 29
Patent Pending
Voltage
kW Power
Results Efficiency vs. Target Efficiency
Voltage would be exceeded
So current must increase
99%
97%
95%
Eff @ max power
93%
Eff @ min power
91%
Target Efficiency
89%
87%
85%
900 1400 1900 2400
Speed, RPM
Material
Slide 30
Patent Pending
Percent
Resulting needed Stator Movement
Voltage would be exceeded
25.0
20.0
circum movement
15.0
for max power
circum movement
10.0
for min power
Ref:
5.0
30 mm=pole pitch
20 mm=slot pitch
0.0
0 1000 2000 3000
Speed, RPM
Material
Slide 31
Patent Pending
mm
Speed and Power vs. Stator Position
Voltage would be exceeded
3000 120
2500 100
2000 80
spd @ max power
spd @ min power
1500 60
max power
min power
1000 40
500 20
0 0
0.0 10.0 20.0 30.0
movement, mm
Material
Slide 32
Patent Pending
Power, kW
speed, RPM
Speed and Voltage vs. Stator Position
Voltage would be exceeded
3000 500
450
2500
400
350
2000
spd @ max power
300
spd @ min power
1500 250
V @ max power
200
V @ min power
1000
150
100
500
50
0 0
0.0 10.0 20.0 30.0
movement, mm
Material
Slide 33
Patent Pending
Voltage
speed, RPM
Other items of interest:
Flux Density in Backiron
1.5
1
Discontinuity is
0.5
not real, it s a
no load B in
backiron
function of
0
load B in backiron
solver accuracy
-0.5
-1
-1.5
Rotor Position
Material
Slide 34
Patent Pending
Tesla
Cogging Controlled via 3D Optimized
Magnet Spacing
Typical approach to
design minimal
cogging into
machine is via 3D
analysis and
variation of magnet
spacing.
Material Maxwell 3D Magnetostatic
Slide 35
Patent Pending
Stator Shifting and Effect on Cogging
Pole Pitch 0% - Slot Pitch 0%
Pole Pitch 25% - Slot Pitch 38%
Pole Pitch 33% - Slot Pitch 50%
Pole Pitch 40% - Slot Pitch 60%
Pole Pitch 67% - Slot Pitch 100%
8
6
4
2
0
0 2 4 6 8 10 12 14 16 18
-2
-4
-6
-8
Rotor Position
Material
Slide 36
Patent Pending
N-m
Unfortunately, Axial Forces Increase with
amount of Stator Shift
6000
5000
4000
3000
2000
1000
0
0% 10% 20% 30% 40% 50% 60% 70%
Pole Pitch Percent
Material
Slide 37
Patent Pending
Axial Force, N
No Load;
Review Flux Density in Magnet Grid
1.2
1.1
Leading OR
1
Central OR
0.9
Trailing OR
0.8
Leading R
0.7
Central R
0.6
Trailing R
0.5
Leading IR
0.4
Central IR
0 5 10 15
Trailing IR
Rotor Position
Material
Slide 38
Patent Pending
Tesla
Rated Load;
Review Flux Density in Magnet Grid
1
Leading OR
0.9
Central OR
0.8
Trailing OR
0.7
Leading R
Central R
0.6
Trailing R
0.5
Leading IR
0.4
Central IR
0 5 10 15
Trailing IR
Rotor Position
Material
Slide 39
Patent Pending
Tesla
3X Rated Load; All current in D-axis
Review Flux Density in Magnet Grid
1.2
1.1
Leading OR
1
Central OR
0.9
Trailing OR
0.8
Leading R
0.7
Central R
De-magnetization
0.6
Trailing R
is a real concern! 0.5
Leading IR
0.4
Central IR
0 5 10 15
Trailing IR
Rotor Position
Material
Slide 40
Patent Pending
Tesla
A Plug for Maxwell 2D: AC Ohmic Loss
" 2D transient analysis
" Determines AC losses
" Due to proximity effects
" +/-20% error vs. test
Material
Slide 41 Maxwell 2D Transient Solver
Patent Pending
Solution Results
Power = 98kW at 2000 rpm
Power follows rotor-speed3 for 2X speed range
Voltage stays within 410  480 Vrms range
Efficiency > 94%
Harmonic content increases (changes) with Stator
Shift
Axial force increases with Stator Shift
Material
Slide 42
Patent Pending