Design of an Outer-rotor Brushless Dc Motor for Control Moment Gyroscope Applications
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Transcript of Design of an Outer-rotor Brushless Dc Motor for Control Moment Gyroscope Applications
DESIGN OF AN OUTER-ROTOR
BRUSHLESS DC MOTOR FOR CONTROL
MOMENT GYROSCOPE APPLICATIONS
MIDDLE EAST TECHNICAL UNIVERSITY
ELECTRICAL AND ELECTRONICS
ENGINEERING DEPARTMENT
MS THESIS PRESENTATION
06/02/2015
Tasnif Dışı
OUTLINE
ACTUATING SYSTEMS IN LEO SATELLITES AND
TYPICAL ELECTRICAL MOTORS
PROBLEM DEFINITON AND MOTOR SELECTION
DESIGN PROCEDURE
ANALYTICAL RESULTS
FINITE ELEMENT METHOD RESULTS
CONCLUSION AND FUTURE WORK
2
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REVIEW OF THE THESIS
AIM: Replacing current BLDC electric motor
with an optimum motor topology
METHOD: Classical Electrical machine
design procedure
PROBLEM: Mass, volume and efficiency
3
2
ACTUATING SYSTEMS IN LEO
SATELLITES AND TYPICAL
ELECTRICAL MOTORS
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LOW-EARTH ORBIT SATELLITES
LEO satellites are used for taking images of the
Earth ground.
In order to take proper images, these systems must have a
sensitive attitude control system.
5
5
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ACTUATING SYSTEMS
Three main actuating systems in LEO satellites
o Reaction wheels
o Momentum wheels
o Control moment gyroscopes (CMG)
Control Moment Gyroscope 6
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CONTROL MOMENT GYROSCOPES
Two motors are used
o Wheel motor
o Gimbal motor
Motor rotation axes are
perpendicular to each
other
Necessary torque is
produced along the third
axis
Design of the motor for
wheel axis is investigated7
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MOTOR TYPES FOR DIFFERENT
APPLICATIONS
8
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BLDC MOTORS
Excited with balanced three-phase windings
Coils wound in stator
Rotor with PM
Torque produced due to interaction of coils and
magnetic field
9
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BLDC MOTORS – CLASSIFICATION (1)
Permanent Magnet structure
Surface-mounted Interior-mounted Buried magnet
10
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BLDC MOTORS – CLASSIFICATION (2)
Flux Direction
Radial Flux Axial Flux
11
Stator
Winding
Rotor
Permanent Magnet
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BLDC MOTORS – CLASSIFICATION (3)
Excitations
Squarewave Sinusoidal
12
0 5 10 15 20 25 30 35 40-1
-0.5
0
0.5
1
Time (s)
Curr
ent
(A)
Typical Current Waveforms in Sinusoidal Excitation
Phase A
Phase B
Phase C
0 5 10 15 20 25 30 35 40-1
-0.5
0
0.5
1
Time (s)
Curr
ent
(A)
Typical Current Waveforms in Squarewave Excitation
Phase A
Phase B
Phase C
13
PROBLEM DEFINITION AND MOTOR
SELECTION
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PROBLEMS IN EXISTING SYSTEM
2 main problems arise:
Compatibility issues
• Over-safe and over-designed motors for CMG’s
Sausage-type commercial designs
• Low inertia contribution to wheel, high inertia
contribution to gimbal
• External coupling
• 4 Bearings – Balance problems
14
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FUNCTIONAL REQUIREMENTS
15
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TORQUE – SPEED CHARACTERISTICS
16
Torque-speed characteristics is taken from Yılmaz’s thesis in
order to provide a comparison.
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FUNDAMENTAL CONCEPTS
Magnetic circuit
Puts forward the characteristics of the motor
Shows the operating point
Can be best characterized by the concentration
factor and permeance coefficient
17
Change the magnet or the air gap so that desired air gap flux
density is obtained
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MATERIAL SELECTION -
FERROMAGNETIC MATERIALS
Ferromagnetic Materials;
Material used in construction of stator and rotor
Characterized by its B-H curve
Loss characteristics are crucial
• Hysteresis losses
• Eddy current losses
18
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SELECTED FERROMAGNETIC
MATERIAL
COGENT Power No.12
19
Wide operating temperatures up to 230 °C
Operate at high frequencies
Manufacturable in thin steels
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MATERIAL SELECTION
Permanent magnets (PM)
Characterized by demagnetization curve
Three main magnetic parameters:
• Remenant flux density
• Coercivity
• Recoil Relative Permeability
Selection criteria:
• Wide operating temperature
• Resistance against corrosion
• Radiation sensitivity20
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MATERIAL SELECTION - PM
VACOMAX 225 HR (Samarium - Cobalt)
21
22
DESIGN PROCEDURE
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OUTER-ROTOR BLDC MOTOR
23
Operate at constant speed : 10000 rpm
Steady – state torque: 32 mN-m
Electrical loading :6000 A-t/m
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OUTER-ROTOR BLDC MOTOR
24
Main Topologies
Sinusoidal Squarewave
2-pole 2-pole
6-pole 6-pole
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DESIGN PROCEDURE
25
TORQUE EQUATION DEPENDING ON THE EXCITATION IN TERMS OF MAIN SIZES
OPTIMUM MOTOR DIMENSIONS
WINDING DESIGN
EQUIVALENT CIRCUIT PARAMETERS
PERFORMANCE EVALUATION
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BASIC EQUATIONS
26
Torque expressions obtained for design
process, for both RF and AF topologies
AF motor torque expression shown for
completeness
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DESIGN PROCEDURE
27
Torque equation is taken depending on
excitation
Electrical loading is defined
Three main unknowns: ℎ𝑠 slot depth, 𝐷𝑖 inner
diameter and L axial length.
𝑅𝐷𝐿 =𝐷𝑖
𝐿ratio is taken as a parameter
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DESIGN PROCEDURE
28
𝑅𝐷𝐿 =𝐷𝑖𝐿
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DESIGN OUTPUTS
Script codes are prepared in MATLAB
Ratio changed from 0.7 to 20 with uniform steps
Parameters are extracted
Changes depending on pole numbers and
excitations are stated
29
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COMPARISONS BETWEEN POLE
NUMBERS - VOLUME
30
0 2 4 6 8 10 12 14 16 18 200
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1x 10
-4
Ratio
Volu
me (
m3)
Sine 2-pole
Sine 6-pole
0 2 4 6 8 10 12 14 16 18 201
2
3
4
5
6
7x 10
-5
RatioV
olu
me (
m3)
Square 2-pole
Square 6-pole
Both 6-pole designs have smaller volume
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COMPARISONS BETWEEN POLE
NUMBERS - MASS
31
Both 6-pole designs have smaller mass
0 2 4 6 8 10 12 14 16 18 200
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Ratio
Mass (
kg)
Sine 2-pole
Sine 6-pole
0 2 4 6 8 10 12 14 16 18 200.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
Ratio
Mass (
kg)
Square 2-pole
Square 6-pole
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COMPARISONS BETWEEN POLE
NUMBERS - INERTIA
32
Both 6-pole designs have smaller inertia
0 2 4 6 8 10 12 14 16 18 200
0.5
1
1.5
2
2.5
3
3.5x 10
-4
Ratio
Inert
ia (
kg.m
2)
Sine 2-pole
Sine 6-pole
0 2 4 6 8 10 12 14 16 18 200
1
x 10-4
RatioIn
ert
ia (
kg.m
2)
Square 2-pole
Square 6-pole
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COMPARISONS BETWEEN POLE
NUMBERS - EFFICIENCY
33
Both 6-pole designs show greater efficiency
characterictics
0 2 4 6 8 10 12 14 16 18 200.89
0.9
0.91
0.92
0.93
0.94
0.95
Ratio
Eff
icie
ncy
Sine 2-pole
Sine 6-pole
0 2 4 6 8 10 12 14 16 18 200.88
0.89
0.9
0.91
0.92
0.93
0.94
0.95
Ratio
Eff
icie
ncy
Square 2-pole
Square 6-pole
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COMPARISONS BETWEEN
EXCITATIONS - VOLUME
34
Sinusoidal larger volume in 2-pole, squarewave larger
volume in 6-pole
0 2 4 6 8 10 12 14 16 18 202
3
4
5
6
7
8
9
10x 10
-5
Ratio
Volu
me (
m3)
Sine 2-pole
Square 2-pole
0 2 4 6 8 10 12 14 16 18 200.8
1
1.2
1.4
1.6
1.8
2
2.2
2.4
2.6x 10
-5
RatioV
olu
me (
m3)
Sine 6-pole
Square 6-pole
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COMPARISONS BETWEEN
EXCITATIONS - MASS
35
Sinusoidal heavier in mass in 2-pole, squarewave heavier
in mass in 6-pole
0 2 4 6 8 10 12 14 16 18 20
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0.55
0.6
0.65
Ratio
Mass (
kg)
Sine 2-pole
Square 2-pole
0 2 4 6 8 10 12 14 16 18 200.04
0.05
0.06
0.07
0.08
0.09
0.1
0.11
0.12
0.13
0.14
RatioM
ass (
kg)
Sine 6-pole
Square 6-pole
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COMPARISONS BETWEEN
EXCITATIONS - INERTIA
36
Sinusoidal larger inertia in 2-pole, squarewave larger inertia in 6-pole
0 2 4 6 8 10 12 14 16 18 201.4
1.6
1.8
2
2.2
2.4
2.6
2.8
3
3.2x 10
-4
Ratio
Inert
ia (
kg.m
2)
Sine 2-pole
Square 2-pole
0 2 4 6 8 10 12 14 16 18 201
1.5
2
2.5
3
3.5
4
4.5x 10
-5
RatioIn
ert
ia (
kg.m
2)
Sine 6-pole
Square 6-pole
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COMPARISONS BETWEEN
EXCITATIONS - EFFICIENCY
37
Sine is efficient in 2-pole, square is efficient in 6-pole
0 2 4 6 8 10 12 14 16 18 200.88
0.89
0.9
0.91
0.92
0.93
0.94
Ratio
Effic
iency
Sine 2-pole
Square 2-pole
0 2 4 6 8 10 12 14 16 18 200.89
0.9
0.91
0.92
0.93
0.94
0.95
Ratio
Effic
iency
Sine 6-pole
Square 6-pole
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COMMON FINDINGS
As the ratio increases;
Reduce in mass, volume and inertia
Reduce in inertia contribution
Increase in phase resistance and phase
inductance
Almost constant RMS current
Increase in electrical loading38
39
ANALYTICAL RESULTS
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ANALYTICAL RESULTS
Designs are chosen according to the ratio at which
both magnetic loading and electrical loading
become 0.43T, and 6000 A-t/m, respectively, for
ease of performance comparison
Performance parameters are presented.
40
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ANALYTICAL RESULTS
41
0 2 4 6 8 10 12 14 16 18 202000
4000
6000
8000
10000
12000
14000
Ratio (RDL
)
q (
A-t
/m)
sin 2-pole
sin 6-pole
square 2-pole
square 6-pole
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ANALYTICAL RESULTS
42
R_DL 17 0,95 10 1,5
D_i (mm) 57,39 22 47,33 25,03
L (mm) 3,38 23,16 4,73 16,69
D_o (mm) 107,07 32,62 85,97 39,33
g (mm) 0,75 0,75 0,75 0,75
h_s (mm) 4,66 5,75 4,70 5,50
l_m (mm) 2,55 1,81 2,10 1,88
h_1 (mm) 1,00 1,00 1,00 1,00
h_2 (mm) 1 1 1 1
w_1 (mm) 0,75 0,75 0,75 0,75
w_2 (mm) 4,20 0,92 3,31 1,22
h_sbc (mm) 21,54 2,75 16,46 4,52
t_1 (mm) 9,27 3,09 7,51 3,62
t_2 (mm) 4,19 0,92 3,31 1,22
J (g.m 2̂) 0,29 0,01 0,17 0,02
V (cm 3̂) 30,39 19,36 27,47 20,27
M_total (g) 210,33 97,11 186,12 113,22
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ANALYTICAL RESULTS –
SINE 2-POLE
43
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ANALYTICAL RESULTS –
SINE 6-POLE
44
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ANALYTICAL RESULTS –
SQUARE 2-POLE
45
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ANALYTICAL RESULTS –
SQUARE 6-POLE
46
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ANALYTICAL RESULTS –
OVERALL PERFORMANCE
47
Parameter Sine 2-pole Sine 6-pole Square2-pole Square6-pole
N_phase 68 26 56 30
R_ph (mOhm) 327,45 82,73 238,38 80,31
L_g (uH) 142,25 181,02 113,31 191,20
L_end (uH) 36,07 1,28 41,22 2,08
L_leak (uH) 110,27 242,58 114,38 193,52
L_ph (uH) 288,58 424,88 268,92 386,79
I_rms (A) 2,65 2,63 2,62 2,63
q (A.t/m) 5993,90 5945,20 5929,94 6010,52
Efficiency 90,32 93,40 90,30 93,39
48
FINITE-ELEMENT METHOD RESULTS
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SIMULATIONS
Simulations are carried out in ANSYS MAXWELL
Meshes are automatically assigned by MAXWELL
Boundaries are assigned so that no flux out of motor.
Models have been run in transient manner
All materials are assigned considering nonlinear
characteristics (B-H curves etc.)
Results are presented based on steady-state
characteristics 49
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SINUSOIDAL 2-POLE
50
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SINUSOIDAL 6-POLE
51
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SQUAREWAVE 2-POLE
52
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SQUAREWAVE 6-POLE
53
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FEM RESULTS - OVERALL
54
Sine 2-pole Sine 6-pole Square2-pole Square6-pole
ToothFlux
Density1.5 T 1.5 T 1.7 T 1.4 T
Torque 32 mN-m 42 mN-m 42 mN-m 31.8 mN-m
Winding Current 4.25 A 2.06 A 2.94 A 2.00 A
InducedVoltage 17 V 16.3 V 13 V 15 V
Torque Ripple 20 mN-m 20 mN-m 5 mN-m 25 mN-m
Tasnif Dışı
COMPARISON WITH AF EQUIVALENT
55
AF 6-pole BLDC Motor designed by Yılmaz.
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COMPARISON WITH AF EQUIVALENT
56
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FEM RESULTS - OVERALL
57
Sine 2-pole Sine 6-pole Square2-pole Square6-pole AF 6-pole
ToothFlux
Density1.5 T 1.5 T 1.7 T 1.4 T 1.4 T
Torque 32 mN-m 42 mN-m 42 mN-m 31.8 mN-m 32 mN-m
Winding Current 4.25 A 2.06 A 2.94 A 2.00 A 2.00 A
InducedVoltage 17 V 16.3 V 13 V 15 V 15 V
Torque Ripple 20 mN-m 20 mN-m 5 mN-m 25 mN-m 13 mN-m
58
CONCLUSION AND FUTURE WORK
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OVERALL RESULTS
Mass Results
59
Sine 2-pole Sine 6-pole Square 2-pole Square 6-pole0
0.05
0.1
0.15
0.2
0.25
Mass (
kg)
(*) AF design is 0.1 kg
Tasnif Dışı
OVERALL RESULTS
Torque/ Mass Results
60
Sine 2-pole Sine 6-pole Square 2-pole Square 6-pole0
0.1
0.2
0.3
0.4
0.5
0.6
0.7T
orq
ue (
N.m
/kg)
Tasnif Dışı
OVERALL RESULTS
Volume
61
Sine 2-pole Sine 6-pole Square 2-pole Square 6-pole0
0.5
1
1.5
2
2.5
3
3.5x 10
-5V
olu
me (
m3)
(*) AF design is 1.89e-5 m^2
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OVERALL RESULTS
Torque/Volume Results
62
Sine 2-pole Sine 6-pole Square 2-pole Square 6-pole0
500
1000
1500
2000
2500
3000
Torq
ue (
N.m
/m3)
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OVERALL RESULTS
Efficiency Results
63Sine 2-pole Sine 6-pole Square 2-pole Square 6-pole
0
10
20
30
40
50
60
70
80
90
100
Eff
icie
ncy in %
(*) AF design is 0.92
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OVERALL RESULTS
Inertia results
64
Sine 2-pole Sine 6-pole Square 2-pole Square 6-pole0
1
2
x 10-4
Inert
ia (
kg.m
2)
(*) AF design is 0.3e-4 kg-m^2
Tasnif Dışı
OVERALL RESULTS
Inertia contributon results
65
Sine 2-pole Sine 6-pole Square 2-pole Square 6-pole0
10
20
30
40
50
60
70In
ert
ia C
ontr
ibution in %
(*) AF design is about 5.6%
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FUTURE WORK
Temperature characteristics and cooling techniques
must be studied
Proper integration to the system must be studied
Mechanical considerations must be taken into
account
Studies can be carried out in order to further
minimize the torque ripples
66
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THANK YOU FOR LISTENING
QUESTIONS
67
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COMMERCIAL
CONTROL MOMENT GYROSCOPE
68
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SIMULATIONS
72