Design of a Super High-Speed Permanent
Magnet Synchronous Motor
Yang Hu and Prof. Thomas Wu
Center for Advanced Electric Machinery
University of Central Florida
Orlando, FL 32816
Outline







Introduction
Preliminary Sizing
Windings and Slots
Design
Rotor and Airgap Design
Optimization and
Simulation
Control and Drive
Conclusion
Super High-Speed Motors

Applications require high-speed drives, such as centrifugal
compressors, vacuum pumps, flywheel energy storage
systems, friction welding units, and machine tools

Increasing speed increases power density.

Development of power electronics makes high speed
electrical machines possible.
Challenges

Super-high speed will
 Increase eddy current loss
 Increase bearing loss of ball bearings
 Increase mechanical stress in the rotor
 Increase switching loss due to high frequency
 Increase difficulties in control
Design Specifications
Value
Performance Specifications
Ouput Power (kW)
Rated Voltage (V)
Mechanical speed (RPM)
Number of Slots in Stator
Number of Poles
3.0
50
150,000
24
2
Material Considerations

Permanent magnet



Winding


Nd-Fe-B (neodymium -iron-boron ): the highest energy density, does
well above 135 K.
Sm-Co (samarium cobalt): does quite well at both cryogenic
temperature and higher temperature.
Multi-strand Litz-wire to reduce proximity effect and skin effect.
Stator


Laminated low loss silicon steel.
Thin laminations are required to reduce eddy current loss.
Stator Volume and Size (1)
D2L
τ
Typically
= V0
τ=
Pout
ωm
V0 = 9 ~ 10 in /(ft ⋅ lb) for 10hp or less (air cooled)
3
V0 = 5 ~ 6 in /(ft ⋅ lb) for 10hp or more (water cooled)
3
The unit for D and L is inch.
For initial design, we can have D=L, the stator bore (inner) diameter
will be
1
Destimated ≈ (τV0 ) 3
Stator Volume and Size (2)
Stator Core diameter (outer diameter):
D0 = 1.6 D
Stator active region length:
L=
τV0
D2
Windings Design

Number of effective turns per coil
Nc =
1.1Vφrated C
2 2πf e qk w Bg , pk Dl
Slot Design

Rated current
I Arated =

d sπ Drs
Js
2Nc Ns
𝐽𝑠 determines the slot area.
Rotor and Airgap Design


Super high speed requires
strong mechanical
strength
A sleeve structure is
favorable

Airgap design
 Magnetic circuit equation
0 ⇒ g eff BmR + µ0 H mlm =
0
g eff H g + H mlm =


By properly chossing the
workpoint, and use the
geometry fact that
𝐷 = 2(𝑙𝑚 + 𝑔)
We can get
g eff =
D µ0 H m
2 Br + 2 µ0 H m
Airgap Design

Actual airgap can be found using Carter’s coefficient
g = g eff / kc

Carter’s coefficient is defined as
τ s (5 g + bs )
kc =
τ s (5 g + bs ) − bs2
Rotor Sizing Considerations

High speed will put very high mechanical stress on the
shaft and rotor
Dr max
vr
=
1.2nmπ
Inches per minute
Revolutions per minute

For steel alloys, pick 𝑣𝑟 = 35000
Loss Analysis


Accurate estimation of
loss is very important in
the design
Losses are estimated
based on analytical
analyses and numerical
simulations



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Copper loss
2
 I R Loss
 Eddy Current Loss
Core loss
Rotor Loss
Windage Loss
Motor Losses (1)

Copper loss
 Typical
PCu = I 2 R

Eddy current loss
 Electrical phenomenon such as skin and proximity
effect
PE = B P2 ω 2 d 2 / 32 ρ


Using Liz wires can significantly reduce the loss
Reducing peak flux density of airgap can also reduce
eddy current loss
Eddy Current – Solid Wire
I =∫
S
J
2
I = 582 A
Solid Copper, diameter=1.5 mm
ds
Eddy Current – Litz-wire
I = 37 A
75 strands @ AWG 36 (0.125 mm)
Motor Losses (2)

Stator Core Loss
 Hysteresis loss
 Eddy Current loss
PIron = κ h B f
n

α
+ κ c ( Bf ) + κ e ( Bf )
Mechanical loss
 Windage loss
PWR = Cd πρ airω 3r 4 L

Bearing loss
2
3/ 2
Shaft Strength


Shaft material was chosen to be high-stress Titanium,
which has yield strength of about 1400 MPa and low
coefficient of thermal expansion.
Low density of Titanium is also an advantage to increase
critical speed of the shaft.
Optimization and Simulation (1)

Rmxprt modeling and optimization
Stator
ANSOFT
100.00
Curve Info
Efficiency
Efficiency (%)
80.00
60.00
40.00
20.00
0.00
0.00
20.00
40.00
60.00
80.00
100.00
120.00
Torque Angle +33 (elec. degrees)
140.00
160.00
Permanent Magnet
Stator: 24 slots
Stator inner diameter: 27 mm
Stator outer diameter: 63.2 mm
Motor length: 27 mm
PM radius: 9 mm
Efficiency vs Torque Angle
180.00
Optimization and Simulation (2)
Cogging torque
ANSOFT
0.00006
Curve Info
Cogging Torque
0.00004
0.00002
Torque (N.m)

0.00000
-0.00002
-0.00004
-0.00006
0.00
125.00
250.00
Air-Gap Position (elec. degrees)
375.00
Induced Voltage at Rated Speed
ANSOFT
50.00
Curve Info
Phase Voltage ea
Line Voltage eab
Voltage (V)
25.00
0.00
-25.00
-50.00
0.00
125.00
250.00
Air-Gap Position (elec. degrees)
375.00
Optimization and Simulation (2)

Maxwell 2D and 3D simulation
Winding Currents
Winding Currents
V3_Final
40.00
ANSOFT
Curve Info
Current(PhaseA)
Setup1 : Transient
Current(PhaseB)
Setup1 : Transient
30.00
Current(PhaseC)
Setup1 : Transient
20.00
Y1 [A]
10.00
0.00
-10.00
-20.00
-30.00
-40.00
0.00
100.00
200.00
300.00
400.00
Time [us]
500.00
600.00
700.00
800.00
Flux Linkage
XY Plot 2
V3_Final
0.0020
ANSOFT
Curve Info
FluxLinkage(PhaseA)
Setup1 : Transient
0.0015
FluxLinkage(PhaseA) [Wb]
0.0010
0.0005
0.0000
-0.0005
-0.0010
-0.0015
-0.0020
0.00
100.00
200.00
300.00
400.00
Time [us]
500.00
600.00
700.00
800.00
Bearing Selection

Contactless bearings
 High cost
 High complexity
 Not suitable for the speed and size in our case

“Super precision” ceramic bearings from SKF
 Diameter: 8mm
 Maximum speed: 220000 rpm
Fabrication in Process
Control and Drive (1)

Control and drive systems are designed for the super high
speed motor
 TI TMS320F28335 microprocessor: Fast ADC and PWM
modules
 Modular design for easier debugging and expandability
 Inverter on aluminium based board for better heat
dissipation
 “NexFET” for less switching loss and better switching
performance
 Control logic circuit separated from main circuit to avoid
EMI
Control and Drive (2)
Conclusion

Provided a design methodology for two-pole
super high-speed PM motor

Designed a 3 kW, 150 krpm motor with efficiency
above 95% from RMXprt

Optimized the design by Maxwell 2D&3D
References
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[2] Lin,S.Lin,, Wu, T. X., Zhou, L., Moslehy, F., Kapat, J., Chow, L., “Modeling and Design of
Super High Speed Permanent Magnet Synchronous Motor (PMSM),” Aerospace and Electronics
Conference, pp. 41-44 ,16-18 July 2008.
[3] Zheng,L. “Design of Super-high Speed Miniaturized Permanent Magnet Synchronous Motor”,
PhD thesis, University of Central Florida, 2005.
[3] Riemer, B., Lessmann, M., Hameyer, K., “Motor Design of a High-Speed Permanent Magnet
Synchronous Machine Rating 100,000 rpm at 10kW,” Energy Conversion Congress and
Exposition (ECCE), 12-16 Sept. 2010.
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[7] Fitzgerald, A. H., Kingsley, C. J., Umans, S. D., Electric Machinery, 6th ed., NY: McGraw-Hill,
2003.
References
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http://www.arnoldmagnetics.com/, 2009.
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IEEE Press Series on Power Engineering, John Wiley and Sons, Inc., 2004.
[12] Hanselman, D. C., Brushless Permanent-Magnet Motor Design, McGraw-Hill, 1994.
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