The Design of High-Speed
High-Power Density Machines
Liping Zheng
Tasks
Design two kinds of motors (1kW and
3kW) using sizing equations combined
with FEM simulation and calculate the
machine parameters and performance.
Consider both axial flux and radial flux
structure to compare the performance.
To design radial flux motor, use the same
rotor and stator diameter for two motors to
reduce the manufacture cost.
Sizing Equations
Four types of sizing equations are available
which link the motor torque to the motor size.
T   0 D03 L
T   0D02.5 L
T   r Dr2 L
T   rDr2.5 L
3
0
The D L Sizing Equation
Provides many relations between physical
dimensions and density-like quantities and
is well adaptive to produce a design that is
geometrically compatible from the start.
Electrical Constraints
Current density
J1  2m1N1I1 /( S1 Acu )
Induced voltage
E ph  (1 / 2 )2fN1kw
Output power
Pout    m1VI1 cos
Output torque
T  0 D L
3
0
0  ( / 8 2 ) Bg J1 f 0 ( ) ku
Maximizing the Coefficient
Specify current density: J1=10000A/in
flux density at stator: Bt=1.8T, Bc=1.4T
flux density at airgap : Bg=0.8T
Get the maximum value of f 0 ( )
  Di / D0
D L  T / 0
3
0
Select the number of slots and the winding
structure to meet the induced voltage and
input current requirement.
Rotor Design
Design the rotor structure using magnetic
equivalent circuit method.
 4 poles.
 High energy PM: NdFeB (Neodymium-iron-boron).
 Design airgap length.
 Design permanent magnetic structure.
FEM Analysis
Calculate flux density in airgap, rotor and
stator core.
Calculate back emf and inductance.
Calculate torque and torque ripple.
Calculate losses.
Performance Analysis
All performance must meet the required
specification.
Thermal consideration.
Tradeoff may be necessary for the best
performance.
Estimated Results Using Sizing Equations
Estimated Design Size for 40Krpm Motor
(Case not included)
Output Power (W)
Radial Flux Stator Outer Diameter (in)
Motor
Length (in)
1000
1.95
0.608
3000
1.95
1.823
Axial Flux
Motor
1.442
1.406
1.898
2.217
Rotor Outer Diameter (in)
Length (in)
Axial flux motor size parameters are calculated according to the same
airgap surface and stator volume as those of the radial flux motor.