IEEE Electrification Magazine - December 2017 - 20

The location of the
landing gear for
the electric taxi
gear presents a
severe environment
for the TM.

portion of the motor (the rotor). The
torque production of any motor
depends on the area of this swept
surface between the stator and the
rotor. This torque production-for a
given maximum magnetic flux density in the air gap, as well as a given
circumferential density of ampere
conductors in the stator-is a function of the air gap swept area.
The magnetic flux density is a
function of the magnetic materials
used, specifically, the magnet strength and permeability
of the iron magnetic circuit. The ampere conductor loading depends on the conductor materials used, as well as
the stator winding conductor density, which is a result of
winding techniques. Therefore, motor sizing, for a given
use of materials, depends on the maximum torque that
must be provided. The air gap shear stress (that is, the
tangential force per unit of air gap swept area) for this
motor at the maximum torque condition is 9.77 lb/in2.
The total weight of the TM with the cooling fan is 36 kg.
The motor no-load flux distribution is shown in Figure 13.

TM Controller Integration

Integration of the motor with the
power electronics controller is required
for any electric drive. Specifically,
for electric taxi operation, a certain
amount of phase advance is advantageous for several reasons. It reduces
the maximum current the controller
supplies at maximum torque conditions. Limiting the maximum BEMF at
maximum speed conditions is a power
controller requirement. The limitation
of the maximum BEMF is a function of the maximum
power electronic controller link voltage and the power
semiconductor device voltage ratings. Phase advance
reduces the maximum voltage required to achieve the
maximum speed for the motor. The optimum amount of
phase advance is a function of the maximum required
torque, the duty cycle, and the power electronic controller
component ratings.
Another significant consideration for the motor with
respect to the power electronics controller is the motor
reactance. A high motor reactance is desired to achieve
good power quality. Lower filter weight and minimized
high-frequency losses are achieved with higher motor
reactance. The motor pole number and the amount of
phase advance influence the motor inductance.

Environment

1.4

The location of the landing gear for the electric taxi gear
presents a severe environment for the TM. In addition to
the landing shock and operational vibration mentioned
earlier, runway debris and brake dust present a significant
challenge for a forced-air-cooled motor. Clogging of the
cooling passages poses a difficult problem. Also, significant exposure to moisture and water spray is prevalent.
The electrical components should be sealed and isolated
from any water; this requirement places demands on the
cooling because the motor electrical components must be
totally enclosed to prevent exposure to moisture and
water spray, resulting in a more difficult heat transfer
path. Additionally, electrical connectors must also be
sealed from the environment.

1.2

Thermal

Figure 12. The TM with the integral cooling fan.

2.0
1.8
1.6

1.0
0.8
0.6
0.4
0.2
0.0
°F
Figure 13. The no-load flux plot.

20

I E E E E l e c t r i f i cati o n M a gaz ine / DECEMBER 2017

The thermal performance is critical with respect to the
resulting component temperatures and, therefore, the
life of the electrical components. In addition to the general heat rejection capability of the cooling fan, the dissection of the duty cycle and the resulting heat loss
versus time are also critical. Some items to be considered
include the time at the gate between successive taxi
operations and the time in flight, which benefits from a
low ambient temperature due to altitude. Because of the
impact of runway debris and the potential clogging of
cooling passages, the thermal design of the electrical



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