IEEE Electrification - June 2022 - 55

discharge voltage, which needs to be
designed around the source voltage
and coil-insulation level.
Technology Trends
Cryogen-Free Cooling System
With a Rotor-Integrated
Cryocooler
A rotor-mounted cryocooler and
conduction cooling can overcome
some of the existing challenges in an
external cryogenic system and the
reliability concerns associated with
cryogen-transfer couplings. Several
ongoing projects have attempted to
achieve this, including the High Efficiency
Megawatt Motor by NASA, using a cryocooler that
can lift a 50-W heat load from a 50- to a 300-K ambient
temperature. With the existing technology, maintaining a
temperature below 20 K would require a two-stage cryocooler.
A two-stage cryocooler introduces significant challenges
to a rotating structure due to the imbalance, in
addition to the large size and weight. Current developments,
including those by SunPower, are attempting to
reach a no-load temperature of 20 K while providing a 10-W
heat-load lift at 30 K.
Significant improvements are needed in areas involvSignificant
improvements
are
needed in areas
involving the design
of coil assembly
and suspension to
achieve conduction
cooling from a rotormounted
cryocooler.
coupled to a propulsor is displayed
in Figure 15. The motor employs a
large number of high-strength nylon
fibers that connect the ambient
shaft and cold coil assembly. The
fibers are connected using an angle
on both the axial and circumferential
directions by applying a loading
on it. The rotor is designed such that
the coil assembly will shrink more
relative to the motor frame, and the
loading on fibers will increase. When
the machine is loaded with torque,
half of the fibers will experience an
increased tension, while the tension
in the remaining half is reduced. The
suspension system is designed to
withstand the peak torque while also maintaining structural
integrity at high-speed rotations.
ing the design of coil assembly and suspension to
achieve conduction cooling from a rotor-mounted cryocooler.
A proposed partial SC machine design directly
Integrated Propulsors
An integrated modeling approach is a design procedure
of electrified aircraft propulsor systems where the motor
and propulsor are designed simultaneously to achieve
optimal performance. The design framework can be further
extended to modeling the distributed boundary-layer
ingesting the fan module and electric motors together.
Using an all-at-once simultaneous optimization approach
eliminates external design iterations between modules,
and the framework provides sensitivities to design parameters
as a part of the optimization problem solution. This
Ambient AirCore
Stator
Sub-20 K Cooler
Embedded Within
a Rotor Shaft
SC
Assembly
Tensioned
Fiber-Suspension System
Figure 15. An integrated propulsor with the proposed high-power-density partially SC motor.
IEEE Electrification Magazine / JUNE 2022
55

IEEE Electrification - June 2022

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