IEEE Electrification Magazine - December 2017 - 7

components harder makes them smaller and
lighter but may cause higher dissipation, raising
thermal management issues and ultimately
adding weight and volume to the cooling system. A system-level trade to optimize the component-level efficiencies versus system-level
weight and volume is thus required for an electric powertrain. New and less conventional highheat flux cooling systems and materials will
need to be brought out of the laboratory and
matured for flight. Any system with electronic
devices must also deal with EMC, EMI, and lightning strikes. Meeting those requirements has
typically involved bulky and heavy common and
differential modes filters and voltage-transient
suppressors. With the emphasis on minimizing
weight and volume, it is imperative that power
circuit topologies are designed to minimize radiated and conducted emissions to minimize
those filters.
Each of these issues poses an additional challenge when integrating the powertrain with
the airplane. The composite wings or structures
impose thermal and EMI requirements. The
maximum operating temperature of systems
and components must be limited, and heat
must be exhausted by the addition of heat
exchangers and ram air circuits, given that conduction via the skin is no longer an option
unlike with a metal airframe. The integration of
the motor and the propulsor must address the
dynamics of the integrated assembly, including
extreme loading such as during a bird strike or
propeller blade failures. Even snaking heavyduty, high-frequency electrical cables and sensors to where the electric motors are located can
be a challenge in some configurations.
On many fronts, considerable progress is
being made. Wide band-gap semiconductor
devices, such as silicon (Si) carbide and gallium
nitride, are showing performance improvements
over Si devices in the form of higher operating
temperatures, lower losses, better switching, and
smaller die size. These characteristics will allow
the power converter circuits to operate at higher
temperatures, thereby reducing the load on the
thermal management system. The superior
switching capabilities will also result in lower EMI
signatures and smaller filters, reducing the size,
weight, and potentially the cost of motor controllers and other power converters in the system.
NASA and other government agencies have
invested in advanced motor topologies, such
as axial flux switching and Hallbach array

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Table of Contents for the Digital Edition of IEEE Electrification Magazine - December 2017