Aerospace & Defense Technology - October 2022 - 15

eVTOL Technology
Figure 2. eVTOL designers can benefit from working with manufacturers who can design, customize, manufacture, and implement all the components along the wire.
include: cable attachment (termination
technology), contact interfaces (crimps
and contact types), and contact materials
- as well as applying optimized
high-voltage contactors and relays.
Thermal sensing, thermal system protection,
and thermal modeling can also
be used to avoid hot spots and design
an HV path that can carry short-time
dynamic loads.
Power-Management Challenges
(9) Handling power management
- Designers need to use high-frequency
switching to enable rapid bus transfer
in the event of power loss.
Variable frequency AC power is used
for typical aircraft loads. But fixed-frequency
400 Hz AC power enables
smaller and lighter transformers and
motors - and faster transfer of bus
power if power is lost - all of which is
desirable for eVTOL applications. Used
throughout the aviation and aerospace
industry, HARTMAN power switching
technology from TE offers 400 Hz AC
contactors. They are rated up to 500
A, and offer lightweight high-performance
DC contactors, up to 1,000A.
Hermetically sealed enclosures provide
protection in severe environments.
Multiple main contact configurations
and auxiliary contact configurations
are available. Additionally, modular
power distribution units or backAerospace
& Defense Technology, October 2022
plane-type panels can be customized
for fixed-wing aircraft and rotorcraft
applications.
(10) Using hybrid electromechanical
and solid-state power switching technologies
- Designers need to evaluate
advantages and disadvantages of both.
Solid-state relays (SSRs) offer silent
operation, low electrical interference,
functionality over a wide range of
input voltages, low power consumption,
and no electrical arcing. Additionally,
zero-voltage crossover minimizes
surge currents. Essentially an
electronic circuit, an SSR employs
no moving parts and resists physical
shock, vibration, or changes in altitude.
But as with any electronic circuit,
SSRs are sensitive to ambient heat
and require a heat sink. They are also
vulnerable to power surges.
Electromechanical relays (EMRs) are
far more tolerant of surges and overloads
and can switch any AC or DC
load up to their maximum rating. EMRs
will operate at full load over a wide
temperature range without requiring
a heat sink. However, EMRs arc when
contacts open and close, which may
affect nearby equipment sensitive to
radio frequency interference (RFI).
Consequently, EMRs are suitable in
applications with heavy surge currents
or spike voltages that tolerate RFI.
Relay manufacturers should be conmobilityengineeringtech.com
sulted
for SSR and EMR selections that
fit particular applications.
" Follow-the-Wire " Methodology
To uncover hidden factors compromising
power and signal reliability,
designers can employ a " follow-thewire "
methodology. Success depends
on viewing interconnects holistically
as part of the system rather than
a last-minute afterthought. Industry
standards groups also provide insights
to solve technology problems at the
subsystem and component level.
Solution providers with extensive
high-power expertise and a broad
product portfolio can help designers
strike the right balance between performance,
cost, and time to market.
Designers who need to iterate prototypes
and products rapidly benefit by
working with a manufacturer who can
design, customize, manufacture, and
implement all the components along
the wire. A connectivity partner with
broad experience can also offer innovative
solutions that help eVTOL and
UAM projects soar over high-voltage,
high-current hurdles.
This article was written by Karl Kitts,
Senior Manager R&D and Product
Development Engineering, TE Connectivity
(Berwyn, PA). For more information,
go to https://www.te.com.
15

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