IEEE Electrification Magazine - December 2014 - 48

VIEWPOINT

Challenges of the More
Electric Aircraft
By Nick Nagel

OMMERCIAL AEROSPACE
candidate. Instead, a
has typically been fairly
disciplined systems
slow to adopt new technolapproach must be used
ogy when compared to other market
to determine the techsegments. This movement is not due
nology that provides an
to a lack of vision or progressiveness
optimal solution at the
but rather the constraints of the maraircraft level.
ket. Commercial aircraft are designed
Aircraft have into last for decades, not years, so the
creased power generatechnology selected for any application, distribution, and
tion must continue to be viable for its
consumption. The most
life span. Additionally, regulatory and
recent aircraft have inNick Nagel.
safety requirements place stringent
creased electrical power
rules on any new technology introby an order of magnitude compared to
duced. But despite the challenges of
just two decades ago. But modern pownew technology introduction, there
er systems have eliminated constanthas been a wealth of electrical sysspeed transmissions, which maintained
tem developments in the pursuit of
generator operation at a fixed frequenthe More Electric Aircraft (MEA).
cy. Without the constant-speed transThis technology push represents
mission, the engine-driven generators
an exciting time to be an electrical
are operated over more than a 2:1 speed
engineer in the aerorange. This means that
space community, but
many applications historiAircraft have
we must not forget
cally run with conventional
increased power
the fact that the chalthree-phase induction molenges in front of us
tors are now replaced with
generation,
are truly a multidiscipower converters, inverters,
distribution, and
plinary engineering
and permanent-magnet
consumption.
problem. The MEA inisynchronous motors. For
tiative is not, or should
safety-critical systems in
not be, focused on the
which a failure would be
arbitrary replacement of current
catastrophic, designs must meet a probhydraulic systems with all-electric
ability of failure of fewer than one in 1
systems, at least not until the all-elecbillion failures per hour. This requiretric system proves itself the better
ment can only be met with redundancy
in complex electronic systems. While
redundancy is used to mitigate probaDigital Object Identifier 10.1109/MELE.2014.2365620
Date of publication: 9 February 2015
bility of failure risks, it does so at the

I E E E E l e c t r i f i c ati o n M agaz ine / DECEMBER 2014

expense of reliability.
Adding more components means there are
more things to fail.
This ultimately reduces reliability.
While converting to
complex electrical systems has its share of
problems, it is not without benefit. Increasing
component count
through redundancy
may reduce the calculated reliability,
but it may also increase availability (the
ability for the aircraft to depart as
scheduled). Availability is an extremely
important measure for airline operators. Also, the increase in electrical
power has reduced or eliminated the
need for hydraulic and pneumatic
power. Pneumatic power is generated
from bleed air systems on the engine
but is done so at very poor efficiencies.
The bleed air system is used in cabin
pressurization, air conditioning, and
icing protection. According to the Boeing Aero quarterly publication, replacing
the bleed air systems with electrical
systems can save roughly 35% of power
from the engine, clearly highlighting
some of the benefits of the MEA.
While the developments in key
areas (power electronics, electric
machine design, and controls)
enabling electromechanical actuation
(continued on page 46)

Table of Contents for the Digital Edition of IEEE Electrification Magazine - December 2014