Aerospace & Defense Technology - October 2024 - 12

Military Vehicles
spare parts and fuel types required in
remote field environments.
Power supplies and power converters
supply electrical power to a load in the
format it's designed to receive (e.g., voltage,
current, frequency). Rectifiers, inverters,
and DC/DC converters are common
across industries, including aerospace
and defense. While they function the
same way, power supplies and converters
in military applications are subject to
functionality specifications determined
by MIL standards. For example, MIL-PRFGCS600,
MIL-STD-1275, MIL-STD-1399,
Generator
200kW
AC
ISGC
AC/DC
600VDC
MIL-STD-461, MIL-STD-704, and MILSTD-810
detail key standards for factors
like voltage level and electromagnetic
interference (EMI) tolerance to maintain
consistent, high quality and support size,
weight, and power optimization.
Electric Architecture in Military
Vehicles
The U.S. Army recently investigated
a 600V electrical supply platform for all
land systems to replace its current 28V
system. This change would increase available
power and reduce cabling losses. At a
HVPC
DC/DC
600VDC
BDC
DC/DC
600VDC
28VDC
LVPC
DC/DC
28VDC
given power level, losses decrease at higher
voltages. This is observable in commercial
electric vehicles as well. Many manufacturers
opted for 800V electrical supplies so
they could leverage thinner, lighter cables.
The example of vehicle electrification
architecture (VEA), shown in Figure 1,
includes a battery pack, electric motor,
power electronics, a vehicle control unit
(VCU), and a charging system. Here, the
integrated starter/generator controller
(ISGC) converts AC power from the
onboard generator to the 600V high-voltage
direct current (HVDC) bus voltage.
The import/export power converter (IEPC)
covers bidirectional conversion between
600V DC and external AC source of power.
The system also includes a high-voltage
power controller (HVPC), bidirectional
converter (BDC), and low-voltage power
controller (LVPC) for DC/DC conversions.
In the power architecture of an F-35
IEPC
DC/AC
600VDC
120VAC
240VAC
Figure 1: Example of vehicle electrification architecture (VEA). (Image: Knowles Corporation)
Avionics
DC/DC
270VDC
28VDC
Generator
80kW
AC
ICC
AC/DC
270VDC
EDU
DC/DC
270VDC
EHAS
DC/DC
270VDC
Joint Strike Fighter, shown in Figure 2, the
power architecture includes an inverter/
converter/controlled (ICC), electrical distribution
unit (EDU), electro-hydrostatic
actuation system (EHAS), environmental
control system (ECS), avionics supplies,
and legacy AC supplies. While these architectures
represent two different applications
in the military domain, they share
operations (e.g., AC/DC, DC/AC, DC/DC
conversions) and characteristics, like high
voltage. Efficient power conversion is the
foundation for a high-efficiency system.
By reducing losses in a DC/DC converter,
the converter, and by extension, the vehicle,
benefits from better energy efficiency
and less heat generation.
Advancing Power Efficiency at the
Circuit Level
For the sake of example, we'll focus
Battery &
Charger
270VDC
ECS
DC/DC
270VDC
Legacy AC
DC/AC
270VDC
115VAC
on resonant DC/DC converters. Resonant
converters are switching-based
and incorporate a resonant tank to help
manage input-to-output power flow.
They're known for smoothing waveforms,
improving power factor, and
reducing switching losses exacerbated
by high-frequency power switches like
MOSFETs and IGBTs. These capabilities
make resonant converters particularly
common in high-voltage applications.
The LLC circuit is a common resonant
Figure 2: A simplified view of the electrical power architecture in the F-35 Joint Strike Fighter. (Image:
Knowles Corporation)
12
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converter implementation because it
achieves zero voltage switching (ZVS)
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Aerospace & Defense Technology - October 2024

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