Next-Generation, Power-Electronics Materials for Naval Aviation Applications
AREA(S): Electronics, Materials/Processes, Weapons
PROGRAM: PMA 262 Persistent Maritime Unmanned Aircraft Systems
Develop wide-band gap (WBG) electronic material systems for naval aviation applications.
The energy optimized aircraft (EOA) technology concept is continually evolving
and being recognized as a game-changer for war fighting capabilities. The main
objective of EOA is to systematically replace on-board hydraulic and pneumatic
systems with electrical systems to power flight controls, landing gear, and
engines starts. The key feature of EOA includes a switch from AC (alternating
current) to DC (direct current) power distribution to allow exchanges of energy
between equipment, which minimizes electromagnetic interferences (EMI) and
energy dissipation, and allows regeneration of air-powered electrical power
Power electronics is the discipline that deals with electrical power
generation, distribution and energy storage by conversion, control, and
management of electrical power. However, the power conversion forms for
electrical power categories (i.e., generation, transmission, and use/storage)
differ significantly. For example, the main AC power must be converted to DC
power for electronic devices; circuits require DC-DC conversion from one
voltage level to another; and DC power from renewable energies (i.e.,
batteries, solar cells, and fuel cells) can be converted to AC electrical
Power electronics is a key enabling technology for the advancement of EOA to
improve both generator (mechanical to electrical) and actuator (electrical to
mechanical) energy conversion and includes novel materials capable of
withstanding high temperature and high-power density with reduced weight used
in Navy-unique, harsh environmental conditions including EMI. With Next
Generation Air Dominance (NGAD) on the horizon, it is important to realize the
full potential of power electronics to achieve high power and volume density,
high efficiency, reliability, and affordability.
A wide band gap (WBG) system would have a positive impact on the
next-generation aircraft platform by combining secondary power distribution
with emerging power electronics. The current distribution system is made up of
bulky, low-efficiency, mechanical-based circuit breakers, contactors, and
control systems. Replacing such components with power electronics transforms
inefficient systems into simple and intelligent power solutions. With
diagnostic and prognostic capabilities, power distribution becomes compact and
efficient, which results in significant cost, energy, fuel, and weight
savings. Thus, modernization of Navy aircraft is enabled though the
application of a WBG system.
Switch-mode power circuits (i.e., the electronic circuits utilizing switching
frequencies) use two types of semiconductor-based switches: two-terminal
rectifiers (diodes) and three-terminal switches (transistors). These switches
include inherent material properties, such as electron mobility and thermal
conductivity [Ref 1], which result in salient features such as the following:
(1) high blocking/breakdown voltage [1-10 kilo Volt]; (2) low loss
(conversion efficiency of 99%); (3) large current-carrying capacity (kilo Ampere
range); (4) high operational frequency (i.e., 1-100 gigahertz]); (5)
high-temperature tolerance (i.e., 300 deg C); and (6) low specific ON-contact
resistance [~ 0.01 milliohm cm2]. [Ref 2]
These devices are silicon (Si)-based and have several advantages and
disadvantages. Advantages include that they operate efficiently, are mass
produced, are affordable and reliable, and are used in low-power and
low-voltage applications. Disadvantages include that the devices have ohmic
losses and generate more heat at higher switching frequencies, which
necessitate a complex thermal management solution with a limited operating
temperate range. The failure rates of the devices double for every 10 deg C
increase in temperature. In short, the limits of the physical properties of
Si-based devices are fast approaching, which are hindering further progress.
Currently naval electronic applications with Si-based devices operate up to 125
deg C. As the demand for high-voltage devices for switching applications
increases, a need exists for materials with much higher breakdown fields.
Silicon Carbide (SiC), gallium Nitride (GaN), and gallium arsenide (GaAs)
materials within electronics have band-gaps up to 3X higher than that of 1.12
electron volts, and hence WBG materials are the choice for next-generation
WBG devices can operate at a voltage 10 times higher than Si-based power
devices because of their higher maximum electric fields and operating
temperatures well over 350 deg C. The higher-temperature operation eliminates
the need for complex thermal management solutions such as heat sinks and
cooling media. WBG systems have the ability to switch at higher frequencies,
enabling equipment to drastically reduce in space, weight, and cost. A
high-voltage system has the potential to use lightweight materials, resulting
in weight savings for the wires and overall aircraft. WBG systems eliminate up
to 90% of power losses currently occurring in the energy conversion process and
impart huge energy benefits.
Challenges associated with the WBG systems include: (1) the hurdles in
crystal growth, both from wafer size (6 inches or more) and
drastically-reduced, defect densities (i.e., 5000/cm2), need to be overcome;
(2) the devices need to exhibit higher power density (i.e., 3MW/m3) to be more
efficient (> 98%) and must be affordable (up to 10X reduction from the
current price of $1,000/mm2); (3) the processing temperature for SiC (>
2000deg C) compared to Si is high, which requires innovation in synthesis and
processing of these classes of materials; and (4) the yield for WBG materials
is much lower than Si, resulting in a high market price.
Other remaining challenges include identifying substrate materials, epitaxial
film growth, and the back-end process of solving interface, interconnect, and
package issues towards successful device development and integration. The
reliability and durability (i.e., mean-time-between-failure of 2,000 hours) of
the devices to meet various MIL-STD specifications for electrical power
quality, environmental control, and EMI are major hurdles to overcome [Refs
I: Establish the structure-property relationship for WBG systems (i.e., SiC,
GaN, and GaAs). For instance, demonstrate feasibility of improved wafer
quality (up to 8 inches) by reducing the dislocation defect density with
salient device features. Apply modeling and simulation tools as necessary.
The Phase I effort will include prototype plans to be developed under Phase II.
II: Based upon Phase I results, fully develop the technology into a prototype
and demonstrate on an electrical power system application.
III DUAL USE APPLICATIONS: Fully develop the airworthy product with performance
specifications satisfying targeted acquisition requirements (e.g., F/A-18,
MQ-8B, and H-60) coordinated with Navy technical point of contacts.
Improve the technology readiness level/manufacturing readiness level (TRL/MRL)
of the electrical power system component and transition to platform (F/A-18,
MQ-8B, and H-60).
For such a representative aircraft EPS, demonstrate the positive SWaP-C (space,
weight, and power - cooling) benefits of the relevant showing compactness, high
electrical and thermal efficiencies, and miniaturization leading to a
next-generation power generation system architecture for EOA.
Demonstrate hardware with in-the-loop testing, along with the electrical load
analysis of EPS, as an integral part of this effort. The effort will result in
developing compact, miniature electronic products that will benefit automobile
and consumer electronic market sectors.
Wide Bandgap Power Electronics Technology Assessment, https://energy.gov/sites/prod/files/2015/02/f19/QTR%20Ch8%20-%20Wide%20Bandgap%20TA%20Feb-13-2015.pdf
Tolbert, L. M., Ozpineci, B., Islam, S. K., and Chinthavali, M. Wide Bandgap
Semiconductors for Utility Applications. IASTED International Conference on Power
and Energy Systems (PES 2003), (Palm Springs, CA), page 315 and references
MIL-STD-810G(1) Department of Defense Test Method Standard: Environmental
Engineering Considerations Laboratory Tests (15 Apr 2014). http://quicksearch.dla.mil/qsDocDetails.aspx?ident_number=35978
MIL-STD-461G Department of Defense Interface Standard: Requirements for the
Control of Electromagnetic Interference Characteristics of Subsystems and
Equipment (11 Dec 2015). http://quicksearch.dla.mil/qsDocDetails.aspx?ident_number=35789
MIL-STD-704F(1) Department of Defense Aircraft Electrical Power
Characteristics (05 Dec 2016). http://quicksearch.dla.mil/qsDocDetails.aspx?ident_number=35901
KEYWORDS: Power Electronics Materials;
Wide-band Gap Systems; Wafers; Power Electronic Equipment; Aircraft
Applications; Affordable Cost
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