Dielectric materials, which store energy electrostatically, are ubiquitous in advanced electronics and electric power systems. Compared to their ceramic counterparts, polymer dielectrics have higher breakdown strengths and greater reliability, are scalable, lightweight and can be shaped into intricate configurations, and are therefore an ideal choice for many power electronics, power conditioning, and pulsed power applications. However, polymer dielectrics are limited to relatively low working temperatures, and thus fail to meet the rising demand for electricity under the extreme conditions present in applications such as hybrid and electric vehicles, aerospace power electronics, and underground oil and gas exploration. Here we describe crosslinked polymer nanocomposites that contain boron nitride nanosheets, the dielectric properties of which are stable over a broad temperature and frequency range. The nanocomposites have outstanding high-voltage capacitive energy storage capabilities at record temperatures (a Weibull breakdown strength of 403 megavolts per metre and a discharged energy density of 1.8 joules per cubic centimetre at 250 degrees Celsius). Their electrical conduction is several orders of magnitude lower than that of existing polymers and their high operating temperatures are attributed to greatly improved thermal conductivity, owing to the presence of the boron nitride nanosheets, which improve heat dissipation compared to pristine polymers (which are inherently susceptible to thermal runaway). Moreover, the polymer nanocomposites are lightweight, photopatternable and mechanically flexible, and have been demonstrated to preserve excellent dielectric and capacitive performance after intensive bending cycles. These findings enable broader applications of organic materials in high-temperature electronics and energy storage devices.

Flexible high-temperature dielectric materials from polymer nanocomposites

The latest advances in electric and electronic aircraft technologies from the point of view of an "all-electric" aircraft are presented herein. Specifically, we describe the concept of a "more electric aircraft" (MEA), which involves removing the need for on-engine hydraulic power generation and bleed air off-takes, and the increasing use of power electronics in the starter/generation system of the main engine. Removal of the engine hydraulic pumps requires fully-operative electrical power actuators and mastery of the flight control architecture. The paper presents a general overview of the electrical power generation system and electric drives for the MEA, with special regard to the flight controls. Some discussion regarding the interconnection of nodes and safety of buses and protocols in distributed systems is also presented

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Moving towards a more electric aircraft

AC distributed power systems (DPS) can be found in several new and emerging applications. Similar to dc distributed power systems, an ac DPS relies on power electronics and control to realize its functions and achieve the required performance. System stability and power quality are important issues in both types of systems due to the complex system behavior resulted from active control at both the source and the load side. Traditional small-signal analysis methods cannot be directly applied to an ac DPS because of the periodically time-varying system operation trajectory. Possible solutions to this problem include transformation into a rotating (dq) reference frame, modeling using dynamic phasors, reduced-order modeling, and harmonic linearization. This paper reviews these small-signal methods and discusses their utilities as well as limitations. Compatibility of each type of models with state-space and impedance-based system analysis approaches will also be discussed. Problems related to the linearization of phasor-based models and their use in impedance-based system analysis are highlighted in particular.

Small-Signal Methods for AC Distributed Power Systems–A Review

The fundamental issues faced in the aircraft electrical power systems are addressed. A brief description of the conventional and advanced aircraft power system architectures, their disadvantages, opportunities for improvement, future electric loads, role of power electronics, and present trends in aircraft power system research is given, followed by a brief outline of projected future advancements.

Aircraft power systems: technology, state of the art, and future trends

The constant growth of air traffic, the demand for performance optimization, and the need for decreasing both operating and maintenance costs have encouraged the aircraft industry to move toward more electric solutions. As a result of this trend, electric power required on-board of aircraft has significantly increased through the years, causing major changes in electric power system architectures. Considering this scenario, this paper gives a review about the evolution of electric power generation systems in aircraft. The major achievements are highlighted and the rationale behind some significant developments discussed. After a brief historical overview of the early dc generators (both wind- and engine-driven), the reasons which brought the definitive passage to the ac generation, for larger aircraft, are presented and explained. Several ac generation systems are investigated with particular attention being focused on the voltage levels and the generator technology. Furthermore, examples of commercial aircraft implementing ac generation systems are provided. Finally, the trends toward modern generation systems are also considered giving prominence to their challenges and feasibility.

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Electrical Power Generation in Aircraft: Review, Challenges, and Opportunities

The Air Force's More Electric Aircraft (MEA) initiative embraces the concept of utilizing electrical power for driving aircraft subsystems currently powered by hydraulic, pneumatic or mechanical means including utility and flight control actuation, environmental control system, lubrication and fuel pumps, and numerous other utility functions. An important part of this initiative is the development and demonstration of electrical power and power electronic components and systems to enhance reliability, fault-tolerance, power density and performance. This paper describes some of the key electrical power and power electronic technologies being pursued by the Air Force to make the concept of a MEA a reality. The paper describes the results or progress to date of Air Force funded MEA programs such as the Power Management and Distribution for the More Electric Aircraft program, Integral Starter Generator program, and MOS Controlled Thyristor program. A brief discussion of future related programs is included. The integration of advanced MEA technologies is expected to increase dramatically aircraft reliability and reduce susceptibility to battle damage. The needs for aircraft maintenance and support are also expected to be reduced along with ground support equipment and maintenance personnel. >

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J.A. Weimer

Papers

Electrical power technology for the more electric aircraft