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Minimizing energy use on more electric aircraft (MEA) requires examining in detail the important decision of whether and when to use engine bleed air, ram air, electric, hydraulic, or other sources of power. Further, due to the large variance in mission segments, it is unlikely that a single energy source is the most efficient over an entire mission. Thus, hybrid combinations of sources must be considered. An important system in an advanced MEA is the adaptive power and thermal management system (APTMS), which is designed to provide main engine start, auxiliary and emergency power, and vehicle thermal management including environmental cooling. Additionally, peak and regenerative power management capabilities can be achieved with appropriate control. The APTMS is intended to be adaptive, adjusting its operation in order to serve its function in the most efficient and least costly way to the aircraft as a whole.

Fuel has been a popular choice for thermal system designers to use for absorbing aircraft accessory heat load due to its consumable nature. However, the shortcoming of using fuel as a heat sink is the dependency of environmental conditions. This deficiency has plagued the current United States Air Force fleet operation especially performing ground hold and low altitude attack mission during hot days. A Northrop Grumman led industrial team, commissioned by AFRL Power directorate through the INVENT program, has vigorously explored potential technologies to assist air force to enhance the mission capability. The results show various promising technologies not only can extend the hot day operational limit but also can potentially have an unrestricted capability. This paper describes the results from the study performed by Northrop Grumman for an advanced unmanned air vehicle (AUAV) for potential technologies and discusses the modeling approach in support of the analytical process.

The characteristics of large electrical loads encountered in the modern More Electric Aircraft (MEA) require regenerative power processing in order to preserve the power quality within acceptable transient and steady state limits. In an MEA with large active loads and pulsed power demands, it is necessary to employ an architecture that safely and effectively processes regenerative energy resulting from the dynamic loads. For instance, the electrical flight control actuation presents one of the largest regenerative power sources encountered by the generation system. Typical approach is to dissipate this energy through resistors of the power electronics which increases the size and penalizes the aircraft.

A dc-dc converter and a dc-ac inverter have been developed for More Electric Aircraft (MEA) use. They are both highly compact and are designed to operate from 270 Vdc input power and produce output power that meets requirements for fighter aircraft, including compliance with MIL-STD-704E and MIL-STD-461D guidelines. Both units are designed to be cooled with Poly Alpha Olefin (PAO) at 30°C maximum inlet temperature and to operate for 30s after a loss of coolant flow before shutting down. Both units incorporate under/over voltage, short circuit, and over temperature protection. The dc-ac inverter also has over/under frequency, dc content, waveform distortion, and zero voltage content protection. The dc-dc converter provides 5.6 kW at 29±0.5 Vdc with an efficiency of 85%. It weighs 9.1 lb and is 6″ long by 5″ wide by 5.5″ high (165 in3). The dc-ac inverter provides 8 kVA of three phase power at (115±1.5)/200 Vac and 400 Hz with an efficiency of 75%.