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Several concurrent trends are forcing a reevaluation of the electrical power quality which is most practically and suitably delivered to aircraft electrical utilization equipment. Military applications have focused on 270 Vdc and the system integration issues of more-electric aircraft. Most civil applications are yet to become very much “more-electric”, though their increasing capacity and electronic load content has invalidated many of the assumptions upon which traditional power quality documents were based. This paper discusses the development of new guidelines for a variety of interface parameters essential to safe, effective application of both constant and variable frequency ac electric power.

This paper summarizes progress for the “Integrated Power Unit - Advanced Development” program under contract with the U.S. Air Force at the Air Force Research Laboratory in Dayton, Ohio. This is a 58 month program beginning in February 1996, and ending in December 2000. Figure 1 is a program schedule that identifies major tasks and timing of the phases. The scope of this effort is to design, build, and ground test a highly integrated, air-breathing, electrical power unit which demonstrates the critical design and integration features required for a simple, durable, and reliable Integrated Power Unit (IPU). The IPU must be electrically linked for self starting, main engine electrical starting and as a major source of redundant electric power for the aircraft's main electric power system. Figure 2 shows a mockup of a prototypic IPU design.

A cavity heat pipe experiment has been designed to test the critical issues involved with incorporating thermal energy storage canisters into a heat pipe. The experiment is a replication of the operation of a heat receiver for a Brayton solar dynamic power cycle. The heat receiver is composed of a cylindrical receptor surface and an annular heat pipe with thermal energy storage canisters and gaseous working fluid heat exchanger tubes surrounding it. Hardware for the cavity heat pipe experiment will consist of a sector of the heat pipe, complete with gas tube and thermal energy storage canisters. Thermal cycling tests will be performed on the heat pipe sector to simulate the normal energy charge/discharge cycle of the receiver in a spacecraft application.

Most electronic systems, including electric motor drives and electric power conditioners, require the use of electromagnetic devices, such as inductors and transformers as circuit components to carry out any of the following functions: a) Suppressing or isolating specific harmonic components in voltages and currents. b) Providing electrical isolation from one circuit to another. c) Limiting the currents under fault conditions. d) Increasing or decreasing the voltage or current levels. e) Integrating voltages, currents, or power. f) Providing neutral line, phase shift. The performance of the electronic systems is dependent upon the design of the electromagnetic components that are used. For the aerospace quality hardware, the weight, size, cost, reliability, and efficiency of the electronic systems are substantially dependent upon the design of electromagnetic components.

The Air Force Research Laboratory is currently funding efforts under the More-Electric Aircraft (MEA) Generation II Study for developing a preliminary design of an electrical power generation and distribution system (EPGDS) for flight demonstration of an Internal Starter/Generator (IS/G) for the main engine on an advanced fighter-class aircraft. The MEA Initiative is a phased, goal-oriented, effort that develops technologies to enable the use of electrical power to perform aircraft functions that historically have been powered hydraulically, mechanically, or pneumatically. The use of electrical power for these functions has the potential for enhanced aircraft performance through improved efficiency, reliability, maintainability, and supportability. Today, the MEA effort is in its second phase, with an anticipated technology availability date of 2005.

No-break power transfer (NBPT) has been used in the 400 Hz aircraft electrical power business for over 30 years. Initially, NBPT was performed on military aircraft or large commercial jets where the interest was to maintain availability of critical equipment during dispatch. Recent-NBPT equipped aircraft such as the 747-400 and MD-11 have demonstrated the desirability of this feature in commercial airline service. Some compatibility issues with solid-state ground power units (GPUs) have also been uncovered.