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This paper describes a framework for developing an Integrated Electrical Power System (EPS) Health Management System. The framework is based on the perspective that health management, unlike other capabilities, is not a self-contained, stand-alone system, but is rather an integral part of every aircraft subsystem, system, and the entire platform. Ultimately, the objective is to improve the entire maintenance, logistics and fleet operations support processes. This perspective requires a new mindset when applying systems engineering design principles. The paper provides an overview description of the framework, the potential benefits of the approach and some critical design and implementation issues based on current development efforts.

This paper describes a novel time-varying prognostic modeling framework for computing condition-based residual life distributions of partially degraded aircraft electrical power system (EPS) components. This advanced methodology is suitable for modeling the evolution of degradation signals acquired from aircraft electrical power system components through condition monitoring techniques. The evolution of the degradation signals is modeled as a stochastic process, with fixed and random parameters, and takes into consideration environmental covariates that capture the time-varying nature of the equipment's operating condition. The modeling methodology correlates the degradation signals with the underlying physical transitions that occur prior to component failures to estimate and update the residual life distribution of the system.

An overview of aircraft DC power quality specifications reveals that only minor changes have occurred in recent years within industry standards. Current and future advanced electronic aircraft are requiring significant power quality improvements due to increased use of digital and COTS (commercial off the shelf) systems. Certain electronic systems do not function properly due to various types of electrical disturbances. Some systems shutdown, fault or exhibit operational delays due to power interruptions or “blackout” conditions. Undervoltage or “brownout” conditions also cause this effect. Some electronic systems exhibit critical faults that can affect safety or mission success due to overvoltage conditions. Additional effects of high voltage spikes or overvoltage transients are known to reduce the life of utilization equipment [1], which is directly related to the health of the aircraft's electronic system and creates an economic burden.

The thick oxide layer of silicon-on-insulator (SOI) devices significantly reduces the junction leakage current at elevated temperatures compared to similar Si devices, resulting in an elevated maximum operating temperature. The maximum operating temperature, specified by manufacturers, of commercial SOI devices/circuits with conventional packaging is usually 225°C. It is important to understand the performance and de-ratings of these SOI circuits at temperatures above 225°C without the temperature limit imposed by commercial packaging technology. This work tested a low frequency square-wave oscillator based on an SOI 555 Timer with a special high temperature ceramic packaging technology from room temperature to 375°C. The timer die was attached to a 96% aluminum oxide substrate with high temperature durable gold (Au) thick-film metallization, and interconnected with Au wires.

The combination of increasing performance demands, increasing system complexity, and the need for reduced program development schedule and budget costs in the aerospace industry is driving engineers to increasingly rely upon modeling, simulation, and analysis (MS&A) in the platform development cycle. One approach to ensuring that such integrated system simulations remain computationally tractable is co-simulation utilizing technology found in commercially available packages, such as PC Krause and Associates, Inc.'s (PCKA's) Distributed Heterogeneous Simulation (DHS) / FastSim software. In such co-simulation environments, dynamic models are executed in independent model spaces, with coupling between subsystems achieved by exchanging a minimal set of required data typically found at subsystem boundaries.

Turboelectric propulsion is a technology that can potentially reduce aircraft noise, increase fuel efficiency, and decrease harmful emissions. In a turbo-electric system, the propulsor (fans) is no longer connected to the turbine through a mechanical connection. Instead, a superconducting generator connected to a gas turbine produces electrical power which is delivered to distributed fans. This configuration can potentially decrease fuel burn by 10% [1]. One of the primary challenges in implementing turboelectric electric propulsion is designing the power distribution system to transmit power from the generator to the fans. The power distribution system is required to transmit 40 MW of power from the generator to the electrical loads on the aircraft. A conventional aircraft distribution cannot efficiently or reliably transmit this large amount of power; therefore, new power distribution technologies must be considered.

This paper presents the Integrated Power Distribution Unit (IPDU) concept, which brings together major electric power Conversion, Distribution, Management, and Protection (CDMP) functions in a single lightweight LRU. The IPDU enables CDMP functionality to be physically located at points-of-use nodes, while maintaining unified control among the several IPDUs used in an Electric Power System. IPDU functions include input power quality sensing, power conversion (Inverter, TRU, Frequency Converter, DC-DC Converter), power management (AC and DC SSPCs and Hybrid Contactors), and a control function consisting of a databus R/T, DSP control core, and a voltage-frequency-current sensor suite. The IPDU is currently being applied as a major electrical power system element within a new aircraft dual channel EPS. The three major goals of the IPDU design are Improved power management functionality (fully observable system), enhanced reliability, and reduced size and weight.

For fast rise time, high peak current pulse power applications, Silicon Carbide (SiC) is ideal due to its ability to tolerate high localized temperatures generated during switching. Several 4 mm × 4 mm SiC Gate Turn-Off thyristors (GTOs) manufactured by CREE were evaluated. Testing for individual and paired devices was performed under both single and repetitive pulsing using variable pulse duration, ring-down capacitor discharge circuit. At 150 °C, maximum single shot currents as high as 3.2 kA have been shown for single devices at a 50% pulse width of 2 μsec while parallel devices have shown a maximum of 4.4 kA at 150 °C.

This paper focuses on advances in active power converter topologies for power quality solutions for More Electric Aircraft (MEA). Advancements in power electronics encompass many technologies including power semiconductors, microprocessors or digital signal processors (DSPs), and component packaging. Hence, active power electronic solutions are becoming more attractive from the perspective of weight, volume, performance and cost. A particular contribution that leads to these advancements is the feasibility of implementing the robust control topologies using faster processors. In this paper various active topologies are reviewed, but a particular emphasis is given to a novel control topology for an active filtering technique where an overall reduction of current harmonics of an aircraft power distribution system can be achieved at the system level rather than at the Line Replaceable Unit (LRU) level.

Historically, electromechanical switching evolved as the standard for switching between and among sources, busses and user loads in high power Electrical Power Distribution Systems. This was the case for essentially all (if not all) complex mobile Electrical Power Distribution Systems, including those employed both in marine and aviation systems. High power, semi-conductor switching has now evolved to the point that it is expected to provide new standards based upon semi-conductor technology. The changes are desirable due to deficiencies in electro-mechanical switching, and improvements offered by semi-conductor technology capability, when considered for high power switching.

This paper explores applications of the novel AC-link™ technology, a fundamentally different method of distributing and converting electrical power that is well suited to a wide variety of power distribution and Directed Energy Weapon (DEW) applications: DC-DC, AC-DC, or AC-AC. In particular, this paper will explore directed energy, load-leveling, and pulsed power applications and the advantages they gain from AC- link™'s low output voltage ripple, <1% to 3% input harmonic currents, and four-quadrant operation. A DC- DC prototype AC-link™ unit has been completed with an output of 50kVDC and power density of 1.4 MW/m3. A preliminary design of a 4,160 V AC 95 kV regulated supply has a projected power density of ~3 MW/m3 with a small internal transformer operating at ~20 kHz. This paper will also present a new transformerless AC-link™ design with a power density of around 5 MW/m3 for diode-pumped laser applications.

This paper describes a program at Boeing Phantom Works designed to evaluate life cycle performance of Lithium -Ion (Li-Ion) cells. The objective was to gather data, which will give us the capability to assess the performance of these cells during typical space missions. Lithium-Ion (Li-Ion) cells can provide higher performance for spacecraft energy storage applications. Li-Ion cells have: (1) reduced mass, (2) increased volumetric efficiency, (3) improved cycle and calendar life, (4) higher power and energy (5) lower self discharge, (6) no “memory effect”, (7) excellent low temperature performance and (8) are more environmentally friendly than other types of batteries, such as Ag-Zn or NiH2 and; therefore, may be a better alternative to these traditional types of cells for space applications. Life cycle testing was performed with Li-Ion cells purchased from three different cell manufacturers.

The modeling and simulation of electrical power systems has become a primary design tool for the synthesis of aerospace power systems with hybrid AC/DC distribution. Although in the past the use of extensive time domain simulations using detailed models has been favored, the need to study stability and associated phenomena in this type of power systems-having a high penetration of power electronics loads-has transformed the modeling requirements for aerospace applications. This paper explores different modeling aspects required to study both small-signal and large-signal stability in these systems, providing insight into the development of key system component models-variable frequency generators, line-commutated converters, PWM motor drives and constant power loads, as well as the theoretical foundations based on the Generalized Nyquist Criterion and the Lyapunov Direct and Indirect Methods to fully assess the stability conditions of these power systems.

The current system requirements for the power management subsystem and ground combat vehicles for the Future Combat System require higher power and voltages for greater energy efficiency, advanced mobility, lethality and survivability. Efficient and reliable electrical power management is an essential capability within current force ground combat vehicles and will become even more important with the increased electrical power demands of future force vehicles which will exceed the capabilities of onboard power generation/storage technologies. This paper describes how to meet the aforementioned power distribution challenges through the development of a power management software interfaces standard that will provide the flexibility required by various programs and vehicles yet still provide a consistent framework for software development providing a consistent environment for all future Army programs.

A status report on the development of an electrical test-facility for the SEAS DTC (Systems Engineering for Autonomous Systems, Defence Technology Centre) project ‘ultra-compact intelligent electrical networks’ is presented. The electrical platform has initially been based on a small, aerial, uninhabited autonomous vehicle architecture, which consists of two electrical generators, a DC distribution system, an energy storage device and various electrical loads. The issues that arise when implementing such a test platform are discussed and a suitable design strategy is proposed along with progress to-date.

Recent advances in the state of the art of space-borne data processors and signal processors have occurred that present some unprecedented constraints relating to their power needs. Such processors include the class of multiprocessors providing computational capabilities in the billions of floating point operations per second. Processors of this type tend to require use of modern radiation tolerant or radiation hardened integrated circuits requiring very low voltage power supplies that place considerable challenge on power distribution and conversion within those processing payloads. The primary challenges are efficient conversion of power from the spacecraft power bus to these low voltages and distribution of the very high accompanying currents within the payload while maintaining proper voltage regulation (typically +/− 5%). Some integrated circuits require 10 Amps or more at 1Volt, as an example [3], [6].

This paper presents the main characteristics related to the design and integration of the Electrical Power Generation and Distribution System (EPGDS) performed by Allied Signal Aerospace Canada for the Bombardier - deHavilland DHC-8 Series 400 airplane. It provides an overview of the system, and describes the development process and the various technical challenges along the way. The EPGDS comprises of a variable frequency AC Power Subsystem and a DC Power Subsystem. Since the commercial aviation industry is showing increasing interest in variable frequency power systems, this paper provides some focus on the use of variable frequency AC power on the Dash 8 platform and its impact on frequency sensitive equipment.

A computerized thermodynamic analytical program is being developed to help investigate the impact of power system requirements on aircraft performance. The Visual Basic for Applications (VBA) program has a user interface that operates in MS-EXCEL, linking several subsystem analysis programs for execution and data transfer in the power systems analysis. The program presently includes an encoded propulsion engine cycle code, which allows the inspection of power extraction effects on engine performance. To validate the results of the encoded engine program, a study was conducted to investigate the separate effects of shaft power extraction and pneumatic bleed. The selected engine cycle was that for a standard tactical fighter, with a flight condition of varied altitude (sea level to 40k-ft.) and constant Mach Number(0.9). As expected, the resultant data showed that the engine performance was more sensitive to pneumatic bleed than to shaft power extraction.

The objective of the work discussed within this paper is to present a modeling methodology to assess thermal management system (TMS) concepts for aircraft to determine adequacy in meeting thermal requirements and constraints for the duration of the flight1. To accomplish this, an analysis tool that has the capability to investigate steady state and transient thermal hydraulic conditions on a component to system-wide level is employed. This is achieved by simulating the conditions within a cooling network to provide temperature, pressure and mass flow rate distributions, as well as the temperature of surrounding engine and airframe structures. With today's reduced budgets, new aircraft systems will be less common and retrofitting existing high performance aircraft will become more common. Pushing these technologies to their thermal limits is resulting in cooling requirements that were not present or even contemplated during their original designs.

This paper describes and discusses ways to improve future transport aircraft through integration within the power generation, distribution and utilization elements of the secondary power systems Integration of hardware and functions along with power management and selection of a common single type of secondary power distribution is shown to offer advantages in cost, weight, fuel efficiency and reliability for the future transport aircraft fleet. Strengths and weaknesses of recent integration efforts, primarily the Power-By-Wire concept are discussed and analyzed. The concept of “revolutionary” versus “evolutionary” technology development and implementation is discussed and it is shown that in the case of secondary power system development, the process must be evolutionary. Also, a set of criteria relating to this implementation is given, and the ideal subsystem for starting this development is shown to be the Environmental Control System (ECS).