More-electric Aircraft Concept Research Articles

An Enhanced Second Carrier Harmonic Cancellation Technique for Dual-Channel Enhanced Power Generation Centre Applications in More-Electric Aircraft

The more-electric aircraft concept has made the extraction of electrical power from both high-pressure shaft and low-pressure shaft of the aircraft engine essential for future aircraft. With each shaft driving one electrical generation channel, an advanced dual-channel enhanced power generation system can be formed. This article aims to address the power quality issues of this dual-channel power generation system, specifically focusing on the reduction of harmonics on a common dc bus. A simplified model to estimate second carrier harmonic of dc current in two-level converters is developed and reveals the fact that while this second carrier harmonic component magnitude can be determined by modulation index and dc-link current, its phase angle is solely dependent on the angle of carrier signals. Based on the developed model and these key findings, a new harmonic cancellation method is proposed through active power sharing and phase angle shifting of the carrier signals within different power sources. The method has demonstrated high robustness and is effective under different fundamental frequencies and power sharing ratio. Both simulation and experimental results are presented in this article to validate the proposed harmonic model and the enhanced cancellation method.

A Generalized Input Impedance Model of Multiple Active Bridge Converter

The electrical power distribution system (EPDS) of the more electric aircraft (MEA) is a fundamental component that needs to be efficient and resilient. The commonly considered architectures feature separate buses to achieve separation between different subsections of the EPDS. Although effective, this implies an over design, since all subsections are sized for the local worst case scenarios. In the MEA concept, multiport converters could connect the whole EPDS while guaranteeing the galvanic isolation between buses. Since multiport converters would give rise to a completely different EPDS topology, dominated by power electronics interfaces, the stability of such a system must be assessed. This article investigates the input impedance of multiple active bridge (MAB) converters when interfaced with a single dc bus and multiple resistive loads. A transfer function-based input impedance model of the MAB converter is proposed. To validate the proposed input impedance model, the verification of input impedances of a triple active bridge (TAB) converter and a quadruple active bridge (QAB) converter is carried out using both simulation and experimental results.

High-Power Machines and Starter-Generator Topologies for More Electric Aircraft: A Technology Outlook

More electric aircraft (MEA) architectures consist of several subsystems, which must all comply with the settled safety requirements of aerospace applications. Thus, achieving reliability and fault-tolerance represents the main cornerstone when classifying different solutions. Hybrid electric aircraft (HEA) extends the MEA concept by electrifying the propulsive power as well as the auxiliary power, and thereby pushing the limits of electrification. This paper gives an overview of the high-power electrical machine families and their associated power electronic converter (PEC) interfaces that are currently competing for aircraft power conversion systems. Various functionalities and starter-generator (S/G) solutions are also covered. In order to highlight the latest advancements, the efficiency of the world’s most powerful aerospace generator (Mark 1) developed within the E-Fan X HEA project is graphically represented and assessed against other rivaling solutions. Motivated by the strict requirements on efficiency, power density, trustworthiness, as well as starting functionalities, supplementary considerations on the system-level design are paramount. In order to highlight the MEA goals and take advantage of all potential benefits, all subsystems must be treated as a whole. It is then shown that the combination of PECs, aircraft grid and electrical machines can be better adapted to benefit the overall system. This survey outlines the influence of these concerns and offers a view of the future technology outlook, as well as covering the present challenges and opportunities.

Conceptual All-Electric Retrofit of Helicopters: Review, Technological Outlook, and a Sample Design

The diffusion of electric system on-board has started after 2000 due to the need of fulfilling new regulations regarding environmental impact of aviation and of reducing maintenance costs. This process has led to the more-electric aircraft concept design, for which several hydraulic and pneumatic systems have been replaced by electric drives. The main obstacles to the switch to electric propulsion and energy storage/production (all-electric aircraft) are the unfavorable energy-to-weight and power-to-weight ratios of battery and fuel cell that represent the two viable technological solutions for energy storage and power generation. Helicopters make no exception in the transition to electric systems, although with a significant lag with respect to fixed-wing aircraft. Nevertheless, it is expected that, in the future, the technological progress will make electric propulsion a standard solution also for rotorcraft. This paper presents a review of the steps toward electrified aircraft taken by the aviation industry in the past decades (mainly concerning fixed-wing vehicles) and the conceptual all-electric retrofit of a case study lightweight helicopter. Different batteries and fuel cell solutions are examined, and the performance (range and endurance) and economic aspects (life cost and investment plan) are critically analyzed, considering both the currently available technology and the expected future developments.

Analysis of the Influence of the Structural Parameters of Aircraft Braided-Shield Cable on Shielding Effectiveness

As the more-electric aircraft concept is accepted as the key feature of the next-generation civil aircraft, the onboard electromagnetic environment is getting much worse than traditional models, and consequently the interconnecting cables as the major coupling path of the electromagnetic interference (EMI) are required to provide more sufficient EMI protection ability. Shielded cables have been considered as reliable carriers and widely used in the aircraft for years, but any differences in shielding structure or the number of shielding layers may lead to a significant change in shielding performance. Based on the transmission line theory, this paper builds the crosstalk prediction model for two different shielded cables first, and compare the calculated crosstalk with simulation result to verify the reliability and the effectiveness of the prediction model. Furthermore, the impact of the structural parameters of the cable shield on the shielding performance is studied, such as the number of shielding layer, the thickness of the shielding layer and insulating layer.

Dual Drive Booster for a Two-Spool Turbofan: High Shaft Power Offtake Capability for More Electric Aircraft and Hybrid Aircraft Concepts

The effects of high shaft power offtake (POT) in a direct drive, a geared drive, and a novel turbofan configuration are investigated. A design and off-design performance analysis shows the configuration specific limitations and advantages. The more electric aircraft (MEA) concept promises to offer advantages with respect to aircraft performance, maintenance, and operating costs. The engines for the MEA concept are based on conventional turbofan architectures. These engines are designed for significantly increased shaft POT that is required by the airframe, and the shaft power is usually taken off the high-pressure (HP) spool. This can impair the off-design performance of the engine and lead to compromises during engine design and to operability limitations. Taking the power off the low-pressure (LP) spool mitigates some of the problems but has other limitations. In this work, an alternative novel turbofan architecture is investigated for its potential to avoid the problems related to high shaft POTs. This architecture is called the dual drive booster because it uses a summation gearbox to drive the booster from both the LP and HP spool. The shaft power, if taken off the booster spool, is effectively provided by both the LP and HP spools, which allows the provision of very high power levels. This new concept is benchmarked against a two-spool direct drive and a geared drive turbofan (GTF). Furthermore, it is described, how the new architecture can incorporate an embedded motor generator. The presented concept mitigates some of the problems, which are encountered during high POT in conventional configurations. In particular, the core compressors are less affected by a change in shaft POT. This allows higher POTs and gives more flexibility during engine design and operation. Additionally, the potential to use the new configuration as a gas turbine-electric hybrid engine is assessed, where electrical power boost is applied during critical flight phases. The ability to convert additional shaft power is compared with conventional configurations. Here, the new configuration also shows superior behavior because the core compressors are significantly less affected by power input than in conventional configurations. The spool speed and its variation are more suitable for electrical machines than in conventional configuration with LP spool power transfer. The dual drive booster concept is particularly suited for applications with high shaft POTs and inputs, and should be considered for propulsion of MEAs.

Finite state machine control for aircraft electrical distribution system

This study deals with the development of new control logic for more electric aircraft (MEA) electrical power systems (EPSs). A key aspect of the MEA concept is that traditional pneumatic and hydraulic loads are replaced by electrical equivalents. These new electrical systems are more reliable, highly efficient, and easier to replace or maintain. However, as the number of on-board electrical loads increases the electrical distribution systems on-board are becoming more and more complex. As a result, the control system needs to be adapted and improved in order to allow better manage the overall electrical energy flow, provide faster computational operations, and ensure operation of safety-critical loads under all fault scenarios. This study first gives a brief analysis of the different electrical system topologies before outlining potential control strategies which may be applicable to future MEA EPSs. A new control concept for MEA EPSs is then investigated and considered as a potential substitute of the classical control systems. Finally, a model of the newly proposed logic is implemented and simulated showing how it is able to select and apply a correct reconfiguration of the electrical system under different operating conditions.

CONCEPT FOR THE DESIGN OF FLIGHT CONTROL ACTUATION AND LAWS FOR FUTURE ALL-ELECTRIC AIRCRAFT

This paper consolidates advanced techniques for flight control law design with the sizing issues of new technology electrical flight control actuators. An automatic optimisation tool is adapted to modify the control laws for minimum actuator deflection rates, which can be turned into weight savings for the overall aircraft. Thus, the paper outlines a new and up-to-date trade-off study, which is motivated by the recent trend towards the more-electric aircraft concept.

The more electric aircraft—assessing the benefits

The concept of the more electric aircraft (MEA), where electrical power is used for at least some of the on-board functions at present powered by hydraulics and pneumatics, has many claimed benefits and is far from new. However, almost all larger aircraft retain hydraulics and pneumatics.Over recent years there has been a great deal of interest in the MEA concept, with developments in relevant technologies and their adoption in other areas of engineering. In support of UK efforts on this and related concepts, the College of Aeronautics has been performing studies since the mid 1980s to assess the benefits of changes. This paper describes the background to these studies and the relationships between them as well as some of their findings, concluding that it is important that such assessment work should be continued in the future.

Air Force Application of Advanced Magnetic Materials

ABSTRACTA national initiative is underway to develop and test a more electric aircraft (MEA) and is being led by the U.S. Air Force Research Laboratory at Wright-Patterson Air Force Base, Ohio. The MEA concept is based on utilizing electric power to drive aircraft subsystems which are currently driven by a combination of hydraulic, pneumatic, electric and mechanical power transfer systems. A major objective of this effort is to increase military aircraft reliability, maintainability and supportability and to drastically reduce the need for ground support equipment. These improvements will be realized through the further advancement of key MEA technologies, including magnetic bearings, aircraft integrated power units (IPU), and starter/generators (IS/G) internal to an aircraft main propulsion engine. These advanced developments, as well as weapon and space power applications, are the driving force for the new emphasis on high temperature and high strength magnetic materials for power applications. In determining the best magnetic material for an application it is typically necessary to conduct an engineering trade-off analysis which takes into consideration mechanical behavior, electrical loss, and magnetic properties under the conditions of actual usage. New materials solutions are required to meet these challenges, as designers often find the magnetic material performance to be the technological limitation.