All-electric Aircraft Research Articles

Promising electric aviation industry and its bright future

There have been rising concerns about the amount of greenhouse gas emissions that commercial aviation produces each year. Greenhouse gases generated by aircraft trap the sunlight in the ozone layer, causing the planet's temperature to rise yearly. Thus, developing more electric aircraft (MEA) and all-electric aircraft (AEA) is crucial to serve as alternatives to traditional fossil-fuel airplanes to avert climate change. Although electric aircraft theoretically provide numerous benefits in improving efficiency, reducing noise levels, and cutting emissions, numerous challenges exist, such as energy density, cost, and power distribution. This paper aims to analyze these challenges and looks for potential technologies or systems, including electromechanical actuators, high energy-density lithium batteries, and superconducting motors, to resolve these challenges. Overall, the electric aviation industry is promising with further improved new technologies. While MEA will become common shortly, there will still be at least two to three decades before AEA establishes ground and become prevalent in the commercial aviation industry.

Life cycle assessment of a two-seater all-electric aircraft

PurposeAviation is an important contributor to climate change and other environmental problems. Electrification is one option for reducing the environmental impacts of aviation. The aim of this study is to provide the first life cycle assessment (LCA) results representing an existing commercial, two-seater, all-electric aircraft.MethodsAn attributional cradle-to-grave LCA was conducted with a functional unit of 1 h flight time. Data and records from an aircraft manufacturer informed much of the study. Detailed modelling of important aircraft components is provided, including the battery, motor, inverter, instrument panel and seats. Impact results are compared to those from a similar but fossil fuel–based two-seater aircraft. A wide range of impact categories was considered, while the focus was on global warming, resource depletion, particulate matter, acidification and ozone formation.Results and discussionThe main contributors to almost all impact categories are the airframe, the lithium-ion battery and emissions (in the use phase). The airframe has a major impact as it contains energy-intensive, carbon fibre–reinforced composites, the impact of which can be reduced by recycling. The battery dominates mineral resource depletion categories and contributes notably to emission-based categories. Producing batteries using non-fossil energy or shifting to less resource-intensive, next-generation batteries would reduce their impact. Use-phase impacts can be reduced by sourcing non-fossil electricity. Despite the need for multiple battery pack replacements, the comparison with the fossil fuel option (based on equal lifetimes) still showed the electric aircraft contributing less to global warming, even in a high-carbon electricity scenario. By contrast, when it concerned mineral resources, the electric aircraft had greater impact than the fossil fuel based one.ConclusionsA sufficiently long lifetime is key to bringing the all-electric aircraft’s environmental impacts (such as global warming) below those of fossil fuel–based aircraft. The high burden of the airframe and batteries can then be outweighed by the benefit of more efficient and emission-free electric propulsion. However, this comes with a trade-off in terms of increased mineral resource use.

Market capabilities and environmental impact of all-electric aircraft

The transportation sector accounts for 28% of US-based and 14% of global greenhouse gas emissions. Transitioning from hydrocarbon-powered vehicles to electric vehicles such as all-electric aircraft (AEA) in parallel with use of reduced-emissions power sources is one possible method to curtail future sector emissions. However, AEA market capabilities and environmental impact are uncertain and insufficiently quantified in the literature. The present work evaluates AEA in the United States on national and state-by-state bases through 2050, considering four emerging battery architectures and two emissions scenarios. AEA using lithium-air cells with a projected specific energy of 915 Wh/kg could achieve 46.6% of total domestic commercial passenger share and 20.9% of total domestic commercial revenue passenger kilometers (RPK) by 2050, corresponding to a net CO2-equivalent emissions reduction of 1.02% – 19.8%. This work demonstrates clear potential for AEA, although achieving substantive aviation sector emissions reductions requires transition to reduced-emissions power generation.

Evolution and comparison of three typical permanent magnet machines for all-electric aircraft propulsion

Evolution and comparison of three typical permanent magnet machines for all-electric aircraft propulsion

Design of High Power Density MVDC Cables for Wide-Body All Electric Aircraft

Aircraft electrification yields the next generation of aircraft such as more electric aircraft (MEA) and all electric aircraft (AEA). These aircraft require high-power-density and low-system-mass electric power systems (EPS). To this end, the voltage of the system must be enhanced to reach medium voltage levels in a few kV ranges. However, using medium voltage (MV) EPS for aircraft exacerbates the challenges of designing aircraft cables such as arc and arc tracking, partial discharges (PD), and thermal management. In this paper, several novel multi-layer based insulation systems for MVDC power cables are proposed to resolve aircraft cables’ challenges while maintaining low weight and size. The proposed cables are thermally and electrically analyzed and compared to cable systems designed based on IEC60502 and AS50881 standards. We use a coupled electrical-thermal-fluid flow dynamic model, for simulations where all possible heat transfer approaches, including conduction, convection, and radiation, to transfer mainly the joule heating generated in the core conductor to ambient with a low pressure of 18.8 kPa which is the air pressure at cruising height of wide-body aircraft (12.2 km) are considered and modeled. To compare the proposed cables to the designs based on IEC 60502 and AS50881, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> is introduced, which is the product of cables’ overall mass in a unit length and diameter. The results show that besides benefiting multi-layer, multi-function insulation systems to resolve aircraft cables’ challenges, the overall diameter and weight of the designed cables are lower than single-layer insulation system designs based on AS50881 and IEC60502.

Dimensionless study of phase-change-based thermal protection for pulsed electromagnetic machines: Towards heat absorption-dissipation matching

The concept of “more- and all-electric aircraft” has become increasingly popular over the last two decades, leading to a boost in the extensive utilization of airborne electromagnetic actuators such as permanent magnet synchronous machines (PMSMs). Inevitably, considerable waste heat is generated during operation due to the incomplete energy conversion, which is a great challenge for conventional onboard thermal control systems. If the huge generated heat cannot be removed efficiently there will be a sharp temperature rise in thermal-sensitive components of the onboard devices. This overheating will cause operational failures which are intolerable in aerospace applications. Aiming to improve the current thermal protection system and gain greater compatibility with the current PMSM system, this paper proposes a phase change material-based (PCM-based) thermal protection strategy using commercial wax in two equivalent PMSMs. A comparative investigation shows that the machine temperature with PCM-based cooling strategy can be reduced under most operating conditions (the maximum temperature drop is 13.7 °C), demonstrating the advantages of deploying the proposed PCM-based cooling scheme. Further data processing towards the heat absorption-dissipation matching between the utilized PCM and the working mode of the cooling object is conducted. A dimensionless correlation of dimensionless temperature peak difference (DTPD) as a function of the pulsed factor, presented in Eq. (17), reveals an average relative error of ±4.5%. Based on the correlation, an optimal pulsed factor of ∼1.764 is calculated to reach a matching condition. Such a method can be promoted to wider applications using PCM as a cooling medium beyond the currently-utilized two types of machines in this paper.

Optimized multi-timescale energy management strategy of a novel all-electric aircraft power system unit based on decentralized control

This paper presents an optimized multi-timescale energy management strategy (MTEMS) for a novel all-electric aircraft (AEA) power system unit, which consists of a hybrid energy storage system comprising super-capacitor (SC), battery and fuel cell (FC), as well as a dual three phase permanent magnet synchronous motor (DTP-PMSM) system serving as the propulsion system. During transient states characterized by rapid load changes, the proposed strategy effectively allocates power from the low-frequency, medium-frequency, and high-frequency domains to their respective units, namely FC unit, battery unit, and SC unit. This power allocation is achieved through decentralized droop control implemented in the proposed MTEMS, ensuring a constant and stable bus voltage throughout the operation. In addition, during the steady-state after the change of the load power, a distributed optimization method of the proposed MTEMS can calculate the ratio of power outputs between the battery and FC to maximize the operational efficiency of the fuel cell while ensuring the battery operates in an economically optimal condition. This ultimately guarantees the entire system operates under optimal operating conditions. The achievement of the output power ratio is attainable through the implementation of decentralized droop control. Finally, a 1 kW experimental platform is constructed to validate the effectiveness of the proposed MTEMS and verify the analytical results.

Methodology for determining the takeoff mass of all-electric aircraft at the early stages of design

Methodology for determining the takeoff mass of all-electric aircraft at the early stages of design

Analysis of Discharge Failure Mechanism of IGBT Power Modules

IGBT power modules are usually used as circuit-breaking components in power systems, and are widely used in solid-state DC circuit breakers, hybrid DC circuit breakers, all-electric aircraft, high-speed railways, new energy vehicles, and power transmission systems. In these systems, IGBT power modules are usually faced with extremely harsh working conditions and there is a failure risk. Insulation degradation should be a cause for concern as a potential path of power module failure. In this paper, the discharge phenomena of the IGBT power module were observed based on Intensified Charge Coupled Devices (ICCD), and the triple junctions composed of copper–ceramic–silicone gel inside IGBT were found as the discharge points. Furthermore, the directed bonded copper (DBC) ceramic filled with silicone gel was used as a test sample to study the discharge failure process, including the partial discharge (PD), surface charges, and electric trees. The mechanism of discharge failure is discussed and analyzed. The insulation degradation process is accompanied by phenomena such as severe partial discharge and rapid electric tree growth. This research provides support for the analysis idea and guidance of the research method for the cause of power module failure.

Protection System Architecture for All-Electric Aircraft

To reduce emissions from the aviation industry and meet the targets set by different countries, research has been focused on investigating all-electric aircraft. To make this vision practical, superconducting machines are expected to power the propellers, as they are half the size and a third the weight of conventional machines. The main purpose of this paper is to do a higher-level study of a reliable holistic protection system for all-electric aircraft; that can reduce heat leakage and be able to detect faults reliably. Thus, three main protection systems were investigated; 1) cryogenic voltage source converter superconducting magnetic energy storage system (VSC-SMES), 2) cryogenic dc breaker integrated with superconducting fault current limiter (SFCL), and 3) machine learning algorithm for fault detection. By immersing the protection system at cryogenic temperature, the paper has shown that passive leakage can be eliminated, and thus more energy can be saved for the fuel cell. The paper has also demonstrated that using machine learning for the SFCL-dc-breaker system can consistently eliminate faults and protect the system.

A Double Rotor Flux Switching Machine With HTS Field Coils for All Electric Aircraft Applications

The increasing demand for high-power density motors in electric transport industries opens a new research opportunity to develop motor topologies with less weight and high efficiency. In particular, all-electric aircraft applications require very high power density motors. This paper shows the design of a new 1 MW 20-pole/15-slot double rotor flux switching machine with high-temperature superconducting field coils and thermal management system. The proposed motor features an air-core stator. Aluminum Litz wire is used for the armature conductors, and the YBCO- high-temperature superconducting material is used for the field coils. The armature winding and field coils operate at 95K and 65K, respectively. The active part power density including rotors, armature windings and field coils obtained with the proposed design is 29.3kW/kg. The specific power density of proposed motor considering mechanical, support structure and TMS is about 18.5 kW/kg. The efficiency can be higher than 98.7% which satisfies the requirement of electric aviation.

Numerical Simulation of Atomization Characteristics of Perfluorohexanone under Low-Pressure Environment

Since perfluorohexanone can play a role in cooling and extinguishing the heat loss of lithium batteries, it is urgent to study the atomization characteristics of perfluorohexanone in different ambient pressures (49 kPa, 75 kPa, 101 kPa) to ensure the flight safety of all-electric aircraft in the future and the storage and use the safety of lithium-ion battery in high plateau areas. The process of the primary and secondary breakup was studied by using the VOF-DPM model, and the influence of different environmental pressures on the development of atomization and its atomization characteristics was analyzed. The results showed that the primary breakup of the perfluorohexanone liquid sheet was caused by Kelvin Helmholtz/Rayleigh-Taylor (KH-RT), while the secondary breakup was mainly caused by RT instability. Under different environmental pressures, the Sauter Mean Diameter of (D32) along the spray axis decreases sharply at first and then increases slowly. As the air density decreases with the decrease of air pressure, D32 gradually increases, resulting in the decrease of atomization mass. Moreover, when the atomization drops from 101 kPa to 49 kPa, D32 of droplets increases by 38% to 51%, which is conducive to providing evidence for the effectiveness of perfluorohexanone in fire extinguishing under low-pressure conditions.

Design of a Direct-Liquid-Cooled Motor and Operation Strategy for the Cooling System

To make an all-electric aircraft possible, both high power densities and efficiencies are needed. However, particularly high demands are also placed on the thermal management system. Often, the electric motor and cooling system are considered without co-optimization. Particularly in the case of electric motors with conductors directly cooled by a liquid, there is great potential for optimization, since the temperature-dependent Joule losses determine the largest part of the losses. This publication shows the main influencing parameters for the electric motor and cooling system: coolant speed and winding temperature. In addition, the influence of the cooling system control during a flight mission is demonstrated and its potential in mass reduction is quantified. It could be shown that with a low utilized electric motor the maximum winding temperature of 130 °C is beneficial, the cooling system should work in almost all operation points in its sized operation and the mass of the heat exchanger and pump is negligible compared to the mass of the electric motor and energy storage.

MODELING AND SIMULATION OF AN AIRCRAFT ELECTRICAL POWER SYSTEM

Although recent developments in aircraft electrical technology have had a significant impact on aircraft electrical power systems (EPS), thus reminding the development and production of more electric aircraft (MEA), but also important steps in the development of all-electric aircraft (AEA), still the EPS of the latest aircraft produced by the two big players in the market, the Neo series from Airbus and the NG or Max from Boeing respectively, is completely traditional – a constant speed constant frequency (CSCF) system. Thus, for an alternating current one, it is composed of the power source – the integrated drive generator (IDG), the command and control system – the generator control unit (GCU), the transmission and distribution system, the protection system – the CBs (circuit breaker) and electrical loads. This paper presents the design and simulation of an aircraft EPS using Simulink’s Simscape package, a MATLAB program, and for the first time in the specialized literature, a model of the constant speed drive (CSD) generated with the same program is used to drive the synchronous generator (SG) in the IDG.

Systems Integration Framework for Hybrid-Electric Commuter and Regional Aircraft

System integration is one of the key challenges to bringing future hybrid-electric and all-electric aircraft into the market. In addition, retrofitting and redesigning existing aircraft are potential paths toward achieving hybrid and all-electric flight, which are even more challenging goals from a system integration perspective. Therefore, integration tools that bridge the gap between the aircraft and the subsystem level need to be developed for use in the conceptual design stage to address current system integration challenges, such as the use of space, the share between propulsive and secondary power, required level of electrification, safety, and thermal management. This paper presents a multidisciplinary design analysis (MDA) framework that integrates aircraft and subsystem sizing tools. In addition, this paper includes improved physics-based subsystem sizing methods that are also applicable to smaller, commuter, or regional aircraft. The capabilities of the developed framework and tools are presented for a case study covering the redesign of the DO-228 with a hybrid-electric propulsion system in combination with the electrification of its systems architecture and different subsystem technologies.

Application analysis of self-bonded electrical steel sheet in high power density PMSM for all-electric aircraft

Driving motor for all-electric aircraft (AEA) needs high power density and high torque density, resulting in the magnetic load and electrical load of driving motor in a limit state. Therefore, it is important to analyze the accurate calculation of core loss and the technology of loss suppression. Firstly, B35A230 self-bonded electrical steel sheet is used as core, which can reduce core loss caused by machining process. Then the ratio-loss curves of B35A230 at different frequencies and different flux densities are measured by Epstein frame and ring sample method, and the increment of core loss after machining is obtained, and the influence of axial welding paths on stator core loss is analyzed. According to experimental results, Based on the classical stator core loss model, machining factors are considered to improve the accuracy of stator core loss, and a core loss model is adopted to improve accuracy, considering processing factor, alternating and rotating magnetization modes and harmonic magnetic field. Finally, an outer rotor SPMSM for AEA is designed and manufactured, and the no-load loss is tested experimentally, which verified that the self-bonded electrical steel sheet has certain advantages in high power density driving motor.

The More-Electric Aircraft and Beyond

Aviation is a significant contributor to greenhouse gas (GHG) emissions in the transportation sector. As the adoption of electric cars increases and GHG emissions due to other modes of transport decrease, the impact of air travel on environmental pollution has become even more significant. To reduce pollution and maintenance, and ensure cheaper and more convenient flights, industry and academia have directed their efforts toward aircraft electrification. Considering various types of aircraft, several frameworks have been proposed: more-electric aircraft (MEA), hybrid electric aircraft (HEA), and all-electric aircraft (AEA). In the MEA framework, propulsion is generated by a conventional jet engine; however, all secondary systems (hydraulic, pneumatic, and actuation) are electrified. By further increasing electrification, electric motors can provide propulsion with the electric power supplied by the conventional engine (i.e., HEA) or from electrical energy storage (i.e., AEA). Power electronics and electrical machines play a key role in this scenario in which electric power must be efficiently generated, distributed, and consumed to satisfy extremely high requirements of aviation safety. This article provides an overview of recent advancements in aircraft electrification, and trends and future developments referenced to the global aviation roadmap.

Special issue on all‐electric and hybrid‐electric flight

Special issue on all‐electric and hybrid‐electric flight

Development and Challenge of More/All Electric Aircraft

With the rapid development of the aviation industry and the increasing environmental concern, the electrification of aircraft has become a leading research topic in aviation. More Electric Aircraft (MEA) and All Electric Aircraft (AEA) are two classifications of this field. MEA is designed to apply electrical structures to update traditional hydraulic and mechanical equipment, so as to improve the fuel efficiency of the aircraft, while the main propulsion power is still provided by aviation fuel. This excogitation has been developed in stages and put into commercial use. AEA is a more idealized design which aims to eliminate all forms of energy other than electrical energy on the aircraft in order to achieve higher efficiency and environmental goals. Research on AEA encounters multiple technical barriers, mainly the battery energy density. This paper introduces developments on the structures involved in the electrification of aircraft and their characteristics, then systematically analyses the main technical factors that limit the development of AEA and the possible technological breakthroughs in the future.

Axial backlash of planetary roller screw mechanisms: Geometric modelling and Sobol's analysis of design parameters

Planetary roller screw mechanisms (PRSMs) are promising for the future all-electric aircraft flight controls because they allow transmission of high loads while being compact. However, impacts after axial backlash transit are critical when loads are alternate. In this paper, the influence of PRSM design parameters on the axial backlash is analysed. First, axial backlash is geometrically modelled. PRSM conformal contacts require multi-precision computation to avoid numerical cancellation. Second, Sobol's analysis is implemented on four industrial PRSMs. Results show that three out of six parameters are influential independently from the geometry considered. Controlling these parameters is thus mandatory for aeronautical applications.