Global warming concern is pushing aviation to introduce innovative technologies for greener flights, since aviation stakeholders committed to ambitious targets of reducing global net aviation carbon emissions by 50% by 2050 compared to 2005. Hybrid-electric propulsion is one of the solutions proposed to reach this ambitious goal. The introduction of such solution opens new opportunities and originates new challenges as well, such as the need for dedicated thermal management systems (TMS) to cool-down electric machines. European Union has co-funded ORCHESTRA(Optimised electric network aRCHitEctures and SysTems for moRe-electric Aircraft) Project to design new technologies allowing 10% efficiency increase and 25% weight reduction of electric power system (EPS) compared to state-of-the-art. Within ORCHESTRA Project, Skylife developed a Dual Active Bridge (DAB) bi-directional modular converter to manage the power transfer between Kilo-Voltage Direct Current (kVDC) bus (1-3kV) and High Voltage Direct Current (HVDC) bus (540V). 

Consortia: University of Nottingham (coordinator), Leonardo, Safran Electrical & Power, Safran, C.I.R.A, Fraunhofer, Aeromechs, AIT (Austrian Institute of Technology), BSIM, Skylife Engineering, VR Aviation Safety Partnership

Introduction

On-board aircraft power demand is continuously increasing, due to both the introduction of new onboard systems requiring additional power, and since the concern related to aviation impact on global warming is increasing, pushing towards aircraft electrification. In particular, the Intergovernmental Panel on Climate Change has set the target of at least 50% reduction of carbon dioxide (CO2) emissions by 2050. However, it is expected that global CO2 emissions produced by mobility sector will increase of 80% by the end of 2050. 

According to ICAO, about 20% of the foreseen increase should be produced by aviation. Thus, to meet overall mobility emission reduction targets, the Advisory Council for Aeronautics Research in Europe (ACARE) has defined the Flightpath 2050, according to which it is expected a reduction of 75% in CO2 and 90% in Nitrogen Oxides (NO) emissions.

These ambitious goals can be achieved by introducing new aircraft configurations and/or disruptive technologies, such as hybrid/electric propulsion for aircraft, changing the paradigm of current aviation market, which is still based on the use of jet engines introduced in 1950s.

The introduction of hybrid/electric power-plants opens new potentialities, but also new challenges to be faced. One of the main challenges to solve is the way to dissipate heat produced by hybrid/electric power-plant components: such systems cannot use conventional techniques applied in current aircraft and have strict thermal constraints to be met. Thus, detailed studies of TMS are needed to unleash the potentialities of hybrid/electric propulsion system.

European Union (EU) has co-funded the ORCHESTRA Project [5] with the aim to design new technologies allowing 10% efficiency increase and 25% weight reduction of electric power system (EPS) compared to state-of-the-art.

In this paper the design of a novel bidirectional modular converter to manage the power transfer between kVDC bus (1-3kV) and HVDC bus (540V) of the multi-Mega Watt (MW) architecture of a future Much More Electric Aircraft (M2EA) is proposed. The selected topology for this equipment is a DAB. Then, the design of an optimized TMS for the thermal control of the DAB is shown, including the feasibility study of SMA to improve off-design performance.

Bi-directional 1-3kV/540 converter for Multi-Megawatt Topology

The power converter designed for this project has one main characteristic to consider: the high voltage input, whether 1 kV or 3 kV. Usually, for that voltage level, the most typical solutions include IGBT (Insulated Gate Bipolar Transistor) modules as semiconductors, for their high voltage withstanding capability, and high current capability. However, in this case, the converter’s size and weight are also critical, and that is the reason that motivated the increasing of switching frequency, making imperative the use of faster devices like SiC MosFETs (Silicon Carbide Metal-OxideSemiconductor Field-Effect Transistors), with good voltage withstand and current capability.

The chosen topology for the DC/DC converter was the Dual-Active Bridge converter. This choice was based on the main characteristics of this topology: bi-directional power flow, high efficiency, voltage regulation, galvanic isolation, reduced harmonics and modularity. This last characteristic was the one that allowed the use of the converter in different modular configurations to work at an input voltage of 1 kV or 3 kV. When the input voltage is 1 kV, the converters have their input connected in parallel in what is called IPOP (Input Parallel, Output Parallel). When the input voltage is 3 kV their input is connected in series, in what is called ISOP (Input Series, Output Parallel). Both connections are represented bellow.

Electrical design

The design of the converters was made to reach the characteristics presented bellow:

• Nominal Power: 70kW
• Nominal Voltage kVDC: 1kV
• Nominal Voltage HVDC: 540V
• Topology: Dual-active bridge

Reference: Diego Giuseppe Romano, Salvatore Ameduri, Antonio Carozza, Bernardino Galasso, Gianluca Marinaro, Edson Lima Junior Manuel Lagares, Carmen Bejarano Espada, María Dolores Jiménez Sánchez (2024),  Development of a bi-directional modular converter and its thermal management system for a future much more electric aircraft, International Conference on More Electric Aircraf, France

This project has received Horizon 2020 funding under the European Union's Horizon 2020 research and innovation program under grant agreement number 101006771.

Se ha recibido un incentivo de la Agencia de Innovación y Desarrollo de Andalucía IDEA, de la Junta de Andalucía cofinanciado en un 80% por la Unión Europea a través del Fondo Europeo de Desarrollo Regional, FEDER para la realización del proyecto "Metallic Environment Research loCation for the Use in the IndustRY" con el objetivo de Promover el desarrollo tecnológico, la innovación y una investigación de calidad.

Since the 1990s, satellite navigation systems have been integrated into many aspects of our lives. However, it is important to have reliable positioning alternatives for when this tool is not available. These advancements mostly focus on military innovation and defense, ensuring the movement of aircraft, vehicles, and troops in electronic warfare environments.

What are Global Navigation Satellite Systems?

Global Navigation Satellite Systems (GNSS) are positioning and navigation systems that use a network of satellites in orbit around the Earth to determine the precise location of a receiver anywhere in the world. These systems are designed to provide three-dimensional positioning information of an object, its speed of movement, and the time it is located at a specific place with very high accuracy.

The most well-known and widely used GNSS is the Global Positioning System (GPS) developed by the United States. There are also other GNSS systems such as Russia's GLONASS, the European Union's Galileo, and China's Beidou. These systems operate through a constellation of satellites that transmit navigation signals to receivers on Earth. These receivers use the signals received from multiple satellites to calculate their position with an accuracy of a few meters or even centimeters, depending on the quality of the receiver and the number of signals received.

GNSS systems have revolutionized the way we navigate and move around the world. They are currently used in a wide range of civilian, industrial, and military applications, including maritime navigation, aviation, mapping, emergency services, and precision agriculture.

Alternatives to GNSS

When it is not possible to use Global Navigation Satellite Systems, either due to their unavailability or their unreliability, such as in dense urban environments, near ports with a saturation of positioning equipment that hinders ship docking, or in cases of electronic attacks, there are a number of experimental alternative technologies.

One of these alternatives is inertial navigation, which uses sensors such as accelerometers and gyroscopes to measure changes in velocity and the orientation of a moving object. These sensors allow determining the relative position and trajectory of the object, although they can accumulate errors over time as measurements accumulate.

Another alternative is the use of terrestrial beacons and radio frequencies. This method is based on receiving signals emitted by ground stations, which contain position and time information. Receivers can measure the time difference between the signals and calculate the position. However, this approach requires considerable terrestrial infrastructure and a good understanding of the location and characteristics of the beacons.

Similarly, there are systems based on radio direction finding, which use directional antennas to measure the direction of arrival of radio signals from known transmitters. However, their range is limited to very specific areas and depends entirely on the available infrastructure.

These alternatives have limitations in terms of accuracy and reliability compared to GNSS systems, so their application depends on the context and specific needs of each case.

The OPTIMISEProject

With the aim of offering a precise and improved alternative for positioning and navigation without relying on GNSS, Skylife Engineering has coordinated the R&D and innovation project OPTIMISE. The main objective is a research effort to enhance positioning, navigation, and timing in areas where access to GNSS systems is not available, through an innovative architecture that combines data from different signals and sensors.

The OPTIMISE platform merges various technologies for PNT (Positioning, Navigation, and Timing), which, when combined, seek to achieve a more reliable result. In addition to using more modern and effective sensors, a significant part of the project seeks to test a wide range of tools based on emerging technologies for specific situations, along with central software that integrates and fuses them to obtain a more accurate and robust solution.

The technologies involved in the project include:

• Feasibility study to bring magneto-inertial technology to the aerial platform.
• Positioning system based on signals of opportunity (SoOp) with parallel processing.
• Advanced integration of synthetic aperture radar (SAR) on aerial platforms to test the technological feasibility of the system.
• MEMS atomic clock and atomic inertial measurement unit (IMU).
• Stellar navigation system.

Firstly, several workshopswere conducted with experts throughout 2021 to define requirements and constraints, as well as to study the current state of available technologies and methods. Based on this, the scenarios and roadmapfor the development of the different systems were defined. Subsequently, prototypes were designed for each technology, and from June 2022 to April 2023, various integration and validation tests were carried out on both land and in-flight at the Žilina airport in Slovakia. To measure the results, a reference trajectory for the aircraft was defined.

After the flight tests, an evaluation of the different technologies was conducted based on sensor reliability criteria, fusion accuracy, latency, update rate and data availability, yielding the following result:

OPTIMISE is another testament to how Skylife actively participates in innovation and the development of new technologies in fields such as PNT technology development in European Union defense programs. In this project, coordinated by Skylife, participants included MBDA, Sener Aeroespacial, ONERA - The French Aerospace Lab, SYRLINKS, STARNAV, SYSNAV, the University of Žilina, and AICIA (Andalusian Association for Research and Industrial Cooperation).

OPTIMISE is part of the European Union program called PADR (Preparatory Action on Defense Research) (GA No 884134), and its results will be taken into account for the allocation of funds for research from the European Defense Fund (EDF).