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.