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par Laurence Laffont - publié le

At the End of the HASTECS Project : "A Great Success for the Powertrain for a Future Hybrid Electric Aircraft More Respectful of the Environment"

The HASTECS -Hybrid Aircraft Project : Academic reSearch on Thermal and Electrical Components and Systems-, as part of the European program "Clean Sky 2" (H2020), exceeds the expected results. It identifies the most promising technologies, breakthroughs and innovative tools to increase the efficiency of electrical processes and reduces the embedded masses in hybrid propulsion systems for future aircrafts that are more respectful of the environment. Leader of the HASTECS project, LAPLACE (UMR CNRS - Toulouse INP - UPS), a laboratory specialized in power conversion, has joined forces with the Institut P’ (UPR CNRS located at ENSMA Poitiers) for the cooling of electrical machines and power electronics ; Toulouse INP coordinating the project.

Ambitious Goals :
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The HASTECS Project (Hybrid Aircraft ; Academic research on Thermal and Electrical Components and Systems), an integral part of the European program "Clean Sky 2" (H2020) took off in September 2016. It aimed to identify the most promising technologies and breakthroughs and to innovate in tools making possible the increase in efficiency of electrical processes and to reduce the on-board masses in hybrid propulsion systems for a future aircraft more respectful of the environment. These objectives applied to the case of a regional aircraft, sized for approximately 70 seats with an action range of less than 1000 km. A serie’s hybrid architecture was chosen by Airbus, coupling a gas turbine and an auxiliary power source with fuel cells or batteries to supply a 100% electric propulsion chain.
But these goals could not be met providing specific powers not hitting high enough : the HASTECS consortium thus set itself the challenge of doubling the specific power of electric machines with cooling and increasing it by 5kW/kg, towards a technological target in 2025, at 10kW/kg in 2035, while the power electronics (cooling included) would evolve from 15kW/kg in 2025 to 25kW/kg in 2035, despite particularly severe environmental constraints (thermal, partial discharges, etc.). To give an idea, the motorization of a Tesla electric vehicle displays a specific power of less than 4kW/kg for the motor with its cooling ...

A Real Technological and Scientific Success

On Friday, April 23rd 2021, the last of the 6 doctoral theses was supported, with also two post-doctorates associated, thus bringing a very fine finish to a scientific adventure particularly rich in results and scientific exchanges.
It should be noted from the outset that all of the project’s expectations have been fulfilled. In particular, the targets in terms of specific power (power - mass ratio) and energy efficiency were even exceeded, which "would contribute to the weight loss and efficiency of a future aircraft !" : HASTECS therefore has been a real technological and scientific success, punctuated by abundant scientific productions, many publications by the consortium’s teams and research institutes, bringing a successful interdisciplinary research.

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High Performance Electric Motors

The electric motors’ design, carried out by the GREM3 team of LAPLACE, lead to high specific powers, exceeding 11kW/kg by integrating the cooling system, with high efficiencies, greater than 97%. This design has been obtained thanks to high-performance permanent magnet synchronous motor with Halbach structure. The optimization under constraints of current densities, magnetic fields and the increase in rotation speeds were key drivers to which was added the use of special windings (compact rectangular Litz wires) and high performance ultra-thin magnetic sheets to limit high frequency copper losses and iron losses : this has been what made it possible to obtain excellent efficiencies exceeding 97%. But optimizing the electromechanical conversion was nothing without an equally powerful cooling system. This was the case of the concepts proposed by Institut P’, which combined glycol water cooling for the stator and the rotor, to which it was necessary to couple an internal cooling, directly within stator slots, to achieve such specific powers.

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Optimization of Power Electronics and High Voltage Network

In order to efficiently convert the power between the electric distribution (high voltage DC bus) and the electric motors, solutions have been proposed by the “Convertisseur Statique” team at LAPLACE to optimise the integration of power electronics. The joint use of a high voltage bus (close to 2kV), with its optimised mechanical structure (bus bar), the best electronic components (7th generation IGBTs) and modulation strategies also optimized for various multilevel-conversion structures has proven to be particularly effective in terms of compactness and efficiency (yield of the order of 99%). As with the machine, optimizing the power electronics was nothing without a very high performance cooling system. This has been the case with the concepts studied by the Institut P’ and the GREPHE team at LAPLACE, which proposed ultra-efficient two-phase capillary pumped cooling systems : the device was capable of extracting 4.5kW of heat losses for 1 kg of cooling system, allowing the complete power conversion system to greatly exceed 30kW/kg, well beyond the targets set !

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Fuel Cells 2 Times More Compact in Specific Energy than the Best "Energy Batteries" by 2030

A study carried out jointly by CIRIMAT and LAPLACE (by the GENESYS group) also concerned the auxiliary electrical sources hybridized with thermal sources (gas turbine) : the conclusions showed that, for this case of application to series hybrid regional aircraft, fuel cells with cryogenic hydrogen storage (stored at 20°K in liquid form) were almost twice as compact in specific energy (Wh/kg) than the best “energy batteries” set by 2030.

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Optimized System Integration : an Improved Compromise between On-Board Weight and Kerosene Consumption

Finally, one of the major expectations of the HASTECS project was the definition of the voltage level of the electric distribution (HVDC bus) which constituted a significant coupling factor on the mass of the main components (electrical machine, power electronics, wiring, etc.) by integrating environmental constraints specific to aeronautics. In this context, an in-depth study on the impact of partial discharges in the electrical machines insulators and power electronics, was carried out by the MDCE team of LAPLACE. In the end, the best system compromise on the choice of this voltage was between 1300 and 2000V. This result could not have been obtained without the overall optimization of the propulsion chain carried out by the GENESYS team at LAPLACE : all the technological choices and scientific concepts were integrated through surrogate models making it possible to offer a global vision on the complete propulsion chain, from sources to propellers.

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Ultimately, these optimized integration results lead to an improved compromise between on board mass and kerosene consumption compared to the targets initially set for the project.

The HASTECS project has received funding from the European Union’s Horizon 2020 (cleansky 2 JTI) research and innovation program (2014–2024), under grant agreement No. 715483.

Contact  : X. Roboam (DR CNRS-LAPLACE coordinator HASTECS)

Some references :
Thesis 1 : S. Touhami, “Analytical Sizing Models to Assess the Performances of High Specific Power Electric Motors for Hybrid Aircraft,” PhD Thesis, Institut National Polytechnique de Toulouse (Toulouse INP), 2020.

Thesis 2 : N. Erroui, “Chaine de conversion forte puissance pour la propulsion aéronautique hybride,” PhD Thesis, Institut National Polytechnique de Toulouse (Toulouse INP), 2019.

Thesis 3 : A. Zeaiter, “Thermal Modeling and Cooling of Electric Motors Application to the Propulsion of Hybrid Aircraft,” PhD Thesis, École Nationale Supérieure de Mécanique et d’Aérotechnique (ENSMA), 2020.

Thesis 4 : F. Accorinti, “Two-phase Power Electronics Cooling Solution Design in Air Context Answer to the Objectives of the Hybrid Aircraft 2035.,” PhD Thesis, École Nationale Supérieure de Mécanique et d’Aérotechnique (ENSMA), 2020.

Thesis 5 : P. Collin “Design, Taking Into Account the Partial Discharges Phenomena, of the Electrical Insulation System (eis) of High Power Electrical Motors for Hybrid Electric Propulsion of Future Regional Aircrafts,” PhD Thesis, Institut National Polytechnique de Toulouse (Toulouse INP), 2020.

Thesis 6 M. Pettes Duler, “Integrated Optimal Design of a Hybrid-Electric Aircraft Powertrain,” PhD Thesis, Institut National Polytechnique de Toulouse (Toulouse INP), 2021.

Post Doc 1 : M. Tognan, Battery & Fuel Cell state of the art & metamodels ; ‘HASTECS Technical rRport, 2019.

Post Doc 2 : M E Banda, D Malec and JP Cambronne, “Partial Discharge (DP) Prevention Within Power Converter Busbars Dedicated to Hybrid Aircraft Propulsion, Hastecs technical report, 2018.

Press release,19992
• Power Trip : HASTECS energizes the path to hybrid-powered flight, 2018,

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