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Power Trip: HASTECS energizes the path to hybrid-powered flight

As aviation evolves towards a more hybrid and more electrically-powered future, it’s imperative for Europe’s aeronautical industry to have the right tools for modelling and assessing the architectures and power management requirements of tomorrow’s propulsion systems – which is exactly the remit of Clean Sky’s HASTECS project.

Clean Sky’s HASTECS (Hybrid Aircraft: Academic reSearch on Thermal & Electric Components & Systems) project is oriented around the creation of innovative models and tools that will enable Europe’s aeronautical industry to design the architecture of the hybrid-electric propulsion systems of future airliners. It’s a research project that focuses on the generation, distribution and conversion of electric power and its thermal management, as well as the associated cabling and insulation techniques. The tools being developed in HASTECS are essential for assessing these requirements and defining the necessary electrical infrastructure that will be needed to manage the multi-megawatt power of hybridpowered aircraft in the coming decades. 

“We’re looking at what the constraints are in terms of design and development, the sizing of the cables, the power requirements for the power conversion systems, the insulation aspects, and we’re also estimating the weight implications of such systems and everything connected with thermal management“ says Sébastien Dubois, HASTECS Project Officer at Clean Sky. “In Clean Sky we’ve been working on the aircraft configuration and on the technological bricks for developing hybrid-electric propulsion system, and it’s essential that we have design tools that are capable of performing rapid assessment of the benefits, and assessment of all those different elements“.

Dubois emphasises that insulation and cabling technology are particularly key: “Today, when you carry several volts within a distribution system you have a certain sizing of cables, you know exactly what kind of isolation to use to guarantee the absence of interaction and to ensure that the system is safe. But with hybrid-electric aircraft, once we start carrying several megawatts, a totally new approach is required, because the size and kind of the cables changes radically due to partial discharge phenomena. Their weight and the kind of insulation techniques that will be needed will all be totally different“. 

The HASTECS project is also taking into account such considerations as whether today’s aircraft cabling technologies based on copper wiring will be suitable, or whether something radically different is required. “We’re entering into unknown territory for which we need tools to assess the main constraints and interactions between the different elements for hybrid electric propulsion systems of the future“ adds Dubois.

At the Laboratoire PLAsma et Conversion d’Energie (LAPLACE) in Toulouse, Xavier Roboam, Directeur de Recherche CNRS and the HASTECS team have been addressing these complex questions, mindful of the need to reduce embedded weight in order to maximize the specific power/energy ratio of each device, whether it’s batteries, fuel cells, power converters, electric motors or various forms of relaying the electric power. 

“The targets proposed in the HASTECS projects are challenging“ says Roboam. “We have set a target to double the specific power of electric machines from 5kW/kg for 2025, and to 10kW/kg for 2035, while the specific powers of converters would evolve from 15kW/kg for 2025 to 25kW/kg for 2035. This expected gap between 2025 and 2035 in terms of specific powers, when installing 4 inverter–motor drives of 1.5MW, would lead to a weight reduction of 1.8 tons, which would offer a significant fuel burn reduction estimated at 3.5% for a short range (~300 nautical miles) flight“. 

Two years on, the project has formed the basis for six ongoing PhD theses, and much more besides, according to Roboam: “So far the first designs of power electronic and electric machines with cooling devices have been made, satisfying roughly the targets for 2025 in terms of specific powers. The electric motors and power converters are designed by LAPLACE Laboratory in Toulouse while innovative solutions for cooling of these devices are proposed by the Pprime institute in Poitiers. Some prospective study on future high energy density auxiliary sources (batteries, Lithium Ion) are currently being developed in LAPLACE with the expertise of the CIRIMAT Centre. A high power (low weight) electric drive system imposes to increase the voltage standards strongly beyond classical voltages in aircrafts. Subsequently, environmental constraints (low pressure, low temperature) involves partial discharges in cable insulators and electric machine windings: such constraints have to be analyzed and technical solutions have to be proposed on that topic. Finally, the overall system will be analyzed and even optimised thanks to an integrated design model which is currently built which involves the whole power system. This system level design tool couples the devices models (efficiency and weights) with the whole weight of the aircraft and subsequently with power and thrust needs to fly the mission“.

Further optimisation is ongoing to reach HASTECS’ 2035 targets in terms of the specific power/energy ratio. The partial discharge constraints will be progressively included in the design of cabling, power electronic and electric machines. Finally, a global optimisation of the overall power system is anticipated to produce improvements in terms of efficiency, embedded weight and fuel burn.

As for the “environmental benefits“, Roboam says that “ one of the major challenge ahead of us is to reduce the embedded weights when hybridising thermal (pollutant) sources with electric auxiliary sources (batteries and fuel cells) in order to produce environmental benefits (fuel burn reduction, less noise on ground with electric taxiing) as has already been the case in the automotive industry with hybrid electric vehicles