Next Generation Composite Air-gap Windings of Future Lightweight Electrical Machines

The goal of reducing CO2 from aircraft will be enabled by the system level energy benefits of electric propulsion. However, this disruptive change in aircraft design and operation will only be realised if the power-density of electrical machines (e-machines) can be substantially increased. Incremental improvements will not meet such targets, thus radical new approaches to design and manufacture using advanced materials and techniques are needed.

High-frequency, air-gap wound machine topologies, Fig. 1, where electrical steel volume is minimised, have been shown to have advantages for aircraft propulsion. However, in this topology, the reaction torque is transferred directly to the conductors requiring them to become a structural element.

Fig. 1 Illustration of an air-gap wound electrical machine (outer rotor), [2]

Fig. 2 a glass-fibre reinforced aluminium winding composite based on a 3D orthotropic weave, [1]

In this feasibility study, we will directly incorporate mechanical supports and structure into a winding layer to create a high-performance (Fig. 2), lightweight composite component for demanding propulsion applications which could yield step changes in achievable power density.

The feasibility study aims to:

  1. Identify composite manufacturing techniques and materials applicable to air-gap windings
  2. Develop material property models of such composite materials feeding into e-machine sizing tools
  3. Draw on existing EPSRC funded PhD research to size an air-gap winding using (1-2)
  4. Manufacture and test a composite air-gap winding electrically, thermally and mechanically

The design and manufacture of the proposed composite air-gap winding is highly interdisciplinary. As such, the team will involve experts in digital design and manufacture of composites structures (Dr Jonathan Belnoue from Bristol Composites Institute and the National Composite Centre), digital design and manufacture of electrical machines (Dr Nick Simpson from the Electrical Energy Management Group at the University of Bristol) and high-performance composites manufacturing (Dr Andrew Limmack from the National Composites Centre).


[1] Mellor, P.H., Heath, C., Collins, S., Simpson, N. and Bond, I., 2019. Addressing the challenges of lightweight aircraft electric propulsion through electrical machines with air-gap windings. In 2019 IEEE Energy Conversion Congress and Exposition (ECCE) (pp. 4470-4476). IEEE.

[2] Yi, X., Yoon, A. and Haran, K.S., 2017, May. Multi-physics optimization for high-frequency air-core permanent-magnet motor of aircraft application. In 2017 IEEE International Electric Machines and Drives Conference (IEMDC) (pp. 1-8). IEEE