Fraunhofer develops lightweight, high-performance electric motor for aircraft

The Fraunhofer Institute for Integrated Systems and Device Technology (IISB) has developed an electric motor weighing just 94 kg for use in hybrid-electric passenger aircraft in regional transport, as the IISB announced on LinkedIn. The electric motor has a comparatively high output of 750 kW for its low weight.

The IISB's permanent magnet electric motor achieves a power-to-weight ratio of 8 kW/kg due to its low weight of 94 kg and an output of 750 kW. In comparison, modern aircraft engines in aviation achieve a power-to-weight ratio of only 5 to about 6 kW/kg. The lower weight can reduce fuel consumption in a hybrid-electric aircraft, for example, thus achieving a higher range. The output of 750 kW is roughly in the range of a small turboprop machine. The electric motor is thus capable of powering a small aircraft for regional passenger transport but is intended to be significantly smaller and lighter.

Higher performance through hairpin winding technology

For the electric motor, the IISB uses hairpin windings instead of conventional winding technology. Insulated copper wires, which look like hairpins, are pressed into a stator with a slight offset. By using 4 × 3 phase hairpin windings, more copper can be accommodated in a smaller space. This not only saves about 20 percent space, but the current flow generated by them also creates a stronger rotating magnetic field that converts electrical energy into mechanical energy.

The IISB engineers also use very thin 0.15 mm NO15 steel in the motor, which is about half as thick as the steel used in conventional electric motors. Due to the lower thickness of the metal, eddy currents in the motor are reduced. This results in less Joule heat caused by them, reduces current heat losses, and thus increases the efficiency of the electric motor. This is particularly noticeable at high speeds. The motor reaches a maximum speed of 21,000 rpm.

The electric motor is divided into four sections. Each of these sections has its own winding, a separate inverter, and its own control system. If one section fails, the motor continues to run, so that the entire engine does not fail in case of a possible damage and the aircraft can continue flying if necessary.

The motor uses oil cooling instead of air cooling. The heat is dissipated more quickly, thus ensuring the high performance of the electric motor despite the compact design of the motor.

Fraunhofer IISB developed the electric motor as part of the EU project Innovative Demonstrator for Hybrid-Electric Regional Application (AMBER). In the project, a drive is to be developed that is powered by a hydrogen fuel cell, which drives an electric motor. The system is then to be used in a propeller-driven passenger aircraft for regional air traffic. The aircraft can also be equipped with a conventional kerosene-powered turboprop drive. This is intended to create a drive for lighter, quieter, and cleaner aircraft to reduce CO₂ emissions in aviation by at least 30 percent in the long term.

(olb)