The fight against global climate change demands the electrification of aircraft propulsion. One of the most significant and distinct challenges that future multi-megawatt electrified propulsion will face is high voltage at high altitudes, which could cause significant partial discharge and reduce the reliability of the propulsion system. Recognizing this challenge, a multi-disciplinary research team has proposed, designed, built, and preliminarily tested a 2-kV 1-MW 20,000 RPM integrated modular motor drive (IMMD) with an unprecedented weight power density of 9 kW/kg. This paper presents the architecture, major design approaches, test results of associated power electronics systems at the rated voltage and current, and preliminary test results of the full IMMD prototype. Full power and system-level altitude tests of the IMMD are already planned at the National Aeronautics and Space Administration (NASA’s) test facility.

High power density electric motors are essential for the electrification of aircraft. Use of a segmented stator, which makes the winding process easier and allows a higher slot fill factor, can help increase the power density as well as the efficiency of a motor. The cooling for the segmented stator can be done using a cooling jacket. In this paper, three different designs are presented. Two designs use the compression sleeve that provides the mechanical support to the stator as the cooling jacket, with radial or axial fins built in. One has a dedicated cooling jacket on top of the sleeve. A numerical study was performed on the three designs. All three have similar cooling capability, with the dedicated cooling jacket having a slight advantage, but it also results in a much higher pressure drop and requires more pumping power to achieve the low resistance.

The desire to reduce carbon emissions, noise, and fuel consumption is driving recent research on electrification of traditional combustion power units. High power density motors are essential for large-scale, heavy-duty applications. To achieve high power density, thermal management systems are critical as, at elevated temperatures, electric motors are susceptible to reduced performance or even catastrophic failure.The stator winding is the primary heat source in high power motors and is the major challenge in cooling system design. Not only is controlling the temperature important for safe operation, but also the resistance of the winding increases with higher temperature, lowering the motor efficiency. As there is a high thermal conductive resistance between the windings and traditional cooling structures built on the outer surface of the motor, direct in-slot cooling is required to achieve the needed thermal management. In this paper, a novel in-slot cooling approach is discussed for a permanent magnet motor with power density higher than 22 kW/kg, based on active mass. In this approach, the stator slot, including the winding within, is encapsulated with high thermal conductivity potting material. Fluid channels are built directly into the winding turns by an investment casting process, reducing the thermal resistance between the winding and the coolant. A manufacturing process is proposed, and five different configurations are simulated and compared.

The electrification of commercial aircraft propulsion requires the development of megawatt-class electrical machines possessing high power density, high efficiency, and effective cooling. These demands are explored in this presentation of a megawatt-class surface permanent magnet (SPM) synchronous machine for aircraft propulsion applications. Substantial losses are produced in the stator windings (> 16 kW), requiring aggressive cooling measures. Three direct in-slot liquid cooling methods are reviewed and analyzed including potted channels adjacent to rectangular litz turns, litz wire with central cooling channels, and solid copper turns with internal axial cooling ducts. Electromagnetic and thermal analyses are performed for each configuration, and machine winding loss and thermal performance tradeoffs are highlighted. It is shown the potted channel approach offers appealing stator cooling performance, contributing to a high machine full-load efficiency (> 97%) and active mass power density (> 20 kW/kg).

Reduction of carbon emissions and energy savings are driving the development of lightweight, high efficiency, electric motor systems containing integrated power electronics. Thermal management is one of the major obstacles in high power density electric motor development. For high power interior permanent magnet motors, the heat loss is mainly generated in three locations: the stator core, the stator windings and the power electronics that are used to drive the motor. A compact thermal management system is developed and presented in this paper, which consists of a manifold microchannel cooling jacket, used for cooling both the stator core and power electronics, and a direct winding cooling approach employing hollow conductors.The cooling jacket has an overall ring-shaped structure, with the inner surface in contact with the stator core, and the outer surface in contact with the power electronics. A complex fluid path is designed inside the cooling jacket to lower the pressure drop and pumping power while increasing its thermal performance. For directly cooling the windings, hollow conductors allow the coolant to flow inside the conductor. This direct contact means it can handle very high heat loss. It also decouples the thermal and electrical aspects for choosing a wire insulation material. Since the heat generated in the conductor flows inwards without passing through the electric insulation, thermal conductivity doesn’t need to be a constraint to the choice of insulation material. Four different hollow conductor configurations, including one circular hollow conductor and three rectangular hollow conductor shapes, are evaluated and discussed in this study.

This paper discusses an approach for thermal management of a smart electric motor for hybrid electric aircraft propulsion. This approach uses indirect liquid cooling because it is a lightweight and reliable method for transferring large amounts of heat. A cooling jacket is designed for the stator of the aircraft propulsion motor and its cooling performance simulated for 200 kW and 1MW motors. For a 200 kW motor, the cooling jacket as designed is sufficient to keep the motor below the maximum recommended operating temperature, but additional cooling is needed for a 1 MW motor. Two approaches are discussed to address this higher cooling requirement 1) using tailored potting and insulation material to lower the internal thermal resistance, and 2) using a more advanced cooling jacket. Rotor cooling is also discussed in this paper. Rotors with light heat loading can be cooled by forced convection airflow; while those with heavy heat loading can be managed with an internal channel design. Two integration schemes of motor and power electronics are presented as well.