Research on key technologies of ultra-high power density motor drive system for electric vehicles

The motor housing adopts an integrated cast water jacket, which reduces costs while also improving the housing stiffness and mode, as shown in Figure 15.

Figure 15 Advanced motor structure and process design

2.3 Improve thermal design and thermal management

2.3.1 Efficient Oil Cooling

Strengthening cooling can reduce temperature rise, reduce copper wire resistance, reduce copper loss, reduce temperature loss of permanent magnet magnetic properties, increase power output, and thus improve efficiency; after strengthening cooling, higher electromagnetic loads can be used, thereby increasing power density; the efficiency and power density of the motor are taken into account in a coordinated manner [27-28].

2.3.2 High thermal conductivity materials

In order to increase the power density of the motor, it is necessary to reduce the thermal resistance of the motor package, reduce the space and cost of the motor, achieve high speed of the motor, and maintain good reliability and stability. This requires improving the thermal conductivity of the motor packaging material (thermal conductive epoxy resin, filler, winding insulation material, etc.) and reducing the contact thermal resistance.

Thermal interface materials (TIMs) are based on polymer systems and are manufactured using advanced filler technology. They can address critical heat dissipation issues and have long-term reliable performance. They are applied between the heat source and the surface of the heat sink (cold plate, fin heat sink, etc.) to exclude air with high thermal resistance, allowing close contact between heat transfer surfaces, improving heat uniformity and thermal conductivity, and helping to achieve lightweighting.

2.3.3 High heat resistant materials

Highly heat-resistant materials can improve the environmental tolerance of components and help to bring into play the high-temperature operation advantages of the next generation of wide-bandgap semiconductors. For example, the DC-link capacitor currently in mass production is based on polypropylene winding technology and has a maximum temperature tolerance of only 105°C, which is the shortest temperature resistance of the inverter.

Recently, PolyCharge has developed a solid-state capacitor technology, NanoLamTM, as shown in Figure 16. It uses thin polymer dielectrics to produce self-healing high-voltage capacitors. The size and weight are half of the current capacitors, and they have higher temperature resistance (140°C), higher energy density, more stable capacity, lower equivalent series resistance and equivalent series inductance.

Figure 16 NanoLam high temperature film capacitor

3 Conclusion

The Energy-saving and New Energy Vehicle Technology Roadmap 2.0 was released on October 27, 2020. The roadmap was organized and compiled by the China Society of Automotive Engineers. The electric drive assembly was promoted to a key area as an independent chapter. The roadmap clearly states: By 2025, the 30 s three-in-one electric drive system will have a specific power of 2.0 kW/kg, the 30 s motor effective specific power of 5 kW/kg, and the inverter power density of 40 kW/L; by 2030, the 30 s three-in-one electric drive system will have a specific power of 2.4 kW/kg, the 30 s motor effective specific power of 6 kW/kg, and the inverter power density of 50 kW/L[1]. According to the strict technical indicators defined in the roadmap, this is an encouraging average goal that the top 10% of the industry's leading companies have to challenge, and a series of forward-looking technologies need to be overcome.