Drive Motor Technology and Trends
Flat wire motor
Flat wire motor refers to replacing the traditional cylindrical enameled copper wire in the stator winding with enameled copper flat wire processed into a hairpin shape. In the stator cross section of the round wire motor, there are a lot of gaps between the round copper wires, while in the stator cross section of the flat wire motor, the rectangular copper wire can better fill the space and improve the slot fill rate, which is the fundamental difference between flat wire motors and round wire motors.
Compared with traditional round wire motors, the bare copper slot fill rate of flat wire motors can be increased by 20%-30%. The increase in slot fill rate is equivalent to the motor being able to output higher power and torque under the condition of the same volume; or under the condition of the same power, the outer diameter and volume of the motor can be reduced, thereby reducing the weight of the motor, so the flat wire winding motor has a higher power density, which can make the permanent magnet motor continue to develop in the direction of miniaturization.
Compared with round wire motors, the primary advantage of flat wire motors is reduced losses and improved efficiency. Among the losses of permanent magnet synchronous motors, copper loss (mainly loss in stator winding) accounts for about 65%, iron loss (loss in stator core and rotor core) accounts for about 20%, and the remaining losses account for relatively low proportions. The iron loss level of flat wire motors and round wire motors is similar, and the main difference is copper loss. Compared with traditional round wire motors, the bare copper slot full rate of flat wire motors can be increased by 20%-30%, the total copper loss is reduced by 21%, and the efficiency is increased by about 1%.
Oil cooling technology
Air cooling, liquid cooling and evaporative cooling are three commonly used motor cooling systems. Air cooling has been widely used in the field of low-power motor cooling due to its advantages of low cost, high reliability and easy installation. Liquid cooling has a higher heat dissipation power, and its heat dissipation efficiency can reach 50 times that of the former. It is suitable for heat dissipation occasions with high motor heat generation and high heat flux density. However, the liquid cooling system requires additional circulating liquid circuits and sealing systems, which increases the cost and complexity of the motor system. The evaporative cooling system is mainly used in the cooling system of large-capacity megawatt-class generator sets, and uses the gas-liquid phase change cycle to achieve efficient cooling of the motor.
The liquid cooling forms of automotive permanent magnet synchronous motors are roughly divided into two types: direct cooling and indirect cooling. Indirect cooling is a cooling channel designed in the casing, where the coolant flows through the entire casing to take away the heat. Direct cooling is to inject cooling oil into the sealed motor and use the high specific heat capacity of the cooling oil for cooling. In addition, direct cooling can increase the contact area with the heat source and achieve better cooling effect. The winding end of the permanent magnet synchronous motor generates a lot of heat. The coolant cannot directly contact the winding under water cooling, but the cooling oil can directly contact the winding under oil cooling, which has higher cooling efficiency and more prominent advantages.
Under oil cooling technology, the cooling oil can directly contact the heating components of the motor, and the heat dissipation efficiency is much higher than that of the traditional water cooling system. The oil medium has the advantages of good insulation, high dielectric constant, low freezing point and high boiling point.
