Winding design and skin effect of flat wire motor

The difference between flat wire motors and round wire motors lies in the way the copper wire is formed. Flat wire is conducive to improving the slot fill rate of the motor. Generally, the slot fill rate of round wire motors is about 40%, while the slot fill rate of flat wire motors can reach more than 60%. The improvement of the slot fill rate means that more copper wire can be filled in under the premise of unchanged space, which will generate a stronger magnetic field strength and improve power density. Based on the current development trend of flat wire, Wangcai Motor and Electric Control has opened a flat wire column for fans to facilitate communication.

As the core component of new energy vehicles, the drive motor is equivalent to the engine of traditional vehicles, providing power output for the whole vehicle. Its performance will directly affect the performance of the whole vehicle. Therefore, the research and development and manufacturing of drive motors have received extensive attention from major vehicle manufacturers and parts giants around the world. According to the requirements of new energy vehicles for cruising range, acceleration, low cost and comfort, the technical requirements for drive motors can be summarized as two highs and two lows, namely high efficiency, high power density, low cost and low noise. In order to meet the above technical requirements, engineers and technicians from various countries have tried various methods to improve the performance of drive motors, and flat copper wire winding technology is widely regarded as one of the main development directions of drive motor technology in the future.

Compared with traditional round copper wire winding motors, flat copper wire winding motors perform better in terms of efficiency, power density, cost and noise, and are in line with the technical development direction of drive motors.

From the figure we can see that due to the use of square flat copper wire windings, more copper conductors can be arranged in the stator slots to improve the slot fill rate of the motor. At present, the slot fill rate of the Hair-pin flat copper wire winding motor designed by Huayu Motor can reach more than 90%, while the slot fill rate of the traditional round copper wire winding motor is about 75%.

Schematic diagram of flat copper wire winding and round copper wire winding

Winding design and skin effect

Skin effect: When there is alternating current or alternating electromagnetic field in the conductor, the current distribution inside the conductor is uneven, and the current is concentrated in the "skin" part of the conductor, that is, the current is concentrated in the thin layer on the surface of the conductor. The closer to the surface of the conductor, the greater the current density, and the current inside the conductor is actually smaller. As a result, the resistance of the conductor increases, and its power loss also increases. This phenomenon is also called skin effect.

At high speeds, the skin effect will reduce the effective copper wire area, increase the equivalent resistance of the winding, and increase the loss;

The higher the speed, the more uneven the conductor heating becomes, increasing the heat load near the insulating paint.

The skin effect of the same-slot winding b is more serious than that of the different-slot winding a.

Skin effect and proximity effect of flat copper wire winding

Multilayer flat wire conductor design structure diagram

Effect of multi-layer flat wire conductor winding on motor performance

Peak performance (same peak duration):

Output capacity in constant torque range:

Low-speed area: 4th floor > 6th floor > 8th floor

High-speed area: 8th floor > 6th floor > 4th floor

Difference in efficiency map between 4-layer and 8-layer motors

In terms of technology, domestic enterprises have adopted the mainstream hair-pin technology, and the winding technology has broken through 8 layers. Currently, there are three third parties with the ability to mass-produce 8-layer flat wire motors: Founder Motor, Tianjin Songzheng, and Huayu Electric. In terms of assembly production lines, flat wire motor assembly can be divided into three major process links: stator, rotor, and assembly. Among them, the rotor line and assembly line are relatively simple, while the stator assembly line is the most technically difficult link due to many complex processes. At present, domestic Haosen Co., Ltd. and Kelai Electromechanical have the ability to undertake flat wire motor stator assembly lines. Let's talk about this for today and continue another day.