Discussion on Rectangular Copper Wire Driving Motor Technology

A technical paper by Song Zhihuans, Senior Manager of Electrical Engineering Section at Hasco, China, on lessons learnt from their R&D and manufacturing processes while using rectangular copper wire winding in traction motor technology.

In recent years, new energy vehicles have gradually entered into the lives of ordinary consumers due to the rapid development of electric drive technology and the strong support of new energy policies from countries all around the world. Taking China as an example, the sales of new energy vehicles in 2018 and 2019 both exceeded 1.2 million. It can be foreseen that in the near future, new energy vehicles will replace traditional fuel vehicles and become the main means of daily transportation.

As the core part of the new energy vehicle, the traction motor, which is equivalent to the engine of traditional vehicles, provides power output for the vehicle. The performance of the motor directly affects the vehicle performance. Therefore, the R&D and manufacture of traction motors has been of growing concern among the world's major vehicle and parts manufacturers. According to the requirements of new energy vehicles for cruising range, acceleration, cost and comfort, the technical requirements for driving motors can be summarized as “two high and two low”, which is interpreted as high efficiency, high power density, low cost and low noise. In order to meet the above technical requirements, engineers and technicians in various countries tried their best to improve the performance of traction motors. The technology of rectangular copper wire winding is widely regarded as one of the main development directions of traction motor technology in the future.

Compared with the traditional round copper wire winding motor, the rectangular copper wire winding motor has better performance in terms of efficiency, power density, cost and noise, which conforms to the technological development direction of the traction motor. Fig.1 is a schematic diagram of rectangular copper wire winding and a round copper wire winding. It can be seen from the figure that more copper conductors can be arranged in the stator slots due to the use of rectangular copper wire windings, which improves the slot fill factor of the motor. The slot filling factor of Hair-pin rectangular copper wire winding motor designed by HASCO E-DRIVE could reach as high as 90%, while that of the traditional round copper wire winding motor is about 75% at present.

Fig.1 Schematic diagram of rectangular copper wire winding and round copper wire winding

A higher slot filling factor means that the resistance of stator is smaller than the same size motor. The smaller resistance means that the loss of power is lower under the same current which is conducive to improving efficiency. Due to the use of rectangular copper wire conductors, the thermal conductivity of the armature winding is higher than that of the traditional round copper wire. Thus, the temperature of the armature winding can be reduced by 10 to 15°C. Since the wave winding connection is utilized as the form of rectangular copper wire winding, the length of the end winding can be shortened by about 50%, to reduce the amount of effective material and the cost. While the copper loss of the end winding is reduced, the motor efficiency can be improved.

Compared with the radial embedding of traditional round copper wire, the axial embedding method is adopted in the Hair-pin rectangular copper wire winding, which makes the smaller stator slot or even closed slot possible, and the impact of the tooth harmonics on the torque ripple and radial electromagnetic force can be effectively suppressed, so as to achieve the purpose of suppressing the motor NVH. Rectangular copper wire winding motors are more suitable for the production and manufacturing of automated production lines. When the output reaches a certain amount, the manufacturing cost of the motor can be reduced.

But the rectangular copper wire winding also has its shortcomings, the AC winding loss, which is mainly produced by the skin effect and proximity effect. Fig.2 shows the skin effect and proximity effect of rectangular copper wire windings.

Fig.2 Skin effect and proximity effect of rectangular copper wire windings

The round copper wire winding is composed of multiple strands of thin round copper wires wound in parallel, thus the skin effect and proximity effect of the winding are so small, they can be ignored. The AC winding loss of the rectangular copper wire winding increases more significantly as the operating frequency of the motor increases. In order to suppress the influence of AC winding loss on motor performance, HASCO E-DRIVE adopts the method of increasing the number of winding layers per slot to balance the performance of motor. The rectangular copper wire motor products produced by HASCO E-DRIVE have developed from 2-layer to 4-layer, then to 8-layer rectangular copper wire motor products which was officially mass-produced in the first half of this year. Figure 3 shows the 8-layer rectangular copper wire motor of HASCO E-DRIVE. This product is used in the pure electric vehicle ER6 launched by SAIC ROEWE.

Fig.3 8-layer Hair-pin rectangular copper wire motor produced by HASCO E-DRIVE

Due to the application of 8-layer Hair-pin technology, the high efficiency range with motor efficiency ≥90% can be increased from 83% to 88%, while the power density of the motor can be increased by 53% to nearly 6kW/kg, and the torque density increased by 12% to nearly 12Nm/kg, compared with the previous generation of 4-layer Hair-pin rectangular copper wire motor.

Benefits from to the latest 8-layer Hair-pin rectangular copper wire motor, the average NEDC power consumption of ER6 launched by SAIC ROEWE has decreased from 13.8kWh/100km to 12.2kWh/100km, which has fallen over 11.5%. Under the same driving conditions, the vehicle equipped with 4-layer Hair-pin rectangular copper wire motor can only drive about 548km, which is nearly 72km less than ER6 which is equipped with 8-layer Hair-pin rectangular copper wire motor.

At present, two generations of rectangular copper wire motor have been mass-produced in HASCO E-DRIVE, among which the first generation of 4-layer Hair-pin rectangular copper wire motors are used in many popular vehicle models, such as Marvel X, ERX5, EI5 which are all launched by SAIC ROEWE and EZS launched by SAIC MG. The EZS of above vehicle models have also been sold to many overseas regions, such as the United Kingdom and Thailand.

Fig.4 EZS model launched by SAIC MG

In the first half of this year, the 8-layer rectangular copper wire motor products were mass-produced and applied to pure electric vehicle RE6, which belongs to premium R-series launched by SAIC ROEWE. The maximum speed of ER6 can reach 185km/h, as the cruising range can be 620km while the power consumption is 12.2kWh/100km.

Fig.5 ER6 model launched by SAIC ROEWE

HASCO E-DRIVE has been committed to R&D and manufactures the core parts for the new energy vehicle, traction motor and controller since its establishment. We began the R&D of the rectangular copper winding motor in 2013 and through years of unremitting efforts and exploration, HASCO E-DRIVE became the first company in China which truly realized the mass production of rectangular copper winding motors in 2017. Then the motors were successively used in many pure electric vehicle models launched by SAIC ROEWE and SAIC MG. The cumulative shipment of HASCO E-DRIVE rectangular copper winding motor products is about 150 thousand up to now. At the beginning of 2020, the mass production of 8-layer Hair-pin rectangular copper winding motors was first realized in HASCO E-DRIVE within China.

HASCO E-DRIVE not only provides SAIC with drive motors for pure electric vehicle and hybrid vehicles, but also cooperates with and provides products for many world-famous vehicle enterprises, such as the project “Base of Volkswagen MEB platform and the project “BEV3 “of General Motors. HASCO E-DRIVE is equipped with automatic, semi-automatic and manual production lines, which can meet the needs of mass production and prototype manufacturing, while the total capacity can reach to 800 thousand. Since the establishment of HASCO E-DRIVE, promoting the innovation and development of new energy driven technologies was regarded as the goal and direction of company. HASCO E-DRIVE is looking forward to further communication and cooperation with you!

About the Author

Song Zhihuans
Senior Manager of Electrical Engineering Section
Hasco Automotive Electric Drive System Co.,Ltd.

Senior engineer. Graduated from Shenyang University of technology, majoring in electrical machinery and electrical appliances, doctor's degree, the main research direction is permanent magnet synchronous machine and its control technology. Engaged in the electromagnetic design of permanent magnet machine for a long time and is good at the calculation and analysis of electromagnetic field and the research of electric machinery NVH suppression technology.

Company Profile:

Hasco Automotive Electric Drive System Co.,Ltd., is a joint venture built by Huayu Automotive Systems Company Limited (subordinated to SAIC group) and Guizhou Aerospace Industry Company(subordinated to China Aerospace Science and Industry Corporation), commitment to providing the new energy vehicle drive system’s integrated solutions, and R&D and manufacturing of core parts of motor and controller system, who is the core parts suppliers of new energy vehicle with leading technology in domestic.

HASCO E-DRIVE has its own intellectual property rights on the core technology of new energy traction motor and controller system and has the outstanding product R&D, software development, system integration and complete sets of manufacturing capability as well. The platform products have the characteristics of high performance and high reliability, and at the same time, flexible modular design can provide efficient customized integrated solutions for different application requirements of multiple new energy vehicles. The company now has two production bases, forming a multi-series, multi-variety motor and controller production line, to meet the manufacturing need of customers’ different production scale.  HASCO E-DRIVE has introduced advanced and complete testing and verification equipment and automatic production line, our testing capacity has reached the requirements of national standards. It takes the lead in establishing a relatively perfect vehicle driving motor performance and reliability verification system in China.


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