On October 19th, 2021, NIO held a technology exchange meeting for its second-generation electric drive system, which will be installed on the upcoming ET7 model, at its affiliated company, WEYERHAUPT. Attendees included Zeng Shuxiang, Vice President of NIO ES & EI, Bi Lu, Head of NIO Electric Drive System and Integration Department, and Hong Wencheng, Head of NIO Intelligent Power Electronics System Department.
The electric drive system is mainly composed of three parts: the motor, the reducer, and the controller, with two types of motors available – permanent magnet synchronous motors and induction asynchronous motors. As of now, NIO has obtained and applied for 215 patents in the field of electric drive systems, including 81 invention patents. The electric drive system is not only an important endorsement of the brand’s high performance, but also a moat for accurately meeting the needs of users and a core factor in stable supply.
Silicon Carbide (SiC) Power Modules Improve Energy Efficiency under Low Load
Silicon carbide has the advantages of high switching speed, high turn-off voltage, and strong high-temperature resistance, which can improve the driving range of electric vehicles when applied to main drives.
Considering the improvement that silicon carbide can bring to the ET7 user experience, NIO has accelerated its research and development and manufacturing processes, planning to achieve mass production by the end of 2021, making the upcoming NIO ET7 the first model to be equipped with a silicon carbide electric drive system.
The 180 kW permanent magnet synchronous motor responsible for front axle drive on the ET7 is the first to adopt the application of silicon carbide modules, which can reduce losses by 4% to 6%, improve energy efficiency under city driving conditions, and have the following specific advantages:
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Stronger high-temperature resistance, with maximum current capacity increased by over 30% for the same volume.
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Suitable for working in a wider voltage range, with better compatibility.
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Faster switching speed and smaller power loss during switching.
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High-speed drive circuit design with multi-objective optimization, using smaller loop inductance and stronger drive chips to achieve faster switching speed.- The efficiency control strategy of multi-target optimization can greatly reduce switch losses by changing the switch frequency and discrete PWM scheme, reducing them by 35% and 33.3%, respectively. Meanwhile, the modulation optimization strategy can effectively increase the system power by 5% to 10%. The incorporation of these three technologies can comprehensively improve the efficiency of electric drive.
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The CLTC efficiency of the main driving motor is ≧ 91.5%.
More than just high performance at 3.9 seconds per hundred kilometers
Compared to existing 160 kW and 240 kW electric drive systems, the ET7 electric drive system’s overall peak power and peak torque are increased by 20% and 23%, respectively. The front permanent magnet synchronous motor has a maximum power of 180 kW and the rear asynchronous induction motor has 300 kW, providing excellent dynamic performance to achieve a 3.9-second speed-up to one hundred kilometers per hour.
Reducing electric drive noise by 5-15 dB is also a detail improvement that users will appreciate. Compared to the 160 kW electric drive system, through the optimization of the electric drive system’s modal fusion control, non-uniform air gap of motor, high pole ratio magnetomotive force, tooth-axis structure, and controller harmonic injection and control strategies, ET7 has achieved better NVH results.
From the beginning of the development of the electric drive system, it was optimized and designed for the entire vehicle system. The application of measures such as the matching of dynamic and static stiffness of the suspension system, decoupling of the modal map of the electric drive system, ensures the best NVH performance of the overall architecture of the electric drive system.
Other details optimization include:
- Non-uniform air gap and high pole ratio magnetomotive force of the motor. While improving performance, the motor balances the radial electromagnetic force with electromagnetic optimization (non-uniform air gap) and optimizes torque fluctuation through positive rotatization of the air gap, achieving better NVH performance.
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Precision optimization design of the shape and direction of the gears. By precision machining the internal gears of the ET7 electric drive system, superior precision control of micrometer level was achieved under mass production. Therefore, when the vehicle is in operation, the gears mesh more tightly, improving the transmission efficiency and reducing noise, further optimizing the NVH performance of ET7.
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The harmonic injection algorithm iteratively optimizes noise and jitter. After calculating the harmonic voltage, the iterative optimization harmonic suppression algorithm can better compensate for the voltage with the harmonic voltage, reducing the overall noise of the electric drive system by 5-15 dB and providing users with a quieter driving environment.
- A new challenge to NVH caused by motor heating battery. The battery performs poorly in low temperatures. Through the development of special features, the system can use waste heat from the motor to heat the battery at low temperatures, providing up to 4 kW of heating power and keeping the battery at its optimal operating temperature, resulting in better performance and endurance in low temperature conditions. However, this feature also brings new challenges to NVH. NIO injects corresponding wavelength signals using software harmonic control algorithms to eliminate noise under this condition.
🔗Source: NIO
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