作为一名优秀的翻译请你用正式的表达用英语翻译以下公司新闻内容注意语言的规范性和正确性和简洁性并按照原文格式进行排版。和骋科技黄双意：800V高压电机的轴电压问题及轴承电腐蚀解决方案 2022年9月21-22日由NE时代主办2022第二届全球xEV驱动系统技术暨产业大会在上海嘉定圆满召开。 在22日论坛上和骋新材料科技上海有限公司副总黄双意分享的是800V高压电机的轴电压问题及轴承电腐蚀解决方案。

HECHENG Technology: Solutions for Shaft Voltage Issues and Bearing Electrical Corrosion in 800V High-Voltage Motors

From September 21st to 22nd, 2022, the "2022 2nd Global xEV Drive System Technology and Industry Conference" organized by NE Times was successfully held in Jiading, Shanghai. On the forum on the 22nd, Huang Shuangyi, Deputy General Manager of HECHENG New Materials Technology (Shanghai) Co., Ltd., shared the solutions for shaft voltage issues and bearing electrical corrosion in 800V high-voltage motors. The issue of shaft current in 800V high-voltage motors has always been a pain point and difficulty in the industry. HECHENG Technology has conducted detailed research on the principles of electrical corrosion, shaft voltage testing methods, and solutions for bearing electrical corrosion.

The following is the live transcript:

HECHENG Technology was established in 2013 and has been focusing on the research of bearing electrical corrosion since its inception. Initially, the company acted as an agent for related foreign products until it successfully developed its own proprietary product, the "Hucheng Core" high-conductivity fiber grounding ring, in 2019. Starting from 2020, it has been successfully installed in batches in new energy commercial vehicles. This year, it has been installed in batches in multiple popular models in the passenger vehicle field.

Why does shaft voltage occur? Shaft voltage or shaft current is not a new issue. It has existed since the day when frequency converters were used to drive motors, and it is very common in industries such as industrial manufacturing, wind power generation, and rail transportation. Why didn't bearing electrical corrosion occur in automotive motors in the past few years? It is because the voltage platform, speed, and motor power of past new energy vehicles were relatively low. However, in recent years, the development of automotive electric drive systems with the "Four Highs" (high voltage, high power, high frequency, and high speed) has compressed the survival space of the bearing oil film against electrical corrosion. The higher voltage platform increases the shaft voltage, the greater power generates more induced energy, the high switching frequency leads to a higher attack frequency on the oil film, and the viscosity of lubricating oil/grease decreases to adapt to high speeds, resulting in a thinner oil film and reduced bearing capacity. Therefore, bearing electrical corrosion has become a prominent issue in the past two years. Without reasonable protective measures, it will become an inevitable problem, especially in the 800V electric drive platform, which can cause uneven surfaces on the bearing balls and raceways, resulting in abnormal noise from the motor bearings. Almost every automaker is facing this challenge now.

Typical shaft voltage waveforms. High common-mode voltage with characteristics of high dv/dt and di/dt can induce shaft voltage on the motor shaft through stray capacitance in the motor.

There are several typical discharge waveforms of shaft voltage. When the operating conditions are relatively good, the motor speed is relatively uniform, and the oil film reaches a certain thickness to withstand the voltage on the bearing, the bearing is protected by the oil film and remains intact, showing a complete common-mode voltage waveform. However, due to the complex operating conditions of automobiles, this situation does not last long. Even if the voltage is not sufficient to break through the oil film, partial discharge still occurs within the oil film, slowly corroding the grease, resulting in degradation over time. The waveform on the far right is the waveform of capacitive breakdown discharge. If the thickness and strength of the oil film are insufficient to withstand the component of the common-mode voltage on the bearing, it will be broken through. At the moment of breakdown, a large current is generated, which not only damages the bearing but also interferes with electronic components. Therefore, bearing electrical corrosion and EMI issues coexist.

Both resistive discharge and capacitive breakdown discharge cause significant damage to bearings. Resistive discharge only transforms the instant capacitive breakdown discharge into a continuous resistive conduction discharge, which still causes damage but requires a certain amount of time and mileage accumulation to demonstrate negative effects. If it is capacitive breakdown discharge, the attack is stronger, and the instantaneous temperature is high, causing surface metal splashing.

How much shaft voltage is safe? There is no definitive answer. NEMA MG1 Part 31.4.4.3 once defined that shaft voltage above 20Vp-p carries a higher risk of breakdown discharge, but this was for traditional industrial motors, and current standards no longer have such descriptions. With the continuous development of motor technology, the speed is increasing, and the viscosity of the corresponding bearing lubricating oil has decreased significantly compared to the past, resulting in a significant reduction in the thickness of the oil film during operation. Therefore, the bearing's ability to withstand shaft voltage has become weaker. Some high-speed motors still have the risk of oil film breakdown discharge with shaft voltages below 10Vp-p. The operating conditions of automotive motors are even more complex and variable, and the stability of the oil film is more unstable. Therefore, it is difficult to provide an absolute safe voltage.

Approaches to solving the bearing electrical corrosion issue. Generally, there are three approaches to solve the problem of bearing electrical corrosion: limitation, isolation, and diversion. Of course, it can also be a combination of several methods.

These measures have their own advantages and disadvantages. Limitation, such as choke treatment, is usually done through common-mode magnetic rings. By simulating circuits, harmonic energy can be shielded. This can help improve the EMI performance of the system to some extent but does not provide much help in reducing bearing electrical corrosion caused by common-mode voltage. Some customers have used common-mode magnetic rings to filter out the voltage caused by harmonic components, reducing the shaft voltage from around 25V to about 19V. However, 19V is still a very dangerous value. In addition, this method usually requires a relatively large installation space, which is difficult to achieve for automotive motors that require compact designs.

The simplest way to isolate is to use insulation. By replacing the bearings with insulated ones, there will be no electrical corrosion in that part. However, this method can only solve the problem itself and cannot solve the system's problem. The source of induction still exists, and the shaft voltage is still present. If both ends of the motor, the front and back, use insulated bearings, the voltage will be discharged on the gearboxes, causing corrosion on the tooth surfaces. This is very common in the wind power generation and rail transportation industries. Some customers in the automotive industry have also reported finding electrical corrosion on gear surfaces.

Since it is harmful energy, it is best to discharge it rather than block it. There are many studies on diversion methods, and different methods have their own advantages and disadvantages