Since last year, domestic electric vehicles have ushered in explosive growth, and the electric drive system of its core components has also attracted the attention of the industry. Although the value of the electric drive system is not the highest in electric vehicles, it is very important.

　　Generally speaking, an electric drive system includes a motor, a motor controller, a motor driver, and an assembly. At present, there are three development directions for automotive motors: asynchronous motors, permanent magnet synchronous motors, and switched reluctance motors. Since the motor is mainly composed of shell, stator, rotor, bearing, end cover and other parts, the nails are silicon steel sheets and copper wires, and the rotor is magnetic steel embedded in silicon steel sheets, so the price of the motor is relatively transparent, and the main cost is aluminum. , copper wire, silicon steel sheet and other raw material costs. In other words, to achieve the same target power, if the motor design is more reasonable and the materials used are more economical, the cost of the motor manufactured by the manufacturer will be lower, and the correspondingly more competitive.

　　However, the motor controller is different. In addition to the hardware cost of MCU and power module, the motor controller also includes software. Therefore, its premium will be relatively higher. At present, international suppliers such as Bosch, BorgWarner, Continental, and Nidec have layouts, and domestic suppliers such as Fudi Power, Inbore, Inovance Technology, Sunshine Electric Power, United Electronics, and CRRC Times Electric Giant Power have also appeared. goods.

　　Industry insiders predict that the motor electronic control industry will evolve in the future, where suppliers provide hardware and underlying software, and host manufacturers develop application layers, software and functions themselves. Because suppliers can do better in terms of raw material bargaining power, logistics, quality control and cost control. If the host manufacturer's installed capacity does not reach a certain scale, it does not make much sense to develop it by itself.

　　The development trend of electric drive system

　　At present, the whole vehicle requirements of electric vehicles are high safety, high performance, low power consumption, low cost, small size and light weight. Correspondingly, the electric drive system also needs to match the development trend of the automobile. Therefore, the future development direction of the electric drive system will be all-in-one, high integration, high voltage, high power density, high safety level, high cost performance, low noise and high efficiency. .

　　First of all, integration is an inevitable trend. Putting many parts or functional parts together can save space, and some parts can be shared. However, there is currently no particularly good integration solution, and most suppliers are still groping forward. In the future, whether to do three-in-one, six-in-one, or eight-in-one, or integrate DCDC, OBC, etc. into the battery pack, etc. are all things that all suppliers are considering.

　　The second is the trend of high voltage. Many car manufacturers have turned to the 800V platform. The benefit of the 800V platform is that it can greatly shorten the charging time and relieve mileage anxiety. At the same time, there are also many challenges. Due to the increase in voltage, the charging speed is faster, some components need to be re-developed, the battery pack needs a charging rate of more than 4C, and there are higher requirements for the insulating paint material and thickness of the motor wires. Higher requirements are also placed on insulating paper (the medium between copper wire and silicon steel sheet) and safety distance. These requirements will lead to component upgrades, which will increase the cost of the motor. In addition, because the increase in charging power will bring about an increase in current and an increase in temperature, most suppliers of 800V motors will choose to use oil cooling technology. The oil cooling technology has the characteristics of uniform heat dissipation and higher heat dissipation efficiency.

　　The third is the trend of high power density. In 2017, US DRIVE, a subsidiary of the US Department of Energy, proposed a roadmap plan for the development of electric vehicles in 2025. In this plan, they set a goal for the development of motors and electronic controls, that is, by 2025, the efficiency of motor controllers should not be lower than 98%; the power density should reach 100kW/L; the cost should be reduced to 2.7 US dollars /kW. The efficiency of the motor should not be lower than 97%; the power density should be 50kW/L or 5.7kW/kg; and the cost should be lower than $3.3/kW.

　　Table 1: Target planning for motor controllers and motors published by US DRIVE. (Data source: US DRIVE, Electronic Enthusiasts Watchmaking)

　　We can clearly see that the biggest improvement is power density, which has two values, one is relative to volume and the other is relative to weight. Motors for automobiles are more focused on the power-to-volume ratio because volume is related to the efficient use of space in the car and the passenger experience. The power density of the motor controller has increased from 13.4kW/L in 2020 to 100Kw/L, an increase of 7.46 times. The power-to-volume ratio of the motor is increased by 8.77 times.

　　That is to say, power density will become a very important indicator in future motor controller and motor design. Why is power density so important? Because a motor with high power density can make the motor body smaller, lighter and more efficient.

　　The fourth is high safety level. As the electric drive system has more and more integrated functions and more and more components, the corresponding safety level requirements will also become higher.

　　In addition, high cost performance, high electromagnetic compatibility and low noise are also the development directions of future electric drive systems. So, in order to realize these development trends, what key technologies are needed to support?

　　Analysis of key technologies of electric drive system

　　In order to successfully achieve the development goals of the electric drive system, it needs the support of some key technologies, such as new configuration integration innovation, 800V electric drive technology, electric drive system NVH improvement technology, electromagnetic compatibility forward design, advanced thermal management technology, new Motors, new cooling technologies, wide bandgap semiconductors, etc.

　　The first is the innovation of new configuration integration. In addition to the popular three-in-one electric drive system, new configuration designs such as all-in-one and two-speed dual motors have emerged. At the same time, the integration depth has also shifted from the early physical integration to deeper integration of electrical and electronic functions. However, there is no unified integrated solution at present, and various suppliers are constantly exploring and moving forward. I believe that after the test of the market, a better solution will eventually be explored.

　　The second is the 800V high-voltage platform, which can greatly reduce the charging time of the car, and the improvement of the voltage platform helps to improve the specific power of the motor/electric drive system.

　　The third is the NVH promotion technology of the electric drive system. NVH (Noise Vibration Harsheness) is usually used to describe the noise, vibration and ride comfort of the car. According to relevant statistics, about 1/3 of car failures are caused by car NVH problems, which will directly affect the user's driving experience. Therefore, it is necessary to comprehensively improve the design system and design methods to further improve the technical level of the electric drive system.

　　The fourth is the forward design of electromagnetic compatibility. Due to the increasingly obvious trend of automobile electrification, intelligence and networking, it has brought new challenges to automobile electromagnetic compatibility. In addition, the product iteration speed of electric vehicles is accelerated, and the development cycle of new products is shortened. , the traditional electromagnetic compatibility development based on rectification has been unable to meet the existing needs, and the importance of electromagnetic compatibility forward design has become more important.

　　The fifth is advanced thermal management technology. The traditional thermal management technology is based on monitoring the temperature on the motor and the inverter to plan the cooling strategy. This has a certain lag and cannot reflect the drastic changes in the working conditions of the electric vehicle. For components such as windings Due to the influence of temperature rise, there is still the risk of over-temperature failure under heavy load conditions, and the cooling system needs greater redundancy. By building a high-precision temperature prediction model for key components of the electric drive system and lean design of thermal management strategies, the temperature change trend can be predicted in real time according to the load conditions, the cooling demand and output capacity of the system can be dynamically adjusted, the reasonable operating temperature can be controlled, and the cooling energy can be reduced at the same time. It helps to optimize the cruising range of the vehicle and improve the user experience.

　　Six is a new type of motor. In order to achieve higher efficiency and higher power density, two methods are generally used to achieve it. One is to increase the speed of the motor and design the motor as a high-speed motor; the other is to design a new type of motor, such as flat wire. motor etc. However, increasing the motor speed to 18,000rpm or even above 20,000rpm will require higher requirements for motor bearings, punching strength and dynamic balance.

　　The seventh is the new cooling technology. As the electric drive system develops in the direction of high power density and high speed, the heating of the stator winding and the magnetic steel poses a greater challenge to the cooling capacity of the system. The traditional water cooling of the casing has gradually been difficult to meet the demand, and it is imperative to develop a new cooling technology. So oil cooling technology has surfaced. The current popular oil cooling technology can take into account the temperature rise of the winding under low speed and high torque, and the temperature rise of the magnetic steel under high power under high speed through stator spraying, rotor oil rejection, etc., which can improve the continuous output capacity of the motor by 20% At the same time, it can also be integrated with the lubricating oil circuit of the reducer to realize the compact design of the all-in-one system. Of course, for the problems of insufficient cooling of the stator slots by spray oil cooling and uneven cooling of the winding ends, oil-water mixed cooling and winding immersion cooling can be considered.

　　Eighth, wide bandgap semiconductors, because SiC devices have the advantages of low loss, high frequency, high voltage resistance, high temperature resistance, and high efficiency, which can improve the efficiency of electric drive systems. At present, many companies have launched related products, such as ROHM, ST, Infineon, Cree, etc. have launched SiC products. And there are already many application cases of SiC products in new energy vehicles.

　　Epilogue

　　With the development of electric vehicles, the technologies they need to use are also constantly developing. At present, many domestic electric vehicle supply chains are new suppliers. Some of them used to be industrial products, and some of them were consumer products. They entered because they saw the development prospects of the auto industry changing the track. It is precisely because of their participation that the electric vehicle industry has more fresh blood, and the product form and technology development have greater impetus.