1. Comparison of domestic and foreign technologies in automotive drive motors
The electric motor drive system is a crucial actuator in the operation of new energy vehicles, and its drive characteristics determine the vehicle's key performance indicators. Benefiting from the huge domestic market, the domestic drive motor industry has developed rapidly, and the drive motors used in domestic electric vehicles are basically manufactured locally, which can largely meet the requirements of domestic new energy vehicles.
In terms of drive motor technology development, if we consider patents as a technological reserve, then in the past decade, my country has ranked among the top in the total number of patent applications for automotive drive motors. However, invention patents, which best reflect the level of technology, account for only 50% of these applications, while foreign invention patents account for more than 90% of the total applications. From this perspective, my country's patent applications place more emphasis on "quantity," while foreign countries place more emphasis on "quality."
Regarding the power density of drive motors, the "13th Five-Year Plan" clearly states that motor efficiency should exceed 4KW/KG. Many domestic companies' products have already reached this standard, but compared with international advanced products, there is still a significant gap in terms of size and manufacturing process.
Currently, the motors used in my country's new energy vehicles are mostly permanent magnet synchronous motors, AC asynchronous motors, and other types of motors. In terms of market structure, permanent magnet synchronous motors dominate, accounting for 685,100 units installed in the new energy vehicle sector in 2017, representing over 78% of the total; AC asynchronous motors accounted for nearly 190,000 units, or 21.4%.
Tesla Model Smotor
When comparing power density with foreign motors, one point to note is that Tesla Model S uses induction motors. Directly comparing the power density of induction motors and synchronous motors is inappropriate for at least two reasons: First, AC motors do not have permanent magnets and use less material, which reduces weight to some extent; second, AC motors can self-excite, enabling them to establish a higher magnetic field strength than synchronous motors. Furthermore, Tesla's patented copper-core rotor technology addresses a significant issue. These three points allow Tesla's induction motor power density to rival that of domestic permanent magnet synchronous motors.
While power density can represent motor performance to some extent, it's unsuitable in certain situations. For example, in applications requiring low speeds, high speeds cannot increase power density, while excessively high speeds can lead to problems such as wind-induced wear, bearing issues, and NVH (noise, vibration, and harshness) problems. In these cases, another indicator is needed to characterize motor performance: torque density. This is because, in many situations, torque is more correlated with weight and volume than power.
There are many ways to increase torque density. For example, Toyota Prius and BMW achieve this by increasing the reluctance torque ratio. Another approach is from the control side, utilizing harmonic injection to incorporate the harmonic torque generated by the motor. Finally, the last method is to increase the magnetic field energy per unit volume.
Torque density has become a development trend because of another driving factor: the increasingly thriving independent drive technology, also known as distributed drive.
In this type of application, the motor is mounted vertically beside the wheel. With a speed reducer, it's called a wheel-side motor; without a speed reducer, it's called a hub motor. The hub motor drives the wheel directly and rotates synchronously with it. Since the wheel's rotational speed is actually quite low, typically only a few hundred revolutions per minute, in this case, the only viable option for achieving high power density is torque density.
However, torque density also varies depending on the application. Passenger vehicles mostly use high-speed motors, making it difficult to achieve high torque density, while commercial vehicles, which require low speed and high torque, find it relatively easier. Currently, domestic drive motors need to focus on enhancing rotor shape and reluctance torque utilization during magnetic circuit design; the key design consideration is how to significantly increase the heat conduction area without affecting magnetic circuit performance.
In the choice between induction motors and synchronous motors, Tesla's induction motors are no less capable than domestic synchronous motors. So why did the Model 3 choose a synchronous motor? This may be related to several factors: First, Tesla has entered my country, and using a synchronous motor has the implication of appeasing my country's neodymium iron boron material industry. Second, it has signed agreements with relevant Chinese companies, ensuring a worry-free supply chain. Third, to increase the power density of induction motors, the only way is usually to increase the current, but the side effects are quite obvious, while permanent magnet motors still have room for improvement and performance enhancement.
In terms of core components, although my country has the world's richest rare earth resources, the top-level technologies for refining and producing rubidium iron boron are controlled by Japan and Germany. In terms of silicon steel sheets, my country can produce 0.35mm, while Japan has already reached 0.27mm, and high-performance silicon steel sheets still rely on imports. The gap is even greater in high-speed bearings, with almost all high-speed motor bearings relying on imports, and virtually no domestically produced bearings are used.
2. Comparison of domestic and international technologies for lithium-ion batteries in electric vehicles
Currently, the trend of developing power lithium-ion batteries abroad from 18650 to 21700 is inevitable.
According to data released by Tesla, the energy density of the 21700 battery is 300 kW/kg, which is 20% higher than the 250 kW/kg of the 18650 battery. However, in terms of cost, the 21700 battery costs $170/kWh, while the 18650 battery costs $185/kWh. It can be seen that compared with the 18650 battery, the 21700 battery has a 20% increase in energy density while reducing costs by 8%.
What does 21700 mean? 21 is the outer diameter of the battery, and 70 is the height of the battery.
Are thicker and longer batteries always better? Theoretically, capacity will increase accordingly, but the side effects are also distinct: for every 10% increase in energy density, cycle life decreases by 20%, charge/discharge rate decreases by 30-40%, and the cell temperature rises by about 20%. Therefore, the 21700 is a result of a balance between overall performance and economy.
From a manufacturing perspective, the process of switching from 18650 to 21700 is basically universal and will not require too much investment in equipment and technical upgrades.
In terms of individual battery capacity, the 21700 is 35% larger than the 18650, reducing the number of individual cells by one-third. The number of metal structural components and conductive connectors required for the battery pack will also be reduced accordingly, resulting in an expected weight reduction of 10% and a cost reduction of 24%.
The 21700 batteries manufactured by Panasonic will be used in the Model 3. There are no passenger cars in China that use 21700 batteries yet, but many domestic battery manufacturers have already started to manufacture 21700 batteries, and the switch from 18650 is not too complicated.
In the development of lithium-ion batteries for electric vehicles, domestic manufacturers mainly use lithium iron phosphate, while foreign manufacturers primarily use ternary materials; and graphite-based materials are the main anode materials.
In terms of the overall technological level of the industry chain, China, Japan, and South Korea are in the first group. Japan is in a leading position in the development of battery technology, South Korea has done more in terms of product application, while my country has the most complete industry chain in the world, the largest output in the world, and the largest investment in R&D and industrialization in the world.
Overall, the new energy vehicle battery market in Europe and the United States is still dominated by Japan and South Korea. Chinese battery companies are also actively cooperating with international automotive giants in order to open up a broader market.
In terms of market share, domestic companies such as BYD, CATL, Lishen, and BAK are among the world's leading players in the lithium-ion battery field. However, their average product consistency and system integration, including the degree of automation in their processing lines, still lag behind advanced international levels.
Breakdown of the top 5 international electric vehicle power lithium-ion batteries:
(1) The key models of the Renault-Nissan-Mitsubishi Alliance, which ranks first, include the Nissan Leaf, e-NV200 and Renault Zoe. The Nissan Leaf ranked first in the global sales of new energy vehicles in 2017 and fourth. It is a very mature model. Previously, it used AESC batteries, which are a joint venture between Nissan and NEC.
Nissan began searching for new battery suppliers for the Leaf as early as 2015, with LG Chem frequently mentioned. The Renault Zoe, another best-selling all-electric vehicle, also uses batteries supplied by LG Chem.
(2) BYD, ranked second, naturally uses its own batteries, needless to say. As a representative of my country's new energy vehicles, BYD has established a complete industrial chain from batteries to complete vehicles. Facing the rapidly changing new energy market, BYD is also trying to transform itself. In addition to shifting to ternary lithium-ion batteries in the passenger vehicle sector, battery splitting and external sales have become a major business for BYD.
(3) BAIC Group has long dominated the sales charts for single models with its EC series. BAIC has close cooperation with battery companies such as Guoxuan High-tech and Farasis Energy. On May 28, 2017, BAIC signed a 1.875 billion yuan order with Guoxuan High-tech. At the end of December 2017, BAIC signed a five-year strategic procurement agreement with Farasis Energy for 1 million batteries.
(4) Geely Group's ability to rank fourth is largely due to the strong performance of the Zhidou D2, as well as Geely's Emgrand EV, Global Hawk, and other models. The Zhidou mainly uses batteries from Boston and Do-Fluoride, while the Geely Emgrand EV uses ternary lithium-ion batteries from CATL.
(5) Tesla ranks fifth. Due to production issues, the sales volume of Tesla Model 3 is not large, and it has not yet completed the mass production ramp-up problem. As a result, Tesla has brought together Samsung and LG to try to open up new suppliers.
3. Comparative Analysis of Chinese and Foreign Technologies in Electric Vehicle Controllers
The motor controller is the energy conversion unit that connects the battery and the motor. It is the core of the electric drive control system and mainly includes hardware components such as IGBT power semiconductor modules and related circuits, as well as software components such as motor control algorithms and logic protection.
my country's current level of electrical control lags significantly behind that of foreign countries, and its industrial manufacturing capabilities are insufficient. China's power electronics technology started relatively late, and power electronics has always been a bottleneck restricting the development of motor controllers in my country.
If money isn't an issue, most people would choose European, American, or Japanese brands, and only then would they consider domestically produced ones. Based on past experience, the basic performance of domestically produced servo motors is generally fine; the main difference lies in the control algorithms, integration, and stability of the servo controllers.
Power electronics technology mainly refers to power device technology, which is not just about modules, but also includes chip R&D technology, packaging materials and packaging processes, and motor controller integration technology.
Due to the time lag in these technologies, the power density of domestically produced motor controllers differs somewhat from that of mass-produced foreign products. Most companies tend to choose imported products when launching electric vehicle products. Furthermore, basic hardware testing tools for controllers are largely imported.
Power density is an external indicator, but it is actually closely related to the power modules used and their packaging. Therefore, we can see that the power density of our current products still lags behind that of foreign packaged motor controllers.
In integrated circuits, especially system-level integration, which integrates the internal structure of semiconductor wafers and controllers, this is an area where we currently lag significantly behind foreign countries and is a key area for catching up.
Currently, new energy vehicles abroad are mainly hybrid vehicles, which use permanent magnet synchronous motors and controllers. Major motor controller manufacturers include Toyota, Honda, Hitachi, Bosch, Ford, GM, Meidensha Electric, Toshiba, UQM Electric, ACPROPULSION, ENOVA Electric, Freescale, MM, and Yaskawa Electric.
In recent years, domestic companies have increased their investment in new energy vehicles and their core components. The development of motor controllers has rapidly shifted from technology research to product development. Several industrial companies specializing in the research and development and processing of automotive motor drive systems have emerged, gradually forming an industrial chain that is conducive to improving product quality and reducing costs.
The major domestic companies that have already supplied motor controllers in bulk include Huichuan, Blue Ocean Huateng, Shanghai Electric Drive, Shanghai Dajun, Tianjin Songzheng, Shenzhen Wuzhoulong, and CNR Times.
In detail, automotive-grade motors are required to have a compact structure, small size, light weight, high reliability, high efficiency, low cost, wide speed range, good environmental adaptability, and high regenerative braking efficiency.
Due to the backwardness of my country's motors and electronic control systems in terms of technology and manufacturing equipment, there is still considerable room for improvement in technical indicators such as torque density and power density of motors, as well as performance indicators such as reliability and consistency of motor products.
4. Comparative Analysis of Electric Drive Assembly and Detection Evaluation
4.1 Integrated design has become the mainstream
With the continuous development of new energy vehicle technology, integrated design of components has become an inevitable trend. Through integrated design, on the one hand, it can simplify the assembly process for OEMs and improve the product qualification rate; on the other hand, it can significantly reduce the number of suppliers and achieve goals such as weight reduction and cost savings.
In terms of electric drive technology, there are currently two approaches: a "two-in-one (motor + reducer)" approach, represented by the Chevrolet Bolt; and a "three-in-one (motor + reducer + motor controller)" approach, represented by the Tesla series.
There is also the "all-in-one" approach (which includes a motor + reducer, motor controller, charger, DC converter, high-voltage junction box, and part of the vehicle controller), represented by the BMW i3.
Currently, the three-in-one electric drive assembly method is gradually becoming the mainstream. In the long run, components such as motor, reducer, motor controller, high-voltage junction box, DC/DC, DC/AC, and charger will all be integrated into a large powertrain.
Regarding the electric drive system assembly, different powertrain configurations include commercial vehicle motor and gearbox assemblies, dual-motor assemblies, etc. Currently, passenger vehicle powertrain systems are also exploring whether they can be used in buses.
I personally believe that hub motors are a very good form of distributed drive, but it will take a lot of time to turn hub motors into a product.
4.2 The cost of electric drive remains a bottleneck restricting the development of the domestic industry.
High cost remains the most critical factor restricting the development of electric vehicles.
Excluding subsidies, electric vehicles will only have a market advantage if their price is on par with or even lower than that of gasoline vehicles. At that time, the price of the entire electric drive system assembly (motor + controller + reducer) should drop below 10,000 yuan.
In the future, the price of an electric drive system (with a power of around 130KW) used in a B-class car will drop to below 10,000 yuan. Some foreign giants have already achieved this, but domestic motor companies are still far from this goal. 10,000 yuan represents the level of next-generation technology and products worldwide, but the price of domestic electric drive system assemblies is generally still above 25,000 yuan.
In a new energy vehicle, the cost of the motor and controller accounts for 25%, while the cost of the power lithium-ion battery is as high as 45%. Therefore, to reduce the cost of new energy vehicles, we need to focus on the battery, motor, and electronic control system.
After 2018, more and more foreign motor brands and automakers will participate in market competition, making the electric drive system market increasingly competitive. It is foreseeable that once subsidies are completely phased out, domestic electric drive system companies will face a huge "survival crisis".
4.3 Detection and Evaluation Techniques for Electric Drive Systems
From the perspective of electric drive assembly detection and evaluation, it is mainly divided into the electric drive system level and the key materials and devices level.
At the electric drive system level, evaluations include system assembly evaluation, power calibration evaluation, load-bearing EMC evaluation, NVH evaluation, and electrical safety evaluation.
For power calibration and evaluation, there are many dimensions to evaluate power density. Various boundary conditions need to be defined to ensure the objectivity of the detection method.
In terms of electromagnetic compatibility, the use of load-bearing detection is still relatively limited. The difference between the no-load state and the actual operating conditions of the drive motor is significant, which can lead to huge discrepancies in the detection results.
The NVH characteristics and electrical safety performance of the drive motor are also crucial aspects of detection and evaluation.
In summary, the gap between my country and international advanced levels in the three core electric systems of new energy vehicles is not significant. The main reason for the gap is the constraint of some basic industrial technologies. However, my country's new energy vehicle market is huge, leaving considerable room for domestic companies to upgrade and improve their products. Domestic companies have ample time and space to perfect their products. But with the liberalization of national automotive industry policies, international advanced companies will inevitably gradually enter the Chinese market. Therefore, while facing market opportunities, Chinese companies also face challenges.
