High-performance digital integrated automotive motor drive system trends

In recent years, China's auto industry has developed rapidly. In 2009, the domestic automobile production and sales exceeded 13 million vehicles, marking China becoming the world's first automobile production and consumption country. It is worth noting that China’s current car ownership is around 80 million, and it is expected that China’s car ownership will exceed 200 million by 2020, and it may reach the level of developed countries by 2030, reaching 450 million vehicles. Therefore, there is a huge gap between the market demand and supply of fuel. To a certain extent, the sustainable development of the Chinese auto industry depends on the development of new energy vehicles, especially electric vehicles.

The development of electric vehicles depends on the development of core technologies, namely, the development of batteries, motor drives and electronic control of vehicles. On the basis of classification and development of electric vehicles, attention should be paid to the demand of electric vehicles for motor drive technologies. High-efficiency, digitization, and integration have become the technological development trend of automotive motor drive systems.

Any electric vehicle needs electric motor vehicles including pure electric vehicles, hybrid electric vehicles, and fuel cell electric vehicles. The power system structure is shown in Figure 1.

A pure electric vehicle is powered by a battery. The converter of the vehicle-mounted motor drive system converts the direct current through PWM modulation to an alternating current with a controllable frequency and amplitude. The electromagnetic torque generated by the motor drives the electric vehicle through the gearbox. The technical bottleneck of pure electric vehicles is the battery. The most promising energy-consuming battery for pure electric vehicles is a lithium iron phosphate battery. The lithium iron phosphate battery has good safety, an energy density of 80 to 120 wh/kg, and a cycle life expectancy of 2,000 times. It is estimated that by 2012 each watt-hour The cost can be reduced to 1.0 to 1.5 yuan, that is, the battery cost of an electric vehicle with a driving range of 200 kilometers can be controlled at around 30,000 yuan. So far, Nissan has introduced the Leaf pure electric car, BMW has launched MINIE, and the Chinese government and car manufacturers have also attached great importance to the development of pure electric vehicles, including China FAW, Chery, Beijing Automotive, and other major automobile manufacturers in Beijing in 2010. Auto electric prototypes have been introduced at auto shows.

There are two kinds of power sources for hybrid electric vehicles: internal combustion engines and electric motors, that is, the power systems of hybrid electric vehicles, including internal combustion engines and electric motors, have complex structures. Utilizing the characteristics of a motor with a wide range of high efficiency and four-quadrant operation, when the resistance is large, the motor is used to provide assistance, and when the resistance is small, the motor is used to generate electricity, so that the internal combustion engine is always operating in the optimal efficiency zone and the energy efficiency of the entire system is improved. Therefore, the hybrid vehicle's internal combustion engine not only has a smaller displacement than a conventional internal combustion engine, but also reduces energy consumption by 5% to 50%. Take Toyota PRUIS as an example, PRUIS is equipped with a 1.5-liter engine, but its power performance is even higher than that of a 2L ordinary internal-combustion engine, and the efficiency from well to wheel increases from 16 to 18% to 32%. So far, the cumulative sales of Toyota Hybrid has exceeded 2 million units, indicating that hybrid electric vehicles have entered a large-scale market.

The fuel cell electric vehicle uses a proton exchange membrane fuel cell system to generate electricity. Its fuel is hydrogen fuel in the vehicle and oxygen in the air. Hydrogenation generates electricity and water, so the fuel cell electric vehicle is a zero-emission electric vehicle. In the fuel cell electric vehicle, the fuel from the fuel cell has the characteristics of large voltage variation range and poor dynamic response, and usually needs to be boosted and regulated by a first-order DC-DC converter (DC-DC), together with the battery. The motor drive system supplies power.

Since the 1960s and 1970s, the United States and other Western countries have turned military and aerospace applications of fuel cells to civil power generation and used them as power sources for automobiles and submarines. Well-known automobile companies in the world have invested a lot of manpower and material resources to develop fuel cell electric vehicles. Research on the development of automobiles. The above efforts reached a peak around 2002-2003. In June 2002, the 14th World Conference on Hydrogen Energy was held in Canada and the concept of a hydrogen energy society based on fuel cells as the leading product was proposed.

As a result, the development of the hydrogen society has become a major focus of the human social energy revolution. Time magazine ranks the fuel cell as the top 10 high technology in the 21st century. In 2002, President Bush announced the "Freedoncar" plan, which determined that the use of fuel cells would become the main energy source in the society, first of all in automotive products. U.S. General Motors CEO Gwanner said: The goal of GM is to produce 1 million electric vehicles in 2010, the most important being the fuel cell hybrid electric car. Ford CEO Bill Ford said: For 25 years, Ford will use hybrid electric vehicles on 75% of light vehicles. However, as of 2010, the promotion of fuel cell electric vehicles still has problems such as high battery costs, hydrogen storage technology, and the construction of hydrogen refueling station infrastructure. The large-scale marketization schedule of fuel cell electric vehicles has been delayed again.

Electric vehicles promote the development of the motor industry as one of the important development directions of permanent magnetization into motor drive technology.

The requirements of electric vehicles for motor drive systems can be summarized as: low speed and high torque. This requirement is due to the requirements of initial accelerations for climbing and starting of automobiles. In wide constant power zones, the constant power zone of electric vehicle motor drive system is 3 to 10 times that of constant torque zone. This requirement is due to the power requirements for high-velocity vehicles and high-speed overtaking; the area where the motor drive system efficiency reaches 80% or more is greater than 50%. This requirement stems from the requirement for high efficiency in the entire work range of electric vehicles; high power density, such as motor power density greater than 1kW/kg, and controller capacity density of 3 to 4kVA/kg and above. This requirement comes from the requirements of vehicle space and high efficiency and energy saving; the harsh operating environment usually requires the working environment temperature of the electric vehicle motor drive system to be -40°C to 105°C, and the maximum vibration acceleration is greater than 10g; high reliability. Usually the life of electric vehicle motor drive system is more than 200,000 kilometers; low cost. The United States FCVT plan to reduce the cost of the motor drive system to 8-12 dollars per kilowatt.

Therefore, the requirements for electric motor drive systems for electric vehicles have given rise to the development trend of motor drive technology for electric vehicles, namely high-efficiency permanent magnetization, digitization and integration.

In the motor drive technology of electric vehicles, the motor drive system for electric vehicles is different from the ordinary electric drive system because of space constraints and the use environment. It requires higher performance, higher volume/weight density, and higher ambient temperature. The power electronics and motor technology used for ordinary motor drives have not been able to meet their requirements. In the research and development of the electric vehicle drive technology, the technology development trend of automotive motor systems can be basically summed up as high-efficiency permanent magnetization, digitization and integration.

Permanent magnet motors have the advantages of high efficiency, high specific power, high power factor, high reliability and easy maintenance. The vector control of the variable frequency speed control system allows the permanent magnet motor to have a wide speed range. Therefore, the permanent magnetization of the motor becomes one of the important development directions of the motor drive technology.

Digitization is also an inevitable trend in the future development of motor drive technology. Digitization not only includes the digitalization of the drive control, the digitization of the interface to the CNC system, but also the digitization of the measurement unit. With the development of microelectronics and computer technology, the advent and commercialization of high-speed, high-integration, low-cost microcomputer-specific chips and DSPs have made digital control systems possible. The use of software to replace hardware to the greatest degree, in addition to the completion of the required control functions, can also have protection, fault monitoring, self-diagnosis and other functions. Full digitalization is one of the important development directions for electric vehicle control and even AC drive systems.

There are two aspects to the integration of the motor drive system: one is the integration of the motor and the engine assembly or the motor and the gearbox. The development of the motor drive technology towards the integration helps to reduce the weight and volume of the entire system and can be effective. Reduce the manufacturing cost of the system, such as Honda's ISG system and Toyota's THS system; integrate the switching devices, circuits, controls, sensors, power supplies, and passive components of the electric vehicle drive controller into standard modules to form power electronic components. (PowerElectronBuildingB1ock-PEBB), this integrated method can better solve the problems of the combination of different circuits and high voltage isolation between different processes, has a higher degree of integration, and can also reduce the size and weight effectively, but at present There are also technical problems with high difficulty such as distribution parameters, electromagnetic compatibility, and heat transfer, and it is not yet possible to effectively reduce costs and achieve higher reliability.

In recent years, automotive motor drive system technology has made great progress. Since the beginning of the 21st century, the US Department of Energy organized the FreedomCAR and Vehicle Technology (FCVT) program, which aims to develop advanced automotive technologies to change the current energy consumption structure of the United States and promote energy security. There are 7 sub-projects in the FCVT project. Power electronics and motors are among them. Under the organization of the US Department of Energy, the FreedomCar Alliance was formed by a number of research institutes, automobile manufacturers, and related companies to jointly conduct research on advanced power electronics for automotive applications. Significant progress has been made, and international auto giants and electric manufacturers have also made progress. Great achievements have been made. The current status of foreign advanced motor drive system technology is shown in Table 1. Although overall motor drive technology has made great progress, product cost is still the largest distance from large-scale marketization.

Since the 10th Five-Year Plan, the Ministry of Science and Technology has initiated major special projects for electric vehicles, which has played a major role in the development of electric vehicles in China. The following table takes the development of motor drive technology as an example. China has approached or reached international advanced level in some single indicators of motor vehicles, but we still have considerable world advanced level in power electronics integration, thermal management, and mass production processes. gap. With the implementation of the national electric vehicle related plan, we have reason to believe that the gap between China's motor drive system technology and the international level will further narrow.

Electric vehicles are classified into pure electric vehicles, hybrid vehicles and fuel cells based on energy or power sources. The motor drive system is one of its three core technologies. The article reviews the history of the development of electric vehicles and summarizes the technical requirements for electric vehicle motor drive systems. It points out that the technology development trends of electric vehicle motor drive systems are permanent magnetization, digitization and integration.