1 Introduction
The application of high-efficiency wireless charging technology for electric vehicles has benefited the daily life of the public, further improved people's quality of life, and provided people with better living conditions. The emergence and application of high-efficiency wireless charging technology for electric vehicles has also provided people with More job opportunities.
2 Brief introduction of electric vehicle wireless charging technology
2.1 R&D Background of Electric Vehicle Wireless Charging Technology
The rapid development of social economy benefits the people and increases people's average income and expenditure level, but at the same time it also seriously damages the domestic ecological cycle system, which is not conducive to the realization of my country's sustainable development goals. In order to further save natural resources and reduce pollution to the ecological cycle system, domestic environmental protection agencies have proposed the concept of "electric vehicles", and jointly developed high-efficiency wireless charging technology in the fields of production, processing and manufacturing, which reduces the impact of travel and tourism. The usage rate of ordinary cars [1].
In the actual application process of electric vehicles, due to the limitation of objective factors of charging conditions, problems such as inconvenient use have been caused. In order to promote the convenient application of electric vehicles in the current society, it is necessary to develop a new electric vehicle charging technology. Based on this, wireless charging technology came into being. With the popularization and application of wireless charging technology in society, it provides a good environment for the widespread use of electric vehicles in China, and also promotes the stable development of automobile-related manufacturing industries.
2.2 Advantages and disadvantages of wireless charging technology for electric vehicles
So far, my country's sustainable development is still in the implementation stage. In order to further promote the in-depth penetration of the concept of sustainable development in the current society, the application of electric vehicles and their wireless charging technology is imperative. As the research on electric vehicles by relevant institutions becomes more and more comprehensive, the charging methods of electric vehicles show a trend of diversification. At this stage, the forms of wireless charging technology for electric vehicles mainly include charging piles, replacement battery packs, and DC fast charging, etc. [2] ].
Of course, everything has two sides, and so does wireless charging technology for electric vehicles. In order to take full advantage of the advantages of wired and wireless charging technologies for electric vehicles, relevant organizations should carefully and comprehensively analyze the application paths of electric vehicles and their compatibility with wired and wireless charging technologies. Wired charging technology includes the advantages of one-time conversion of energy, low power loss, energy saving and environmental protection, while wireless charging technology includes the advantages of convenience, high safety, and no contact loss.
3 Research status of high-efficiency wireless charging technology for electric vehicles at home and abroad
3.1 Current status of research on high-efficiency wireless charging technology for electric vehicles in China
With the increasing damage to the ecological environment caused by social development, people are paying more and more attention to the research and development of new energy, especially the application of wireless charging technology for electric vehicles. In recent years, domestic scientific research organizations have successively carried out research and application work on wireless power transmission technology. In order to express the high importance attached to the new energy industry, the China Association for Science and Technology held the academic salon of the "China International Electric Vehicle Conference" in Shenyang in 2017 [3].
Throughout the history of Chinese science, this is the first time that an academic conference on wireless power transmission is held in China. The technical academic conference aims to conduct in-depth and comprehensive research on the technical points of wireless power transmission, not only for electric vehicles, but also to provide solid, reliable and practical new processing technology for other manufacturing fields.
3.2 Research status of high-efficiency wireless charging technology for electric vehicles abroad
Some advanced western countries have already implemented research and development of wireless charging technology for electric vehicles, such as the United States, Germany, Japan, etc. Now, some western countries have mastered relatively mature wireless power transmission technology and implemented strict confidentiality on its core technology This also fully confirms the importance of wireless power transmission technology to the overall development of the country. As early as the early 20th century, countries such as New Zealand, Japan, the United States, and South Korea conducted research on the technical difficulties of high-efficiency wireless charging for electric vehicles.
The first is the Oak Ridge National Laboratory in the United States, which carried out in-depth research on the coupling mechanism, transmission characteristics, dielectric loss and electromagnetic radiation of high-efficiency wireless charging technology in the early stage, and tried to apply the research results to actual development. The second is the University of Tokyo in Japan. In the early 20th century, Japan proposed the maximum efficiency control method for the secondary side based on the DC/DC converter, which may be the most efficient current conversion control method in the world so far.
4 Key projects in the research of high-efficiency wireless charging technology for electric vehicles
4.1 Design technology of magnetic coupling mechanism
So far, China has developed discrete continuous single coil structure, rectangular long coil type and double magnetic pole type wireless power supply guide rail technology, which provides a solid and powerful technical basis for the research and development work in the field of wireless power transmission, and also guarantees the data obtained in the research. The authenticity and reliability of this is enough to prove the importance of the magnetic coupling mechanism. Supported by new technologies and concepts, China has recently developed a three-phase AC excitation energy emission guide rail and a Quadraturetype receiving end. This magnetic coupling mechanism can effectively eliminate the cross-coupling between the three ACs, and at the same time greatly improve the energy pickup mechanism. Tolerable level of lateral offset.
Based on the development needs of the new era, in addition to the long-coil power supply rail, the domestic market has independently developed a dual-pole power supply rail mode, which expands the research content of high-efficiency wireless charging technology for electric vehicles, and essentially changes the traditional wireless charging technology. charging technology. External factors have little influence on the double magnetic pole type power supply rail, but its own magnetic field distribution is not uniform, there is a zero coupling coefficient, and the manufacturing cost is relatively high. Even so, there are many advantages of dual-pole power supply rails, such as high power density, compact size, unaffected by the site, strong adaptability to lateral movement, low construction difficulty, and horizontal exposure.
4.2 Robust control technology for energy transmission
Robust control technology for energy transmission is one of the key points in wireless charging technology, and it is also a key research project in the field of wireless energy transmission. data to support its diversified and efficient development. The University of Tokyo adopts a secondary side control strategy, adding a Buck converter after the rectifier circuit, using the state space averaging method to establish a small signal model, and designing a proportional-integral (PI) controller based on the pole configuration method to achieve stable control of constant power or maximum power .
In the process of researching high-efficiency wireless power transmission technology, robust control is the key point, and when implementing robust control research, the checking methods adopted by domestic and foreign scientific research institutions have their own advantages and disadvantages. Through observation, most foreign research institutions usually use PI control algorithm, and the control parameters are generally selected independently through the pole allocation method. The advantage of this method is that it is relatively simple and easy to implement, and the accuracy and credibility of the calculation results are relatively high. .
4.3 Electromagnetic Compatibility Technology
The current wireless power transmission realizes the transmission function through a high-frequency strong magnetic field. Due to the high complexity of the electromagnetic environment and the need to achieve a high transmission frequency, electromagnetic compatibility design has become a key research project for wireless power transmission. First of all, what relevant scientific research institutions need to do is to continuously optimize the design ideas of electromagnetic compatibility and improve the efficiency of wireless power transmission. The second is to ensure the safety and quality of wireless power transmission and reduce personnel contact during wireless power transmission.
The current electromagnetic compatibility design mainly includes magnetic shielding design, frequency configuration, grounding design, residual magnetism design, software anti-interference design, etc., and in the design process, the staff also need to pay attention to the electromagnetic interference factors of wireless power transmission, these interference factors It can be roughly divided into two types, one is active shielding and the other is passive shielding. As the name suggests, the shielding subjects of the two are just opposite. Therefore, designers should pay attention to distinguishing between the two types of electromagnetic interference factors when optimizing ideas.
4.4 Multi-rail charging technology
In recent years, domestic research on high-efficiency wireless charging technology for electric vehicles has become more in-depth, and a comprehensive study has also been carried out on the concept of multi-rail charging. Up to now, the guide rail modes of the electric vehicle wireless power supply system mainly include a single-stage guide rail mode and a multi-stage guide rail mode. For the single-stage guide rail mode, the primary circuit is the basis, and there is only one corresponding guide rail and a set of primary power conversion devices; for the multi-stage guide rail mode, multiple sections of guide rails are added to the primary circuit.
There are two forms of power transmission in the multi-level DIN-rail power supply, one is the single-layer multi-level DIN-rail power supply mode, and the other is the relatively complicated double-layer multi-level DIN-rail power supply mode. During the operation of the former, the system power supply guide rail is basically divided into N sections of guide rail, and each section of guide rail will be equipped with an independent conversion device, resonance compensation device, etc.; Based on the level guide rail power supply system, N sections of guide rails are perfected to form N guide rail groups.
Compared with the single-layer multi-level rail power supply system, the double-layer multi-level rail power supply system has higher operating efficiency, stronger stability, higher safety quality, effectively reduces the bad contact between each section of the rail, and avoids problems such as current disturbances happened. The double-layer multi-level guide rail power supply mode has technical advantages such as time-sharing and segmental power supply, reducing system power loss, improving power transmission efficiency, easy maintenance and control, reducing power conversion devices, reducing electronic device requirements, and reducing sensitivity to parameter changes.
5 Conclusion
Economic growth not only benefits the people, but also damages the natural ecology. Therefore, it is necessary to protect the ecosystem while taking into account economic development. Therefore, it is imperative to reduce the number of traditional fuel vehicles, and the new electric vehicles will It has become a new development trend of the domestic automobile manufacturing industry.
Source: "Time Auto" Issue 23, 2021
