1 Introduction

　　With the rapid development of my country's economy, the country has introduced a series of policies for energy vehicles such as corresponding preferential policies, subsidy policies, and trade-in policies for old ones, which further promotes the increase in private cars. Internationally, energy and environment have become the most concerning issues in the world. The shortage and substitution of energy, environmental pollution and protection have jointly promoted the vigorous development of new environmentally friendly cars.

　　Electric vehicles are the first environmentally friendly new energy vehicles developed, including battery electric vehicles, hybrid electric vehicles and fuel cell electric vehicles. Among them, fuel cell electric vehicles are environmentally friendly new energy vehicles that will be the mainstream development in the future, but their technology is still in the research and development stage and the cost is too high; the power supply of hybrid electric vehicles mainly comes from generators driven by internal combustion engines, which can only be used under the energy crisis. It is a transitional product. This article mainly studies pure battery electric vehicles.

　　Battery electric vehicle technology has been basically mature, many manufacturers are already vigorously producing them, and charging stations are also being constructed in various places. However, the charging problem of battery electric vehicles has always been a headache for researchers. According to existing application results, it takes half an hour to charge a general battery, and more than 8 hours to fully charge it. Moreover, a fully charged car can generally only travel more than 100 kilometers. . This obviously makes battery electric vehicles incomparable with internal combustion engine vehicles. Therefore, the solution of charging technology will greatly promote the development of battery electric vehicles.

　　2 History of wireless charging technology

　　More than 100 years ago, a Serbian-American electrical engineer and physicist named Nikola Tesla was already dreaming of a world without wires. In 1891, he invented the Tesla coil, which produced high-frequency wireless High-voltage current, but the current of this high-voltage current is extremely small and cannot be applied in actual use. At that time, Tesla used these coils to conduct a series of experiments, pioneering wireless power transmission. Tesla once said that wireless charging will be the ultimate way to make the electric power industry prosperous. In 1901, Tesla began his research in Long Island, New York. His goal was to make electrical energy travel across the ocean like radio waves. However, due to the huge investment, this technology was stillborn.

　　3 Development status of wireless charging technology

　　Although the Tesla coil was not implemented at the time, later generations completely confirmed the feasibility of this solution in theory. After years of research, scientists believe that wireless power transmission is possible. Wireless power transmission is a special power supply method that is different from wired transmission. Currently, it mainly includes three different methods: electromagnetic induction, electromagnetic resonance and radio waves.

　　3.1 Electromagnetic induction

　　This is currently the most common transmission method. The coils at the transmitting end and the receiving end induce each other to generate current, thereby realizing power transmission. In 2010, a technology company displayed a mobile phone wireless charger that used the principle of electromagnetic induction. The power of this method can reach several hundred watts, but the distance between the two coils cannot exceed 1 cm, and the coil and circuit of the end product must be shielded to prevent interference. In addition, the transmitter must have the ability to intelligently identify the product being charged. Prevent energy from being transmitted to other devices, causing energy waste.

　　3.2 Electromagnetic resonance

　　Electromagnetic resonance is a method of power transmission currently being researched. In 2008, Intel engineers used this technology as a basis to make a 60 W light bulb glow 3 feet away from the power source. According to calculations by relevant scientists, the power of this method can reach several kilowatts and the distance can reach 3 to 4m. However, due to the large diameter of the coil required for the current experiment, it is still in the experimental stage. In addition, the corresponding frequency must be tested. Protection to prevent electromagnetic waves of the same frequency from interfering and reducing efficiency.

　　3.3 Radio waves

　　Radio waves are another relatively mature wireless charging method. Its principle is similar to the early use of mineral radios. It uses miniature high-efficiency receiving circuits to capture radio waves reflected from obstacles, and then converts them into stable DC voltage. Powercast claimed as early as 2007 that it could use RF broadcasts to charge consumer electronics devices smaller than a cellular phone from up to several meters away. However, the power of this method is low: no more than 100mW; the distance is short: no more than 10m; the efficiency is low; and the charging time is long.

　　4. Application of wireless charging in electric vehicles

　　How is wireless charging applied to electric vehicles? Below, we will briefly study and analyze charging locations, charging methods, and rechargeable batteries, and finally propose specific application methods of wireless charging in electric vehicles.

　　First, choose the charging location. Wireless charging technology is related to the distance and status of the charger and the device being charged. That is to say, the distance between the two cannot be too large, and there is no relative movement between the two, otherwise power cannot be transmitted stably and effectively. Therefore, the charging location can only be the place where the car stays, that is, a garage, a parking lot, an intersection, etc. The bus charging device can also be set up at a bus stop. Of course, special charging stations can also be set up in places or beside highways where conditions permit to facilitate vehicle charging.

　　Secondly, the choice of charging method. It can be seen from the three charging methods that the distance required for electromagnetic induction charging is too small and the efficiency of radio wave charging is too low, while the distance and efficiency of electromagnetic resonance charging can meet the needs of battery cars.

　　Finally, the choice of rechargeable batteries. Electric vehicles will be charged at any time in the city, so it is necessary to choose batteries that are pollution-free and have no memory effect for charging.

　　After comparison and selection, we have a clearer idea of the application of wireless charging in electric vehicles: On the one hand, in the construction of roads and construction projects, the power supply unit will pre-install parking spaces at intersections, public parking lots, units or according to the planning drawings. Wireless charging chargers should be buried under parking spaces and garages in the community, and the chargers should be connected to the power grid or solar panels; on the other hand, car manufacturers should install wireless charging receiving devices at the bottom of the car and connect them to the battery, etc. Equipment connection; in addition, relevant national departments must unify the frequency of transmitting and receiving signals to make them universal.

　　5 Issues that should be paid attention to in the application and development of wireless charging technology

　　(1) The state should introduce corresponding policies to encourage, support and regulate the development of wireless charging vehicles and the construction of charging facilities. The development of an industry or enterprise, especially an industry or enterprise that benefits the country and the people, cannot be separated from the support of the state. Wireless charging is a field that has just started. Its effective development can largely solve a bottleneck in the development of electric vehicles. However, due to the huge investment in its research and development, it requires more encouragement and support from the state to speed up its research and development process. , so that it can be applied as soon as possible.

　　(2) No matter what charging method is used and what kind of battery is used, relevant national and local departments must conduct research on its frequency, safety, environmental protection, energy saving and other aspects to avoid waste, adverse effects on human health, and It will cause new pollution to the environment, and at the same time, publicity must be in place to avoid people's fear of electromagnetics.

　　(3) In practice, since the transmitter is placed underground, attention should be paid to its protection.

　　(4) In areas with a lot of rain, in addition to the waterproofing of underground facilities, the waterproofing treatment of the vehicle receiving end is also an issue that needs to be considered.

　　6 Conclusion

　　Wireless charging technology is still in the research and development stage, but many countries have applied it to charging mobile phones, computers, Walkmans and other devices. Among them, the United States, South Korea, Japan and other countries have also begun research on wireless charging cars. As this technology continues to improve, it will surely promote the development of battery vehicles, reduce our dependence on oil, protect the environment, and benefit mankind.

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