What is the trend of wireless charging technology for electric vehicles?
ZTE has been working in the field of wireless charging for many years. Through industry-university-research cooperation, product development was launched in 2013, and mature products and solutions were launched in September 2014. ZTE’s wireless power supply system uses non-contact electromagnetic induction for power transmission. After the electric vehicle is parked in the charging parking space, it can automatically wirelessly access the communication network of the charging station to establish the communication between the ground system and the vehicle system. link, and complete vehicle authentication and other related information exchange. The charging parking space can also be interconnected with the cloud service center through wired or wireless means. Once any hidden danger of charging and receiving electricity occurs, the ground charging component will immediately stop charging and alarm to ensure the safety and reliability of the charging process. Best of all, the wireless charging system doesn’t work at all while the vehicle is running, ensuring safety even when the vehicle is driving over it or in severe weather conditions such as thunderstorms.
ZTE’s wireless charging solution has realized the transformation from “metal dielectric contact conduction” to “electromagnetic induction wireless power transmission”. The charging process is simple, the reliability is high, and the maintenance cost is low; the charging facilities are buried underground, which requires less construction site and is not afraid of Flooding, snow, mud, gravel and dust, etc.
At present, ZTE’s wireless charging technology has been commercialized in some cities, as shown in Figure 1. In December 2014, ZTE and Yutong signed a strategic cooperation agreement on wireless charging technology. In January 2015, Chengdu No. 1058 micro-circulation wireless charging bus was officially put into operation; in September 2015, ZTE and Dongfeng Motor launched in Xiangyang. The world’s first wireless charging bus commercial demonstration line; in October 2015, ZTE and Shudu Bus released the world’s first wireless charging urban microcirculation bus solution.
Audi’s wireless charging technology instrument needs to install a charging board equipped with coils and inverters on the parking space of the user’s vehicle and connect it to the grid. When the vehicle is parked on the charging board, the charging process will automatically start. The charging principle is that the alternating magnetic field in the charging board induces the alternating current of 3.3kW into the secondary coil of the vehicle, so as to realize the transmission of electric energy from the grid to the charging system of the electric vehicle. When the battery pack is fully charged, charging will stop automatically. Inductive wireless charging takes about the same charging time as cable charging, and the user can interrupt charging and use the vehicle at any time. Audi’s wireless charging technology is more than 90 percent efficient and unaffected by weather factors such as rain, snow or ice. At the same time, the alternating magnetic field is only generated when the vehicle is over the charging pad and does not cause harm to humans or animals.
In response to the transmission efficiency problem in wireless charging, Audi has proposed a different solution, that is, it has developed a wireless charging system that can be raised and lowered, as shown in Figure 2. Its biggest feature is that it can make the power supply coil closer to the vehicle. The power receiving coil at the bottom achieves a power transmission efficiency of more than 90%, which allows some high-chassis SUVs to ensure better charging efficiency when charging. In the future, using the charging principle of induction coils, Audi electric vehicles can not only automatically start charging after driving into the parking space, but can even be charged while driving on roads with induction coils.
In the 1890s, Nicola? Tesla invented the “Tesla Coil”, which can transmit electricity through the air, ushering in the era of wireless power transmission. At the “2011 International Consumer Electronics Show”, Fulton Innovation, a subsidiary of Amway Corporation, demonstrated wireless charging technology and launched the world’s first wireless charging Tesla car. At present1, Tesla hopes to establish an interconnected charging network in various large cities to solve the problem of insufficient power that is prone to occur in electric vehicles.
The Plug less wireless charging system developed by Evatran, an American manufacturer, uses electromagnetic induction technology to wirelessly charge vehicles. Their scheme is that when the vehicle adapter installed on the vehicle chassis is aligned with the charging platform installed on the ground, the entire system will be awakened and automatically transmit energy through electromagnetic induction, as shown in Figure 3.
Evatran’s Plug less system provides parking guidance and allows drivers to aim the charging unit more quickly when parking, and the system’s software is compatible with the vehicle’s existing software. The system has been practically tested and installed in electric vehicles such as the Nissan Leaf or Chevy Volt.
Similarly, HEVO Power, a company from the United States, plans to install wireless charging stations on the road, so that electric trucks and electric vehicles can be wirelessly charged at certain parking spots.
The road wireless charging station device developed by HEVO is a bit like a manhole cover on the road, while the electric vehicle is equipped with a receiver that can charge at 10kW of power, even higher than some wired charging solutions. The HEVO system also includes a mobile app that displays the vehicle’s parked location and charging status.
Nissan has publicly demonstrated the wireless power supply system experiment of “HYPER mini” and “LEAF” to the news media. The maximum output power of the wireless power supply system displayed is 3.3kw. It takes 8 Hour. The ground coil is set in the car owner’s own parking lot instead of a public place. The prototype EV “LEAF” model is shown in Figure 4.
Nissan’s wireless charging system uses electromagnetic induction, and the vehicle is charged by induction with an induction coil. The charging system can be built into the floor or installed outdoors in the form of charging piles. When charging is required, the car owner only needs to drive the car within the range of the induction coil, the system will automatically detect the vehicle, and the car owner will start and close the charging process through the app. The installation location of the charging system and the weather conditions outside will not affect the charging time.
Toyota also joined the wireless charging bandwagon in 2014. Unlike Nissan, the wireless charging system developed by Toyota uses electromagnetic resonance. Since wireless charging technology has high requirements on location, Toyota has specially developed a parking assist system that can display the position of the transmitter coil on the central control display of the electric vehicle for drivers to align when parking, as shown in Figure 5. In order to realize the practical use of wireless power supply for electric vehicles, Toyota has started a verification experiment in Toyota City, Aichi Prefecture in February 2014. The company has developed a car equipped with a magnetic resonance wireless power supply system based on the plug-in hybrid electric vehicle (PHEV) “Prius PHV” as a prototype. The output power of the wireless power supply system is 2kW, and the frequency band used is the 85kHz frequency band that has basically been agreed as an international standard. The power transmission efficiency is about 80%. In the verification experiment, the distance (coil spacing) between the power supply coil (set on the ground) and the power reception coil (set at the bottom of the vehicle) is about 15cm. The maximum allowable range of horizontal misalignment is the width of a tire (about 20cm). The front and rear directions are assisted by the car navigator, and there is basically no misalignment.
Recently, Honda also announced its latest progress in wireless charging. The Honda wireless charging system consists of two coils. The receiving coil on the car is responsible for receiving and converting the magnetic force into electrical energy and storing it in the car battery. Honda partnered with Witricity to develop a new system that uses power waves of specific frequencies to achieve magnetic resonance. Even if the two coils are not perfectly aligned, nearly 100% energy transfer can be achieved, as shown in Figure 6.
According to Honda, the coil can still achieve a transmission rate of 80%-90% under the conditions of a lateral error of ±10cm, a longitudinal error of ±5cm, and a parallel error of ±2°. The output power of the wireless charging system is about 2.2kW, which is only 1kW lower than that of ordinary plug-in chargers (generally, the power of wireless charging systems is much lower than that of plug-in chargers).
The Qualcomm Halo wireless charging device uses magnetic resonance induction technology to wirelessly transmit electrical energy between the ground charging substrate and the electric vehicle on-board charging board, which is converted into on-board battery charging. Ground charging substrates can be installed in garages, driveways, or even buried in the surface of the road. Therefore, in addition to high charging efficiency, car owners can make full use of the parking gap to complete charging. At present, there are three types of Qualcomm Halo wireless charging devices with rated powers of 3.3kW, 6.6kW and 20kW. The first two products need to be charged overnight, while the latter can fully charge the on-board battery of an electric vehicle within half an hour.
At the Formula E Championship on April 22, 2015, Qualcomm demonstrated the Halo wireless car charging system developed by itself, as shown in Figure 7. As long as the car is directly above the charging base plate, the on-board battery will start to be charged after the on-board charging coil is aligned with the ground charging base plate. The Halo wireless car charging system currently has the capability of semi-dynamic charging. If there is a foreign object between the on-board charging coil and the ground charging substrate, the system can automatically suspend charging.
8) BMW, Benz
In July 2014, Mercedes-Benz and BMW jointly announced that they would cooperate in the research and development of wireless charging technology for electric vehicles. The rendering of BMW wireless charging is shown in Figure 8. Mercedes-Benz wireless charging renderings are shown in Figure 9
The wireless charging technology jointly developed by Mercedes-Benz and BMW consists of two parts: one is the coil mounted on the car chassis; the other is the charging substrate with built-in coils. When the coil mounted on the car chassis is aligned with the coil on the charging substrate, wireless charging can be realized. . Mercedes-Benz is already testing the technology in the S-Class, while BMW is applying it to the hybrid i8. The current charging time is less than two hours, and the next cooperation goal between the two parties is to further reduce the charging time.
The two parties said that they are currently further transforming the coils, so that the output power will eventually reach 7kW, and it will be used in more electric vehicle products of BMW and Mercedes-Benz in the future. For example, Mercedes-Benz has announced that it will offer wireless charging on the upcoming S500 plug-in hybrid, while BMW plans to bring the technology to more electric vehicles in the i-series, including the i8, i3 and, in development, the i5.
For automakers, wireless charging makes a lot of sense. If wireless charging technology can be fully popularized, the convenience of electric vehicle charging can be greatly improved. Whether it is in the charging process or in terms of battery life, it will greatly increase people’s acceptance of electric vehicles. It can be said that mature wireless charging technology will be the pioneer of electric vehicles to occupy the market.
(1) Safety issues. Whether the wireless charging technology adopts electromagnetic induction or magnetic field resonance, it has the process of emitting energy and receiving energy. Therefore, the safety of the charging process has been questioned, and people are worried about whether it will cause radiation. Although the MIT and Volvo research teams have shown that the magnetic field used by MRI is similar to the earth’s magnetic field and has no effect on human health, it is still a long process to gain user trust.
(2) There is no unified standard. Like wired charging technology, standardization is one of the obstacles hindering the development of wireless charging technology. The advantages and disadvantages of electromagnetic induction and magnetic resonance are still inconclusive. For one method alone, different companies and research organizations also use different standards. Among them, the shape of the coil used in wireless charging technology is a problem. At present, there are mainly two types of circles and squares used in the industry. With different shapes and different magnetic circuits, the coils cannot transmit energy efficiently. Round and square coils also have their pros and cons, and manufacturers’ choices vary. Incompatible methods and devices make it difficult to develop and popularize wireless charging technology without a unified standard.
(3) Cost and grid load. There is always a typical “chicken and egg” problem between cost and popularization. In order to ensure transmission efficiency, current wireless charging devices use large coils, high costs, and high maintenance costs. In addition, it is not difficult to see from the experimental data of Volvo charging equipment that the energy conversion rate in the current magnetic resonance method is still very low, and the cost of electricity will increase accordingly. At the same time, the loss of energy will increase with the increase of transmission power and transmission distance. When multiple electric vehicles are charged at the same time, the load on the power supply system will also increase greatly. If it is necessary to carry out corresponding transformation of the city’s power grid, it is also a large economic investment, which may not be worth the loss. Wireless charging technology cannot support v2G and simply increases grid load.
At present, most of the wireless charging adopts the electromagnetic induction type, represented by BMW and Mercedes-Benz, and has been verified on some models. The electromagnetic induction type has a relatively simple structure and large transmission power. However, the receiving coil and the transmitting coil need to be aligned. In order to ensure accurate alignment, it is generally combined with automatic vehicle control to ensure normal charging. Compared with European manufacturers, Japanese vehicles are more inclined to magnetic resonance wireless charging. Magnetic resonance transmission is more efficient, the transmission distance is long, and the induction coils do not need to be aligned, but the technology is complex, and it is easy to cause radiation, which may bring electromagnetic damage. .
The popularity of wireless charging technology will bring great convenience. Wireless charging equipment is easy to install and can be installed in parking lots, highway service stations, etc. However, in order to popularize the application of wireless charging technology, there are still the following problems to be solved:
(1) Transmission efficiency is a problem faced by all wireless charging, especially for “electrical appliances” with higher charging power such as electric vehicles. The electrical energy is first converted into radio waves, and then radio waves are converted into electrical energy. These two Each conversion will lose a lot of energy.
(2) Electromagnetic compatibility is also one of the technical bottlenecks that wireless charging needs to solve. Electromagnetic waves are easy to leak. When high-power wireless charging equipment for vehicles is running, it will also have an impact on surrounding biological and electronic equipment, and even endanger human health. Using a closed automatic intelligent garage to install wireless charging equipment is a better way to solve electromagnetic compatibility, but the cost is really high.
(3) Issues such as electrical standards.