[Source: Xcar]　　Xcar has learned from relevant sources that Tesla may soon acquire German wireless charging startup Wiferion to develop wireless charging features for Tesla vehicles.。　　WiTricity is a startup attempting to promote the concept of wireless charging to automakers. It obtained a license for inductive charging technology from the German startup Wiferion. After unsuccessful cooperation with its first partner Toyota, WiTricity tried to market vehicle inductive charging as an aftermarket solution.　WiTricity modified a Tesla Model 3 by installing a power receiver that allows the electric vehicle to charge simply by parking over the corresponding charging pad. WiTricity's solution can charge a car at 11 kW; for a Tesla Model 3, it would take six hours to fully charge once.　　Tesla has been researching inductive charging solutions for a long time. During the Investor Day on March 1, Tesla’s head of global charging infrastructure, Rebecca Tinucci, introduced a wireless charging solution, though details were not provided at the time. Combined with the latest acquisition information, Tesla is likely interested in WiTricity’s solution and may have decided to acquire its technology source directly—Wiferion.　　Editorial opinion: Wireless charging is common in our daily lives, such as for phones, watches, and electric toothbrushes, and it indeed provides a convenient charging experience. However, applying this technology to vehicles still seems to face many challenges. We look forward to Tesla offering a better solution.

 To promote energy conservation and emission reduction, decrease vehicle exhaust emissions, and prevent air pollution, electric vehicles (EVs) have become a new type of transportation widely promoted around the world. However, due to battery capacity limitations, electric vehicles have a short driving range, and charging issues have always been one of the main bottlenecks restricting their development.With the development of wireless power transfer technology, static wireless charging technology for electric vehicles based on magnetic coupling has received increasing attention. Compared to traditional wired charging systems, wireless charging systems have no electrical connections and offer advantages such as convenience, low maintenance costs, waterproof and dustproof capabilities, and fully automatic charging processes.A typical electric vehicle static wireless charging system structure is shown in Figure 1, including power electronic converters, primary side compensation networks, transmitting coils, receiving coils, secondary side compensation networks, high-frequency rectification and filtering circuits, and battery loads. In recent years, domestic and international scholars and research institutions have conducted extensive research on magnetic coupling-based static wireless charging technology for electric vehicles.However, as research has deepened, there are still many key issues that need to be addressed, such as system anti-offset capability, environmental sensitivity, system structure optimization, and stability control. Currently, the research on static wireless charging technology for electric vehicles is in a stage of tackling difficult problems, and further improvement and application of existing theories, as well as innovation and breakthroughs in principles, are still needed.Based on the research status of static wireless charging technology for electric vehicles at home and abroad, it can be seen that this technology has been relatively well studied in various aspects, but there are still many problems to be solved. The main issues are as follows:(1) System Anti-Offset CapabilityHow to improve the system's anti-offset capability has always been a research hotspot in electric vehicle wireless charging technology. In practical applications, influenced by the user's parking position, the relative position of the primary and secondary coils may vary within a certain range, causing changes in the coupling coefficient. This requires the system to have strong anti-offset capability.Currently, the system's anti-offset capability is mainly improved through the design of magnetic coupling mechanisms or system closed-loop control. However, these technical measures have limited improvement effects, and it is necessary to seek breakthroughs from a mechanism perspective. In recent years, wireless power transfer technology based on Parity-Time Symmetry (PTS) principles has been proposed, which can achieve constant output power and efficiency within a certain range regardless of the coupling coefficient. In addition, wireless power transfer technology based on fractional-order circuits has also demonstrated excellent characteristics. Applying these new wireless power transfer technologies to electric vehicle wireless charging is expected to further enhance the system's anti-offset capability.

 Although there is currently no widely implemented technology for wireless charging of cars, the technology itself is being actively researched by various automakers and other companies. Do you know what types of wireless charging technologies exist for electric vehicles?1. Static Wireless ChargingStatic wireless charging technology charges an electric vehicle while it is stationary. Based on its characteristics, it is typically suitable for places like shopping mall or residential parking lots.Radiative wireless power transfer technology transmits energy over long distances and mainly includes radio wave and laser methods. Due to its low efficiency and limited power output, it has not yet matured.2. Dynamic Wireless Charging TechnologyDynamic wireless charging technology for electric vehicles primarily transfers electrical energy through power rails embedded in the ground, using high-frequency alternating magnetic fields to the energy receiving device on vehicles within a certain range on the ground.This supplies power to the onboard energy storage system, allowing electric vehicles to carry fewer battery packs, extend their range, and make energy replenishment safer and more convenient.3. Magnetic ResonanceMagnetic resonance technology can transfer energy through high-frequency electromagnetic fields based on the principle of resonant energy coupling. In electric vehicle systems based on magnetic resonance, the AC power from the source is converted through rectification, filtering, and high-frequency inverter circuits into high-frequency AC to achieve resonant conditions for optimal energy transfer.4. Charging While DrivingThis requires the installation of wireless charging transmitters along specific road sections. Electric vehicles traveling on these sections can receive power from the charging system's transmitters, enabling rapid charging in a short time and allowing vehicles to replenish energy while driving, reflecting a dynamic system function for on-the-go charging.

At present, domestic and international universities and research institutions are mostly at the engineering prototype stage in the development of static wireless charging systems for electric vehicles, while major companies focus on providing solutions. There are still many issues that need to be resolved in the industrialization and commercialization process of EV wireless charging technology.  The development of wireless charging products for electric vehicles should rely on the latest research results, strengthen the organic integration of industry, academia, and research, make full use of cutting-edge core technologies mastered by major universities and research institutions, and leverage the innovative role of enterprises to promote the transformation of research achievements. This will help advance the commercialization process of static wireless charging technology for electric vehicles.  1. International Research Achievements and Industrial Status  Major foreign universities and research institutions conducting research on static wireless charging technology for electric vehicles include the University of Auckland (New Zealand), Korea Advanced Institute of Science and Technology (KAIST), Oak Ridge National Laboratory (ORNL, USA), University of Utah (USA), University of Michigan (USA), Saitama University (Japan), and the University of Tokyo (Japan).  Research mainly focuses on system modeling and control, magnetic coupling mechanisms, compensation topologies, offset resistance, as well as electromagnetic leakage and shielding.  The research team at the University of Auckland has done extensive work on magnetic coupling mechanisms, proposing a series of innovative coil structures that effectively improve the performance of magnetic coupling mechanisms. They have also established deep cooperation with Qualcomm Halo to develop a series of products.  The KAIST team achieved a transmission power of 6.6 kW over a 20 cm transmission distance in 2014, with an overall efficiency of 95.57%. In the same year, they proposed a coupling mechanism of large and small coils, greatly improving the system's offset resistance, and applied the large and small coils to 5–15 kW wireless charging systems.  Oak Ridge National Laboratory successfully developed a 20 kW EV wireless charging system in 2016 and announced in 2018 that they had achieved a high-power 120 kW wireless charging system with efficiency up to 97%. Professor Chris Mi's team at the University of Michigan proposed a bilateral LCC compensation topology in 2015 for electric vehicles, achieving decoupling between output current and load, which has been widely adopted.  In addition, major international companies such as Qualcomm Halo, Evatran, Momentum Dynamics, WiTricity, HEVO POWER, as well as Canadian companies ELIX and Bombardier, have also invested significant financial and material resources in researching wireless charging technology for electric vehicles.Among them, the Halo system by the American company Qualcomm has achieved an output power of 3.3 to 20 kW, with an overall efficiency of over 90%; the Drive 11 wireless charging system by the American company WiTricity, designed for pure electric and hybrid vehicles, can provide a maximum output power of 11 kW with an efficiency of up to 93%. In 2018, WiTricity collaborated with BMW to launch the world's first factory-equipped vehicle with wireless charging capability—the BMW 530e iPerformance, with a charging power of 3.6 kW.  The Canadian company ELIX uses magnetic dynamic coupling (MDC) technology to achieve an output power of 7.7 kW; the PLUGLESS wireless charging system proposed by the American company Evatran has achieved power transfers of 3.6 kW and 7.2 kW, with devices priced at $5,999 and $12,999, respectively, and provides wireless charging technology support for models such as the Tesla Model S, BMW i3, Nissan LEAF, and Chevrolet Volt.  The Momentum wireless charging system proposed by Momentum Dynamics can reach a maximum output power of 200 kW, with an efficiency of 95%, and has been successfully applied to wireless charging of electric buses in cooperation with the American company Link Transit. Additionally, on February 11, 2019, WiTricity announced the acquisition of certain technology platforms and intellectual property from Qualcomm Halo. Previously, Qualcomm and WiTricity had been working with international standards organizations, and this acquisition is expected to help unify standards and accelerate the commercialization of wireless charging for electric vehicles.  Overall, major foreign companies are relatively advanced in the field of wireless charging for electric vehicles and have also made certain attempts at commercialization.

 Wireless charging technology is divided into static wireless charging (electromagnetic radiation type, electrostatic coupling type, magnetic field coupling type) and dynamic wireless charging.Concept and Principle of Static Wireless Charging Technology for VehiclesStatic wireless charging technology charges electric vehicles when they are stationary, commonly used in shopping malls, parking lots, or parking spaces with self-installed charging stations.Static wireless charging can be classified according to the transmission mechanism: electromagnetic radiation type, electrostatic coupling type, and magnetic field coupling type:Electromagnetic radiation static wireless charging technology: Its transmission technology transfers energy through far-field methods, mainly including radio wave and laser methods, suitable for long-distance wireless power transfer.Electrostatic coupling static wireless charging technology: Its transmission technology transfers electrical energy through the near field, using alternating electric fields to transmit energy.Magnetic field coupling static wireless charging technology: Its transmission technology transfers electrical energy through the near field, using alternating magnetic fields for energy transfer. Magnetic field coupling technology has gained popularity and is widely used in static wireless charging for electric vehicles.Among them, magnetic field coupling static wireless charging technology is a relatively well-discussed mode.The commonly used magnetic field coupling wireless power transmission technologies are inductive and resonant types.Inductive type: An alternating current at a certain frequency is applied to the primary coil, generating a certain current in the secondary coil through electromagnetic induction, transferring energy from the transmitting end to the receiving end. The devices need to be very close during use, with the power transmission distance controlled at about 0–10 cm, and charging must align the coils 1V1. Inductive wireless charging has a high energy conversion rate and a wide range of transmission power, from several watts to several kilowatts. It offers high power and high efficiency at close range, but is sensitive to the coupling coefficient, making it generally suitable for short-distance transmission.