Wireless charging technology for electric vehicles (EVs) operates by embedding power supply rails beneath the ground to generate a high-frequency alternating magnetic field. This field transfers energy to a receiver on the vehicle, which then powers the onboard energy storage system. This technology allows EVs to carry fewer battery modules, extending their driving range while enabling safer and more convenient energy replenishment. Key parameters for dynamic wireless charging include energy transfer distance, power, efficiency, lateral displacement adaptability, and electromagnetic compatibility. As a result, the development of systems that are high-power, high-efficiency, low-radiation, cost-effective, and capable of handling displacement has become a major focus for research institutions worldwide.
Wireless Power Transfer (WPT) Technology
Wireless charging originates from wireless power transfer technology, which enables non-contact energy transmission via electromagnetic induction, electromagnetic resonance, radio frequency, microwaves, or lasers. Depending on the transmission distance, WPT can be categorized into three types:
Short-Range Transmission:
Short-range WPT utilizes Inductive Coupled Power Transfer (ICPT) technology, ideal for portable devices. By coupling primary and secondary coils, ICPT transfers energy efficiently through magnetic fields that can penetrate non-metal materials. It supports high power levels up to hundreds of kilowatts but is limited to a transfer distance of approximately 10 cm.
Mid-Range Transmission:
Mid-range WPT is achieved through Electromagnetic Resonance Power Transfer (ERPT) or Radio Frequency Power Transfer (RFPT). ERPT utilizes resonant coupling to transmit energy efficiently over distances of 3-4 meters, with power levels reaching several kilowatts. RFPT uses amplified radio frequency signals to transmit power up to 10 meters, though its capacity is limited to a few milliwatts.
Long-Range Transmission:
Long-range WPT employs Microwave Power Transfer (MPT) or Laser Power Transfer (LPT). MPT converts electricity into microwaves for transmission over long distances, making it suitable for applications such as space solar power stations. LPT offers high energy concentration with strong directionality, but obstacles can affect transmission efficiency.
Research Progress in Dynamic Wireless Charging for EVs
Prominent research institutions such as the University of Auckland, the University of Tokyo, Oak Ridge National Laboratory (ORNL), and KAIST are addressing the technical challenges of dynamic wireless charging. These include system modeling, energy conversion topologies, electromagnetic coupling optimization, and shielding technologies.
University of Auckland (New Zealand): Collaborated with a German company to develop the first wireless charging bus with a 30 kW capacity and a 100 kW wireless charging train prototype with a 400-meter track.
KAIST (South Korea): Developed the "On-Line Electric Vehicle," incorporating dynamic wireless charging. In 2013, two electric bus routes equipped with 100 kW wireless charging systems began operating over 24 km with an efficiency of 85%.
ORNL (United States): Researched coupling mechanisms and transmission characteristics, demonstrating that transmission efficiency is significantly affected by vehicle positioning.
University of Tokyo (Japan): Proposed a maximum efficiency control method using real-time coupling coefficient estimation through a DC/DC converter.
Korean Railroad Research Institute: Designed a wireless charging system for trains, achieving 1 MW power transmission over a 128-meter track using advanced coupling mechanisms.
Pros and Cons of Wired and Wireless Charging
Wired Charging:
Advantages:
High energy conversion efficiency with minimal losses.
Lower cost and simpler technology.
Disadvantages:
Requires manual handling, leading to wear and tear.
Occupies significant space for charging infrastructure.
Wireless Charging:
Advantages:
Convenient and safe, with no risk of sparks or electrocution.
Minimal maintenance and adaptable to harsh environments.
Disadvantages:
High cost of installation and maintenance.
Relatively higher energy losses and potential electromagnetic radiation concerns.
Future Trend or Gimmick?
Wireless
charging for EVs offers convenience and flexibility, but it remains in the developmental stage. Large-scale industrialization of high-power wireless charging systems is still premature, especially considering current energy challenges. However, as a forward-looking charging method, it warrants ongoing exploration. With advancements in this technology and the integration of smart grid infrastructure, wireless charging is poised to play a significant role in accelerating the adoption of EVs in the future.
、