Contents I. Introduction
With the increasing pressure on the environment and resources, the development and popularization of electric vehicles has received strong support from China, the United States, the European Union and other countries or international organizations [1]. The limited energy density of on-board batteries usually leads to frequent charging or batteries swap of electric vehicles. The lack of efficient and convenient charging or swap methods is one of the bottlenecks restricting the promotion of electric vehicles. At present, solutions to the problem mainly include battery swap, wired charging and wireless charging. Battery swap has problems such as poor compatibility of batteries of different brands, rapid increase in batteries reserves, large area and high construction cost of battery swap stations, etc. Wired charging methods have shortcomings such as being easy to wear and tear, poor adaptability to bad weather, cable constraints that may reduce user experience, etc [2]. In response to the above problems, wireless charging technology based on the principle of magnetic coupling resonance has shown its superiority. Firstly, wireless charging requires no direct electrical connection and it has no exposed interface, which help to avoid wear and tear on cables and improve charging convenience. Secondly, the energy transmitter does not take up space on the ground, so the maintenance cost is low. In addition, it helps to promote the interaction between the vehicle and the grid, which is in line with the development trend of intelligent and unmanned electric vehicles [3].
