Charging uses a new type of energy transmission technology - wireless power technology. This technology frees the charger from the limitations of the line and allows the appliance and power supply to be completely separated. It shows better advantages than traditional chargers in terms of security, flexibility and so on. Today, with the rapid development of science and technology, wireless charging has shown broad development prospects. At present, wireless charging technology has begun to explore and apply in various fields. Because the farther the wireless transmission distance is, the higher the energy consumption of the device is. In order to realize long-distance high-power radio electromagnetic conversion, the energy consumption of the equipment is high. Therefore, the realization of efficient energy transmission of wireless charging is the primary issue of the popularization of wireless chargers. On the other hand, the problem to be solved is to establish a unified standard, so that different types of wireless chargers can match with different electronic products, so as to achieve wireless charging. Advantage: (1) Convenience: Non-contact, one-to-many charging reduces the trouble of plugging and unplugging compared with ordinary chargers, and avoids the phenomenon of inappropriate interface and poor contact, which can be easily used by the elderly. A charger can charge multiple loads, and a family can buy a charger to meet the needs of the whole family. (2) Universality: As long as the same wireless charging standard is used in a wide range of applications, no matter which device of any manufacturer can be charged wirelessly. (3) Novelty and good user experience (4) General standards Mainstream wireless charging standards are Qi standard, PMA standard and A4WP standard. Qi standard: Qi standard is the first standard organization to promote wireless charging technology in the world - Wireless Charging Alliance (WPC, established in 2008), which adopts the most mainstream electromagnetic induction technology, and has two major characteristics: compatibility and versatility. As long as the product with Qi logo can be charged with Qi wireless charger. In February 2017, Apple joined the WPC. PMA Standards: PMA Alliance is committed to building wireless power supply standards for mobile phones and electronic devices that meet IEEE standards, and has a leading position in the field of wireless charging. PMA also uses electromagnetic induction principle to realize wireless charging. AT&T, Google and Starbucks have joined the PMA Alliance. A4WP: Alliance for Wireless Power Standard, launched in 2012, aims to establish technical standards and industry dialogue mechanism for wireless charging devices for electronic products, including portable electronic products and electric vehicles. A4WP uses the principle of electromagnetic resonance to realize wireless charging. Disadvantages: (1) Short working distance At present, the wireless charging technology mostly charges the electronic equipment in the short distance in the near magnetic field. Because the farther the radio energy transmission distance is, the greater the power loss will be, the lower the energy transmission efficiency will be, and the higher the energy consumption of the equipment will be. (2) Low conversion efficiency and slow speed Although wireless charging technology is simple and convenient, its hard injury lies in slow charging speed and charging efficiency. (3) High power consumption, more power consumption With the increase of distance and power of wireless charging equipment, the loss of reactive power will increase. (4) High costs, high maintenance costs, and potential safety hazards if they do not meet the standards. Principle and implementation of wireless power supply: Wireless charging is based on electromagnetic induction principle, which is similar to transformer. There is a coil at the sending and receiving ends. The transmitting end coil connects with the cable power supply to generate electromagnetic signals. The receiving end coil induces the electromagnetic signals at the sending end to generate current. In June 2007, MIT's Marin Soljacic-led research team demonstrated for the first time the technology of wireless power supply for bulbs based on electromagnetic induction principle. They can provide power to 60-watt bulbs in a one-meter distance wirelessly, and the efficiency of power transmission is as high as 75%. Researchers assume that the power supply can charge batteries wirelessly in this range, and then assume that only one power supply is needed to supply electricity for the whole house. The working frequency of the transmission coil is in the MHz range. The receiving coil resonates in the non-radiating magnetic field, oscillates at the same frequency, and then effectively transmits electric energy through magnetic induction.