New electronic products, especially portable electronic products such as digital cameras, mobile phones, tablet computers, etc. are increasingly used in people's work and life, and the matching chargers also use traditional wired chargers. The compatibility and versatility of wired chargers are relatively poor, and it is inconvenient for users to carry and charge. At the same time, waste post-treatment increases environmental pollution. Therefore, it is urgent to provide users with more reliable, convenient, convenient and timely charging equipment. The development of wireless technology has made the transmission of radio power possible, and the research and development of wireless chargers will also meet the requirements of users.
There will be three main forms of battery charging in the future: visual charging, smart charging, and wireless charging. In 2016, there were only 138 members of the International Wireless Power Alliance (WPC), but this year WPC's technology companies have exceeded 200, such as Apple, Samsung, HTC, Huawei, Lenovo, Xiaomi, Nokia, Sony and many other mainstream mobile phone manufacturers. Generally, a Qi wireless charger has a flat surface, called a charging pad, on which mobile devices can be placed to charge. Qi specifies three different methods for coil calibration, namely guided positioning (magnetic gravity) (as shown in Figure 1(a)), free positioning (moving coil) (as shown in Figure 1(b)), and free positioning (coil array) (as shown in Figure 1(c)), which are briefly described below.
First, guided positioning (magnetic gravity): that is, a one-to-one fixed position charging to guide the placed charging equipment and achieve accurate calibration, this calibration method has the advantage of being simple, but it requires a series of materials attracted by magnets in the charging equipment, so the eddy current related power loss (and thus temperature rise) will be induced by the magnetic attractor. Second, free positioning (with a movable primary coil): is also one-to-one can position the charging equipment charging, this method requires a mechanically movable primary coil, tuned to couple it with the position of the charging equipment, however, movable mechanical components often make the system reliability reduced, in addition, for charging multiple devices, the motor control of the primary coil is complex and expensive. Third, free positioning (coil array): allows multiple devices to be charged without considering their position, which provides more user-friendliness at the expense of more expensive and complex winding structures and control electronic elements than the above two methods.
