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    2021-10-21 17:39:46
    Introduction to Wireless Charger


    Ⅰ Introduction
    Ⅱ Battery wireless charging mode
    Ⅲ Research status
    Ⅳ Main ways of wireless power transmission
    Ⅴ Use standard

    Ⅰ Introduction

    With the continuous improvement of the requirements for power supply quality, safety, reliability, convenience, immediacy, special occasions, and special geographic environments, the contact-type power transmission method is becoming less and less able to meet actual needs.

    A wireless charger is a charging device that operates on the principle of electromagnetic induction. It works on the same premise as a transformer. To achieve wireless charging, the transmitting end coil delivers an electromagnetic signal to the outside under the action of electric power. Then the receiving end coil receives the electromagnetic signal and converts it into an electric current. Wireless charging is a unique form of energy delivery. It operates without the use of a power cord and instead relies on the propagation of electromagnetic waves. It transforms electromagnetic wave energy into electrical energy, allowing for wireless charging.

    Wireless charger.jpg

    Wireless charger

    People are rapidly using new electronic items such as mobile phones, and tablet computers, in their daily lives. Traditional wired chargers are also used in the matching chargers. However, wired chargers' compatibility and versatility are limited, making them cumbersome for users. At the same time, post-disposal treatment contributes to contamination in the environment. As a result, providing users with more dependable, convenient, and timely charging equipment is critical. The advancement of wireless technology has enabled the transmission of radio power.

    Ⅱ Battery wireless charging mode

    Visual charging, smart charging, and wireless charging will be the three main types of battery charging in the future. In 2016, there were only 138 members of the International Wireless Power Consortium (WPC), but now there are more than 200 WPC technology companies, such as Apple, Samsung, HTC, Huawei, Lenovo, Xiaomi, Nokia, Sony, and many other mainstream mobile phone manufacturers. A Qi wireless charger features a flat surface-a charging pad that can charge mobile devices. Qi specifies three different methods for coil calibration, namely: guided positioning (magnetic attraction) (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)).  Let's briefly explain the three methods below.

    Model of wireless charging system.png

    Model of the wireless charging system

    Guide positioning (magnetic attraction)

    It is a one-to-one fixed position charging is used to guide the placed charging equipment and achieve accurate calibration. The advantage of this calibration method is simple, but It requires a series of materials attracted by magnets in charging equipment. Therefore, the power loss associated with the eddy current (and thus the temperature rise) will be attracted by the magnetic attractor.

    Free positioning (movable primary coil)

    It is also a one-to-one charging device that can be positioned and charged. This method requires a mechanically movable primary coil that is tuned to couple with the position of the charging device. However, movable mechanical parts often reduce the reliability of the system. In addition, for multiple charging devices, the motor control of the primary coil is complex and expensive.

    Free positioning (coil array)

    It lets you charge several gadgets without having to worry about their position. Compared with the above two methods, this calibration method is based on a more expensive and more complex winding structure and control electronic elements. But it provides us with more user-friendliness.

    Ⅲ Research status

    Wireless charging breaks the way that electric energy transmission can only rely on the direct contact transmission of wires. It belongs to non-contact transmission and can avoid contact sparks, sliding wear, and explosive electric shocks that may be caused by contact electric energy transmission.

    Electromagnetic induction is currently the most commonly used wireless power transmission method. Its technology has been mass-produced, and its manufacturing costs are lower than those of competing technologies. Currently, there are three major alliances dedicated to the development and standard formulation of wireless charging technology. The Alliance for Wireless Power (A4WP), Power Matters Alliance (PAM), and Wireless Power Consortium are the three alliances (WPC).

    The Qi standard is the "wireless charging" standard launched by WPC, which uses the most mainstream electromagnetic induction charging technology. The Qi standard mainly targets portable electronic products such as cameras, video, and music players, toys, and mobile phones. At present, the research and design of low-power wireless chargers are mainly for mobile phone wireless charging, using TI's BQ500211 dedicated chip. Some low-power terminals also use dedicated integrated chips, which are developed in the initial stage using dedicated integrated chips. It can save development time, but it is not conducive to cost reduction and later expansion and upgrade in the long run.

    Technical issues to overcome

    Despite the fact that wireless charging technology has progressed to some level, there are still some significant technical issues to overcome in the development process. First, the charging efficiency is not high. Once the distance is a little farther, the efficiency of charging will decrease sharply. Second, safety issues during the charging process. High-power wireless charging equipment will generate a large amount of electromagnetic radiation, which will cause certain adverse effects on health, and will also have interference effects on aircraft and communications. The third aspect is practicality. The existing wireless charging technique can only be implemented by affixing it to a certain fixed spot. Fourth, the price is expensive. Since wireless charging technology is still in the preliminary stage of research and application, the cost of research is relatively high, so the price of the products developed by it is relatively high.

    Ⅳ Main ways of wireless power transmission

    There are three main ways of wireless power transmission: electromagnetic induction, electromagnetic resonance, and electromagnetic radiation.

    Electromagnetic induction

    This is the most common working method of wireless chargers. It uses the principle of electromagnetic induction to generate an electric current through electromagnetic induction between the primary and secondary coils, so as to realize the transmission of energy within the space. The Wireless Charging Alliance has advocated for the use of this wireless charger.

    Radio wave

    Radio waves are a relatively mature wireless charging method for wireless chargers at this stage. Its working idea is to capture radio waves in space using small and efficient receiving circuits, then convert electromagnetic energy into steady electrical energy. There are currently firms claiming to be able to charge electrical gadgets smaller than a cellular phone wirelessly from a distance of a few meters.

    Electromagnetic resonance

    This is a new wireless charging technique that is currently in its early stages of development. This technology is mainly researched by a team led by a professor of physics at the Massachusetts Institute of Technology. Intel’s engineers use this technology as a basis to achieve a distance of about 1% from the power supply. A 60-watt bulb is lit up about a meter away, and it has a transmission efficiency of 75%. Intel engineers stated that the next goal will be to use this wireless charging technology to charge modified laptops. However, in order to reach this goal, the interference and influence of electromagnetic fields on other computer components must be resolved.

    Ⅴ Use standard

    In order to enable products of different brands to share the same charger and improve the versatility of wireless chargers, the world’s first standardization organization for wireless charging technology-the Wireless Charging Alliance, launched the "wireless charging" standard.

    Under the standard of Wireless Charging Consortium (WPC), the power consumption of wireless transmission is only 0~5W. Systems that meet this standard range use inductive coupling between two planar coils to transmit power from the power transmitter to the power receiver. The distance between the primary and secondary coils is generally 5mm, and the output voltage adjustment is handled by a global digital control loop. At this time, the power receiver communicates with the power transmitter and generates power consumption. This communication is a one-way communication from the power receiver to the power transmitter through backscatter modulation. The power receiver changes the load in backscatter modulation, adjusting the current consumption of the power transmitter. These current changes are monitored and demodulated into the information required for two devices to work together. Communication protocols include analog, digital sound pulse (ping), identification, configuration, and power transmission.

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