Wireless power transmission is a special power supply mode different from wired transmission. In fact, the concept of wireless power supply technology existed many years ago. After inventing AC and building AC power supply system, Trass began to conceive wireless transmission scheme and put it into practice at the same time.
At present, wireless power supply technology has the following three methods:
First, electromagnetic coupling. The earliest applied wireless power supply technology is the transformer which was successfully developed by 1885 and is still widely used today. It is a typical example of electromagnetic coupling wireless power supply, and its basic principle is Faraday electromagnetic induction theory. The two groups of wires are wound on an iron frame, which are not directly connected, and the energy transmission depends entirely on electromagnetic induction. In modern social life, this electromagnetic induction wireless power supply system has been widely used, and the electric toothbrush is one of them. Electric toothbrushes are often in contact with water, so they cannot be directly charged. Researchers use electromagnetic coupling wireless charging technology. There are coils in the charging stand and toothbrush. The toothbrush is placed on the charging base, which has magnetic coupling effect, similar to a transformer, and can charge the nickel-cadmium battery after the induced voltage is rectified. Another more widely used example is all kinds of smart cards we use, such as bus cards, second-generation ID cards and many cards that can record information. All adopt wireless power supply technology. These cards are similar in internal structure and consist of a small chip and a coil. There is no power module in the card's circuit. When the card shakes around the card reader, a rapidly changing magnetic field will be formed around the card reader. The coil in the card generates induced current, which supplies power to the internal chip. The chip sends a signal and sends its own information to the card reader. Then the card reader can judge how much balance is left in the card and complete the deduction operation. This is the principle of contactless IC card, and wireless power supply technology has been applied in essence. Although the electromagnetic induction wireless power supply technology is mature, this power supply technology will be subject to many restrictions. The biggest problem is that the low-frequency magnetic field will decay rapidly with the increase of distance. In practical application, if we want to increase the power supply distance, we can only increase the magnetic field intensity as needed, but the increase of the magnetic field intensity will not only increase the power consumption, but also cause the magnetic signal recording equipment to fail at close range. For example, the magnetic stripe on a bank card will be demagnetized under a strong magnetic field. In addition, the electromagnetic induction wireless power supply technology directly transmits and receives in the form of electromagnetic waves within a relatively short distance below 1cm, and the electromagnetic waves radiate in all directions, wasting a lot of energy and being inefficient. Usually it is only suitable for low-power electronic products that are "attached" to each other.
Second, photoelectric coupling. Photoelectric coupling wireless power supply technology is to convert electric energy into light energy, such as laser, and transmit energy to the destination through light and then convert it into electric energy. Photoelectric coupling wireless power supply technology is intuitive, photoelectric conversion technology is mature and widely used. But we know that there must be no obstacles in the light transmission path. Therefore, the photoelectric coupling wireless power supply technology has great application obstacles.
Third, electromagnetic vibration. The principle of electromagnetic vibration is similar to that of acoustic vibration. If the vibration frequencies of the two media are the same, they can be used to transfer energy, which is called radiation-free electromagnetic vibration. Scientists at MIT are developing a non-radioactive wireless energy transmission method to drive electrical appliances, whether mobile phones, laptops or digital cameras. If this research is successful, their chargers can be retired. Electromagnetic waves with specific frequencies will cause vibration of objects. If the natural frequencies of two objects are the same, this vibration can be transmitted, that is, energy can be transmitted. The researchers let the antenna emit electromagnetic waves, which are received by the receiver and converted into energy. This is the basic principle of electromagnetic vibration wireless power supply technology. According to this principle, all electrical appliances using batteries can be powered by electromagnetic vibration wireless power supply technology. In the future, electromagnetic vibration wireless power supply technology will have a great application space. For example, after laying underground lines, we can charge running mobile phones and even cars at any time.
According to the above analysis, we think that the magnetic coupling vibration wireless power supply technology is the most likely technology to be widely used. Wireless power supply technology (wireless charging) can transmit electric energy through air and plastic shell, which greatly facilitates the application.
The wireless power transmission scheme is shown in figure 1.
Figure 1 Schematic Block Diagram of Wireless Power Transmission Scheme
The power consumption of magnetically coupled vibration is only one millionth of that of traditional electromagnetic induction power supply technology. When the transmitter is energized, it does not emit electromagnetic waves to the outside world, but only forms a radiation-free magnetic field around it. This magnetic field is used to communicate with the receiver and excite the receiver to vibrate, which is only a small consumption cost of transmitting energy. In this technology, the strength of the magnetic field is similar to that of the earth, so people don't have to worry about the adverse effects on the body and other equipment.
Using XKT80 1 chip, we conducted the following wireless power supply experiments.
The wireless power supply module consists of oscillation circuit, shaping circuit, detection circuit, frequency interference suppression circuit, current automatic control, wireless power transmission circuit, etc.
Fig. 2 Circuit composition of wireless power supply module
The receiving coil is wound with the same number of turns as the transmitting coil. After determining the distance, it is best to adjust the number of turns of the coil until the received voltage is slightly higher than the load. The receiving coil outputs high-frequency AC voltage, which can directly supply power to the small bulb. To supply power to other electrical appliances, DC 5V working voltage (red line is 5V, black line is grounded) must be output through the switching regulator module. If the voltage of 12V is to be output, the resistance of 6.2K on the module can be changed to 18K, and the measured no-load voltage is 12.45V (the current will decrease accordingly after the voltage rises).
We used XKT80 1 wireless power supply module to successfully carry out wireless power supply experiment, and lit four groups of 16 LED lights.