Analysis of four infinite charging schemes: magnetic induction, magnetic resonance, radio wave and electric field coupling

“Wireless charging is currently an emerging charging technology, but there are many difficulties in current R&D and testing, among which power efficiency is particularly difficult. This article summarizes the current problems and solutions encountered during testing in many companies, universities, and research institutes, and hopes to help the industry Solve problems and promote industry development.

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Wireless charging is currently an emerging charging technology, but there are many difficulties in current R&D and testing, among which power efficiency is particularly difficult. This article summarizes the current problems and solutions encountered during testing in many companies, universities, and research institutes, and hopes to help the industry Solve problems and promote industry development.

01. Types of wireless charging methods

Wireless charging methods can be divided into four types according to their principles: electromagnetic induction, magnetic resonance, radio wave, and electric field coupling.

1. Electromagnetic induction type

The alternating current of a certain frequency in the primary coil generates a certain current in the secondary coil through electromagnetic induction, thereby transferring energy from the transmitting end to the receiving end. At present, the most common charging solution uses electromagnetic induction, which is characterized by short transmission distance and relatively fixed use position, but with high energy efficiency and simple technology, it is very suitable for use as a wireless charging technology. .

2. Magnetic field resonance type

It consists of an energy transmitting device and an energy receiving device. When the two devices are adjusted to the same frequency, or resonate at a specific frequency, they can exchange each other’s energy. It is a technology currently under research and can be used for Long-distance charging, the charging distance can reach thousands of meters.

3. Radio wave type

Its use is similar to wifi, using a 2.45GHz radio wave generating device to transmit power, and the sending device is basically the same as the “magnetron” used in a microwave oven. The transmitted microwaves are also alternating current waves, which can be received by antennas in different directions and converted into direct current by a rectifier circuit to charge the car battery. The main problem is that the efficiency is too low.

4. Electric field coupling

The principle is inductive coupling. When two coils that are close together are magnetized, a magnetic field is generated, and the other coil induces a magnetic field to generate a magnetic induction current. The advantage is that the device can be made small and embedded in the product, and it also solves the problem. In order to solve the problem of temperature rise, there are few researchers at present.

02. Principles and test difficulties

At present, the mainstream wireless charging method is still electromagnetic induction. Its research is the earliest, the deepest, and there are the most researchers. The standard is gradually popularized, forming two major industrial chains of transmitter and receiver. The wireless charging industry is booming, but the current testing On the one hand, due to the high frequency of wireless charging, for example, car wireless charging currently generally uses 85KHz, so the test difficulty lies in power consumption and efficiency testing, as shown in the figure below. Generally, the DC-DC end efficiency and the AC of the transmitting and receiving ends are required to be tested. -AC efficiency, DC-DC end is easy to test, the difficulty lies in the efficiency test of AC-AC end.

03. Instrument bandwidth accuracy

At present, it is difficult to improve the efficiency of wireless charging. The improvement of efficiency is calculated at the level of thousandths. Therefore, the accuracy of the test instrument is required to be high. Secondly, the wireless charging frequency is high, so the bandwidth of the ordinary power test instrument cannot be satisfied. Less, it is necessary to use a high-bandwidth, high-precision power analyzer for testing. At present, the best measured effect is the PA8000 power analyzer of Zhiyuan Electronics, with an accuracy of up to 0.01% and a bandwidth of up to 5MHz.

04. Instrument delay

The delay of the high frequency band has a great influence on the efficiency. In actual testing, the delay of ns may cause the efficiency error to be at the level of 1%. Therefore, the test has extremely high requirements for the channel delay of the instrument. The delay is controlled at the ps level. The PA8000 power analyzer can perform special delay calibration for the wireless charging frequency band, and input the delay data into the instrument to ensure the accuracy of the wireless charging test time phase.

05, sensor requirements

For mobile phone wireless charging, the current is low, and some power test instruments can meet the requirements of direct input and do not need to use sensors. However, for car wireless charging, the power range of the charging module is relatively large, from several kilowatts to tens of kilowatts. The power charging object can reach hundreds of kilowatts or even megawatts, and the current of a single module can reach hundreds of amperes or even thousands of amperes. Secondly, the sensor itself will introduce a delay. Although the Hall sensor itself has high accuracy, its delay Larger, it is difficult to apply directly. The Rogowski coil itself has a large current test range and small delay, which is currently a better solution for wireless charging testing.

06. Channel requirements

As mentioned above, high-power wireless charging schemes need to increase current. Another method is to cascade multiple modules, which requires a lot of test channels. For example, if 6 groups of modules are cascaded, 6 channels of test input are required, 1 channel of test output is required, and 7 power channels are required, which ordinary test instruments cannot To meet such a complicated parallel calculation, if there are more than 7 channels, a single instrument currently on the market cannot basically meet the demand. The current test method is to perform parallel cascading through PA8000 to achieve high-power wireless charging test of multiple groups of modules in parallel.

07. Resonant capacitor voltage test

In wireless charging, there is usually a resonant capacitor between the inverter/rectifier and the transmitter/output coil. Sometimes it is necessary to test the loss on the resonant capacitor. Through the resonant capacitor, the voltage will usually reach thousands of volts. Power analyzers currently on the market The direct input voltage is generally around 600V or 1000V. The PA8000 power analyzer of Zhiyuan Electronics directly inputs 1500V. If the resonance voltage is high, a voltage sensor is needed. Currently, there is no voltage sensor with a small delay. The solution is to specifically measure the voltage. The sensor is calibrated with delay, and the delay value is input to the PA8000 power analyzer for manual calibration.

For wireless charging testing, ZHIYUAN Electronics has rich experience, reliable solutions, and can provide prototype test demonstrations. If necessary, please feel free to contact local sales. We will provide the best quality service throughout the process.