Electromagnetic compatibility analysis of wireless power transfer systems

In the past decade, domestic and foreign scholars have made many progress in the field of electromagnetic compatibility of radio transmission (WPT) systems, but there is still room for progress. The electromagnetic compatibility of free radio transmission technology (Ubiquitous IPT, U-IPT) systems and dynamic WPT systems will be prospected in the future.

1. Mechanism analysis

Currently, scholars have studied the electromagnetic compatibility mechanism of WPT based on the resonance state, and the coils on both sides of the transceiver usually need to be fully aligned. In the practical application process of WPT system, due to environmental factors and load changes, the WPT system deviates from its original expected working state, coil offset, or coil overcoupling.

Taking coil offset as an example, when a magnetic coupling coil undergoes lateral offset, it can cause severe deformation of the electromagnetic field, significantly enhancing electromagnetic interference at certain locations. Changes in the coil self-induction coefficient caused by environmental factors can also cause the WPT system to deviate from the original resonance state, making the distribution and resonance state of the electromagnetic field different.

In addition, the electromagnetic environment of inductive and resonant WPT systems also has different electromagnetic mechanisms. Researchers also need further theoretical research to further study the electromagnetic field mechanisms in the near and far field regions.

2. Impact medium

One of the issues that must be considered in the practical application of WPT technology is the impact of environmental media. At present, scholars mainly focus on the research of metal and water media, among which metal media have rich theoretical achievements, but related literature on water media, especially in the seawater environment, is relatively rare.

Compared to metal and freshwater media, the corresponding electromagnetic field analysis is more complex because of the simultaneous existence of eddy current losses, shielding refraction, and other phenomena in the seawater environment. At the same time, the interference, salt content, and temperature of seawater will further reduce the electromagnetic field distribution of the WPT system, making the electromagnetic radiation phenomenon more serious. Exploring the impact mechanism of environmental media can promote the application of WPT and better adapt to changing environmental factors.

3. Electromagnetic compatibility U-IPT system

At this stage, commercial WPT products are mainly one-on-one charging, and charging devices often need to fully match the transmission coil. In the future, regardless of the location and direction of the battery, WPT technology can achieve ubiquitous non-contact charging, which means that U-IPT can achieve non-contact charging services in a three-dimensional space.

In order to meet the safety limit of electromagnetic radiation, the U-IPT system achieves effective electromagnetic interference suppression through electromagnetic shielding, while maintaining a uniform magnetic field distribution in a large area and space.

Some scholars first explored the electromagnetic radiation suppression effect of conductive electromagnetic shielding on U-IPT systems, and placed an aluminum plate shield on one side of the coil conductor, which is close to unexpected magnetic flux. This scheme can effectively counteract the distribution of unexpected magnetic fields, enhance the magnetic flux density in the expected area of the U-IPT, and validate nine U-IPT systems that receive electrical power loads through experiments. Currently, there is less research on the electromagnetic compatibility of U-IPT systems, which may become the research direction of future researchers.

4. Dynamic WPT system for electromagnetic compatibility

Dynamic wireless charging technology is an extension of static wireless charging technology, which can continuously provide charging services during the driving process of electric vehicles. Dynamic WPT systems need to face rapid changes in the coupling coefficient between coils, which means that the electromagnetic environment of dynamic WPT systems is constantly changing, which brings some challenges to the electromagnetic compatibility research of WPT systems.

Currently, KAIST has successfully applied this technology to OLEV and realized commercialization. At the same time, Kaist proposed a series of electromagnetic interference suppression measures for OLEV WPT systems, effectively limiting the electromagnetic radiation of WPT systems to a range that does not harm human safety, in order to meet the limit requirements of ICNIRP derivatives. In order to better promote the commercialization of dynamic WPT systems, their electromagnetic compatibility research will become a research hotspot for future scholars.