Research on Novel Flexible High-Saturation Nanocrystalline Cores for Wireless Charging Systems of Electric Vehicles

The ferrite core plays an essential role in coupling enhancement and magnetic shielding for the wireless power transfer of electric vehicles. However, ferrite has apparent defects, such as a low saturation and brittleness, especially at the vehicle side. Therefore, a novel flexible nanocrystalline core is proposed in this article, which has high flexibility and high saturation limits. However, the nanocrystalline core has a large eddy current under 85-kHz excitation, so the refinement crushing process and alternating seamless stitching process are adopted to reduce the eddy loss. The feasibility of the improvement process is preliminarily verified via finite element simulations, and four nanocrystalline cores with different permeabilities are obtained. Through static parameter measurements and 7.7-kW loading tests, the modified nanocrystalline cores achieve excellent results. Based on the above, the nanocrystalline core with the best performance is further selected for an anti-saturation test and leakage measurement at 11 kW. Even when the thickness is reduced to 2 mm, the ac-ac efficiency remains 97.408%. The maximum core temperature is only 80.9 °C, and the flux leakage completely satisfies the limit requirements of ICNIRP 2010. In contrast, the ferrite core cannot withstand the impact of a strong alternating field and fails.