Abstract
The Society of Automotive Engineers (SAE) Recommended Practice (RP) J2954 (November 2017) was recently published to standardize the wireless power transfer (WPT) technology to recharge the battery of an electric vehicle (EV). The SAE J2954 RP establishes criteria for interoperability, electromagnetic compatibility (EMC), electromagnetic field (EMF) safety, etc. The aim of this study was to predict the magnetic field behavior inside and outside an EV during wireless charging using the design criteria of SAE RP J2954. Analyzing the worst case configurations of WPT coils and EV bodyshell by a sophisticated software tool based on the finite element method (FEM) that takes into account the field reflection and refraction of the metal EV bodyshell, it is possible to numerically assess the magnetic field levels in the environment. The investigation was performed considering the worst case configuration—a small city car with a Class 2 WPT system of 7.7 kVA with WPT coils with maximum admissible ground clearance and offset. The results showed that the reference level (RL) of the International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines in terms of magnetic flux density was exceeded under and beside the EV. To mitigate the magnetic field, the currents flowing through the WPT coils were varied using the inductor-capacitor-capacitor (LCC) compensation instead of the traditional series-series (SS) compensation. The corresponding calculated field was compliant with the 2010 ICNIRP RL and presented a limited exceedance of the 1998 ICNIRP RL. Finally, the influence of the body width on the magnetic field behavior adopting maximum offset was investigated, demonstrating that the magnetic field emission in the environment increased as the ground clearance increased and as the body width decreased.
Highlights
In the future, electric vehicles (EVs) are expected to become the most widely used vehicles due to the increasing demand for reduction of exhaust gas emissions
As for the vehicle assembly (VA) coil, a magnetic shield made of ferrite tiles was placed over the winding to improve the coupling factor and to reduce the magnetic field leakage, and two aluminum (Al) layers were adopted over the ferrite to shield the magnetic field and protect the passengers in the EV cabin as well as the onboard electrical/electronic systems
The magnetic field levels for the SS and the LCC compensations with different configurations corresponding to k = 0.072 and k = 0.148 were numerically calculated on the measurement lines, as shown in Figure 19, where the calculated values were compared with the reference level (RL) of International Commission on Non-Ionizing Radiation Protection (ICNIRP) 1998 and
Summary
Electric vehicles (EVs) are expected to become the most widely used vehicles due to the increasing demand for reduction of exhaust gas emissions. In the future, autonomous drive systems will require automatic battery recharge without any human intervention To this aim, wireless charging is a very suitable solution. One of the main issues that needs to be addressed before the WPT technology is commercialized is the compliance with the EMF safety standards and regulations [9,10] for people located inside the vehicle (passengers) or in close proximity (pedestrians) while the wireless charging process is occurring. The magnetic field level produced by a WPT charging system applied to a city-car with the coil configuration as recommended by SAE standard was numerically assessed and compared with. The use and the tuning of the inductor-capacitor-capacitor (LCC) compensation was presented to reduce the magnetic field without affecting the WPT electrical performances
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