224 – Stray Loss Analysis of Wireless Power Transfer

Application Note / Model Data

Overview

In recent years, using an electromagnetic induction type power supply system has been studied in Wireless Power Transfer systems for electric vehicles (hereinafter referred to as EVs) and plug-in hybrid cars (hereinafter referred to as PHEVs) for which practical applications are being sought. Wireless Power Transfer systems for EVs and PHEVs are required to maintain power transmission with high efficiency, and many studies on magnetic resonance coupling (magnetic resonance) schemes with resonance capacitors have been made.
However, metal steel plates such as SUS plates are used for the housings of mounted Wireless Power Transfer devices in consideration of corrosion resistance and strength. Because of this, if leakage flux components generated from a power supply interlink with metal, stray loss will occur resulting in a decrease in efficiency. Therefore, when the loss is high, it is necessary to suppress the loss by providing a shield or the like.
In this example, we introduce where stray losses are reduced by evaluating the stray loss occurring in a housing and providing a shield.

Stray Loss Distribution

Fig. 1 shows the Joule loss distribution of a chassis with aluminum shield. Regardless of the presence or absence of the aluminum shield, it can be seen that Joule loss due to leakage flux is generated around a ferrite core. After installing an aluminum shield on the surface of the chassis, it is possible to confirm that almost no loss is generated in the chassis due to shielding with loss occurring only on the aluminum shield surface. Moreover, it can be confirmed that there is a region where the Joule loss density is higher when an aluminum shield is installed.

Difference in Stray Loss With and Without an Aluminum Shield

Table 1 shows Joule loss values due to eddy currents. It can be confirmed that the stray loss could be reduced when an aluminum shield was installed even though the Joule loss density on the surface was higher. This is because, since aluminum was used which has higher conductivity than the SUS material used for the chassis, the skin depth decreased and the volume where the loss occurred decreased.

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