“Pushing Power Through Walls” - Wireless Power Transfer Through Stainless Steel

This paper focuses on wireless power transfer (WPT) through an electrically conductive stainless steel (SS) enclosure necessary for high-purity environments such as required for chemical or pharmaceutical industry. The alternating electromagnetic field penetrates the SS and induces eddy currents that are opposing the field of the primary coil and reduce the coupling and efficiency of the WPT system. Considering a WPT system with E-core geometry, we show how to simplify its modeling with an equivalent circuit approach, while including SS enclosure effects. We show that with such WPT system, special care must be taken when designing resonant compensation, because compensating self-inductances, as typically done for WPT systems, results in larger SS losses than if stray inductances are compensated. Additionally, we show that there is an optimal number of turns, for the primary and secondary windings, which depends on the nominal output power and voltage. Finally, the proposed model is verified with measurements on a hardware demonstrator built with two 0.5 mm thick SS walls that emulate the enclosure. The demonstrator is designed for 50 V output voltage, equal numbers of primary and secondary side turns and is operated at 2250 Hz up to 70 W output power.