In a specialist article of “Elektronik automotive” journal, Dr. Christof Ziegler and Dr. Stefan Weber of EPCOS describe the influence of coupling factor, load impedance and losses in the transfer coils on the transfer efficiency of a wireless power transfer (WPT) system.

It is shown, that the losses in the transfer coils are a very critical design criterion and need to be considered as exact as possible to enable a cost-efficient mass production.

Another point to consider is the variation of the transfer system resonance frequency, which can be considerably reduced by adding serial compensation chokes. The realization of this fact bears a significant influence on the development of the complete WPT system, since the requirements for compensation circuitry in the inverter and resonance circuit can be reduced. The lower system complexity hence also leads to reduced cost.

Within the mutual research project, Finepower, especially co-author Georg Heiland, is responsible for the general system concept and design of the primary side power electronics (ground assembly).

The full article (in German language) can be found on the website of or here as PDF file.