Abstract
The high switching frequency of wireless power transfer systems makes soft switching important due to switching losses. In the current literature, numerous solutions have been proposed for maintaining soft switching within the entire operating range. However, this study shows that variable frequency control can cause loss of zero voltage switching (ZVS) during system transients, even if soft switching during steady-state operation is ensured. The causes of this phenomena are analyzed thoroughly and two approaches to address such issue are discussed. Firstly, a limitation on the changing rate of the frequency can alleviate the issue. Secondly, phase advance control could also be possible, although this approach requires further studies. Results from both simulations and laboratory experiments are presented to verify the analysis and the control method proposed to avoid losing ZVS during transient conditions.