A wireless power transfer system for electrical vehicles exploiting magnetically coupled resonance and a tapped capacitance impedance transformer

The input impedance of a wireless power transfer system is heavily influenced by variation of the load impedance, distance between coils and presence of any massive conducting or shielding structures that may exist around the system. To achieve the maximum efficiency for the wireless link transfer one has to ensure good matching between the power source and the wireless power transfer (WPT) system for different working conditions. In this paper an equivalent circuit of the WPT which accounts for the effects of the proximity of massive conducting structures is developed. A novel tapped capacitance impedance transformer for dynamic matching purposes is introduced and its presence incorporated into the equivalent circuit; its effect on the efficiency of the system is investigated.