In a wireless power transfer (WPT) system via the
magnetic resonant coupling, one of the most challenging design
issues is to maintain a reasonable level of power transfer efficiency
(PTE), even when the distance between the transmitter and the
receiver changes. When the distance varies, the PTE drastically
decreases due to the impedance mismatch between the resonator
of the transmitter and that of the receiver. This paper presents
a novel serial/parallel capacitor matrix in the transmitter, where
the impedance can be automatically reconfigured to track the optimum
impedance-matching point in the case of varying distances.
The dynamic WPT matching system is enabled by changing the
combination of serial and parallel capacitors in the capacitor matrix.
An interesting observation in the proposed capacitor matrix
is that the resonant frequency is not shifted, even with capacitormatrix
tuning. In order to quickly find the best capacitor combination
that achieves maximum power transfer, a window-predictionbased
search algorithm is also presented in this paper. The
proposed resonance WPT system is implemented using a resonant
frequency of 13.56 MHz, and the experimental results with
1W power transfer show that the transfer efficiency increases up
to 88% when the distance changes from 0 to 1.2 m.