Novel active tuning approach for resonant-mode wireless charging system

Wireless charging is a safe and clean technique of contactless charging over a wide range of power levels for portable electronic products. Although the market for wireless charging in Watts to tens of Watts is growing rapidly, the performance of such wireless charging products is still inferior when compared to those utilizing traditional charging, especially when the resonant frequencies are not well matched. Another prominent issue of wireless charging system is that the efficiency and power transfer capability for the input equivalent AC source would drop due to the variation of the passive components. Traditional tuning approaches are used only in secondary side, which would not solve the whole system problem. This paper presents a novel active tuning approach for series-series compensated wireless charging system. In this paper, a detailed solution for both sides of wireless charging system is presented: firstly a maximum reflected impedance checking method is used to check the resonant frequency of the secondary side of the system; and then a variable series compensated capacitor is used on the primary side to guide the primary circuit to track the secondary resonant frequency. In this case, the resonant frequencies of both sides would be well matched. The validity of the approach is verified through simulations of a simplified wireless charging system based on inductive power transfer.