Impedance Matching in Wireless Power Transfer

Impedance matching is a common issue in a wireless power transfer (WPT) system. This paper summarizes impedance matching methods reported in the literature and gives a theoretical analysis on dc-dc converter for impedance matching in a WPT system. A buck-boost converter in discontinuous conduction mode has the characteristic of that the input resistance is independent of the load resistance and the input voltage, which seems to be suitable for impedance matching. Furthermore, the impedance matching ability of buck-boost converter will not depend on the frequency of rectifier, because it implements the solution to the dc output of rectifier. To verify those, we give several application examples of this buck-boost converter applied in rectifiers with different frequencies, such as 2.45, 5.8, and 24 GHz. As a result, those rectifiers with the buck-boost converter achieve a constant RF-dc conversion efficiency over an extremely wide load range. In addition, it is also successfully utilized in a microwave power transmission system for driving a dc motor.