Analysis and Prevention of Coupling-Dependent Data Flipping in Wireless Power Transfer Systems

Load shift keying (LSK) is widely used in a wireless power transfer (WPT) system to backscatter secondary side information to the primary side. However, when the coupling coefficient (
k
) between the transmitter and the receiver coils is lower than a critical value (
k
_DF
), the demodulated LSK data may flip from “1” to “0” or “0” to “1,” which is popularly known as coupling-dependent data flipping (CDDF). In this article, the conditions leading to CDDF are analyzed. Parasitic components of the inductive link are included, and both matched and unmatched coupled resonators are analyzed and verified by
SPICE
simulations. An automatic carrier-frequency modulation scheme is proposed to prevent CDDF and is verified by measurement results.