Cross-Interference Free 6.78 MHz Multiple-Transmitter Using Power Factor Based Control for Wide-Area Wireless Power Transfer Systems

Simultaneous wireless powering of mobile devices and home appliances over a wide area using multiple transmitters operating at 6.78 MHz is an attractive application of resonant inductive coupling wireless power transfer. Nevertheless, this application often suffers from two types of cross-interference. The first is cross-interference among the transmitters, which may cause the hard-switching of the inverter within the transmitter. The second is cross-interference among the receivers via the transmitter, which may not only cause the output power reduction but also complicate the power distribution control for the receivers. To solve the two cross-interference, this paper proposes a novel 6.78 MHz multiple-transmitter. The proposed multiple-transmitter adopts a simple active variable reactance component called an automatic tuning assist circuit (ATAC) for each transmitter. The ATAC works to fix the phase of each transmitter current regardless of the magnetic coupling among the transmitter, eliminating the cross-interference among the transmitters. Furthermore, the proposed multiple-transmitter also incorporates inverters with power factor based control effectively utilizing the transmitter current phase fixed by the ATAC. This inverter controls each transmitter current amplitude to be constant regardless of the receiver, removing the cross-interference among the receivers via the transmitter. The effectiveness of the proposed multiple-transmitter was verified by experiments.