Multiple-input multiple-output (MIMO) wireless power transfer (WPT) technology which employs multiple transmitter (TX) coils to simultaneously couple power to the receiver (RX) coil has proved to be an effective technique to enhance power transfer efficiency (PTE). Conventional MIMO-WPT systems rely on the phase-calculation method based on the phased-array beam steering concept to constructively combine the magnetic fields induced by the multiple TX coils at the RX coil. However, increasing the number and distance of the TX coils in an attempt to enhance the PTE tends to deteriorate the received signal at the RX coil. In this paper, a phase-calculation method is presented that enhances the PTE of the MIMO-WPT system. The proposed phase-calculation method considers the coupling between the coils and applies the phase and amplitude to calculate the coil control data. From the experimental results, the transfer efficiency is enhanced as a result of the transmission coefficient improvement from a minimum of 2 dB to a maximum of 10 dB for the proposed method as compared to the conventional one. By implementing the proposed phase-control MIMO-WPT, high-efficiency wireless charging is realizable wherever electronic devices are located in a specific space.
Keywords: beam steering; multiple transmitters; multiple-input multiple-output (MIMO); phase control; power transfer efficiency (PTE); wireless power transfer (WPT).