30.8 3D Wireless Power Transfer with Noise Cancellation Technique for -62dB Noise Suppression and 90.1% Efficiency

Compared with the inductive wireless power transfer (WPT), the resonant WPT has more spatial freedom due to its advantage of long distance power transfer [1]. However, a single coil transmitter (TX) has its limitation in one dimension in Fig. 30.8.1, if the receiver (RX) has an angle θ with respect to the TX [2]. When θ increases to 90 circ, the grade of coupling expressed by the coupling factor k decreases to zero. At the same time, the communication strength is weakened between the RX and the TX sense coil, which is connected in parallel with the TX main coil, and is easily affected by noise. Through the TX2 coil perpendicular to TX1, the RX can still receive energy in case θ changes. However, when TX2 sense coil takes over the charging control, it does not have any communication with the TX1, causing power loss. Therefore, this paper proposes a three dimension (3D) WPT system with the ability of controlling X, Y, and Z axes coils through the central controller (bottom left of Fig. 30.8.1). The central controller communicates with the three TXs in the vector detection control loop. Since the RX changes position in 3D relative to each TX, the central controller needs to detect the vector of RX based on the position of each TX. Although the k sensor in [3] can extract the coupling coefficient [4], the coupling factor in 3D is still a problem. Thus, the vector detector loop is proposed to determine the k factor for each TX in 3D. The central controller will decide the power distribution of each TX and effectively control the power transfer of the TX for high efficiency. To ensure the communication between the RX and each TX will not be affected by ambient noise and interference from the adjacent TXs, the noise cancellation technique is proposed (bottom right of Fig. 30.8.1). If communication is established in the communication main coil, the induced magnetic flux in the auxiliary coil will enhance the received signal. Conversely, if communication is not established, the induced magnetic flux in the auxiliary coil will cancel the signal received in the communication main coil for noise cancellation. That is, when one of the TXs communicates with the RX, the other two TXs have no influence on the central controller.