摘要
The reconfigurable resonant regulating ( R3 ) rectifier is widely used in modern wireless power transfer (WPT) systems for efficiency improvement. To reduce power loss when R3 rectifier is in freewheeling mode, transmission power control is essential, with accurate detection of the receiver (RX) mode being the key requirement. Currently, most detecting methods rely on a fixed threshold derived from the steady-state transmission current amplitude, which is only effective in a narrow-range coupling coefficient k . In this article, phase shift and near-zero-time detection methods are proposed to detect the RX mode correctly under a wide range k . The proposed method is based on the transient behavior in mode transition, which is insensitive to k . Moreover, a hybrid transmission power control, composed of a 1/15-density pulse frequency modulation and power transistors size-switching control, is introduced for further efficiency improvement. Both the transmitter (TX) and RX chips in the proposed WPT system have been fabricated in a 0.18- μ m CMOS process. Measured under the coil distance dcoil from 2 to 20 mm ( k ranging from 0.39 to 0.1), the maximum output power PO is 950 mW, and the peak efficiency reaches 74.3%. Furthermore, efficiency improvement is observed across various values of k , with a 27.9% peak enhancement at 75-mW PO and 10-mm dcoil ( k of 0.23).