A High-Efficiency Wireless Power Transfer System Under Wide Coupling Coefficient Range Based on Phase Shift and Near-Zero-Time Detection

The reconfigurable resonant regulating (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i><sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup>) rectifier is widely used in modern wireless power transfer (WPT) systems for efficiency improvement. To reduce power loss when <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i><sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> 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 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i>. In this article, phase shift and near-zero-time detection methods are proposed to detect the RX mode correctly under a wide range <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i>. The proposed method is based on the transient behavior in mode transition, which is insensitive to <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i>. 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-μm CMOS process. Measured under the coil distance <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>coil</i></sub> from 2 to 20 mm (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> ranging from 0.39 to 0.1), the maximum output power <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>O</i></sub> is 950 mW, and the peak efficiency reaches 74.3%. Furthermore, efficiency improvement is observed across various values of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i>, with a 27.9% peak enhancement at 75-mW <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>O</i></sub> and 10-mm <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>coil</i></sub> (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> of 0.23).