A 6.78-MHz Multiple-Transmitter Wireless Power Transfer System With Efficiency Maximization by Adaptive Magnetic Field Adder IC
Hao Qiu, Takayasu Sakurai, Makoto Takamiya
Abstract
A 6.78-MHz multiple-transmitter (TX) wireless power transfer (WPT) system was presented. An adaptive magnetic field adder (AMFA) IC was proposed, for the first time, to enable the maximization of the system efficiency ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\eta _{\mathrm {SYS}}$ </tex-math></inline-formula> ) by adaptively optimizing the amplitude and phase of the current in each TX coil on the basis of the coupling coefficient ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$k$ </tex-math></inline-formula> ) between each TX coil and the receiver (RX) coil. Under the optimal condition, the current in each TX coil is proportional to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$k$ </tex-math></inline-formula> between the TX coil and the RX coil. For the independent control of the current in each TX coil, a selectively activated shared-half-bridge (HB) power amplifier (PA) together with an alternate TX coil array was proposed. To sense a small <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$k$ </tex-math></inline-formula> , duty-ratio control was proposed in the integrated <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$k$ </tex-math></inline-formula> sensor. The AMFA IC was fabricated by a 0.18- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> CMOS process with 1.8-V devices. The peak power conversion efficiency of the proposed PA reached 74%. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$k$ </tex-math></inline-formula> sensor could accurately measure <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$k$ </tex-math></inline-formula> with a percentage error within ±2.5%. A WPT system consisting of a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\times 4$ </tex-math></inline-formula> TX coil array driven by four AMFA ICs and a single RX coil was implemented. Experimental results showed that, compared with the conventional system, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\eta _{\mathrm {SYS}}$ </tex-math></inline-formula> was increased from 0.11% to 51% with a load power of 576 mW when the RX coil was perpendicular to the TX coils. When the RX coil was parallel to the TX coils, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\eta _{\mathrm {SYS}}$ </tex-math></inline-formula> of 63%, which is higher than those in previous works, was also achieved.