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An inductive power transfer system is able to charge multiple receivers (RXs) through a single transmitter. In order to develop suitable control methods, this article explores and compares the influence of driving current and loading resistance on the efficiency and power distribution. It starts from a simple system with equal coupling and then extends the discussion to a general one. With proper simplification, an optimization problem is defined to derive several important factors, including the optimal driving current, optimal loading resistance, and the corresponding optimized efficiency under various application constraints. In the final experiments, the dynamic tuning of driving current is able to maximize the system efficiency to 92.1% for a general three-RX system. In another customized system with equal coupling, the maximum error between the achieved efficiency and the real maximum efficiency is 0.4% through the calculation-based current control. [ABSTRACT FROM AUTHOR]

This article explores the potential of relay coils (ReXs) to extend the horizontal charging area for planar inductive couplers. It focuses on the coupling mechanism and derives the equivalent coupling coefficient for model simplification. Based on the new model, a one-ReX coupler is proposed to enhance the coupling under large misalignment. Besides, the influence of coupling polarity change is evaluated and well compensated. In order to further enhance the coupling, a multiple-ReX technique is proposed and justified by a two-ReX coupler and a three-ReX coupler. The experimental result shows that the enhanced coupling coefficient helps maintain the efficiency to be above 92.5% under large misalignment when the one-ReX coupler is used. With three ReXs, the achieved efficiency is further improved by 2.3%. [ABSTRACT FROM AUTHOR]

Capacitive power transfer is becoming an attractive alternate for wireless chargers. A coupler with large self- and mutual capacitance is desirable from the power and efficiency perspective. However, state-of-the-art couplers suffer from the tradeoff design issue between these two types of capacitance. In order to improve the required capacitance, an interleaved capacitive coupler is proposed and evaluated based on the Maxwell-based simulation. Using more plates, it can effectively use the coupling space to maintain the required self- and mutual capacitance, while minimize the cross coupling effects. Meanwhile, the new coupler is also helpful to reduce the radioactive electric field, and the high-radiation region is reduced dramatically. In the experiment, three types of couplers are built with the same coupling space, compensations, and output power. The proposed interleaved structure can achieve the highest efficiency and minimum radiation. [ABSTRACT FROM AUTHOR]

Capacitive power transfer is a promising mid-range wireless charging technique. The existing induced current source model suffers from the coupling variation issue, which causes troubles in resonance design and compensation development. This article explores an induced voltage source model for the capacitive coupler. Using this model, the six coupling-dependent capacitors between each pair of plates are equivalently represented by the self-capacitors and induced voltage sources. The self-capacitance is verified to be coupling independent. Based on this model, the power transfer capability, the efficiency, and the influence of adding external shunt capacitors are easily analyzed. This model is very helpful in investigating the existing topology and developing new compensations, such as the CLL-L compensation. Finally, a capacitive coupler is built to verify the model, based on which a CLL-L compensation is implemented for constant output voltage application. The achieved system peak efficiency is 88%. [ABSTRACT FROM AUTHOR]