Wireless power transfer with self-tuning LCC inverter using PWM-controlled switched capacitor is proposed in order to compensate for the variations of TX inductance. Usually, receivers contain magnetic and conductive materials for shielding and mechanical support. The inductance of TX coil is sensitive to the variation of TX-RX alignment because the interaction between TX coil and RX magnetic-conductive materials is also varied. It is shown that the detuning of TX inductance value exacerbates the losses in LCC inverter. In proposed method, the PWM duty ratio of a single capacitor adjusts the effective output impedance of LCC inverter. The PWM feedback loop is designed such that the power factor and real-part impedance of LCC inverter is maximized. The PWM switch is turned-on at zero voltage and turned-off with low dv/dt, minimizing switching losses. Such soft-switching tunable capacitor can handle higher power compared to traditional hard-switching capacitor, pn-junction capacitor, or analog-IC capacitor. Other advantages of proposed technique are the continuity in achievable capacitance value using only one capacitor. The feedback can fully be implemented by analog components, obviating the necessity of digital samplings, ADC/DACs, and microcontrollers. 54 W is transferred at 76.6% and 60.7% with and without the proposed method, respectively.

We propose a maximum efficiency tracking for multiple-transmitters system that optimizes both the current ratios of transmitter (Tx) coils and the effective Rx load. It is found that unlike single-Tx case, the optimal load impedance of multiple-Txs system depends on the current ratios among Tx coils. Meanwhile, the Tx current ratios should be controlled to be the same with magnetic coupling ratios between each Tx and Rx. Hence, we propose a two-step tracking method that first optimizes the Tx current ratios and then optimizes the Rx load impedance. To match the Tx current ratio with magnetic coupling ratio, it is analyzed that the reflected resistances at every Txs become identical each other when the Tx coil current ratios are equal to the magnetic coupling ratios. It is also revealed that the reflected resistance at specific Tx is reduced (increased) when its Tx current is increased (reduced) relative to other Tx currents. The proposed feedback equalizes all reflected resistances based on this property. After that, the second step of the proposed tracking is to optimize the Rx load while fixing the Tx current ratios by globally scaling up or down the strengths of whole Tx currents. Maximum 478W is delivered at 79% efficiency.

We propose a fast maximum efficiency tracking, which instantly optimizes all. TX coils' currents using runtime-extracted mutual inductances, for simultaneously activated multiple TXs whose output levels are different each other. For fast control, we propose a theory to runtime extract all the mutual inductances between multiple TXs and an RX. Here, one prerequisite of extracting the values of mutual inductances is to acquire its relative ratios between the mutual inductances. It is proposed that the relative ratio can be obtained by reflected resistances and coil currents of each TX, which are ac quantities but can easily be measured using dc input property of LCC inverter. Using the ratio information in conjunction with RX dc output, the exact values of mutual inductances can be extracted. The aim of the proposed method is to enable fast (no iteration) maximum efficiency tracking for multiple TXs, which entails the optimization of the relative ratios among TX currents, as well as the RX load optimization. A 200-W RX moves at 10 km/h, and the controller can track the optimum target TX currents in response to time-varying magnetic couplings.

An efficient wireless power transfer (WPT) system is proposed using two self-resonant coils with a high-quality factor (Q-factor) over medium distance via an adaptive impedance matching network using ferrite core transformers. An equivalent circuit of the proposed WPT system is presented, and the system is analyzed based on circuit theory. The design and characterization methods for the transformer are also provided. Using the equivalent circuit, the appropriate relation between turn ratio and optimal impedance matching conditions for maximum power transfer efficiency is derived. The optimal impedance matching conditions for maximum power transfer efficiency according to distance are satisfied simply by changing the turn ratio of the transformers. The proposed WPT system maintains effective power transfer efficiency with little Q-factor degradation because of the ferrite core transformer. The proposed system is verified through experiments at 257 kHz. Two WPT systems with coupling efficiencies higher than 50% at 1 m are made. One uses transformers at both Tx and Rx; the other uses a transformer at Tx only while a low-loss coupling coil is applied at Rx. Using the system with transformers at both Tx and Rx, a wireless power transfer of 100 watts (100-watt light bulb) is achieved.

Accurately analyzing power losses in inductive wireless power transfer including lossy magnetic sheet is challenging, as coils have mutual influences on each other's power dissipation. This paper proposes a precise analytic model for inductive wireless power transfer (WPT) with lossy magnetic sheets. Combining a partial element equivalent circuit (PEEC) with a 2–port network, both self– and mutual impedances of coupled coils are accurately calculated considering eddy current effects. Furthermore, the proposed PEEC–based model incorporates the complex permeabilities of lossy magnetic sheets, thus addressing a critical gap in previous studies that have not considered magnetic sheets with losses in their analysis. The suggested model is verified with finite element method (FEM) simulations and measurements. Compared with an FEM simulator, the proposed model calculates impedances about 31 times faster, substantially reducing the number of meshes. Finally, the ohmic and magnetic losses in coil windings and magnetic sheets are investigated with the proposed model, demonstrating that the phase adjustment of currents using the compensation capacitor is effective to reduce the losses caused by eddy currents and lossy magnetic sheets. The proposed model offers more detailed and accurate loss analysis, compared to conventional methods based on circuit analysis.

Multi-hop communication is commonly observed in mobile ad-hoc wireless networks. It is known that the stability of multi-hop paths formed by mobile nodes is affected by node mobility degree and node density. However, a closed-form model of multi-hop path performance and an in-depth investigation is still missing. In this paper, we derive a analytical model of packet delivery ratio for multi-hop paths from the average packet delivery ratio of each individual link and the distribution of hop count of multi-hop path between an arbitrary source node and a destination node. The corresponding results demonstrate that the proposed approach can provide an efficient method of estimating and evaluating the performance of multi-hop paths in mobile ad-hoc wireless networks.