In a wireless power transfer system via coupled magnetic resonance, the power transfer efficiency (PTE) drastically decreases with the transfer distance and the changing load. To solve this problem, an automatic impedance matching system is usually embedded in an intelligent algorithm. However, the traditional algorithm cannot dynamically track the impedance due to its slow matching speed. In this paper, an automatic impedance matching method based on adaptive network based fuzzy inference system (ANFIS) is proposed to overcome this disadvantage. A simulation system is constructed, and results show that the efficiency of the proposed ANFIS method is 80.26% higher than that of the genetic algorithm. Moreover, an automatic impedance matching prototype is built and dynamic matching experiments are carried out, showing that the PTE is up to 84.76% when the distance increases from 4.5 to 50 cm. The simulation and experimental results are basically consistent, which prove the validity of the novel method.

Wireless sensor networks (WSNs) have broad application prospects due to having the characteristics of low power, low cost, wide distribution and self-organization. At present, most the WSNs are battery powered, but batteries must be changed frequently in this method. If the changes are not on time, the energy of sensors will be insufficient, leading to node faults or even networks interruptions. In order to solve the problem of poor power supply reliability in WSNs, a novel power supply method, the single-wire power transfer method, is utilized in this paper. This method uses only one wire to connect source and load. According to the characteristics of WSNs, a single-wire power transfer system for WSNs was designed. The characteristics of directivity and multi-loads were analyzed by simulations and experiments to verify the feasibility of this method. The results show that the total efficiency of the multi-load system can reach more than 70% and there is no directivity. Additionally, the efficiencies are higher than wireless power transfer (WPT) systems under the same conductions. The single-wire power transfer method could satisfy the characteristics of WSNs and effectively solve the problem of poor power supply reliability.

The technology of wireless power transfer via coupled magnetic resonances (CMR-WPT) has a good transfer performance in the “middle range”, but it is far from satisfying the application requirements in practice. To achieve a longer transfer distance, coils are usually complicatedly designed, making the system unwieldy and costly. Based on the intuitive and easily adjustable coil parameters, a design and optimization method was proposed in this paper, which can realize the minimum size coil that meets the requirements at 6.78 MHz. First, an equivalent model of the CMR-WPT system was developed, and the influences of coil parameters on the effective transfer distance and power transfer efficiency (PTE) were analyzed, indicating that the effective transfer distance and PTE were not always proportional to the coil radius, the number of turns or the pitch. Then, the coil impedance and the quality factor of different coils were calculated. In addition, the influence degree of coil parameters on the transfer performance was also compared using variable control. Finally, an experimental platform was built, and experimental results agreed well with the simulation results.

In a wireless power transfer (WPT) system based on coupled magnetic resonance, 2-D planar coils are commonly used as coupling structures. As the spatial position between the coupling structures changes, the system transmission efficiency decreases dramatically, seriously reducing the flexibility of power transfer. To solve this problem and achieve a power transfer with a high degree of freedom in a 3-D space, a novel 3-D coil based on a 26-faced polyhedron is proposed as the transmitting coil winding structure, which is wound using the regular monolithic winding method without overlapping. By means of this coil, it is ensured that the winding direction of each planar coil is different from those of the adjacent planes so that the magnetic fields between adjacent coils are mutually reinforced, thus enhancing the spatial magnetic field density of the system and enabling a stable and efficient transmission of power at any position. The transmitting coil can be enlarged by changing the coil structure, thereby enabling omnidirectional WPT in a larger space. Through experimental research, the system can achieve omnidirectional WPT with an efficiency of 60%, and its transmission efficiency can remain stable within a defined range as the receiver moves.

To solve the battery power supply problem with wireless sensor networks (WSNs), a novel bidirectional wireless charging system is proposed, in which an unmanned aerial vehicle (UAV) can fly to the WSNs to charge sensors through high-frequency wireless power transfer (WPT) and also obtain energy for its own battery in the same way. To improve the performance of the UAV bidirectional wireless charging system, a lightweight design is adopted to increase its loading capacity and working time. Moreover, the radii and the numbers of turns and pitches of coupling coils were designed and optimized on the basis of simulations and experiments. Experimental results show that the weight of optimized UAV coil was reduced by 34.45%. The power transfer efficiency (PTE) of the UAV coil to sensor coil increased from 60.2% to 74.4% at a transmission distance of 15 cm, while that of the ground transmitting coil to UAV coil increased from 65.2% to 90.1% at 10 cm.

The wireless power transfer (WPT) system via coupled magnetic resonance (CMR) is an efficient and practical power transmission technology that can realize medium- and long-distance power transmission. People’s requirements for the flexibility of charging equipment are becoming increasingly prominent. How to get rid of the “flitch plate type” wireless charging method and enhance the anti-offset performance is the main research direction. Directional characteristics of the system can affect the load receive power and system efficiency in practical applications. In this paper, the power and efficiency of the WPT system via CMR were analyzed according to the principle of near-field strong coupling at first. The expression of the mutual inductance between the transmitting and the receiving coils under angular offset was derived from the perspective of the mathematical model, and the influences of angular deviation were analyzed. Second, simulation models were established under different distance between coils, different coil types, and different coil radius ratios in symmetrical and asymmetrical systems. Afterwards, the directional law was obtained, providing reference for the optimal design of coupling coils. Finally, an experimental system was built, and directional characteristic experiments were carried out under different conditions. Experimental results were consistent with simulation results, which verified the theoretical analysis.