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Wireless power transfer (WPT) technology has become a popular research direction in the field of industrial applications, with the advantages of contactless operation, high degree of freedom, and great controllability. However, there are still some challenging issues that need to be resolved. First of all, more advanced circuit topologies and magnetic coupling structures need to be designed to achieve the power conversion goals of diversified applications. Second, novel control methods, optimization algorithms, and modeling methods enable systems to be better controlled and designed. Finally, potential application scenarios need to be discovered so that this novel power transfer method can be applied in more suitable applications. Therefore, this topic is organized by the responsible editor to gather the power of more scholars. With reviewers' hard work and considerations, 32 papers were finally accepted for publication in this Special Issue. [ABSTRACT FROM AUTHOR]

A three-coil wireless charging system is proposed for full metal-cover smartphone applications. Considering the space limitation and other antennas in the smartphone, the receiver coil embedded in the smartphone is designed to be miniaturized as 16 mm × 65 mm. By integrating a series capacitance at the end of the 2-mm width narrow horizontal slot loading on the metal cover, the metal cover is converted to a relay coil of the three-coil system and wireless power transfer (WPT) through the metal cover is thus achieved. A prototype of the proposed three-coil system has been built and WPT through metal cover has been validated via experiment. The experimental results show that the prototype achieves 5 W output power with 71% coil-to-coil efficiency. [ABSTRACT FROM AUTHOR]

In high-power electric vehicle wireless charging systems, the charging distance is short, and the coupling is strong in order to increase the power density and reduce the coil size and the system cost. With a strong coupling, the receiver-side compensation can be eliminated, and a high efficiency can still be obtained. The inductor-capacitor-inductor-none (LCL-N) topology is formed with the LCL compensation on the primary side. The phase difference between the transmitter and receiver currents is larger than 90°, leading to the magnetic flux cancelation in the ferrites. Thus, the required ferrite thickness of the LCL-N topology is smaller than the fully-compensated topologies. Therefore, a compact, lightweight, and low-cost receiver structure is achieved with the omitted compensation and thinner ferrite. Moreover, the LCL-N topology can achieve zero voltage switching for all loading conditions, withstand open-circuit and short-circuit faults, and is suitable for constant-current and constant-voltage charging due to the fact that it has neither a CC nor a CV output characteristic. A 100-kW system is designed and simulated. A downscaled 1-kW system is implemented. The simulations and experimental results verify the effectiveness of the analysis. [ABSTRACT FROM AUTHOR]

A dual-coupled inductor-capacitor-capacitor and series (LCC-S) compensated wireless power transfer (WPT) system with a compact receiver size is proposed in this paper to improve the misalignment performance and achieve fault tolerant operation as well as a stable output power. The compensation coil and the main coil are integrated as two decoupled unipolar coils on the transmitter side, while they are both coupled with the receiver coil. The two mutual inductances among the two decoupled coils and the receiver coil have opposite impacts on the output power when they both increase or decrease. Therefore, the output power can remain stable when the misalignment increases. The short- and open-circuit characteristics are analyzed, which demonstrates that the proposed topology can achieve both short- and open-circuit protection. A prototype was built and the experimental results verified the theoretical analysis and simulations. The system can deliver from 297 W to 321 W when the x-misalignment increases from 0 mm to 90 mm, with a dc-dc efficiency of 92.78% to 93.56%. The proposed WPT system can be used for the wireless charging of e-mobility scooters and autonomous underwater vehicles. The system can provide a stable output and can tolerate both short- and open-circuit faults at the output. [ABSTRACT FROM AUTHOR]

This letter proposes a novel capacitive coupler array with free-positioning feature for mobile tablet applications. The capacitive coupler consists of three printed circuit boards, two of which constitute the transmitter and the third one is the receiver. The coupler is vertically arranged to make the charging system compact and feasible for mobile tablet applications. By applying a repetitive structure on the transmitter side and properly designing the receiver, free-positioning capacitive charging is realized and the coil-to-coil charging efficiency is not affected by the variation of the receiver position. Only two series inductances are utilized for compensation purposes, which makes the system more compact and easy to be fabricated. This proposed capacitive coupler is studied via finite-element analysis and verified by the experimental results at 1, 2.17, and 3.45 MHz. [ABSTRACT FROM AUTHOR]

Wireless power transfer (WPT) has attracted much attention in recent years. In an underwater WPT system, the eddy current loss tends to be non-negligible as the frequency or the coil current increases. Thus, it is crucial to analyze the eddy current loss in an underwater WPT system. The analytical model of the eddy current loss of a coreless WPT system in the seawater is established with Maxwell's equations. The expressions of the electric field intensity and the eddy current loss are derived. The eddy current loss is analyzed in different circumstances to illustrate the impacts of related factors. For a WPT system in the air, there is an optimum resonant frequency, for a higher frequency leads to a larger induced voltage, but will result in larger coil losses simultaneously. However, the optimum resonant frequency will be shifted because of the eddy current loss in the seawater. Then, the optimum operating frequency is obtained based on the analytical model. It is found that the optimum operating frequency is supposed to be larger than the resonant frequency to achieve the maximum dc–dc efficiency in the seawater. An underwater WPT prototype was built and the experimental results verified the theoretical analysis. [ABSTRACT FROM AUTHOR]

In some applications of wireless power transfer, such as wireless charging of consumer electronics and electric buses, the coupling between the transmitter and the receiver is strong in order to improve efficiency. With a strong coupling, the compensation on the receiver side can be eliminated to achieve a high-level integration of the receiver device and a smaller receiver-side loss, forming a series-none (SN) topology, which has not been fully investigated before. The commonly used first harmonic approximation method for the SN topology has discrepancies with a low-power output and cannot fully reveal the characteristics of the SN topology. Therefore, this paper establishes a model of the SN topology and derives the analytical expressions of the transmitter and receiver currents based on differential equations. The distortion of the receiver current is studied. The coil-to-coil efficiency is obtained and its maximum condition is investigated. The SN topology offers approximately the same efficiency as the SS topology when the coupling is strong and the coil quality factors are large. Theoretical calculations and experimental results confirm the analysis. [ABSTRACT FROM AUTHOR]

Wireless power transfer systems in seawater inevitably suffer some energy loss as a consequence of eddy current loss. Here, we present a coil structure utilizing two transmitter coils placed symmetrically adjacent to each side of the receiver coil. This coil arrangement, termed a 1 × 1 × 1 structure, yields improved power transfer efficiency. The eddy current loss caused by the transmitter coils in a 1 × 1 × 1 system can be reduced to roughly half of that in a 1 × 1 system, with one transmitter coil and one receiver coil. The experimental results show that the power transfer efficiency from the transmitter to the receiver is improved by nearly 10%. After the introduction of equivalent eddy current loss impedance into the circuit, two arrangements of the 1 × 1 × 1 circuit topology are investigated. They consist of a shared or separately compensated capacitance topology. It is found that the shared-compensated capacitance topology is more robust to the change of mutual inductance than the separately compensated capacitance topology. This kind of structure is very useful in underwater vehicle applications. [ABSTRACT FROM AUTHOR]

This paper presents a rotation-resilient wireless charging system with a reversely wound receiver that supports efficient charging for lightweight autonomous underwater vehicles. By employing a two-part reversely wound receiver coil structure, the total mutual inductance of the proposed coil structure remains relatively constant when rotational misalignment between the transmitter and receiver coils occurs, thereby ensuring wireless charging power is nearly continuous during rotational misalignment. Finite element analysis was performed with ANSYS Maxwell to verify the proposed coil structure. Double-sided LCC compensation topology was applied and circuit analysis was conducted via a mesh current method. A prototype of the rotation-resilient wireless charging system with the proposed coil structure was built and tested. Experimental results are well-matched to simulations, demonstrating that the system can deliver 745 Watts at a dc-dc efficiency of 86.19% when the system is fully aligned, and efficient under worst-case rotational misalignment. [ABSTRACT FROM AUTHOR]

Lightweight autonomous underwater vehicles (AUVs), powered by rechargeable batteries, are widely deployed in inshore surveying, environmental monitoring, and mine countermeasures. While providing valuable information in locations humans have difficulty accessing, limited battery capacity of such systems prevents extended mission times. In order to extend mission times, this paper proposes a three-phase wireless charging system that could be used in a field-deployable charging station capable of rapid, efficient, and convenient AUV recharging. Wireless charging should not, however, affect instrumentation located inside the AUV. Thus, a three-dimensional finite element analysis tool is employed to study the characteristics of magnetic fields inside the AUV during three-phase charging. Simulation results reveal that the magnetic field generated by the proposed three-phase coil structure is concentrated away from the center of the AUV, where instrumentation would nominally be located. Detailed circuit analysis and compensation method to achieve resonance on both transmitter's and receiver's sides are also given. To validate the proposed concept, a three-phase wireless charging system is developed. Experimental results demonstrate that the system is able to transfer 1.0 kW with a dc–dc efficiency of 92.41% at 465 kHz. [ABSTRACT FROM AUTHOR]

This paper proposes a dual-coupled LCC-compen-sated inductive power transfer system with a compact magnetic coupler to improve misalignment performance. In the magnetic coupler, the main coils form the first coupling, and compensation inductors are integrated with the main coils to form a second coupling. In the design presented in this paper, the main coils are unipolar and the compensation inductors are in a Double D structure. The fundamental harmonics approximation method is used to analyze the circuit, and the couplings between the main coils and compensation inductors are considered to determine the net power flow. In misalignment cases, it is shown that the coupling between the compensation inductors, and the cross couplings between the compensation inductors and main coils, contribute to increasing the system power. A 3.5 kW prototype is designed and implemented to validate the proposed dual-coupled system. The primary coil size is \text450 mm\times \text450 mm, and the secondary coil size is \text300 mm\times \text300 mm. Experimental results show that the proposed dual-coupled system can significantly improve the misalignment performance, and retains at least 56.8% and 82.6% of the well-aligned power at 150 mm misalignment in the x- and y-directions, respectively. [ABSTRACT FROM PUBLISHER]

This paper proposes a continuous dynamic wireless power transfer system for electric vehicles that reduces power pulsations during the charging process. Multiple rectangular unipolar coils are used at the primary side as the transmitters, and another unipolar coil works as a receiver at the secondary side. The transmitters are placed closely together to reduce the variation of magnetic fields along the moving track of the receiver. This structure induces self-coupling between the adjacent transmitters. An LCC-compensated circuit topology is utilized, and a compensation parameter design is provided which considers self-coupling between the primary coils. Finite-element analysis of the dynamic charging system is performed using Maxwell. The receiver size is optimized to reduce the variation of the coupling coefficient. A 1.4-kW dynamic charging prototype is constructed according to the designed coil structure and circuit parameters. There are six transmitters, each with dimensions 388 mm×400 mm, and one receiver with dimensions 485 mm×400 mm. Experimental results show that the output power pulsation is within ±7.5% in the dynamic charging process, and the maximum efficiency is 89.78%. If the edge effects of the transmitters are neglected, then the power pulsation is within ±2.9%. [ABSTRACT FROM PUBLISHER]

This paper presents an integrated LCC compensation topology for electric vehicle/plug-in hybrid electric vehicle wireless chargers. The effect of the coupling between the additional coil and the main coil on the LCC compensation topology is studied. The proposed topology will reduce the size of the additional coil and make the system more compact with extremely high efficiency. The basic characteristics of the proposed topology are analyzed based on fundamental harmonic approximation. Furthermore, based on the steady-state model, three categories of operation modes are presented and analyzed. In order to realize zero-voltage switching, the series capacitor C2 on the secondary side is tuned. A numerical method is used to analyze the impact of different values of \Delta C2 on the turnoff current, and the best value of C2 is chosen to build a prototype to verify the analysis. [ABSTRACT FROM PUBLISHER]