In this paper, the electric field resonance (EFR) method, similar to the four-coil configuration of the magnetic field resonance wireless power transfer, is proposed for the capacitive coupling power transfer. The characteristics of the proposed method are derived and analyzed. With the EFR method, not only unity power factor for the power source is achieved, but also high power factor and low reactive power for the capacitive coupling stage are achieved. Effective power transfer is realized by the EFR method. Based on the proposed method, a dynamic charging concept for railway vehicles is then proposed. A prototype powering system is designed and built to prove the validity of the proposed method. Analytical, simulation, and experimental results are given and compared. A 23-cm model vehicle is put on a 150-cm track. It is shown that about 700-W power is transferred through a 24-pF coupling capacitor. The proposed method reaches 91% dc–dc overall efficiency at switching frequency 2 MHz.

Capacitive power transfer (CPT) has garnered significant interest in recent years, driven by efforts to enhance power and efficiency. This article presents advancements in CPT technology, focusing on the design of a novel five-plate coupler and the optimization of CPT systems. The proposed five-plate coupler features single-side shielding, which aims to simplify design complexity and reduce costs while maintaining performance. This study characterizes the five-plate coupler and compares its performance to traditional even-numbered plate configurations, highlighting the differences between odd and even plate designs and the unique characteristics of asymmetric couplers. In addition, the factors influencing efficiency are investigated, and an optimization method for CPT systems with asymmetric couplers is proposed to enhance the overall system performance. Experimental validation includes the development of a 5-kW prototype CPT system with a 100 mm airgap, achieving an impressive efficiency of 96.5%. These findings underscore the potential of the proposed design and optimization approach to set new benchmarks for CPT systems, facilitating their broader application in high-power scenarios.

Aiming at the power supply solution of online monitoring equipment for high-voltage transmission lines, a dual-frequency dual-load multirelay magnetic coupling wireless power transfer (MC-WPT) system using a shared power channel has been proposed. The proposed MC-WPT system provides the selective power distribution for different loads and has the constant current output characteristic. First, a dual-frequency inverter is introduced to provide the ac voltage of two frequencies. The compensation network that includes the band-stop filter can reduce the cross interference of the nontarget frequency from another power channel. Second, the system is modeled and analyzed based on the quadratic eigenvalue problem. Considering the cross-coupling mutual inductance, operating frequencies that make the system have constant current output characteristics are obtained. Finally, three evaluation indices are proposed: average current gain, load-independent index, and average sensitivity index of operating frequencies. Optimized operating frequency is selected according to these evaluation indices. The experimental results verify constant current output characteristics and the selective power distribution of two power channels.

Inductive power transfer and capacitive power transfer (CPT) are two of the most commonly used near-field wireless power transfer technologies, and these two systems share similarities and symmetries. This article proposes a hybrid wireless power transfer (HWPT) system to achieve load-independent characteristic and anti-misalignment capability. The HWPT system utilizes the compensation inductors of the CPT system to create an additional inductive channel in which the capacitive and inductive channels are compensated for each other. Based on the modeling of the HWPT system, the load-independent and enhanced constant current output is derived. In HWPT system, the inductive coupler is employed with the capacitive coupler, which forms a compact hybrid coupler. As the coupler becomes misaligned, the loss of power transferred through the inductive channel can be compensated by the increase of power transferred through the capacitive channel. A 200 W experimental prototype is built to validate the performance of the HWPT system. Experimental results show that as the load resistance ranges from 20 to 40 $\Omega$ and the coupling misalignment ranges from 0 to 100 mm, the output current remains nearly constant and the input current stays in phase with the input voltage. According to the experimental findings, the output current of the HWPT system is approximately twice as high as that of the CPT system when using the same capacitive coupler.

Bidirectional Inductive Power Transfer (IPT) systems could enhance the flexibility of energy interaction between electric vehicles (EVs) and the grid, as well as other electrical equipment. Achieving zero-voltage switching (ZVS) conditions is a critical factor in improving the efficiency of bidirectional IPT systems. This paper proposed a double-sided LCC compensation parameter design method, particularly suited for Vehicle-to-Grid (V2G) applications, which realizes the constant current (CC) output during charging process and the constant voltage (CV) output during discharge process of the bidirectional IPT system. A detailed analysis of parameter tuning methods is provided, with the aim of achieving CC/CV output and wide ZVS operation during charging and discharging processes. The inverter turn-off current is accurately estimated, considering the impacts of higher harmonics and the reflected reactance of the rectifier, to optimize the system’s compensation parameters. The effectiveness of the proposed method is verified by a 10-kW bidirectional IPT prototype, and the CC/CV feature and wide ZVS range are achieved. The experimental results demonstrate that the peak efficiency reaches 96.6% when transmitting power as a current source during charging, and 96.2% when transmitting power as a voltage source during discharging.

Apart from the load variation, the coupling misalignment of a capacitive power transfer (CPT) system can change the resonant frequency, which results in the variation of the output voltage/current. This article proposes a dual-loop control CPT system aiming at reducing the effect of the coupling misalignment and load variation. Based on the modeling of the LC – LC compensated CPT system, the constant-current (CC) and constant-voltage (CV) frequencies are derived. Then the frequency splitting and frequency bifurcation are illustrated. The frequency tuning is realized by tracking the input and output voltage rather than the input voltage and current. This method is helpful for tracking CV frequency accurately, and it can avoid the system operating at other resonant frequencies caused by frequency bifurcations. Based on the proposed control method, a 250-W experimental prototype with a 20-mm transmission distance is built. The CPT system can always operate in the load-independent CC/CV mode and the output voltage/current can be controlled to the target value with 2% error, when the load resistance and coupling misalignment vary from 5 to $50~\Omega $ , 0- to 100-mm $x$ -misalignment, and 0- to 20-mm $z$ -misalignment.