An Overview of Regulation Topologies in Resonant Wireless Power Transfer Systems for Consumer Electronics or Bio-Implants

Ferrite Concentrating and Shielding Structure Design of Wireless Power Transmitting Coil for Inductively Coupled Capsule Robot

High permeability material, especially the ferrite, has been widely used in wireless power transfer (WPT) to enhance the power transfer efficiency (PTE). However, for the WPT system of inductively coupled capsule robot, the ferrite core is solely introduced in power receiving coil (PRC) configuration to enhance the coupling. As for the power transmitting coil (PTC), very few studies focus on the ferrite structure design, and only the magnetic concentrating is taken into account without careful design. Therefore, a novel ferrite structure for PTC giving consideration to the magnetic field concentration as well as the mitigation and shielding of the leaked magnetic field is proposed in this paper. The proposed design is realized by combing the ferrite concentrating part and shielding part into a whole and providing a low reluctance closed path for magnetic induction lines, thereby improving the inductive coupling and PTE. Through analyses and simulations, the parameters of the proposed configuration are designed and optimized in terms of average magnetic flux density, uniformity, and shielding effectiveness. Prototypes of PTC with different ferrite configurations are established, tested, and compared to validate the performance enhancement. The experimental results indicate that the proposed design notably improves the average power delivered to the load from 373 mW to 822 mW and the PTE from 7.47% to 16.44%, with a relative percentage difference of 119.9%. Moreover, the power transfer stability is slightly enhanced from 91.7% to 92.8%.

Zero Voltage Switching Condition in Class-E Inverter for Capacitive Wireless Power Transfer Applications

This paper presents a complete design methodology of a Class-E inverter for capacitive wireless power transfer (CWPT) applications, focusing on the capacitance coupling influence. The CWPT has been investigated in this paper, because most of the literature refers to inductive power transfer (IWPT). However, CWPT in perspective can result in lower cost and higher reliability than IWPT, because it does not need coils and related shields. The Class-E inverter has been selected, because it is a single switch inverter with a grounded MOSFET source terminal, and this leads to low costs and a simple control strategy. The presented design procedure ensures both zero voltage switching (ZVS) and zero derivative switching (ZDS) conditions at an optimum coupling coefficient, thus enabling a high transmission and conversion efficiency. The novelties of the proposed method are that the output power is boosted higher than in previous papers available in the literature, the inverter is operated at a high conversion efficiency, and the equivalent impedance of the capacitive wireless power transfer circuit to operate in resonance is exploited. The power and the efficiency have been increased by operating the inverter at 100 kHz so that turn-off losses, as well as losses in inductor and capacitors, are reduced. The closed-form expressions for all the Class-E inverter voltage and currents waveforms are derived, and this allows for the understanding of the effects of the coupling coefficient variations on ZVS and ZDS conditions. The analytical estimations are validated through several LTSpice simulations and experimental results. The converter circuit, used for the proposed analysis, has been designed and simulated, and a laboratory prototype has been experimentally tested. The experimental prototype can transfer 83.5 W at optimal capacitive coupling with operating at 100 kHz featuring 92.5% of the efficiency, confirming that theoretical and simulation results are in good agreement with the experimental tests.

Analysis of an Operating State of the Innovative Capacitive Power Transmission System with Sliding Receiver Supplied by the Class-E Inverter

In recent years, there has been a significant increase in interest in applications of wireless power transmission (WPT). The development of electromobility and consumer electronics creates a need for newer and more effective systems for wireless charging. In spite of the unceasing progress in the research area of wireless energy transmission systems, the significant problem of the motion of the receiver has still not been solved. In this work, an innovative capacitive power transmission (CPT) system with a sliding receiver has been proposed, which enables efficient energy transmission regardless of the location of the receiver system relative to the transmitter system. The analysis of the operating states of the considered system has been conducted with the use of an in-house algorithm, in which the parameters of the equivalent circuit of the CPT system have been implemented. The parameters have been determined by the finite element method (FEM) using the electric scalar potential V. The system of capacitive power transmission was supplied from an E-class inverter. Selected results of calculations of the considered system have been presented and discussed.

Characteristic Analysis of Electromagnetic Force in a High-Power Wireless Power Transfer System

In order to explore the influence of the electromagnetic force (EMF) on the coupling mechanism in a high-power wireless power transfer (WPT) system, the characteristics of the EMF are investigated by theoretical calculation and simulation. The expressions of the EMF on the WPT structure with magnetic shielding are derived in time domain and frequency domain, respectively. The EMF is divided into Lorentz force and Kelvin force. The distribution and changing regularity of the EMF on the coil and the magnetic shield under different exciting currents are solved by the finite element model, and the harmonic of the EMF is analyzed in detail. The results show that the coil is subjected to the EMF in both radial and axial directions. The EMF on the magnetic shield is opposite to the EMF on the coil, and the force between the transmitting coil and the receiving coil is repulsive. The frequency of the EMF is twice that of the system resonant frequency. An experimental prototype is built to prove the correctness of the predicted characteristics. It is shown that the EMF should be carefully considered in the application of high-power WPT systems.