Derivation of the Resonance Mechanism for Wireless Power Transfer Using Class-E Amplifier

In this study, we investigated the resonance mechanism of 6.78 MHz resonant wireless power transfer (WPT) systems. The depletion mode of a gallium nitride high-electron-mobility transistor (GaN HEMT) was used to switch the states in a class-E amplifier circuit in this high frequency. The D-mode GaN HEMT without a body diode prevented current leakage from the resonant capacitor when the drain-source voltage became negative. The zero-voltage switching control was derived according to the waveform of the resonant voltage across the D-mode GaN HEMT without the use of body diode conduction. In this study, the effect of the resonant frequency and the duty cycle on the resonance mechanism was derived to achieve the highest WPT efficiency. The result shows that the power transfer efficiency (PTE) is higher than 80% in a range of 40 cm transfer distance, and the power delivered to load (PDL) is measured for different distances. It is also possible to cover different applications related to battery charging and others using the proposed design.

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Three-Port Converter for Integrating Energy Storage and Wireless Power Transfer Systems in Future Residential Applications

Energies ◽

10.3390/en13010272 ◽

2020 ◽

Vol 13 (1) ◽

pp. 272

Author(s):

Hyeon-Seok Lee ◽

Jae-Jung Yun

Keyword(s):

Energy Storage ◽

Wireless Power Transfer ◽

Power Transfer ◽

Wireless Power ◽

Leakage Inductance ◽

Zero Voltage Switching ◽

High Voltage Gain ◽

Receiving Coil ◽

Resonant Capacitor ◽

Zero Voltage

This paper presents a highly efficient three-port converter to integrate energy storage (ES) and wireless power transfer (WPT) systems. The proposed converter consists of a bidirectional DC-DC converter and an AC-DC converter with a resonant capacitor. By sharing an inductor and four switches in the bidirectional DC-DC converter, the bidirectional DC-DC converter operates as a DC-DC converter for ES systems and simultaneously as a DC-AC converter for WPT systems. Here, four switches are turned on under the zero voltage switching conditions. The AC-DC converter for WPT system achieves high voltage gain by using a resonance between the resonant capacitor and the leakage inductance of a receiving coil. A 100-W prototype was built and tested to verify the effectiveness of the converter; it had a maximum power-conversion efficiency of 95.9% for the battery load and of 93.8% for the wireless charging load.

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

Energies ◽

10.3390/en14040911 ◽

2021 ◽

Vol 14 (4) ◽

pp. 911

Author(s):

Fabio Corti ◽

Alberto Reatti ◽

Ya-Hui Wu ◽

Dariusz Czarkowski ◽

Salvatore Musumeci

Keyword(s):

Conversion Efficiency ◽

Coupling Coefficient ◽

Design Procedure ◽

Wireless Power Transfer ◽

Power Transfer ◽

Wireless Power ◽

Zero Voltage Switching ◽

Zero Voltage ◽

Voltage Switching ◽

Class E

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.

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