This paper proposes the load-independent class-E Zero-Voltage Switching (ZVS) power oscillator. Conventional class-E power oscillator has a load-dependent phase shift, which hinders sustained oscillation under varying load conditions. Hence, we introduce the class-E power amplifier that ensures the load-independent phase shift in the output current. By incorporating it into an LCLC filter with a resonant-capacitor feedback network, the load-independent self-oscillation is realized. The proposed power oscillator satisfies a phase-shift requirement for sustained oscillation regardless of the load resistance. Furthermore, the proposed circuit exhibits load independence in ZVS, output current, and gate-drive voltage. This paper provides a thorough analysis of the proposed power oscillator, covering its operating principle, power loss prediction, design, and limitations. This paper also gives two design examples with 0.8 MHz and 6.78 MHz oscillation frequencies. In the experiment, the prototype power oscillators achieved 93.8 % and 87.4 % power-conversion efficiencies, respectively. The validity and effectiveness of the proposed power oscillator are demonstrated from the experimental verifications.

This paper proposes a machine learning (ML)–based design for a load-independent (LI) wireless power transfer (WPT) system. The fundamental concept of the proposed design strategy is to solve an optimization problem for achieving high-frequency LI operation by full numerical computations. An evaluation function for optimization is formulated, taking into account output voltage regulation against load variations and high power-delivery efficiency. The developed optimization software provides the best parameter set of coupling coil parameters and circuit-component values. In addition, the ML-based optimization finds the optimal parameter set from parameters outside the range that it had considered to be common sense, which is an unexpected but valuable result. The WPT system, designed through the proposed method, achieved ideal LI operation in the experiments. The quantitative agreements between experimental and numerical waveforms substantiate the validity of the proposed design.

In this paper, a WPT system that can switch between constant current (CC) and constant voltage (CV) in a single circuit is proposed. In the proposed WPT system, the CC and CV modes are achieved by varying the on-duty ratio of the buck converter. In addition, the proposed system also keeps the zero-voltage switching against coil misalignment and load variations without any information feedback from the rectifier to the inverter. This is because the load-independent behavior is built into the proposed system. The experimental results are consistent with the analytical predictions, which show the validity of the proposed circuit design strategy and the derived analytical expressions. Under rated conditions, the output power was 36.9 W and the power conversion efficiency was 86 % at the operating frequency of 6.78 MHz.

In this research, we propose a variable-gain load-independent class-E rectifier with fixed input reactance for wireless power transfer (WPT) system. Featuring an adjusting network, the proposed rectifier can adjust its voltage gain to maintain a constant output voltage against load variations and coil misalignment, eliminating the need for additional regulators. Based on equations derived from circuit analysis, we present a design method to achieve the zero-voltage switching (ZVS) condition, ensuring high efficiency even at multi-MHz frequencies. Additionally, the input reactance of the proposed rectifier remains fixed, which is beneficial for maintaining ZVS of the inverter. To validate the design method, a WPT system at 6.78 MHz was built. The experimental results confirmed the successful voltage-gain adjustment to compensate for coil misalignment. Furthermore, load-independent ZVS and fixed input reactance were achieved, demonstrating the effectiveness of the proposed rectifier.

This paper proposes a machine learning (ML)-based design for a load-independent (LI) wireless power transfer (WPT) system. The proposed design strategy formulates the WPT design as an optimization problem and solves it by fully-numerical computation to achieve high-frequency LI operation. A multi-objective evaluation function is given to achieve the LI operation, which evaluates output voltage, power-delivery efficiency, and total harmonic distortion. The class-EF WPT system designed using the proposed method achieved narrower output voltage variations and higher power-delivery efficiency than the analysis-based design system. Additionally, the proposed design algorithm identifies parameter sets that were never found through the analysis-based design. Namely, only a small amount of current flows through the previous harmonic resonant filter of the class-EF inverter. These results demonstrate the potential of ML-based design in the field of power electronics.

This paper presents the design of the class-Φ3power oscillator. The topology of the proposed power oscillator features the feedback network from the resonant capacitance, which allows for the application of wireless power transfer (WPT) systems. Furthermore, the required phase shift necessary for applying the proposed feedback network is achieved by employing the class-Φ3inverter, which has a finite input inductance. Closed-form design equations for the proposed power oscillator are provided, which allows a quick and intuitive design. An experimental verification is conducted with the prototype power oscillator. The measured power-conversion efficiency was 92.2 % with 70 W output power at 1 MHz operation. The experimental results agreed quantitatively with the analysis, which shows the validity of the design.

This paper proposes the load-independent (LI) class-E frequency multiplier along with a unified circuit analysis method with the LI class-E amplifier. A circuit-parameter determination strategy is presented to achieve LI operation and maximum power output capability at the rated condition. We designed the class-E amplifier and frequency doubler using the unified analytical expressions. Both the implemented circuits achieved the LI operation, namely constant output voltage amplitude and zero-voltage switching against load variations without any control. The experimental results showed quantitative agreements with the analysis results, namely waveforms and power conversion efficiency, which indicates the validity of the derived analytical expressions and design procedure.

This paper proposes a load-independent high-frequency wireless power transfer (WPT) system for multiple receivers with a single transmitter. The proposed system achieves zero-voltage switching (ZVS) at the transmitter and constant output voltages at all the receivers against load variations without any control. Moreover, the proposed system keeps the load-independent operation even when the number of receivers changes. The circuit analysis for the proposed WPT system is given. Experimental verifications for the proposed WPT systems with two receivers were conducted, which showed the effectiveness. The implemented WPT system achieved a peak efficiency of 83.4% at 6.78 MHz and total output power of 50 W.

This paper presents a simulator-based design-optimization software for high-frequency power-electronics circuits, which consists of the heuristic algorithm, magnetic-component design tool, and commercial simulator, SPICE. Because we can use the SPICE component library, the software suggests high-accurate design results, and the experimental adjustments can be reduced. Besides, by using the heuristic algorithm, the optimization algorithm converges stably. The magnetic-component design tool provides a precise estimation of the power losses, which is important for high-frequency power-electronics circuit designs. As an example, we design the class-DE inverter by applying the developed software, which shows the usefulness of the software.

This study proposes a self-tuned series resonant power oscillator capable of load-independent operation. The proposed power oscillator has a self-tuning feedback loop that provides a gate-driving voltage with a constant phase shift and amplitude. Therefore, it is robust against component tolerances in a series resonant filter. It is also robust against load variations owing to its load-independent design. Consequently, it maintains a high-efficiency and constant AC output against load variations and component tolerances. Experimental results demonstrated the effectiveness of the proposed power oscillator.

In this research, a novel load-independent Class-E/F inverter with constant voltage (CV) and constant current (CC) output modes is proposed. By adding one auxiliary switch to the class-E/F inverter, the proposed inverter can change into the class-E topology. A components design method is proposed to achieve load-independent conditions for both topologies by merging the design conditions of the load-independent class-E and class-E/F inverters together. Therefore, the proposed inverter can switch between CV and CC output modes against load changes at the same switching frequency. Additionally, zero-voltage switching (ZVS) can be maintained for both modes despite load variation. The proposed inverter has a simplified topology, making it suitable for minimized wireless power transfer applications as the transmitter part. A 1 MHz experimental prototype circuit was designed and implemented. A circuit experiment was conducted, which confirmed the usefulness of the proposed inverter.