小宮山 裕太郎

This paper presents a design of a load-independent wireless power transfer (WPT) system with multiple receivers and unified coupling coils. Various applications in each receiver require individual output voltages. In the proposed WPT system, LCC filters are adopted in front of transmission coils to improve the degree of freedom. The design theory of the LCC filter for achieving load-independent operation and the required individual output voltage is given. Consequently, the receiver can obtain the specified output voltages in each transmission coil; however, the variations of the coupling coefficient affect the output voltage. Since the load-independent operation can be maintained by satisfying specific conditions of the LCC filter, the proposed system always achieves zero-voltage switching and constant output, regardless of receiver load resistances in high power-delivery efficiency. From the experimental results, the effectiveness of the proposed WPT system and the validity of the design strategy can be confirmed. The experimental prototype of the two-receiver WPT system achieved 86.1% power-delivery efficiency at 6.78 MHz operating frequency and 19.6 V and 29.7 V output DC voltages.

This paper proposes a high-frequency multiple-receiver wireless power transfer (WPT) system with a load-independent class-E/F inverter. Each receiver has a post-regulator, which changes the equivalent resistance seen from the inverter to obtain the necessary power for output voltage regulation. Because the load-independent class-E/F inverter generates constant AC current ( CCAC$$ {\mathbf{CC } }_{\mathbf{AC } } $$), the transmitter supplies the minimum required power to the receivers by the change of the equivalent resistances. Besides, the load-independent inverter consistently achieves zero-voltage switching (ZVS) without any control. As a result, no information feedback by wireless communication is necessary for output regulation and ZVS achievement, simplifying the system configuration and improving the transient response of the control. This paper presents analytical expressions of the proposed system. Besides, the experiment was carried out with a two-receiver WPT system. The implemented system worked well by individual and independent output regulation of the post regulator at each receiver. The implemented WPT system achieved the power-delivery efficiency of 83.4% at the 6.78 MHz transmission frequency and the total output power of 40 W. The proposed WPT system: (A) The circuit configuration; (B) The inverter waveforms. Green and red lines are overlapped with black and red lines, respectively, for vS$$ {v}_S $$ and i2$$ {i}_2 $$. All lines are overlapped for vg$$ {v}_g $$ and it; and (C) The receiver waveforms. Blue and red lines are overlapped with black and green lines, respectively, except VOn$$ {V}_{On} $$. All lines are overlapped for VOn$$ {V}_{On} $$. image

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 article presents an analysis and design of a load-independent (LI) series resonant (SR) power amplifier with constant current (CC) output, along with its application for an MHz wireless power transfer (WPT) system. A novel inverse Class E power amplifier is introduced, which essentially produces a sinusoidal output current even with a low-$Q$ SR filter. Besides, the proposed amplifier achieves zero-current switching and CC output simultaneously, regardless of the load resistance. The LI operation is obtained for a specific set of component values, whose design conditions are clarified analytically in this article. The experiment was carried out with a WPT system incorporating the proposed amplifier as a transmitter and the Class D rectifier as a receiver. Although the input reactance of the Class D rectifier changed against dc-load variations due to the parasitic capacitances, the proposed amplifier showed consistent CC operation by using the low-$Q$ SR filter. Also, the proposed WPT system maintained a low total harmonic distortion of the transmission current over the wide load range, even with the low-$Q$ output filter. The prototype WPT system with the proposed amplifier achieved 88% power-delivery efficiency with 60 W output power at 3.39 MHz transmission frequency. The experimental results showed the effectiveness of the proposed amplifier.