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.

This paper presents an analysis and design of the load-independent (LI) high-frequency magnetic resonant wireless power transfer (MR-WPT) system with robustness against load variations and coil misalignments. It is clarified from the analysis that robustness against load variations and coil misalignment can be obtained when LI inverter, series-resonant to series-resonant (S-S) coupling topology, input-reactance invariant rectifier against load variations, and post regulator are adopted. The output reactance of the transmitter does not vary against load variations and coil misalignment. Therefore, the inverter works with the LI mode, achieving soft switching without control. As a result, the system ensures soft switching and output regulation against both load variations and coil misalignment without wireless communication feedback. The design example of the system with LI class-E/F inverter, class-D rectifier, and buck converter is given. The quantitative agreements between the analytical prediction and experiment show the effectiveness and validity of the system and its analysis.

This article presents a load-independent zero-current switching (ZCS) parallel-resonant inverter with a constant output current. The proposed inverter features constant-current output inherently without the need for any control method. Moreover, ZCS is achieved despite load variations, ensuring high power efficiency even at MHz-order switching frequencies. We conduct a comprehensive circuit analysis of the proposed inverter and provide a step-by-step parameter design method for achieving load-independent conditions. Additionally, a 25 W, 1 MHz prototype of the proposed inverter was implemented. In the circuit experiment, constant current output and ZCS were achieved across the entire range of load variations, which demonstrated the effectiveness of the proposed load-independent inverter.

This article presents a design procedure for wireless power transfer (WPT) systems with the load-independent class-E inverter family. The design procedure guarantees that the WPT system will achieve constant output and soft switching in response to load variations without particular control, which can apply not only single-hop single-output but also multihop multioutput WPT system designs. It is analytically explained that a WPT-system output type is determined by properly selecting the inverter, rectifier, and coupling resonant structure. As a concrete design example, we designed the three-hop three-output WPT system for installation into a robot arm. Experimental results exemplified the validity and usefulness of the established procedure.

This paper proposes a wireless power transfer (WPT) system using the load-independent inverse class-E oscillator. The proposed system realizes autonomous operation without using external driving circuits. Therefore, it is easier to design the power-transmission inverter at high frequencies, in particular. Moreover, the proposed WPT system has load-independent characteristics. It maintains constant output voltage and zero current switching (ZCS) of the MOSFET without applying any controls for load variations. We conducted the circuit analysis and the experimental verifications for the proposed system. In the experiment, the proposed system achieved 76.5 % power-delivery efficiency with 20 W output power and 1 MHz operating frequency at the rated state.