In existing capacitive wireless power transfer (CPT) systems, the coupling capacitance of the traditional couplers is usually small, which will lead to a significant decrease in the power transfer capability when the transfer distance increases. Thus, it is a big challenge to achieve stable output power and constant transfer efficiency under different coupling capacitance. In this work, the circuit model of the CPT system with double-side LC compensation network is established firstly. Then, based on the parity-time (PT) symmetric theory, a primary-side control strategy is presented to achieve stable output power and constant high transfer efficiency when the coupling capacitance changes. Finally, the experimental results show that when the insertion depth of the stack array coupler changes from 60 to 180 mm, the output power of the proposed CPT prototype is almost stable at 25W, and the transfer efficiency is kept at around 88%, which verifies the feasibility and effectiveness of the proposed design.

The application of wireless power transfer (WPT) has become more and more extensive, and the parity-time (PT) symmetric principle has been proved to significantly improve the degree of freedom of the WPT system without increasing the control complexity. However, the PT-symmetric region of the original WPT system with series-series (SS) compensation is limited. To overcome this drawback, a novel PT-symmetric WPT system with series-parallel-series (S-PS) compensation is proposed in this paper. The PS compensation network is converted to the S compensation network by equivalent circuit method. Then a mathematical model of the proposed system is established by circuit theory. It is found that the critical coupling coefficient of the proposed system are much smaller than the original PT-symmetric system. Furthermore, the proposed system has a compromise between transmission distance and transfer efficiency by setting the capacitance distribution ratio. A 26W prototype is built to verify the feasibility of the proposed method. Experimental results demonstrate that the proposed method doubles the transmission distance and improves the output power.

In recent years, the concept of the negative resistor (NR) has been proposed and applied in the magnetic coupled wireless power transfer (MC-WPT) system to improve the stability of power transfer. However, it remains a fundamental challenge to find the characteristic differences and applications of the four basic NR-based MC-WPT topologies. In this paper, the circuit models of the four basic NR-based MC-WPT topologies: series-series (SS), series-parallel (SP), parallel-parallel (PP), and parallel-series (PS) are established, and their characteristics are analyzed and compared by using circuit theory, which enables engineers to determine and select topologies to suit different applications and requirements. Theoretical analysis shows that the compensation methods of the transmitter and receiver of the NR-based MC-WPT system would affect the operating frequency and output characteristics of the system. Moreover, by comparative analysis, the conditions and applicable ranges for a stable output of different topologies were provided. Finally, the experimental prototypes are set up by using the power electronic inverter and operational amplifier, and the voltage gain ratios of the four basic NR-based WPT topologies under the variations of transfer distance and load are observed. The experimental results validate the correctness of the theoretical analysis.

Magnetic Coupling Wireless Power Transfer (MCWPT) technology has broad application prospects due to its high degree of freedom in energy exchange and unparalleled security. In recent years, various controllers have been added to WPT systems to improve energy transfer performance. Among them, the Dual-Side Control (DSC) approach, which employs Dual-Active Bridge (DAB) converters with simultaneous control of the transmitter and receiver, has made great progress. The DAB structure has a compromise between cost and complexity, and the DSC can bring a high enough degree of control freedom to the MCWPT system to easily achieve efficiency optimization and desired output characteristics. However, various DSC methods have different characteristics. Therefore, this paper reviews and summarizes the current research status of DSC methods based on the DAB converters in MCWPT systems. Wireless communication is one of the decisive factors in the design of a control strategy, which is categorized in this paper according to the main approaches used in all the papers. Various DSC strategies are described in detail and compared comprehensively according to the control variables and control objectives. This review will be highly beneficial to research entities and industry professionals as a ready reference for the control design in MCWPT.

Capacitive power transfer (CPT) technique uses coupled metal plates for energy transmission, which has the advantages of negligible eddy-current loss and low weight. To achieve efficient power transfer, CPT system often adopts circuit resonance and impedance compensation, which are generally realized by integer-order components, such as inductors and capacitors. However, it remains a fundamental challenge to create a CPT system whose transfer efficiency and output power are robust against the variation of resonant frequency and the coupled plates’ relative position. Therefore, this paper proposes a robust fractional-order autonomous CPT system containing a fractional-order inductor. Theoretical analysis shows that the transfer efficiency and output power of the proposed fractional-order CPT system are inherently robust not only to the variation of the coupled plates’ relative position but also to the resonant frequency. In contrast, the transfer efficiency and output power of traditional integer-order CPT systems are sensitive to the resonant frequency. The available experimental results verify the effectiveness of the proposed system.

In this paper, an autonomous wireless power transfer (WPT) system with constant voltage output in a wide load range is presented. Here, combining self-oscillating control and phase-shift control, a new implementation of the autonomous WPT system is proposed. The proposed autonomous WPT system operates using a self-oscillating control method in the strong coupling region, which can automatically maintain the constant output voltage. In the weak coupling region, a phase-shift control method with a fixed frequency and a variable duty cycle is implemented, and a control strategy based on output voltage estimation is proposed to obtain the constant output voltage. In addition, according to the operating frequency characteristic of the proposed autonomous WPT system, a corresponding coupling region judgment method is presented to guarantee the realization of switching between the two control methods. An experimental prototype with a 24 V output voltage is constructed to validate the practicability of the proposed method. The experimental results show the proposed autonomous WPT system can obtain constant output voltage in a wide load range.