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In general, for the WPT (Wireless Power Transfer) system, as the mutual inductance and load resistance are calculated according to the measured data of both the transmitter and receiver, the wireless communication modules are needed to share data. A method for estimating mutual inductance and load resistance without wireless communication is proposed, based on the fundamental and third harmonic components. The circuit is decomposed with respect to the frequencies, by which the mathematic model is established. The fundamental and harmonic components of the output voltage and current of a high-frequency inverter are found by FFT (Fast Fourier Transform). The experimental WPT system with a SiC power MOSFET is designed, and the effectiveness of the proposed method is verified by the simulation and experiment results. Additional hardware and frequency scanning operation are not needed because of the use of the harmonic components.Generally, the Magnetic Resonance Coupling Wireless Power Transfer (MRC-WPT) system consists of three parts, namely a high-frequency power supply, a coil set (transmitting and receiving coil; some systems may have more than one intermediate coil in the coil set), and a receiver circuit. The coupling coefficient (or mutual inductance) between the coils and the load resistance are directly related to the performance of the system (for example, efficiency, transfer power, etc.) [29][30][31].The measured data of the load voltage and/or current of the receiver are transferred to the transmitter through wireless communication, and these data take part in realizing the constant current, constant voltage, or constant power of the load.In [32,33], the methods for keeping the constant voltage of the load were represented using the communication module. In [34], the method for maintaining the constant voltage and the current of the load was realized using the communication module. It was implied that the relative position between the transmitter and the receiver moved infrequently, and the internal resistance of the battery was very slowly changed when charging the battery of an electric vehicle, then the concept of the weak communication was defined. In spite of the communication environment being unstable, the load resistance and mutual inductance could be derived, but the communication function was not completely removed from the system. Due to the use of the wireless communication module, the power consumption may be increased, and the normal communication function cannot be performed in some severe situations. It is more unacceptable that if only one of the communication modules among the transmitter and the receiver is damaged, the whole WPT system cannot be operated. In [35], a method in which power and data were transferred at the same time through only one coil was proposed.If the load voltage and/or current can be estimated without any measured data of the receiver, the difficulties mentioned above do not need to be considered; while, if the inductance and capacitance of the receiver (L 2 , C ...

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Coaxial coil topology is used as the transfer medium in traditional MCR-WPT (Magnetic Coupled Resonant Wireless Power Transfer) systems to improve the transfer characteristics. The intermediate coils are added to extend the transmission distance, whose positions are critical. This paper focuses on the optimal intermediate coil positions for an MCR-WPT system with four coaxial planar circular spiral coils. By modeling the MCR-WPT system, the mathematical expression of the self-inductance and the mutual inductance are used to calculate the load power of the MCR-WPT system, which is composed of four planar circular spiral coaxial coils, and using MATLAB. The optimal distance ratio between the adjacent coils for maximizing the power of load is proposed. Furthermore, the experiments are implemented from the network analyzer and the experimental platform. In the platform, the load power is measured at the different intermediate coil positions, and the optimal position at which the load power is maximized is found. Both experimental results obtained by the network analyzer and the experimental platform have validated the theoretical and simulation results and provided the correctness of the suggested ratios.

Magnetic coupled resonance wireless power transfer system has the advantages of long transfer distance and high efficiency. However, it needs a high-frequency AC power, and the influence of the circuit parasitic elements at high frequency cannot be ignored, which brings challenges to the research and the design of the high-frequency power for the wireless power transfer system. In this paper, the effect of the parasitic elements in the full-bridge inverter and the reasons of high-frequency ringing generated are analyzed in detail. The influences of device packaging and the printed circuit board (PCB) layout on circuit parasitic elements are studied. An optimized inverter PCB layout design that aims to reduce the parasitic elements and to provide a stable and high-quality AC power for the wireless power transfer system is presented. Finally, the performance of the conventional PCB layout design and the proposed optimized PCB layout design are compared through experiments. The experiment results show that the proposed design not only reduces the parasitic inductance in the circuit, but also reduces the electromagnetic interference noises and improves the stability of the inverter at 900kHz switching frequency.INDEX TERMS Magnetic coupled resonance, wireless power transfer, high-frequency inverter, parasitic elements, PCB layout.

The characteristic of the Magnetic Resonance Wireless Power Transfer (MR-WPT) system is related on the coupling coefficients between coils, so it is very important to accurately measure mutual inductance. The method of measuring mutual inductance using the primary current and the secondary voltage, when the secondary circuit is opened, is commonly used and most reliable. However, a standard sine wave generator and a linear power amplifier are needed for measuring the mutual inductance. Due to the high frequency inverter of WPT system may be has distortion, it is not recommended to be as the sine wave generator for measuring the mutual inductance. The proposed method demonstrate that, although the output current waveform of the high frequency inverter and the voltage waveform on the secondary coil are highly distorted in PWM (Pulse Width Modulation) control mode, the base component’s amplitudes of these waveforms are investigated by FFT (Fast Fourier Transform), and then, the mutual inductance is calculated by using these values. According to the above contents, the experimental platform is built, and then the experiments on the different duty cycle ratio and the different frequencies, that is, including the different quantities of its high-frequency harmonics, has been done. In addition, the same operation as above is repeated on the different distances, and the results are compared with the theoretical calculation values. Consequently, the results show that the method is very close to the theoretical value, and it is very stable in whole distance range.