Synchronization between the primary and secondary sides is very important in wireless power transfer (WPT) systems. Especially in secondary-side control and bi-directional applications, the rectifier on the secondary side needs an accurate phase synchronization signal to properly control the conduction angle of the switches. However, the rectifier generates harmonic currents, making it impossible to obtain the synchronization signal directly by zero-crossing comparison of the secondary-side currents. The operating principle of the active rectifier in the WPT system is described. The harmonic currents generated by the active rectifier and the phenomenon of zero-crossing point forward shift caused by it are analyzed. The differences in the zero-crossing point forward shift between S-S and LCC-LCC systems are compared. In order to circumvent the effects of harmonics, a synchronization method based on a peak filter is proposed. The method is verified in simulation. The results show that after adding the filter to the control circuit, an accurate synchronization signal can be generated, and the circuit operates stably.

To improve the power supply reliability of the wireless power supply system of the transmission line online monitoring equipment and realize the information transmission at the transmitting side and the receiving side, this paper uses the coupling coil with taps to realize the coordinated transmission of power and information based on the wireless power transmission system with multiple relay coils. A power transmission model and information transmission equivalent circuit for the multi-relay coil wireless power transmission system are established in this paper to analyze the working characteristics of the power and information transmission paths and verifies the effectiveness of the proposed scheme through simulation. The simulation results show that the proposed scheme can achieve the cooperative transmission of information under the condition of satisfying the transmission power. The proposed scheme in this article can reduce the system size and is beneficial for adapting to the working environment of high-voltage insulator strings.

The coupler is essential in energy conversion in the wireless power transfer (WPT) system. Depending on the requirements of the appliances, the receiving coils have different structures, and their coupling magnetic fields are diverse, such as circular coils and solenoidal coils. Transmitters that generate flux in a single direction are difficult to compatible with different types of receiving coils, so this paper proposes a new transmitter with compatibility that can generate flux in two directions. Through finite-element analysis (FEA), the ferrite width, transmitter diameter, and coil position are discussed to find the best coupling design and compare and analyze the compatibility of the proposed circular and solenoidal structures. Simulation results show that the proposed structure has good coupling performance and is compatible with circular and solenoidal receiving coils. An experimental platform is built to verify the rationality of the proposed coupler structure.