EMI Reduction Method for Wireless Power Transfer Systems With High Power Transfer Efficiency Using Frequency Split Phenomena

This article describes a method to reduce electromagnetic interference (EMI) components at odd harmonic frequencies of a wireless power transfer (WPT) system. In a WPT system, a leakage magnetic field is generated, which may adversely affect the human body or other electronic devices. The previous reactive shielding method could reduce the magnetic field, but it has the disadvantage of reducing the power transfer efficiency (PTE). By using frequency split phenomena, the reactive shielding method can reduce the EMI components with increasing PTE. In this article, a reactive shielding method that can reduce the magnetic field while increasing PTE is proposed. Specifically, the method for designing resonant system of transmitting, receiving, and shielding for the WPT system is proposed. In addition, a method for obtaining a coupling coefficient between a shielding coil and a transmitting coil for designing structure in which magnetic field reduction can be maximized is also proposed. The theoretical analysis based on the impedance of each part is strongly correlated with the simulation and measurement result. As a result of the experiment, the PTE is increased by about 2.7%, and EMI components at odd harmonic frequency can be reduced by up to 6.81 dB in a 50 W-WPT system.