EMI reduction in wireless power transfer system using spread spectrum frequency dithering

This paper presents the use of spread spectrum technique to reduce electromagnetic interference caused by fast switching transitions of a resonant inverter and rectifier used for wireless power transfer (WPT) systems. We investigate the magnetic field emission from a series-resonant WPT system having the resonance frequency of 20 kHz in a frequency band from 9 kHz to 150 kHz. The averaging spectral estimate (Welch's Periodogram) of the simulated leakage magnetic field shows that a harmonic peak can be reduced up to 8.7 dB by dithering the switching frequency with a triangular modulation profile.