EMI Reduction Method for Wireless Power Transfer Using Broadband Topology and Spread-Spectrum Frequency Modulation

Wireless power transfer (WPT) systems offer a convenient method for charging devices without electrical contact, but they generate electromagnetic interference (EMI) noise, posing safety, and compatibility challenges. Spread-spectrum frequency modulation (SSFM) theoretically provides high EMI attenuation but also introduces design challenges for WPT systems. This article presents an innovative transmitter and receiver circuit architecture to meet the stringent requirements of high modulation rates and broadband variations in WPT systems using SSFM. Unlike conventional fixed-frequency WPT systems, our design features a variable frequency WPT system comprising a class D inverter driving the transmitter coil and a nonlinear resonant circuit receiver. SSFM is achieved by modulating the inverter frequency with a triangular wave from 19 to 21 kHz. Experimental results demonstrate that the proposed method achieves approximately 15 dB attenuation in both near-field radiation from the coils and dc conducted emission from the power lines compared to fixed-frequency operation at 20 kHz, validating the effectiveness of the theoretical, simulation, and experimental approaches. In addition, our broadband IPT system is simple, requiring no active feedback control or frequency tuning, making it highly practical.