Conducted Emission in an 85 kHz, 50 kW WPT System with Opposite-Phase Transfer and Spread Spectrum

For field operations of wireless power transfer (WPT) systems using operating frequencies of 10 kHz or above, electromagnetic and conducted emission levels must be reduced to within regulatory limits such as those in the CISPR guidelines. Electromagnetic interference reduction technologies for WPT systems have therefore been intensely investigated in recent years. There are many reports of radiation noise reduction technologies for WPT systems, but relatively few reports regarding conducted emissions. This paper proposes an 85 kHz, 50 kW WPT system including parallel power transmission with opposite phase and spread spectrum to reduce radiation and conducted noise. Compared with use of co-phased parallel power transmission, using opposite phase reduces conducted emissions in the third harmonic of the WPT system by about 20 dB. Moreover, conducted emission from 150 kHz to 30 MHz is reduced by about 10 dB. Consequently, the conducted emission is reduced to within CISPR 11 limits.