Low-EMF Wireless Power Transfer Systems of Four-Winding Coils with Injected Reactance-Compensation Current as Active Shielding

This paper proposes and analyzes low-radiation noise wireless power transfer (WPT) systems with active shielding. Current flowing on the additional windings around the WPT coils is compensated with additional power supplies to cancel the magnetic field generated by the WPT coils. The current of the additional windings is controled with the additional power supplies to achieve zero magnetic field at rated power. The additional power supplies increase in the RMS current of the additional windings to inject reactance-compensation current. As a result, a transmission power of 1 kW and a reduction in radiation noise by 39.5 dB are achieved with the proposed active shielding. In addition, it is revealed that the transmission power with the proposed method is increased by the magnetic field reduction.