Series-series resonant IPT system analysis under frequency mismatch

Inductive Power Transfer (IPT) is a promising solution for charging the electric vehicles (EVs). The first IPT systems (IPTSs) were needing a strong coupling between transmitter and receiver coils to achieve a satisfactory efficiency in the power transfer. Nowadays this drawback has been overcome by the resonant technology, which ensures an efficiency higher than 90% even with loosely coupled coils. Enforcement of this result requires that the transmitter and receiver stages of the IPTSs have the same resonance frequency, and that the supply frequency of the IPTSs coincides with the resonance one. In practice, any deviation in the values of the reactive parameters of the IPTSs produces a mismatch between supply and resonance frequency. This paper analyzes the impact of such a mismatch on both the efficiency and the power supply sizing factor of an IPTS with series-series resonant topology. The analysis embraces the mismatches ensuing from an update of the supply frequency to make resonating either the transmitter stage or the receiver stage or the IPTS input impedance. Throughout the paper, the IPTS developed to charge an electric city-car is taken as a study case.