Frequency and Parameter Combined Tuning Method of LCC-LCC Compensated Resonant Converter With Wide Coupling Variation for EV Wireless Charger

The characteristics of inductive power-transfer (IPT) systems are sensitive to the variation of the coupling coefficient caused by misalignment conditions or different gaps. This results in a reduction in transferred power and efficiency. The output characteristics considering frequency modulation applied in series-series (SS), inductor-capacitor-capacitor (LCC)-S and LCC-LCC compensated IPT systems have been explored, revealing that high-order compensation topologies hold limited power regulation ability if coupling varies significantly. The parameter sensitivity of LCC-LCC-compensated topology is investigated through the singular values (SVs) analysis. It is found that the variation of the parallel-compensated capacitors has the greatest impact on the output power. Aiming at alleviating the power drop caused by the coupling variation, a parameter offline tuning method realized by switching the parallel-compensated capacitance for a detuned LCC-LCC resonant converter is proposed for electric vehicle (EV) wireless charging. Analytical expressions have been derived in aiding the design of modified value of capacitance ensuring primary zero voltage switching (ZVS) operation. Thus, the detuned parameter combinations, which deliver rated power even with the worst coupling, are obtained. Finally, a 6.6-kw prototype has been built to verify the validity of the proposed topology, which can deliver 6.1 kW with an efficiency of 94% even when the coupling drops from 0.3 to 0.15.