An Improved LCC-S Compensated Inductive Power Transfer System With Wide Output Voltage Range and Unity Power Factor

Inductive power transfer (IPT) technology becomes highly attractive option for wireless battery charging applications. To fulfill the charge profile of battery packs, wide output voltage regulation is always necessary. In this paper, an improved inductor-capacitor-capacitor-series (LCC-S) compensated IPT system utilizing variable frequency switched capacitor control is put forward. Compared with the traditional LCC-S compensation topology, an extra capacitor is connected in series with the compensation inductor to form a symmetrical T-network. Switched capacitor is utilized to regulate the equivalent capacitance of the middle branch of T-network, which has the advantages of low voltage stress. In the proposed control method, the variation range of switching frequency is in compliance with SAE J2954 Standard and frequency bifurcation can be avoided. The detuning issue at receiver side caused by switching frequency variation is solved by using the variable inductor. The proposed IPT system is able to realize nearly unity power factor with high efficiency in the whole voltage range. Finally, a 592-W prototype with 112–168-V output voltage is built to verify the proposed IPT system. Experimental results show that the peak efficiency of the improved LCC-S compensated IPT system reaches 94.6% at full load when the coupling coefficient
$k= 0.2$
.