Exact Analysis of Frequency Splitting Phenomena of Contactless Power Transfer Systems

Frequency splitting phenomena are investigated systematically by circuit theory in a series-tuned contactless power transfer (CPT) system. First, in a symmetrical CPT system, the splitting equation is defined and the key frequency splitting characteristics are described by the trough and the ridge equations in a complete fashion. The even and the odd splitting frequencies are exactly two roots of the ridge equation; the splitting coupling is determined theoretically when the even and odd splitting frequencies merge together. Second, in an unsymmetrical CPT system, the idea of the trough and the ridge equation is exploited to find exactly the splitting coupling. Next, the relationship between frequency bifurcation and splitting is elucidated; and a zero-phase control method is suggested to track the splitting frequency when the coupling changes in the splitting region. Finally, the theoretical results are validated by a 10-W prototype with planar spiral coils.