Frequency analysis and computation of a current-fed resonant converter for ICPT power supplies

Current-fed resonant converters used in ICPT (inductively coupled power transfer) power supplies are normally controlled to operate with ZVS (zero voltage switching) so as to minimize the losses and EMI (electromagnetic interference). However, the ZVS operating frequency and how it varies with the system parameters remains an unsolved theoretical problem of practical importance. After identifying different types of resonant frequencies of a typical series loaded parallel resonant tank, this paper develops an iterative algorithm for ZVS frequency computation of a current-fed resonant converter for ICPT power supplies. The numerical analysis is based on a step current injection model over a half-switching cycle. Different resonant frequencies are compared and the necessary bounds on Q to maintain resonance are defined. The validity of the analysis is proven with PSpice simulation results